Acier ternaire faiblement allie au cr, mo ,v : caracterisation et evolution des carbures au cours de differents traitements thermiques

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The structural evolutions of a ternary high mechanical resistant steel (nuance 40CDV13) have been approached by the characterization of its receipt state. In this state the studied steel presents a structure composed of ferrite, pearlite and bainite. The primary carbides initially present in this state are essentially M23C6, M7C3, MC and Fe3C. The dissolution of the cementite and the M23C6-type carbide, in the austenitic matrix, is observed at 950 °C, the one of the M7C3 carbide intervenes from 1050 °C. The carbides of MC-type dissolve from 1100 °C which is translated by a very important evolution of the austenitic grain size. The precipitation of secondary carbides during four different continuous coolings, after a 10 minute austenitization to 950°C, has been followed by X-ray diffraction on residues extracted from the samples by an electrolytic process at the end of each cooling. This precipitation relates to cementite and M23C6 carbide type. For a cooling speed of Vr = 75 °C/h ,there is prevalent precipitation of the cementite which is attenuate thereafter, as the cooling rate become lower, giving rise to the precipitation of carbide M23C6 For Vr = 25 °C/h , the precipitation of cementite considerably has decreased and only primary MC and secondary M23C6 carbides remained and attest by the XRD diffraction