Introduction of Japanese high-strength rods and wires

(7) The key to high strength is the transformation of pearlite

As mentioned above, the pearlite of high-carbon steel has much higher strength than the single ferrite phase of low-carbon ordinary steel. From this, it can be seen that pearlite is easy to obtain high strength under a small amount of drawing deformation, so it becomes an important factor for industrialization. On the contrary, it is difficult to achieve the effect of increasing the strength of pure iron no matter how strong the pressure is applied to cold drawing.

The mechanism by which pearlite can rapidly increase its strength through wire drawing is not yet fully understood. An important reason is that the “fine-grain strengthening” that thins the thickness of the lamellae after the crystallization is refined by wire drawing, and the “dislocation strengthening” that hardens the number of dislocations by processing have played an important role. , This is the same phenomenon that the place becomes hard when the steel wire is continuously bent.

For other organizations, such as cementite without grain boundaries before drawing, the strength of cementite can be improved after drawing to the nanometer level; there is also cementite that stabilizes the metal flower (Fe3C) It is decomposed by wire drawing, and the decomposed carbon adheres to dislocations to make it difficult to move, resulting in “solid solution strengthening” which increases the strength. In the past, it was only known that metal compounds would decompose under the action of a large external force. Recently, it has been discovered that all cementite is decomposed, which has attracted attention from all parties.

As a pioneer in the development of high-carbon steel wires, Nippon Steel takes the strength and elongation changes caused by cementite decomposition as an important research topic, and develops high-strength steel wires by studying its mechanism.

The reason why the decomposition mechanism of cementite is not ascertained is that iron is an excessively fine structure, and the cementite after strong processing is also an excessively fine structure of a few nanometers, which is difficult to observe with ordinary equipment, so its mechanism is difficult to explain. But now, through the “high resolution transparent microscope” that can analyze nanostructures and an atomic observer that can magnify 1 million times, the structure of single iron atoms, ferrite, and cementite can be clearly observed. , The research has made great progress and it is expected to be solved in the near future.

(8) The challenge of strength and extensibility

In order to make high carbon steel wire practical, not only the strength, but also the problem of insufficient elongation caused by breaking must be solved. From the perspective of the relationship between the two, when the strength of the steel wire for bridges exceeds 2000 MPa, its extensibility drops rapidly, that is, the highest practical strength should be balanced with the extensibility. From a technical point of view, the pure pursuit of strength can be further improved, but considering the significant decrease in extensibility, the ultimate strength of the radial steel wire is now only specified below 4000MPa.

A steel wire with high extensibility is subjected to a thermal break test by applying uniform pressure on the cross section of the steel wire. After dozens of twists, the vertical direction of the drawn wire breaks (normal breaking), but the steel wire with low extensibility deforms under torsion In the early stage, cracks (twisting) occurred along the vertical direction of the wire drawing. The occurrence of this phenomenon is known as an important reason for high strength. In addition, when the wire diameter is large, twisting occurs at about 2000 MPa, and when the wire diameter is small, it does not occur until 4000 MPa. This is called the “wire diameter effect”. There are many opinions on the causes of twisting cracks. According to research, the decomposition of cementite is the main cause.

(9) Minimize the high-strength steel processed by wire drawing

Use a processing process that takes into account both the strength and elongation of the steel. When strengthening the steel wire, first increase the strength by toughening treatment, and then increase the increase in strength per deformation (work hardening rate) by increasing the wire drawing (processing deformation) , As well as steel wire for bridges, some measures should be taken to suppress the strength drop caused by heating such as galvanizing (450℃) and bluing treatment.

While adopting the above methods to maintain high strength, it should also prevent the decrease in extensibility, that is, starting from the causal relationship that maintaining extensibility can avoid twisting, the test results prove that the toughened material is used to increase the strength and reduce the amount of wire drawing. The method of increasing the work hardening rate is more effective than increasing the amount of wire drawing to maintain the elongation. For example, when the final strength target is 2000 MPa, for low toughness treated materials (1000-1300 MPa level), twisting will easily occur when the target is reached by increasing the amount of drawing processing; if the 1400 MPa toughness treatment material is appropriately reduced It does not happen when measuring. It can be seen that the latter is more effective for maintaining the necessary extensibility under high strength. Precision spring

There are also many strengthening methods for toughening materials, and the representative method is alloying. That is, increasing the content of carbon, vanadium, chromium, silicon and other elements in the steel can increase the strength. Among them, the general basic method is to increase the carbon content; silicon can play a positive role in the solid solution strengthening of ferrite; chromium can make the thickness of the lamellae finer during the toughening treatment, so that the effect of increasing the strength is obvious. In addition, adding 0.2 to 0.5% of chromium to high carbon steel (containing C0.82%) can significantly increase the work hardening rate during wire drawing, so it is very helpful to increase the strength of high carbon steel wire. The application of meridian steel wire and bridge steel wire has been introduced in the previous article.

