Effect of Mn Addition on Hot-Working Behavior and Microstructure of Hot-Rolled Medium-Mn Steels

Abstract

Hot plastic working behavior and microstructure evolution were investigated during a production process of four medium-Mn steels, which differed in Mn (3 and 5%) and Nb contents. The production process started with casting, followed by hot forging, rough hot-rolling and concluded with final thermomechanical processing, which was performed to obtain multiphase bainite-based alloys with some fractions of retained austenite. The rough rolling was composed of four passes with total true strain of 0.99 and finishing rolling temperature of 850 °C, whereas thermomechanical processing contained five passes and total true strain of 0.95 at a finishing rolling temperature of 750 °C. During the process, the force parameters were recorded, which showed that the rolling forces for steels containing 3% Mn are higher compared to the 5% Mn alloys. There was no significant influence of Nb on the rolling parameters. The produced as-cast microstructures were composed of dendritic bainitic-martensitic phases. A positive effect of Nb micro-addition on a refinement of the as-cast structure was noticed. The thermomechanical processed steels showed fine multiphase microstructures with some fractions of retained austenite, the fraction of which depended on the Mn content in steel. The steels containing 3% Mn generated higher forces both during rough and thermomechanical rolling, which is related to slower recrystallization softening in these alloys compared to the steels containing 5% Mn.

Advanced Multiphase Steels

“…The manuscripts gathered in this Special Issue are committed to a variety of steel grades, embracing DP (Dual Phase) steels [1], medium-Mn steels [2,3], CFB (Carbide Free Bainitic steels) [4], nano-bainitic cast steel [5], δ-TRIP (TRansformation Induced Plasticity) [6] and precipitation hardened ferritic stainless steel [7].…”

“…A wide range of topics are researched that comprise the alloy design [2,6,7], optimization of both the hot working process [2] and the final heat treatment [5], and the final mechanical properties [1,3,4,6].…”

“…When looking at the alloying effects, Mn content relevance both on medium-Mn steels [2] and on δ-TRIP steels [6] is analyzed in detail. The role of Nb additions is also tackled as an element that may control and optimize the hot rolling behavior [2], the microstructure development during the whole industrial process [1,2], and also enhance the mechanical properties [1,7].…”

“…The optimization of the final bainitic heat treatment is analyzed for nano-bainitic cast steel [5] In references [3][4][5][6], the mechanical stability of the retained austenite during tensile testing is studied deeply, whereas its thermal stability upon final thermomechanical or thermal treatment is analyzed in [2,6]. It is a pivotal phase to optimize the mechanical behavior of various multiphase steels.…”