Defects of Vacuum heat treatment quenching

                       

Defects of Vacuum heat treatment quenching

Vacuum quenching technology gradually spread, but also began to point out its problems.
First evaporated Cr, Mn and other alloying elements, and from the heat to the surface of abnormal tissue clamp the work piece by the vacuum vapor deposition cr generated. Measures taken in response. Is to reduce the degree of vacuum, the gas is introduced into the furnace control.
Second, the problem of insufficient cooling capacity of SKH51 punch, with pressurized nitrogen cooling 5 ~ 6Bar of, for SKD6l die casting, with 20Bar super pressurized nitrogen cooling, it is close to be resolved.
Third, deformation hardening, vacuum hardening, quenching deformation is its commodity features, but we all know that this is a false consciousness, although small deformation, recently also tended to improve in order to reduce deformation hardening furnace structure.
Fourth, coloring problem, although the work piece can actually use, but reduces the value of goods, an increase from the mold user claims.
Today, there are a lot of the heat treatment plant in the vacuum hardening furnace for heat treating bearing rings, will produce deformation of the work piece, SIMUWU vacuum equipment for everyone to do a simple analysis of the deformation of the products in question, and I hope to help everyone .
The first is the use of vacuum hardening furnace before quenching problem, there may be processed before quenching deformation of the bearing rings formed mainly in the following ways:
(1) Cold rolled bearing steel, hot-rolled bearing steel after annealing of the ball according to the specifications required by the mill, cold-rolled into cold-rolled steel corresponding specifications, and then turning forming, or directly turning cold roll forming steel molding, maybe Ways processed residual stress will be relatively larger, it increases the amount of distortion in the subsequent heat treatment.
(2) forging the way, refers to the cold forging steel ball annealing after the first, and then the cold forging or cold grind, and finally turning forming. This approach may also cause deformation of the work piece prior to hardening heat treatment in a vacuum furnace.
(3) forging the way, refers to the steel first by forging ball annealing, cool before turning forming. The same may cause deformation of the work piece before the vacuum heat treatment.
(4) refers to the hot-rolled steel hot-rolled steel to spheroidizing annealing, and then turning way forming.
For the outer diameter of the bearing rings ≤100mm, the current majority grind with cold forming process. This process is due to the energy-saving, can effectively reduce the cost, it is widely used. But the stress produced by this process is relatively large, to the final heat treatment also brings some difficulties. Thus requiring heat treatment process needs to be more precise, the operation to be more serious, while equipment for the heat treatment (optional SIMUWU vacuum hardening furnace can meet the requirements) are also more demanding, and only then will we be able to achieve the required product technical Claim.

The Future of vacuum carburizing.

   The Future of vacuum carburizing

Aerospace and automotive specifications need to be reviewed in light of rapid developments underway with these new materials. Serious consideration must be given to the use of elevated temperatures above 1900oF (1040oC) for carburizing and direct quenching, to minimize cycle times and reduce carbon absorption without adversely affecting microstructure. Preoxidation treatments have been found to be unnecessary, and rules for the use of high gas pressure quenching need to be better established and realized throughout the industrial sectors. Once this is accomplished, vacuum carburizing technology offers almost limitless possibilities.

