Effect of Strain and Strain Path on Texture and Twin Development in Austenitic Steel with Twinning-Induced Plasticity

  • PDF / 1,330,984 Bytes
  • 12 Pages / 593.972 x 792 pts Page_size
  • 3 Downloads / 220 Views

DOWNLOAD

REPORT


ODUCTION

SIR Robert Hadfield is generally credited with the discovery of high-Mn content austenitic steel in the last half of the nineteenth century. Over the past few decades, however, interest has been renewed in highMn content (~15 to 30 wt pct) austenitic steel that exhibits twinning-induced plasticity (TWIP steel), often interpreted as a dynamic Hall–Petch effect.[1,2] Much of this interest in TWIP steel is being driven by its fascinating microstructural behavior, unique mechanical properties, and potential applicability in transportation industries. As a member of the so-called ‘‘second generation’’ of advanced high-strength steels (AHSS),[3] TWIP steel offers the combination of high strain hardening (n > 0.35),[4,5] ultimate tensile strength (500 to 1500 MPa),[6,7] and elongation to fracture (58 to 95 pct).[8–10] Yield strengths (400 to 500 MPa) of TWIP steels are similar to those of conventional high-strength low alloy steels and AHSS such as dual-phase and transformation-induced plasticity (TRIP) steels.[11] Young’s modulus values in the 189 to 202 GPa range were measured in Reference[7] for TWIP steel with 17.2 wt pct Mn. These properties are attractive to the SUSHIL K. MISHRA and SHASHANK M. TIWARI, Senior Researchers, and ARUN M. KUMAR, Lab Group Manager, are with the India Science Lab, General Motors Global Research and Development, GM Technical Centre India Pvt Ltd, Bangalore 560 066, India. Contact e-mail: [email protected] LOUIS G. HECTOR Jr., Technical Fellow, is with the Chemical Sciences and Materials Systems Lab, General Motors Global Research and Development, Warren, MI 48090. Manuscript submitted April 19, 2011. Article published online November 30, 2011 1598—VOLUME 43A, MAY 2012

automotive industry, for example, where concerns with reducing vehicle mass and enhancing energy absorption with geometrically complex components are being driven by passenger safety, fuel economy, and demands to reduce greenhouse gas emissions. New TWIP alloy chemistries have been explored to improve metallurgical and mechanical properties. These include the following: Fe25Mn3Al3Si, Fe22Mn0.6C, Fe27Mn0.02C, Fe30Mn3AL3Si, Fe12Mn1.1C, Fe12 Mn1.2C, Fe13Mn1.2C, Fe32Mn12Cr0.4C, and Fe23 Mn2Si2Al.[6] The predominant plastic deformation mechanism in TWIP steels is dislocation glide.[12] However, as strain is applied, twins form because of a low stacking fault energy (SFE), which typically falls in the 18 mJ/m2 < SFE < 50 to 80 mJ/m2 range.[12] This encourages the formation of partial dislocations that inhibit glide and promotes twin formation. If the SFE falls well below this range, then deformation is dominated by martensitic phase transformations.[13] Plastic deformation by dislocation glide predominates if SFE values exceed this range. Strain-induced twinning promotes retention of the austenitic microstructure and impedes local neck formation, which enhances strain hardening. This continuous strengthening process is absent in TRIP steels, for example, where elongation is limited by the complete transformation of residual

Data Loading...