【作者】 黄治军；

【导师】 胡伦骥； 刘振清；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2007， 博士

【摘要】 本课题选用多种基材、研制了多种焊丝、采用了不同焊接工艺对我国最新研制的低硫、细晶、高性能的X70及X80管线钢的焊接性能及焊接材料进行了系统的研究。对于管线钢的抗裂性能,提出了一个用于预测现代低碳高强管线钢焊接热影响区最高硬度的计算式,并根据试验结果进行了验证。从室温到100℃预热,X70及X80钢焊接热影响区最高硬度(HV₁₀)低于248。结果表明,X70及X80钢淬硬倾向小,且硬度满足管线钢抗H₂S应力腐蚀要求。采用现有高性能埋弧焊丝及气保焊丝分别对X70、X80钢及与X80钢相当的低CE钢进行了焊接性能试验。现有埋弧焊丝及WER60气保焊丝用于X70钢、WER70气保焊丝用于X80钢均能满足要求,但现有埋弧焊丝用于X80钢性能还不能满足要求,因此需要开发新的埋弧焊丝。结合常用的管线钢厚度及焊接工艺,分别研究了埋弧焊及气体保护焊填充金属在焊缝金属中所占的比例,并建立了预测这一比例的较为实用的计算式,作出了埋弧焊填充金属面积与焊缝金属面积比值同钢板厚度与坡口大小比值的关系曲线;作出了气保焊填充金属面积与焊缝金属面积比值同钢板厚度的关系曲线;提出了焊缝强度预测的方法,并利用excel进行高效运算,为实现最终焊缝成分和焊接工艺较为准确的控制奠定了坚实的基础。埋弧焊丝的试制以熔敷金属强度作为主要目标,采用正交设计方法,将C含量、Mn含量及Ni、Cr、Mo等合金元素含量的折算总量作为试验因子,并设为两个水平。在焊丝钢中加入微量的Ti和B对焊缝金属进行微合金化。匹配CHF101或CFH105进行焊接熔敷金属试验,新研制的埋弧焊丝强度为560⁶90MPa,发现焊接熔敷金属强度与焊丝的碳当量有较好的关联性。采用新研制的系列埋弧焊丝及不同的焊接工艺对X70钢及X80钢进行了实验室对接试验及实管焊接试验,得到了焊缝性能最佳的焊丝成分,焊丝化学成分有所创新,且使用了资源丰富的Cr元素。X70钢焊缝与焊接热影响区半平台能转变温度VTE均为约-80℃,焊缝冲击功的平均值AKV（-20℃）一般达到200J以上。X80钢接头-20℃各区冲击功不小于127J,焊缝抗拉强度为710～740MPa,接头硬度在技术条件规定的范围内。热处理后,含Cr焊缝强度有所上升。管线钢高速埋弧焊工艺有利于提高对接焊缝的韧性,X80钢及其埋弧焊丝具有优良的工艺适应性。所研制的焊丝性能明显优于现有焊丝,达到国际先进水平。埋弧焊对接焊条件与熔敷焊接条件有较大的差别时,对接焊缝强度将会有明显变化。建立了埋弧焊丝与基材的碳当量差值和熔敷金属与对接焊缝强度差值的关联性。对于试验所用的X70钢及X80钢,埋弧焊丝熔敷金属最低强度分别高于560MPa及620MPa时,可以满足对接焊缝强度要求。合金元素对低温冲击韧性的影响较为明显。采用Ni、Cr及Mo等多元合金化及Ti、B微合金化的焊缝金相组织含较多针状铁素体,因此焊缝具有较高的强韧性。不仅基材的化学成分,而且基材的组织结构也会对焊缝金属组织性能产生影响,从而会导致不同方向的焊缝之间、不同钢种的焊缝之间的韧性差异。埋弧焊热影响区存在一定的软化,对于低CE高强度钢软化更为明显,但气保焊接头的软化程度即使对于低CE高强钢也是基本上可以接受的。X80钢焊接接头金相组织过热区为贝氏体,正火区和不完全正火为贝氏体和铁素体,焊缝组织为针状铁素体加极少量的先共析铁素体。焊接粗晶区晶粒尺寸埋弧焊大于气保焊,大线能量时也较大,但均明显小于传统钢。EBSD分析显示,X80钢具有明显细小的焊缝晶粒,晶粒取向分布也比较均匀,热处理后焊缝针状铁素体有一定的粗化。高韧性断口表面韧窝中含有直径0.5¹.0μm的颗粒,颗粒主要由Ti、Ca等组成。埋弧焊缝冲击断口所含的颗粒直径2⁵um,颗粒主要含有Al、Si时,焊缝韧性下降。焊丝中含有较高的Ti及较低的Als是使焊缝中形成以Ti为主的微细质点的关键。更多还原

