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Abstract
Railway vehicle makers manufacture the bogie frame by welding medium-strength carbon steel sheets. It has been a long-standing practice to perform post-weld heat treatment (PWHT) to remove welding-residual stress, but rail car manufacturers are moving toward producing bogie frames without PWHT. Since securing the fatigue strength of the bogie frame is essential for vehicle operation safety, it is necessary to systematically evaluate the effects of PWHT on hardness, microstructure, mechanical properties, corrosion, fatigue strength, etc. In this study, small-scale welding specimens and full-size components were produced using S355JR used in general structures, automobiles, shipbuilding, railroad vehicles, etc. The effect of PWHT on material properties-the hardness of the base material, heat-affected zone and weld metal, microstructure, shock absorption energy, yield strength, tensile strength, and fatigue were investigated. When the weld specimen was annealed at 590 °C and 800 °C for 1 h, the yield strength and tensile strength of the specimen decreased, but the elongation increased. For specimens not heat-treated, the parent material’s yield strength, the yield strength in HAZ, and the yield strength of the weld metal were 350 MPa, 345 MPa, and 340 MPa. For specimens heat-treated at 590 °C, they were 350 MPa, 345 MPa, and 340 MPa. For specimens heat-treated at 800 °C, they were 350 MPa, 345 MPa, and 340 MPa. Annealing heat treatment of the specimen at 800 °C homogenized the structure of the weldments similar to that of the base material and slightly improved the shock absorption energy. For specimens not heat-treated, the Charpy impact absorption energies at 20 °C of the parent material and weld metal were 291.5 J and 187 J. For specimens heat-treated at 590 °C, they were 276 J and 166 J. For specimens heat-treated at 800 °C, the Charpy impact absorption energy at 20 °C of the parent material was 299 J. PWHT at 590 °C had the effect of slightly improving the fatigue limit of the specimen but lowered the fatigue limit by 10.8% for the component specimen.
Highlights
Welding is a convenient and economical technology for joining steel, alloy, and non ferrous metals, and is used in various fields such as automobiles, railways, aviation, bridges, pressure vessels, construction, etc. [1]
We investigated the post-weld heat treatment (PWHT) effect of the mechanical properties and fatigue behavior using butt-weld specimens and T-shape fillet weld specimens made from similar carbon steel [18]
The upper and lower yield strengths observed in low carbon steel appeared, and a Lüders band having almost constant stress was observed past the upper yield strength
Summary
Welding is a convenient and economical technology for joining steel, alloy, and non ferrous metals, and is used in various fields such as automobiles, railways, aviation, bridges, pressure vessels, construction, etc. [1]. The state of the residual stress will change after the applied load is removed. The residual stress may have a significant effect on the crack life [6,7,8,9,10,11]. The effect of residual stress on the fatigue life of butt-weld joints was significant. Methods to reduce or remove the residual stress in the structure are applied. In most cases on the weld tow surface, tensile residual stress occurs and hardness and microstructures change. A more active way is to extend the fatigue life by striking the toe, the weak part of the welded structure, with a metal pin using a 20–30 kHz ultrasonic exciter (impact pin peening) to generate compressive residual stress from the toe surface to a certain depth. Galtier and Stanikov [24,25] compared the fatigue life of samples treated with sand-blast, low transformation temperature welding, and ultrasonic peening on hightensile steel welded specimens and showed that ultrasonic peening was the most effective in improving fatigue life
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