Surface treatment technology of titanium

Surface treatment technology of titanium
Titanium easily reacts with O, H, N and other elements in the air and Si, Al, Mg and other elements in the embedding material at high temperatures, forming a surface contamination layer on the surface of the casting, making its excellent physical and chemical properties worse, and hardness Increase, plasticity and elasticity decrease, and brittleness increases.

The density of titanium is small, so the inertia of titanium liquid is small when it flows, and the fluidity of molten titanium is poor, resulting in low casting flow rate. The difference between the casting temperature and the mold temperature (300℃) is large, the cooling is fast, and the casting is carried out in a protective atmosphere. It is inevitable that there are defects such as pores on the surface and inside of the titanium casting, which have a great impact on the quality of the casting.

Therefore, the surface treatment of titanium castings is more important than other dental alloys. Due to the unique physical and chemical properties of titanium, such as low thermal conductivity, low surface hardness, and low elastic modulus, high viscosity, low conductivity, and easy oxidation This brings great difficulty to the surface treatment of titanium, and it is difficult to achieve the desired effect with conventional surface treatment methods. Special processing methods and operating methods must be used.

The later surface treatment of the casting is not only to obtain a smooth and shiny surface, reduce the accumulation and adhesion of food and plaque, and maintain the patient’s normal oral microecological balance, but also to increase the beauty of the denture; more importantly, through These surface treatment and modification processes improve the surface properties and suitability of castings, and improve the physical and chemical properties of dentures such as wear resistance, corrosion resistance and stress fatigue resistance.

1. Removal of surface reaction layer

The surface reaction layer is the main factor affecting the physical and chemical properties of titanium castings. Before the titanium castings are ground and polished, the surface contamination layer must be completely removed to achieve a satisfactory polishing effect. The surface reaction layer of titanium can be completely removed by pickling after sandblasting.

1. Sandblasting: For the sandblasting of titanium castings, rough blasting of white corundum is generally better. The pressure of sandblasting is lower than that of non-precious metals, and it is generally controlled below 0.45Mpa. Because when the injection pressure is too high, the sand particles impact the titanium surface to produce intense sparks, and the temperature rise can react with the titanium surface, forming secondary pollution and affecting the surface quality. The time is 15~30 seconds, and only the sticky sand, surface sintered layer and part and oxide layer on the surface of the casting can be removed. The remaining surface reaction layer structure should be quickly removed by chemical pickling.

2. Pickling: Pickling can quickly and completely remove the surface reaction layer, and the surface will not be polluted by other elements. Both HF-HCl series and HF-HNO3 series pickling liquids can be used for pickling of titanium, but HF-HCl series pickling liquids have a larger hydrogen absorption capacity, while HF-HNO3 series pickling liquids have small hydrogen absorption and can control HNO3 The concentration of HNO3 can reduce hydrogen absorption, and the surface can be brightened. Generally, the concentration of HF is about 3% to 5%, and the concentration of HNO3 is about 15% to 30%.

2. Treatment of casting defects

Internal pores and shrinkage cavity internal defects: can be removed by hot isostatic pressing, but it will affect the accuracy of the denture. It is best to use X-ray inspection to remove the exposed pores on the surface and use laser repair welding. Surface pore defects can be directly repaired by laser local welding.

Three, grinding and polishing

1. Mechanical grinding: Titanium has high chemical reactivity, low thermal conductivity, high viscosity, low mechanical grinding and grinding ratio, and it is easy to react with abrasives. Ordinary abrasives are not suitable for grinding and polishing titanium. It is better to use good thermal conductivity. For ultra-hard abrasives such as diamond, cubic boron nitride, etc., the polishing linear speed is generally 900~1800m/min. Otherwise, grinding burns and micro-cracks may occur on the titanium surface. compressed spring

2. Ultrasonic grinding: Through the action of ultrasonic vibration, the abrasive grains between the grinding head and the ground surface and the ground surface move relative to each other to achieve the purpose of grinding and polishing. The advantage is that the grooves, dimples and narrow parts that cannot be ground by conventional rotating tools become easier, but the grinding effect of larger castings is not yet satisfactory.

3. Electrolytic mechanical composite grinding: Using conductive abrasive tools, applying electrolyte and voltage between the abrasive tools and the grinding surface, through the combined action of mechanical and electrochemical polishing, reduce surface roughness and improve surface gloss. The electrolyte is 0.9NaCl, the voltage is 5v, and the speed is 3000rpm/min. This method can only grind flat surfaces, and the grinding of complex denture supports is still in the research stage.

4. Bucket grinding: Use the centrifugal force generated by the revolution and rotation of the grinding barrel to make the denture and the abrasive in the barrel frictionally move to reduce the surface roughness. The grinding is automatic and efficient, but it can only reduce the surface roughness but not increase the surface gloss. The grinding accuracy is poor, and it can be used for deburring and rough grinding before denture fine polishing.

5. Chemical polishing: Chemical polishing is the purpose of leveling and polishing through the oxidation-reduction reaction of metal in a chemical medium. The advantage is that chemical polishing has nothing to do with the hardness of the metal, the polishing area and the shape of the structure. All parts in contact with the polishing liquid are polished, no special complex equipment is required, and the operation is simple. It is more suitable for polishing complex structure titanium denture stents. However, the process parameters of chemical polishing are difficult to control, and it is required to have a good polishing effect on the denture without affecting the accuracy of the denture. A better titanium chemical polishing solution is HF and HNO3 prepared in a certain proportion. HF is a reducing agent, which can dissolve titanium metal and have a leveling effect. The concentration is less than 10%. HNO3 has an oxidizing effect to prevent excessive dissolution of titanium and hydrogen absorption. , At the same time can produce bright effect. Titanium polishing solution requires high concentration, low temperature and short polishing time (1~2min.).

