Abstract
1. An optimum combination of mechanical properties for the VNL-3 steel grade composition is achieved by a double heat treatment: heating to 1100°C (1 h) with air cooling, annealing at 600°C for 1/2 h plus quenching from 970°C, cold treatment at −50 to −70°C and annealing at 450°C. This heat treatment system can be recommended for obtaining high strength, although in order to secure better ductility, a strengthening heat treatment is carried out as follows: quenching from 970°C, annealing at 450°C and cold treatment at −50 to −70°C. 2. The heating temperature for the second heat-treatment stage is increased to 1100°C in order to correct casting defects (carburization). This yields σB ≥ 1000 N/mm2, σ≥18%, and a1=90–110 J/cm2. 3. Heating of the VNL-3 steel should be carried out in a shielding atmosphere or in a vacuum. The component surface can also be protected by applying the EVT-10 enamel.
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