【作者】 陶学理；

【导师】 吴开明；

【作者基本信息】 武汉科技大学 ， 材料学， 2009， 硕士

【摘要】 本文采用气电立焊和热模拟研究了实验室试制的两种不同铌量钢热影响区的组织和性能,并对工业试制的含铌高强度低合金钢的焊接性能进行了研究。实验室试制两种不同铌含量钢的实际焊接结果表明,焊接接头组织可划分为:焊缝、粗晶区、细晶区和不完全淬火区。在80kJ/cm左右的大热输入条件下,随着铌含量从0.014%变为0.17%,粗晶区的宽度增加约1.5mm,而总的热影响区宽度从7.5mm增加到8mm左右。粗晶区的组织则由低铌钢的针状铁素体和晶界铁素体组织变为高铌钢的粒状贝氏体,细晶区和不完全淬火区及母材的组织则由铁素体和珠光体转变为铁素体和贝氏体,这与铌的固溶抑制晶界铁素体的形核,推迟转变开始温度,促进了粒状贝氏体形成有关。实验室试制两种不同铌含量钢的焊接热模拟结果表明,不同峰值温度模拟后的组织比实际焊接热影响区各个区域的组织粗大,但组织类型基本一致。不同热输入模拟焊接粗晶区的结果表明,随着热输入的增大,粗晶区的组织发生了显著变化,低铌钢粗晶区组织由GB和一定量的AF为主,逐渐转变为PF和AF,最后完全转变为PF和P。而高铌钢粗晶区组织则由GB和少量的M,变为B+F,最后变为PF。硬度测试结果表明,焊缝由于含有大量针状铁素体硬度最高,而在靠近熔合线附件的粗晶区和不完全淬火区出现一定的软化,且高铌钢热影响区的硬度高于低铌钢,这与不同峰值温度模拟焊接热影响区的硬度结果相一致。另外,随着热输入的增大,两种钢粗晶区的硬度均不断降低。工业试制含铌低合金高强钢的实验结果表明,在42kJ/cm和55kJ/cm的实际线能量焊接时,粗晶热影响区仍具有良好的低温冲击韧性。更多还原

【Abstract】 In this thesis, the microstructures and properties of heat affected zones (HAZ) in two different Nb content steels melted in laboratory were investigated by actual electro-gas welding and welding simulation, the welding properties of Nb-containing high strength low alloy steel (HSLA) produced in industry were also studyied.The results of actual welding showed that the microstructures of welding joints consisted of weld metal, coarse-grained region, fine-grained region and incomplete quenched region. At large heat input of 80kJ/cm, the width of coarse-grained heat affected zone (CGHAZ) increased approximately 1.5mm when the content of Nb increased from 0.014% to 0.17%, the whole HAZ width varied from 7.5mm to 8mm. with low Nb content steel, the microstructures of CGHAZ were AF and GF (grain boundary ferrite), which was granular bainite (GB) when Nb content increased. Correspondingly, the microstructures of fine-grained region, incomplete quenched region and base metal varied from polygonal ferrite (PF) and pearlite to ferrite and bainite. These changes of microstructures can be attributed to the Nb in solid solution, which suppressed GF nucleation, decreased transformation start temperature and promoted the formation of GB.Results of welding simulation with different peak temperature indicated that the microstructures of HAZ were coarser than that of actual welding, but the type of microstructures was in a good accordance. Welding simulation results showed that the microstructures of CGHAZ were obvious different with different heat input. With low Nb content, the microstructures varied from predominately GB and AF to PF and AF, finally they completely changed to PF and P with large heat input. While the microstructures of high Nb content steel varied from GB and a little amount of martensite to bainite and ferrite, then transformed to PF.Vickers-hardness tests showed that the weld metal had highest hardness because of a large amount of acicular ferrite, both the coarse-grain region near fusion line and incomplete quench region softened after welding. The hardness of steel with high Nb content was a little higher than that of the steel with low Nb content. Welding simulation also showed that the vickers-hardness decrease with heat input increasing.Results of Nb-containing HSLA steel produced in industry showed that the steel had good low temperature ductility with a heat input of 42kJ/cm and 55kJ/cm welding.更多还原