铸铁拘束试件的拘束度计算及铸铁焊缝裂纹倾向定量评定

本文提出了一种试件拘束度分级可调的铸铁焊缝拘束裂纹定量新方法,采用有元元方法对铸铁试件拘束度进行了计算,并做了实测验证,应用本试验方法测定了石墨形态对铸铁焊缝裂纹倾赂的影响。     

铸铁拘束试件的拘束度计算及铸铁焊缝裂纹倾向定量评定

本文提出了一种试件拘束度分级可调的铸铁焊缝拘束裂纹定量试验新方法、采用有限元方法对铸铁试件拘束度进行了计算,并做了实测验证。应用本试验方法测定了石墨形态对铸铁焊缝裂纹倾向的影响。     

刚性对接裂纹试件和VRC试件拘束度有限元模拟

采用有限元方法研究了试件尺寸对刚性对接裂纹试件和可变拘束裂纹试件拘束度的影响规律.结果表明,两种试件的拘束度均随着厚度的增加而增大,随着厚度由20 mm增加至50 mm,刚性对接裂纹试件中心拘束度由14.87 kN/（mm·mm）增加至20.72 kN/（mm·mm）,可变拘束裂纹试件中心拘束度由10.46 kN/（mm·mm）增加至16.23 kN/（mm·mm）;对于40 mm厚的刚性对接裂纹试件,其拘束试件宽度由125 mm增加至275 mm时,试件的拘束度下降,但拘束试件宽度继续增加,试件的拘束度不再发生显著变化;对于40 mm厚可变拘束裂纹试件,随着拘束试件宽度由125 mm增加至575 mm,其拘束度呈连续下降趋势.     

大拘束度ZG20MnMo钢焊缝裂纹分析及处理

对ZG20MnMo钢大拘束度焊缝裂纹,采用插销试验方法,在不同的预热温度下,对试件进行临界断裂应力、金相与断口形貌分析,找出该钢焊缝产生裂纹的原因及主要影响因素,提出了防止ZG20MnMo钢大拘束度焊缝产生裂纹的措施.     

拘束应力对厚壁管焊接裂纹影响的实例分析

火力发电厂施工的现场大口径厚壁管焊接中，拘束应力过大往往是造成焊接裂纹产生的主要原因。本文以一具体实例分析了拘束应力使高温下焊缝残余塑性降低，导致焊接裂纹的产生，并就该例拘束应力的影响作了量的分析，同时提出了相应的改善措施。     

浮头式换热器浮头盖焊接冷裂纹的消除

钢材的淬硬倾向、焊接接头含氢量及其分布,以及接头所承受的拘束应力状态是产生焊接冷裂纹的三大主要因素.对于低淬硬倾向的钢材,采用低氢型焊材,合理设计焊接结构,降低接头的拘束应力状态,通过合理的焊接工艺,可以消除浮头式换热器浮头盖焊接时出现的焊接冷裂纹.     

高强度钢焊接区拘束应力的有限元分析

采用ANSYS有限元软件计算分析了HQ130高强钢焊接接头区拘束应力的分布。计算和分析结果表明,在气体保护焊线能量16kJ/cm条件下,HQ130钢焊缝表面的瞬时拉伸拘束应力最大达到800－1000MPa,焊缝底部的瞬时拉伸拘束应力达到500－600MPa。熔合区附近的应力梯度较大,这是高强度钢熔合区部位容易产生冷裂纹的重要原因之一。通过严格控制焊接线能量能减小焊接区的热应力,可防止焊接裂纹的产生。     

Weldability and toughness evaluation of pressure vessel quality steel using the shielded metal arc welding (SMAW) process

The present study was carried out to assess the weldability properties of ASTM A 537 Cl. 1 pressure-vessel quality steel using the shielded metal arc welding (SMAW) process. Implant and elastic restraint cracking (ERC) tests were conducted under different welding conditions to determine the cold cracking susceptibility of the steel. The static fatigue limit values determined for the implant test indicate adequate resistance to cold cracking even with unbaked electrodes. The ERC test, however, established the necessity to rebake the electrodes before use. Lamellar tearing tests carried out using full-thickness plates under three welding conditions showed no incidence of lamellar tearing upon visual examination, ultrasonic inspection, and four-section macroexamination. Lamellar tearing tests were repeated using machined plates, such that the central segregated band located at the midthickness of the plate corresponded to the heat-affected zone (HAZ) of the weld. Only in one (no rebake, heat input: 14.2 kj cm^-1, weld restraint load: 42 kg mm^-2) of the eight samples tested was lamellar tearing observed. This was probably accentuated due to the combined effects of the presence of localized pockets of a hard phase (bainite) and a high hydrogen level (unbaked electrodes) in the weld joint. Optimal welding conditions were formulated based on the above tests. The weld joint was subjected to extensive tests and found to exhibit excellent strength (tensile strength: 56.8 kg mm^-2, or 557 MPa), and low temperature impact toughness (7.4 and 4.5 kg-m at-20 °C for weld metal, WM, and HAZ) properties. Crack tip opening displacement tests carried out for the WM and HAZ resulted in δ_m values 0.36 and 0.27 mm, respectively, which indicates adequate resistance to brittle fracture.     

