High Strength Steel solutions for automotive parts : State of the art of machinability enhancement and further developments

Abstract

For many decades ArcelorMittal has been developing solutions to enhance machinability of high strength steels for automotive parts. Many well-known metallurgical solutions create or retain inclusions in the metal and then promote machinability without decreasing the mechanical characteristics. Such metallurgical treatment usually leads to the formation of so-called Built-Up Layers (BUL) or transfer layers on the cutting tool while machining. The tool wear rate decreases and thus allows a longer tool life or a better productivity. The existence of such BUL on the cutting tool depends on many parameters i.e. tool geometry, tool material, cutting parameters… There is a growing need in the automotive industry for lighter parts. This has led to a global trend to develop new steel grades with higher mechanical properties. ArcelorMittal is currently developing new metallurgical solutions to optimize steel grades to ensure a better machinability thus preventing productivity losses. BUL characteristics are being studied for the most important machining operations. This paper summarizes the main developments in steel machinability for many decades. Some results from research works into turning and drilling highlight the benefits of these new steels.