6. Electrolytic polishing: also known as electrochemical polishing or anodic dissolution polishing. Due to the low conductivity of titanium, the oxidation performance is very strong. The use of acidic electrolytes such as HF-H3PO4 and HF-H2SO can hardly affect titanium. After polishing and applying external voltage, the titanium anode will be oxidized immediately, making the anode dissolution impossible. However, the use of anhydrous chloride electrolyte at low voltage has a good polishing effect on titanium. Small specimens can be mirror polished, but for complex restorations, complete polishing can not be achieved. Maybe change the cathode shape and add cathode The method that can solve this problem needs further research. Extension spring

Fourth, the surface modification of titanium

1. Nitriding: chemical heat treatment techniques such as plasma nitriding, multi-arc ion plating, ion implantation and laser nitriding are used to form a golden yellow TiN infiltration coating on the surface of the titanium denture, thereby improving the wear resistance and corrosion resistance of titanium And fatigue resistance. However, the technology is complicated and the equipment is expensive, and it is difficult for the surface modification of titanium dentures to achieve clinical practicality.

2. Anodizing: Titanium anodizing technology is relatively easy. In some oxidizing media, under the action of applied voltage, titanium anode can form a thicker oxide film, thereby improving its corrosion resistance, wear resistance and weather resistance. The electrolyte for anodic oxidation generally uses H2SO4, H3PO4 and organic acid aqueous solutions.

3. Atmospheric oxidation: Titanium can form a thick and firm anhydrous oxide film in the high temperature atmosphere, which is effective for overall corrosion and crevice corrosion of titanium, and the method is relatively simple.

Five, coloring

In order to increase the beauty of titanium dentures and prevent the discoloration of titanium dentures from continuous oxidation under natural conditions, surface nitriding treatment, atmospheric oxidation and anodic oxidation surface coloring treatments can be used to form light yellow or golden yellow on the surface to improve the titanium denture’s Beauty. The anodic oxidation method uses the interference effect of the titanium oxide film on the light to produce natural color, which can form colorful colors on the titanium surface by changing the cell voltage. Torsion spring

6. Other surface treatment

1: Surface roughening: In order to improve the bonding performance of titanium and facing resin, the surface of titanium must be roughened to increase its bonding area. In clinical practice, sandblasting is often used for roughening treatment, but sandblasting will cause contamination of aluminum oxide on the titanium surface. We use oxalic acid etching to obtain a good roughening effect. The surface roughness (Ra) can reach 1.50 after 1h of etching. ±0.30μm, 2h etching Ra is 2.99±0.57μm, which is more than double the Ra (1.42±0.14μm) of sandblasting alone, and its bond strength is increased by 30%.

2: Surface treatment for high temperature oxidation resistance: In order to prevent the rapid oxidation of titanium at high temperatures, titanium silicon compounds and titanium aluminum compounds are formed on the surface of titanium to prevent oxidation of titanium at temperatures above 700°C. This kind of surface treatment is very effective for the high temperature oxidation of titanium. Perhaps this kind of compound coated on the titanium surface is beneficial to the combination of titanium and porcelain, and further research is needed.

Powder injection molding process of nickel-free high nitrogen stainless steel

Nickel-free high-nitrogen austenitic stainless steel is a type of stainless steel with high mechanical properties and corrosion resistance. In particular, it does not contain nickel, which can cause severe allergic reactions in some people, and can effectively prevent the “nickel sensitivity” problem. Therefore, there is a broad market space in biomedical materials, which is currently attracting much attention from academic and industrial circles at home and abroad.

Although hot isostatic pressure smelting, pressure induction smelting, pressure plasma smelting, pressurized slag smelting, nitrogen slag smelting and other new technologies and new processes have been adopted, many brands of nitrogen-containing stainless steel materials have been developed. However, to varying degrees, the above-mentioned production technologies have problems such as complicated equipment, dangerous high-pressure gas, difficult process control, and high production cost, and there are certain difficulties in obtaining higher nitrogen content in materials.

The powder metallurgy production of high-nitrogen steel has many advantages, such as no high-pressure smelting facility in production, and low cost; fine-grain strengthening, dispersion strengthening, etc. strengthen the material properties. In addition, experimental facts show that nitrogen is solid in solid austenitic stainless steel. The solubility is greater than the solubility in the liquid state, so the powder metallurgy solid nitriding process is an economically and technically feasible method for producing high nitrogen steel.

Metal injection molding (MIM), as a product of the combination of traditional powder metallurgy and advanced plastic injection molding process, has unique advantages in preparing near-net shape products with three-dimensional complex geometric shapes, uniform structure and high performance. The fine powder particle size is conducive to diffusing nitrogen into the powder particles to increase the nitrogen content, and finally obtain high-nitrogen stainless steel. At present, the research on the production of nickel-free high-nitrogen austenitic stainless steel materials by injection molding technology at home and abroad is still in the preliminary stage.

The experiment uses the 0Cr17Mn11Mo3 stainless steel powder produced by the high-pressure inert gas atomization method. It can be seen that the powder has high sphericity, its average particle size is small (D50=17.4μm), and the bulk density and tap density are high (3.67 and 3.67 and respectively). 4.95g·cm-3), these characteristics of the powder are conducive to improving its fluidity and loading during the injection molding process.

