直接淬火-碳分配处理后高强度钢的组织与力学性能

采用一种中碳低合金高强度钢,在轧后进行直接淬火后再快速升温至400～600℃进行碳分配处理的直接淬火-碳分配(Quenching Partitioning)处理(DQP),研究DQP工艺对钢的组织与力学性能的影响。利用扫描电镜和透射电镜观察组织及析出物的变化,采用X射线衍射仪分析了钢中残留奥氏体体积分数。结果表明:DQP处理后,钢的组织为板条马氏体组织和残留奥氏体。马氏体板条宽150～250 nm;残留奥氏体位于马氏体板条间,随工艺参数不同,其体积分数在4%～8%。钢中析出物尺寸大多为20 nm左右。经过DQP处理后,钢的抗拉强度达到1200 MPa以上,伸长率15%～17%。-40℃冲击功达到30 J以上。合理的淬火终淬温度可以获得更多残留奥氏体,而升高分配温度会增加析出、并使析出物长大,这是提高钢的强度和韧性的主要原因。

Microstructure and mechanical properties of high strength steel after direct quenching and partitioning

Medium carbon high strength low alloy steel was directly quenched and then tempered by rapidly heating to 400-600 ℃ for carbon partitioning,named direct quenching and partitioning(DQP) process.Effect of DQP process parameters on microstructure and mechencial properties of the steel was studied.Microstructure and precipitates of the steel were investigated by SEM and TEM.The retained austenite volume fraction was measured by means of X ray diffraction.The results show that the microstructure of the steel consists of martensite and retained austenite.The martensite lath is about 150-500 nm in width and the retained austenite of(4-8)vol.% is located between the martensite laths,and the amount of retained austenite depends on treatment parameters.The precipitate size in the steel matrix is about 20 nm.After DQP treatment,the mechanical properties of the steel are improved,its tensile strength is above 1200 MPa,total elongation is 15-17% and Charpy notch toughness at-40 ℃ is above 30 J.The proper final quenching temperature makes more retained austenite and higher partitioning temperature leads to the precipitates amount increase and its growth,which are the main reasons of for the improvement of strength and toughness.