The maximum value and the rate of rise of the internal plastic deformations (that the metal can withstand without destruction in the process of welding) have been accepted as the evaluation criterion of the weld metal resistance to the formation of hot cracks.
The tests are conducted as follows. A bead is deposited into the sample’s groove (Fig. 1) with the use of the tested welding materials. By means of the Ǿ22 mm holes, the sample is secured inside the testing machine’ grip and can be stretched while being welded along an axis with a specified speed A, in mm/min.
The sample’s stretching does not start simultaneously with the arc initiation, but at the moment when the arc passes the medium cross-section where the Ǿ7 mm holes have been perforated that serve as the deformation raisers. The presence of the raisers causes bending of individual sample’s arms. The gap between the arms grows, which results in the appearance of the weld metal transverse tension, along with the axial one. This allows approximating the test conditions to the deformation pattern that appears in the weld in real life conditions while the welding is performed.
If, at a known traverse speed of the testing machine grip’ movement within the brittleness temperature range, the weld metal has been destroyed and a crack has appeared, the further sample’s deformation will be instrumental in revealing this crack up to the distinctly observable dimensions. When the hot cracks are absent, the weld metal is deformed plastically until the end of the test. Thus, by changing the speed (rate) of the grip’s movement during different tests (all other conditions being constant), it is possible to find the sample’s critical extension rate which, when exceeded, causes the appearance of the weld metal hot cracks. It is this critical rate Acr that has been accepted as the criterion of the weld metal resistance to the hot cracks appearance during welding; i.e. it is the measure of its weld strength.