Trans-Varestraint試験法による溶接金属の凝固割れ感受性の研究(1)

Abstract

In fusion welding of constructional ferrous and non-ferrous materials solidification cracking frequently occurs in the weld metal when a great deal of distortion and shrinkage takes place in the parent and weld metals due to a local rapid weld heat cycle. The occurrence of this solidification cracking, which is a kind of hot cracking, often gives rise to serious problems for some constructional materials from a view-point of weldability.Meanwhile those constructional materials including commercially pure metals have a brittleness temperature range during solidification whose ductility is very low to cracking.The properties in the solidification brittleness range such as temperature difference, minimum ductility and shape of ductility curve depend upon the kind and amount of impurities or alloying elements in the materials. Increasing the temperature interval and decreasing the minimum ductility are considered to increase the susceptibility of solidification cracking for the material in general.Unfortunately, however, there are few reports, so far, concerning the properties in the solidification brittleness range during welding of the constructional materials in spite of their close relation to solidification cracking.In this report authors have firstly investigated the nominal susceptibility of solidification cracking during TIG arc bead-on-plate welding for various constructional materials of carbon steels, low alloy high tensile strength steels, austenitic stainless steels, aluminum and aluminum alloys and brass, using the Trans-Varestraint Tester which was modified from the original Varestraint. Secondly, utilizing the relationship between the maximum crack length occurring in the center of weld metal with the Trans-Varestraint Test and the temperature distribution during welding which was actually measured, the properties of the solidification brittleness range have been investigated for the weld metals of the materials.Lastly, authors have proposed new indices, the critical strain rate for temperature drop (CST), which reasonably evaluates the solidification crack susceptibility of material during welding and the critical strain rate to time (CSS), which is easy to measured and is substituted for (CST) under a limited condition.