Introduction of Japanese high-strength rods and wires

At present, in order to reduce CO2 emissions, automobile manufacturers are generally adopting measures to reduce fuel consumption by lightening the car body. Recently, high-strength aluminum alloy materials composed of aluminum with a small specific gravity are used, and the simple evaluation of the materials used uses the specific strength per unit weight. (Tensile strength/specific gravity).

Steels of 800 to 1200 MPa, which are generally called high-strength steels, have less specific strength than aluminum alloys, but steel materials have various structures. As methods to increase the strength of steels, there are “fine grain strengthening”, “solid solution strengthening”, and Organizational control techniques such as precipitation strengthening” and “dislocation strengthening”. Taking fine grain strengthening as an example, the following is an explanation. The method of refining the crystals of usually 20-30um ferrite to increase its strength, especially the effect of increasing the strength when the grain diameter is refined below 1um (see Table 2). The combination of microstructure technology and processing and heat treatment may achieve ultimate strength. Based on this, “ultra-high-strength steel” that rivals aluminum alloys has been developed.

Table 2 The relationship between ferrite grain refinement and strength

Grain diameter (um) 1251020304050

0.2C% strength (MPa) 920 700 400 325 280 240 230 220

Solid solution strengthening refers to the hardening phenomenon caused by the increase of a large amount of intrusive atoms such as C and N and substitution elements such as Si and Mn. Precipitation strengthening is due to the increase of compounds, and dislocation strengthening is due to the increase in the number of dislocations in the steel produced by processing. The hardening phenomenon caused.

(5) High carbon steel wire pursuing the ultimate strength

In rod and wire products, the material that pursues ultimate strength is high-carbon steel wire. The process technology of steel wire for bridge is described as follows.

Secondary processing companies require toughening treatment for hot-rolled semi-finished products to improve their strength while requiring good workability. This technology obtained a British patent in the 19th century. This kind of heat treatment adopts isothermal and homogenized heat treatment in a metal bath with good thermal conductivity to transform the ferrite and cementite structure existing in the steel into austenite at room temperature, and then transform it into austenite by rapid cooling Pearlite (Layered structure composed of cementite and ferrite). In the pearlite structure produced by this method, the strength of the wire is determined by the spacing between cementites (that is, the thickness of the lamellae). The smaller the thickness, the higher the strength. If it is cooled to room temperature without toughening treatment, the thickness of the lamellae is not uniform and the drawing processability is reduced, and the final strength is also reduced. For this reason, toughening treatment is an indispensable process for the production of steel that requires high strength.

In the process of the steel structure from high temperature to low temperature, austenite forms pearlite and grows up; but when it is rapidly cooled from 950°C to a low temperature of 550°C, it becomes uniform pearlite, which changes from hard and brittle cementite phase. It is formed side by side with the soft and good extensibility ferrite phase in the same direction; while for automotive plates and other materials with good workability, a softer single ferrite phase is formed.

If the toughening treatment can be omitted, it will bring great benefits to the user to simplify the processing. The above-mentioned “DLP” equipment can play this role, that is, uniformly adjust the cooling in a salt bath at 550°C to make it a semi-finished product When it turns into pearlite. For the production of high-strength steel wire for concrete shrinkage, Nippon Steel also uses “DLP” equipment processing to create conditions for users to eliminate toughening processing. In the production of steel wire for bridges, after toughening treatment, it is first subjected to pickling and zinc phosphate film treatment for “lubrication” treatment after being toughened, and then drawing is performed in multiple stages at room temperature. The hot-rolled Φ13mm semi-finished wire rod is cold drawn to Φ7mm, and finally galvanized to improve the corrosion resistance. However, the radial steel wire for tire reinforcement has many processing steps, that is, it uses Φ5.5mm wire, which is drawn into a Φ3mm steel wire. After intermediate toughening treatment, it is then drawn to a Φ1.5mm steel wire, and then finally toughened. Treatment and brass plating (which can improve the adhesion to rubber) treatment, and finally wire drawing to Φ0.3mm and composed of 5 pieces. The reason for the intermediate toughening treatment is to prevent wire breakage due to poor toughness when the wire is drawn from Φ5.5mm to Φ1.5mm at a time. In short, when all steels become higher in strength, their extensibility decreases as their strength increases. Therefore, the key to practical high-strength limit is extensibility. The key technology of high-strength high-carbon steel wire is also how to maintain extensibility.

(6) High carbon steel wire with finer diameter and higher strength

The strength of the steel wire has an obvious relationship with the wire diameter. For example, the wire diameter of the steel wire for bridges is Φ5~7mm, and its strength is below 2000MPa, while the radial steel wire for tires with a wire diameter of Φ0.2~0.4mm has a strength of about 4000MPa. . By increasing the strength of the steel wire, it is helpful to reduce the construction cost and reduce the weight of the tire.

When the diameter of the steel wire is reduced, due to the pressure applied during the wire drawing process, the strength will increase correspondingly as the degree of thinning (deformation processing amount) increases, which is the fundamental principle. Although there are certain differences between different steel grades, the strength of the steel wire with a strength of 1200~1500MPa after toughening treatment continues to increase when it continues to be drawn. The deformation of steel wire for bridges is about 1.5, and the deformation of meridian steel wire is as high as 3.5 to 4. The relationship between the deformation and strength of the processing is shown in Table 3.

