Martensitic stainless steel vacuum sintering heat treatment

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As a special steel with high alloy content, martensitic stainless steel has become an indispensable material in engineering and daily life. Adding carbon to chromium-containing steel expands the austenite, making it like carbon steel to transform austenite into martensite through heat treatment, and obtain strengthened stainless steel, which not only has good corrosion resistance, but also has good wear resistance. sex. Because stainless steel is difficult to machine, the complex shape stainless steel parts are mostly manufactured by precision casting process, and its application is limited to a certain extent. With the development of powder metallurgy technology, the use of molding and vacuum sintering methods to manufacture stainless steel parts has been applied on an industrial scale. Due to the relative compactness of vacuum sintered stainless steel parts, the internal pores make the heat transfer rate much lower than that of dense stainless steel, so the hardenability of vacuum sintered stainless steel is relatively poor, and its vacuum heat treatment process has certain particularities.

410L is equivalent to my country’s martensitic stainless steel 1Cr13 in composition, and the vacuum quenching temperature of 1Cr13 is 1000-1050℃. Since 410L adds a certain amount of graphite to the steel powder before sintering, although the graphite is partially burned during the vacuum sintering process, the remaining carbon content still makes its composition fluctuate greatly, which will make the use of 410L The sintered 410 martensitic stainless steel formed after powder pressing and sintering has some characteristics in terms of heat treatment. As far as the quenching method is concerned, the common quenching methods of 1Cr13 are water quenching and oil quenching. For parts with complex shapes and cross-sections or stainless steel powder metallurgy parts used in special industries such as food machinery, the above two quenching methods are easy. The surface contamination of the parts is caused, and the large quenching deformation is difficult to meet the high-precision size requirements of the parts. At present, vacuum air-cooling quenching has become a new heat treatment technology for high-alloy steel, which is characterized by small deformation of parts after quenching, clean appearance and no pollution. Although the air cooling capacity is slightly insufficient for parts with large section size, it has shown obvious advantages for small and complex thin-walled parts. At present, 5 × 105 ~ 6 × 105Pa single-chamber vacuum high-pressure gas-cooled furnaces have been widely used in the world.

Tempering temperature depends on hardness requirements. Low temperature tempering can eliminate the internal stress formed in the quenching process, and high temperature tempering can obtain excellent comprehensive mechanical properties, but martensitic stainless steel tends to be brittle during tempering, so the cooling rate after tempering should be considered.

The sintered density has a great influence on the heat treatment hardness of the samples. The graph below shows the relationship between sintered density and quenched hardness (970 °C. 0.55 MPa gas quenching).

The sintering density directly affects the hardenability of the material. As the sintering density increases, the thermal conductivity of the material increases, and the surface hardness of the material increases after quenching. The sintered density is very sensitive to the quenching hardness, and a 4% increase in the sintered density can increase the quenching hardness by 11%. Therefore, on the premise of ensuring the pressing conditions, the sintering density of the material before vacuum heat treatment can be improved as much as possible, which can effectively improve the quenching hardness of the material; at the same time, ensuring the uniformity of the sintering density of the material before vacuum heat treatment can effectively ensure the uniformity of quenching hardness. It is of great benefit for mass production quality assurance of materials.

Equipment selection: The RVS series vacuum heat treatment furnace produced by SIMUWU is a high-quality product for the vacuum heat treatment process of tooling and molds. Good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum heat treatment process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum tempering furnace, vacuum annealing furnace, etc., which are widely sold in developed and developing countries.