Weld Seam Optimization of Roll Formed TRIP690********

Nova Steel主要为汽车行业生产高质量的辊压成型钢管产品。Nova Steel生产的直管通常经过弯曲，然后由一级汽车零部件供应商进行液压成形操作。目前，Nova Steel生产的75%的汽车管材使用屈服强度相对较低的传统钢，而Nova Steel生产的管材中只有25%是由屈服强度高达900兆帕的高级高强度钢(AHSS)生产的。汽车制造商正在实施AHSS材料，以努力使他们的汽车轻量化，以提高燃油经济性并减少温室气体排放，因此，Nova Steel希望到2020年将AHSS管的产量提高到85%。目前一项为期5年(5000万美元)的计划要求Nova Steel使用TRIP690生产15种不同的产品，TRIP690是一种新型的多相AHSS，由铁素体/残余奥氏体/贝氏体/马氏体组成。最初的油管试验导致在液压成形过程中焊缝过早破裂，导致显著的废品率~15%。由于TRIP690的复杂焊接响应，Nova Steel没有专业知识来确定辊压成型工艺参数(磨机速度、焊接温度、焊接频率和接触压力)对焊缝组织/机械性能的影响。了解这些轧制成形参数对焊接性能的影响是Nova Steel和Guelph大学提出的项目背后的动机。将进行大规模的滚压成形试验，完成焊缝的深入表征，焊接性能测试将有助于确定此类管材的最佳滚压成形参数。

Nova Steel manufactures high quality roll formed steel tubular products, primarily for the automotive industry. The straight tubes that Nova Steel produces are typically followed by bending and then hydroforming operations by a tier-1 automotive parts supplier. Currently, 75% of the automotive tubes manufactured by Nova Steel utilize conventional steel with relatively low yield strengths, while only 25% of the tubes manufactured by Nova Steel are produced from Advance-High-Strength-Steel (AHSS) where yield strengths can reach up to 900 MPa. Carmakers are implementing AHSS materials in an effort to lightweight their vehicles for improved fuel economy and reduced greenhouse gas emissions, hence, Nova Steel hopes to increase AHSS tube production to 85% by 2020. A current 5-year ($50 million) program requires Nova Steel to produce 15 different products using TRIP690, which is a novel multi-phase AHSS consisting of ferrite/retained austenite/bainite/martensite. Initial tubing trials resulted in premature burst failures at the weld seam during hydroforming, resulting in a significant scrap rate of ~15%. Due to the complex welding response of TRIP690, Nova Steel does not have the expertise to identify the effect of roll forming process parameters (Mill Speed, Weld Temperature, Weld Frequency and Contact Pressure) on the weld seam microstructure/mechanical properties. Understanding the effect of these roll forming parameters on the weld properties is the motivation behind the proposed project between Nova Steel and the University of Guelph. Large scale roll forming trials will be conducted, in-depth characterization of the welds will be completed and weld performance tests will aid to identify optimal roll forming parameters for this class of tubular material.