Method of inspecting steel inclusions

Method of inspecting steel inclusions
Inclusions in steel have an important impact on the performance of steel. Inclusion qualification inspection is an important part of ensuring the quality of steel. There are three current inspection methods:
1. Metallographic sample method
At present, steel companies generally use the metallographic sample method to inspect the inclusions in the steel, that is, after grinding and polishing the sample to be tested into a metallographic sample, it is exposed to the surface of the metallographic sample under an optical microscope or a scanning electron microscope. The inclusions are tested and studied. The advantages of the metallographic specimen method are simple, intuitive and fast. However, since the content of inclusions in steel is very small, their distribution is irregular. However, it is easy to use this method for single or multiple metallographic surfaces to replace the entire surface with a single point, which has serious unreliability.
2. Aqueous electrolysis
In order to avoid the randomness of the metallographic sample method, many researchers use electrolysis to extract the inclusions in the steel from the matrix. The electrolysis method is that after the sample is energized, the steel matrix enters the solution and dissolves in the form of ions, and the non-metallic inclusions are not electrolyzed and remain in the state of solid ions, and then the inclusions are collected for a comprehensive study. However, most of the electrolytes currently used are acidic aqueous solutions with PH<3, and most of the inclusions in steel are composite inclusions. The composite inclusions are unstable in acidic aqueous solutions, and acidic aqueous solutions can easily destroy many inclusions in steel. . It is difficult to make a rigorous argument as to which inclusions are destroyed and the rate of destruction. Therefore, the electrolysis method also needs to be improved.
3. Non-aqueous electrolysis method
The pH value of the non-aqueous solution is 8, and the radioisotope tracer method proves that the non-aqueous electrolysis method does not damage the inclusions during the separation process, and can completely preserve the various inclusions in the sample, including nano-inclusions. Then use scanning electron microscope and energy spectrum or transmission electron microscope, high resolution electron microscope and energy spectrum to analyze the inclusions. This is a highly accurate and efficient method for detecting inclusions in steel.

Density of commonly used metal materials

Density of commonly used metal materials
Serial number / material name / density (g/cm3) Remarks
421/ Steel /7.85
422/ Carbon steel/ 7.85
423/ Steel /7.85
424 /Carbon steel /7.85
425/ Steel /7.85
426 /Carbon steel /7.85
427/ Industrial pure iron/ 7.87
428/Industrial Pure Iron/7.87
429/ Industrial pure iron / 7.87
430/alloy steel/nickel-chromium steel/7.9
Serial number / material name / density (g/cm3) / remarks
431/Stainless Steel/7.9
432/ Alloy steel/Ni-Cr steel/7.9
433/ stainless steel /7.9
434/alloy steel/nickel-chromium steel/7.9
435 /Stainless Steel /7.9
436 / high speed steel / 8.3-8.7 / tungsten content 9%-18%
437/ high-speed steel/8.3-8.7/tungsten content 9%-18%
438/High speed steel/8.3-8.7/Tungsten content 9%-18%
439/ Brass/ 8.4-8.85
440/ brass/ 8.4-8.85
Serial number/ Material name Density (g/cm3)/ Remarks
441 / brass /8.4-8.85
442/ Cast brass/ 8.62
443 /cast brass /8.62
444 / cast brass / 8.62
445/ Tin bronze /8.7-8.9
446/ Tin bronze /8.7-8.9
447/ Tin bronze/ 8.7-8.9
448/ Rolled phosphor bronze/ 8.8
449/cold drawn bronze/8.8
450/ rolled phosphor bronze/ 8.8
Serial number Material name Density (g/cm3) Remarks
451/ cold drawn bronze/8.8
452/ Nickel-copper alloy/ 8.8
453 / rolled phosphor bronze / 8.8
454/ Cold drawn bronze/ 8.8
455/ Nickel copper alloy/ 8.8
456/ Nickel-copper alloy 8.8
457 //Pure copper /8.9 /Red copper
458 / pure copper / 8.9 / red copper
459/ Nickel /8.9
460/ Nickel/ 8.9
Serial number/ Material name Density (g/cm3)/ Remarks
461 / pure copper / 8.9 / red copper
462/ Nickel/ 8.9
463/ Tin-based bearing alloy/ 9.33-10.68
464/ Tin-based bearing alloy /9.33-10.68
465 / Tin-based bearing alloy / 9.33-10.68
466/ Cemented Carbide/(Tungsten Cobalt Titanium)/ 9.5-12.4
467/ Cemented Carbide/(Tungsten Cobalt Titanium)/ 9.5-12.4
468/ Cemented carbide/(tungsten cobalt titanium) /9.5-12.4

