The same catalog states that the frames were heat treated "to a tensile strength over 90 tons per square inch. This is far better than the usual case hardened frame." 90 long tones = 201,600 psi (possibly a bit of marketing hyperbole!)
There is no mention of heat treating the barrels

Edwin Pugsley in a letter to F.W. Olin April 11, 1932
“Both (Model 21) frames were heat treated, then one was case hardened and the other blued. The case hardened frame had a tensile strength of 94,200 psi, an elastic limit of 85,400 psi, and elongation of 2%. The blued frame had a tensile strength of 174,600 psi, an elastic limit of 160,950 psi, (and) an elongation of 12%.”

By the late 1920s AISI 1040 was fairly standard for U.S. maker's double's barrels; including Crescent. Frames were 1020.

Resulfurized AISI 1137 (“gun barrel steel”) & 1144 low alloy carbon steels are commonly used for modern shotgun barrels and are easily machined. 1144 has an industrial standard tensile strength of 108,000. Neither would have the corrosion resistance of 4140.