控轧控冷工艺对440 MPa级船体钢组织与性能的影响

通过CCT曲线和实验室控轧控冷工艺试验,研究了440 MPa级船体钢的过冷奥氏体连续冷却(CCT)过程的相变以及组织性能。结果表明:试验钢在较宽的冷速范围内容易得到贝氏体组织,随着终轧温度的降低,试验钢的强韧性得到提高。轧后空冷条件下,试验钢得到铁素体+珠光体组织,韧性较好,但强度富余量相对较小。轧后加速冷却,试验钢的强度得到明显提升。模拟卷取温度为550 ℃时,试验钢的强韧性相对更好。综合分析,较优的控轧控冷工艺参数为:终轧温度840 ℃,轧后冷速(20±5) ℃/s,卷取温度550~560 ℃。

Effect of controlled rolling and controlled cooling process on microstructure and properties of 440 MPa grade hull steel

Through measuring the continuous cooling transformation (CCT) curves and controlled rolling and controlled cooling test, the phase transformation characteristics, microstructure and properties of 440 MPa grade hull steel were studied. The results show that the bainite microstructure can be obtained under a wide range of cooling rate. With the decrease of final rolling temperature, the strength and toughness of the steel are improved. Under the condition of air cooling after rolling, the ferrite and pearlite microstructure are obtained with good toughness, while the reserve for strength is relatively low. With the accelerated cooling after rolling, the strength is obviously increased. At the simulated coiling temperature of 550 ℃, the match of strength and toughness is comparatively better. In conclusion, the preferred process parametons of controlled rolling and controlled cooling are finial rolling at 840 ℃, accelerated cooling with (20±5) ℃/s after rolling and coiling at 550-560 ℃.