Vacuum heat treatment of 0Cr17Ni4Cu4Nb stainless steel base

0Crl7Ni4Cu4Nb steel is a typical precipitation hardening martensitic stainless steel with high strength, corrosion resistance, oxidation resistance, excellent formability and weldability, etc. It is widely used in aerospace, petroleum, chemical, nuclear industry, energy, etc. In the industrial field, it can be used as structural parts that require wear resistance, corrosion resistance and high strength below 370 °C, such as shafts, gears and other transmission devices, valves, pump parts and fasteners such as bolts. The stainless steel usually adopts the solid solution and aging heat treatment process, in which the purpose of the solid solution treatment is to partially eliminate the inhomogeneity of the composition, so that the alloy carbides dissolve into the austenite, strengthen the solid solution, and obtain supersaturated martensite after cooling. ; The purpose of aging treatment is to use aging to precipitate strengthening phases ε-Cu, NbC, M2C. and other carbides to achieve precipitation hardening to obtain the desired mechanical properties. At present, the research on this stainless steel at home and abroad mainly focuses on the microstructure and mechanical properties after heat treatment, and the experimental research on heat treatment distortion is rare. The 0Crl7N4Cu4Nb stainless steel base described in this paper is prone to the problem of unqualified workpiece due to the flatness exceeding tolerance during solution heat treatment. Therefore, it is particularly important to control the distortion of the workpiece and take into account the structure and properties of the production practice.

As shown in the figure is a schematic diagram of the base on a construction machine, which is a special-shaped part with unequal wall thickness. The material is OCrl7Ni4Cu4Nb precipitation hardening martensitic stainless steel. The technical requirements of the product are tensile strength ≥ 1420 MPa, hardness ≥ 42.5 HRC, and the flatness of the mounting surface of the parts after heat treatment ≤ 0.5 mm. The test equipment is a vacuum quenching furnace.

The vacuum heat treatment process of 0Crl7Ni4Cu4Nb stainless steel base is solid solution at 1060 °C for 1.5 h, oil cooling +460 °C × 4 h aging, and air cooling. The workpieces treated by this process meet the technical requirements: tensile strength ≥ 1420 MPa, hardness ≥ 42.5 HRC , the flatness of the installation surface is less than or equal to 0.5 mm.

The distortion of the workpiece generally occurs in the cooling process of the solution treatment, which is mainly caused by the uneven temperature field. The higher the solution temperature, the greater the solid-liquid temperature difference during initial cooling, and the greater the heat flow on the surface of the workpiece. Influence, the more uneven the temperature field of the workpiece, the easier it is to produce distortion. When the solution temperature is high, measures such as increasing the temperature of the quenching oil and prolonging the pre-cooling time of the gas can be taken to reduce the distortion of the workpiece and achieve dimensional control.

Equipment selection: The VOGQ 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 oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.