304奥氏体不锈钢应变诱发马氏体的研究

Study on strain induced martensite in 304 austenitic stainless steel

用X射线衍射(XRD)、磁针法、力学性能和显微分析研究了商用热轧态和冷轧态304奥氏体不锈钢在不同变形方式下应变诱发马氏体的行为。结果表明:304钢热轧态由于存在多量碳化物和组织不均匀性,其奥氏体稳定性低,拉伸应变诱发马氏体量达40%,冷轧(固溶)态组织均匀、奥氏体稳定性高,拉伸应变诱发马氏体量仅9%;304冷轧板材扩孔、杯突成形时其切向和径向的二向拉应力有助于γ→α'转变,诱发马氏体量(30%～35%)多于单向拉应力的拉伸诱发马氏体量(8%～10%)。对于冷轧304不锈钢,在20%以上拉伸工程应变的驱动下才能较明显地诱发马氏体。304明显的强化效果(△σ达320～400 MPa)来自应变硬化和马氏体相变强化两方面:冷轧304钢的强化主要来自应变硬化本身;热轧304钢的强化不光有应变硬化的贡献,还有应变诱发的多量马氏体的重要贡献,而且后者是主要的。

Behavior of strain induced martensite（SIM） by different deformation processes for commercial hot rolled and cold rolled 304 austenitic stainless steel was studied by means of XRD,magnetic method,optical microscope observation and mechanical property tests.The results show that amount of SIM of hot rolled 304 steel reaches 40% after tension deformation,because of precipitation of alloy carbides,un-uniform microstructure resulting in low austenite stability,and that of cold rolled and solution-treated 304 steel is only 9% due to the uniform microstructure and high austenite stability.The amount of SIM in hole expansion and cupping forming of cold rolled 304 steel,which is 30%-35%,is much more than that of uniaxial tension,because biaxial tension stresses in the former deformation are favourable for γ→α′ transformation.It is found that the obvious SIM can be observed in cold rolled 304 steel with tensile strain more than 20%.The strengthening mechanism of the 304 steel is strain hardening and martensite phase transformation hardening,and the strengthening of cold rolled 304 steel being mainly strain hardening and that of hot rolled 304 steel resulting from not only strain hardening but also the contribution of a large amount of SIM.