CHARACTERIZATION OF CHROMIUM BEARING SURFACE ALLOYS PRODUCED BY LASERALLOYING ON LOW-CARBON STEEL SUBSTRATES

High-chromium ferritic alloys were produced on mild steel substrates b y laser surface alloying. For this, chromium-plated mild steel samples were treated with a pulsed Nd:YAG laser (300 W maximum power) by vary ing the average power level from 21.6 W to 30.0 W. The chromium conten t of the surface alloys was in the range of 3.0-27.0 wt%, with fairly uniform depth of alloying. Microscopy showed very fine austenite needl es within elongated/equiaxed ferrite grains in the laser-alloyed zone (LAZ). X-ray diffraction indicated several peaks, which were identifie d as being from ferrite, austenite, (CrFe)(7)C-3 and Cr23C6. Microhard ness was higher in the LAZ than in substrate and varied widely dependi ng on the chromium content. Anodic potentiostatic polarization studies in deaerated 0.1 M Na2SO4 solution showed improvement in corrosion re sistance over mild steel by several orders of magnitude. Increasing ch romium content in the LAZ caused shifting of the open-circuit potentia l towards the more noble side and reduced the critical current density for passivation as well as the current density in the passive range.