Metals and various heavy industrial maintenance materials are basically dumb. There is no consciousness on their part that knows bad heat from intentional thermal processing. It’s all just heat. There is no discernment of difference between machining, grinding, and in-service abrasive wear. Remember that when you are reviewing specs on a new material that has the incredible ability to resist wear in the application, but it is listed as “Free-Machining”. Think about it a bit. If the steel can’t tell good wear from bad wear, or good heat from bad heat, how can that be? What an intelligent piece of steel! It knows exactly what you want and when you want it.
What about a dead hard piece of steel that has been flash tempered to 500bhn at 300F. We are not talking about a high grade rich chemistry tool steel here. More like a good quality 500bhn wear plate. Good quality from a fine mill. How is that going to work in a service temperature that gets up to 500F? What is going to happen to the hardness when you torch cut it or weld it?
These are the differences between “production steels”, and critical service maintenance replacement steels. If you want it to machine easily, you are not interested in the piece lasting a long time in abrasive service. If the steel requires rapid cooling and a low temperature temper to achieve hardness, know that even a very low temperature will begin to soften the material. You can’t have it both ways.
If you are working in customer service for a steel service center, or, if you are requisitioning materials for replacement parts. Remember that steels are dumb. If you want a high speed rotating or reciprocating shaft to last a long time in a very contaminated environment, with lots of particulate matter in the atmosphere, be willing to exercise some precautions and learn how to machine hardened steels like a pro.
Don’t opt for a “Free-Machining” shaft because that is not going to last long in service. Also, if it is Free-Machining, has sulfur been added to obtain that property? If it has, and you are contemplating any welding, be careful. Welding does not like sulfur.
Welding Dead Hard (500bhn) steel strips into place will require familiarity with some cautions and restrictions if you want them to remain hard in service.
Successful processing and installation of the right product for the application will most likely require some experience and talent. Getting material that is the easiest to machine and weld will probably insure poor service life.