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发表于 2009-6-3 13:54:07
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The structure of the 40Cr steel in the annealed state constitutes a ferrite--pearlite mixture having a microhardness 2.1 GPa. After volume heat treatment, the 40Cr steel has a bainite structure with individual martensitic sections.Its microhardness reaches then 5.4 GPa. In the laser-action region, a martensite--troostite structure is formed on the annealed 40Cr steel. Regions of metastable austenite were additionally observed. With increase of the distance from the surface, the fraction of the martensite decreases and that of the troostite increases. Laser treatment by a round spot ensures a 650 微米 maximum hardening zone. The depth of the hardened zone formed by a strip-shaped beam does not exceed 450 微米. These values, as well as the values of the microhardness, are governed by the attained surface temperature. |
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