| 摘要 |
<p>Press hardening of steel, comprises cold pre-forming a steel sheet made of a hardenable steel alloy, transforming in a mold, which has the contour of the preformed component, heating to perform a complete austenitization, and cooling at a speed higher than the critical hardening speed, such that a quenching of the preformed element takes place. A press hardness number is determined e.g. for adjusting the suitable steel alloy to known plant geometry, where the press hardness number is equal to the cooling rate in the mold/theoretical press cooling rate. Press hardening of steel, comprises either: cold pre-forming a steel sheet made of a hardenable steel alloy, transforming in a mold, which has the contour of the preformed component, heating to perform a complete austenitization, and cooling at a speed higher than the critical hardening speed, such that a quenching of the preformed element takes place; or heating a sheet of a steel with a composition, which allows a press hardening, to a temperature above the austenitizing temperature, hot molding in a mold, cooling at a speed which is higher than the critical hardening speed, such that hardening takes place, where the austenitic structure is transformed into a martensitic structure optionally with residual austenite. A press hardness number is determined for: adjusting the suitable steel alloy to known plant geometry, and the cooling rate achieved during operation in the mold; or adjusting a required mold to a given grade of steel, where the press hardness number is equal to the cooling rate in the mold/theoretical press cooling rate. The cooling rate in the mold is predetermined for a required thickness. The determination of the theoretical press cooling rate for steel material, which contain greater than 5 ppm boron dissolved in the starting material is represented by: theoretical press cooling rate is equal to 1750/(28.5% carbon + 3.5% silicon + 2.3% manganese - 2% aluminum + 4% chromium + 3% nickel + 25% molybdenum - 20% niobium - 6.3) 2>.7. The determination of the theoretical press cooling rate for steel material, which contain less than 5 ppm boron dissolved in the starting material is represented by: 2750/(28.5% carbon + 3.5% silicon + 2.3% manganese - 2% aluminum + 4% chromium + 3% nickel + 25% molybdenum - 20% niobium - 7) 1>.8, where: when press hardness number is less than 1 the complete hardening by martensite formation does not takes place; when press hardness number is equal to 1 an undeformed or preformed sheet is cured via an indirect process; and when press hardness number is less than 1, in addition to the indirect process, the sheet is thermoformed or increased security against plastic deformation during hardening takes place.</p> |
