Been asked to make 50 simple components that need a hard surface. I'm having problems finding a source of case hardening steel. I'll need about 3 metres of 1/4" or 8 mm round bar.

Either 130M15 (EN21) or 080M15 (EN32C) would be best but I imagine there may be other more readily available steels that take a case without core properties being too badly affected. Only about half the length needs to be hardened and these things need to be quite stiff.

An alternative that might do would be a pre-hard steel equivalent to the American ANSI 4140 pre-hard as RC 35 to 40 ought to be fine for this job.

Worst case fall-back would be linear rail but I'll need to put a thin spiral groove of around 50 tpi, fortunately not critical, along about half of it. Finding a tool up to the job may be a problem. My machines are ex-industry and well up to the task given suitable tooling

Heating and quenching ANSI 4140 at below the critical temperature which is is said to produce a case of around RC 40. As 709M40 (EN19) is essentially the same as ANSI 4140 I guess its possible to do the same. Quenching from 1375° F / 745° C is said to be best. As critical temperature for ANSI 4140 is given as 1575°F / 875°C there seem to be reasonable margin for error but one does wonder if a tempering stage will be needed to ensure that there is no possibility of the core cracking.

Although this would get me to what seems to be an appropriate surface hardness for the job it seems an awful faff unless you are set up for this sort of job. Which I'm not. Case hardening about 3 times a decade is about my speed.

Clive

JohnF, Duncan.

Thanks for the quick response. Looks like 070M20 (EN3) from M-Machine is a good fall back position if I can't find proper case hardening steel.

(Dunno what the last lot of so called EN3 supplied locally actually was but 070M30 it certainly wasn't as only carbide tooling would touch the stuff! 40 ft of grief in 12 mm bar form.)

Given the opportunity I always prefer to have the right thing rather than something which "can" do the job. Most of the time "can" do works just fine but there are always "gotchas" lying in wait for the unwary and inexperienced.

This particular job landed on my doorstep because commercial supplies are what the customer calls "cheap crap" and the good makes don't produce that size and style. Why the commercial supplier produces essentially unhardened crap rather than doing it right is beyond me, hardening isn't exactly expensive in commercial quantities, and the machining is basic.

John, producing a hard case on ANSI 4140 by quenching from below the critical temperature certainly seems to be a known, considered reliable, technique in certain quarters. That sort of below critical temperature quenching will do "something" to the surface hardness of any steel with sufficient carbon to be heat treatable by simple means. Whether the "something" is actually what you expect, or the results even desirable, and whether the results are reliable without doing unpleasant things to the core properties of the material being horses of a completely different colour of course.

Clive