Properties of doped boiler steel after controlled rolling

Conclusions

• 1. Controlling rolling (t_er=800±20°C) of steels type 20–22K makes it possible to increase short-time (σ_u, σ_0.2) and long-time (σ ¹⁰⁰⁰⁰₄₅₀ ) strength: by 5–15% and 10–15%, respectively, for steel without additives, and by 20–30% and 30–40% for steel doped with vanadium or niobium, with ductility maintained at the level δ≥25% and a₁≥70 J/cm².

• 2. Controlled rolling with controlled subsequent cooling enhances the level of short-time strength of carbon steel by a factor of 1.3–1.5, and of doped steel by a factor of 2.3.5 while the characteristics of ductility are maintained (δ≥14–18%, a₁≥70 J/cm²). The characteristics of long-time strength of steel from ordinary production without additives are 10–20% poorer, and of doped steel 30–40% better than of steel after controlled rolling.

• 3. We suggested a refined algorithm for calculating the cooling regimes of sheet in TMT and from the results structural phase diagrams of carbon boiler steel 20K and steel type 20K doped with vanadium (0.06%) or niobium (0.05%) were plotted. According to the diagrams we can evaluate the distribution of structures over the section of sheet with different thickness (h=5–40 mm), both with cooling in air and in accelerated cooling (cooling in water for 2.5 to 20 sec).