500MPa级螺纹钢焊接热影响区组织和性能的研究

Study on Microstructure and Properties of Heat-affected Zone of 500 MPa Grade Screw Thread Steel

使用焊接热模拟技术对500 MPa IV级螺纹钢进行试验,研究不同热输入时,焊接热影响区显微组织、冲击韧性和显微硬度的变化规律。结果表明:当t8/5<20 s时,热影响区粗晶区由羽毛状上贝氏体和铁素体组成,随着t8/5的增大,粗晶区组织转变成粒状贝氏体、羽毛状贝氏体、珠光体和铁素体混合组织,且粒状贝氏体含量逐渐增加,羽毛状贝氏体含量减小。当t8/5增大到300 s时,粗晶区组织只有铁素体和珠光体。焊接热影响区(HAZ)的室温冲击功随着t8/5的增大而呈增大的趋势,当t8/5为60 s时热影响区的室温冲击功达到最大值,进一步增加t8/5,HAZ室温冲击功呈减小的趋势,且冲击后的断口形貌由脆性断裂的准解理断口形貌转向韧窝和河流花样的解理混合形貌。焊接热影响区最大硬度和硬化比随着t8/5的增大呈减小的趋势。

500 MPa IV screw thread steel was tested with welding thermal simulation in Gleeble3500.Effect of heat input on the microstructure,impact toughness and microhardness of HAZ was studied.The results showed that with increasing t8/5 the microstructure of the coarse grain region changed from ferrite to pearlite,upper bainite and then to lower bainite,and when t8/5 increased to 300 s there were only ferrite and pearlite in the microstructure of HAZ;The impact toughness also increased with increasing t8/5,and it reached the highest when t8/5 was 60 s,with further increasing of t8/5 then the impact toughness decreased,the fracture morphology also changed from quasi-cleavage fracture morphology to cleavage fracture morphology mixed with dimple and river pattern;The maximum hardness and the hardening ratio of HAZ decreased with increasing t8/5.