A little searching of "Ordnance Steels" with Google will get you the following:
1137 Carbon steel
4140 Chrome moly
8620
416R stainless.
All are heat treated after machine work to relieve stresses, and annealed - meaning tempered dead soft. That is because of the heat build up that would draw the temper out anyway - no sense having blowups, make it dead soft and as strong in cross section as required.
Unlike knife steels that are drawn to RC 54-62, gun steels are not. Ever.
Hi performance barrels seem to use the higher graphite and carbon materials to resist wear, cheap barrels use a low grade high phosphorous and lead alloyed steel because it reduces machining costs. Strength is an afterthought.
If you are buying a barrel, a quality maker should be happy to tell you exactly what the material is. After all, he's paying the insurance tab, and they don't want to shell out on a liability suit cutting corners. So, buy direct, or a recognized name in barrel making circles.
Polymer is a catch all term - but the most used is fiberglass reinforced nylon type 66. The Remington Nylon 66 started this off long ago, in the early '60s. Glass content affects the strength considerably, low glass increases flexibility and deformation, high glass increases strength with a corresponding increase in molding costs due to the higher pressures. You can quickly tell the difference in comparing a cheap import FRN knife handle to a high quality designer from a reputable maker. One's greasy and flexible, the other has a dry, stiff feel similar to G10 fiberglass.
When it comes down to it, guns by their very nature are much simpler metalurgically, and have simple stress relief treatments. Knife steels are completely the opposite, exotic high alloys with expensive heat treats and cryogenic tempering.
Which make a S30V Bos heat treated Titanium framelock a lot more sophisticated than a dumb ol' 1911.