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Semi-industrial simulation of hot rolling and controlled cooling of Mn-Al TRIP steel sheets

Grajcar A., Skrzypczyk P., Woźniak D., Kołodziej S.

Journal of Achievements in Materials and Manufacturing Engineering

2013

Vol. 57, nr 1

38--47

Purpose: The aim of the work is a semi-industrial physical simulation of thermomechanical rolling and controlled cooling of advanced high-strength steels with increased Mn and Al content. Design/methodology/approach: Four steels of various Mn and Nb concentration were thermomechanically rolled in 3 and 5 passes using a modern LPS line for physical simulation of hot rolling at a semi-industrial scale. The hot deformation course is fully automated as well as controlled cooling applied directly after finishing rolling. Temperature-time and force-energetic parameters of hot rolling were continuously registered and assessed. Findings: The applied line consisting of two-high reversing mill, roller tables with heating panels, cooling devices and controlling-recording systems reflects industrial hot strip rolling parameters sufficiently. Reduction values and temperature-time regimes are similar to those used in industrial practice whereas strain rate is limited to about 10 s-1 what requires taking into account during comparison. All the steels investigated have high total pressure forces due to the high total content of alloying elements. The critical factor making it possible to obtain high-quality sheet samples with a thickness up to 3.3 mm is applying isothermal heating panels which decrease a cooling rate of thin sheets. Research limitations/implications: The real complete simulation of hot strip rolling requires extension of a used line with a further module for simulation of continuous finishing rolling stages. The work is in progress. Practical implications: The results can be successfully utilized in industrial hot rolling and controlled cooling practices after necessary modifications. Originality/value: The efficient semi-industrial physical simulation of hot strip thermomechanical rolling of some new model AHSS grades containing increased Mn and Al content as well as Nb microadditions was presented.

Selection of direct cooling conditions for automotive lever made of microalloyed steel

Skubisz P., Sińczak J., Skowronek T., Rumiński M.

Archives of Civil and Mechanical Engineering

2012

Vol. 12, no. 4

418--426

The paper presents issues concerning determination of forging and controlled cooling conditions in aspect of application of direct cooling of as-forged microalloyed steel. The study concerns realization of thermomechanical treatment directly after forging, oriented at producing desired microstructure and required final mechanical properties. In order to determine forging conditions and most favourable cycle of cooling, numerical modelling with finite element method was used. To select appropriate forging temperature, actual temperature in critical locations of the part was traced during the entire forging cycle. On assumption of predefined parameters of forging process and subsequent forced-air continuous cooling, effectiveness of forced-air acceleration was investigated from the standpoint of producing necessary cooling rate. The direct cooling regimes were verified with tensile testing and hardness measurement, illustrating qualitative analysis of obtained microstructure. Determined forging/cooling conditions served as guidelines for industrial realization of controlled processing of drop forged automotive lever oriented at fine-grained ferrite–pearlite or acicular ferrite microstructure and required level of mechanical properties.