THE INFLUENCE OF LASER-SURFACE MELTING ON THE RESISTANCE OF AISI-4135LOW-ALLOY STEEL TO HYDROGEN-INDUCED BRITTLE-FRACTURE

Flat and cylindrical heat-treated AISI 4135 low alloy steel specimens were surface treated using power levels of 50, 100 and 200 W. The resu lts of hydrogen permeation and slow strain rate tension (SSRT) tests s how the following. (1) Laser surface treatment of AISI 4135 low alloy steel results in a reduction in the hydrogen absorption kinetics as me asured by the permeation test: and also an improved resistance to hydr ogen-induced fracture in the SSRT test under galvanostatic charging co nditions. (2) The degree of effectiveness in reducing the hydrogen abs orption rate is shown to occur at all power levels, and is greatest at the 50 W level. (3) A clear qualitative relationship is described bet ween the hydrogen absorption rate and the time to failure in the SSRT test. This relation was even more striking in terms of the fractograph ic detail of the fracture face. (4) A possible explanation for the red uced hydrogen absorption as a result of low power laser surface meltin g treatment is the influence of the rapidly quenched metal surface on the steady state degree of hydrogen adatom coverage or the absorption kinetic rate constant or both. (5) Reverse membrane permeation experim ents indicated that the effect of laser surface melting on the permeat ion flux at constant charging current was not due to barriers in the m etal which alter the hydrogen flux gradient across the membrane.