Stainless steel powder metallurgy is prone to pores during manufacturing, which will affect its use, reduce its mechanical properties, corrosion resistance and wear resistance, and limit the application of stainless steel powder metallurgy. These properties of stainless steel powder metallurgy are all improved with the increase of density. Therefore, it is necessary to increase the density of stainless steel powder metallurgy. So how to increase the density of stainless steel powder metallurgy?
Super solid phase wire sintering:
1. Traditional stainless steel sintering generally uses solid phase sintering. However, a large number of pores will remain in the stainless steel during solid phase sintering, which will reduce its density and performance. The super solid phase line liquid phase sintering makes the stainless steel pre-alloy powder form a liquid phase during sintering, and the liquid phase fills the pores through flow to improve the density and performance of the sintered body.
2. Unlike ordinary liquid phase sintering, super solid phase sintering is the sintering of pre-alloyed powder, and it is always a single phase during the sintering process. The sintering temperature is between the solid phase line and the liquid phase line. At temperature, the pre-alloyed powder particles form a liquid phase in the grains, at the grain boundaries and on the surface of the particles. The particles are rearranged under the action of the capillary force of the liquid phase. The places where the surface curvature changes greatly will be preferentially dissolved and flow through the liquid phase. Mass transfer, precipitation in the recesses or pores of large particles, to achieve the purpose of rapid material transfer, so that the sintered body can be compacted.
3. The density, hardness, wear resistance and corrosion resistance of 316L stainless steel obtained by super solid phase sintering at 1400 ℃ are higher than those of solid phase sintering at 1200 ℃. However, because the sintering temperature is too high, the crystal grains will grow too much and cause overburning, which should be avoided.
Use suitable additives:
1. Adding certain low-melting alloy elements to the powder can greatly reduce its porosity through the liquid phase formed during sintering, so that stainless steel can meet higher performance requirements. For example, adding 2% to 8% copper-based alloy to 304 stainless steel powder, due to the low melting point of copper, a liquid phase begins to form at 960 ℃, and all forms a liquid phase at 1000 ℃. When the temperature is higher than that of copper At the melting point, the flow of the liquid phase makes the surface pores continue to spheroidize and shrink; because copper has good wettability to the stainless steel matrix, it can be evenly distributed on the stainless steel matrix, so that the sintered body has a significant reduction in pores, and the microhardness is also obvious. improve. When the additive amount is 8%, the density after sintering at 1350℃ increases to 7.05g/cm3.
2. The properties of powder metallurgy stainless steel can also be improved by adding suitable strengthening phases, especially the mechanical properties. For example, adding 1.5% to 3% (volume fraction) SiC to 316L stainless steel, due to the interaction between SiC and the stainless steel matrix, forms a low melting point Fe-SiC phase, which improves the density of the sintered body and makes it harder And abrasion resistance have been improved.
Compared with stainless steel produced by traditional smelting processes, stainless steel powder metallurgy has the advantages of producing parts close to net shape, high dimensional accuracy, high material utilization, and uniform structure. It has been widely used in machinery, chemicals, ships, automobiles, and instruments. Instruments and other industries.
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