冷却工艺对抗大变形管线钢X70HD热涂敷性能的影响

抗大变形管线钢加热并保温一段时间后,钢管力学性能将发生变化,通常会有屈服强度、屈强比升高,均匀延伸率降低,应力—应变曲线形状改变等,这些性能变化将降低钢管抵抗变形的能力。利用扫描镜等设备研究了冷却工艺对21mmX70HD抗大变形管线钢组织、性能和应变时效硬化的影响。结果表明,随着开始冷却温度的降低,先共析铁素体含量逐渐增加,贝氏体组织含量逐渐降低,贝氏体的组织相态由粒状贝氏体逐渐向板条贝氏体转变。当开始冷却温度在700℃时,试验钢板具有最佳的综合力学性能。试验钢板制成1016mm钢管后,钢管在200℃时效保温5min下,纵向屈服强度Rt0.5为497MPa,抗拉强度Rm为695MPa,伸长率为41%,屈强比Rt0.5/Rm为0.72,Rt1.5/Rt0.5为1.24、Rt2.0/Rt1.0为1.09,均匀变形伸长率达到9.0%。

Effect of cooling process on heat coating property of X70HD high deformability resistance pipeline steel

After heating and temperature preserving for a while,the mechanical properties of high deformation resistance pipeline steel will be changed.Usually,the yield strength and yield ratio will be risen,uniform elongation decreased,and stress-strain curve varied,etc.These variations in properties will decrease the ability of deformation resistance of pipe.By using SEM and other apparatus,the effect of cooling process on microstructure,mechanical properties and strain age hardening of 21 mm X70HD grade high deformation resistance pipeline steel is studied.The result shows that,as the start cooling temperature is decreasing,the content of pro-eutectoid ferrite is gradually increasing,the content of bainitic microstructure reducing,and the phase state of bainite is transforming from granular bainite to lath bainite.When the start cooling temperature is at 700℃ the experimented steel plate has the excellent integrated mechanical properties.After making the pipe 1 016 mm,it is heated at 200℃holding for 5 minutes,the longitudinal yield strength:Rt 0.5=497 MPa; tensile strength:Rm=695 MPa; elongation:A=41%; yield ratio:Rt 0.5/Rm=0.72,Rt 1.5/Rt 0.5=1.24,Rt 2.0/Rt 1.0=1.09,and uniform elongation:UEL=9.0% are achieved.