The binder adopts a thermoplastic paraffin-based binder system with good fluidity, and the formula is 65wt%PW+30wt%HDPE+5wt%SA. The stainless steel powder was mixed with an appropriate amount of binder to make a feed. The powder loading was 64%, and then the rheological properties of the feed were tested. The injection process is carried out on the CJ-80E injection molding machine.

The feed is injection molded into a rod blank with a size of 8mm×70mm, and then a pre-sintered blank with a certain strength is obtained after solvent debinding, thermal debinding and pre-sintering at 800°C. After the pre-sintered compacts were sintered in high-purity nitrogen at different pressures at a temperature range of 1200 to 1350°C for 1 to 2.5 hours, the density of the sintered body was measured by Archimedes method (drainage method), and inert gas pulse-infrared -Thermal conductivity method (QB-Q-02-1997) measures the nitrogen content of the sintered body.

The sintered body is machined into a standard tensile bar of 5mm×60mm according to the national standard, and after 1150℃×90min solution treatment and water quenching, its tensile mechanical properties (such as yield and tensile strength) are measured with the Instron universal testing machine And elongation, etc.), and compare the performance with the nitrogen-free samples prepared by the same sintering process in argon atmosphere.

1) 64vol% gas atomized 0Cr17Mn11Mo3 powder mixed with a binder with a composition of 65wt%PW+30wt%HDPE+5wt%SA has good rheological properties; the optimal injection process parameters of the feed are The injection pressure is 60~85MPa, and the corresponding injection temperature is 160~170℃;

Increasing the sintering temperature is beneficial to increase the density of the sintered body, but is not good for obtaining a high nitrogen content. Increasing the pressure of the sintering nitrogen atmosphere can obtain a higher nitrogen content, but is not good for increasing the density of the sintered body. Experiments show that the best sintering process is sintering at 1300°C for 2 hours under a nitrogen pressure of 0.1 MPa. At this time, the relative density of the sintered body can reach 99%, and the nitrogen content can reach 0.78%. After the sintered body is solution treated at 1150℃ and cooled by water quenching, the yield strength, tensile strength, elongation, reduction of area and hardness reach 580MPa, 885MPa, 26.0%, 29.1%, and 222HV10, respectively.

How to clean stainless steel spring

General precautions When washing, please be careful not to scratch the surface. Avoid using bleaching ingredients and detergents containing abrasives, steel balls (brush roller balls), grinding tools, etc., in order to remove the detergent, rinse with clean water at the end of the wash Superficial.
Surface condition and washing method

Dust and easy to remove scale-wash with soap, weak lotion or warm water;

Labels and films-scrub with warm water and weak detergent;

Binder composition-use alcohol or organic solution;

Fat, oil, lubricating oil pollution-wipe dry with a soft cloth or paper and then wash with a neutral detergent or ammonia solution or special detergent;

Bleaching agent and kind of acid attachment-rinse immediately with water, soak in ammonia or neutral carbonated soda aqueous solution, and then wash with neutral detergent or warm water;

Organic carbide adhesion-soak in hot neutral detergent or ammonia solution and then wash with weak abrasive detergent;

Fingerprints-use alcohol or organic solvents (ether, benzene), dry with a soft cloth and then wash with water;

Too much rainbow pattern-caused by using detergent or oil, use mild detergent in warm water when washing;

Welding heat discoloration-wash with 10% nitric acid or hydrofluoric acid solution, then neutralize with ammonia water and carbonated soda solution and then wash with water-special washing medicine use;

Rust caused by surface contaminants—wash with nitric acid (10%) or abrasive detergent—use special detergents.

Stainless steel spring_stainless steel surface washing

Stainless steel spring_stainless steel surface washing
Washing method according to surface condition:

General notes

When washing, please be careful not to scratch the surface. Avoid using bleaching ingredients and detergent containing abrasives, steel balls (brush roller balls), abrasive tools, etc. To remove the detergent, rinse the surface with clean water after washing.

Surface condition and washing method

Dust and easy to remove scale, wash with soap, weak lotion or warm water

Labels and stickers wipe with warm water and weak detergent

Binder ingredients use alcohol or organic solution

Fat, oil, lubricating oil pollution Wipe dry with a soft cloth or paper and then wash with neutral detergent or ammonia solution or special detergent

The bleach and the kind of acid are attached. Rinse immediately with water, soak in ammonia or neutral carbonated soda aqueous solution, and then wash with neutral detergent or warm water

Organic carbides are attached, soak in hot neutral detergent or ammonia solution and then wash with weak abrasive detergent

Fingerprints Use alcohol or organic solvents (ether, benzene), dry with a soft cloth and then wash with water

Too much rainbow pattern caused by detergent or oil, use mild detergent in warm water when washing

Welding heat discoloration Wash with 10% nitric acid or hydrofluoric acid solution, then neutralize with ammonia water and carbonated soda solution, and then wash the stainless steel spring with water–specially used for washing chemicals

Rust caused by surface contaminants Wash with nitric acid (10%) or abrasive detergent-use special detergent

Spring heat treatment equipment

Spring heat treatment equipment
Heat treatment equipment is an important basis for ensuring spring quality.

1. Resistance furnace Resistance furnace is one of the most commonly used equipment in general spring manufacturing plants. There are the following types of resistance furnaces.

a. Box furnace The medium temperature box furnace is widely used in spring production. The equipment is easy to operate and maintain, which can meet the general process requirements of heat treatment and heating. The disadvantage is that it is heated in the air medium, which is easy to produce an oxidation and decarburization layer on the surface of the spring. Important springs should not be heated in this type of furnace. The series specifications are shown in Table 1.

