Abstract
The effect of preheating temperature on the mechanical and fracture behavior, hardness, and the microstructure of slot welded pearlitic rail steel were studied. Railhead sections with slots were preheated to 200℃, 300℃, 350℃ and 400℃ before gas metal arc filling to simulate defects repair. Another sample, welded at room temperature (RT) with no preheat, was studied in comparison. The parent rail steel has ultimate strength, yield strength and strain to failure of 1146 MPa, 717 MPa and 9.3%, respectively. Optimum values of these properties for the welded rail steels were found to be 1023 MPa, 655 MPa and 4.7%, respectively, for the 200℃ preheat temperature. On this basis, the optimum weld efficiency was found to be 89.2%. The average apparent fracture toughness KI for the parent rail was 127 MPa.m0.5, while that for the optimum welded joint (200℃ preheat) was 116.5 MPa.m0.5. In addition, the average hardness values of the weld, fusion zone, and heat affected zone (HAZ) were 313.5, 332 and 313.6 HB, respectively, while that for parent rail steel was about 360 HB. Dominance of bainite and acicular ferrite phase in the weld microstructure was observed at 200℃ preheat.
Highlights
Preheating can be defined as heating the base metal(s) to a certain temperature before welding
Typical weld microstructure of high strength filler material alloyed with metals such as, Ni, Mn, Cr and Mo consists of a mixture of acicular ferrite, bainite, and low carbon martensite
Hardness of the weld zone and heat affected zone (HAZ) depends on heat input, cooling rate, and peak temperature reached during welding [18]
Summary
Preheating can be defined as heating the base metal(s) to a certain temperature before welding. Typical weld microstructure of high strength filler material alloyed with metals such as, Ni, Mn, Cr and Mo consists of a mixture of acicular ferrite, bainite, and low carbon martensite. Relative proportion of these phases mainly depends on chemical composition and thermal cycle during welding [8,9]. Cooling rate decreases with increasing preheat temperature and heat input. Hardness of the weld zone and HAZ depends on heat input, cooling rate, and peak temperature reached during welding [18]. The optimum preheat temperature has been identified in view of the welding efficiency and the fracture resistance of the welded rail head
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