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Title: Dual phase versus TRIP strip steels: Microstructural changes as a consequence of quasi-static and dynamic tensile testing

Abstract

The development of present day and future vehicles is being driven by the need to simultaneously reduce mass and increase passenger and pedestrian safety. For this reason, the steel industry has developed strip steel grades with suitable properties, as required for meeting the demands placed on the automotive manufacturers. Two of these strip steel grades are the Dual Phase (DP) and the Transformation Induced Plasticity (TRIP) steels, which are thought to offer solutions for critical crash component criteria. Limited published information is available on the changes in microstructure of these novel strip steel grades at different rates of deformation. This paper examines the change in microstructure of a range of both commercial and experimental DP and TRIP strip steel grades, which were tensile tested at low (0.001 s{sup -1}) and very high strain rates (200 s{sup -1}). The DP and TRIP microstructures were characterised in terms of ferrite grain size, ferrite grain elongation and volume fraction of constituent phases. The specimens were examined following deformation and compared to the as-received condition to assess microstructural changes. This paper concentrates only on microstructural changes through dynamic tensile testing of DP and TRIP grades at low and high strain rates. The full crashmore » performance data from the dynamic tensile tests and crushing of box sections is presented in a separate publication. [S. Oliver, G. Fourlaris and T.B. Jones, 'Dual Phase versus TRIP strip steels: a comparison of dynamic properties for automotive crash performance', Materials Science and Technology, 2006 (submitted for publication)].« less

Authors:
 [1];  [2];  [1];  [3]
  1. ECM2, Heol Cefn Gwrgan, Port Talbot, SA13 2EZ (United Kingdom)
  2. (United Kingdom)
  3. Engineering Doctorate Centre, Materials Research Centre, School of Engineering, University of Wales Swansea, Singleton Park, Swansea, SA2 8PP (United Kingdom). E-mail: g.fourlaris@swan.ac.uk
Publication Date:
OSTI Identifier:
21003552
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Characterization; Journal Volume: 58; Journal Issue: 4; Other Information: DOI: 10.1016/j.matchar.2006.07.004; PII: S1044-5803(06)00226-9; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CRUSHING; ELONGATION; FERRITE; FERRITES; GRAIN SIZE; MATERIALS TESTING; METAL INDUSTRY; PERFORMANCE; PLASTICITY; STEELS; STRAIN RATE; SULFUR IONS

