Sheet Steel Technology for the Last 100 Years: Progress in Sheet Steels in Hand with the Automotive Industry

Abstract

Development in sheet steels has progressed in strong relation with automotive industry in Japan. To meet the requirements from automotive industry, various types of sheet steels including high and ultrahigh strength steel sheets have been developed. Progresses in three types of steel series will be discussed by checking the historical facts and technologies and their contributions. Introductions of interstitial free (IF) steel and continuous annealing system are the important events in mild steel developments for panels. Extensive work on finding the optimum mixtures of hard and soft phases to improve elongation of steels contributed to improve the crashworthiness of autobodies. Continuous annealing system also played an important role in producing these advanced high strength steels. Precipitation is used in a particular way which is to scavenge solute carbon and nitrogen and to prevent coarse cementite particle precipitation. It is also worth to point out that the collaborative activities particularly strong in Japan between steel manufacturers and auto companies have affected the progress in advanced sheet steels.

Bake hardening effect of the low strength interstitial free steel

“…Thus, it is necessary to optimize the processing conditions to increase the ductility because the microstructure with high dislocation density increases the strength significantly. The YS of the initial steel was 137 MPa, indicates that the strength of the present study was lower than that of the automotive IF steels, which exhibit typically 200-280 MPa of YS and 30-47% of EL [15][16][17]. The YS after baking is usually used to evaluate the dent resistance of the steel; therefore, BH response is essential for the products which are made of the low strength IF steel when the paint is baked.…”

“…YS and UTS) than the initial one. Because the higher YS significantly promotes the surface deflections, it is recommended to apply the steel with YS less than 240 MPa [17]. Thus, the present steel with the YS of 137 MPa would be a promising material for the application of deep drawability.…”

“…However, Bhagat et al applied the Cottrell theory and explained that the rise in YS was associated with the formation of solute atmospheres and saturation of stress field around the dislocations which formed during the deformation [7]. More solute C in the ferrite increases the strength of the steel, but may cause the stretcherstrain pattern due to local yielding during the press forming; as a result, adding Ti and/or Nb as carbides of nitrides is the effective way to reduce the amount of solute C and N in the steels [17,19]. Fig.…”

Baking Effect on Desorption of Diffusible Hydrogen and Hydrogen Embrittlement on Hot-Stamped Boron Martensitic Steel

“…The global trend of reducing carbon dioxide emissions from vehicles has focused on weight reduction in automobiles. Owing to legislative and customer demand, one significant issue involves weight reduction and crashworthiness properties [1,2]. Recently, hot stamping technology has been increasingly used in automotive structural parts with ultrahigh strength to meet the standards of both high fuel efficiency and crashworthiness [3].…”

Effects of Hot Stamping and Tempering on Hydrogen Embrittlement of a Low-Carbon Boron-Alloyed Steel

“…One of the most important challenges for the automobile industry is to further enhance passenger safety coupled with a simultaneous reduction of vehicle weight regarding energy consumption and exhaust emissions [1]. This has notably promoted the research and development of ultra-high strength steels (UHSSs) in the modern automobile industry.…”