Research on Stress-Induced Nucleation ofε-Martensite in Fe-17Mn-10Cr-5Si-4Ni Polycrystalline Alloy

The relation between stacking fault overlap and martensitic nucleation in Fe-17Mn-10Cr-5Si-4Ni alloy was studied.The arrayed structure of dislocations and characteristics ofε-martensite formation under stress were in-situ observed by TEM.The results reveal thatε-martensite nucleates at the top of stacking faults overlapped band,where the ordered arrayed structure of Shockley partial dislocations exists.External stress promotesε-martensitic nucleation ability because of accelerated ordering of Shockley partial dislocations in stacking faults overlapped band.

Effect of Chromium-enhanced Diffusivity on Reverted Transformation in Metastable Austenitic Stainless Steels:Theoretical Calculation and Experiment

Effects of nucleation sites and diffusivity enhancement of chromium on reverted transformation of AISI 304 stainless steel during annealing process were investigated.Dynamics calculation revealed that the reverted transformation of strain-inducedα’-martensite→γaustenite could were closely associated with active nucleation sites and diffusivity enhancement of chromium in nanocrystallineα’-martensite.The experimental data and the results were in accordance with 2-grain austenite/α’-martensite junctions calculated theoretically,which could result from high chromium diffusion rate in nanocrystallineα’-martensite.In addition,low temperature is not conducive to reversed transformation,while high temperature and long annealing time will lead to inhomogeneous grain size distribution.

Effect of Adding Nitrogen on Microstructure and Property of Vanadium Microalloyed Reinforcing Bar Steel

The relation between stacking fault overlap and martensitic nucleation in Fe-17Mn-10Cr-5Si-4Ni alloy was studied. The arrayed structure of dislocations and characteristics of ε-martensite formation under stress were in-situ observed by TEM. The results reveal that ε-martensite nucleates at the top of stacking faults overlapped band, where the ordered arrayed structure of Shockley partial dislocations exists. External stress promotes ε-martensitic nucleation ability because of accelerated ordering of Shockley partial dislocations in stacking faults overlapped band.

Effect of Melt Scan Rate on Microstructure and Macrostructure for Electron Beam Melting of Ti-6Al-4V

Microstructure and variations in porosity in Ti-6Al-4V samples built with electron beam melting (EBM) over a range of melt scan speeds, ranging from 100 mm·s-1 to 1000 mm·s-1 were examined. Microstructure was characterized by refinement of α-phase and transformation to α′-martensite. Light optical microscopy, scanning electron microscopy, and transmission electron microscopy were used to observe these phenomena, while corresponding tensile testing and associated macro and microindentation hardness measurements were used to define the microstructural variations. Relative stiffness was observed to be linearly log-log related to relative density, corresponding to ideal porosity associated with open-cellular structures.

X-ray Diffractions of Deformation Structurein Polycrystalline Fe-32Mn-5Si Alloy

The change of microstructure with strain was investigated in a Fe-32Mn-5Si austenitic alloy at room temperature by X-raydiffraction profile analysis.The experimental results show that the Fe-32Mn-5Si alloy is deformed by the strain—induced γ→εtransformation and the twinning except dislocation slip at room temperature.The amount of strain-induced ε-martensite,thestacking fault probability and the twinning probability all exhibit parabolic relationship with increasing strain.The stackingfault probability is higher than the twinning probability.

Effect of the cold deformation regime on microstructure and mechanical properties of AISI 301LN stainless steel

This study analyzed the effect of cold-rolling reduction （in a wide range of 10% - 80% ） and subsequent annealing on the microstructure and mechanical properties of AISI 301LN stainless steel. Results indicated the formation of shear bands and nucleation of strain-induced α＇-martensite at their intersections. The volume fraction of α＇-martensite increased with increase in cold-rolling reduction by the continuous growth of embryos. This, in turn,resulted in an increase in yield and tensile strengths. The reversion of α＇-martensite to austenite occurred after subsequent annealing. The observed variation in the grain size of reversed austenite can be related to the annealing regime. A good combination of strength and ductility can be obtained upon annealing at 650 ℃ for 30 min. The effect of grain size on yield strength conformed to the Hall-Petch relationship in the entire range of our analysis.

