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.