Process for making a steel part, characterized in that: - a half-product is prepared, having the following composition: * 0.30% < C ≤ 0.46%; * 1 % ≤ Mn ≤ 2%; * 1 % ≤ Cr ≤ 1.5%; * 2.3% ≤ Mn + Cr ≤ 3% * traces ≤ Si ≤ 1.5%; * traces ≤ Ni ≤ 2%, preferably traces < Ni ≤ 0.5%; * 0.04% ≤ Mo ≤ 0.50%, preferably 0.04% ≤ Mo ≤ 0.25%; * traces ≤ Cu ≤ 0.5%; * 0.005 ≤ Ti + Nb ≤ 0.06%; * traces ≤ V ≤ 0.3%; * 0.001 % ≤ Al ≤ 0.1 %; * traces ≤ B ≤ 0.01 %, preferably 0.0005% ≤ B ≤ 0.01 %; * traces ≤ S ≤ 0.1 %, preferably 0.002% ≤ S ≤ 0.1 %%; * traces ≤ N ≤ 200 ppm; * traces ≤ P ≤ 0.020%; * traces ≤ O ≤ 35 ppm; the remaining elements being Fe and impurities resulting from the steelmaking process; * with Ms = 561 - (474 x C%) - (33 x Mn%) - (17 x Cr%) - (21 x Mo%) - (17 x Ni%) °C ≤ 330 °C; - this half product is hot-formed at 1100-1300 °C by rolling or forging; - it undergoes an isothermal bainitic quench at a temperature Tb in the bainitic range, with a duration sufficient so as to give it a bainitic structure with less than 20% of martensite and/or pearlite and/or ferrite; Steel part made according to this process.
The invention relates to steel for manufacturing carburized steel parts, characterized in that the composition thereof is: 0.1 wt % ≤ C ≤ 0.15 wt %; 0.8 wt % ≤ Mn ≤ 2 wt %; 1 wt % ≤ Cr ≤ 2.5 wt %; 0.2 wt % ≤ Mo ≤ 0.6 wt %; trace elements ≤ Si ≤ 0.35 wt %; trace elements ≤ Ni ≤ 0.7 wt %; trace elements ≤ B ≤ 0.005 wt %; trace elements ≤ Ti ≤ 0.1 wt %; trace elements ≤ N ≤ 0.01 wt % if 0.0005 wt % (5ppm) ≤ B ≤ 0.005 wt %, and trace elements ≤ N ≤ 0.02 wt % if trace elements ≤ B ≤ 0.0005 wt % (5ppm); - traces ≤ Al ≤ 0.1 wt %; trace elements ≤ V ≤ 0.3 wt %; trace elements ≤ P ≤ 0.025 wt %; trace elements ≤ Cu ≤ 1 wt %, preferably < 0.6 wt %; and trace elements ≤ S ≤ 0.1 wt %, the remainder being iron and impurities resulting from production. The invention also relates to a carburized steel part produced with said steel, and to the method for manufacturing same.
Mechanical part made of steel having high properties and process for manufacturing same. Mechanical part made of steel having high properties, characterized in that its composition, in percentages by weight, is: 0.05% ≤ C ≤ 0.25%; 1.2% ≤ Mn ≤ 2%; 1% ≤ Cr ≤ 2.5%; (830 - 270 C% - 90 Mn% - 70 Cr%) ≤ 560; traces ≤ Si ≤ 1.5%; traces ≤ Ni ≤ 1%; traces ≤ Mo ≤ 0.5%; traces ≤ Cu ≤ 1%; traces ≤ V ≤ 0.3%; traces ≤ Al ≤ 0.1%; traces ≤ B ≤ 0.005%; traces ≤ Ti ≤ 0.03% traces ≤ Nb ≤ 0.06%; traces ≤ S ≤ 0.1%; traces ≤ Ca ≤ 0.006%; traces ≤ Te ≤ 0.03%; traces ≤ Se ≤ 0.05%; traces ≤ Bi ≤ 0.05%; traces ≤ Pb ≤ 0.1%; the balance being iron and impurities resulting from the smelting, and in that its structure is bainitic and contains at most 20% in total of martensite and/or proeutectoid fernite and/or perlite. Process for manufacturing a mechanical part having this composition.
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