Determining the Conditions for Dynamic Recrystallization in Hot Deformation of C–Mn–V Steels and the Effects of Cr and Mo Additions

Abstract

The refinement of microstructure and its homogeneity during controlled hot strip rolling is primarily achieved by controlling the austenite recrystallization before its transformation during accelerated cooling. The paper describes the methodology to determine the deformation conditions favorable for dynamic recrystallization (DRX). Using this methodology it becomes possible to delineate the conditions for postdeformation static and metadynamic recrystallization as well. The work is based on viscoplastic power law formalism applied to steady state flow within wide range of deformation temperatures and strain rates. Two equations of the same form but with different coefficients can be used depending on whether the steady state flow is controlled by dynamic recovery (DRV) or DRX. The transition from DRV-to DRX at the corresponding value of Zener-Hollomon parameter Zt can be viewed as the demarcation between static and metadynamic recrystallization occurring after deformation. The approach is illustrated using low carbon Mn-V steel. Alloying with Cr and especially with Mo suppresses DRX and MDRX as manifested by increasing Zt.

Comparative Effect of Mo and Cr on Microstructure and Mechanical Properties in NbV-Microalloyed Bainitic Steels

“…This could result from the variation in recrystallization stop temperature, T nr , and prior austenite grain size (PAGS) in the studied steels. Our measurements have shown T nr to be higher in the MoNbV-steel,~1000 • C, compared to the CrNbV-steel,~975 • C, which is in-line with Mo being a stronger recrystallization retarding element than Cr [36,37]. Therefore, after 0.3 strain at 1175 • C and 0.35 strain at 1100 • C (modest strain levels with respect to the rate of DRX) the PAGS could be slightly larger in the MoNbV-steel as a result of partial DRX.…”

“…In particular, Cr was observed delaying Fe 3 C precipitation in low carbon steel [34]. However, the solid solution strengthening effect of Cr is~6 times weaker than this of Mo [35], and, therefore, Cr is less affective in retarding recrystallization [36,37].…”

Softening kinetics in the process of stress relaxation after hot deformation of HSLA steel

“…The thermally activated mechanisms, mainly those of dynamic and static recrystallization, are mostly identified based on the shape of flow curves or kinetic curves and changes in the share of the recrystallized fraction in the function of *Corresponding author: e-mail address: wojciech.ozgowicz@tlen.pl isothermal holding and cooling after the hot deformation. These relations have been determined in various mechanical tests or metallographic investigations [8][9][10][11][12][13][14]. Different experimental approaches are used for the study and quantification of the recrystallization kinetics, i.e.…”

Efeitos De Temperatura De Austenitização, Taxa De Resfriamento E Elementos De Liga Nas Transformações De Fases De Um Aço C-Mn-V

“…A bainita também pode ser obtida durante o resfriamento contínuo em taxas muito elevadas para as transformações ferrítica e perlítica, porém não rápidas o suficiente para a obtenção da martensita. Há publicações mostrando que adições de Cr e Mo elevam a temperabilidade, principalmente devido ao efeito de arraste de soluto, causando um endurecimento pela presença de estruturas aciculares como a bainita e martensita [4][5][6][7][8]. Entretanto, não se encontra informações relativas a seus efeitos em aços C-Mn-V. O presente trabalho objetiva apresentar uma avaliação por dilatometria da influência da temperatura de austenitização, taxa de resfriamento e adições de Cr ou Mo nas transformações de fases em um aço 0,12C-1,70Mn-0,2V, elaborando os diagramas de transformação em resfriamento contínuo (TRC) desses aços.…”