Metallurgical Analysis and Economic Feasibility of Thermite Welding Applied to Railway Rail Surface Repair

Thongchai Khrueaphue, Parinyawatr Dhinnabutra, Charoenchai Ridtirud, Narong Srihajong, Saksit Chuenchomnakjad

Abstract

This study developed welding molds and investigated the metallurgical behavior of thermite repair welds for R260 grade railway rail surface repair using a Mixture Design approach, together with an economic feasibility analysis in comparison with conventional welding. Mold compressive strength increased significantly with slica sand content (p-value < 0.01), while graphite and water exerted negative effects on strength (p-value < 0.05) and increased porosity through a significant interaction effect. With thermal resistance ranged from 1,430 to 1,570 °C, Runs 1, 2, and 6 provided the best balance of properties, with all models demonstrating high accuracy (R² > 0.90). Mold Type 1 produced rough weld surfaces with slag residue and numerous pores, while Mold Type 2 produced smoother surfaces with minimal porosity and no cracks, neither mold type exhibited macro-level cracking. SEM analysis revealed that the base metal consisted of lamellar pearlite (α + Fe₃C). Mold Type 1 produced coarse pearlite with grain boundary ferrite and significant pore accumulation, whereas Mold Type 2 yielded fine, uniform pearlite with virtually no porosity. EDX analysis indicated micro-segregation in Mold Type 1 welds, suggesting structural non-uniformity and potential stress concentration sites, while Mold Type 2 welds exhibited more uniform elemental distribution, which may promote fine pearlite formation and defect reduction. Economic analysis showed that thermite welding costs 290 THB per joint versus 960 THB for SMAW (Cost Ratio, CR = 3.31; cost savings of 69.8%), and requires only 15–20 minutes compared to 90 minutes (Time Reduction Ratio, TRR = 4.5), suggesting promising economic feasibility under the conditions evaluated. The hardness test results showed that Mold Type 2 provided uniform hardness values, with HAZ hardness ranging from 360–410 HV and weld zone hardness ranging from 320–360 HV. These results were consistent with the SEM and EDX analyses, which revealed a fine pearlitic microstructure and homogeneous elemental distribution, indicating that Mold Type 2 was more suitable for railway rail surface repair than Mold Type 1.

Keywords

References

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DOI: 10.14416/j.asep.2026.07.011

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