Process Metallurgy & Product Applications
Significant progress has been achieved in recent years in the industrial-scale production of retained austenite–containing advanced high-strength steels that exhibit tensile strengths greater than 1,000 MPa. Application and implementation of this new class of steel to the automobile body structure is intended during the latter years of this decade, but persistent technical challenges remain to ensure the actualization of targeted and concurrent benefits to vehicle mass reduction, vehicle cost, and passenger safety. These challenges are demonstrated, and strategies for retained austenite containing advanced high-strength steel application are outlined.
This study focuses on developing dual-phase steels using grades with non-peritectic carbon content and microalloy addition. The connection between microstructure and mechanical properties is studied, with focus on the microstructure development after hot rolling and during annealing in a continuous galvanizing line. In-line plant trials were carried out in order to investigate the impact of alloying elements and process parameters on the microstructure.
Metallurgical length control is important for operations such as soft reduction. This work explores the small potential to control deviations in metallurgical length during casting speed changes. By dropping spray water flowrates from their greatest to smallest levels, results show that a speed drop of 0.2 m/minute can be accommodated in a 221-mm-thick slab caster while maintaining constant metallurgical length during steady casting. Under transient conditions, however, there is always some deviation.
This paper will examine toughening mechanisms that address deficiencies by utilizing a customized Charpy V-notch (CVN) impact test to quantitatively assess the toughness of selected press-hardened steel materials. Microstructural features such as refined prior austenite grain size, retained austenite and surface decarburization zone are shown to enhance impact performance as measured by thickness-normalized CVN energy.
Levels of C, Mn and Si in new advanced high-strength steel grades lead to a complex evolution of microstructure during solidification and can lead to slab cracking. Three lab-cast ingots (3 wt.% Mn; 0.5, 1.5 and 3.0 wt.% Si; and 0.2 wt.% C) and one production slab (1.5 wt.% Mn, 0.5 wt.% Si and 0.2 wt.% C) were characterized by their microstructure, secondary dendrite arm spacing, hardness and tensile properties. Segregation of elements, especially silicon, was found to play an important role in determining microstructure, hardness and strength.
There are two popular tapered roller bearing arrangements in use in today’s ferrous and non-ferrous rolling mills: tapered quadruple outer and tapered quad double inner, tapered bore. This work discusses basic handling and maintenance of these bearings necessary to maximize bearing life and the differences between these two bearing types. Proper bearing handling and maintenance practices are paramount for achieving maximum bearing life and trouble-free operation.