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ABSTRACT
TIG welding process parameters were analysed for joining duplex stainless-steel plates. Signal to noise (SN) ratio and Analysis of Variance (ANOVA) analyses were applied for investigating the selected welding parameters. The selected parameters were current (A), gas flow rate (L/min) and speed (mm/min). The purpose of this work is to produce weld joints with maximum impact of strength and hardness. L9 orthogonal array was selected according to the aforementioned factors with three levels. The impact strength of the joints was found using the Izord impact testing machine and hardness of all joints was measured using the Brinell Hardness machine. From the SN ratio analysis, it was observed that for the high impact strength, the required welding current was 150 A, gas flow rate was 14 L/min and the welding speed was 210 mm/min while for high hardness, the welding current was 190 A, gas flow rate was 12 L/min and the welding speed was 175 mm/min. ANOVA analysis indicated that the gas flow rate was the most significant one for both impact strength and hardness of the joints.
Keywords: TIG welding; duplex stainless steel; SN ratio analysis; ANOVA.
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INTRODUCTION
There are different types of stainless steels; when nickel is added, the crystal structure makes such steels virtually non-magnetic and less brittle at low temperatures. For greater hardness and strength, more carbon is added. Duplex stainless steels have a mixed microstructure of austenite and ferrite, the aim usually being to produce a 50/50 mix, although in commercial alloys, the ratio may be 40/60 [1, 2]. Duplex stainless steels have roughly twice the strength compared to austenitic stainless steels and also improved resistance to localised corrosion, particularly pitting, crevice corrosion and stress corrosion cracking. They are characterised by high chromium (19-32%) and molybdenum (up to 5%) and lower nickel contents than austenitic stainless steels. The properties of duplex stainless steels are achieved with the overall lower alloy content than similar-performing super-austenitic grades, making their use cost-effective for many applications [3-5]. Arc welding is a type of welding that uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point. Gas tungsten arc welding is also called...