回火工艺对超低碳微合金钢组织和性能的影响

Effect of tempering technology on microstructure and mechanical properties of ultra-low carbon microalloy steel

研究了超低碳微合金钢880℃×1 h水淬、不同温度及时间回火后的显微组织及力学性能,结果表明:试验钢经淬火后的显微组织是由粒状贝氏体、板条状贝氏体和残留奥氏体所组成,屈服强度799 MPa,抗拉强度986 MPa,伸长率14.5%,屈强比0.81。随回火温度的升高,屈服强度和抗拉强度增大,并于300℃时达最大值,分别为949 MPa和1053 MPa,此时显微组织中开始有析出物产生,随着回火温度继续升高,析出物开始聚集并长大,屈服强度和抗拉强度逐渐降低,屈强比增加,在450℃处达到最大值后开始下降。试验钢的伸长率与回火温度的变化未发现有明显规律。适当延长于380℃回火的保温时间后,试验钢的显微组织类型无明显变化,但析出物有聚集长大现象,强度稍有降低,塑性略有增加。

Microstructure and mechanical properties of ultra-low carbon alloy steel after water quenching at 880 ℃ for 1 h and tempering at different temperature for different time. The results show that after quenching,microstructure of the tested steel constitute granular bainite,plate strip bainite and retained austenite,yield strength and tensile strength are 799 MPa and 986 MPa respectively,elongation rate is14. 5% and yield ratio is 0. 81. With the increase of tempering temperature,both yield strength and tensile strength increase and reach the highest values for 949 MPa and 1053 MPa respectively,meanwhile the precipitates appear. When tempering temperature continue to increase,the precipitates grow up and both yield strength and tensile strength gradually decrease. The yield ratio increased and then begins to drop at 450 ℃. There is no significant regularity between the elongation and tempering temperature of the tested steel. Prolonging properly the tempering time at 380 ℃,it can be found that there is no significant change in the type of microstructure,just a sign of growing up in precipitates and grain size and a slight decrease in strength and increase in plasticity.