Table 30. Relationship between processing deformation and strength of 82%C steel

Machining deformation (%) 012345

Tensile strength (MPa) 120017002000280035004300

This principle can be explained by the changes in the structure of steel. The smaller the width of the ferrite interval (that is, the thickness of the lamella), the higher the strength. Because the steel wire that has just been toughened, the crystal directions of ferrite and cementite are random and irregular. The crystals of high-strength cementite and good elongation ferrite are processed by wire drawing. The direction becomes uniform, so the thinner the steel wire, the smaller the thickness of the sheet and the higher the strength. For example, the grain size of ferrite in steel is Φ10~30um, which is only 0.5~0.8um as the “super metal (high-strength steel)” in national project development; while the thickness of steel wire after toughening is only It is about 0.1um (1200~1500MPa). The most advanced radial steel wire becomes 0.01um after about 20 times of drawing, and the corresponding strength also rises to 4500MPa.

It is a common phenomenon of steel materials to increase the strength if the crystallographic direction after rolling is the same, but the crystals only extend in the rolling direction and not in the width direction during rolling of products such as thin plates. Therefore, the crystal grain size varies with the direction. Also different. The cold drawing die used in the wire drawing process uses a strong pressure different from the rolling method to uniformly squeeze the wire from all around, so the crystallization can only develop in the drawing direction. As a result, the lamellae are uniform and the thickness is reduced, which makes the strength Improve quickly. In order to apply strong pressure to ultra-high-strength steel wire, ultra-high hardness diamond molds are often used when drawing. Stainless steel spring

Introduction of Japanese high-strength rods and wires

Introduction of Japanese high-strength rods and wires
(1) Rods and wires can be processed into a variety of products

In addition to being directly used in construction, rods and wires can also be processed into various parts for other purposes. Taking a common car as an example, each car uses about 150Kg of rods and wires, which is about 10% of the car’s weight. Among them, the materials used for engine components (crankshafts, camshafts, valve springs, etc.) and drive system components (various gears, screw shafts, etc.) are inseparable from rods and wires. “Driving, turning and stopping” are the basic actions of a car. If a component supporting these actions is damaged, the car will stop running. This shows their importance.

In addition, as a reinforcing material for automobile tires, some organic fibers were used in the past. Later, the rigidity of automobile tires has been significantly improved after the use of radial steel wires. Therefore, in recent years, the tire damage and deflation accidents during automobile driving have been greatly reduced; now as a standard The Φ0.3mm radial steel wire used in the product has made a significant contribution to saving resources and improving tire performance through high-strength (an annual output of 300,000 tons). According to statistics, the amount of meridian steel wire in 1975 was ~ 20,000 tons, which increased sharply to 100,000 tons in 1985, 200,000 tons in 1995, and 300,000 tons in 2005, showing its rapid development.

In buildings and steel structures, high-strength rods and wires have also begun to be widely used. Among them, such as telegraph poles and concrete reinforcement materials, suspension bridges, cable-stayed bridges, etc., their strength is generally reinforced 3 to 4 times, which also brings many benefits.

In addition, various bolts, nuts and springs made of rods and wires are also widely used in various aspects, led by the machinery industry; even our common daily necessities such as piano wires, guitar strings and fishing wires are processed by wires. Become. Although their final products have different shapes and properties, they have in common that they are all processed from steel rods and wires. Nippon Steel produces rods and wires, including Muroran Steel Plant, Kamaishi Steel Plant, and Junjin Steel Plant. The classification and use of wire products are shown in Table 1.

Table 1 Classification and use of rods and wires

Classification specification name JIS symbol main purpose

Ordinary wire, mild steel wire SW(-)RM nail, steel wire, traveller, etc.

Special wire rod hard steel wire rod

Piano wire

Spring steel wire

Very low carbon steel wire SW(-)RH

SW(-)RS

SUP

Steel rope, tire wire, spoke wire

Meridian steel wire, steel wire for bridge, steel wire for compaction of concrete

Suspension spring, valve spring

Steel wire for glass enclosure

Wire rod for cold working Wire rod for cold rolling

Low alloy steel spring wire

Wire rod for polished steel

Wire for reinforced concrete SW(-)RH

SCM

SGD

SD various steel bolts, nuts, mechanical parts

Various steel bolts, nuts, mechanical parts

Polished rod, wire

Rebar

(2) Bars and wires supplied as semi-finished products

The difference between bars, wire rods and other hot-rolled steels is that they are supplied as semi-finished products in a hot-rolled state, which are then processed and heat-treated by users such as automobile manufacturers and component manufacturers to become final products; and medium-thick plates and thin plates Steels such as steel pipes, steel pipes and H-beams are supplied by steel mills rolled into finished steel products of a certain shape and strength.

