Stainless steel smelting production process commonly used, due to its cutting difficult, so there are parts made poor dimensional accuracy, surface roughness and other deficiencies, so far there are still many technical problems. Compared with the traditional production process, the production of which with powder metallurgy parts near net shape, high dimensional accuracy, material utilization, uniform organizational structure, etc., have been widely used in machinery, chemicals, shipbuilding, automobiles, equipment instrumentation and other industries. However, since the pores in the powder metallurgy stainless steel interior easily, which makes the mechanical properties, wear resistance and corrosion resistance greatly decreased, thereby severely limiting its application. Studies have shown that almost all of the properties of powder metallurgy steel are improved as the density increases. Therefore, how to increase the density of steel metallurgy, reduce porosity, to improve the performance of the stainless steel powder metallurgy key issues.
Traditional stainless steel sintered commonly used solid phase sintering, however, when the solid-phase sintered interior will be left a lot of voids to reduce the density and performance. In recent years, people began to use super solidus liquid phase sintering, pre-alloyed stainless steel to form a liquid phase during sintering powder, liquid and to improve the performance of sintered density and flow through the pore filling. Unlike ordinary liquid phase sintering, liquid phase sintering of super solidus pre-alloy powder is sintered, and the sintering process is always in a single phase, the sintering temperature lies between the solidus and liquidus temperature at the pre-alloy powder particles within the grains, grain boundaries are formed at the surface of the liquid and particles, the particles in the liquid phase to achieve rearrangement capillary force, the surface curvature changes will place greater priority dissolved by liquid flow and mass transfer In large particles or pores of the precipitate depression, achieve the purpose of rapid transmission of material, so that to achieve a dense sintered body. According to reports, at 1400 â,,? super solidus liquid phase sintering the resulting 316L stainless steel, its density, hardness, wear resistance and corrosion resistance are higher than 1200 â,,? solid-phase sintering products. However, due to the sintering temperature is too high, excessive grain will grow, resulting in over-burning, attention should be avoided.
Some alloying elements in the powder of low melting point, which can greatly reduce its porosity by a liquid phase formed during the sintering, so that the stainless steel meet higher performance requirements. For example, 304 material powder was added 2% to 8% of copper-based alloy, because of the low melting point of copper, at 960 â,,? began to form the liquid phase to form a liquid phase at 1000 â,,? all, when the temperature is higher than the copper When the melting point, the liquid flow so that the surface pores keep the ball in and out; Because copper on stainless steel substrate has good wettability and can be evenly distributed substrate, making a significant reduction in porosity of the sintered body, micro-hardness significantly improved. In addition level 8%, 1350 â,,? sintered density increased to 7.05g/cm3. By adding suitable strengthening phase can also improve the performance of stainless steel powder metallurgy, especially mechanical properties.
