What is the hardness of 40Cr alloy tube?

In annealed condition, hardness ≤207HBS.
Elastic modulus of 40Cr alloy tube: elastic modulus E (20℃) /MPa 200000～211700, shear modulus G (20℃) 80800
Quenching process of 40Cr alloy tube
40Cr alloy tube is quenched at 850℃ and oil-cooled; tempered at 520℃, water-cooled and oil-cooled. The surface quenching hardness of 40Cr alloy tube is HRC52-60, and the flame quenching can reach HRC48-55.

Nitriding treatment of 40Cr alloy tube
The 40Cr alloy tube is a nitridable steel, and its elements are conducive to nitriding. The 40Cr alloy tube can obtain higher surface hardness after nitriding treatment, and the hardness after nitriding treatment after 40Cr tempering can reach HRA72~78, namely HRC43~55.
Nitrided workpiece process flow:
forging-annealing-roughing-tempering-finishing-stress-relieving-rough grinding-nitriding-finishing or grinding. Because the nitride layer is thin and brittle, it requires a high-strength heart structure. Therefore, it is necessary to first carry out tempering and heat treatment to obtain tempered sorbite and improve the mechanical properties of the core and the quality of the nitrided layer. Soft nitriding is active nitriding, and gas nitriding is more commonly used.