Take the processing process of a pinball as an example. The brief introduction is as follows: the wire produced by the steel plant is sent to the secondary processing factory, and is cold drawn -> molded into a ball -> rough polishing -> surface marking -> heat treatment -> grinding -> mirror Polished -> After chrome plating, the product is formed. The small pinball section has three different structures: the surface layer is 3um chromium-plated, the lower 1mm thickness is the martensite structure with 0.8% carbon after carburizing treatment, and the inside is iron with only 0.2% carbon. The soft structure of body + martensite. The above structure makes the surface of the pachinko ball have high hardness and strong impact resistance, and the interior of the pachinko ball can absorb the impact and make the ball difficult to break. This carburizing treatment is also applied when using rods and wires to produce gears and other parts.

In addition, the size, weight, and processing accuracy of the pinball depend on the molding process. The general size tolerance is controlled within 0.01mm and the weight error is within 0.01g. For this reason, the requirements for the workability of the wires used are very strict. This shows the difference between bars, wires and other steels.

(3) Consider the adjustment and cooling of the processing procedure

Generally, the cost of materials made of rods and wires only accounts for 20% of the production cost of the parts (the remaining 80% is forging 20%, cutting 40%, heat treatment 10% and other 10%). Due to the high cost of secondary processing, the development of steel should focus on favoring secondary processing. Even if the final product requires high strength, the rods and wires supplied by steel mills are also required to be “easy to process in order to simplify the processing procedures.” In other words, the rods and wires provided should be the opposite of the high strength required by the final product, that is, they should be softer, thus creating a contradiction. In order to meet this requirement, “adjusted cooling” technology has been adopted. Generally, the strength of the hot-rolled steel material is increased after rapid cooling, and the strength is decreased after slow cooling. “Slow cooling” equipment is to keep the rolled wire coils warm and slowly cool them to reduce their strength. For example, bolts are cold forged with wires at room temperature. The processed steel must be soft to make it easy to form. For this reason, the above-mentioned slow cooling measures are taken for the hot-rolled material to improve its cold forgeability, and the strength is increased by heat treatment after processing to reach the required level.

Due to the different strength requirements of various products, there are also many cooling methods. In addition to the above-mentioned “slow cooling” equipment, there are also cooling methods such as “air cooling” where air is fed for faster cooling, “DLP” through 550°C salt bath cooling, and “EDC” through hot water cooling. Among them, the “DLP” equipment has obvious adjustment effects on the strength and extensibility of high-carbon steels that require high strength, which is beneficial to users to simplify the process in the subsequent toughening treatment, especially the use of salt baths that do not contain metals such as lead, not only thermal conductivity Good, and the salt adhering to the wire can also be simply washed with hot water to remove it and recycled and reused, and it has less pollution than the lead bath treatment.

(4) Master the strength of steel through organizational control

As mentioned above, adapting the properties of rods and wires to the user’s processability is the first condition. However, due to the wide range of purposes and applications, the required strength level of the final product is in the range of 300-5000 MPa. For example, ordinary wires for steel wire and wire mesh are only 300 MPa, while the aforementioned radial steel wires for automobile tires and wire saws for cutting silicon wafers require high-strength wires up to 4000 MPa. For this reason, the chemical composition and crystalline structure of rods and wires are also diversified, because the strength of steel increases with the increase in carbon content, but the corresponding extensibility needs to be considered in thin and medium plate products, so carbon is contained The amount is generally kept below 0.2%. However, in order to meet the requirements of various strengths for rods and wires, the range of carbon content has been expanded to between 0.01 and 1.1%; with such a wide range of carbon content, the organizational forms that affect strength, elongation and toughness are also diverse.

Heat treatment method of long flat steel wire spiral spring

Research on Heat Treatment Method of Long Flat Wire Coil Spring
Summary

This article introduces the use of resistance heating method to heat treat flat steel wire cylindrical spiral compression elastic yellow with a length of 50m and an outer diameter of ф60mm.

When selecting electric heating equipment and determining the basic calculation formula of the process parameters, the test results show that this method can meet the requirements of the spring hot

Management requirements, saving investment, simple and easy.

Preface

The heat treatment of a flat section cylindrical spiral compression spring with a length of 50m and an outer diameter of ф60mm is a foreign aid task we accept.

In foreign countries, this kind of spring is made by using oil-quenched and tempered steel wire to be wound into shape and then tempered at low temperature to eliminate winding stress.

In China, there is no professional factory that produces such flat section springs so far.

It is made of round steel wire rolled or drawn, wound into a spring and then quenched and tempered. Obviously quenching such a long spring

, Tempering treatment is very difficult. After investigation and analysis and a large number of experiments, we have initially explored the resistance method heating and quenching of this long spring.

The fire process has achieved relatively satisfactory results.

1. Determination of resistance heating process plan and equipment design

According to the longer characteristics and technical requirements of this spring, we compared the following three process schemes, namely flame quenching, high frequency

Quenching and resistance heating quenching. After analysis and comparison, it is believed that although the resistance heating quenching scheme also has certain technical difficulties, the most

The major feature is a professional equipment that does not require spring rotation during heating and does not spray coolant. Therefore, it is determined to use the resistance heating quenching method

experimenting. We derive the function of temperature change with time on the basis of heat and electricity, and derive the resistance heating process in turn

The change law of the heat of medium electric energy converted into thermal energy and radiant heat at any time, as a reference basis for determining the parameters of resistance heating workpieces

. Since the derivation is long and does not belong to the main content of this article, it is omitted here and only a brief introduction to equipment selection.

