Molybdenum uses

Metallurgy of Mo in alloy steel & iron

Alloying elements such as chromium, molybdenum, tungsten, etc. are added to carbon steel to improve properties such as hardness, strength and toughness.

The classic methods of strengthening low alloy steels are

solution hardening
quenching and tempering
precipitation hardening
controlled rolling

Molybdenum is an effective strengthener in all cases.

The large majority of low alloy steels are quenched and tempered – Q+T.

From unalloyed Mild Steel to Low Alloy Steel

Literature

Phase Transformation and Hardenability of Medium Carbon Alloy Steels by W.W. Cias : Climax Molybdenum Company, 1972.
Steels; Microstructures and Properties by R.W.K. Honeycombe
Functions of the Alloying Elements in Steel by E.C. Bain, ASM 1939
Molybdenum’s Place in the Pressure Vessel Field. By R G Dunn, G F Whiteley, W Fairhurst, Climax Molybdenum Company 1970
Steel Deterioration in Hydrogen - What API-sponsored Research has explained. Preprint 63-67, API (May 16, 1967)