How to deal with compression springs

How to deal with the compression spring machine to strengthen the circular spring, due to its spiral geometry, it is more difficult to strengthen than the flat surface of the leaf spring. In addition, it is necessary to strictly evaluate the strengthening effect of the circular spring cross section to fully understand The resistance of the round spring against fatigue fracture.
The round springs are individually sent to the shot blasting room through a continuous conveyor chain system. A set of parallel roller tables are installed in the shot blasting room. While strengthening, the roller tables keep rolling, driving the round springs to rotate while moving forward. The passing method allows the high-speed pill flow to pass between the various rings of the circular spring and hit the metal surface of the inner ring, where the stress of the circular spring is most concentrated.
For applications with high productivity requirements, you can choose a strengthening equipment that can spray two round springs at the same time. The latest research and development result is to combine multiple nozzles on the basis of the original shot blasting equipment to target specific areas of the round spring (Stress concentration to please) Shot peening with more targeted and concentrated firepower. ??
   leaf spring reinforcement
A continuous pass-through shot blasting equipment can be used to strengthen the leaf springs one by one, so that the geometric concave surface of the leaf spring is exposed to the high-speed shot flow. The typical model of the computer spring machine includes a throwing head for the ejection plate On the top of the spring, install a polishing head on the side, and spray the left and right sides of the leaf spring at the same time.
The passing speed of this standard leaf spring strengthening equipment is 10 feet per minute. If a higher production speed is required, the number of throwing heads can be increased and the motor frequency can be adjusted. Under working conditions, the leaf spring will be repeatedly subjected to unidirectional bending stress Therefore, it is sometimes stressed by stress. In the strengthening process, it is simulated that the leaf spring will be subjected to “stress strengthening” in the future use process, so that it will apply a “static stress” in the direction of the load. After the strengthening is completed, the applied static stress is released. Experiments have shown that stress strengthening can further extend the service life of the leaf spring than conventional strengthening.

Shot peening technology of torsion spring

The shot peening process of torsion springs can be divided into the following three types:
1) Combined shot peening technology. Combined shot peening is generally called multiple shot peening. Most economical processes use secondary shot peening. This is achieved by using shot peening with different diameters. Large pellets to obtain residual compressive stress and surface finish.
2) Stress shot peening process. The stress shot peening process is also a relatively classic shot peening process, just because it is difficult to apply to mass production, but in recent years, due to the rapid development of stress shot peening equipment, the torsion spring of high-stress automobile suspension Large-scale production has been greatly developed. Especially the combined application of stress-strengthened shot peening and other shot peening processes has a good strengthening effect. The prestress of stress shot peening is generally set at (700~800) MPa, and the stress After shot blasting, the peak value of residual stress can reach (1200~1500) MPa, thereby obtaining high fatigue strength.
3) The hot pressure process of torsion springs. The hot pressure process is mainly applied to spiral torsion springs that require high permanent deformation resistance. It is used as an advanced anti-permanent deformation stabilization process. The heat pressure process can significantly improve the resistance to permanent deformation. In addition to deformation, it can also improve fatigue life.

