I manufacture high carbon small components all the time.
A Brief concept. I use traditional 100's of years old methods.
High carbon steel we take to red/yellow heat and absolutely vertically, (or else distortion occurs), plunge into salt water with a thick covering of oil, (depends on the size of component). The steel is now glass hard and would shatter if dropped on something hard. If this process is done to quickly then fractures in the steel can occur.
We now anneal the hardened steel, depending on the carbon content/quality of steel, but most steels will be very hard but not shatter at a deep BLUE colour. Making springs the light bluing colour must be consistent.
BLUEING we call it, and yes there are many types of Blue colour, can take place in a tray of brass filings, which is heated underneath until a constant blue colour is seen that is even and throughout the complete component. Take your time as the metal bluing colour can change very quickly.
Welded components can be done. But the welding steels will need to be of a high carbon steel. After welding the whole component will require annealing/Blueing to relive any stress that have occurred so the whole component is now neutral. Now take up to cherry red and gently harden by plunging vertically a little slower and a thicker coating of oil. Now everything is about the same hardness and stresses, now BLUE it evenly, hay presto the component is neutrally hardened and tempered and ready for use. But check all the component with the file test. Watch out for distortion.
Hardness testing... I use an old but sharp cut metal file, truly hard the file will just skate over the metal, blued the file will cut but its hard going, file cuts easily and bites, the metal is still soft. (when I purchase bearings, to make sure they are real hardened and tempered shells I use the file test, truly amazing to see how many fakes there are.)
There are many many variables with heat treatment of metals, I am just used to it and 40 years of experience.
