High-carbon Machinery Steel





The carbon content of this steel is above 30 points and is hardly

ever above 60 points or 0.60 per cent. Annealing such steel is

generally in quantity production and does not require the care that

the other steels need because it is very largely a much cheaper

product and a great deal of material is generally removed from

the outside surface.



The purpose for which this steel is annealed is a deciding factor

as to what heat to give it. If it is for machineability only, the

steel requires to be brought up slowly to just below the critical and

then slowly cooled in the furnace or ash pit. It must be thoroughly

covered so that there will be no access of cool air. If the annealing

is to increase ductility to the maximum extent it should be slowly

heated to slightly over the upper critical temperature and kept at

this heat for a length of time necessary for a thorough penetration

to the core, after which it can be cooled to about 1,200 deg.F., then

reheated to about 1,360 deg.F., when it can be removed and put in an

ash pit or covered with lime. If the annealing is just to relieve

strains, slow heating is not necessary, but the steel must be brought

up to a temperature not much less than a forging or rolling heat

and gradually cooled. Covering in this case is only necessary in

steel of a carbon content of more than 40 points.





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