Influence of Heat Input and Preheating on Microstructure and Mechanical Properties of Coarse Grain Heat-Affected Zone of
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JMEPEG https://doi.org/10.1007/s11665-019-04486-1
Influence of Heat Input and Preheating on Microstructure and Mechanical Properties of Coarse Grain Heat-Affected Zone of Metal Arc Gas-Welded Pearlitic Rail Steel Adnan Raza Khan, Yu Shengfu, and Hao Wang (Submitted June 25, 2018; in revised form October 11, 2019) Influence of varying heat input (0.66-1.43 kJ/mm) and different preheat temperatures (150-350 °C) on microstructure and mechanical properties of the coarse-grained heat-affected zone (CGHAZ) of MAGwelded pearlitic rail steel has been investigated. Results show that at low heat inputs (0.66-1.00 kJ/mm), microstructures are mainly composed of martensite, whereas high heat inputs (1.29-1.43 kJ/mm) have coarsened the grains and formed cracks. 1.16 kJ/mm of heat input is found optimum which has produced a crack-free surface with the least martensite. Afterward, by using the optimum heat input of 1.16 kJ/mm samples are welded at different preheat temperatures ranging from 150 to 350 °C, which has reduced the martensite and increased the pearlite, successively. Preheat temperatures of 250 °C are found optimum, where grain size and t800300 C cooling rate are 38.1 ± 9.8 lm and 3.1 °C/s, respectively. Furthermore, hardness is 659 ± 7 HV, tensile strength is 1349 ± 16 MPa, and toughness is 6.4 ± 0.5 J, respectively. Finally, the confocal scanning laser microscopy analysis, at optimum heat input of 1.16 kJ/cm and 250 °C of preheat temperature, is also presented. The entire study concludes that preheating is inevitable in MAG welding of pearlitic rail steel. 1.16 kJ/mm of heat input with 250 °C of preheating temperature is suitable in MAG welding of pearlitic rail steel where microstructure is composed of pearlite, ferrite, and sorbite having no martensite and no cracks. Keywords
coarse grain heat-affected zone (CGHAZ), heat input, metal arc gas (MAG) welding, pearlitic rail steel, preheating
1. Introduction Pearlitic rail steels are commonly used materials in railroad applications (Ref 1-3). The literature reveals that the everincreasing axel load, fast speed train, and heavy haul in the railroad system result in damage to the rail (Ref 2-4). Nevertheless, repairing a damaged section through welding has always been the dominant method (Ref 3-6). Among various welding techniques, metal arc gas (MAG) welding is suitable due to high efficiency and low heat input which produces narrow HAZ (Ref 7, 8). In welded pearlitic rail steel, CGHAZ is the most critical zone that experiences the highest peak temperature and fast cooling rate (Ref 9-14). During welding thermal cycles, high peak temperature produces largesized grains, whereas a fast cooling rate enhances the formation of martensite (Ref 14-17). In CGHAZ of MAG-welded pearlitic rail steel, these large-sized grains with martensite form localized brittle zones (LBZs) that provide poor combination of mechanical properties and are susceptible to the formation of cracks (Ref 12-15). Heat input and preheating are considered as
Adnan Raza Khan, Yu Shengfu, and Hao Wang, St
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