应变时效对X70大变形钢冷弯管拉伸性能和组织的影响

Effect of strain aging on tensile properties and microstructure of X70 cold bending pipe with high deformability

将X70大变形管线钢管冷弯加工后进行不同温度时效处理,利用拉伸试验机和金相显微镜对其拉伸性能及显微组织开展研究。结果表明:230℃和250℃时效后,应力应变曲线出现屈服平台;时效后显微组织仍为铁素体+贝氏体(F+B),随时效温度上升,析出碳化物增多,材料屈强比增大,最高为0.93,应力比Rt1.5/Rt0.5减小,最低为1.01,均匀变形伸长率减小,最低为6.52%;受拉伸应变部位与受压缩应变部位相比,性能改变更明显,说明应变状态是影响应变时效后性能的主要因素;应变时效降低冷弯管塑性变形能力,综合涂覆效率及安全服役因素,防腐涂覆温度应在200℃左右为宜。

Microstructure and tensile properties of X70 cold bending pipe with high deformability after aging at different temperatures were studied by tensile test and metallurgical microscope.The results show that after aging treatment at 230 ℃ and 250 ℃,a platform appears in the stress-strain curve.The microstructure is composed of ferrite and pearlite(F + P) after aging treatment,and carbides precipitation increases with the aging temperature increasing.The yield ratio(Rt0.5/Rm) of the pipe can reach up to 0.93,the lowest Rt1.5/Rt0.5is 1.01 and the lowest UEL is 6.52% as the temperature is increased.The change of properties in the tension side of the cold bending tube is more serious than that of the compression side,indicating that strain is an important factor to affect the properties.Aging decreases the deformability of cold bending tubes,it is suggested that the temperature of anticorrosive coating should be about 200℃,in order to guarantee the service safety of pipeline steel and coating efficiency.