Assessment of Hot Cracking Initiation by Laboratory Test Procedures and FEM-Simulation Associated Experimental Measurements During Welding of Large Weld Components

Abstract

The effects of material, welding procedure and weldment structure are used in the sense of joinability to analyse the complex problem of centreline solidification crack initiation during welding processing. The hot cracking test procedures with externally loaded specimen, based on the theories of Prochorov and Matsuda (MISO-technique, PVR-test and Varestraint-/Transvarestraint-test), are only partly true for the assessment of centreline solidification crack initiation during welding. The measurable condition and quantifying criteria of the tests vary from one to the next. They require a complicated calculation of the theoretical function “strain-rate”. A special measuring technique was developed, tried and tested to estimate the initiation of solidification crack in flat and large components. The combination of measurement and calculation was applied to put the reliability of new derived crack minimizing methods to the test with help of the Finite Element Analysis(FEA)simulation. It takes into account the speed of cross displacement during welding processing, effected by weld component dimension and weldment assembly. The critical speed of displacement during welding processing determines the crack criterion for that moment when the local initiation of a centreline solidification crack is prevented. That is, if no hot crack is diagnosed after the welding. This is the case when the speed of displacement, released by fusion in front of the weld pool and thermal expansion during the welding process, is in equilibrium with the speed of displacement within the brittleness temperature range during solidification behind the weld pool. The centreline solidification crack initiation is assessable by comparison of the critical speed of cross displacement in the welded material (determined by experiment) to the local speed of cross displacement in the weldment (calculation by FEA-simulation). An assessment diagram for centreline solidification crack initiation during one-side welding was arrived at the multitude of results within displacement measurement during welding processing in flat and large components. It was utilized for a predictive assessment of solidification crack initiation of weldment depending on component dimension and welding procedures.