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

Nova Steel生产高质量的辊压成型钢管产品，主要用于汽车行业。Nova Steel生产的直管通常由一级汽车零部件供应商进行弯曲和液压成形操作。目前，Nova Steel生产的75%的汽车钢管采用屈服强度相对较低的传统钢材，而Nova Steel生产的钢管中只有25%采用屈服强度可达900 MPa的高级高强度钢（AHSS）。汽车制造商正在采用AHSS材料来减轻车辆重量，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管产量提高到85%。目前的5年（5000万美元）计划要求Nova Steel使用TRIP 690生产15种不同的产品，TRIP 690是一种由铁素体/残留奥氏体/贝氏体/马氏体组成的新型多相AHSS。最初的管材试验导致在液压成形过程中焊缝处过早爆裂失效，导致约15%的显著报废率。由于TRIP 690的焊接反应复杂，Nova Steel没有专业知识来确定辊轧成形工艺参数（轧制速度、焊接温度、焊接频率和接触压力）对焊缝微观结构/机械性能的影响。了解这些辊轧成形参数对焊缝性能的影响是Nova Steel和圭尔夫大学之间拟议项目的动机。将进行大规模的辊轧成形试验，将完成焊接的深入表征，焊接性能测试将有助于确定这类管材的最佳辊轧成形参数。

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.