摘要
在铁基粉末冶金零件的最终形生产中尺寸精度是一个关键参数。粉末冶金零件生产厂商一直在追求较大的零件,但终端用户规定的绝对公差一般并不随零件尺寸而改变。因此,对较大的零件,尺寸变化或尺寸变化的偏差必须减小。除了与常用低合金粉末冶金钢的压制与烧结相关的尺寸变化外,烧结硬化合金对粉末冶金零件生产还提出了一些独特挑战与机遇。在烧结炉中能淬硬的零件,就不要后续淬火作业了。可是,形成的未回火的马氏体显微结构对尺寸稳定性与力学性能来说并不理想。回火的淬硬钢由于马氏体转变成了密度较高的较稳定的铁素体与碳化物显微结构,从而改善了力学性能并使尺寸产生收缩。另外,许多铜及碳含量高的烧结硬化钢牌号都会导致残留奥氏体的含量较高。残留奥氏体可改进冲击性能与延展性,但是,由于热波动残余奥氏体可转变成密度较低的贝氏体和/或马氏体从而影响尺寸的稳定性。为得到最好的力学性能与尺寸控制组合,烧结硬化钢需要进行适当的热处理。本文考察不同的烧结后热处理对烧结硬化粉末冶金钢尺寸、显微结构以及力学性能的影响。
Dimensional precision is a critical parameter in net shape processing of ferrous PM components. PM parts producers continue to pursue larger parts, but absolute tolerances dictated by the end user generally do not scale with part size. Therefore,in larger parts, the variation in percentage change in size, or dimensional change, must be reduced. Beyond the dimensional changes associated with pressing and sintering of typical low alloy PM steels, sinterhardenable alloys present some unique challenges and opportunities for PM part manufacturing. The ability to harden a part in the sintering furnace eliminates the need for a secondary quenching operation. The resulting mierostructure of untempered martensite is, however, not ideal for dimensional stability and mechanical properties. Tempering hardened steels results in improved mechanical properties and dimensional shrinkage, as the martensite converts to a more stable ferrite and carbide microstrueture of higher density. In adition,many sinter-hard- ening grades contain high Cu and C contents that result in relatively high amounts of retained austenite. Retained austenite can improve impact and ductility properties, but contributes to dimensional instability as it can transform to lower density bainite and/or martensite with thermal fluctuations. Proper thermal treatments of sinter-hardened steels are necessary to ob- tain the best combination of mechanical prop views the effects of different post-sintering t structural and mechanical property changes of erties and dimensional control. This paper re hermal treatments on the dimensional, micro sinter-hardened PM steels.
出处
《粉末冶金工业》
CAS
北大核心
2011年第1期12-18,共7页
Powder Metallurgy Industry
关键词
烧结后热处理
烧结硬化钢
尺寸变化
力学性能
post sintering thermal treatment
sinter hardened steel
dimensional change
mechanical property