Metallographic inspection and analysis of spring products

Metallographic inspection and analysis of spring products:
Commonly used spring materials are carbon spring steel or low-alloy spring steel, with a carbon content in the range of 0.55%-0.75%. Alloy elements such as Si, Mn, Cr, and V are often added.Cr and Mn are mainly to improve hardenability. Si improves the elastic limit, and V improves the hardenability and refines the grain. Commonly used materials are 60, 70, 65Mn, 60Si2Mn, 50CrVA, etc.
The spring uses its elastic deformation to absorb and release external forces. The finished product is required to have high elastic limit, high yield ratio, high fatigue strength and sufficient plasticity and toughness. Generally, the quenching temperature is controlled at Ac3+ (30~50℃) The tempering temperature is controlled at 400~500°C. In actual production, the growth of austenite grains is usually caused by quenching overheating. Although the strength of steel is not affected by normal tempering treatment, the plasticity and toughness are greatly reduced. As a result, the normal use of the spring is affected. Therefore, the qualified limit of the martensite structure can be appropriately grasped according to the actual situation during the metallographic inspection. According to daily production experience, the martensite structure of the silico-manganese steel spring after quenching is fine martensite or finer Martensite, refer to JB/T9211-2008 standard 1-4 grade martensite is qualified. Its austenite grain should be less than grade 5, and the martensite structure with grain size greater than grade 5 is coarser martensite or coarse Martensite. When inspecting quenched martensite, it is corroded with a 3% nitric acid alcohol solution and observed and evaluated at 500X.
Due to the different austenitizing temperature, the martensite shape and size are different. Grade 1 belongs to the low austenitizing temperature, and the quenched structure is hidden needle martensite, fine needle martensite and no more than 5% ferrite Body (volume fraction). Grade 8 belongs to the superheated structure, which is coarse lath martensite + coarse sheet needle martensite. It is controlled at 2-4 grades during normal quenching, and its structure is fine lath martensite + Flaky martensite.
   The structure after normal quenching and tempering is tempered troostite, and the non-martensitic structure that appears, the undissolved ferrite or upper bainite structure should not exceed 10%.
With the rapid development of materials science and the large-scale use of various spring materials, the requirements for the structural strength and fatigue strength of materials are getting higher and higher, and new expectations are put forward for the precision requirements of quantitative analysis in metallographic testing. For testing spring material organization, ensuring product quality is an indispensable and important means.
The analysis of metallographic organization includes not only organizational identification but also evaluation. It has both qualitative, quantitative and semi-quantitative testing. It is based on relevant national standards or industry standards. The interpretation of this article is the current commonly used standards. Timeliness, please pay attention to the validity of the standard in specific applications.
Standard JB/T9211-2008 “Medium Carbon Steel and Medium Carbon Alloy Structural Steel Martensite Grade” is suitable for the inspection of the martensite structure of medium carbon spring steel and medium carbon alloy spring steel after quenching or tempering below 200 ℃ Method and comparison method of martensite metallographic pictures. Sample preparation and corrosion of the sample are the same as general metallographic samples. This standard specifies the grade of martensite structure is 1-8, and the magnification of martensite photo Both are 500X. In the grading process, you only need to compare the martensite structure of the sample after 500X with the standard grading picture to know the martensite grade of the sample.

Processing technology of stamping elbow

(1) The production efficiency of stamping processing is high, and the operation is convenient, and it is easy to realize mechanization and automation. This is because stamping relies on punching dies and stamping equipment to complete processing. The number of strokes of ordinary presses can reach dozens of times per minute. The pressure can reach hundreds or even thousands of times per minute, and each stamping stroke may get a stamped part.
  (2) Stamping generally does not generate chips and scraps, consumes less material, and does not require other heating equipment, so it is a material-saving and energy-saving processing method, and the cost of stamping parts is lower.
(3) Stamping can process parts with a large size range and more complex shapes, such as stopwatches as small as clocks and clocks, as large as automobile longitudinal beams, covering parts, etc., plus the cold deformation and hardening effect of the material during stamping, and the strength of the stamping The stiffness is high.
(4) Since the mold guarantees the size and shape accuracy of the stamping parts during stamping, and generally does not damage the surface quality of the stamping parts, and the life of the mold is generally longer, the quality of the stamping is stable, the interchangeability is good, and it is “identical” Characteristics.

