The hardness test is one of the most significant tests to determine the “hardening” factor in a welded joint.
The Vickers hardness scale compared to the others (Brinell and Rockwell) has the characteristic of using a very small pyramid shaped diamond-shaped penetrator with preloads used just as small; they range from:
0,3 Kg – 0,5 Kg -1 Kg – 3 Kg – 5 Kg – 10 Kg
The load is maintained on the test piece for 10 to 15 seconds at the end of which the diagonals of the impression left on the test piece are measured by means of an eyepiece with a graduated scale. The smaller the footprint, the higher the hardness value and the higher the hardening effect on the welded joint.
An example of a 15 pt hardness seam on a head-to-head welded joint:
Below is the graph showing the classic trend of the values of a welded joint that has undergone a normal tempering effect: