Strain hardening behavior of a Fe–18Mn–0.6C–1.5Al TWIP steel

The strain hardening behavior of a Fe–18Mn–0.6C–1.5Al TWIP steel was investigated through the modified Crussard–Jaoul (C–J) analysis and microstructural observations. The strain hardening rate obtained by modified C–J analysis was high up to the critical strain of 37% and then greatly decreased with further strain. The electron backscatter diffraction (EBSD) observation showed that the deformation twinning rate is greatly decreased beyond about 34% strain, indicating that the reduced strain hardening rate at the large strain region is attributed to the deceleration of deformation twinning rate. The volume fraction of twinned region was increased with tensile strain due to the increase in the number of deformation twins not to the lateral growth of each deformation twin.     

Martensitic transformation and shape memory effect in Fe–Mn–Si based alloys

The research status of the Fe–Mn–Si based alloys is reviewed with emphasis on the recent progress in the martensitic transformation and the associated shape memory effect (SME). Particular interest is given to the fcc(γ)–hcp(ε) transformation mechanism in the alloys featured by low stacking fault energy and the approaches aiming to the enhancement of SME through alloy design including microalloying and microstructure control by introducing texture and precipitates into the parent γ matrix. Potential topics of oncoming focus are briefly highlighted.     

相变诱导塑性钢热镀锌的研究进展

综述了国外相变诱导塑性(TRIP)钢热镀锌的研究进展,重点介绍了TRIP钢的组织结构、力学性能和CMnSi、CMnAl TRIP钢热镀锌的影响因素.     

Solidification microstructures and mechanical properties of high-vanadium Fe–C–V and Fe–C–V–Si alloys

Fe–C–V and Fe–C–V–Si alloys of various C, V and Si compositions were investigated in this work. It was found that the phases present in both of these alloy systems were alloyed ferrite, alloyed cementite, and VC_x carbides. Depending on the alloy composition the solidified microstructural constituents were granular pearlite-like, lamellar pearlite, or mixtures of alloyed ferrite + granular pearlite-like or granular pearlite-like + lamellar pearlite. In addition, it is shown that in Fe–C–V alloys the C/V ratio influences (a) the type of matrix, (b) the fraction of vanadium carbides, f_v and (c) the eutectic cell count, N_F. In Fe–C–V alloys, a relationship between the alloy content corresponding to the eutectic line was experimentally determined and can be described by where C_e and V_e are the carbon and vanadium composition of the eutectic. Moreover, in the Fe–C–V alloys (depending on the alloy chemistry), the primary VC_x carbides crystallize with non-faceted or non-faceted/faceted interfaces, while the eutectic morphology is non-faceted/non-faceted with regular fiber-like structures, or it possesses a dual morphology (non-faceted/non-faceted with regular fiber-like structures + non-faceted/faceted with complex regular structures). In the Fe–C–V–Si system, the primary VC_x carbides solidify with a non-faceted/faceted interface, while the eutectic is non-faceted/faceted with complex regular structures. In particular, spiral eutectic growth is observed when Si is present in the Fe–C–V alloys. In general, it is found that as the matrix constituent shifts from predominantly ferrite to lamellar pearlite, the hardness, yield and tensile strengths exhibit substantial increases at expenses of ductility. Moreover, Si additions lead to alloy strengthening by solid solution hardening of the ferrite phase and/or through a reduction in the eutectic fiber spacings with a decrease in the alloy ductility.     

Study of Formation and Reversion of the Martensitic Phase Induced by Deformation of Lean Duplex Stainless Steel

Lean duplex stainless steels consist of a low percentage of nickel and molybdenum, presenting twice as much resistance compared to austenitic stainless steel and their cost is about twice as low. However, this class of steels has microstructural instabilities, such as the formation of martensite induced by austenite deformation by cold rolling. This feature can significantly alter the properties of interest of this steel. The formation of the martensitic structure, as well as its reversion, is little studied in the steels of the austenitic–ferritic structure. The process of formation and reversal of the martensitic structure in cold rolled stainless steel duplex UNS S32304 was investigated through magnetic measurements, microhardness and X-ray diffraction analyzes. The deformation process allowed the formation of the -martensite phase from the austenite phase with an increase in the values of saturation magnetization, coercive field and micro-hardness values as well as a change in the intensity of the X-ray diffraction peaks. The heat treatment performed at \(650\,^\circ \hbox {C}\) showed an increase in the peak intensity of the austenitic phase and a decrease in the saturation magnetization values, demonstrating a possible reversal of the martensitic structure. The SEM observations after annealing the Beraha’s etched samples revealed the possibility of a martensite transformation and reversion in a Lean duplex stainless steels.