Search Results

Dent performance of steels is increasingly important as the automotive industry continues to reduce vehicle mass and improve vehicle performance. Bake hardenable steels are being applied to closure panels for improved dent resistance. Closure panels require good dent performance, along with good formability to ensure ease of manufacture. This study examines dent performance of various galvanized coated steel grades used in automotive closure panels.

Tailor welded blanks (TWB) afford better utilization of sheet steel for automotive and other applications. However, forming behaviour can be complicated because of the interactions between the different sheet steels comprising the TWB and the welding processes used. At Dofasco we have studied a matrix of different steel types, sheet thicknesses, and welding processes (i.e. mash seam, laser and electron beam) in order to gain an understanding of forming behaviour of tailor welded blanks. Simulative forming tests such as hole expansion, stretch bend, stretch dome and tensile tests were used. Finite element simulations using the FTICASE code were used to determine mechanisms for part failures. In addition, weld “service” characteristics such as corrosion performance and fatigue life were evaluated. Microscopic examinations included microhardness, metallography, and tests for weld porosity and zinc entrapment.

One of the more effective ways of improving automobile fuel efficiency is by reducing vehicle weight. This can be accomplished through the use of higher strength, lighter gauge steels. This study concentrates on two such steels (renitrogenized and dual phase) that potentially could be used in some fatigue applications. Three dual phase steels with different monotonic strengths were tested, as was some dual phase which was exposed to undervehicle corrosion. Two renitrogenized steels were also tested, as well as a mild steel of similar carbon content. These were tested in the hot rolled condition, and also after forming and aging. Some samples were also cycled intermittently to simulate stop-and-go driving. The data was compared to previously determined HSLA data.

The electrocoat operating windows of five automotive sheet steel products (uncoated cold rolled, electrogalvanized, hot dip galvanized, electrogalvanneal, and hot dip galvanneal) were compared. The effect of variations in base steel chemistry and galvanneal coating structure on the operating window were also evaluated. While all variations exhibited an acceptable electrocoat operating window, there was a measurable difference between the five sheet steel products. There was no effect of the galvanneal coating structure or base steel chemistry on the operating window.