Citation Formats

Oliver, S., Engineering Doctorate Centre, Materials Research Centre, School of Engineering, University of Wales Swansea, Singleton Park, Swansea, SA2 8PP, Jones, T.B., and Fourlaris, G. Dual phase versus TRIP strip steels: Microstructural changes as a consequence of quasi-static and dynamic tensile testing. United States: N. p., 2007. Web. doi:10.1016/j.matchar.2006.07.004.
Oliver, S., Engineering Doctorate Centre, Materials Research Centre, School of Engineering, University of Wales Swansea, Singleton Park, Swansea, SA2 8PP, Jones, T.B., & Fourlaris, G. Dual phase versus TRIP strip steels: Microstructural changes as a consequence of quasi-static and dynamic tensile testing. United States. doi:10.1016/j.matchar.2006.07.004.
Oliver, S., Engineering Doctorate Centre, Materials Research Centre, School of Engineering, University of Wales Swansea, Singleton Park, Swansea, SA2 8PP, Jones, T.B., and Fourlaris, G. Sun . "Dual phase versus TRIP strip steels: Microstructural changes as a consequence of quasi-static and dynamic tensile testing". United States. doi:10.1016/j.matchar.2006.07.004.
@article{osti_21003552,
title = {Dual phase versus TRIP strip steels: Microstructural changes as a consequence of quasi-static and dynamic tensile testing},
author = {Oliver, S. and Engineering Doctorate Centre, Materials Research Centre, School of Engineering, University of Wales Swansea, Singleton Park, Swansea, SA2 8PP and Jones, T.B. and Fourlaris, G.},
abstractNote = {The development of present day and future vehicles is being driven by the need to simultaneously reduce mass and increase passenger and pedestrian safety. For this reason, the steel industry has developed strip steel grades with suitable properties, as required for meeting the demands placed on the automotive manufacturers. Two of these strip steel grades are the Dual Phase (DP) and the Transformation Induced Plasticity (TRIP) steels, which are thought to offer solutions for critical crash component criteria. Limited published information is available on the changes in microstructure of these novel strip steel grades at different rates of deformation. This paper examines the change in microstructure of a range of both commercial and experimental DP and TRIP strip steel grades, which were tensile tested at low (0.001 s{sup -1}) and very high strain rates (200 s{sup -1}). The DP and TRIP microstructures were characterised in terms of ferrite grain size, ferrite grain elongation and volume fraction of constituent phases. The specimens were examined following deformation and compared to the as-received condition to assess microstructural changes. This paper concentrates only on microstructural changes through dynamic tensile testing of DP and TRIP grades at low and high strain rates. The full crash performance data from the dynamic tensile tests and crushing of box sections is presented in a separate publication. [S. Oliver, G. Fourlaris and T.B. Jones, 'Dual Phase versus TRIP strip steels: a comparison of dynamic properties for automotive crash performance', Materials Science and Technology, 2006 (submitted for publication)].},
doi = {10.1016/j.matchar.2006.07.004},
journal = {Materials Characterization},
number = 4,
volume = 58,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
  • TRIP-aided multi-phase steels were made by thermo-mechanically controlled process, where the ferrite grain size and the amount of the retained austenite were changed by controlling process conditions. The tensile behavior of four steels was studied by in situ neutron diffraction. It is found that the retained austenite bearing about 1.0 wt% C is plastically harder than the ferrite matrix. The steel with a ferrite grain size of {approx}2.0 {mu}m showed tensile strength of 1.1 GPa and a uniform elongation of 18.4%, in which stress-induced martensitic transformation occurs during plastic deformation but a considerable amount of austenite remains even after themore » onset of necking. It is concluded that the enhancement of uniform elongation is caused mainly by the work-hardening due to the hard austenite and martensite, where the contribution of the transformation strain is negligible.« less
  • Measured responses of advanced high strength steels (AHSS) and their tailor welded blanks (TWBs), over a wide range of strain-rates (10*4 to 103 s*1) are presented. The steels investigated include transformation induced plasticity (TRIP), dual phase (DP), and drawing quality (DQ) steels. The TWBs include DQ-DQ and DP-DP laser welds. A tensile split Hopkinson pressure bar (SHPB) was used for the dynamic experiments. AHSS and their TWB's were found to exhibit positive strain-rate sensitivity. The Khan-Huang-Liang (KHL) constitutive model is shown to correlate and predict the observed responses reasonably well. Micro-texture characterization of DQ steels, DQ-DQ and DP-DP laser weldsmore » were performed to investigate the effect of strain-rate on texture evolution of these materials. Electron backscatter diffraction (EBSD) technique was used to analyze the micro-texture evolution and kernel average misorientation (KAM) map. Measurement of micro-hardness profile across the cross section of tensile samples was conducted to understand the effect of initial microstructure on ductility of laser weld samples.« less
  • Two alloys of high-nitrogen stainless steel have been heat treated to produce dual-phase microstructures. The first alloy, N10CrNiMo17 1, a Ni-containing stainless steel, was processed conventionally. The second alloy, N20CrMo17, a Ni-free stainless steel, was processed to obtain a higher nitrogen content by pressurized electroslag remelting. The martensite in N10CrNiMo17 1 was homogeneously distributed in the ferrite and obtained a near-constant volume fraction as a function of intercritical annealing temperature. Microprobe analysis and microhardness measurements of the martensite constituent suggested that up to 0.4 pct N was dissolved in the austenite before quenching. Austenite formation, martensite transformation, undissolved nitrides, andmore » retained austenite were evaluated by transmission electron microscopy (TEM). The Ni-containing alloy exhibited classic dual-phase tensile behavior in that continuous yielding was observed together with good combinations of ultimate tensile strength and total elongation. The martensite constituent in alloy N20CrMo17 was concentrated within bands. Comparison of tensile properties of the two alloys at similar volume fractions and hardness levels of martensite and ferrite showed that the microstructure containing banded martensite had inferior combinations of strength and ductility. The degradation of tensile ductility was accompanied by a fracture mode transition from microvoid coalescence to transgranular cleavage. The deformation and fracture behavior of both alloys were related to the microstructure.« less
  • A series of dual-phase (DP) steels containing finely dispersed martensite with different volume fractions of martensite (V{sub m}) were produced by intermediate quenching of a boron- and vanadium-containing microalloyed steel. The volume fraction of martensite was varied from 0.3 to 0.8 by changing the intercritical annealing temperature. The tensile and impact properties of these steels were studied and compared to those of step-quenched steels, which showed banded microstructures. The experimental results show that DP steels with finely dispersed microstructures have excellent mechanical properties, including high impact toughness values, with an optimum in properties obtained at {approximately}0.55 V{sub m}. A furthermore » increase in V{sub m} was found to decrease the yield and tensile strengths as well as the impact properties. It was shown that models developed on the basis of a rule of mixtures are inadequate in capturing the tensile properties of DP steels with V{sub m} > 0.55. Jaoul-Crussard analyses of the work-hardening behavior of the high-martensite volume fraction DP steels show three distinct stages of plastic deformation.« less
  • In the strategic industrial sectors such as defense, automotive, precision machine, and space aircraft industries, the demand for structural materials which can be used under severe conditions like dynamic loading has been rising. The lower resistance to deformation and fracture under dynamic loading than under quasi-static loading can fatally affect overall fracture toughness of structural materials. Thus, detailed studies should be made to be able to maintain the deformation and fracture resistance through effective and quantitative evaluation on them, so that the materials can be widely applied to various fields. Because fracture toughness can drastically drop under dynamic loading inmore » the structure containing brittle phase of martensites, especially like in the dual phase steels, it is highly required to clarify the mechanism. This can basically explain the martensite formation and its effect, and the deformation and fracture process under dynamic loading in a more microscopic level. The present study attempted to investigate the micromechanism of dynamic deformation and fracture which affects the martensite morphology by varying the heat-treatment conditions in the ferrite+austenite ({alpha}+{gamma}) temperature region. Dynamic torsional tests using a torsional Kolsky bar were conducted on two kinds of ferrite+martensite dual phase steels. These steels do not have the same martensite morphology, but have a certain volume fraction of about 50%. Detailed investigations were also made on various factors determining the characteristics of dynamic deformation occurring in martensites by observing deformed microstructures and fracture surfaces.« less