Table 1 Specifications and technical data of medium temperature box-type electric furnace series

The index when the furnace temperature is 850℃

Model number







Maximum working temperature


Effective size of furnace


mm mm mm

No-load loss


Start empty furnace heating time at 20℃


Maximum birth


/(kg·h) Furnace bottom

Large load capacity


RX(RXQ) series RX-18-9133801950 300×650×250≤5≤260





RJX series

RX-15-9153801950 300×650×250≤5≤45090





Note: RXQ series furnaces are equipped with inlet pipes and outlet gas combustion pipes for introducing protective gas or dripping liquids such as kerosene.

Table 2 Specifications and technical data of well-type tempering resistance furnace

The index when the furnace temperature is 650℃

Model number


/kw voltage

/V phase

Number heat


Highest number of jobs


/℃ Effective size of furnace


mm mm no-load loss

/kW20℃ start

Empty furnace heating up


/h Max Health



RJ-25-62538011650400× 500≤5≤2140

RJ series RJ-35-63538031650 500×650≤6≤3210




RJJ series JJ-36-63680650500× 650≤6≤3280


b. Pit-type furnace Pit-type resistance furnace is mainly used for spring tempering, stress relief annealing and aging treatment. See Table 2 for series specifications.

c. Continuous hot blast tempering electric furnace The application of continuous hot blast tempering electric furnace has brought extremely significant comprehensive benefits to spring production. The electric furnace is more convenient to install and unload than pit type resistance furnaces and nitrate tempering furnaces, and it also has the characteristics of fast heating, uniform furnace temperature, high productivity and energy saving (compared with pit type resistance furnaces about 50% electricity). Therefore, the spring manufacturing industry has eliminated the long-used well-type resistance furnaces and nitrate tempering furnaces. The series specifications of continuous hot air tempering electric furnaces are shown in Table 3.


Table 3 Specifications and technical data of continuous hot air tempering furnace

Model Effective volume in furnace


mm mm mm Furnace body shape


mm mm mm inlet height

/mm Tempering temperature

/℃ When tempering

Range electrical


/kW temperature


NO treatment material diameter

/mm Tempering

Processing output

/(kg·h) Furnace



RJC-210200× 90×1000670×1200× 2000 500~60050~5005~60810.1~2.620300

RJC-310300× 90×1000770×1200× 2000 500~60050~5005~601210.1~3.230400

RJC-315300× 90×1500770×1200×


RJC-415400× 90×1500870×1200× 2800 500~60050~5005~602020.1~550700

RJC-420400× 90×2000870×1200× 3300 500~60050~5005~602620.5~6601000

RJC-520500×120×2000970×1900× 340070050~50010~603020.5~7901200

RJC-530500×120×30001000×1900× 510070050~50010~604030.5~81401500

RJC-630600×120× 30001120×1900× 510080050~50010~604831.0~101602000


2. Salt bath furnace The salt bath furnace is a heat treatment equipment heated by molten salt. Compared with the box furnace, it has the characteristics of fast heating, uniform temperature, and less oxidation and decarburization. Suitable for heat treatment of small diameter springs and important springs. There are two types of salt bath furnaces: internal heating type salt bath furnace and external heating type salt bath furnace. Salt bath furnaces can be divided into high temperature, medium temperature and low temperature according to the operating temperature. The high temperature is generally 900-1300℃, the medium temperature is 650-900C, and the low temperature is below 650C. Please check the relevant manuals or samples for the specifications and technical data of the salt bath furnace.

3. Protective atmosphere heating furnace, controlled atmosphere heat treatment furnace With the development of industry, the quality requirements of springs in production are getting higher and higher, and the heat treatment of springs does not allow excessive oxidation and decarburization on the surface. In conventional heat treatment, although the salt bath furnace heating can reduce the surface of the spring material or decarburize without oxidation. However, for various leaf springs with complex shapes made of strip steel, if they are heated in a salt bath furnace and quenched in oil, it is difficult to ensure the quality, and it is difficult to clean the spring after quenching, which will easily cause rust and reduce the spring. the quality of.

In recent years, the spring manufacturing industry has successively adopted controlled atmosphere heat treatment furnaces instead of traditional salt bath furnaces, and quenched and tempered valve springs, fuel injector pressure-regulating springs, motorcycle damping springs, planar scroll springs, and wave springs. deal with. The spring after heat treatment in a controlled atmosphere furnace has the advantages of bright surface, hardness, uniform metallographic structure, basically no decarburization and small deformation, which greatly improves the quality of the spring. In addition, after adopting a controlled atmosphere heat treatment furnace, there are benefits such as reducing labor intensity, saving energy, and reducing air pollution.

The specifications of the controlled atmosphere steel belt resistance furnace are shown in Table 4.

Table 4 Main technical parameters of RCG9 steel belt resistance furnace

Model number

Technical parameters RCG9-

22×250× 5


30× 360× 5


30×470× 5


30×470× 5a






Work area size


mm mm mm



300×4700× 50


Rated power/kW 50 807 690 120 150

Maximum temperature/℃920

Steel belt transmission speed




Gas consumption/(Nm ·h )2~33~44~5

Model number

Technical parameters RCG9-

22×250× 5




30×470× 5


30× 470×5






Quenching tank volume/m48

Quenching 80 150 200 250 300

Maximum birth

Yield ①

/(kg·h )Carburizing (carburized layer 0.1mm)








Layer 0.2mm)






Furnace external size


mm mm mm

1600 × 8400






Base surface

Upper size 1mm




Heat treatment of copper alloy

1. Stress-relieving annealing treatment of copper alloys. Copper alloy wires and strips such as tin bronze, silicon bronze, aluminum bronze, cupronickel, etc. have been cold-drawn and strengthened when they are supplied. After cold-formed coiled springs, only stress-relieving annealing treatment is required . The strength increased slightly after treatment, but the strength decreased when the temperature exceeded 220C. 2. Aging treatment of beryllium bronze When the beryllium bronze ribbon material is supplied, it has undergone solution treatment and cold drawing processing. After the spring is formed, the aging treatment is carried out to make the beryllium precipitate around the grain boundary in a dispersed state and increase the strength of the material. Table 1 lists the aging process of beryllium bronze and the comparison of tensile strength before and after aging.