缝隙型焊接试件拘束应力的分析

缝隙型裂纹是一种最接近实际焊接结构受力状态的试件,研究其焊缝拘束应力的计算具有普遍的意义,本文以热弹塑性有限元分析计算作基础,建立了焊根间隙收缩曲线的数学模型,结合Ｓｌｉｔ试件拘束度的分布函数,首次提出了一个描述Ｓｌｉｔ试件拘束度与拘束应力关系的计算公式,计算与试验结果证明它能比较真实地反映实际焊接接头的应力水平,有重要的实用价值。     

Weldability characteristics of shielded metal arc welded high strength quenched and tempered plates

High strength, quench and tempered (Q&T) plates having yield strength of a minimum of 670 MPa and conforming to SA 517 Gr. F specification were successfully developed at Rourkela Steel Plant in plates up to 40 mm thickness. The plates are used extensively for the fabrication of impellers, penstocks, excavators, dumpers, and raw material handling devices, where welding is an important processing step. SA 517 Gr. F plates, characterized by a relatively high carbon equivalent (CE: ∼0.6) and alloyed with Ni, Cr, Mo, Cu, and V, are susceptible to a crack-sensitive microstructure and cold cracking during welding. In view of the above, the present study investigated the weldability properties of 20 mm thick plates using the shielded metal arc welding (SMAW) process. Implant and elastic restraint cracking (ERC) tests were carried out to assess the cold cracking resistance of the weld joint under different welding conditions. Preheat of 100 °C, partial or full rebake, and a heat input of 14.9 to 15.4 KJ/cm resulted in static fatigue limit (SFL) values well in excess of the minimum specified yield strength (MSYS) of 670 MPa and a critical restraint intensity (K _cr) value of 34,650 MPa, indicating adequate cold cracking resistance. Lamellar tear tests conducted using full thickness plates at heat input levels ranging from 9.7 to 14.4 KJ/cm and weld restraint loads (WRL) of 510 to 685 MPa showed no incidence of lamellar tear upon visual, ultrasonic, and four-section macroexamination. The weld joint, based on optimized welding parameters, exhibited adequate tensile strength (812.4 MPa) and low temperature impact toughness 88.3 and 63.4 J (9.2 and 6.6 kg-m) at −40 °C for weld metal (WM), and heat-affected zone (HAZ) properties, respectively. The crack tip opening displacement (CTOD) values of WM and HAZ (0.40 and 0.36 mm, respectively) were superior to that of the parent metal (0.29 mm), indicating adequate resistance of weld joint to brittle fracture. It was concluded that the weld joint conforms to the requirements of SA 517 Gr. F specification and ensures a high integrity of the fabricated products.     

Weldability evaluation of high tensile plates using GMAW process

High tensile plates, SAILMA-450 high impact (HI) (yield strength, 45 kg/mm² minimum; ultimate tensile strength, 57 kg/mm² minimum; elongation, 19% minimum; Charpy impact energy 2.0 kg.m at −20 °C minimum) were successfully developed at the Steel Authority of India Ltd., up to 32 mm plate thickness. Since then the steel has been extensively used for the fabrication of impellers, bridges, excavators, and mining machineries, where welding is an important processing step. The present study deals with the weldability properties of SAILMA-450 HI plates employing the gas metal arc welding process and carbon dioxide gas. Implant and elastic restraint cracking tests were conducted to assess the cold cracking resistance of the weld joint under different welding conditions. The static fatigue limit values were found to be in excess of minimum specified yield strength at higher heat input levels (9.4 and 13.0 kJ/cm), indicating adequate cold cracking resistance. The critical restraint intensities, K _cr, were found to vary between 720 and 1280 kg/mm², indicating that the process can be utilized for fabrication of structures involving moderate to low restraint intensities (200 to 1000 kg/mm²). Lamellar tear tests conducted using full thickness plates at heat input levels ranging from 10 to 27 kJ/cm showed no incidence of lamellar tear upon visual, ultrasonic, and four-section macroexamination. These tests were repeated using machined plates, such that the midthickness of the plates (segregated zone) corresponded to the heat affected zone of the weld. No cracks were observed, indicating good lamellar tear resistance of the weld joint. Optimized welding conditions were formulated based on these tests. The weld joint was subjected to extensive tests to assess the physical properties and soundness of the weld joint. The weld joint exhibited good strength (64.7 kg/mm²) and impact toughness (5.7 and 3.5 kg.m at −20 °C for weld metal and heat affected zone properties. Crack tip opening displacement (CTOD) tests carried out for parent metal, heat-affected zone, and weld metal resulted in δm values of 0.41, 0.40, and 0.34 mm, respectively, which indicates adequate resistance to cleavage fracture. It was concluded that the weld joint conforms to the requirements of SAILMA-450 HI specification and ensures a high integrity of the fabricated products.