Effect of continuous annealing process on microstructure and properties of 780 MPa cold-rolled dual phase steel with high formability
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摘要: 基于产线装备特点设计开发了一种低成本780 MPa级冷轧增强成形性双相钢，并开展连续退火工艺对其组织性能影响的研究。结果表明：不同退火工艺条件下试验钢显微组织主要为铁素体与弥散分布的贝氏体、马氏体和少量马奥岛；快冷结束温度的提高有助于残留奥氏体含量的提升，最高残留奥氏体含量达到3.9%；残留奥氏体呈薄膜状或块状，多分布于B/F与F/F或B/M相界面处，残留奥氏体发挥TRIP效应实现塑性提升。Abstract: A low-cost 780 MPa grade cold-rolled dual phase steel with high formability was designed and developed based on the equipment characteristics of the production line, and the effects of continuous annealing on the microstructure and properties of the cold rolled products were studied. The results show that under different annealing conditions, the microstructure of the experimental steel is mainly composed of ferrite, dispersed bainite, martensite, and a small amount of M/A islands. Increasing the end temperature of rapid cooling can increase the retained austenite content, with the highest content of retained austenite reaching 3.9%. The retained austenite is mostly distributed in the form of thin films or blocks at the interface between B/F and F/F or B/M phases, and the retained austenite exerts the TRIP effect to achieve plasticity improvement.
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Key words:
- dual phase steel /
- annealing process /
- retained austenite /
- TRIP effect /
- mechanical property
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图 2 不同工艺下试验钢的XRD图谱
Figure 2. XRD patterns of the experimental steel under different processes
图 3 不同退火工艺下试验钢显微组织形貌（OM）
(a)方案1；(b)方案2；(c)方案3
Figure 3. OM morphology of experimental steel under different annealing processes
图 4 不同退火工艺下试验钢显微组织形貌（SEM）
(a)方案1；(b)方案2；(c)方案3
Figure 4. SEM morphology of experimental steel under different annealing processes
表 1 试验钢化学成分
Table 1. Chemical composition of experimental steel
% C Si Mn Al Cr Ti 0.17 0.40 2.0 0.85 0.25 0.025 
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表 2 连续退火热模拟工艺方案
Table 2. Thermal simulation process of continuous annealing
℃ 方案 均热温度 缓冷温度 快冷温度 时效温度 1 870 780 480 300 2 870 780 510 300 3 870 780 480 350
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表 3 不同方案下的力学性能
Table 3. Experimental scheme and mechanical properties
方案 Rp0.2/MPa Rm/MPa A/% Rm×A/(GPa·%) 1 459 854 13 11.10 2 429 810 20 16.20 3 403 771 18 13.88
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表 4 退火工艺参数
Table 4. Annealing process parameters
℃ 均热温度 缓冷结束温度 快冷结束温度 过时效温度 865～875 775～785 505～515 290～310
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表 5 工业试制产品性能
Table 5. Performance of industrial trial products
项目 Rp0.2/
MPaRm/
MPaA80/% n0 BH/
MPaRm×A/
(GPa·%)标准
要求440～550 ≥780 ≥18 ≥0.13 ≥30 工业试
制产品470～500 800～830 20.0～24.5 0.140～0.155 50～66 16.00～20.34
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