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<p>High-strength low-alloy (HSLA) steels are valued for their exceptional mechanical properties, combining high strength with excellent formability and weldability. The strength of HSLA steels arises from specific alloying elements that refine microstructural characteristics, minimizing the reliance on carbon content. This study utilized tungsten inert gas (TIG) welding to join 2-mm-thick HSLA steel sheets, aiming to evaluate the mechanical properties, formability, and microstructural attributes of the weldments. Various trials were conducted to select the optimal process parameters, which included welding speeds of 180 and 200&#xa0;mm/min and welding currents of 180, 200, and 220A, based on visual inspections of the welds. Tensile tests, conducted according to ASTM E8 standards, which revealed that the base material exhibited a peak tensile strength of 814&#xa0;MPa and 28% ductility, indicating superior mechanical properties. Conversely, the weldments showed reduced strength (657-693&#xa0;MPa) and ductility (10-14%) compared to the base material. It was noted that with constant currents of 180A and 200A, when the welding speed increased the ductility got reduced, while at 220A, an opposite trend was observed. To investigate, weld macrostructures were analyzed using optical metallography, and fractography studies on tensile fracture surfaces were performed using scanning electron microscopy (SEM) to understand the failure modes. The heat input at each process parameter combination was expressed quantitatively by (welding current/welding speed) ratio and was correlated with the corresponding properties. Excessive heat generation (current/speed = 1.2) at 220A and 180&#xa0;mm/min resulted in non-uniform melting and notch formation around the weld bead, with microvoid coalescence contributing to early failure. Formability assessment via Erichsen cupping test indicated failures primarily in the fusion zone, with the base material achieving the maximum dome height (10.50&#xa0;mm), followed by specimens welded at 220A-200&#xa0;mm/min (10.10&#xa0;mm). Increased welding speed at constant current reduced formability, likely due to decreased heat input, except for the 220A condition. Electron Backscatter Diffraction (EBSD) analysis showed that specimens welded at 220A-180&#xa0;mm/min exhibited low grain orientation spread (GOS: 1.22), because most of the as-welded grains being oriented toward &lt;001&gt;orientation. However, the 220A-200&#xa0;mm/min combination displayed maximum grain stretching from their isotropic as-welded condition and higher average GOS (2.00), reflecting good formability. Microtextural analysis revealed the highest intensity of γ fiber components (114.926) in the 220A-200&#xa0;mm/min welded specimen, achieving superior formability, whereas the 220A-180&#xa0;mm/min specimen showed reduced γ fiber intensity (8.382), correlating with decreased formability.</p>

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Influence of Process Parameters on the Mechanical Properties and Formability Behavior of TIG Welded HSLA Steel Sheets

  • 期刊论文

  • 发表日期：

    2025年10月16日

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  • Rahul Datta,
  • Vanapalli Teja Gayathri,
  • K. V. Sai Srinadh,
  • Marrapu Bhargava

摘要

High-strength low-alloy (HSLA) steels are valued for their exceptional mechanical properties, combining high strength with excellent formability and weldability. The strength of HSLA steels arises from specific alloying elements that refine microstructural characteristics, minimizing the reliance on carbon content. This study utilized tungsten inert gas (TIG) welding to join 2-mm-thick HSLA steel sheets, aiming to evaluate the mechanical properties, formability, and microstructural attributes of the weldments. Various trials were conducted to select the optimal process parameters, which included welding speeds of 180 and 200 mm/min and welding currents of 180, 200, and 220A, based on visual inspections of the welds. Tensile tests, conducted according to ASTM E8 standards, which revealed that the base material exhibited a peak tensile strength of 814 MPa and 28% ductility, indicating superior mechanical properties. Conversely, the weldments showed reduced strength (657-693 MPa) and ductility (10-14%) compared to the base material. It was noted that with constant currents of 180A and 200A, when the welding speed increased the ductility got reduced, while at 220A, an opposite trend was observed. To investigate, weld macrostructures were analyzed using optical metallography, and fractography studies on tensile fracture surfaces were performed using scanning electron microscopy (SEM) to understand the failure modes. The heat input at each process parameter combination was expressed quantitatively by (welding current/welding speed) ratio and was correlated with the corresponding properties. Excessive heat generation (current/speed = 1.2) at 220A and 180 mm/min resulted in non-uniform melting and notch formation around the weld bead, with microvoid coalescence contributing to early failure. Formability assessment via Erichsen cupping test indicated failures primarily in the fusion zone, with the base material achieving the maximum dome height (10.50 mm), followed by specimens welded at 220A-200 mm/min (10.10 mm). Increased welding speed at constant current reduced formability, likely due to decreased heat input, except for the 220A condition. Electron Backscatter Diffraction (EBSD) analysis showed that specimens welded at 220A-180 mm/min exhibited low grain orientation spread (GOS: 1.22), because most of the as-welded grains being oriented toward <001>orientation. However, the 220A-200 mm/min combination displayed maximum grain stretching from their isotropic as-welded condition and higher average GOS (2.00), reflecting good formability. Microtextural analysis revealed the highest intensity of γ fiber components (114.926) in the 220A-200 mm/min welded specimen, achieving superior formability, whereas the 220A-180 mm/min specimen showed reduced γ fiber intensity (8.382), correlating with decreased formability.