TY - JOUR

T1 - Multi-phase microstructure design of a low-alloy TRIP-assisted steel through a combined computational and experimental methodology

AU - Zhu, R.

AU - Li, S.

AU - Karaman, I.

AU - Arroyave, R.

AU - Niendorf, T.

AU - Maier, H. J.

N1 - Funding information: This study is funded by the US National Science Foundation, Division of Civil, Mechanical, and Manufacturing Innovation, Materials and Surface Engineering Program , Grant No. 0900187 . The authors would like to thank Dr. Pedro Rivera, University of Cambridge for discussions during the preparation of this manuscript and Dr. Ray Guillemette, Texas A&M University Geology & Geophysics Department for the microprobe analyses.

PY - 2012/3/7

Y1 - 2012/3/7

N2 - The multiphase constitution of a transformation-induced plasticity (TRIP)-assisted steel with a nominal composition of Fe-1.5Mn-1.5Si-0.3C (wt.%) was designed, utilizing a combination of computational methods and experimental validation, in order to achieve significant improvements in both strength and ductility. In this study, it was hypothesized that a microstructure with maximized ferrite and retained austenite volume fractions would optimize the strain hardening and ductility of multiphase TRIP-assisted steels. Computational thermodynamics and kinetics calculations were used to develop a predictive methodology to determine the processing parameters in order to reach maximum possible ferrite and retained austenite fractions during conventional two-stage heat treatment, i.e. intercritical annealing followed by bainitic isothermal transformation. Experiments were utilized to validate and refine the design methodology. Equal channel angular pressing was employed at a high temperature (950 °C) on the as-cast ingots as the initial processing step in order to form a homogenized microstructure with uniform grain/phase size. Using the predicted heat treatment parameters, a multiphase microstructure including ferrite, bainite, martensite and retained austenite was successfully obtained. The resulting material demonstrated a significant improvement in the true ultimate tensile strength (∼1300 MPa) with good uniform elongation (∼23%), as compared to conventional TRIP steels. This provided a mechanical property combination that has not been exhibited before by low-alloy first-generation high-strength steels. The developed computational framework for the selection of heat treatment parameters can also be utilized for other TRIP-assisted steels and help design new microstructures for advanced high-strength steels, minimizing the need for cumbersome experimental optimization.

AB - The multiphase constitution of a transformation-induced plasticity (TRIP)-assisted steel with a nominal composition of Fe-1.5Mn-1.5Si-0.3C (wt.%) was designed, utilizing a combination of computational methods and experimental validation, in order to achieve significant improvements in both strength and ductility. In this study, it was hypothesized that a microstructure with maximized ferrite and retained austenite volume fractions would optimize the strain hardening and ductility of multiphase TRIP-assisted steels. Computational thermodynamics and kinetics calculations were used to develop a predictive methodology to determine the processing parameters in order to reach maximum possible ferrite and retained austenite fractions during conventional two-stage heat treatment, i.e. intercritical annealing followed by bainitic isothermal transformation. Experiments were utilized to validate and refine the design methodology. Equal channel angular pressing was employed at a high temperature (950 °C) on the as-cast ingots as the initial processing step in order to form a homogenized microstructure with uniform grain/phase size. Using the predicted heat treatment parameters, a multiphase microstructure including ferrite, bainite, martensite and retained austenite was successfully obtained. The resulting material demonstrated a significant improvement in the true ultimate tensile strength (∼1300 MPa) with good uniform elongation (∼23%), as compared to conventional TRIP steels. This provided a mechanical property combination that has not been exhibited before by low-alloy first-generation high-strength steels. The developed computational framework for the selection of heat treatment parameters can also be utilized for other TRIP-assisted steels and help design new microstructures for advanced high-strength steels, minimizing the need for cumbersome experimental optimization.

KW - Computational thermodynamics

KW - Equal channel angular pressing (ECAP)

KW - Mechanical behavior

KW - Phase transformations

KW - TRIP-assisted steels

UR - http://www.scopus.com/inward/record.url?scp=84862810222&partnerID=8YFLogxK

U2 - 10.1016/j.actamat.2012.02.007

DO - 10.1016/j.actamat.2012.02.007

M3 - Article

AN - SCOPUS:84862810222

VL - 60

SP - 3022

EP - 3033

JO - Acta materialia

JF - Acta materialia

SN - 1359-6454

IS - 6-7

ER -