316L stainless steel vacuum sintering

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Powder metallurgy sintered austenitic (SS-300 series) stainless steel is widely used in industry, among which sintered 316L has excellent corrosion resistance. Austenitic stainless steel does not undergo phase transformation after heat treatment, and cannot be hardened by heat treatment. In the case of high requirements on wear resistance and wear resistance, its application is limited. If Cu, Si, Al and other elements are added to the austenitic stainless steel powder, a liquid phase can be formed at the sintering temperature, which is conducive to sintering and densification. Improve the mechanical properties of the material. Adding SiC to 316L and sintering at 1100C for 1h can approach full densification and generate Fe-SiC phase to strengthen the material, but the large shrinkage caused by liquid phase sintering is not conducive to the precise control of product size , the resulting interface phase will reduce the corrosion resistance of the material. In addition, the sintering atmosphere has a great influence on the performance of the sintered 316L material. The hardness and strength of the material sintered in the decomposed ammonia atmosphere are significantly higher than those of the vacuum sintered material, which is due to the decomposition of ammonia. Nitrogen in the atmosphere infiltrates into the sintered parts to form alloy nitrides under sintering conditions. In the sintering and densification process of high-density powder injection molding (MIM) stainless steel, nitrogen can be used instead of argon to achieve nitriding strengthening. When nitriding and strengthening MIM316L stainless steel The maximum nitrogen concentration w(N) = 0.4% for solid-state diffusion.

In this paper, for sintering 316L stainless steel, a new nitriding process is designed, that is, the powder compact is sintered under vacuum conditions, and nitrogen is introduced for nitriding after the sintering shrinkage stage is completed. Sintered 316L parts are precisely dimensioned and have an excellent combination of strength, hardness and corrosion resistance.

The test raw material is 316L stainless steel powder with a particle size of less than 0.150 mm obtained by water atomization. The main chemical components (w/%) are: Cr16.0~18.0, Ni10.0~14.0, Mn 0.0~2.0, Si 0.0~1.0 , S0.0～0.03, C0.0～0.03, Mo 2.0～3.0, Fe balance, add 1% zinc stearate to the powder.

The sample was formed at a pressure of 800 MPa, and the green compact density was 6.680 g/cm3. After degreasing at 550 °C, the molded blank was sintered in a vacuum sintering furnace. The sintering temperature was 1260 °C, and the holding time was 1 h. Nitrogen, nitrogen pressure 0.03-0.13 MPa, nitriding time 30-60 min.

Performance test methods: density test follows ISO2738 standard; hardness test follows ISO6508 standard; flexural strength test follows ISO3325 standard; salt spray corrosion performance test follows ISO9227 standard, nitrogen content test method is standard chemical composition analysis method.

Nitriding and strengthening treatment of sintered 316L material can effectively improve the strength and hardness of the material, but reduce its plasticity and corrosion resistance. The nitrogen content of the material is mainly affected by the nitriding nitrogen pressure and processing temperature. The nitrogen temperature can accurately control the nitrogen content of sintered 316L. The nitrogen content increases with the increase of nitrogen pressure and temperature. The holding time has little effect on the nitrogen content: the chlorine content of the surface layer and the interior of the sample with a thickness of about 10 mm is different Rarely. The sample is slightly enlarged after nitriding; the microstructure of the sample with w(N)=0.41% is basically the same as that of the sintered part without nitriding, but the comprehensive properties of strength, hardness and corrosion resistance are Significant improvement.

Equipment selection: The RVS vacuum sintering furnace provided by SIMUWU is an excellent product for processing this kind of process. It has the characteristics of good temperature uniformity and high temperature control accuracy. SIMUWU provides a professional team of engineers who can solve various problems encountered in the production process and are committed to giving customers the most convenient and efficient experience.