What are the principal alloy elements of an AISI 4340 steel? How much carbon does it have? Is it hardenable? By what techniques?

The principal elements are Iron, Nickel, Chromium

It has 0.37% to 0.43% Carbon

It is hardenable.

It can be hardened by cold working, annealing, quenching.

Explanation:

A)

The chemical composition of AISI 4340 Steel are as follows:

Iron - - - 95% to 96%

Nickel - - - 1.6% to 2.0%

Chromium - - - 0.7% to 0.9%

Manganese - - - 0.6% to 0.8%

Carbon - - - 0.37% to 0.43%

Molybdenum - - - 0.2% to 0.3%

Silicon - - - 0.15% to 0.30%

Sulfur - - - 0.040%

Phosphorous - - - 0.0350%

So, the principal alloy elements from this composition are Iron, Nickel and Chromium

B)

The carbon content in this alloy is 0.37% to 0.43%

C)

Yes, it can be hardened.

D)

It can be Hardened by Cold Working, Annealing or Quenching.