400MPa级低合金高强度钢焊材及组织性能研究

【作者】 李红卫；

【导师】 刘荣佩； 彭云； 何长红；

【作者基本信息】 昆明理工大学 ， 材料学， 2006， 硕士

【摘要】 本文介绍了400MPa级Mn-Ni-Cr-Mo-Ti-B-Ce和Mn-Mo-Ti-B-Ce-Zr系高韧性埋弧焊焊丝焊丝成分设计原则。对所研制的焊丝匹配烧结焊剂进行了熔敷金属的埋弧焊试验。试验结果表明,所研制的焊丝在与两种不同的焊剂匹配时都能获得良好的熔敷金属力学性能,尤其是和较高碱度焊剂匹配时Rm>500MPa;ReL>600MPa;Akv（-20℃）>150J;熔敷金属组织主要是针状铁素体,少量的先共析铁素体。 对超细晶X60管线钢焊接热影响区组织与性能的研究结果表明,随着峰值温度的升高,t_8/5的增加,组织粗化,韧性降低。影响断口冲击韧性的主要原因是原始奥氏体的晶粒尺寸和岛状组织（包括马氏体、M-A组元和碳化物）,降低碳含量有利于减少岛状组织,有利于提高韧性。焊接热影响区的硬度分布表明热影响区存在一软化区,随着线能量的增加,软化区变宽,所以X60管线钢适合在线能量在小于30kJ/cm下进行焊接。 400MPa级超细晶钢经奥氏体化退火后,组织为铁素体和珠光体,晶粒明显长大。在线能量（6kJ/cm～16kJ/cm）范围内,焊接接头拉伸全断在母材;接头冷弯试验结果表明焊接接头具有良好的塑性;经过退火处理试板的熔合线和热影响区的韧性总体高于未经退火处理的试板;在试验的焊接条件下,WCX355超细晶钢在热影响粗晶区未有明显脆化,在回火区也未发生软化现象。焊缝柱状晶区的组织由沿柱状晶界分布的先共析铁素体+侧板条铁素体+块状铁素体+针状铁素体组成;熔合线外的粗晶区组织主要由少量的沿原始奥氏体晶界析出的晶界铁素体+侧板条铁素体+贝氏体+少量的针状铁素体组成;细晶区由细小的铁素体和珠光体组成。更多还原

【Abstract】 The designing principle of chemical compositions of high toughness submerged arc welding wires of 400MPa with Mn-Ni-Cr-Mo-Ti-B-Ce and Mn-Mo-Ti-B-Ce-Zr alloy system is introduced. Submerged arc welding with the test welding wire matching sintered flux was carried out to get the deposited metal. Experiment results indicate that matching the two kinds of flux the developed welding wire can produce deposited metals of good mechanical properties. Matching with flux of higher basicity the deposited metal have better mechanical properties (Rm>500MPa;ReL>600MPa;Akv J(-20℃)>150J). Microstructure of the deposited metals is composed of acicular ferrite and a little proeutectoid ferrite.Microstructure and property of X60 pipeline steel welding heat affected zone(HAZ) was investigated. The results indicated that the microstructure is coarsening and the toughness is worsening when the peak temperature enhances and t8/5 increases. The initial austenitic grain size and island microstructure(martensite> M-A constituent、 carbonide) are the primary reason which affected the fracture impact toughness. Decreasing the percentage of carbon is benefit to reduce island microstructure and enhance toughness. Hardness distribution in welding HAZ indicated that softening zone exist in welding HAZ and the softening zone became wider with the increasing of heat input, So X60 pipeline steel was fit to low heat input welding(<30kJ/cm).Microstructure of 400Mpa ultrafine grain steels are ferrite and pearlite after austenize anneal and the grains became bigger apparently. Welding joints tension sample all fractured in the base metal when heat input ranged between 6kJ/cm and 16kJ/cm. The joints cold bend experiment indicated the welding joints have a good plastic property. The toughness of fusion line and HAZ of annealing simple was higher than non-annealing simple. Under the experiment’s welding condition, WCX355 ultrafine grained steels didn’t distinctly embrittle in CGHAZ and didn’t soften in tempering zone either. The microstructure of weld seam columnar grain are composed of proeutectoid ferrite 、 FSA、 massive ferrite and acicular ferrite. The microstucture of CGHAZ are composed of intergranular ferrite 、 FSA、 bainite and a little acicular ferrite The microstructure of fine grain zone are composed of fine ferrite and pearlite.更多还原