Investigation of the High Strength Steel Al-Si Coating during Hot Stamping Operations

Abstract

To improve the low formability that HSS sheets exhibit at room temperature, innovative forming technologies like the hot stamping process are currently applied. In order to avoid scaling and decarburization during the heating step, metal sheets coated with a specially developed Al-Si coating are utilized. In the present work the coating characteristics in terms of morphology, surface roughness and tribological behaviour are investigated as function of heating temperature, holding time and cooling rate that are typical of hot stamping processes.

Environmentally benign tribo-systems for metal forming

“…Facilities for testing such tribo-systems have been developed by Geiger et al [61,62], Yanagida et al [213] and Borsetto et al [31,32]. Whereas determination of the coefficient of friction is realized in the work of Geiger et al using a combined experimental, analytical and numerical analysis of cup deep drawing tests, Yanagida et al developed an advanced strip drawing test for direct friction measurements.…”

Investigation on Tribological Behavior of Advanced High Strength Steels: Influence of Hot Stamping Process Parameters

“…In recent years, hot stamping of HSS has played an important role in the development of future generation of ground vehicles, because this process can bring the combined benefits of maintaining the high strength of the steel and lowering the spring back of the workpiece when operated at elevated temperatures [2]. However, a major problem in forming of HSS is the galling of the die and the scoring of the workpiece as a result of the high contact pressure and temperature at the tool-workpiece interface [3]. Solving this problem requires the proper design of parameters for the hot stamping process and detailed analysis on wear of the tool steel and attrition of the sheet metal.…”

Tribological characteristics of high strength steel sheets under hot stamping conditions

“…The possibility to form the blank at elevated temperatures guarantees lower stamping loads, higher formability and lower spring-back phenomena compared to the same part obtainable through traditional room temperature processes (Mori et al, 2005); at the same time, the simultaneous die quenching permits to obtain a fully martensitic part, thus characterized by extremely high level of mechanical strength and crashworthiness properties. In order to avoid surface oxidation and decarburization during the heating stage, the metal blanks are covered with an Al-Si layer that has proved to be resistant to temperature as well as to contribute to the friction and die wear reduction (Borsetto et al, 2009). When heated at elevated temperature, diffusive phenomena at the blank-layer interface are activated and determine the formation of an Al-Fe-Si ternary alloy, which presents a melting point considerably higher than the original Al-Si layer (approximately 600 • C) (Fontalvo and Mitterer, 2005).…”