Esa Haruman

Angular Distortion Analysis on Multipassed Welding of Combined Joint Types Using Thermo-Elastic-Plastic FEM

A 2D and 3D thermo-elastic-plastic (TEP) FE Analysis has been developed to simulate the angular distortion induced by Gas Metal Arc Welding (GMAW) process on combination of butt and T-joint with thickness of 9 mm. The material used in this study was low alloy Manganese Carbon steel S355J2G3. In this research, SYSWELD 2010 with its computation management tool known as Multipassed Welding Advisor (MPA) was used to analyze the distortion behaviour of combined joint types. To model the heat source of GMAW, Goldak’s double ellipsoid representation which is available within this FEA code was selected. The final objective of this research is hence aimed to be base line study to provide preliminary information in preparing the tools or equipments for experimental investigation.

An Investigation on Low-Temperature Thermochemical Treatments of Austenitic Stainless Steel in Fluidized Bed Furnace

In this study, the feasibility of using an industrial fluidized bed furnace to perform low-temperature thermochemical treatments of austenitic stainless steels has been studied, with the aim to produce expanded austenite layers with combined wear and corrosion resistance, similar to those achievable by plasma and gaseous processes. Several low-temperature thermochemical treatments were studied, including nitriding, carburizing, combined nitriding-carburizing (hybrid treatment), and sequential carburizing and nitriding. The results demonstrate that it is feasible to produce expanded austenite layers on the investigated austenitic stainless steel by the fluidized bed heat treatment technique, thus widening the application window for the novel low-temperature processes. The results also demonstrate that the fluidized bed furnace is the most effective for performing the hybrid treatment, which involves the simultaneous incorporation of nitrogen and carbon together into the surface region of the component in nitrogen- and carbon-containing atmospheres. Such hybrid treatment produces a thicker and harder layer than the other three processes investigated.

Structural Development of Expanded Austenite on Duplex Stainless Steel by Low Temperature Thermochemical Nitriding Process

This paper describes the results of gaseous thermochemical treatment of nitriding duplex stainless steel using tube furnace. The nitriding was performed in temperature range between 400°C and 500°C for 6 hours, forming a dual layer structure with hard nitrogen layer. The nitriding gas composition used for this process is 50% NH4 + 50% N2 and 25% NH4 + 75% N2. The structural development was characterised using hardness tester, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Based on the experimental results, it was found that nitrided layer produced maximum thickness nitrided layer about 13.96µm and hardness 666.3 HV0.025 at 450°C with 50% NH4. The formation of expanded austenite was observed in temperature range between 400°C and 500°C. However, the cromium nitride has been developed at temperature 500°C which decreased the corrosion properties of duplex stainless steel.

Low Temperature Thermochemical Treatments of Austenitic Stainless Steel Without Impairing Its Corrosion Resistance

Austenitic stainless steel (ASS) is used applied widely owing to its very good corrosion resistance. However, the application of this material as a bearing surface is severely limited by very poor wear and friction behaviour. Consequently, Surface Engineering treatments for austenitic stainless steel are an interesting alternative way to increase the surface hardness and improve the wear resistance. For the purpose of this works, the Surface Engineering design will be classified, very broadly, into three groups : (a) those which coat the substrate: PVD, CVD, etc, (b) those which modify only the structure of the substrate, (c) those which modify the chemical composition and the structure of the substrate: thermochemical, ion implantation, plasma, etc. It is nowadays widely accepted that hard, wear and corrosion resistant surface layers can be produced on ASS by means low temperature nitriding and/or carburizing in a number of different media (salt bath,gas or plasma), each medium having its own strengths and weaknesses. In order to retain the corrosion resistance of austenitic stainless steel, these processes are typically conducted at temperatures below 450oC and 500oC, for nitriding and carburizing respectively. The result is a layer of precipitation free austenite, supersaturated with nitrogen and/or carbon, which is usually referred to as Sphase or expanded austenite.

Surface Modification of 2205 Duplex Stainless Steel by Low Temperature Thermochemical Hybrid Heat Treatment at 450° C

An approach has been made in developing hybrid heat treatment process for improvement of surface properties of duplex stainless steel (DSS). The process was performed using horizontal tube furnace at temperature of 450° C at holding time of 4, 8, 16 and 30 hours. Carbon and nitrogen elements were simultaneously introduced onto the surface of DSS with a ratio of 5% CH4 + 25% NH3 + 70% N2. The microstructure, phase analysis, surface hardness and hardness profile were systematically assessed. Hybrid heat treatment process managed to produce diffusional layer, where longer holding time had increased the thickness of the layer and improved the surface hardness. Expanded austenite phase has been formed at specimens 8, 16 and 30 hours. Longer holding time however gradually diffused Cr2N at the ferrite grains at the substrates. From the process, it can be concluded that low temperature hybrid heat treatment be able to improve the surface hardness of DSS however concern on holding time must be highly considered.

Investigation on Weld Induced Distortion of Butt Joint Using a Local/Global Simulation Approach

In this paper, a local/global approach has been used to predict weld induced distortion in butt joint. This approach combines non-linear thermo-elastic plastic and linear elastic analyses to compute final distortion triggered by the welding process. Distortion can lead to dimensional inaccuracy and thus causing the rise in fabrication cost. In this study, Finite Element Method (FEM) software Sysweld and Pam-Assembly were used for computing the welding deformation. The material used for the simulation was low carbon steel with thickness of 4 mm. Based on the result obtained, it was observed that this approach provides fast computation time and efficient solution.

Investigation on Weld Induced Distortion of Butt and T-Joints Using Thermo-Elastic-FEM and Experimental Study

In this paper, the capability of linear thermo-elastic numerical analysis method to estimate the welding deformations was investigated. The weld induced deformation is considered as the major stumbling block that can affect the dimensional accuracy. Based on this fact, welding distortion is necessarily to be predicted, if experimental investigation becomes expensive, to minimize the negative effects, improve the quality of welded parts and finally to reduce production cost. In this study, the welding distortions on butt and T-joints with thicknesses of 4 mm and 6 mm were simulated using relatively new FEM software WELD PLANNER developed by ESI Group. The material used for the simulation was low Carbon steel. By comparing the results between simulation and experiment, it was found out that this software provided immediate solution for computational analysis time and was capable to predict the distortion within acceptable accuracy.

Low Temperature Thermochemical Surface Treatment of Austenitic Stainless Steel for Improved Mechanical and Tribological

This paper describes the results of four thermochemical surface treatments of austenitic stainless steels carried out at 450oC in a fluidised bed furnace and they are nitriding, carburizing and the newly developed hybrid process involving the simultaneous and sequential incorporation of nitrogen and carbon to form a dual layer structure in order to achieve much enhanced surface hardness and wear resistance without compromising the corrosion resistance of the steel. In all these treatments there formed alloyed layers with a common feature of being precipitation-free and supersaturated with nitrogen, or carbon or both in the austenite lattice which is known as S Phase or expanded austenite. However the layer thickness was not uniform in any of these treatments and an effective layer was produced after 8h treatment duration. The nitriding treatment produced thicker and harder layer compared to other treatments; the maximum hardness was over 1500 Hv for nitriding and the minimum hardness of 500 Hv for carburizing treatment. The nitriding treatment sample gave high wear resistance which corresponded to high hardness values.