Effect of Laser Hardening on the Properties of Pm Steels

Abstract

The article deals with the influence of laser beams, which when acting on materials affect their surface. Depending on the intensity of exposure and the speed of displacement of the beam, due to the heating of the material and the subsequent cooling, there occurs the change in the pattern of the surface and of course to a change in the properties in the volume that was exposed to the temperature changes. For the tests the sintered material based on iron powder type Astaloy CrL and CrM containing 0.7% C was used. Results showed that by the appropriate combination of laser parameters it was be possible to obtain the same structures as by using the technology of "sinterhardening". Compared to sintered state, the hardness of the surface of a material CrL +0.7% C values increased from 248 to 911 -1000 and at material CrM +0.7% C values from 450 to 1043 -1100 HV 0.05, depending on the velocity of displacement of the beam. The same is true for the values of microhardness. Hardness values reflect the structural changes that occur in the material due to rapid heating and subsequent rapid cooling. The first tests of this technology demonstrated its high variability and the potentials of replacing classical procedures.Keywords: laser hardening, sintered material, structure, hardness IntroductionLaser hardening is one of the new technologies, which is currently widely used in the manufacture of machine parts. The principle of laser quenching consists in the rapid heating of the material surface by laser, short holding time at temperature followed by cooling, heat dissipation due to thermal conductivity of the material. A significant advantage of the heat treatment is its speed, quality and especially stable reproducibility. In addition, it provides low thermal load to the ambient material, minimum distortions, low surface oxidation and prevents formation of surface cracks. It is also possible to arrange for local hardening only at the desired location, to control the depth of hardening and the resulting hardness. The temperature is in many cases controlled on-line by a pyrometer directly integrated in the optics. Typical applications include local hardening of molds, tools, gears and racks, guide surfaces, parts of transmissions, shafts, cams and turbine blades and vanes [1][2][3][4][5]. Nowadays, when in the engineering practice, powder metallurgy product are increasingly promoted, knowing the possibilities of using this type of heat treatment at this type steels is quite real. In the actual powder metallurgy practice in connection with the development of steels for highly stressed components, such alloyed materials has been introduced, which following heat treatment by hardening are able to achieve the desired mechanical properties. In addition to conventional quenching, by some suitably alloyed materials, there are currently method in use

Rolling Contact Fatigue of Sintered Steels After Plasma Nitriding

“…The CrM material with 0.3 % C has bainitic structure. All structures are described in our previous work [5][6][7][8][9][10] and correspond to the given chemical composition and to the rate of cooling after sintering (~0.3 K/sec). It is in agreement with observation in literature and with CCT diagram for this type of steels as well [11,12].…”

Laser hardening of steel sintered parts

“…Laser hardening has been conducted using a straight line passing through one diameter of the sample surface. Based on previous results [5][6][7], laser hardening parameters have been chosen as shown in Table I. The laser hardening system is operated in temperature control, hence source power is variable throughout the treatment.…”

“…Hardening of P/M steels by fast laser heating and selfcooling has already been tested successfully by Rowshan, [5], on nearly eutectoidic plain alloy, by Rodziňác et al, [6], on high carbon Cr-alloyed grades, with quenching in a protective argon gas streaming at 15 l/min., and by Bocchini et al, [7][8] on homogeneous or not homogeneous materials, [7][8][9], based on fully Cr-prealloyed materials or on diffusion-bonded powders. Such works all confirm the suitability of application of laser-processing to P/M steel hardenability.…”

Applying “Spark Plasma Sintering” Technology to Enhance the Resistance to Contact Fatigue of Sintered Steel Based on Astaloy CRL

“…At a later stage we used such kinds of technologies which affected only the surface layers critical in terms of contact fatigue destruction. Here, for example, belongs the technology of laser hardening, or methods of applying hard thin coatings such as TiCN type or DLC type respectively to the surface layers [4][5][6]. In all the cases they did improve resistance to contact fatigue destruction.…”