Table 1 Aging specification and strength comparison of beryllium bronze before and after aging

Supply status
Aging temperature
Keep temperature time
Tensile strength, σb/MPa
Before aging
After aging
Soft (M)
Hard (Y)
Hard (Y)

3. Quenching and tempering of copper alloys Aluminum bronze, chromium bronze and aluminum cupronickel with an aluminum mass fraction greater than 9% are all copper alloys that are quenched and tempered.
Taking aluminum bronze as an example, the quenching temperature should be selected to transform the alloy structure into a single unit. Phase, and then cool quickly. For aluminum bronze with an aluminum content of 9% to 10%, this temperature is about 1000 deaths, which is close to the melting temperature of the alloy. Therefore, the quenching temperature should be slightly lower than this temperature, generally 850-950C. Holding time, generally 1-2h, cooling in water.
The tempering temperature is determined according to the required mechanical properties. When high strength, high hardness and low plasticity are required, low temperature tempering can be used at a temperature of 250-350℃; when higher strength, hardness, and high plasticity and toughness are required, high temperature tempering can be used, and the temperature is 500-650’C. The tempering time is generally about 2h.
The copper alloy quenching and tempering process specifications are shown in Table 2.
Table 2 Copper alloy quenching and tempering process specification

Alloy grade
Heating temperature/℃
Holding time/h
Heating temperature/℃
Holding time/h






Bearing heat treatment method

Bearing heat treatment method one
The quality of heat treatment is directly related to the quality of subsequent processing and ultimately affects the performance and life of parts. At the same time, heat treatment is a major energy consumer and a major polluter in the machinery industry. In recent years, with the progress of science and technology and its application in heat treatment, the development of heat treatment technology is mainly reflected in the following aspects:

(1); Waste water, waste gas, waste salt, dust, noise and electromagnetic radiation formed by the production of clean heat treatment will pollute the environment. Solving the environmental pollution of heat treatment and implementing clean heat treatment (or green heat treatment) is one of the development directions of heat treatment technology in developed countries. In order to reduce the emission of SO2, CO, CO2, dust and coal slag, the use of coal as fuel has been basically eliminated, and the use of heavy oil is becoming less and less. Most people switch to light oil.

Natural gas is still the most ideal fuel. The waste heat utilization of the combustion furnace has reached a very high level. The optimization of the burner structure and the strict control of the air-fuel ratio ensure that the NOX and CO are reduced to a minimum under the premise of reasonable combustion; gas carburizing and carbonitriding are used And vacuum heat treatment technology replaces salt bath treatment to reduce the pollution of waste salt and CN-containing toxic substances to water sources; uses water-soluble synthetic quenching oil to replace part of quenching oil, and uses biodegradable vegetable oil to replace part of mineral oil to reduce oil pollution.

(2); Precision heat treatment Precision heat treatment has two meanings: on the one hand, it is based on the use requirements, materials, and structural dimensions of the parts, using physical metallurgy knowledge and advanced computer simulation and testing technology to optimize process parameters to achieve the required performance Or maximize the potential of the material; on the other hand, fully guarantee the stability of the optimized process, and achieve a small (or zero) product quality dispersion and zero heat treatment distortion.

(3); Scientific production and energy management of energy-saving heat treatment are the most potential factors for the effective use of energy. It is the choice of scientific management to establish a professional heat treatment plant to ensure full-load production and give full play to equipment capabilities. In terms of heat treatment energy structure, priority is given to primary energy; waste heat and waste heat are fully utilized; processes with low energy consumption and short cycles are used instead of processes with long cycles and high energy consumption.

(4); Less non-oxidizing heat treatment by using protective atmosphere heating instead of oxidizing atmosphere heating to controllable atmosphere heating with precise control of carbon potential and nitrogen potential, the performance of parts after heat treatment is improved, and heat treatment defects such as decarburization and cracks are greatly reduced. The finishing allowance after heat treatment is reduced, which improves material utilization and machining efficiency. Vacuum heating gas quenching, vacuum or low-pressure carburizing, nitriding, nitrocarburizing and boronizing can significantly improve quality, reduce distortion and increase life.

The heat treatment quality control of bearing parts is the most stringent in the entire machinery industry. Bearing heat treatment has made great progress in the past 20 years, mainly in the following aspects: research on basic heat treatment theory; research on heat treatment technology and application technology; development of new heat treatment equipment and related technologies. 1; Annealing of high-carbon chromium bearing steel The spheroidizing annealing of high-carbon chromium bearing steel is to obtain a structure with fine, small, uniform and round carbide particles uniformly distributed on the ferrite matrix, for the subsequent cold working and final Quench and temper for organization preparation. The traditional spheroidizing annealing process is to keep the temperature slightly higher than Ac1 (for example, GCr15 is 780~810℃) and then slowly cool with the furnace (25℃/h) to below 650℃.

