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利用扫描电镜(SEM)、透射电镜(TEM)对Nb-Ti微合金化热成形钢的微观组织进行观察,采用Kahn撕裂试验对其韧性和撕裂性能进行了研究,并利用Thermo-Calc热力学软件对其析出行为和析出粒子成分进行分析计算.结果表明,含碳质量分数0.13%的热成形钢在Nb-Ti微合金化后的组织为马氏体,和传统热成形钢(22MnB5)相比其奥氏体晶粒、板条块和板条束都得到细化,并且其抗拉强度达到1500 MPa以上,撕裂强度和单位面积裂纹扩展能分别达到1878 MPa、436 kN·m~(-1).在950℃奥氏体化时,Nb-Ti合金元素几乎全部以析出粒子形式存在,能有效阻止奥氏体晶粒长大.另外在基体中主要存在两种析出物,一种是尺寸在100~200 nm的Ti(C,N);另一种是纳米级别的钛铌复合碳氮化物,能有效强化基体,提高强度.
The microstructure of Nb-Ti microalloyed thermoformed steel was observed by scanning electron microscope (SEM) and transmission electron microscope (TEM). The toughness and tearing properties of the steel were studied by Kahn tear test. The results show that the microstructure of the thermoformed steel with 0.13% carbon content is martensite after Nb-Ti microalloying, which is similar to that of the conventional thermoformed steel (22MnB5) Its austenite grains, slab and slab beams are refined, and their tensile strength reaches more than 1500 MPa, the tear strength and the crack propagation energy per unit area reach 1878 MPa and 436 kN · m ~ ( -1) .At austenitization at 950 ℃, Nb-Ti alloy elements are almost all in the form of precipitated particles, which can effectively prevent the austenite grain growth.In addition, there are mainly two kinds of precipitates in the matrix, one Is Ti (C, N) with a size of 100-200 nm; the other is a nano-titanium-niobium composite carbonitride, which can effectively strengthen the matrix and improve the strength.