Makoto Okumura

Susceptibility and Occurrence Condition of HAZ Liquation Cracking on Rail Steels. Study on Rail Welding with High-C Welding Materials. (Report 4).

The conventional manual enclosed arc welding process, which has been. employed as a field welding process for rails, has shortcomings that the liquation cracks are likely to occur at the boundaries of coarsened austenite grains in the heat-affected zone.This paper describes the susceptibility of HAZ liquation cracks for rails and the causes of crack incidence. Experiments have been done to define the critical carbon content of weld metal and critical welding condition necessary for avoiding the cracks by employing some electrodes with various carbon content. And also, in order to discuss the crack susceptibility and the crack causes of rail steels comparing to those of general structural steels, the synthetic test has been done to simulate the HAZ liquation cracks.The main experimental results are as follows :(1) The crack incidence increases with decreasing weld metal carbon content when the difference in the carbon content between the weld metal and rail steel is 0.3% or more.The cracks are eliminated when the former difference is less than 0.2%.(2) The cracking tendency increases with increasing electrode diameter and weld current or weld heat input.(3) The liquation crack susceptibility of rail steel is nearly equal to that of plain carbon steel, for which the crack dose not become a subject of discussion in actual welded joint.(4) The main cause of HAZ liquation crack for rail enclosed-arc welding is the considerable difference of liquidous & solidous temperature depended on the difference of carbon content between the weld metal and base metal.

Effect of Welding Conditions on Residual Stress and Bending Fatigue Strength of Rail Enclosed Arc Welded Joint. Study on Rail Welding with High-C Welding Materials (Report 3).

The welding method which provides the welded joint with high performances, especially high bending fatigue strength, at as-welded condition has been studied in consideration of welding residual stress which has an effect on fatigue properties.The results of this study are as follows:(1) The formation of welding residual stress is subjected to three internal stress balances, that are a) the stress balance between the surface and the inside at final welding section followed by the expansion through transformation and the heat contraction, b) the stress balance along the longitudinal direction followed by the heat expansion and contraction of weld metal and HAZ, c) the wholly secondary stress balance followed by the solidification of weld metal and the heat contraction during the welding progress from rail base to rail head.(2) It was found that there is the difference in residual stress between the high C weld and low C-low alloy weld and that the good residual stress distribution of welded joint can be obtained by the combination of both weld metals, and the new welding method has been developed.