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本文研究了不同马氏体含量的双相10号及20号钢经80～500℃回火后拉伸性能的变化。结果表明,随回火温度的升高,两种双相钢的抗拉强度均明显下降,而延伸率大为提高。屈服强度在低于160℃回火时略有升高而后下降。高于120℃回火时,屈服平台开始出现并不断增大。剪切滞后分析证实,回火后双相钢强度的下降由两部分组成,即马氏体和铁素体分别承受的载荷的下降。马氏体含量和马氏体合碳量的增高,会使前者所占的比份增大。马氏体的软化本身还减弱了铁素休的相硬化和加工硬化能力,因而对双相钢强度的降低有着重要的影响。马氏体含碳量越高,这种回火效果越明显。低温回火时延性的改善主要归因于铁素体中间隙原子的析出。随回火温度的升高及淬火态马氏体含碳量的增多,马氏体软化则逐渐成为双相钢延伸率大幅度提高的主要原因。
In this paper, the changes of tensile properties of dual-phase 10 and 20 steels with different martensite contents after tempering at 80-500 ℃ were studied. The results show that with the increase of tempering temperature, the tensile strength of two kinds of duplex steels decrease obviously, while the elongation increases greatly. The yield strength slightly increased and then decreased at tempering below 160 ° C. Above 120 ℃ tempering, the yield platform began to appear and continue to increase. Shear hysteresis analysis confirmed that after tempering the decline in strength of dual-phase steel consists of two parts, namely, martensite and ferrite, respectively, to withstand the load decline. The increase of martensite content and martensite carbon content will increase the proportion of the former. The softening of the martensite itself also weakens the phase hardening and work hardening ability of the ferrite and thus has an important effect on the strength reduction of the duplex steel. The higher the martensite carbon content, the more obvious this tempering effect. The improvement of ductility at low temperature tempering is mainly attributed to the precipitation of interstitial atoms in the ferrite. With the increase of tempering temperature and the increase of carbon content in quenched martensite, the softening of martensite gradually becomes the main reason for the substantial increase of ductility of dual phase steel.