H13 Tool Steel Heat Treatment Technology

H13 Tool Steel Heat Treatment Technology

H13 tool steel after heat treatment to obtain excellent performance, such as high strength, red hardness and high impact toughness. From the analytical H13 steel chemical composition start the selection of high-temperature ball annealing, quenching and tempering made secondary instructions provided process data, and gives five production practice experience gained in the conclusion.
H13 steel is widely used internationally a hot die steel, because it has a good impact toughness at high temperatures, wear resistance, ductility, hot hardness and applied die casting, forging die and extrusion die manufacturing. This article describes a heat treatment process H13 steel after forging change.
1, The chemical composition of the steel
H13 steel is the American National Standard ANSI steel, the equivalent of China GB / T1299 4Cr5MoSiV1. H13 steel in Cr, Mo, Si, V and other alloying elements [1], shown in Table 1, except Si element does not form carbides, Cr, Mo, V three elements will combine to form special carbides with carbon, these special carbide will improve the steel tempering resistance.
Chemical composition Table 1 H13 tool steel.
Influence of Cr: Cr with carbon to form special carbide, chromium carbide as a solid solution in austenite can increase over the stability of supercooled austenite. When it is dissolved in the tempered martensite contribute to enhancing its ability to promote secondary hardening effect, more Cr main purpose is to raise H13 steel hardenability, high temperature strength and high temperature oxidation resistance [2].
Influence of Mo: Mo is a carbide-forming elements, in H13 steel can improve the steel tempering stability and wear resistance.
Influence of Si: increase steel strength, hardness and resistance to tempering, heat treatment furnace at the same time weaken the oxidizing atmosphere.
Effect of V: The lower thermal sensitivity of steel to improve stability of steel tempering and secondary hardening effect, the vanadium carbide particle dispersed can greatly improve the wear resistance of steel.
2, The heat treatment process selection
2.1, The critical point
The heat treatment temperature, cooling method depends on the critical transition point of steel and isothermal transformation diagram. 1) H13 steel critical point: Ac1,850 ~ 885 ℃, Ac3: 910 ℃. 2) cooling transition critical point: Ar1,700 ℃; Ar3,820 ℃; Ms, 335 ℃. 3) austenitizing temperature: 1 010 ℃.
2.2, Annealing
In order to H13 steel forgings eliminate stress, improve the organization, grain refinement, lower hardness, ease of machining, the need for annealing. H13 alloy elements more change when heated slowly, it can not and should be used with conventional annealing temperature ball annealing, the alloy carbides form a uniform granular material, to give a fine granular pearlite. High temperature ball annealing temperature should be slightly higher than the heating temperature of Ac1 critical point of steel, were kept at the same temperature, is conducive to retain undissolved carbide particles, the cooling process, these dots can become granular structure of nuclei, guaranteed uniform fine granular structure.
Cooling ball annealing in Ar transformation point should be in the region isothermal treatment, prompting the formation of fine granular pearlite and carbide aggregation of fine particles contribute to reduce hardness, ease of machining.
2.3, Quenching
H13 steel has good hardenability, of less than 150 mm thick parts oil quenching to achieve a uniform hardness. But because the steel contains Mn, Si element prone to oxidation and decarbonization. In the production practice, the proposed salt bath, controlled atmosphere heat treatment, vacuum heat treatment can also be used for anti-covering or coating decarbonization protection.
Select 1 030 ℃ quenching temperature can be obtained hardness 54 ~ 55 HRC, 1 040 ℃ grain begins to grow. It is recommended heat treatment temperature range 1 030 ~ 1 040 ℃. Special attention should also be released when the pre-cooling to Ac3 above 20 ~ 30 ℃ (950 ~ 980 ℃) in order to reduce stress concentrations, thus avoiding cracking.
2.4, Tempering
In order to eliminate stress and improve the toughness of H13 forging at high temperatures must be tempering. The use of H13 steel alloying elements good resistance to tempering and secondary hardening effect, using secondary tempering can improve die life. Tempering temperature (580 ± 20) ℃ obtain hardness 47 ~ 52 HRC. Organization after tempering is tempered martensite and a small amount of granular carbide.
3. Conclusion
H13 steel after heat treatment has a good red hardness, high-temperature toughness and thermal fatigue resistance. To ensure the quality of heat treatment, production should pay attention to the following points:
1) Inspection of raw materials: the need to make the macro defect inspection, to discover such as slag, center shrinkage, folding, surface cracks and other defects.
2) After forging Forging should slow furnace cooling or cold, and timely annealing.
3) The H13 steel is easy to oxidation and decarbonization, so die blanks allowance should be increased after the soft spot in order to avoid hardening.
4) After the mold rework must be low-temperature annealing in order to avoid re-quench cracking.
5) during heat treatment operations should be strictly in accordance with operating instructions.

Gas circulation technology of vacuum tempering furnace and gas quenching furnace

Gas circulation technology of vacuum tempering furnace and gas quenching furnace

 In order to overcome the low temperature vacuum tempering, easy to cause uneven heating and vacuum tempering after cooling speed slower, etc, were using forced gas circulation at the time of heating and cooling heat transfer technology, using two gas circulation system in the structure.
  Vacuum tempering furnace gas circulation system, set on the top of the furnace thermal cycling fan, when heated to charge a small amount of N2 (about 0.05 MPa), and start the fan, the gas flow through the heater to workpiece, the formation of convection heating, in order to ensure the uniformity of heating workpiece, at the same time, improve heating efficiency.
  Gas circulation second measures is set up in the back of my furnace cooling fan, cooling the recharge N2 of 0.12 ~ 0.13 MPa, can join a proportion of H2, when necessary to prevent oxidation, cooling gas through the heat ex-changer and the wind deflector, forced convection flow artifacts formation circulation cooling, because the cooling speed increases, helps to avoid some of the steel tempering brittleness, shorten the production cycle, improve the productivity.