What are the spring oxidation treatments

What are the spring oxidation treatments:
A dense protective film is formed on the surface of the spring, and oxidation treatment and phosphating treatment are usually used. Oxidation treatment and phosphating treatment have low cost and high production efficiency. General spring manufacturers use oxidation treatment as anti-corrosion treatment. .
The oxidation treatment of oxidized steel is also called bluing, blacking, and boiling black. After oxidation treatment, protective magnetic iron oxide is formed on the surface of the spring. This oxide film is generally blue or black, and sometimes dark brown. Its color determines It depends on the surface state of the spring, the chemical composition of the spring material and the oxidation treatment process.
The methods of oxidation treatment include: salty oxidation method, alkali-free oxidation method and electrolytic oxidation method. Alkaline oxidation method is mostly used.
The alkaline oxidation method is to put the spring into a sodium hydroxide solution containing an oxidant at a temperature of about 140°C for a certain period of time. The oxidant and sodium hydroxide react with iron to generate sodium ferrite and sodium ferrite, and then react with each other. This produces magnetic iron oxide.
The thickness of the oxide film layer is about 0.6~2μm. Although the oxide film can improve the corrosion resistance of the spring, because the film is thin and has pores, its protection ability is poor and can only be used in non-corrosive media. The spring working in the middle. The level of its anti-corrosion performance depends on the density of the oxide film and its thickness, which is also determined by factors such as the concentration of sodium hydroxide, the concentration of the oxidant, and the temperature of the solution.
In order to improve the corrosion resistance and lubricating ability of the oxide film, the treatment before and after the oxidation treatment should be strengthened. Before the oxidation treatment, the rust, oxide scale, oil stain, heat-treated salt residue, surface contact layer, etc. on the spring surface must be thoroughly removed. After that, the spring is usually filled in a soap solution or dichromate, and then washed with running warm water, blown dry or dried, and finally replaced with a water film to replace the anti-rust oil or a certain temperature of mechanical oil for immersion Oil treatment.
  Oxidation treatment erodes the surface grain boundaries of some hot-rolled spring materials, which will reduce the fatigue strength to a certain extent.Therefore, caution should be taken when using oxidation treatment.
  The traditional oxidation treatment requires heating. In recent years, some domestic manufacturing units have used room temperature blackening agents, which overcome the defects of traditional blackening processes and save a lot of energy.
   The blackening agent is a concentrated liquefaction of blue-green, no impurities, no peculiar smell, non-flammable, non-explosive, non-corrosive, and safe to transport. The blackening agent is diluted with water, and the commonly used dilution ratio when the spring is blackened is about 1:5.
The operation process of the blackening agent is relatively simple, and the process route is: degreasing, rinsing, acid washing, rinsing, blackening (2~5min at room temperature), rinsing, and water film replacement anti-rust oil. It should be noted that: Remove the oil on the spring workpiece and clean it before putting it in a room temperature agent for oxidation treatment.
The oxidation treatment cost is low, the process formula is relatively simple, the production efficiency is high, and the oxide film has a certain degree of elasticity, which basically does not affect the characteristic curve of the spring. Therefore, the oxidation treatment is widely used as the anti-corrosion and anti-corrosion treatment of formed coil springs, spring washers and leaf springs. Decorative measures.
  The quality inspection of the spring after oxidation treatment includes visual inspection and corrosion resistance inspection.

What is the process of cold forming of the spring?

Generally speaking, the manufacturing materials of springs should have high elastic limit, fatigue limit, impact toughness and good heat treatment performance. Commonly used are carbon spring steel, alloy spring steel, stainless spring steel, copper alloy, nickel alloy and rubber. Wait.
There are cold-rolling methods and hot-rolling methods for springs. Cold-rolling methods are generally used for spring wire diameters less than 8 mm, and hot-rolling methods are used for spring wire diameters greater than 8 mm. Some springs must be subjected to strong pressure or shot peening after they are made. Can improve the load capacity of the spring.
   Spring cold forming process one-time automation capability. The cold forming machine has been developed to 12 jaws. Steel wires in the range of (0.3~14) mm can basically be formed at one time by the 8-jaw forming machine. The current development direction of forming process equipment:
①Increase the forming speed, the main development trend is to increase the forming speed of the equipment, that is, the production efficiency; ②Improve the durability of the equipment by improving the precision of equipment parts and strengthening the effect of heat treatment; ③Increase the length sensor and laser rangefinder to form CNC The machine performs automatic closed-loop control of the manufacturing process.
  Cold forming process range capability. At present, the maximum specification of large wire diameter spring coiling machine can reach 20mm, 2000MPa, and the winding ratio is 5. The cold forming process of variable diameter or equal diameter material Minic-Block spring and eccentric spring still has limitations.

