Rail flash butt welding process: Effect of the preheating stage on the heat-affected zone

Flash butt welding is an important rail welding process for the construction and maintenance of railroads. However, despite the efforts to improve the parent metal rail quality, the rail welded zones are still prone to being sensitive to defects. This work focuses on the Preheating process stage, and it presents a study on the influence of this stage on the heat-affected zone (HAZ). Two types of rail base metal were studied: Premium and Super-premium. A novel categorization and assessment of the process variables effects on the HAZ width and its minimum hardness are presented. Taguchi’s method was applied to analyze the effect of three welding parameters (Current Pulse, Number of Heating Impulses and Upset Force) on the HAZ. The results showed that the effect of the heat input generated by the preheating stage also contributes to the HAZ formation and cannot be neglected. It was demonstrated that the parameters in the preheating stage influence the HAZ width (40% reduction in HAZ) and its Minimum Hardness value (raised by 10%). Preheating stage can be used to control and optimize the width and the minimum hardness of the HAZ.