This process has a long heat treatment time (above 20h) [1], and the carbide particles are not uniform after annealing, which affects the subsequent cold working and final quenching and tempering structure and performance. Afterwards, according to the transformation characteristics of undercooled austenite, an isothermal spheroidizing annealing process was developed: after heating, it was quickly cooled to a temperature range below Ar1 (690~720℃) for isothermal, and the austenite orientation was completed in the isothermal process.

The transformation of ferrite and carbide can be directly discharged and air cooled after the transformation is completed. The advantage of this process is to save heat treatment time (the whole process is about 12~18h), and the carbides in the treated structure are fine and uniform. Another time-saving process is to repeat the spheroidizing annealing: heating to 810°C for the first time and then cooling to 650°C, then heating to 790°C and then cooling to 650°C and then air cooling. Although this process can save a certain amount of time, the process operation is more complicated.

2; Martensite quenching and tempering of high carbon chromium bearing steel

2.1 The structure and performance of conventional martensite quenching and tempering In the past 20 years, the development of conventional high-carbon chromium bearing steel martensite quenching and tempering process is mainly divided into two aspects: on the one hand, the development of quenching and tempering process parameters affects the structure And the influence of performance, such as the structure transformation during quenching and tempering, the decomposition of retained austenite, the toughness and fatigue properties after quenching and tempering, etc. [2~10]; the other hand is the process performance of quenching and tempering, such as The effect of quenching conditions on size and deformation, dimensional stability, etc. [11-13].

The structure of conventional martensite after quenching is composed of martensite, retained austenite and undissolved (residual) carbides. Among them, the structure of martensite can be divided into two categories: under a metallographic microscope (magnification is generally less than 1000 times), martensite can be divided into lath martensite and lamellar martensite Typical structure, generally after quenching, is a mixed structure of lath and flaky martensite, or an intermediate form between the two-jujube-shaped martensite (the so-called cryptographic martensite in the bearing industry, crystalline Martensite); Under high-power electron microscopy, its substructure can be divided into dislocation entanglement and twinning. The specific structure mainly depends on the carbon content of the matrix.

The higher the austenite temperature, the more unstable the original structure, and the higher the carbon content of the austenite matrix. The retained austenite in the quenched structure will be ?? Xianxianjiao, Jiaobao, Jiaoqiang, Jiangtang, the wall, strange new time Уmouyang, Jiangxi, Yizi, weft, and halo ⒘ Salt beer, R paradox, Kangtuo, at 3%, Ma’s The body is mainly lath martensite with dislocation substructure; when the matrix carbon content is higher than 0.6%, the martensite is lamellar martensite with a mixed substructure of dislocations and twins; the matrix carbon content is 0.75% At the time, large flaky martensite with obvious ridges appeared, and the flaky martensite had microcracks where it collided with each other when it grew.

At the same time, as the austenitizing temperature increases, the hardness after quenching increases and the toughness decreases. However, if the austenitizing temperature is too high, the hardness decreases due to excessive retained austenite after quenching. The content of retained austenite in the structure after conventional martensite quenching is generally 6~15%. Retained austenite is a soft metastable phase. Under certain conditions (such as tempering, natural aging or the use of parts) In), its instability occurs and decomposes into martensite or bainite.

The consequence of decomposition is that the hardness of the parts is increased, the toughness is decreased, and the size changes, which affect the dimensional accuracy of the parts and even normal operation. For bearing parts that require high dimensional accuracy, it is generally hoped that the less retained austenite, the better, such as supplementary water cooling or cryogenic treatment after quenching, and higher temperature tempering [12-14].

However, retained austenite can improve toughness and crack propagation resistance. Under certain conditions, the retained austenite on the surface of the workpiece can also reduce contact stress concentration and increase the contact fatigue life of the bearing. In this case, the process and material composition Take certain measures to retain a certain amount of retained austenite and improve its stability, such as adding austenite stabilizing elements Si, Mn, and stabilizing treatment, etc.

2.2 Conventional Martensite Quenching and Tempering Process Conventional high-carbon chromium bearing steel martensite quenching and tempering is as follows: After the bearing parts are heated to 830~860°C, they are quenched in oil and then tempered at low temperature. The mechanical properties after quenching and tempering are not only related to the original structure and quenching process before quenching, but also largely depend on the tempering temperature and time.

As the tempering temperature increases and the holding time increases, the hardness decreases, and the strength and toughness increase. The appropriate tempering process can be selected according to the working requirements of the parts: GCr15 steel bearing parts: 150~180℃; GCr15SiMn steel bearing parts: 170~190℃. For parts with special requirements, use higher temperature tempering to increase the service temperature of the bearing, or perform a cold treatment at -50~-78℃ between quenching and tempering to improve the dimensional stability of the bearing, or use martensite Step quenching to stabilize retained austenite to obtain high dimensional stability and high toughness.

Many scholars have studied the transformation during heating [2,7~9,17], such as the formation of austenite, the recrystallization of austenite, the distribution of residual carbides and the use of non-spheroidized structure as the original structure Wait. G. Lowisch et al. [3, 8] studied the mechanical properties of bearing steel 100Cr6 quenched after twice austenitization: First, austenitize at 1050°C and quickly cool to 550°C and then air-cooled to obtain a uniform The flake pearlite is then subjected to secondary austenitization at 850°C and quenched.

The size of martensite and carbides in the quenched structure is small, and the carbon content and retained austenite content of the martensite matrix are relatively high. , The austenite is decomposed by tempering at a higher temperature, and a large number of fine carbides are precipitated in the martensite, which reduces the quenching stress and improves the hardness, toughness and bearing capacity of the bearing.

