Effect of coiling temperature on the microstructure and mechanical properties of a Ti-Nb microalloyed steel
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摘要: 利用试验轧机和热处理炉进行了低碳Ti-Nb微合金钢的模拟轧制和卷取试验，研究卷取温度对微观组织和力学性能的影响。结果表明，随着卷取温度的降低，钢的相变过程逐步由扩散型相变过渡到切变型相变，微观组织由等轴铁素体依次转变为多边形铁素体、粒状贝氏体、板条贝氏体；由于析出强化和相变强化的综合作用，卷取态试验钢强度先降低后升高，延伸率持续降低；卷取过程微合金碳氮化物的析出强化导致卷取态试验钢强度高于空冷态试验钢，且随着卷取温度的降低，卷取态试验钢较空冷态试验钢强度的增量逐步降低；Ti-Nb微合金钢的卷取温度设定在560～630 ℃时，钢屈服强度744～754 MPa，延伸率19%～20.9%，可获得良好的综合性能。Abstract: The effect of coiling temperature on the microstructure and mechanical property of a Ti-Nb microalloyed steel was studied by simulated hot rolling and coiling tests conducted on a pilot hot rolling mill and heat treatment furnace. The results show that the phase transformation process of steel gradually changes from diffusion-type phase transformation to shear-type phase transformation, and the microstructure changes from equiaxed ferritic grain to polygonal ferrite, granular bainite, and lath bainite with the coiling temperature decreases. In addition, the strength first decreases and then increases, while the elongation decreases due to precipitation strengthening and phase transformation strengthening. The strength of the steel at the coiling state is higher than that of the steel after air-cooled due to the precipitation and strengthening of micro-alloy carbonitride during the coiling. With the decrease in coiling temperature, the strength increment of steel at the coiling state gradually decreases compared with the steel after air-cooled. The yield strength is 744～754 MPa, and the elongation is 19%～20.9%, which can obtain good comprehensive properties when the coiling temperature of Ti-Nb microalloyed steel is set at 560～630 ℃.
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Key words:
- Ti-Nb microalloyed steel /
- coiling temperature /
- mechanical property /
- microstructure
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图 2 试验钢板的光学显微组织
Figure 2. Optical microstructures of tested plates
(a) A630; (b) C630; (c) A560; (d) C560; (e) A490; (f) C490; (g) A420; (h) C420; (i) A350; (j) C350
图 3 试验钢板的扫描电镜微观形貌
Figure 3. SEM microstructures of tested plates
(a) A630; (b) C630; (c) A490; (d) C490; (e) A350; (f) C350
图 4 Nb-Ti复合析出相形貌
(a) 片状析出相1；(b) 片状析出相2；(c) 团簇状析出相；(d) 粒状析出相；(e) 球形析出相 ；(f) 纺锤状析出相
Figure 4. Morphological characteristics of Nb-Ti precipitates
图 6 卷取态较空冷态的强度增加量
Figure 6. The steel strength increment of the steel at the coiling state compared to the steel after air-cooled
图 7 试验钢Nb-Ti复合析出相形貌
Figure 7. Morphological characteristics of Nb-Ti precipitates in C630
表 1 试验钢的主要化学成分
Table 1. Main chemical composition of the experimental steel
% C Si Mn Nb Ti P S Al N 0.08 0.15 1.81 0.05 0.11 0.0038 0.0043 0.018 0.0050 
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表 2 试验钢板的拉伸性能
Table 2. The tensile properties of the tested plates
编号 屈服强度/MPa 抗拉强度/MPa 延伸率/％ C630 754 775 20.9 C560 744 761 19.0 C490 714 760 15.8 C420 720 756 15.0 C350 736 780 12.3 A630 621 700 19.0 A560 654 737 18.0 A490 664 740 15.3 A420 675 743 13.5 A350 706 770 10.4
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