Reversed Microstructures and Tensile Properties after Various Cold Rolling Reductions in AISI 301LN Steel (original) (raw)
Related papers
ISIJ International
Microstructure evolution during the reverse transformation of low alloy steel consisting of lath martensite and chromium carbide was examined using in-situ electron backscatter diffraction at high temperatures. Austenite grains nucleated during the reverse transformation were categorized into two types: austenite grains nucleated along the lath boundaries with almost the same crystal orientation as the prior austenite (type A), and austenite grains nucleated at the prior austenite grain boundaries or inside the prior austenite grains with a different crystal orientation (type B). After the reverse transformation was finished, the prior austenite grains were reconstructed by the rapid growth and coalescence of type-A grains, which was called the "austenite memory phenomenon." Here, misorientation remained in the reconstructed austenite grains. Hence, upon heating to a higher temperature, type-A grains were invaded and were eventually replaced by type-B grains, resulting in a new fine-grained microstructure; this was similar to recrystallization. Therefore, these results showed that the austenite memory phenomenon occurred when the nucleation and growth of type-A grains was more dominant than those of type-B grains and that the degree of grain refinement depended on the nucleation and growth rate of the type-B grains.
Characterization of Cold Rolling-Induced Martensite in Austenitic Stainless Steels
2016
The deformation-induced phase transformation hardening phenomenon is normally observed in austenitic stainless steels of the AISI 300 series. The amount of hardening is limited by the structural stability of the material. In fact, during the cold forming process, low nickel austenitic stainless steels can undergo deformationinduced phase transformation of fcc gamma-austenite to bcc alpha'-martensite. On the other hand, by heat treatments, the austenitic structure can be recovered. The reversion of martensite to austenite is studied on a set of austenitic stainless steel specimens existent at our laboratory. These had been submitted to 63% deformation at a temperature of (-70oC), followed by isochronic, isothermal heat treatments at temperatures between 250 and 800oC. Thus, series of specimens with different phase content were available. The reversion of martensite in the specimens is studied by optical and electron microscopy, X-ray diffraction, and electromagnetic non destructi...
MORPHOLOGICAL DETAILS OF STRAIN-INDUCED MARTENSITE IN COLD-ROLLED Cr – Ni STEEL
International Journal of Modern Manufacturing Technologies, 2022
The investigation presents the evolution of straininduced martensite during cold rolling of AISI 304 stainless steel at 10% and 50% degree of deformation. The morphologies and characteristics of ' martensite have been studied using optical-image analysis, scanning and transmission electron microscope. The influence of straininduced martensite on mechanical properties and hardness of AISI 304 steel have been reported. Plastic deformation during the cold rolling of AISI 304 steel induces a martensitic transformation (γ→α') in the whole range of applied deformation degree. The equiaxial grains of austenite containing annealing twins were observed within the microstructure of steel at delivery state. During the deformation process the shape of austenite grains was changed into long slim bands parallel to the rolling direction. Many shear bands and micro-twins were observed in the microstructure at large deformations degrees. The martensite, which was formed as a result of the transformation (γ→α') induced by deformation, has a distinct influence on properties of the investigated steel grade. It was found that the effect of steel hardening is a result of a significant increase of the volume fraction of the '-martensite in the structure.
Materiali in tehnologije, 2016
The performed investigations concerned the influence of the degree and temperature of deformation on the microstructure of metastable austenite in the stainless steel X5CrNi18-10 after its strain-induced martensitic transformation. Samples of steel strip were cold rolled within a degree of deformation from 20 % to 70 % and stretched at a low temperature of-196°C. The microstructure was observed by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM, HREM). It wasen found that after cold rolling with a small degree of deformation (20 %) in the tested steel, generally a single-phase microstructure of the matrix g is found with a high density of dislocations and numerous deformation bands morphologically characteristic of stainless steel with a low stacking-fault energy. After rolling with a 50 % thickness reduction, however, the microstructure displayed deformation twins as well as refined morphologic formations of the phase a', mostly localized in the vicinity of the grain boundaries of the metastable matrix g, and also trace amounts of carbide precipitates. In samples stretched at a temperature of-196°C the microstructure of the matrix displayed a considerable density of dislocations with lath areas of the martensite a' and precipitations of the carbides M23C6. Moreover, the tested steel revealed a crystallographic dependence of the planes and directions on the identified phases g and a', corresponding to dependences of the Kurdjumov-Sachs type, independent of the method and temperature of the plastic deformation. Tests carried out in the TEM proved that the typical sites of nucleation induced by the plastic deformation of martensite are the shear bands, particularly their intersection. The preferred mechanism of transformation, observed in the conditions of cold rolling is, however, a direct transformation of the type g (fcc) ® a' (bcc).