Spring_Modification method of damping spring

The modification of the spring is mainly to improve the controllability, that is, to use a harder spring or a shorter spring. The spring controls many factors related to the control, and the change of the spring will cause a very complicated change in the control characteristics. In addition, it can improve the rolling suppression ability of the suspension and reduce the rolling of the body when cornering. The reduction of the height of the car can also reduce the center of gravity of the body, reducing the transfer of body weight when cornering, and improving the stability. Lowering can also take into account the aesthetic effect.
  The most important way to improve handling is to lower the center of gravity of the body, which can reduce the weight transfer of the body and the rolling of the body when cornering. The easiest way to reduce the body is to start with the spring. Using a short spring is the easiest and fastest way.
  The effect of spring hardness change:
  1. Increase the spring hardness of the front and rear suspension: the road performance becomes harder, and the tracking performance of the tire meridian road undulation will be worse, and the anti-roll ability will be improved
  2. Only increase the spring hardness of the front suspension: the front wheels become harder, and the anti-roll resistance of the front wheels increases, increasing understeer or reducing the tendency of oversteer
  3. Only increase the spring hardness of the rear suspension: the rideability of the rear wheel becomes harder, and the anti-roll resistance of the rear wheel increases, which increases the tendency of oversteer or reduces understeer
  4. Only reduce the spring hardness of the front and rear suspension: the road performance is soft, the tracking performance of the tire may become better when the road is undulating, and the anti-rolling ability will be worse
  5. Only reduce the spring hardness of the front suspension: the front wheel has a soft road and the front wheel anti-roll resistance is reduced, reducing understeer or increasing the tendency of oversteer
  6. ​​Only reduce the spring hardness of the rear suspension: the road performance of the rear wheel becomes soft, the anti-roll resistance of the rear wheel is reduced, and the tendency to oversteer or understeer is reduced
  7. Increase the hardness of the front anti-roll bar: The anti-roll resistance of the front wheels increases, increasing understeer or reducing the tendency of oversteer, which can reduce the change of the front suspension camber angle and make the tires closer to the road
   8. Increase the hardness of the rear anti-roll bar: The anti-roll resistance of the rear wheels increases, which increases the tendency of oversteer or understeer, which can reduce the change of the rear suspension camber and make the tires closer to the road
When refitting the spring, pay attention. Many people will only change the spring without changing the shock absorber. This modification method can easily deteriorate the control, because the damping of the original shock absorber cannot withstand the hardness of the modified spring, so when the spring expands and contracts When it is working, the original shock absorber cannot restrain the movement of the spring in such a short period of time. This will cause the vehicle to bounce more than ever. Not only is the modification effect of the spring difficult to play, but it will also shorten the life of the original shock absorber. .

How to strengthen the technology of torsion spring

Heat treatment can be used to strengthen the technology of torsion spring
1) Protective atmosphere heat treatment. In our country, the heat treatment of torsion springs, oil-quenched and tempered steel wires and toughened steel with a wire less than 15mm use protective atmosphere heat treatment. Protective atmosphere heat treatment can eliminate surface decarburization and oxidation, and improve the surface of the material quality.
2) Induction heating or protective atmosphere induction heating heat treatment. This process is generally carried out on the wire before the spiral torsion spring is formed. Some torsion spring factories combine the heat treatment of the wire material and the production of torsion springs to reduce costs. Induction heating treatment has more advantages. Good strengthening effect and fast induction heating speed can help refine crystal grains and reduce surface decarburization, which can give full play to and improve the strength and toughness of the material.
3) Surface nitriding heat treatment technology. In recent years, high-stress valve torsion springs or other high-stress clutch torsion springs have also adopted surface nitriding technology to achieve reliable fatigue life. Now the more advanced technology is low-temperature gas nitriding technology , The general nitriding temperature is (450~470)℃, and the gas nitriding time is (5~20)h.