Characterization and methodology for calculating the mechanical properties of a TRIP-steel submitted to hot stamping and quenching and partitioning (Q&P)

https://doi.org/10.1016/j.msea.2016.06.038Get rights and content

Abstract

Thermomechanical simulation of quenching, hot stamping, and quenching and partitioning processes of a high-strength TRIP-assisted steel were carried out in a Gleeble®3S50 thermo-mechanical simulator, coupled to the synchrotron X-ray diffraction line. The microstructures and mechanical properties were analyzed using Field Emission Gun Scanning Electron Microscopy (FEG-SEM), X-ray diffraction, and nanoindentation. The microstructures of thermomechanical treated specimens were modeled using the Object Oriented Finite Element (OOF) technique. The modeled microstructures were then fed into a finite element model to predict the mechanical behavior. By using a reverse algorithm method, the elasto-plastic mechanical properties of different microconstituents were determined. This was done through the analysis of instrumented nanoindentation loading-penetration curves. Tensile properties of the thermomechanical processed steels were measured by tensile testing of subsized specimens cut from samples processed on the Gleeble®3S50. The comparison between the experimental results and those of the reverse algorithm and the OOF modeled microstructure showed quite good agreement.

Introduction

Increased requirements for low fuel consumption and improved safety in the automotive industry have stimulated the development of new generations of high strength steels. To reduce fuel consumption, the decrease of the car's body weight is achieved by using thinner and therefore necessarily stronger and ductile steel sheets. A promising way of obtaining a favorable compromise between strength and ductility is the Quenching and Partitioning (Q&P) heat treatment [1]. Q&P heat treatment can produced a martensitic microstructure with a considerable amount of fine-dispersed retained austenite (RA).

In this process, the steel is austenitized (either fully or partially) and then quenched to a temperature between the martensite start (Ms) and martensite finish (Mf) temperatures, to create a controlled mixture of martensite and austenite (and any intercritical ferrite present during annealing). The steel is then isothermally held at the quenching temperature (QT) (one-step Q&P treatment) or heated to a higher temperature (PT) (two-step Q&P treatment) to allow carbon partition from martensite towards austenite. At this step, carbon diffusion occurs from the supersaturated martensite to the untransformed austenite (carbon partitioning), stabilizing this phase during the final quench to room temperature. Carbon-enriched austenite, which is stable at room temperature, is capable of contributing to mechanical properties in the same manner as it does in transformation induced plasticity (TRIP) steels [2]. The carbon distribution, specifically the local concentration of carbon in the individual phases, grain boundaries or interface boundaries, is assumed to be the key parameter that influences the phase transformation and mechanical properties.

Additionally, hot stamping (HS), also known as hot press forming or press hardening, is one of the most effective methods to produce ultra-high strength steels for automotive bodies. HS is a non-isothermal process designed for sheet metals, in which forming and quenching take place at the same forming stage [3]. Its main advantages are the excellent shape accuracy of the components, allowing the use of thinner gauge sheet metal. Thus, weight reduction can be achieved while maintains structural integrity, by enabling the production of ultra-high strength parts without any springback [4]. Recently, Liu et al. [5] pointed out that although the Q&P process is one of the most promising methods for producing advanced high-strength steels (AHSS) with both high strength and ductility, the heat treatment methods do not consider the strain induced phase transformations. Few studies investigated the potential of combining the hot stamping process with the quenching and partitioning [5], [6], [7], [8], [9]. However, these studies were limited to isothermal deformation with fully austenitized samples and one-step Q&P treatments. An exception is the work of Chang et al. [7], who performed two-step Q&P treatment with quenching time of one minute before the partitioning treatment. De Knijf et al. [10] pointed out that the isothermal holding time at the quenching temperature in Q&P steels need to be kept short (usually five to ten seconds), in order to avoid the precipitation of isothermal transformation products at the quenching temperature. In this work, a novel process (herein referred to as HSQ&P) applied to TRIP-assisted steels is proposed, which combines intercritical annealing with non-isothermal hot stamping, followed by two-step Q&P treatment. Experiments were conducted using thermo-mechanical simulation equipment, in order to compare the microstructure and the mechanical properties of a TRIP-assisted steel submitted to quenching (Q), HS, Q&P, and HSQ&P. Several characterization and modeling techniques were used: nanoindentation, object-oriented finite element method, and micro-tensile tests. The influence of time, temperature, and strain on the retained-austenite (RA) stability, as well as the role of transformation induced plasticity on the formability and energy absorption of AHSS sheets were studied in situ, using time resolved X-ray diffraction on the XTMS synchrotron radiation beamline of the Brazilian synchrotron facility. The combination of thermomechanical and thermal treatments suggest a new generation of high strength, formable sheet steel that answers the demands of the automotive industry.

Section snippets

Material and thermomechanical treatments

TRIP-assisted steel (Fe-0.23C-1.23Si-1.50Mn, wt%) sheets were subjected to Q, HS, Q&P, and HSQ&P heat and thermomechanical treatments. Q&P and HSQ&P cycles were designed in order to obtain ferrite, martensite, and retained austenite at the end of both processes. A Gleeble®3S50 thermomechanical simulator was used to reproduce the thermo-mechanical treatments conditions (heating and cooling rates, and deformations) as schematically depicted in Fig. 1. The as-received multiphase specimens

Intercritical temperature

The volume fractions of the constituent phases as predicted by Thermo-Calc® based on an equilibrium thermodynamic analysis are shown in Fig. 5. In this figure it is possible to see that when the temperature is below the Ae1 temperature (≈700 °C), the material consists of approximately 98% of ferrite (α) and 2% of cementite (θ). Both cementite and ferrite start to transform to austenite (γ) above the Ae1 temperature, until the Ae1 temperature (≈715 °C) is reached, at which the cementite is