2. Test equipment and results

1. Test equipment

The equipment used in the test includes: (1) a ZUDG—253 salt bath furnace transformer; (2) insulation for spring heating and quenching

One set of fixing devices; (3) One cooling water tank; (4) One WGG2-302 optical pyrometer, one IRT-1200 infrared measuring instrument

; A stopwatch.

2. The main content of the test

Determine the quenching heating time and tempering time, select the quenching medium and observe the metallographic structure.

3. Test results

(1) The quenching heating time is determined according to the resistance heating is the internal heat source heating, and the temperature is a function of time. This test

A stopwatch, an optical pyrometer and an infrared thermometer are used to measure the continuous heating that the specimen can reach different temperatures under certain electrical parameters.

Time to determine the quenching heating time.

(2) For the selection of tempering time, use a stopwatch and infrared thermometer to test. The results show that the tempering heating time is 25—

30S is more suitable.

(3) The selection of quenching medium was tested according to the three quenching mediums of water and oil polyvinyl alcohol. From the test results

It can be seen that these three quenching media can meet the hardness and hardenability requirements, but the water-quenched specimens are obviously brittle, and the oil pollution is large.

Easy to catch fire. After a large number of experiments and comparisons, it is more appropriate to choose a polyvinyl alcohol quenching agent with a concentration of 0.5%.

(4) Metallographic structure. The test results show that this kind of spring is suitable for selecting electrical parameters and can ensure stable electrical parameters.

Under the quenching heating for 2 minutes, the temperature can reach 860-880℃, and the extremely fine quenched structure can be obtained.

Obvious characteristics of martensite needle-like structure can be observed. The tempering process is 380℃×28S, and the hardness can reach 39-43HRC. Metallographic Group

The weave is tempered troostite + a small amount of tempered aritite, and there is no obvious decarburized layer, so it has good comprehensive mechanical properties.

3. Analysis of test results

1. Resistance heating has a higher heating rate, which can refine the austenite grains when the steel is heated.

When the time is properly controlled, overheating will generally not occur. The relationship between oil quenching hardness and heating time is known: although the electrical parameters

Under stable conditions, the hardness requirement can be achieved by heating for 1.5 minutes, but considering the factor that the inner side of the coil is thicker than the outer side during winding

, So it is more appropriate to extend the heating time by 2 min.

2. In terms of resistance heating, time is very sensitive to temperature, so the material and cross-sectional dimensions are required to be uniform

Consistent. On the whole, the resistance method has a fast heating speed and proper time control will not cause overheating. But when the working section is obvious

When it changes, it may cause the local temperature to be too high, or even over-burning or even fusing, so when using resistance heating equipment to heat the workpiece

At the same time, especially when dealing with such special-shaped cross-section springs, it is necessary to prepare an air compressor for local cooling and reduce the temperature difference; at the same time

Before heating, the rust on the surface of the workpiece must be removed to prevent poor electrical heating from causing electrical sparks to burn the workpiece.

3. This test uses polyvinyl alcohol fire agent, which can meet the requirements of spring quenching hardness, and reduce the deformation and the phenomenon of opening out.

The cooling rate can be between water and oil, which can greatly reduce the thermal stress and transformation stress of the transformation from austenite to martensite

How to calculate the core shaft of a core coil spring

How to calculate the core shaft of a core coil spring
When there is a cored coil spring, due to the elastic deformation of the material to recover, the spring diameter, number of turns and pitch of the coiled spring will change after relaxation, resulting in elastic rebound, so the core shaft diameter D should be smaller than the spring inner diameter D1 There are many kinds of information about the calculation formula of the mandrel, but the calculation is more troublesome. Experience has proved that the following formula is more general.

Namely: D=(0.75~0.85)D1

Where D—the diameter of the mandrel;

D1—The inner diameter of the spring.

Applicable standards for steel wire products

Applicable standards for steel wire products
1. Carbon spring steel wire for mechanical spring 0.4~6.0mm YB/T5220 Suitable for cold drawn carbon spring steel wire for furniture, car seat cushions, interior decoration, etc.

2. Carbon spring steel wire 0.4~6.0mm gb4357 Cold drawn carbon spring steel wire with circular section suitable for machinery

3. Carbon spring steel wire for important purposes 0.4~6.0mm gb/T4358 is suitable for manufacturing springs with high stress, valve springs and other important purposes without heat treatment

4. Mattress steel wire 0.4~6.0mm BS4637 is suitable for cold drawn carbon spring steel wire for furniture, interior decoration, etc.

