应变时效对X90冷弯管组织与性能的影响

Influence of strain aging on microstructure and properties of X90 cold bending pipe

对不同角度X90管线钢冷弯管进行应变时效处理,利用拉伸试验和SEM对时效前后管线钢的组织特征与力学性能开展研究。结果表明:拉伸应力-应变曲线有出现屈服平台的趋势,不再呈"Round House"型。在200℃时效下,冷弯管横向试样未出现屈服平台,而在250℃时效下,冷弯管横、纵向试样均出现明显的屈服平台;时效后,横向试样的屈服强度和抗拉强度分别增长了83、55 MPa,而纵向试样的屈服强度和抗拉强度分别增长了130、95 MPa,屈强比增大,最高达到0.99;管材横、纵向伸长率分别从20.2%和22.4%减小至16.56%和17.68%。在相同的温度条件下时效,随着冷弯角度的增大,铁素体晶粒尺寸增大,而板条状贝氏体逐渐向粒状贝氏体转变,M/A组元数目增多,M/A组元附近位错密度增高。当时效温度升高时,贝氏体中出现黑色点状析出物。说明应变时效降低冷弯管塑性变形能力。

The effect of strain aging on the microstructure and mechanical properties of an industrially produced X90 pipeline steel was investigated by tensile test and SEM. The results show that the tensile stress-strain curves show the trend of yield platform,which is no longer the ＂Round House＂type. Cold bending transverse specimens aging at 200 ℃ do not appear yield platform,while at 250 ℃ aging,the transverse and longitudinal specimens of cold bending pipe show obvious yield platform; after aging,the yield strength and tensile strength of transverse specimens are increased by 83,55 MPa,respectively,while the yield strength and tensile strength of longitudinal samples are increased by 130,95 MPa,the yield strength ratio also increases,the highest reach 0. 99; the transverse and longitudinal elongation reduce from 20. 2% and 22. 4% to 16. 56% and 17. 68% respectively. Aging in the same temperature conditions,with the increase of cold-formed angle,ferrite grain size increases,and lath bainite transforms to granular bainite gradually,the number of martensite / ausustenite（ M / A）blocks increase,the dislocation density near the M / A component increases. When the aging temperature is increased,the black spots appeare in the bainite. This indicates that strain aging reduces the plastic distortion ability of cold bending pipe.