【Abstract】 Systematical researches were carried out on the weldability and welding materials of/for the newly developed low sulphur, fine grain and high performance X70 steel and X80 steel by using differnent kinds of steels, developing several grades of welding wires and taking various welding procedures.For the cracking susceptibility of pipeline steels,a calculation formula was proposed for the prediction of the maximum hardness on heat affected zone for modern high strength pipeline steels. The formula was checked according to the results of the tests, showing good accordance and good adaptability. Maximum hardness HV₁₀ on heat affected zone for either X70 steel or X80 steel, from room temperature to 100℃preheat, is below 240, indicating low hardenability of the steels and good H₂S corrosion resistance of the weld joints as well.The current high performance SAW and GMAW wires were used for the welding tests of X70 steel,X80 steel and low CE high strength steel equivilent to X80. The present 10# SAW wire and GMAW wire WER60 for X70 steel and GMAW wire WER70 for X80 can meet the current technical requirements, but 10# SAW wire for X80 steel can’t,so new SAW wires need developing.Based on the commonly used wall thicknesses and welding procedures of pipeline steel, the ratios of exotic filling metal to the weld metal in SAW and GMAW were analyzed respectively, and practical calculation formulas for the ratios were set up. According to the calculation results, for SAW, a curve describing the relationship between the ratio of exotic filling metal to the weld metal and the ratio of plate thickness to face root was made; for GMAW, a curve describing the relationship between the ratio of exotic filling metal to the weld metal and the plate thickness was made. A method for a quick prediction of weld strength was proposed with the aid of Excel software,which paved the way for accurate control of the goal composition and the strength of the weld metal.By using orthordonal designing,with the strength of weld metal as controlling objective, with C content, Mn content and modified combination of Ni, Cr and Mo,etc. as testing factors set at two levels, and with the addition of Ti and B at micro level, SAW wires were manufactured and studied. Standard SAW welding test was carried out to examine the properties of the weld deposits by use of CHF101 flux and CHF105 flux. The strength of deposit weld metal is from 560MPa to 690MPa and found correspondant well to the CE value of the wire.The newly developed SAW welding materials were employed for lab flat SAW and pipe SAW experiments on X70 steel and X80 with different welding procedures and the chemistry of the wire with best mechanical properties was obtained. The compositions of the SAW wires are innovative,and Cr which is abundant in the earth is a main alloying element in these wires. The transition temperatures of half energy of the upper shelf for weld metal and heat affected zone were respectively around -80℃, and the average Charpy impact energy at -20℃generally reach to 200J. The average impact energies in various zones of the joint of X80 steel at -20℃were not lower than 127J,and the strengths of weld metals were from 710 to 740MPa,and the hardnesses of the joints were within the required range. The high speed SAW welding procedure is producible to the improvement of the weld metal toughness. After the weld metal subjected to post welding heat treatment,the strength obviously increased for Cr bearing weld metal. X80 steel and its welding wire exhibit good weldability and good adaptability.These wires have better properties than the current wires,reaching to an internationally advanced level.When the procedures vary from wire depositing welding to pipe steel plate butt welding, the strength of the weld metals will also vary.The relationship between the strength variation and the CE difference between the wire and the base metal was set up. For X70 steel and X80 steel examined, if the minimum strengths of deposit metals of the welding wires are 560MPa and 620MPa respectively, they can meet the strength requirements of the butt welds too.There exist obvious influences of types of alloying elements on low temperature toughness. Multi-alloyed with Ni and/or Cr and/or Mo and micro-alloyed with Ti and B, weld metals feature dominant acicular ferrite microstructure, and have high strength and high toughness. Not only the composition but also the microstructure of base metal exerts influence on the microstructure and properties of weld metal resulting in variations in toughness of weld metals produced in different welding directions or with different base metals.The SAW joints exhibit softened zones especially for low CE high strength steel, But the softening of GMAW joint is acceptable even for low CE high strength steel.The microstructures of the welded joint of X80 steel are bainite in coarse-grained HAZ, mix of bainite and ferrite in normalized zone and incompletely normalized zone as well and mix of acicular ferrite and minor prior ferrite in weld metal. The grain size in CGHAZ is coarser in SAW than in GMAW and also coarser in higher linear energy, but significantly smaller than that of traditional steel.EBSD analysis shows that X80 weld metal has obvious finer grain with more uniformly distributed orientation and the acicular ferrite coarsen after heat treatment. In the tough dimples of high toughness fracture surface there are fine particles sized 0.5¹.0μm in diameter, mainly composed of Ti, Ca ,Si and so on. In the dimples of SAW weld fracture surface there are particles sized 2⁵μm in diameter, mainly composed of Al, Si, and the weld metal has low toughness. Reletively high Ti and low Als is the key to the formation of Ti-dominant fine particles in weld metal.更多还原