The effect of strain rate on stress-strain behavior of austenitic stainless steel 309 and 304L was investigated. Tensile tests were conducted at room temperature at strain rates ranging from 1.25×10−4s−1 to 400 s−1. The evolution of volume fraction martensite that formed during plastic deformation was measured with X-ray diffraction and characterized with light microscopy. Alloy 304L was found to transform readily with strain, with martensite nucleating on slip bands and at slip band intersections. Alloy 309 did not exhibit strain-induced transformation. Variations in ductility and strength with strain rate are explained in terms of the competition between hardening, from the martensitic transformation and a positive strain rate sensitivity, and softening due to deformational heating. Existing models used to predict the increase in volume fraction martensite with strain were examined and modified to fit the experimental data of this study as well as recent data for alloys 304 and 301LN obtained from the literature.

Effect of strain rate on stress-strain behavior of alloy 309 and 304L austenitic stainless steel

Experimental investigation on martensitic transformation and fracture morphologies of austenitic stainless steel

Transformation mechanism of α′-martensite in an austenitic Fe–Mn–C–N alloy

Deformation induced martensitic transformation was investigated in metastable austenitic stainless steel. This steel can present a microstructure of austenite (γ), α′ martensite and non magnetic e martensite. Uni-axial tensile test was used for loading at different temperatures below room temperature (from −120 to 20 °C). During the deformation the transformation takes place at certain places in an anisotropic way and texture also develops. Quantitative phase analysis was done by X-ray diffraction (XRD) and magnetic methods while the texture was described by X-ray diffraction using a special inverse pole figure. The quantitative phase analysis has shown that the formation of α′ and e martensite from austenite is the function of deformation rate, and deformation temperature. The transformation of the textured austenite takes place in an anisotropic way and a well defined crystallographic relationship between the parent and α′ martensite phase has been measured.

Deformation induced martensitic transformation in stainless steels

Role of residual stresses induced by industrial fabrication on stress corrosion cracking susceptibility of austenitic stainless steel

The metastable austenitic steels have a tendency to transform to ɛ (hexagonal) and α′ (tetragonal) martensites during thermomechanical treatment (e.g. under tensile stress). The formation of these martensitic phases affects the strength, toughness, formability and corrosion resistance of the steel. The martensitic transformation of an austenitic steel at various temperatures and strain rates was studied in this work. The effects of loading parameters and temperature on the texture and volume fraction of the martensite were investigated. Also, the effect of various martensitic structures on the stress–strain curve and work hardening was investigated. We have observed a very stable deformation texture feature of austenite (γ) and α′ martensite which was observed even if a small amount of deformation takes place. Finally we will show the texture evolution during transformations.

Strain-induced martensitic transformation in textured austenitic stainless steels

The characterization of the heat effect of thermoelastic martensitic transformation is usually carried out in a heat-flux differential scanning calorimetry (DSC) device. The temperature of the sample during a DSC cycle differs from the temperature of the reference. This means that the measured heat flow covers both the latent heat and the heat quantity needing to heat up (cool down) the sample. The later heat quantity is the temperature balancing between the sample and the reference. Furthermore, the temperature balancing is still measured when the transformation is finished. According to this, using the peak endpoint to determine the transformation (austenite or martensite) finish temperature gives an error, which depends on the device's time constant. The temperature balancing is sensitive on the rate of heating (and cooling) and the mass of the sample. When evaluating DSC curves of heat-flux DSC, one must take into account these facts not to get false results. Cu–Al–Ni single crystal was examined to show the above-mentioned phenomena, and an evaluation program was developed to improve the quantitative analyzing of DSC peaks.

Effects of heat-flux features on the differential scanning calorimetry curve of a thermoelastic martensitic transformation

Consolidation of Cu58Zr42 amorphous/nanocrystalline powders by PM

A group of austenitic steels exhibit high deformability and strength due to TRansformation Induced Plasticity (TRIP) and/or TWinning Induced Plasticity (TWIP). The phase transformations of the TRIP and TWIP steels have been examined in details in many FeMnX alloy systems (X: Ni, Al, Si). However, less attention was given to the FeMn(Cr) alloys. The γ ↔ e transformations in the austenitic FeMn(Cr) alloys have been examined during heat cycling by in situ optical microscopy and DSC measurements.

Ferenc Tranta

Papers

Deformation induced martensitic transformation in stainless steels

Strain-induced martensitic transformation in textured austenitic stainless steels

Effects of heat-flux features on the differential scanning calorimetry curve of a thermoelastic martensitic transformation

Consolidation of Cu58Zr42 amorphous/nanocrystalline powders by PM

In Situ Optical Microscope Examinations of the ε↔γ Transformations in FeMn(Cr) Austenitic Steels during Thermal Cycling