5. Umbrella steel wire 1.0~6.0mm YB/T097 is suitable for cold drawn round steel wire for umbrella making

6. Spoke wire 1.75~4.5mm  YB/T5005

Suitable for cold drawn carbon structure steel wire for bicycle spokes, and for motorcycle spokes, please refer to the implementation

7. High-quality carbon structural steel wire 0.35~10mm GB3206 Suitable for cold drawn and silver-bright high-quality carbon structural steel wire

8. Cored steel wire for ACSR 1.2~5.5mm GB/T3428ASTMB498—93 Galvanized steel wire for the manufacture of ACSR for overhead power lines

9. Galvanized low carbon steel wire for communication lines 1.2~6.0mm GB346 is suitable for transmission lines such as telegraph, telephone, cable broadcasting and signal transmission.

10. Flattened steel wire 1.0~4.0mm 2002-15 monitor

2003—3 Supervisor Applicable for manufacturing hair clips, umbrella ribs, bras and other rolling steel wires

11. Pipe-making steel wire 1.0~2.2mm 2001-11

2003-10 Supervision Applicable to manufacturing steel wire for automobile cable

12. Hardware spring steel wire 1.0~5.0mm 2004-8 Supervision Spring steel wire suitable for hardware products

13. Galvanized steel wire for galvanized steel strand 1.0~3.5mm YB/T5004—2001 Galvanized steel wire for the manufacture of steel strand for overhead power lines

Three ways to remedy unqualified heat treatment

Three ways to remedy unqualified heat treatment
Introduce several methods of using heat treatment to remedy unqualified parts, so that heat treatment can meet the requirements of performance and avoid unnecessary losses.

1. Improve graphitization annealing process to remedy ductile iron castings

For fork rods with a grade of 0o-7, considering the processing performance and use performance, the technical requirements for its graphitization annealing are: annealing hardness 147-210I-IB; matrix structure 50%-80% pearlite (P) +Add% to 50% ferrite (F). The graphitization annealing process is 900-920oC×1.5h, the furnace is cooled to 720oC, and the furnace is air cooled.

There are a batch of fork rods after annealing, the test hardness is 180I-IB; the metallographic structure is 4%-5% pearlite + 95%-96% ferrite. The matrix organization is unqualified. The chemical composition of this batch of fork rods is unqualified, and the carbon content is low, which is the reason for the too little pearlite in the matrix structure after annealing. The air-cooling temperature of nodular cast iron during graphitization annealing process determines the content of pearlite and ferrite in the matrix structure after annealing. This is due to the higher the eutectoid transformation temperature. The higher the actual carbon content in austenite, the more pearlite content after eutectoid transformation and the less ferrite content. Through process tests, we can find out the reasonable temperature of the fork rod to reach the annealing technology requirements to make up for its lack of chemical composition. The process test method is: install 40 pieces of furnace, 900-920oC×1.5h. Respectively furnace-cooled to 850oC, 800oC, 780oC, 750oC, air-cooled 10 pieces each.

It is known from the above test results that when the air cooling temperature is 780°C, it meets the requirements of the hardness and matrix structure of the workpiece after graphitization and annealing. The improved graphitization annealing process was used to remedy the deficiencies of this batch of ductile iron castings due to the low carbon content.

2. Normalizing to refine the grains and remedy the coarse-grained carburized parts

The clutch for XYD1 drilling rig is made of cr, the carburizing layer depth is 1. plus l+50mm, and the tooth quenching hardness is 56-62HRC. During the gas carburizing process of a furnace clutch, the temperature of the carburizing furnace was caused by a temperature control instrument problem. The metallographic structure of the furnace workpiece was detected. The carburized layer was about 1.70tma; the grain size was 4-6, and a small amount was 5. The carburized part of this furnace has an out-of-poor penetration and coarse grains, which are unqualified parts. From the shape and use of the clutch, the clutch tooth thickness is 7.5mm, and the carburized layer is 1.70tran, which will not affect the use of the workpiece. We can adjust the induction hardening parameters to control the hardened layer of the tooth within 1.50mm. Coarse grains can be refined by normalizing. In order to prevent the surface oxidation and decarburization of the workpiece during the normalizing heating process, kerosene can be dropped during the heating process to control the atmosphere in the furnace. The process is 880-900℃×lh, kerosene 6o drops/min, and the furnace is cold.

After normalizing, the metallographic inspection result of the clutch is that the carburized layer is 1.73nm; the grain size is 6-7. After high-frequency quenching and tempering, the tooth hardness reaches the technical requirement of 56-Co2HRC.

3. Increase the carburizing process to remedy the parts with insufficient carbon content

Fork rod N58/4-57 for automobile drilling rig, material 35 steel, technical requirement: z and 16tara×20ram notch quenching hardness 40-45mtc. After a batch of workpieces are high-frequency quenched, the hardness is tested to 2OHRC, and the carbon content is 0+15% after testing.

From the perspective of its use, the fork lever only requires wear resistance at the notches and grooves, but the overall strength is not required. Therefore, the carburizing process is used to remedy the low carbon content of the workpiece. The carburized layer is 0.801.20ram. After carburizing, high-frequency quenching and tempering are performed on the f section and the 16ram × plus Ⅱ Ⅱ rI. The hardness of the two parts has reached the technical level. Claim.

