Papers by Keyword: Stainless Steel (SS)

Abstract: Three studies on the oxidation behaviour of austenitic stainless steels were described in the present paper. (1) High temperature oxidation behaviour and its mechanism in austenitic stainless steels with high silicon: Sulfur contained as impurity in steel showed a harmful influence to the oxidation resistance of 19Cr-13Ni-3.5Si stainless steels. It was found that the abnormal oxidation was caused from the surroundings of MnS inclusions. (2) Effect of a small addition of yttrium on high temperature oxidation resistance of Si-containing austenitic stain less steels: The oxidation resistance of 19Cr-10Ni-1.5Si steels was improved remarkably even with only 0.01%Y addition, which is the same concentration as added for de-oxygenation. Y was enriched at the grain boundary of oxide scale and metal-oxide interface. It was suggested that Y-containing steels shoed good oxidation resistance, because the enriched Y at the grain boundary and metal-oxide interface prevented the diffusion of iron and oxygen ions through the oxide scale. (3) Effect of grain size on the oxidation behaviour of austenitic stainless steels: Type 304, 316 and 310 steels with finer grain size showed better oxidation resistance than those with coarser grain size at 850°C. The oxide scale of steels with coarser grain size easily spalled during the cooling process.

Abstract: The superaustenitic stainless steel ASTM A 744 Gr. CN3MN (22Cr-25Ni-7Mo-0.2N) has as mainly characteristic high corrosion resistance in severe environment. As the corrosion resistance depends on the microstructure, it was investigated the phase transformations after a solution treatment at 1200°C. Thermocalc calculation for 53Fe-25Ni-22Cr alloy indicates austenitic phase between 1300 and 800°C and austenite + sigma phase below 800°C. The as-cast steel studied presented 2.7 % of precipitates volume fraction and the precipitates were located on the grain boundaries and inside the austenitic grains. X-ray diffraction confirmed the presence of sigma phase in as-cast sample. Scanning electron microscopy showed that the level of Cr and Mo was higher in the precipitates than in the austenitic matrix and the Ni content was higher in matrix compared to precipitates. After heating at 1200°C during 90 minutes, the precipitate volume fraction was reduced to 2.1 % and the grain boundaries precipitates were dissolved. The microstructural analyses made through transmission electron microscopy and X-ray diffraction showed the presence sigma phase and M6C carbide.

Abstract: Nickel-free high nitrogen stainless steel has become more important due to its impressive mechanical and corrosion properties. In contrast to high pressure processes, melting plasma in a normal atmosphere is an alternative way of obtaining high nitrogen content at low cost. However, melting in such an atmosphere will bring some surface impurities, like sulfur and oxygen, into the stainless steel through the refractories or the materials themselves. Therefore, this research aims the relationship between the sulfur and nitrogen content, and their influence on biocompatibility. Thermo-Calc is first used to design the composition of Fe-Cr based austenitic nitrogen stainless steel, and melted with different melting techniques, including plasma and an induction melting furnace. The results indicate that the nitrogen content varies with different sulfur content. It is also found that α-Fe (Ferrite) plates are observed near the grain boundaries when the sulfur content reaches a certain level. Besides, the Sulfur content has an obvious influence on the biocompatibility rather than nitrogen contents.

Abstract: In most superplastic forming process, one or more sheets of superplastic grade materials are heated and forced onto or into single surface tools by gas pressure. Since the assembly includes only clamping dies, temperature chamber and regulated gas pressure to provide forming force, the assembly is easy to use for aircraft components. However, it is not easy to control process variables at high temperature. This paper presents an economic machinery method to develop hot press machine for manufacturing complex contoured components using superplastic forming and diffusion bonding technology.

Abstract: The stainless steel slag contains chromium and iron as well as significant levels of heavy metals, such as Cr(VI). Therefore, to efficiently recovery the valuable components in the stainless steel slag has potential environment and economic profit. In this paper, the physical and chemical properties as well as the leaching properties of the stainless steel slag were summarized. In addition, the treatment processes which can recovery or utilize the valuables in the slag and other potential measures to reduce the environmental pollution of the stainless steel slag were also discussed.

Abstract: Experimental explorations for optimal cutting conditions on high speed drilling processes could be expensive and risky both to machine tools and operators. In this study, high-speed drilling of SUS304 stainless steel with a TiN-coated drill was simulated for optimized drilling conditions. Tool wear mechanism as well as chip formation processes was also explored based on finite element analysis (FEA). It was found with the simulations that higher cutting speed came up with smaller tool wear.

Abstract: Time of flight neutron diffraction method was applied to measure elastic lattice strains in austenitic steel during "in situ" tensile test. Comparing experimental data with self-consistent model, the critical resolved shear stress and hardening parameters were determined for polycrystalline grains. The result allowed us to determine the main component of the stress localization tensor, relating the rate of grain stress with the applied macrostress rate. The evolution of concentration tensor in function of the applied macrostress was analyzed. Finally, the load transfer between grains during yielding of the sample was studied.

Abstract: The motivation of this study is to investigate micro warm coining of metals with high strength (e.g. austenitic steels) in the field of fabricating micro functional surface structures. The current micro cold coining technology, which uses punches made out of steel, is limited to soft metals, such as Al and Cu. Conducting micro cold coining on steels, leads to high tool wear and bad form filling. The approach of this study is integrating electric conductive heating into a micro coining system to realize micro warm coining of stainless steel. This paper presents the experimental and numerical analysis of micro warm coining technology using the material stainless steel 1.4401. A coupled thermal-mechanical model in the commercial Finite-Element-code ABAQUS is used to help analyzing the micro warm coining process. The results are summarized as follows: (1) Open die micro warm coining has been realized. The form filling achieved was 56%, which was three times larger than the form filling of cold micro coining on the same material. (2) Both the experiments and simulations showed that faster processing, by increasing the punch velocity, resulted in a slightly improved form filling (5% from 5 mm/s to 100 mm/s). (3) Surface chilling hindered the filling of thin ribs.

Abstract: In many applications, negative effects of residual stresses in the material stemming from the production process, are regularly encountered. These residual stresses in cold-rolled steel tubes are mainly due to two mechanisms: (i) the rolling of the flat plate into a circular cross-section and (ii) afterwards closing this section with a weld bead. This research focuses on the residual stresses due to the welding process. In an experimental setup abstraction is made of the real production process of the tube. A finite element model is built of this experimental setup. Validation of the welding simulations is done by comparing the strain evolution in both the experiment and the simulation. In this validation process, sometimes a discrepancy between the measured strain evolution and the one obtained from the numerical analysis is seen. In this contribution it is numerically investigated how initial residual stresses affect the thermal strain evolution in the tube during the welding process. This is done in two ways: firstly an initial stress field in hoop direction, based on the spring back of the tube when cut is taken as the reference state and secondly the stress/strain state after the first weld is used in stead of the virgin material state. The conclusion for both assumptions is that the strain evolution during the welding is affected by the initial stress/strain state of the material.

Abstract: The effects of environmental factors, such as pH and buffer capacity, on the pitting break potential (Ebreak) and protect potential (Eprotect) of type 304 stainless steel was investigated by cyclic voltammetry sweeps method. The buffer capacity and the concentration of non-aggressive anions in the solutions indicate some effects on the pitting initiation and repassivation of stainless steel. Nevertheless, the pitting Ebreak and Eprotect show a strong dependence on a parameter J as general environmental factor, which is defined as the product of concentration of aggressive anions and buffer capacity. Study pitting Ebreak and Eprotect of 304 stainless steel by environmental factor suggested a new method to investigate the anti-corrosion ability of iron base metal.