レール鋼のＨＡＺ液化割れ発生条件と割れ感受性 レールの高炭素溶融溶接技術の研究 （第４報）

Abstract

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.