A Study on the Modified Murex Hot-Crack Testing Method (Report 1)

Abstract

An experimental study was made on the hot-crack sensitivites of 5 kinds of rolled steel plates and 7 kinds of coated electrodes by means of "the modified Murex Hot-Crack Testing Method." In this testing method, the crack sensitivity is determined by examining cracks in the test fillet weld bead which has been laid in the groove constructed by two end surfaces of the two test steel plate pieces, one of which being fixed and the other being forced to turn simultaneously with the progress of welding in the opposite direction to the natural cooling contraction of the test fillet bead.
The main results were as follows :
( i ) The hot crack sensitivity became larger as the bending angular speed of test fillet bead became larger (from 30°/34.4 sec to 30°/17.2 sec). The large parts of hot-cracks revealed were oxidised or nonoxidised iceflower-like structures (intergranular crackings in primary dendritic structures).
(ii) The shot-crack sensitivities of test steels as well as electrodes could be determined clearly by this test. The results on hot-crack sensitivities of test materials were analysed statistically.
(iii) It may be said that the modified Murex Hot-Crack Testing Method is a very useful method to test hot-crack sensitivities of steels as well as electrodes.