For the specific requirements of unqualified parts, heat treatment can be used to meet the performance requirements and reduce unnecessary losses. Of course, for parts with strict requirements that cannot meet the performance requirements by heat treatment, they must be scrapped.

Analysis and measures of 7 kinds of cracks in die steel quenching

6 cold treatment cracks

Die steels are mostly medium and high-carbon alloy steels. After quenching, some of the subcooled austenite has not been transformed into martensite, and it remains in use as retained austenite, which affects the performance. If it is placed below zero to continue cooling, it can promote the martensite transformation of retained austenite. Therefore, the essence of cold treatment is to continue quenching. The quenching stress at room temperature and the quenching stress at zero are superimposed, and cold treatment cracks are formed when the stack response force exceeds the strength limit of the material.

Precaution:

(1) After quenching, place the mold in boiling water for 30-60 minutes before cold treatment, which can eliminate 15%-25% of the internal quenching stress and stabilize the retained austenite, and then perform conventional cold treatment at -60℃, or -120℃ Cryogenic treatment, the lower the temperature, the greater the amount of retained austenite transformed into martensite, but it is impossible to complete the transformation. Experiments show that about 2%-5% of retained austenite remains, and a small amount of retained austenite is retained as needed. The tensite can relax the stress and act as a buffer. Because the retained austenite is soft and tough, it can partially absorb the energy of the rapid expansion of martensitization and ease the transformation stress;

(2) After the cold treatment is completed, take out the mold and put it in hot water to heat up, which can eliminate 40%-60% of the cold treatment stress. After heating to room temperature, it should be tempered in time, and the cold treatment stress will be further eliminated to avoid the formation of cold treatment cracks, obtain stable tissue performance, and ensure the mold No distortion occurs during product storage and use.

7 Grinding cracks

It often occurs in the grinding and cold working process of the finished mold product after quenching and tempering. Most of the micro cracks formed are perpendicular to the grinding direction, and the depth is about 0.05-1.0mm.

(1) Improper pretreatment of raw materials, failure to fully eliminate lumps, nets, and bands of raw materials, and serious decarburization;

(2) The final quenching heating temperature is too high, overheating occurs, the grains are coarse, and more retained austenite is generated;

(3) Stress-induced phase transformation occurs during grinding, which transforms the retained austenite into martensite, and the structure stress is large. In addition, due to insufficient tempering, there is more residual tensile stress, which is superimposed with the grinding structure stress , Or due to the grinding speed, large feed rate and improper cooling, the metal surface grinding heat will rise sharply to the quenching heating temperature, and then the grinding fluid will be cooled, resulting in secondary quenching of the grinding surface. Various stresses are integrated, exceeding this The material strength limit causes grinding cracks on the surface metal.

Precaution:

(1) The raw material is reformed for forging, and the double cross shape is changed to upsetting for multiple times. After four upsetting and four pulling, the forged fiber structure is symmetrically distributed around the cavity or axis, and the final high temperature residual heat is used for quenching. Subsequent high-temperature tempering can fully eliminate lump, mesh, band and chain carbides, and refine the carbides to 2-3 levels;

(2) Formulate advanced heat treatment technology to control the final quenched retained austenite content not to exceed the standard;

(3) Tempering in time after quenching to eliminate quenching stress;

(4) Appropriately reducing the grinding speed, grinding amount, and grinding cooling rate can effectively prevent and avoid the formation of grinding cracks.

8-wire cutting crack

Precaution:

(1) After quenching, the die steel should be tempered in time, fully tempered, and repeatedly tempered to eliminate the internal stress of quenching;

(2) After quenching, the mold steel is generally not suitable for tempering at 350-400~C, because T structure often appears at this temperature, the mold with T structure should be reprocessed, and the mold should be rust-proofed to improve corrosion resistance;

(3) Low-temperature preheating of hot-worked molds before service, and a low-temperature tempering after a period of service of cold-worked molds to eliminate stress, not only can prevent and avoid stress corrosion cracking, but also greatly increase the service life of molds. Significant technical and economic benefits.

Analysis and measures of 7 kinds of cracks in die steel quenching

4 peeling crack

When the mold is in service, under stress, the quenched hardened layer is peeled off from the steel matrix piece by piece. Due to the difference in specific volume between the surface layer structure and the core structure of the mold, the surface layer forms axial and tangential quenching stresses during quenching, tensile stress is generated in the radial direction, and sudden changes in the interior, and peeling cracks occur at a narrow range of sharp stress changes, which often occur in During the cooling process of the surface chemical heat treatment mold, the inner and outer layers of quenched martensite will not expand at the same time due to the different time between the chemical modification of the surface and the phase transformation of the steel matrix, resulting in a large phase transformation stress, resulting in the chemical treatment of the permeated layer from the matrix structure Peel off. Such as flame surface hardened layer, high frequency surface hardened layer, carburized layer, carbonitrided layer, nitrided layer, boronized layer, metalized layer, etc. After quenching, the chemically infiltrated layer is not suitable for rapid tempering, especially the rapid heating of low temperature tempering below 300~C, which will promote the formation of tensile stress on the surface layer, while the core of the steel matrix and the transition layer will form compressive stress. The chemically permeable layer was peeled off by tear.

