Papers by Keyword: Ferritic Stainless Steel (FSS)

Abstract: The hot deformation behavior and microstructure evolution of 430 ferritic stainless steel (430 FSS) were investigated within the temperature range of 950°C~1150°C at the strain rate of 0.01 s^-1, 0.1 s^-1, and 1.0 s^-1 using a thermo-mechanical simulator. The effects of temperature and strain rate on the flow behavior and microstructures of 430 ferritic stainless steel at reduction ratio 50 % were analyzed. Results indicated that the apparent stress exponent and the apparent activation energy of the steel were about 1.08 and 344 kJ/mol, respectively. The hot deformation equation of 430 was considered as. There was a relationship between the softening mechanism and Zener-Hollomon parameter (abbreviated Z). With the Z value increasing from 4.30×10¹⁰ to 5.00×10¹⁴, the hot deformation peak stress correspondingly increased from 10.74 MPa to 76.02MPa.

Abstract: The tensile test of casting ferritic stainless steel was conducted on SHIMADZU AG-10 at different temperatures of 300, 500, 600, 700, 800, and 950°C, respectively. The engineering stress-strain curves with the thermal deformation at the different temperatures, the tensile strength and elongation curves were obtained. Metallographic test samples were prepared and the morphology of deforming zone was observed by optical microscopy. The experimental results showed that the tensile strength of the test samples decreased with increasing temperature. From 300 to 500°C, the work hardening occurred and the tensile strength increased with increasing engineering strain. The softening occurred and the tensile strength decreased with increasing engineering strain at temperatures from 600 to 950°C. The strength of 430 stainless steel decreased, and the plasticity increased with the increase in temperature. The fractures were basically intergranular fractures within the range of 300~950°C. A transition occurred to the form of fracture from the ductile to the brittle, which might be related to the nitrogen atom in the 430. Grain deformation along specimen tensile direction concentrated in the necking region, where appeared banded structure in martensite. The organization at the edge of the sample was fine, while the organization at the central region was coarser.

Abstract: Corrosion resistance of gas-tungsten arc welds in two 21% chromium ferritic stainless steels was benchmarked against ferritic type 441 and austenitic type 304L stainless steels. Salt spray, pitting corrosion and ferric chloride tests were carried out for autogenous welds. Also, electron microscopy and glow discharge optical emission spectroscopy examinations were made.The corrosion resistance in 21% chromium ferritic steel welds in chloride environments was seen comparable to those in type 304L, and an improvement was observed when compared to type 441 steel. However, the Mn-Cr-Ti-S sulfide domain may have an undesirable influence on end-grain pitting in ferric chloride test. Weld oxidation results in poor corrosion protection, and artificial mechanical cleaning alone is inadequate for restoring this, and hence pickling is advised.

Abstract: The effect of hot deformation temperature on the deformed microstructures and evolution of microstructure and texture of a 21Cr Ti-Nb dual-stabilized ferritic stainless steel was studied using plane strain hot compression tests on a Gleeble 1500 thermomechanical simulator. The deformation was carried out at 550 - 950 °C with a strain of 0.5 at 1 s^-1. The compression was followed by fast cooling to room temperature in order to study the deformed microstructures. Some specimens were heated from the deformation stage to either 750 or 950 °C and held for 0 or 30 s in order to study the nucleation process of recrystallization. The electron backscatter diffraction technique was used to analyze the resultant microstructures and textures. Lowering of the deformation temperature increased the rate of static recrystallization (SRX) and decreased the recrystallized grain size. After deformation at 550 and 600 °C and complete SRX, beneficial γ-fibre texture formed presumably as a result of nucleation at in-grain shear bands. SRX after deformation at 750 °C or above led to the formation of harmful α-fibre textures with weak γ-fibre.

