Improving fatigue properties of welded structural steels

Motor Coach Industries（MCI）为北美的各种运输机构生产公共汽车及其零部件。由于其有效性、生产率和经济效益，MCI在主要车辆部件的制造中使用电弧焊。然而，在该公司，焊接钢部件的疲劳失效直接源自焊缝或其紧邻区域。焊接过程中，在焊缝熔合区和热影响区（HAZ）中形成的有害微观结构特征会对焊接材料的疲劳抗力造成损害。这些包括裂纹、夹杂物、孔隙和由快速焊接热循环引起的有害的第二相。这些显微组织特征受焊接参数的显著影响，不幸的是，焊接参数影响焊接钢材料的显微组织和疲劳性能。因此，本研究的目的是系统地研究电弧焊接参数如何改变焊缝内部和周围的微观结构，以及这如何影响用于生产公共汽车的钢材的疲劳性能。在疲劳试验之前和之后，将对不同焊接参数产生的焊缝和HAZ进行详细的微观结构分析，以确定与疲劳裂纹萌生和扩展相关的焊接参数相关的微观结构特征。这对合理选择焊接工艺参数以提高电弧焊钢结构的抗疲劳性能具有一定的参考价值。生产具有上级抗疲劳性的焊接客车将使客车更安全，使用寿命更长，维修服务更少。研究结果不仅对汽车工业有益，而且对加拿大其他工业也有益，在这些工业中，焊接结构钢受到重复载荷条件的影响。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.