调质低碳贝氏体钢的组织和性能

研究了C--Mn--Mo--Cu--Nb--Ti--B系低碳微合金钢915℃淬火和490～640℃回火的调质工艺对钢的组织及力学性能的影响.用扫描电镜和透射电镜对实验钢的组织、析出物形态和分布以及断口形貌进行观察,采用X射线衍射仪分析钢中残余奥氏体的体积分数.结果表明:调质后,实验钢获得贝氏体、少量马氏体及残余奥氏体复相组织,贝氏体板条宽度只有250 nm,残余奥氏体的体积分数随着回火温度的升高而降低,经淬火与520℃回火后残余奥氏体的体积分数为2.1%.调质后析出物的数量激增,6～15 nm的析出物占70%以上.实验钢经过915℃淬火与520℃回火后,其屈服强度达到915 MPa,抗拉强度990 MPa,-40℃冲击功为95 J.细小的析出物及窄的板条提高了钢的强度.板条间有残余奥氏体存在,改善了实验钢的韧性.

Microstructure and mechanical properties of low carbon bainite steel treated by quenching and tempering

The effects of quenching at 915 ℃ and tempering at 490~640 ℃ on the microstructure and mechanical properties of C-Mn-Mo-Cu-Nb-Ti-B based low-carbon microalloyed steel were investigated.The microstructure,the shape and distribution of precipitates,and the fractograph of the steel were observed by scanning electron microscopy(SEM) and transmission electron microscopy(TEM).The volume fraction of retained austenite was measured by X-ray diffractometry(XRD).The results show that a multiphase microstructure with bainite,martensite and retained austenite is achieved after quenching and tempering.The bainite lath is 250 nm in width.The volume fraction of retained austenite decreases with the tempering temperature rising,and it is 2.1% after tempering at 520 ℃.The quantity of precipitates increases sharply after heat treatment,and the proportion of precipitates in a size range of 6 to 15 nm is above 70%.After quenching at 915 ℃ and tempering at 520 ℃,the test steel has a yield strength of 915 MPa,a tensile strength of 990 MPa and a-40 ℃ impact energy of 95J.Fine precipitates and narrow lath bainite can enhance the strength,but the retained austenite existing between bainite laths can significantly improve the toughness.