Improving fatigue properties of welded structural steels

汽车客车工业公司(MCI)为北美的各种交通机构制造巴士及其零部件。由于电弧焊的有效性、生产率和经济效益，MCI将其用于汽车主要零部件的制造。然而，在该公司，焊接钢件的疲劳失效直接源于焊缝或其邻近区域。焊接过程中在焊接熔合区和热影响区(HAZ)形成的有害组织特征会对焊接材料的抗疲劳性能造成损害。这些缺陷包括快速焊接热循环造成的裂纹、夹杂物、气孔和有害的第二相。这些微观组织特征受焊接工艺参数的影响很大，但焊接工艺参数对焊接钢材的组织和疲劳性能影响较大。因此，这项研究的目的是系统地研究电弧焊接参数如何改变焊缝内和焊缝周围的组织，以及这如何影响客车生产中使用的钢材料的疲劳性能。在疲劳试验前后，将对不同焊接参数产生的焊缝和HAZ进行详细的微观组织分析，以确定焊接参数与导致疲劳裂纹萌生和扩展的微观组织特征有关。这对合理选择焊接工艺参数，提高钢结构电弧焊的抗疲劳性能具有一定的参考价值。具有优异抗疲劳性的焊接客车的生产将使客车更安全，使用寿命更长，维修服务更少。这一研究成果不仅对汽车工业有益，而且对加拿大其他焊接结构钢承受反复加载条件的工业也是有益的。这将加强安全，并通过促进加拿大企业来帮助该国的经济。

Motor Coach Industries (MCI) makes buses and their parts for various transit agencies in North America. Electric arc welding is used in the manufacturing of main vehicle parts at MCI due to its effectiveness, productivity and economical benefits. However, fatigue failures of welded steel parts, at the company, originate directly form the weld or in its immediate vicinity. Damage to fatigue resistance of welded materials can ensue from detrimental microstructural features formed in weld fusion zone and in the heat affected zone (HAZ) during welding. These include cracks, inclusions, porosity and deleterious secondary phases caused by the rapid welding thermal cycle. These microstructural features are significantly influenced by welding parameters, unfortunately welding parameters influence the microstructure and fatigue properties of welded steel materials. Therefore, the objective of this proposed research is to systematically study how electric arc welding parameters alter the microstructure in and around welds and how this influences fatigue properties in a steel material that is used in the production of buses. Detailed microstructural analyses of welds and HAZs produced by different welding parameters will be performed both prior to and after fatigue testing to determine welding parameters dependent microstructural features that are responsible for fatigue crack initiation and propagation. This would be valuable in the proper selection of welding parameters for improving fatigue resistance of electric-arc welded steel structures. The production of welded coaches with superior fatigue resistance will enable safer bus coaches with increased service life and reduced repair services. The research outcome would be beneficial not only to the automotive industry but also to other Canadian industries, where welded structural steels are subjected to repeated loading conditions. This will enhance safety and aid the economy of the country by facilitating Canadian businesses.