CAJ | 학술논문

尺寸精度是铁基粉末冶金零件生产工艺的关键参数.除了和标准粉末冶金低合金钢的压制与烧结相关的尺寸变化外,烧结-硬化合金还会产生从奥氏体转变为马氏体的相变.马氏体是钢中密度最低的相,因此,冷却时马氏体的形成会导致零件显著胀大.当马氏体转变为密度较高的铁素体与碳化物显微组织时,回火的淬硬钢发生收缩.这两种相变对零件的尺寸变化都有很大影响.另外,在Cu与C含量高的马氏体区可能有大量残余奥氏体存在.奥氏体相密度最高,所以残余奥氏体会导致压坯胀大较小.除回火处理外,马氏体与残余奥氏体的存在都会影响零件的最终尺寸.本文考察了两个烧结-硬化钢牌号,同时通过不同的后烧结热处理,研究了这两个牌号钢的尺寸变化和显微组织变化.
척촌정도시철기분말야금령건생산공예적관건삼수.제료화표준분말야금저합금강적압제여소결상관적척촌변화외,소결-경화합금환회산생종오씨체전변위마씨체적상변.마씨체시강중밀도최저적상,인차,냉각시마씨체적형성회도치령건현저창대.당마씨체전변위밀도교고적철소체여탄화물현미조직시,회화적쉬경강발생수축.저량충상변대령건적척촌변화도유흔대영향.령외,재Cu여C함량고적마씨체구가능유대량잔여오씨체존재.오씨체상밀도최고,소이잔여오씨체회도치압배창대교소.제회화처리외,마씨체여잔여오씨체적존재도회영향령건적최종척촌.본문고찰료량개소결-경화강패호,동시통과불동적후소결열처리,연구료저량개패호강적척촌변화화현미조직변화.
Dimensional precision is a critical parameter in net shape processing of ferrous PM components. Beyond the dimensional changes associated with pressing and sintering of typical low alloy PM steels, sinter-hardening alloys undergo a transformation from austenite to martensite. The formation of martensite results in a large expansion during cooling, as martensite is the lowest density phase in steels. Tempering hardened steels results in shrinkage, as the martensite converts to a ferrite and carbide microstructure of higher density. Both of these transformations have a large impact on the dimensional change. In addition, martensitic regions with high Cu and C contents may contain large amounts of retained austenite. As austenite is the highest density phase, retained austenite results in less growth of the compact. The presence of martensite and retained austenite, in addition to the tempering step, all play a role in the final dimensions of a component. This paper reviews two sinter-hardening grades and investigates the dimensional and microstructural changes of those grades through different post-sintering thermal treatments.