Influence of modification by vanadium nitrides on the mechanical and physical properties of 25L constructional steel

The effect of use of vanadium nitrides for increasing the mechanical properties of 25L steel occurs in redistribution of the nitrides in the liquid and solid states, and a necessary condition for use of vanadium nitrides is correct choice of the heat-treatment cycle.

The quantity of vanadium nitride additions and the heat-treatment cycle of 25L steel providing the optimum combination of mechanical properties (short-term strength, hardness, plasticity, etc.) at 20°C are 0.05–0.1 wt.% vanadium nitrides, harden from 950–100°C, and temper at 600–650°C.

In the 20–400°C temperature range the short-term strength characteristics of 25L steel modified with vanadium nitrides are higher (σ_t by 17–18% and σ_0.2 by 44–49%) than those of the standard with practically the same characteristics of plasticity δ and ϕ.

The impact strength of the modified 25L steel both at room and at increased (250 and 400°C) temperatures is higher (by an average of 40%) than of the standard. The modulus of elasticity E of the modified steel is an average of 6% higher and the Poisson's ratio μ an average of 10% lower than of the standard. The physical properties of the average coefficient of linear thermal expansion and the corrosion resistance of the modified and standard steels are practically the same.