Abstract: Grain growth during welding and the level of impact toughness in thermally simulated high-temperature heat-affected zones were determined for a series of AOD-level laboratory melted 21% chromium ferritic stainless steels. The effects of niobium and titanium stabilizing elements on microstructure were evaluated by optical and scanning electron microscopy. Overall, grain growth was only slightly affected by the stabilizing element ratio. On a weight percent basis, niobium was the most effective for restricting the grain growth in the heat-affected zone either alone or in the presence of a small amount of titanium. The predominantly niobium-stabilized heats also had the highest impact toughness in both air-cooled and water-quenched conditions, differences in transition temperatures being up to 55 °C. However, all the simulated heat-affected zones fit into a narrow ductile-to-brittle transition temperature band width of 30 °C, even including variations in heat input. This was attributed to intense grain boundary precipitation, which occurred even with a low heat input.

Abstract: In this paper, the influence of finish rolling temperature during hot rolling on microstructure and mechanical properties of ferritic stainless steel containing vanadium was investigated. It showed that with the rolling temperature increasing, the tensile strength and hardness value fell down, while the value of ductility rising and less precipitates appearing. If the finish rolling temperature was set too high, the grain would get coarsened and the α-fiber get strengthened, which had an adverse effect on the formability and wrinkle resistance of the production sheet. 850°C was a reasonable finish rolling temperature.

Abstract: Intergranular corrosion behavior of 00Cr12 ferritic stainless steels with different amounts cerium was evaluated. For this evaluation, electrochemical measurements - polarization curves - were obtained for tested materials, and optical microscope was used to observe corrosive microstructure. Experimental results shows: cerium reduces grain sizes and improves intergranular corrosion resistance of test materials. Through mechanism analysis: cerium reduces grain sizes, increases grain boundary density, therefore might improve distribution aspects of carbides and nitrides, chromium depletion situation near grain boundary would be improved, this work worth further study.

Abstract: High temperature oxidation of ferritic stainless steel 21Cr-0.6Mo-Nb-Ti was carried out isothermally at 1100 oC under different water vapour content conditions in an electrical furnace. Water vapour does accelerate the formation of oxide scale of stainless steel 21Cr-0.6Mo-Nb-Ti, however, it is not significant. Some oxide grains consist of spinel crystal structure, which should be spinel Manganese Chromite. In dry air atmosphere, the grain of the spinel is more and bigger than that in wet air. No breakaway oxidation occurs in the experiment indicating that 21Cr-0.6Mo-Nb-Ti has very high oxidation resistance, which might be contributed by the formation of MnCr₂O₄ and compact protective chromia. In addition, continuous silica formed along and accumulated at the oxide metal interface performs like a diffusion barrier.

Abstract: Experimental studies for single shear bolted connection of cold-formed ferritic stainless steel fastened with two bolts (2×1 bolt array) and 3.0 mm thick plate has been performed by T.S. Kim etc. End distances parallel to the direction of applied force were considered as the main variables of specimens. Curling (out of plane deformation) was observed in bolted connection with 60mm end distance and it caused abrupt strength reduction. The purpose of this paper is to compare the analysis results with test results and investigate the curling influence on ultimate strength through numerical modelling. FE models with restrained curling were also simulated for strength comparison with the curled specimen. Therefore, the validation of finite element(FE) analysis in predicting ultimate strength and curling behaviour was verified and the strength reduction ratio by the curling was estimated.

Abstract: In this work, the conventional rolling (CR) and warm rolling (WR) have been carried out with an ultra purified ferritic stainless steel. After different rolling processes and subsequent recrystallization annealing, different recrystallized microstructure characteristics had been obtained. It was observed that as compared to the conventional process, the warm rolling and subsequent recrystallization annealing could obviously refine the recrystallized microstructure of the hot band. The ductile-to-brittle transition for the ultra purified ferritic stainless steel can be closely related to the occurrence of deformation twinning. The refined microstructure can decrease the temperature at which twinning occurs and, consequently, the ductile-brittle transition temperature for the ultra purified ferritic stainless steel was lowered to be below -40°C, and its notch toughness was significantly improved when the fine grain route can be applied.