Summary and conclusions

A novel process (HSQ&P) applied to TRIP-assisted steels was proposed, which combines intercritical annealing with non-isothermal hot stamping (HS), followed by a two-step quenching and partitioning (Q&P) treatment. Experiments were conducted using a Gleeble®3S50 thermo-mechanical simulator equipment, in order to compare the microstructures and the mechanical properties of a TRIP-assisted steel submitted to quenching (Q), HS, Q&P, and HSQ&P. From the obtained results, the following conclusions

Acknowledgments

The authors gratefully acknowledge financial support from CAPES (Process n° 23038.006737/2012-56), CNPq (Grant 235297/2014-3 PVE), and FAPESP (through Grant 2014/11793-4). The Brazilian Nanotechnology National Laboratory (LNNano) and the Brazilian Synchrotron Light Laboratory (LNLS) are also acknowledged for the use of the XTMS facility at the XRD1 beamline. To Dr. Arun Sreeranganathan, M.Sc. Vanessa Seriacopi, and Dr. Kyoo Sil Choi for their helping during the construction of the OOF-Abaqus

References (66)

  • H. Hosseini-Toudeshky et al.

    Microstructural deformation pattern and mechanical behavior analyses of DP600 dual phase steel

    Mater. Sci. Eng. A

    (2014)
  • V. Uthaisangsuk et al.

    Modelling of damage and failure in multiphase high strength DP and TRIP steels

    Eng. Fract. Mech.

    (2011)
  • Y. Schneider et al.

    Plastic deformation behaviour of Fe–Cu composites predicted by 3D finite element simulations

    Comput. Mater. Sci.

    (2010)
  • S. Sodjit et al.

    Microstructure based prediction of strain hardening behavior of dual phase steels

    Mater. Des.

    (2012)
  • K.K. Tho et al.

    Simulation of instrumented indentation and material characterization

    Mater. Sci. Eng. A

    (2005)
  • S.A.R. Pulecio et al.

    Finite element and dimensional analysis algorithm for the prediction of mechanical properties of bulk materials and thin films

    Surf. Coat. Technol.

    (2010)
  • Z.S. Ma et al.

    Characterization of stress-strain relationships of elastoplastic materials: an improved method with conical and pyramidal indenters

    Mech. Mater.

    (2012)
  • M. Dao et al.

    Computational modeling of the forward and reverse problems in instrumented sharp indentation

    Acta Mater.

    (2001)
  • T.K. Eller et al.

    Determination of strain hardening parameters of tailor hardened boron steel up to high strains using inverse FEM optimization and strain field matching

    J. Mater. Process. Technol.

    (2016)
  • M.J. Santofimia et al.

    New low carbon Q&P steels containing film-like intercritical ferrite

    Mater. Sci. Eng. A

    (2010)
  • M.J. Santofimia et al.

    Microstructural development during the quenching and partitioning process in a newly designed low-carbon steel

    Acta Mater.

    (2011)
  • M.J. Santofimia et al.

    Model for the interaction between interface migration and carbon diffusion during annealing of martensite–austenite microstructures in steels

    Scr. Mater.

    (2008)
  • M. Nikravesh et al.

    Phase transformations in a simulated hot stamping process of the boron bearing steel

    Mater. Des.

    (2015)
  • H. Dong et al.

    Deformation induced ferrite transformation in low carbon steels

    Curr. Opin. Solid State Mater. Sci.

    (2005)
  • R. Ding et al.

    A novel design to enhance the amount of retained austenite and mechanical properties in low-alloyed steel

    Scr. Mater.

    (2014)
  • G. Gao et al.

    Enhanced ductility and toughness in an ultrahigh-strength Mn–Si–Cr–C steel: The great potential of ultrafine filmy retained austenite

    Acta Mater.

    (2014)
  • X. Tan et al.

    Effect of partitioning procedure on microstructure and mechanical properties of a hot-rolled directly quenched and partitioned steel

    Mater. Sci. Eng. A

    (2014)
  • H. Ghassemi-armaki et al.

    Deformation response of ferrite and martensite in a dual-phase steel

    Acta Mater.

    (2014)
  • V.H. Baltazar Hernandez et al.

    Nanoindentation and microstructure analysis of resistance spot welded dual phase steel

    Mater. Lett.

    (2010)
  • Q. Han et al.

    Suppression of M s temperature by carbon partitioning from carbon-supersaturated ferrite to metastable austenite during intercritical annealing

    Mater. Des.

    (2013)
  • I. de Diego-Calderón et al.

    Deformation behavior of a high strength multiphase steel at macro- and micro-scales

    Mater. Sci. Eng. A

    (2014)
  • I. de Diego-Calderón et al.

    Global and local deformation behavior and mechanical properties of individual phases in a quenched and partitioned steel

    Mater. Sci. Eng. A

    (2015)
  • N. Maheswari et al.

    Influence of alloying elements on the microstructure evolution and mechanical properties in quenched and partitioned steels

    Mater. Sci. Eng. A

    (2014)
  • Cited by (35)

    • Development of a complex multicomponent microstructure on commercial carbon-silicon grade steel by governing the phase transformation mechanisms to design novel quenching and partitioning processing

      2022, Journal of Materials Research and Technology
      Citation Excerpt :

      They confirmed that carbon partitioning from martensite provides a more satisfactory explanation, although bainite formation during partitioning cannot be wholly excluded. Finally, Ariza et al. [4,6,12,13] proposed that the crystallographic orientations and interface boundaries between austenite and ferrite/martensite phase could influence the carbon partitioning mechanism. This paper studied the tempering behavior of a commercial medium carbon-silicon steel followed by tempering through dilatometry to design a novel Q&P path.

    View all citing articles on Scopus
    View full text