Effect of heat on microstructural, mechanical and electrochemical evaluation of tungsten inert gas welding of low-nickel ASS

• Published in: Anti-corrosion methods and materials 2018-10, Vol.65 (6), p.605-615
• Main Authors: Bansod, Ankur V., Patil, Awanikumar P., Shukla, Sourabh
• Format: Article
• Language: English
• Subjects: Argon; Austenitic stainless steels; Carbon dioxide; Coarsening; Corrosion; Corrosion potential; Corrosion resistance; Corrosion resistant alloys; Crystal defects; Current density; Defects; Delta ferrite; Electrochemical analysis; Electrochemistry; Electrodes; Electron microscopy; Evaluation; Fabrication; Flow rates; Flow velocity; Gas tungsten arc welding; Gas welding; Hardness; Heat; Heat affected zone; Heat treating; Heavy metals; Industry; Manganese; Mechanical properties; Microstructure; Morphology; Nickel; Optical properties; Passivity; Rare gases; Scanning electron microscopy; Sodium chloride; Solidification; Solutions; Stainless steel; Steel; Sulfuric acid; Sulphuric acid; Tensile strength; Textiles; Tungsten; Water hardness; Welded joints; Welding
• ISSN: 0003-5599; 1758-4221
• DOI: 10.1108/ACMM-05-2018-1941

Purpose The purpose of the study is to evaluate Cr-Mn ASS weld using different heat inputs for its microstructure, mechanical properties and electrochemical behavior. The microstructural examination used optical and scanning electron microscopy. It was observed that ferrite content decreases with increasing heat input. The length of dendrites, inter-dendritic space and volume of lathy ferrite increase with increasing heat input. The increasing heat input caused grain coarsening near the fusion boundary and produced wider heat-affected zone (HAZ). It also decreases hardness and tensile strength. This is attributed to formation of more δ ferrite in the weld. The electrochemical evaluation suggested that the δ ferrite helps in improving the pitting potential in 3.5 per cent NaCl solution saturated with CO2. Whereas in 0.5-M H2SO4 + 0.003-M NaF solution, higher passivation current density was observed because of dissolution of dferrite. The interphase corrosion resistance decreased with increasing heat input. Design/methodology/approach The Cr-Mn austenitic stainless steel or low-nickel ASS was procured in form of 3-mm sheets in rolled condition. The tungsten inert gas welding was performed at three different heat inputs (100 A, 120 A and 140 A), argon as shielding gas with a flow rate of 15 L/min. Different welded regions were observed using optical microscope and scanning electron microscope. Electrochemicals test were performed in solutions containing 3.5 per cent NaCl with saturated CO2 solution and 0.5 M sulfuric acid + 0.003 M NaF at a scan rate of 0.1667 mV/s at room temperature (30 °C ± 1 °C) using a potentiostat. Findings The test steel Cr-Mn ASS is suitable with the selected electrode (308 L) and it produces no defects. Vermicular ferrite and lathy ferrite form in welds of various heat inputs. The increase in heat input reduces the formation of lathy ferrite. The width of HAZ and un-mixed zone increases with increase in heat input. The weld zone of low heat input (LHI) has the highest hardness and tensile strength because of higher δ ferrite content and small grain size in the weld zone. The hardness at high heat input (HHI) is found to be lowest because of grain coarsening in the weld. With increase in δ ferrite, the pitting resistance increases. In 0.5-M sulfuric acid + 0.003-M NaF, the increase in ferrite content reduces the passivation current density. Interphase corrosion resistance increases with increase in δ ferrite content as higher per cent