EBSD and TEM investigation of the hot deformation substructure characteristics of a type 316L austenitic stainless steel

The evolution of crystallographic texture and deformation substructure was studied in a type 316L austenitic stainless steel, deformed in rolling at 900 °C to true strain levels of about 0.3 and 0.7. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were used in the investigation and a comparison of the substructural characteristics obtained by these techniques was made. At the lower strain level, the deformation substructure observed by EBSD appeared to be rather poorly developed. There was considerable evidence of a rotation of the pre-existing twin boundaries from their original orientation relationship, as well as the formation of highly distorted grain boundary regions. In TEM, at this strain level, the substructure was more clearly revealed, although it appeared rather inhomogeneously developed from grain to grain. The subgrains were frequently elongated and their boundaries often approximated to traces of {111} slip planes. The corresponding misorientations were small and largely displayed a non-cumulative character. At the larger strain, the substructure within most grains became well developed and the corresponding misorientations increased. This resulted in better detection of sub-boundaries by EBSD, although the percentage of indexing slightly decreased. TEM revealed splitting of some sub-boundaries to form fine microbands, as well as the localized formation of microshear bands. The substructural characteristics observed by EBSD, in particular at the larger strain, generally appeared to compare well with those obtained using TEM. With increased strain level, the mean subgrain size became finer, the corresponding mean misorientation angle increased and both these characteristics became less dependent on a particular grain orientation. The statistically representative data obtained will assist in the development of physically based models of microstructural evolution during thermomechanical processing of austenitic stainless steels.

Microstructure evolution modeling during and after deformation in 304 austenitic stainless steel through cellular automaton approach

A 2D cellular automation approach was used to simulate microstructure evolution during and after hot deformation. Initial properties of the microstructure and dislocation density were used as input data to the cellular automation model. The flow curve and final grain size were the output data for the dynamic recrystallization simulation, and softening kinetics curves were the output data of static and metadynamic recrystallization simulations. The model proposed in this work considered the effect of thermomechanical parameters (e.g., temperature and strain rate) on the nucleation and growth kinetics during dynamic recrystallization. The dynamic recrystallized microstructures at different strains, temperatures, and strain rates were used as input data for static and metadynamic recrystallization simulations. It was shown that the cellular automation approach can model the final microstructure and flow curve successfully in dynamic recrystallization conditions. The postdeformation simulation results showed that the time for 50% recrystallization decreases with increasing strain for a given initial grain size and that dynamic recrystallization slows the postdeformation recrystallization kinetics compared to a model without dynamic recrystallization.

Numerical simulations on warm forming of stainless steel with trip-effect

In steels with TRIP-effect, a phase transformation from the retained-austenite to martensite occurs during forming, and it significantly affects hardening behaviours. Such an effect is sensitive to the amount of strain as well as the temperature variation. For materials with a strong TRIP-effect, new forming techniques are needed to develop that can lead to lighter and stronger components in automotive industry. This paper presents a coupled thermo-mechanical finite element modelling and simulation of a warm deep drawing of austenitic stainless steel (including a TRIP-effect) using LS-DYNA and temperature effect on forming process of such materials is investigated.

Effective grain orientation on the substructure development of 304 stainless steel and NA-30% fe

This data is the result of an investigation into the effect of grain orientation on the substructure development of 304 stainless steel and a Ni-30wt.%Fe alloy. Both alloys have been used as model alloys to study the high temperature deformation of austenite. The development of the dislocation substructure as a function of strain, temperature and grain orientation was investigated using a combination of electron backscatterd diffraction (EBSD) and transmission electron microscopy (TEM).

21Cr - 10Ni - 3Mo duplex stainless steel high temperature deformation microstructures

Data includes EBSD orentation maps of the specimens deformed in torsion at 1200 degrees celsius to strains of 0.1, 0.5, 0.9 and 1.3. The phase ratio is about 60% austenite and 40% ferrite. The miscrostructure is dynamically recovered and there is also some dynamic recrystallisation at strains of 0.9 and 1.3. The main portion of softening can be attributed to dynamic subgrain coalescence in austenite.

Corrosion properties of a RF-magnetron-sputtered TiN coating deposited on 316L stainless steel

The effect of rf-power in the range from 100 to 200 W on the electrochemical properties of TiN coatings deposited on 316L stainless steel was investigated by using various electrochemical techniques in a 3.5-wt\% NaCl solution. Surface analyses were also conducted to analyze the coating characteristics. X-ray diffraction (XRD) and atomic force microscopy (AFM) analyses confirmed that increasing the rf-power led to a preferred orientation of the TiN(200) microstructure and decreased the surface roughness. The potentiodynamic test results confirmed the passive behavior of all of the specimens with low passive current densities and demonstrated that the effective pitting resistance of the TiN coatings increased with increasing rf-power. The electrochemical impedance spectroscopy (EIS) tests showed that the TiN films deposited with high rf-power had excellent corrosion resistance during an immersion time of 720 h due to their high total resistance and low porosity.

A novel sensing technique for monitoring pitting corrosion of stainless steel type 316L

A novel electrochemically integrated multi-electrode array namely the wire beam electrode(WBE) in combination with noise signatures analysis has been designed to monitor pittingcorrosion of one of the best corrosion resistance ferrous alloys, stainless steel type 316L.From the direct correlation of electrochemical potential noise signatures and galvanic currentdistribution maps during pitting corrosion processes, two characteristic noise patterns wereobserved prior to stable pit formation: (i) the characteristic ‘peak’ of rapid potential transient,towards less negative direction, followed by recovery (termed noise signature I) was found tocorrelate with the disappearance of unstable anode; (ii) the characteristic noise pattern ofquick potential changes towards less negative direction followed by no recovery (termed noisesignature II) was found to correspond with the massive disappearance of minor anodes leadingto formation of highly localized major anodes in the galvanic current distribution maps.