Microstructures and Hardness Properties for β-Phase Ti-24Nb-4Zr-7.9Sn Alloy Fabricated by Electron Beam Melting

Atomized, pre-alloyed Ti-24Nb-4Zr-7.9Sn （wt%） powder was used to fabricate solid, prototype components by electron beam melting （EBM）. Vickers microindentation hardness values were observed to average 2 GPa for the precursor powder and 2.5 GPa for the solid, EBM-fabricated products. The powder and solid product microstructures were examined by optical and electron microscopy. X-ray diffraction analyses showed that they had bcc β-phase microstructure. However, it was found by transmission electron microscopy that the EBM-fabricated product had plate morphology with space -100-200 nm. Although the corresponding selected area diffraction patterns can be indexed by β-phase plus α＂-martensite with orthorhombic crystal structure, the dark-field analyses failed to observe the α＂-martensite. Such phenomenon was also found in deformed gum metals and explained by stress-induced diffusion scattering due to phonon softening.

Signifcant impact of cold-rolling deformation and annealing on damping capacity of Fe-Mn-Cr alloy

The infuences of cold-rolling deformation and annealing on the damping capacity of Fe-19Mn-8Cr alloy were investigated.It was observed that the cold-rolled Fe-19Mn-8Cr alloy with a reduction of 10%showed the relatively excellent damping capacity because of the relatively moreε-martensite and lower dislocation density,and the reduction of slopes of diferent damping curves increased along with increasing the cold-rolling reduction.Besides,the subsequent annealing process can further enhance the damping capacity.After 70%cold-rolling deformation,the austenite grain would grow up with the increase in the annealing temperature,which resulted in a signifcant change in the content and morphology ofε-martensite infuencing the damping capacity of the experimental steel.The damping capacity was optimum when annealed at 800°C for 30 min,displaying that the size ofε-martensite has a vital infuence on the damping capacity of the experimental alloy.This study may enrich the fundamental knowledge about how to ameliorate the damping capacity of Fe-Mn-Cr damping steels.

Martensitic transformation fcc(γ)→hcp(ε)

Criteria of the thermoelastic martensitic transformation are suggested, on the basis of which the martensitic transformation fcc(γ)→hcp(ε) in Fe-Mn-Si based alloys is classified as a semi-thermoelastic transformation In contrast with the martensitic transformation fcc(γ)→bct(bcc)α’ in iron-based alloys, the thermoelastic transformation in Cu-based alloys and the t→m transformation in ceramics containing ZrO2, in γ→ε of Fe-Mn-Si, the strengthening and grain size of the parent phase will not markedly affecl the Ms and the internal friction peak indicating the martensitic Transformation does not correspond to a significant lowering of the elastic modulus, implying that the nucleation of ε-martensite may occur directly through the stacking fault and may not strongly depend on soft mode. A comparison between the thermal and stress induced ε martensites is made and a brief discussion is given.

Microstructural Development and Deformation Mechanisms during Cold Rolling of a Medium Stacking Fault Energy TWIP Steel

The magnetic response, microstructural and texture changes occurring during cold rolling of a Fe-14Mn-0.64C-2.4AI-0.25Si medium stacking fault energy TWlP （twinning induced plasticity） steel have been studied by X-ray diffraction and magnetic techniques. The changes in the sub-grain size （Ds）, probability of stacking fault formation （Psf） and microstrain in the material as cold rolling progressed were determined by using a modified version of the Williamson and Hall equation. A strong development of the crystallographic texture with increasing deformation was observed. Deformation-induced formation of a small fraction α＇-martensite was observed, indicating that the steel also exhibits γ→α＇-martensite transformation during cold rolling, which is discussed via the changes of the stacking-fault probability and the texture development during cold rolling.