利用热模拟技术并结合组织分析和硬度测试,测定出X70管线钢焊接热影响区连续冷却转变曲线并研究其组织转变规律.结果表明：当冷却速率大于15 ℃/s 时,焊接热影响区组织由板条状贝氏体、粒状贝氏体和少量铁素体组成,细小的马氏体-奥氏体组元呈弥散分布;但随着冷却速率的减小,贝氏体比例逐渐减小,铁素体比例逐渐增大,晶粒明显长大,性能恶化.在实际焊接中将热输入控制在9.3～18.6 kJ/cm(壁厚14.6 mm)可获得强韧性良好的焊接热影响区组织.

The simulated heat affected zone (HAZ) continuous cooling transforming curve of X70 pipeline steel was measured by thermal simulated test,microstructural and hardness analysis,and the microstructure of simulated HAZ was investigated.Lath bainite,granular bainite and a small quantity of ferrite were obtained in HAZ when cooling rate was above 15 ℃/s,Fine M-A(martensite-austenite)constituent dispersed homogenously.The slower the cooling speed,the more the ferrite,the less the bainite and the lager the austenite grain size.Therefore,the strength and toughness of actual HAZ in X70 pipeline steel with a wall thickness of 14.6 mm will be good when welding heat input is between 9.3-18.6 kJ/cm.