Materials Science and Engineering: A, 2019
In this study, the microstructure-texture-mechanical properties relationships in AISI 304 austenitic stainless steel processed by asymmetric cold rolling investigated. With increasing the deformation, the number of twins and deformation-induced martensites including α′ and ε increased. Interestingly, after 30% rolling, the volume fraction of martensite decreased from 47.34% to 32.69% due to the occurrence of recrystallization. Texture results indicated that after 30% and 40% deformation, the recrystallization texture increased. Two texture transitions from Goss to Brass at 30% deformation and from Copper to Brass at 40% strain observed. The Copper to Brass transition occurred in three distinct paths. The 40% rolled sample exhibited a quite high hardness of 448.3 HV due to the increasing strain hardening, mechanical twins, martensite phases, and grain refinement. The deformed samples exhibited strong anisotropy of hardness and the hardness on the RD-TD plane is higher than two other planes. The results showed a significant increase in yield (1203.2 MPa) and ultimate tensile (1229.2 MPa) strength in the 40% deformed samples with respect to the initial austenitic steel, while a considerable ductility (23.3%) remained. With increasing the rolling reduction from 10% to 40%, the diameter and depth of the dimples reduced and uniformity of dimples decreased. However, the fracture mode was ductile with sufficient plastic deformation before failure. Finally, with increasing the deformation, the number of striations and fine dimples increased due to the formation of more mechanical twins and fine grains, respectively.
international journal of iron and steel society of iran, 2017
Formation of nano/ultrafine grain structure in AISI 304L austenitic stainless steel through the martensite reversion treatment was studied. The solution annealed specimens were cold rolled up to 95 % thickness reduction at -15°C. The cold-rolled specimens were subjected to reversion annealing treatment at the temperature range of 700-1000 °C for 10–150 min. Microstructural evolutions were analyzed using ferritscopy, X-ray diffraction, and field emission scanning electron microscopy techniques, whereas mechanical properties were determined by hardness test. The saturation strain during cold rolling was about 56 % reduction. The mean austenite grain size of 135 nm was obtained by 95 % cold reduction and annealing at 700 °C for 10 min. It was found that increasing cold reduction resulted in grain refinement at the same condition of reversion annealing and higher hardness.
Journal of Materials Processing Technology, 2010
In this paper, the effect of different thickness reductions by cold rolling on the microstructure and mechanical properties of AISI 304L austenitic stainless steel were investigated. The hot rolled steel strips were subjected to cold rolling at 0 • C from 10 to 90% thickness reduction. Microstructures, strain-induced martensitic transformation and mechanical properties of the cold-rolled specimens were characterized by X-ray diffraction, Feritscope measurements, optical metallography, hardness and tensile tests. The resulting transformation curve showed a sigmoidal shape with the saturation value of strain-induced martensite of approximately 100%. A good agreement was found between the experimental results and the Olsen-Cohen model. The results indicated that formation of strain-induced martensite clearly resulted in a significant strengthening of the steel. .ir (A. Kermanpur). Angel (1954). Angel's equation demonstrates the relation between M d30 temperature and the chemical composition. Nohara et al. (1977) modified Angel's equation and also considered the effect of grain size in this equation: M d30 ( • C) = 551 − 13.7(%Cr) − 29(%[Ni + Cu]) − 8.1(%Mn) − 18.5(%Mo) − 9.2(%Si) − 68(%Nb)
Characterization of reverse martensitic transformation in cold-rolled austenitic 316 stainless steel
Matéria (Rio de Janeiro)
In this work the reversion of the strain-induced '-martensite to '-austenite was studied in a series of AISI 316 stainless steels (SS) specimens. The samples were submitted to 63% reduction in thickness by rolling at a temperature of-70ºC, to achieve high martensite content. The reversion of martensite to austenite was made by means of isochronic, isothermal heat treatments at temperatures between 200 and 900ºC, so as to induce partial martensite-austenite phase transformation. The samples were studied by optical and electronic microscopy, X-ray diffraction, magnetization measurements, microhardness, and electromagnetic non destructive methods: feritscope, conductivity measurements using Van der Pauw's technique, and magnetic permeability assessments by an eddy current inverse method. The metalography study showed an ' lath martensite type structure and a similar one for the reverted austenite ('). Magnetization measurements and magnetic permeability showed that the reversion is active between 400 and 800°C. From the magnetic saturation measurements, a new calibration curve for the assessment of %' through the feritscope readings was obtained. The results of the different techniques were compared, in order to assess the scope of the studied techniques in the characterization of rolled SS products, and in the evaluation of progress of reversion reaction.
Development of ultra fine grain structure by martensitic reversion in stainless steel
Journal of Materials Science Letters, 2002
The austenite-martensite transformation followed by annealing for austenite reversion in AISI 304 stainless steel has been investigated in order to study the effect of this thermo-mechanical process on grain refinement. In particular the effect of cold reduction, annealing temperature and annealing times have been analysed. After getting ultrafine grains the effect of the grain size on the hardness and on the tensile properties has been evaluated, showing a Petch-Hall dependency in the fully analysed range (down to 0.8 µm grain size). C 2002 Kluwer Academic Publishers