New low carbon structural steels hardened by aging

Conclusions

• 1. Nickel steels (9–20% Ni) containing Al, Ti, or Mo together with Co are susceptible to aging and considerable hardening during a short period of tempering at 400–550°C (maximum hardening occurs at about 500°C).

• 2. The hardening of steels containing 9% Ni is accompanied by a drop of plasticity and ductility. In high-nickel steels (18–20% Ni) the plasticity and ductility do not decrease so much: δ=10–12%; ψ=∼60%; a_k=5.0–6.0 kgm/cm² after a strength of δ_b=150–170 kg/mm² is reached, depending on the combination of the alloyed elements.

• 3. Sulfur and phosphorus sharply decrease the plasticity and ductility and the impact strength of steels containing 18–20% Ni with martensite which can be aged, and therefore the amounts of these impurities should be strictly limited to less than 0.010% of each.

• 4. High-nickel steels of both types with martensite which can be aged are characterized by a high resistance to brittle fracture; these steels are not susceptible to brittleness due to tempering, and are very little sensitive to cuts; they are hardenable in air to a depth of 200 mm.

• 5. Hardened steels with martensite which can be aged have a high fatigue resistance in both smooth and notched samples (70–72 and 28–30 kg/mm² respectively).