含B钒微合金钢的连续冷却相变行为

Phase Transformation Behaviors of Boron-Vanadium Microalloyed Steels During the Continuous Cooling

为开发一种新的低成本高性能含B钒微合金钢和建立其TMCP生产工艺,用MMS-200热力模拟试验机研究了实验钢在连续冷却条件下的相变规律,绘制出实验钢的静态CCT曲线和动态CCT曲线.结果表明:微量的B提高了钒微合金钢过冷奥氏体稳定性,促进了针状铁素体形成,在比较宽的冷却速度范围内能得到贝氏体组织;未变形钢相比于变形钢,在更低的冷却速度甚至0.5℃/s的冷却速度下能得到大部分的贝氏体组织,但两者在5℃/s以上的冷却速度下都得到全部贝氏体组织;变形降低了奥氏体稳定性,促进铁素体转变,含硼钢铁素体转变存在的冷速升高到2℃/s,不含硼钢的其冷速升高到15℃/s;钒微合金钢中B有利于获得高强度的贝氏体组织,冷速5℃/s以上时相变后含硼钢的硬度都高于变形及未变形不含硼钢的硬度.

In order to develop a lowcost and high performance boron-vanadium microalloyed steel and establish its TMCP process, the transformation mechanism of the test steel under continuous cooling was studied and the static and dynamic CCT curves of the test steel were also obtained by means of MMS-200 thermo-mechanical simulator. The results showed that, by addition of the trace boron,the stability of overcooling austenite of the vananium microalloyed steel was increased,and the formation of acicular ferrite was promoted,while the bainite can be obtained under wider cooling rates. Compared to the deformed steel,bainite was the major microstructure which obtained in the undeformed steel under the very slowcooling rate even only0. 5 ℃ / s,but when the cooling rate was higher than 5 ℃ / s,fully bainite was obtained in both the deformed and undeformed steels. The stability of austenite was reduced and the formation of the ferrite was promoted by deformation,thus ferrite transformation proceeded under cooling rate lower than 2 ℃ / s and 15 ℃ / s in the boron steel and non-boron steel,respectively. For vanadium microalloyed steel,boron is beneficial to obtaining high strength bainite,therefore when the cooling rate is higher than 5 ℃ / s,Vickers hardness of boron steel is higher than that of non-boron steel under deformed and undeformed status.