Fundamental Investigations on Solidification Crack Susceptibility for Weld Metals with Trans-Varestraint Test

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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-onplate welding for various constructional materials of carbon steels including sulphur and phosphorus added submerged arc weld metals, 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 a new index, the critical strain rate for temperature drop (CST), which reasonably evaluates the solidification crack susceptibility of material during welding. The main conclusions which have been obtained from this investigation are as follows : (1) Sulphur gives a strong deteimental effect on the susceptibility of solidification cracking of carbon steel in comparison with carbon and phosphorus. (2) The properties of ductility curve in the brittleness range are almost the same regardless of welding variables as far as the same material is concerned. (3) In the weld metals of four kinds of austenitic stainless steel, the crack susceptibility decreased in order of AISI 310, 316, 321 and 304. (4) In the weld metals of three kinds of aluminum alloys, the crack susceptibility decreased in order of 5083, 2024 and 1050. (5) The temperature difference in the brittleness range for cracking is almost in proportion to the nominalsolidifica tion temperature difference of the alloy but is not always in inverse proportion to the minimum augmented-strain required to cause cracking. Therefore the CST in which the properties of the brittleness range are taken into consideration is the most reasonable index for the evaluation of the solidification crack susceptibility.

Fundamental Investigations on Solidification Crack Susceptibility for Weld Metals with Trans-Varestraint Test

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