4Cr13、9Cr18、9Cr18Mo Steel Heat Treatment

4Cr13, 9Cr18, 9Cr18Mo, 9Cr18MoV have belonged to other steel eutectoid stainless steel, obtained after quenching martensite and carbides of the organization, with a high hardness. Mainly used for high hardness, high wear resistance of cutting tools, bearings, bushings and other components. Sometimes there is resistance to corrosion used in the manufacture of flexible components, such spring.
⒈ annealing
Martensitic stainless steel such hypereutectoid purposes under the deal, the role can be fully annealed, isothermal annealing and low temperature annealing, process methods, see part of the contents 3Cr13 steel annealing.
4Cr13, 9Cr18 fully annealed steel, mechanical properties measured in Table 1.
Table 1 4Cr13, 9Cr18 fully annealed steel, mechanical properties (measured data, for reference)
Mechanical properties of fully annealed steel (measured data)
  Rp0.2 (N/mm2) Rm (N/mm2) A (%) Z (%) HBS
4Cr13 870 ~ 900 ℃ • furnace cooling 4126662560135 ~ 185
9Cr18 885 ~ 920 ℃ • furnace cooling 4127551530--

⒉ quenching
Type of steel because of its high carbon content, there are more organizations carbide alloy, so the quenching temperature should increase the number to ensure the full dissolution of alloy carbides. Insoluble carbide heating to prevent grain growth of a certain role in order to ensure the feasibility of increased quenching temperature. In general, 4Cr13, 9Cr18 steel quenching temperature can have 1050 ~ 1080 ℃, 9Cr18MoV the quenching temperature can be 1060 ~ 1090 ℃. Heating rate should be strictly controlled.
In addition to further enhance the quenching temperature to cause grain growth, but can not be dissolved in austenite due to excessive carbon and alloying elements to improve the stability of austenite, may increase the amount of retained austenite, and to quench decrease in hardness.
Type of steel for high hardness conditions, high hardness after quenching and low temperature tempering, heat treatment can only be processed by grinding or polishing, is not suitable for other mechanical processing, therefore, quenching the best vacuum heating equipment Yeah protective atmosphere furnace furnace. When using the general air dielectric heating, the surface oxidation and decarbonization protection should be treated to prevent surface decarburization, oxidation.
Quenching medium used oil medium. Make use of air cooling the workpiece surface decarburization, oxidation, reduce the hardness.
4Cr13, 9Cr18 steel transition point in Table 2.
Table 2 4Cr13, 9Cr18 steel phase transformation point (approximate) (℃)

Ac1 Ac3 Ar3 Ar1 Ms
4Cr13 820 1100 - - 230
9Cr18 830 - - 810 145

⒊ tempering
Such steel is mainly used for high hardness, high wear resistance of the workpiece, generally use the low-temperature tempering after quenching. Such as the manufacture of cutting tools, measuring tools, bearing rings, balls, etc. can be 150 ~ 170 ℃ tempered, hardness greater than 60HRC; general wear parts with the 200 ~ 240 ℃ tempered, hardness assurance 55 ~ 60HRC.
4Cr13 steel sleeve, may on the surface after quenching in the tempering range of 360 ~ 400 ℃, the surface hardness of up to 45 ~ 50HRC, in the range of 200 ~ 240 ℃ annealing, the hardness of up to 50 ~ 55HRC.
4Cr13 steel components for the production of flexible, spring, use a 450 ~ 500 ℃ temperature tempering, hardness 45 ~ 50HRC in ensuring the conditions, but also has high flexibility.
4Cr13 steel is generally not used when high-temperature tempering, but sometimes for the surface hardening or quenching for the whole organization and preparation, in the rough after quenching, after quenching in the range of 650 ~ 700 ℃ annealing, the hardness can reach 280 ~ 320HB.
9Cr18 type martensitic stainless steel in the manufacture of high hardness, used, and requires the organization, a high steady-state size of the parts, in the quenching and tempering a cold treatment processes before the increase, that is between -78 ~ -60 ℃ cold treatment, to ensure full hardening of retained austenite into martensite, to minimize the amount of retained austenite after tempering. www.cn-bxg.com have information to report, 9Cr18 steel quenched after heating at 1050 ℃, up to 25% of retained austenite, the -70 ℃ cold treatment, the retained austenite can be reduced to 10% to 15 %, the hardness can be increased 2 ~ 3HRC, but also to ensure the long-term use of parts in the process of organizing and dimensional stability.
Cooling after tempering air cooling available.

⒋ heat transfer problems
Such an eutectoid steel martensitic stainless steel, carbon, chromium content is high, especially 9Cr18 higher carbon content steel. Therefore, heat treatment, the first to be taken to avoid quenching cracks, to take control of the heating ramp rate of the cooling oil temperature control, tempering and other measures in a timely manner.
Another issue is the control of the amount of retained austenite quenching. Appropriate choice of quenching temperature, and prevent quenching temperature is too high, excess dissolved carbon and chromium to increase the austenite stability, thereby increasing the residual austenite after quenching. Then there are quenched by the cold treatment by return fire way exists to promote the decomposition of retained austenite, but also to control the ultimate purpose of the organization retained austenite.

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