研究了回火温度对Mn系低碳贝氏体钢(LCMB)组织及低温冲击韧性的影响. 显微组织分析表明, LCMB钢的轧态组织以贝氏体板条为主, 经460 ℃回火2 h后, 部分贝氏体板条开始粗化, 经600 ℃回火2 h 后, 出现准多边形铁素体组织, 并观察到少量铁素体再结晶现象. 对力学性能的测试结果表明, LCMB钢板经460 ℃回火2 h后达到最佳的强韧性配合, 屈服强度保持在725 MPa, -40 ℃ Charpy冲击功 AKV为146 J, 冲击断口呈现明显的韧性断裂形貌, 韧脆转变温度由轧态的-18 ℃降低至-48 ℃. EBSD和TEM分析表明, 低温韧性的改善是由于在回火过程中贝氏体板条的回复引起的大角度晶界比例增加及有效晶粒尺寸降低造成的.
In order to reduce the cost of alloying elements, low carbon Mn series bainitic steels have been developed. The effect of tempering temperature on the microstructure and low temperature impact toughness of a low carbon Mn-series steel has been investigated in the present study. The as rolled steel plate samples with 30 mm thickness were tempered from 280 ℃ to 600 ℃ for 2 h. Metallographic microstructure show that the< microstructure of the as-rolled steel is mostly bainite laths. Bainite laths start to merge and broaden after tempering at 460 ℃, and quasi--polygonal ferrite structures could be revealed after tempering at 600 ℃. Compared with the as-rolled steel, after tempering at 460 ℃, the yield strength of the steel changes slightly, remaining 725 MPa, while the Charpy absorbed energy at $-$40 ℃ increases from 38 J to 146 J, and the ductile-brittle transition temperature (DBTT) decreases from -18 ℃ to -48 ℃. The EBSD and TEM results indicate that the improvement of low temperature impact toughness after tempering at 460 ℃ is caused by the increase of fraction of high angle boundaries and the decrease of effective grain size during the recovery process of bainite laths.
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