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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 accuracy is a key parameter in the final production of iron-based powder metallurgy parts. Powder metallurgy parts manufacturers have been pursuing larger parts, but the absolute end-user-specified tolerances generally do not vary with the part size. Therefore, deviations from larger parts, dimensional changes or dimensional changes must be reduced. In addition to the dimensional changes associated with the pressing and sintering of commonly used low alloy powder metallurgy steels, sinter hardened alloys present some unique challenges and opportunities for the production of powder metallurgy parts. In the sintering furnace can be hardened parts, do not follow-up quenching operation. However, the untempered martensitic microstructure formed is not ideal for dimensional stability and mechanical properties. Tempered hardened steel is transformed into a denser and more stable ferrite and carbide microstructure due to martensite, resulting in improved mechanical properties and dimensional shrinkage. In addition, many grades of copper and carbon hardened steels result in higher levels of retained austenite. Residual austenite improves impact performance and ductility, however, retained austenite can change to lower density bainite and / or martensite to affect dimensional stability due to thermal fluctuations. In order to get the best combination of mechanical properties and dimensional control, sinter hardened steels require proper heat treatment. This article examines the effect of different post-sintering heat treatments on the size, microstructure, and mechanical properties of sinter-hardened powder metallurgy steels.