The effect of nitrogen and vanadium on hardenability of medium carbon 0.4 %C and 1.8 %Cr steel

Purpose: To investigate the effect of V and N on hardenability of steel containing 0.4 % C and 1.8 % Cr. Design/methodology/approach: Four laboratory melts with different N and V contents were used. Hardenability of steel was investigated using standard Jominy test and Grossmann analytical method. The effect of calculated undissolved carbonitride V(C,N) content on austenite grain size was investigated. Findings: Nitrogen addition without microalloying elements increased the austenite grain size. Very high hardenability was obtained in steel containing 0.004 %N and 0.08 %V at 870°C. Addition of 0.08 %V at elevated nitrogen content significantly decreased the grain size and at 870°C increased the hardenability of steel. Practical implications: Investigated steel showed very high hardenability with ideal critical diameter DiJ approximately 200 mm, at appropriate austenitizing temperature. Higher nitrogen content in steel with vanadium addition retards austenite grain growth in broad austenitizing temperature range. Originality/value: Results of investigations provide valuable information on the effect of vanadium and nitrogen content on the hardenability of quenched and tempered steel with 1.8 % Cr. Thermodynamic calculations enable to select the optimum austenitizing temperature range.