Under the action of contact stress, its performance needs to be further studied, but it can be inferred that its contact fatigue performance should be better than conventional quenching. Sakai Jiuyu et al. [7] studied the microstructure and mechanical properties of SUJ2 bearing steel after cyclic heat treatment: first heating to 1000°C for 0.5h to make spherical carbide solid solution, and then pre-cooling to 850°C to quench the oil.

Then repeat the heat cycle from rapid heating to 750°C for 1 minute and then oil cooling to room temperature for 1 to 10 times, and finally rapid heating to 680°C for 5 minutes oil cooling. At this time, the structure is ultrafine ferrite plus fine carbides (ferrite grain size less than 2μm, carbides less than 0.2μm), superplasticity appears at 710℃ (elongation at break can reach 500%), which can be used This feature of the material is used for warm processing and forming of bearing parts. Finally, it is heated to 800°C to keep the quenching oil and tempered at 160°C. After this treatment, the contact fatigue life L10 is greatly improved compared with the conventional treatment, and the failure mode is changed from the early failure type of the conventional treatment to the wear failure type.

After being austenitized at 820℃, the bearing steel is subjected to short-time hierarchical isothermal air cooling at 250℃, followed by 180℃ tempering, which can make the carbon concentration distribution in the martensite after quenching more uniform, and the impact toughness is better than conventional quenching and tempering Doubled. Therefore, В.В.БЁЛОЗЕРОВ et al. proposed that the uniformity of carbon concentration of martensite can be used as a supplementary quality standard for heat-treated parts.

Foreign heat treatment technology and heat treatment equipment

Foreign heat treatment technology and heat treatment equipment
1. Current status of heat treatment technology

(1) Promote the application of high-pressure air quenching

Foreign heat treatment manufacturers attach great importance to cooling during the heat treatment process. According to the technical and technological requirements of the product, slow cooling, oil quenching, and one-time gas quenching can be performed. Rapid atmosphere circulation cooling uses high-pressure gas injection into the cooling chamber, and the computer controls the flow rate and flow rate changes to achieve the cooling rate within a specific time, so as to achieve the required cooling curve during the heat treatment process and ensure the heat treatment quality of the parts. In the past, the quenching gas used in the gas quenching method was nitrogen, helium, etc., but now it is strongly sprayed with air to cool the workpiece at a very rapid rate. After quenching, the surface has only a very thin oxide film, which is off-white, and the color of the parts is still beautiful. , And save a lot of nitrogen and inert gas, so that the cost of heat treatment is further reduced.

The combination of vacuum low pressure carburizing and high pressure gas quenching is an advanced carburizing and quenching process today. It has fast carburizing speed, excellent carbide structure, small quenching cracking and deformation, energy saving and carburizing agent raw materials, carburized parts The surface quality is good and it is conducive to environmental protection.

(2) The heat treatment equipment adopts oil cooling

Fan cooling, heat exchanger cooling, quenching oil tank cooling and other cooling devices all adopt oil-sealed self-cooling, completely replacing the water-cooled circulation system, and the entire heat treatment furnace does not require any cooling water. For example, hot air circulation fan cooling: change the inlet and outlet pipes of the original water cooling jacket to oil pipes, and place a small oil tank with a diameter of 102mm near the fan. The oil cooling system is fully enclosed. When the fan bearing heats up, the proportion of heated oil is small. , Naturally float upward, causing natural circulation of oil. In the case of a small oil tank with oil storage and natural heat dissipation, the hot oil is added to the circulation after being cooled, so as to completely replace water cooling without fuel consumption and no power. The water in the plate heat exchanger of the quenching oil tank is replaced with cooling oil. The cooling oil is heated by the heat exchange of the hot oil. The change in the specific gravity of the oil causes the cooling oil to circulate by itself. A heat sink is added to the oil tank on the top of the furnace to match the fan. It can achieve the effect of full oil cooling and save a lot of cooling water.

(3) Hydrogen probe is used on the nitriding furnace

The German company Ipsen has applied hydrogen probes and corresponding technologies to measure and control the nitrogen potential in the nitriding furnace to adjust and control the atmosphere of the nitriding furnace and realize the modernization of the nitriding furnace.

(4) Gas radiant tube

At present, most of the heat treatment equipment in Europe has adopted gas radiant tubes and natural gas heating. Gas heating technology and equipment are very mature in Europe. Natural gas burners have a standard series, which are manufactured and supplied by professional burner factories. The inner tube of the gas radiant tube is replaced from stainless steel to ceramic to extend the service life and increase the power. Natural gas heating improves energy utilization and reduces production costs.

2. Heat treatment deformation and prevention methods

There are two types of heat treatment deformation: one is the change of size, and the other is the change of part geometry. The heat treatment technology is different, the deformation of the part size and geometry and the method of preventing deformation are also different.

In the process of heat treatment heating austenitization, the longer the holding time and the higher the temperature, the more carbon is dissolved into austenite and the greater the expansion during martensite transformation. During cooling, martensite expands the most, followed by upper bainite, and the volume changes of lower bainite and troostite are small. When tempering at low temperature, martensite shrinks, and the shrinkage is proportional to the supersaturated carbon content. When heated at room temperature -200°C, part of the retained austenite will be transformed into martensite and will expand. However, due to the decomposition of martensite near 200°C, the expansion has little change in performance.