Precaution:

(1) The concentration and hardness of the chemical infiltration layer of mold steel should be gradually reduced from the surface to the inside, and the bonding force between the infiltration layer and the matrix should be enhanced. After infiltration, the diffusion treatment can make the transition between the chemical infiltration layer and the substrate uniform;

(2) Diffusion annealing, spheroidizing annealing, and quenching and tempering treatment are carried out before the chemical treatment of die steel to fully refine the original structure, which can effectively prevent and avoid peeling cracks and ensure product quality.

5 mesh cracks

The depth of the crack is relatively shallow, generally about 0.01-1.5mm deep, radial, alias crack.

The main reasons are:

(1) The raw material has a deep decarburization layer, which is not removed by cold cutting, or the finished mold is heated in an oxidizing atmosphere furnace to cause oxidative decarburization;

(2) The metal structure of the decarburized surface layer of the mold is different from the martensite of the steel matrix. The carbon content and specific volume are different. The steel decarburized surface layer produces large tensile stress during quenching. Therefore, the surface metal is often pulled into a network along the grain boundary. ;

(3) The raw material is coarse-grained steel, the original structure is coarse, there is large ferrite, which can not be eliminated by conventional quenching, and it remains in the quenched structure, or the temperature is not accurately controlled, the instrument fails, the structure is overheated, or even burned, The grains are coarsened and the grain boundary bonding force is lost. When the mold is quenched and cooled, the carbides of the steel precipitate along the austenite grain boundaries. The grain boundary strength is greatly reduced, the toughness is poor, and the brittleness is large. It is networked along the grain boundaries under tensile stress. split.

Precaution:

(1) Strict chemical composition of raw materials. Metallographic structure and flaw detection inspection, unqualified raw materials and coarse grain steel are not suitable for mold materials;

(2) Choose fine-grain steel and vacuum electric furnace steel, review the depth of the decarburization layer of the raw materials before putting it into production, and the cold cutting machining allowance must be greater than the depth of the decarburization layer;

(3) Develop an advanced and reasonable heat treatment process, select a microcomputer temperature control instrument, and the control accuracy can reach ±1.5℃, and the instrument will be checked on site regularly;

(4) The final treatment of mold products selects vacuum electric furnaces, protective atmosphere furnaces and fully deoxidized salt bath furnaces to heat the mold products to effectively prevent and avoid the formation of network cracks.

Analysis and measures of 7 kinds of cracks in die steel quenching

3 arc cracks

It often occurs in sudden changes in the shape of mold corners, gaps, cavities, and die wiring flash. This is because the stress generated at the corners during quenching is 10 times the average stress of a smooth surface.

In addition,

(1) The higher the carbon (C) content and alloying element content in steel, the lower the Ms point of steel. If the Ms point decreases by 2℃, the quenching cracking tendency increases by 1.2 times, the Ms point decreases by 8℃, and the quenching cracking tendency increases by 8 Times;

(2) The transformation of different structures in steel and the transformation of the same structure are not at the same time. Due to the different structure specific tolerances, huge structure stress is caused, which leads to the formation of arc-shaped cracks at the boundary of the structure;

(3) After quenching, it is not tempered in time, or the tempering is not sufficient, the retained austenite in the steel is not fully transformed, and it remains in the service state to promote the redistribution of stress, or the retained austenite becomes martensite when the mold is in service The change produces new internal stress, and when the comprehensive stress is greater than the strength limit of the steel, an arc-shaped crack is formed;

(4) It has the second type of tempered brittle steel. After quenching, high temperature tempering and slow cooling will cause harmful impurity compounds such as P and s in the steel to precipitate along the grain boundary, which will greatly reduce the grain boundary bonding force and strength and toughness, and increase the brittleness. Arc-shaped cracks are formed under the action of external force.

Precaution:

(1) Improve the design, try to make the shape symmetrical, reduce shape mutations, increase process holes and reinforcing ribs, or use combined assembly;

(2) Filled corners instead of right angles and sharp edges, and through holes instead of blind holes, improve processing accuracy and surface finish, reduce stress concentration sources, and generally have low hardness requirements for unavoidable right angles, sharp edges, blind holes, etc. , It can be bandaged or stuffed with iron wire, asbestos rope, refractory mud, etc., artificially create a cooling barrier, so that it can be slowly cooled and quenched to avoid stress concentration and prevent arc-shaped cracks from forming during quenching;

(3) The quenched steel should be tempered in time to eliminate part of the quenching internal stress and prevent the quenching stress from expanding;

(4) Tempering for a longer time to improve the fracture toughness of the mold;

(5) Fully tempered to obtain stable tissue performance;

(6) Multiple tempering can fully transform the retained austenite and eliminate new stress;

(7) Reasonable tempering to improve the fatigue resistance and comprehensive mechanical properties of steel parts; for mold steels with the second type of temper brittleness after high temperature tempering, they should be cooled quickly (water cooling or oil cooling) to eliminate the second type of temper brittleness. Prevent and avoid arc crack formation during quenching.