การเชื่อมซ่อมรางรถไฟ

Abstract

The rail steel is the main equipment for the railway. When the surface of rail is worn, the welding repair was performed to prolong rail service life and to reduce cost for new rail replacement. The objective of this research is to study welding repair of the top surface in rail steel grade 900A. The Shielded Metal Arc Welding (SMAW) and Flux Cored Arc Welding (FCAW) Process were conducted with the various electrode which give similar hardness to this rail steel. The ten welding conditions were investigated with three layers deposition. The SMAW process consisted of six welding conditions using different types of electrodes (type A, B and C) and welding current (140 A and 180 A). Four different welding conditions of FCAW process applied the electrode type D with different welding currents (200 A and 250 A) and shielding gases (100% CO2 and 80% Ar mixed with 20% CO2). The results showed that invisible defect was observed in Weld Metal (WM) and Heat Affected Zone (HAZ) of all weldments. The microstructure of Base Metal (BM) revealed pearlite structure (Hardness 282.3 HB and Toughness 8 J). The HAZ mostly presented bainite structure. The weld metal of both processes largely also displayed bainite structure (Hardness 289.1 HB to 356.1 HB). The high hardness of weld metal resulted from high alloys in weld metal. The SMAW results indicated that using electrode type C and welding current 140 A exhibited the good condition due to the high toughness (15 J) and the weld metal hardness (315.7 HB) that meets the criteria of EN 15594 standard. The FCAW results revealed that applying electrode type D with welding current 200 A and 100% CO2 shielding gas was the best condition. This is because of the highest toughness (32 J) and also the weld metal hardness (290.2 HB) according to the acceptance criteria of EN 15594 standard.