Investigation on the nucleation mechanism of deformation-induced martensite in an austenitic stainless steel under severe plastic deformation

Abstract

The nucleation mechanism of deformation-induced martensite was investigated by x-ray diffraction and transmission electron microscope in an ultra-low carbon austenitic stainless steel deformed by equal channel angular pressing at room temperature. It was found that two types of martensite transformation mechanism, stress-assisted and strain-induced, occurred via the sequences of γ (fcc) → ɛ (hcp) → α′ (bcc) and/or γ → α′. In both cases, the crystallographic relationships among γ, ɛ, and α′ followed the Kurdjumov-Sachs orientation relationships: {111}γ //{0001}ɛ //{011}α′ and 〈110〉γ//〈1120〉ɛ//〈111〉α′.

A new nanoscale metastable iron phase in carbon steels

“…Based on the structure parameters of well-known carbides 30 31 , we confirmed that these extra diffraction spots cannot be indexed as any well-known carbide. Taking ε carbide for example, it is well documented that it has the orientation relationship [ ] bcc // [ ] ε , (011) bcc // (0001) ε 32 33 34 35 36 37 38 . However, when the martensite plate is tilted to the [100] or [111] zone axis, no diffraction spots other than the fundamental bcc diffraction spots were observed.…”

Influence of processing temperature on the microstructures and tensile properties of 304L stainless steel by ECAP

“…Therefore, the processing temperature becomes an important parameter that can affect the microstructure and related mechanical properties of these materials obviously. As to SS, though there have been several studies on the microstructure/grain refinement of SS processed by SPD [23][24][25][26][27], the application of ECAP to SS is still quite rare and the influences of the processing temperature on the deformation microstructures and corresponding mechanical properties are not adequately explored. In this work, 304L austenitic SS was selected to be processed by ECAP for one pass in the temperature range from 500 to 900 • C. The main goal is to investigate the influences of processing temperature on the microstructures and room-temperature (RT) tensile properties developed by ECAP.…”

Ultrafine-Grained Austenitic Stainless Steels X4CrNi18-12 and X8CrMnNi19-6-3 Produced by Accumulative Roll Bonding

“…Above a certain strain level, they observed that the twin density is decreasing, while the martensite density is further increasing. Huang et al [28] performed detailed TEM-investigations on the nucleation mechanism of deformation-induced martensite in an austenitic steel under ECAP-deformation. They observed similar behavior as described above; however they could also find α' nucleating at the intersection of two deformation twins and micro shear-bands.…”

“…In TEM investigations γ-austenite, martensitic areas as well as twinning were found. Accordingly, in [28], the observed diffraction patterns were quite complex. In Figure 5d the diffraction pattern of such an area is representatively shown.…”