Heat treatment on powder metallurgy effect

Heat treatment is one of the technological means to improve the mechanical properties of iron-based P / M parts. Heat treatment can improve the strength, hardness and wear resistance of P / M sintered steel, especially for sintered alloy steel, only after heat treatment can the alloying function be fully exerted. One of the biggest differences between PM sintered steel parts and cast forged steel parts is that there are pores in the former, and there may be inhomogeneity in structure and density, which will obviously affect the mechanical properties of the parts after heat treatment.

In order to further improve the strength and hardness of the sintered body, people began to heat treat the sintered body, and obtained the tensile strength of 1086mpa and the elongation of 3.7%. But the research is not systematic and in-depth.

Sample preparation and test methods

Sample preparation

The test raw material is the special powder for warm compaction produced by hagnash Co., Ltd. with high-efficiency special lubricant for warm compaction. The chemical composition is fe-3.5ni-1.95cu-0.5mo-0.2c, the bulk density is 3.11g/cc, and the flow rate is 24.5s/50g. The warm pressed powder is pressed in the ph-80t warm pressed powder molding machine produced by Yangzhou Weida Machinery Co., Ltd. the pressing pressure is 800MPa and the warm pressing temperature is 100 ℃. The blank sample is obtained by pressing. The sample size is the flat plate tensile sample specified in gb7963-1987. Then in the decomposition ammonia atmosphere, the sintered alloy samples were obtained by natural cooling after sintering in a mesh belt continuous sintering furnace with sintering temperature of 1120 ℃ for 30 minutes. Some samples were carburized and quenched at 850 ℃× 2H (carbon potential 0.7%) and tempered at 180 ℃× 1.5h.

test method

The density of sintered sample was measured by drainage method, the Rockwell hardness values HRC and HRB were measured by Bromwell optical hardness tester, the tensile test was carried out by the universal testing machine controlled by electro-hydraulic servo microcomputer, and the elongation after fracture of sintered sample was calculated, and the microstructure was observed by optical microscope after the sample was polished and then etched by 4% nitric acid alcohol solution;