Physical principles of simulation and optimization of laser-induced surface hardening of steels

Autor: Valerii I Igoshin, Igor Shishkovsky, V A Katulin, I N Zavestovskaya, B I Bertyaev
Rok vydání: 1996
Předmět:
Zdroj: Scopus-Elsevier
ISSN: 1573-8760
1071-2836
DOI: 10.1007/bf02115474
Popis: beam. This paper contains a theoretical analysis of the physical model of processes in laser steel hardening without melting the surface, and on its basis the problem of the proper choice of a l£ser thermohardening regime is discussed. The heat treatment of steels is based on different abilities of the high-temperature ('/-phase) and the lowtemperature (a-phase) modifications of iron to dissolve carbon and alloying elements. The carbon solubility in a-iron is of 0.01%. The upper limit of the carbon solubility in 7-iron is 2%. The constructional steels contain from 0.3 to 0.7% of carbon, while the carbon content in tool steels is from 0.7 to 1.3%. Excess carbon in these steels precipitates as iron carbide, so a homogeneous mixture of ferrite crystals (0.01% solid interstitial solution in a-iron) and plate cementite (iron carbide FeaC) is formed. When a steel with a carbon content, e.g., of 1%, is heated to the temperature of the a-- 7 transformation and then kept for some time at this temperature, all carbon will pass into solution. The state of solid carbon solution in the 7-phase is referred to as austenite. The process will be reversed on cooling, i.e., 7-Fe transforms to a-Fe, whereas the excess carbon precipitates as iron carbide. A different situation arises in the presence of fast cooling. The diffusion of atoms, which is necessary for the crystal lattice to be rearranged and for carbon to precipitate, has no time to occur. At a temperature below 200 °C an extended (tetragonal) crystal lattice is formed like in the a-phase, though it contains an amount of carbon possible only in the 7-phase. This basic component of the hardened steel is ca~ed martensite. The formation of martensite is accompanied by a reduction in the size of the original metal grains to smaller blocks having size
Databáze: OpenAIRE
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