I know there is soft steel and sturdier steel they use in products. The sturdier often used for equipment that requires more durability when in operation.
harder steel has a higher carbon and chromium content
It kind of depends on the application. It can be anywhere from simple to very difficult depending on what exactly you are talking about. Hardening a small piece of carbon tool steel for a chisel or punch consists of simply heating it till its red hot and then quenching it in water. This is done after the tool is formed. Hardening also means making the steel brittle, so it must be tempered after hardening to make it hard and strong. Hardening large or huge pieces like that used for equipment is done at the foundry, where they have equipment to do such a job.
Some steel won't 'harden' very much to begin with. Mild steel found commonly around the shop/farm/house has few alloys other than carbon, and may not get the desired hardness no matter what you do. A quick test to see what type you have (mild steel vs. alloy) is to touch it to a grinding wheel.
