Laser and laser-microplasma alloying of surface of 38KhN3MFA steel specimens

Abstract

Considered are the technologies of laser and laser-microplasma alloying of surface layers of 38KhN3MFA structural steel specimens with introduction of powder filler materials based on tungsten and chromium carbide, promoting increase of physical-chemical properties of the parts, manufactured from these steels. Structural transformations, concentration variations and reasons of crack formation in treated surface layers were investigated at different modes of alloying using the methods of light microscopy and analytic scanning electron microscopy. It is shown that susceptibility to crack formation in laser and laser-microplasma alloying of specimens of 38KhN3MFA steel is caused, first of all, by structural (size of crystalline particles, coefficient of their shape) and concentration variations, related with redistribution of the elements, in particular, chromium, that results in formation of grain boundary concentration gradients. Absence of microcracks in a fusion zone at laser-microplasma method of alloying allows making a conclusion about perspective of application of this method for surface treatment of parts, manufactured from 38KhN3MFA steel. 6 Ref., 9 Figures.

Effect of technological parameters of laser and laser-plasma alloying on properties of 38KhN3MFA steel layers

“…Experimental information on structure-phase condition of alloyed layers of structural steel 38KhN3MFA (surface of circular specimens 187 × 125 × 30 mm) and its changes was received for conditions of laser and laser-plasma alloying [6] using mechanical mixture of powders of 0-40 μm fraction of the following composition, wt.%: 46(WC-W 2 C) + 46Cr + 4Al + 4Si (laser alloying) and 48(WC-W 2 C) + 48Cr + 4Al (laser-plasma alloying). Following modes of treatment were used at that: power P = 3.5-4.4 kW; alloying speed v = 400-750 mm/min at radiation defocusing ΔF = +(30-45) mm at laser alloying method.…”

“…However, if cracks are observed not only in alloyed layer, but also in fusion zone and base metal under conditions of laser treatment, then areas of crack propagation are significantly reduced under laser-plasma alloying. No cracks are found in fusion zone and, moreover, in base metal [6]. More detailed parallel investigations were carried out using specimens produced at optimum technological modes (absence of cracks or their minimum quantity) and at deviations from optimum mode (conditions of formation of significant quantity of cracks) for detection of reasons of crack formation appearing under specific technological modes of surface treatment.…”