Study On The Process Of Fabricating Fine Stainless Steel Powder By Gas And Solid Dual-phase Atomization

Fine powder of stainless steel is a kind of dominant semifinished material of MIM industry now. Products made by it have been extensively used in many fields because of its excellent abilities of corrosion resistance and so on. This paper proposes a new process of atomization—Solid and Gas dual-phase atomization, in which the media of atomization contains many solid particles that can be separated from the target powder. In this way , a kind of stainless steel powder of the grain size of 20 μm was prepared in the condition of the temperature of the liquid metal 1550~ 1700℃, the gas pressure 0.9MPa and its flow rate 6m~3/min,the molten metal flow rate 42g/s and the salt flow rate 58g/s. Additionally, the sphere degree and smooth of the powder is well.Firstly ,processes of gas atomization and Solid and Gas dual-phase atomization were researched, the results showed that the finer stainless steel powder with narrower particle size distribution can be prepared by the newly developed technology under the same processing parameters condition in contrast to conventional gas atomization, and the grain size of the powder fabricated by Solid and Gas dual-phase atomization is about 1/2- 1/3 of the powder fabricated by the gas atomization; Moreover,the cooling rate of the powder is higher than the latter, which is above 10~5K/s ,and microcosmic structure is finer than the latter. Then,the influence of solid particle/gas mass ratio,liquid metal mass flow,gas pressure,gas mass flow and other parameters to the particle size of powder were investigated. The conclusion indicated that the mean particle size of the powder decreases with the solid particle/gas mass ratio increasing,but when the solid particle/gas mass ratio is higher than the critical value(140g/s),the mean size of the powder increases with the solid particle/gas mass ratio increasing,besides it decreases with the liquid metal mass flow, the gas pressure and the gas volume flow increasing. Colligating the above analysises ,a group of better parameters were prepared.Secondly ,the shattering mechanism of Solid and Gas dual—phase atomization has been studied.There is three kinds of shattering modes were suggested: 1 ,Mode of the airflow shattering to liquid colum.2,Mode of the solid particles piercing centrally or tangentially through liquid drop.3,Mode of the solid particles shattering to liquid film.Finally,in order to optimize the atomization process, solid medium whose components were the same as the powder was choosed to produce the stainless steel powder. The results indicated that the percentage of finer powder obtained in this way is much higher than in the way of conventional gas atomization,moreover, not any it was not necessary of separating the media powder from the target powder, but also...