The effects of substituting W for Mo in a quenched-and-tempered martensitic AISI4340 steel was investigated. Tungsten contents were varied from 0.3% to 0.6%, and molybdenum contents employed were 0.1% and 0.25% (standard 4340 steel). The tungsten containing alloys displayed 35-75% increase in room temperature impact toughness under 600℃ tempered condition over the standard molybdenum containing alloy.
However, the yield and tensile strength did not change significantly by substituting W for Mo.
The Mechanical properties does not improve greatly with increasing tungsten content above 0.4%. Therefore it is recommended that 0.3-0.4% W or 0.15% Mo - 0.15% W is suitable in optimizing strength and toughness in 4340 steel.
