We used to make steel for spark plugs. Thousands of tons a year. Also used for other end use.
It is a low carbon steel, similar to EN1A spec.
0.1%carbon so at the lowest mild steel spec. It was also a resulphurised steel as rhe sulphur content helped with machining. A bit of extra manganese to combine with the sulphur and help in oxygen control , everything else at low levels. It was not easy to make as whhen you go that low in carbon content in the molten bath of metal the oxygen level shot up and there was a danger of ending up with ingots like Aero bars, full of holes that would self weld inside but those at th3 surface split open to leave a useless finish. When ready to tap the furnace a " block" was put in with so that refinement was stopped for long enough to tap into a ladle. The block was a deoxidiser to "kill" the reaction temporarily. Tapped a5 1600 degC. Rolled to billets and sent to a finishing mill in the Birmingham area where it would be rolled to hexagon shaped feedstock to high speed maching units.
We'd also add lead shot during casting as the lead helped lubricate during high speed machining.
We started with open hearth furnaces and moved to two 150tonne electric arc furnaces. From an art to brute forde!
Great memories of those days.