回火温度对二次硬化马氏体不锈钢组织和性能的影响

二次硬化对回火温度非常敏感,研究了某含Mo二次硬化马氏体不锈钢在250~650 ℃回火时组织和性能的演变过程,并利用XRD、SEM、TEM以及冲击测试等手段分析了显微组织与力学性能之间的关系,着重讨论了试验钢二次硬化与残留奥氏体增韧机理。结果表明: 480~500 ℃回火时,试验钢同时出现了二次硬化和回火脆性现象,宏观硬度达到了56 HRC以上,冲击性能为14 J·cm^-2左右,显微组织主要由纳米级合金碳化物、板条马氏体以及残留奥氏体构成,其中纳米级合金碳化物弥散强化引起了二次硬化,体积分数约为10%的残留奥氏体有利于提高钢的冲击性能。而在上述温度区之外低温和高温回火时,试验钢均具有较高的冲击性能,但宏观硬度相对较低。

Effect of tempering temperature on microstructure and properties of secondary hardening martensitic stainless steel

Considering that the secondary hardening is very sensitive to the tempering temperature, the evolution of microstructure and properties was systematically studied when a Mo-bearing secondary hardening martensitic stainless steel tempered at 250-650 ℃, and the relationships between the microstructure and the mechanical properties were analyzed by using XRD, SEM, TEM and impact testing. In addition, the mechanisms of the toughening by retained austenite and the secondary hardening for the tested steel were discussed in detail. The results show that when tempered at 480-500 ℃, the phenomena of secondary hardening and temper embrittlement appear simultaneously in the tested steel, so the macrohardness and the impact property are respectively above 56 HRC and about 14 J·cm^-2, with the corresponding microstructure being composed of nanometer-sized alloy carbides, lath martensite and retained austenite. The secondary hardening is attributed to dispersion strengthening of nanometer-sized alloy carbides, and about 10% retained austenite in volume fraction is beneficial to improve the impact property. When the tested steel is tempered at temperatures lower or higher than 480-500 ℃, the impact property is relatively higher, but the macrohardness is lower.