In conventional heat treatment, the main reason for the shape change of parts is the thermal stress and phase transformation stress that occur during heat treatment heating and quenching. The heating speed is too fast, the parts are too large compared to the heating furnace, and the temperature of each part of the parts is different, which will cause thermal deformation. During heat preservation, the residual stress of processing will be released and deform, and the weight of the part will also cause deformation. When cooling, due to the different cooling rates of different parts of the part, thermal stress will be formed and the part will be deformed. Even if the cooling rate is the same, the cooling is always fast on the surface and slow at the heart. Therefore, the previously transformed surface plastically deforms the untransformed core. If there is segregation of alloy components in the material, or the surface is decarburized, the phase transformation stress will be more uneven and the parts will be more likely to deform. In addition, if the thickness of the parts is uneven, the cooling rate will be different.

In the heat treatment of forgings, the ways to place the parts to reduce deformation are as follows: one is to hang vertically as much as possible, the other is to place it vertically at the bottom of the furnace, and the third is to use two points of horizontal support. The fulcrum positions are at one-third and four of the full length. Among them, the fourth is to lay flat on the heat-resistant steel tooling.

In the cooling process of parts, the type of quenching medium, cooling performance, hardenability, etc. are related to deformation. The change of cooling performance can be adjusted by changing the viscosity, temperature, surface pressure of the medium, using additives, and stirring. The higher the viscosity of the quenching oil and the higher the temperature, the smaller the elliptical deformation. In a static state, the deformation is small.

The spring factory can effectively reduce the deformation in the following ways: ①Salt bath quenching; ②High temperature oil quenching; ③QSQ method; ④Reduced pressure quenching; ⑤One trough three-stage quenching. Salt-bath quenching is similar to high-temperature oil quenching, both of which are quenched at the martensite transformation temperature to increase the uniformity of the martensite transformation. QSQ is double liquid quenching. Decompression quenching is to reduce the liquid surface pressure of the quenching medium, thereby extending the vapor film stage, the cooling rate of the high temperature zone is reduced, and the cooling rate of each part of the part is uniform. The structure of one-tank three-stage quenching is simple. First, the parts are oil-cooled from the quenching temperature to a temperature slightly higher than the Ms point, then out of the furnace, and maintained in the atmosphere to make the overall temperature of the parts uniform, and then oil-cooled to transform the martensite Evenly, the irregularity of deformation is greatly improved.

Galvanizing process

Galvanizing process
1. Process introduction

Zinc is a silver-white metal, brittle at room temperature, with an atomic weight of 65.38 and a density of 7.17g/cm3. It is an amphoteric metal that can interact with acids and alkalis. The actual zinc coating is passivated. Because the galvanized layer is passivated in a solution containing chromic acid, a chromate film of various colors with higher chemical stability can be obtained on the galvanized surface, and its protective ability can be increased by 5 to 8 times, and the surface Beautiful, increased decorative effect.

2. Process characteristics

1. Available gloss, smooth coating

2. It can be directly plated on carbonized, nitrided steel and cast iron

3. Higher current efficiency

4. The waste liquid is easy to handle, just use high pH to precipitate zinc

5. Good conductivity, save power

6. Low hydrogen embrittlement

7. Glossy coating can be obtained at higher temperature

8. Stable plating bath, low toxicity and low cost

3. Various performance parameters

Film thickness (μm) Hardness Gloss Color difference Adhesion Corrosion resistance Galvanized 7~12 90° bending without cracking 12H (National standard neutral salt spray test)

Professional production of heat treatment is booming

Since the country implemented a market economy, the specialized production of heat treatment has developed rapidly since 1995, which is mainly reflected in the rapid growth of private and joint-stock companies specializing in heat treatment processing. In 2003, the total number of such enterprises mainly concentrated in coastal cities was at least 2,000. In recent years, private heat treatment companies in North China, Northeast China and the Mainland have also seen a significant growth trend. There may be 3,000 specialized heat treatment plants nationwide. The average annual turnover of each enterprise is conservatively set at 2 million yuan. The annual turnover of such enterprises in the country can reach 6 billion yuan, accounting for about 20% of the total turnover of heat treatment in the country. This ratio is greater than 10% in the United States and less than 30% in Japan. It is undeniable that this is the greatest achievement made in recent years since the country promoted specialized production in the 1980s, and it is also an inevitable product of deepening reform and promoting a socialist market economy.

Heat treatment production technology transformation and equipment renewal are in full swing

Most private enterprises recognize the importance of a high-tech starting point in maintaining their strong competitiveness. They have sufficient funds and capabilities to purchase advanced heat treatment equipment. Aviation, weapons, and shipbuilding industries have benefited from the country’s national defense modernization policy in recent years and have carried out large-scale technological transformations and equipment updates. The unprecedented development of the automobile industry has created a large demand for advanced heat treatment technology and high-precision heat treatment equipment. Aviation industry companies and coastal private enterprises that mainly target light industrial product molds have added a large number of vacuum heat treatment equipment in recent years, especially high pressure gas quenching equipment. . Automobile and weapon industry enterprises and private enterprises mainly focusing on automobile and motorcycle parts use the multi-purpose furnace production line as the main technical transformation content. The heat treatment department of individual automobile companies has also introduced low-pressure carburizing and high-pressure gas quenching heat treatment production lines. Shipbuilding enterprises take the large-scale pit carburizing furnace with precise control of the carbon potential of the blast furnace temperature uniformity as the technical transformation target. In these enterprises, due to the vigorous development of production technology transformation, the proportion of non-oxidizing heat treatment has reached more than 90%. Basically realize the advanced heat treatment production with less oxidation, less distortion, less pollution, less waste, less labor, less quality dispersion.