Interpretation of creep crack initiation and growth data for weldments

Creep crack growth testing of macroscopically homogeneous materials is well established and standardised test procedures are detailed in ASTM E1457. In ASTM E1457 the use of the compact tension C(T) specimen is specified and crack growth data are interpreted using the fracture mechanics parameter C^∗. The resulting benchmark crack growth data are used in assessment procedures, together with estimates of the value of C^∗ in the component, to predict creep crack growth behaviour. In this work, the results of a series of creep crack growth tests performed on a Type 316 stainless steel weldment at a temperature of 550 °C are presented. The initial crack is located within the heat affected zone (HAZ) of the weldment. Since there are currently no agreed methods for determining C^∗ in inhomogeneous laboratory specimens, this paper examines the application of procedures in ASTM E1457 for the characterisation of crack growth in weldments. In addition, the creep toughness parameter is evaluated for the material. It is shown that the creep crack growth rates in the weldment may be described by the C^∗ values obtained following ASTM E1457 in conjunction with parent material properties. Comparison of the results with similar data for Type 316H stainless steel parent material shows that the crack growth rates for the crack located within the HAZ are higher and the initiation times lower than the parent values, for the range of test conditions examined. Simple analytical models based on ductility exhaustion arguments have been shown to bound the crack initiation and growth data for the weldment.     

Effect of Aluminum and Titanium Treatment on Non-Metallic Inclusions and Microstructures of CGHAZ in HSLA Steel

The Effect of A1 and Ti treatment on non-metallic inclusions and microstructures of coarse-grain HAZ in HSLA stee1 was investigated in this paper based on experiments and thermodynamic calculations.The results showed that the inclusions in A1 treated steel were mainly aluminum oxides and titanium nitrides which could not promote the formation of acicular ferrite microstructures.Microstructure of coarse-grain HAZ in A1 treated steels consists of heavy grain boundary ferrite and ferrite side plate.The inclusions in Ti treated steel were A1,Ti,Mg,Ca composite oxides with size in the range of 0.5-3μm and titanium nitrides with size less than 0.3μm.Ti composite oxide could promote the formation of acicular ferrite and microstructures of coarse-grain HAZ in Ti treated steel consists of grain boundary ferrite,small amounts of ferrite side plate and large amounts of intragranular acicular ferrite.The size of grain boundaries ferrite was increased and the amount of ferrite side plate was decreased with the increase of soaking time at the peak temperature.The amount of grain boundary ferrite and the size of acicular ferrite were also increased with the increase of cooling rate during ferrite phase formation.     

F460高强韧厚船板焊接热影响区的组织和冲击断裂行为

使用Gleeble-3800热模拟试验机模拟单道次焊接条件下大厚度(50 mm)F460钢板热影响区(HAZ)热循环过程,通过OM,SEM,EBSD和TEM研究了HAZ的显微组织随热输入(E)的演化规律.测试了不同E下HAZ的室温硬度(HV),在-40和-60℃下进行了Charpy冲击示波实验(CVN).当E=15 k...     

纵向焊接铝合金构件的试验和设计研究

大多数结构用铝合金通常要经过热处理或加工硬化以得到比退火状态更高的力学性能。这种合金焊接后,焊接热会使焊缝附近局部区域(称为热影响区HAZ)强度降低。而对于钢结构,由于其热导率比铝材小得多,因此只有高强钢才可能产生强度降低的热影响区,而且其强度的降低没有铝合金显著,热影响区宽度也比铝合金小得多。这将使焊接铝合金构件的设计变得更为复杂。由于我国目前还没有关于铝合金结构的设计规范,为此本文通过试验研究及对已有试验数据的分析,并在参考国外规范的基础上,提出了纵向焊接铝合金构件的设计建议公式,并将公式计算结果与试验结果进行了比较,两者吻合较好,从而验证了建议设计公式的适用性。     

超级钢焊接温度场的数值模拟

针对等离子焊接方法,选择适当的热源模式,利用Fortran语言编制热源模式程序,根据温度场的数学模型,利用工程模拟软件MSC．marc对超级钢焊接温度场进行数值模拟并进行温度场分析,模拟结果与实验结果对比表明模拟结果基本准确。     

X100管线钢管埋弧焊焊接接头性能分析

对X100管线钢管直缝双面埋弧焊接头进行了微观组织、显微硬度、拉伸及冲击试验。试验结果表明:X100管线钢双面埋弧焊焊缝金属的显微硬度高于母材,热影响区的显微硬度低于母材,焊接接头存在HAZ软化问题;横向焊接接头的抗拉强度满足ISO 3183—2007的要求,抗拉强度值高于母材纵向,但低于母材横向;埋弧焊焊缝金属的韧性良好,韧脆转变温度为-53℃;焊接热影响区的韧性较差,韧脆转变温度约为7℃。     

热循环对高铌管线钢焊接热影响区冲击韧性的影响

采用Gleeble-3500型热模拟试验机,研究了焊接热循环对Mn-Mo-Nb和高铌 HTP X80管线钢焊接热影响区(HAZ)冲击韧性的影响.结果表明,随焊接热输入量的增加,两种X80管线钢粗晶HAZ的冲击韧性均降低,但在相同的焊接热输入条件下,高Nb钢粗晶HAZ的冲击韧性均高于Mn-Mo-Nb管线钢.其原因是高Nb钢中由于未溶Nb(CN)状的存在,抑制奥氏体晶粒长大,在高的线能量条件下,能够保证奥氏体晶粒的细小均匀.     

Effects of Nb on stress corrosion cracking of high-strength low-alloy steel in simulated seawater

In this study, simulated heat-affected zone (HAZ) of Nb-free and Nb-bearing steel were obtained, and SEM, TEM, and slow strain rate tensile (SSRT) tests were performed to investigate the effect of Nb on the stress corrosion cracking (SCC) behavior of high-strength low-alloy (HLSA) steel in simulated seawater with or without hydrogen charging. The addition of Nb significantly refined the grains and uniformed the microstructure of HLSA. Nb hardly affected the SCC susceptibility of BM and HAZ without hydrogen-charging. However, after charging with 10 mA cm⁻², the SCC resistance of Nb-bearing steel, especially the coarse grain HAZ (CGHAZ) improved drastically, and the process of crack initiation and propagation was inhibited owing to the hydrogen trap function of NbC precipitates.     

特厚高强钢Z向成分差异对焊接接头热输入的影响

文中以两种150 mm特厚高强先进610CFD钢为试验对象，基于材料Z向成分的差异，分析组织不均匀性对焊接接头热输入的影响，利用金相显微镜，SEM，EBSD和冲击试验对结果进行表征.结果表明，提高铸坯厚度、降低易偏析元素C，Mn等合金元素含量，可以有效的减小1/2处偏析程度并避免冶金缺陷，使宏观偏析转化为微观偏析；比较严重的宏观偏析造成1/4处、1/2处热影响区组织存在明显区别是造成其Z向各位置焊接工艺适应性差异的主要原因；而微观偏析造成Z向各位置焊接工艺适应性差异的机理是合金元素微观偏析造成热影响区MA数量、形貌、分布差异.