Getting the Strain Under Control: Trans-Varestraint Tests for Hot Cracking Susceptibility

Abstract

A new method for conducting Trans-Varestraint tests for assessing hot cracking susceptibility is proposed. Experiments were carried out, to validate the new method, with an industrial scale rig using tungsten inert gas welding. The hot cracking susceptibility of API-5L X65 and EN3B steel was compared. The results indicated that, by using the new method, the strain applied to the welding bead and consequently to the solidification front was controlled in a repeatable and reliable way. The results also indicated that EN3B has a maximum crack length (a parameter in the test) higher than X65 and it is reached at lower augmented strain thus demonstrating it is more susceptible to hot cracking, while also indicating that there is a capability of predicting the initiation position of hot cracks during welding. By using the method proposed, the capability of setting standardized test procedures for Trans-Varestraint tests is improved. It is recommended that future tests for assessing hot cracking susceptibility should employ the proposed method in order for the results to be comparable and to also study the effect of strain rate in hot cracking of materials.

Effect of weld travel speed on solidification cracking behavior. Part 2: testing conditions and metrics

“…Subsequently crack length criteria were not capable in excessive applied strain conditions to investigate the effect of welding speed on cracking susceptibility. Care must be taken regarding the solidification cracking susceptibility as strains and strain rates applied in the mushy zone during TVT are far exceeding what is needed to initiate solidification cracking [26].…”

“…Two standpoints for relationship between BTR (equals to the ratio CSZ/s with s the welding speed) and SCTR cracking indexes highlighting the effect of welding speed [26].…”

“…These measurements are difficult to perform because they must be performed in-situ and near to the mushy zone. This is important as the strains in the mushy zone can exceed, by several orders of magnitude, the overall applied strain [26]. Of particular interest are the digital image correlation (DIC) methods that enable the contactless measurements of strain fields behind the weld pool [54].…”

“…Because cracking depends on weldment geometry, the crack length metrics may be more comparable if using the ratio of crack lengths on cross-sectional areas [61]. Issues remain in comparing different alloys at the same heat input and manufacturing a testing device that leads to high repeatability of crack length indexes [26].…”

A New Test Method for Evaluation of Solidification Cracking Susceptibility of Stainless Steel during Laser Welding

“…At present, the test methods for evaluating the solidification cracking susceptibility include mainly two categories. One is an external restraint test method, like Varestraint test [ 4 , 5 , 6 ], Sigmajig test [ 7 , 8 ], Rapid tensile test [ 9 , 10 ], etc. The other category is self-restraint test methods, like Houldcroft cracking test [ 11 , 12 ], FISCO hot cracking test [ 13 , 14 ], Circular patch test [ 15 , 16 ], etc.…”