Non hardening high tensile steel

After last weekends hydro high speed dunking in the lake I require a high tensile steel that will not harden when red hot then quenched suddenly as happened to my EN8 manifold that became brittle and broke when tightened.

I have had this en8 type on for many years with no problems apart from renewing when threads get worn with the higher temperatures now things have changed.

EN36 has been suggested what are other materials that might be suitable that is easily available and possible suppliers of small quantities.

Round bar about 1.25" or flat bar 1.25" x 0.75" will do.

Paul

Hi Paul,

Would titanium be ok for the part, rather than steel?

Regards,
Ed.

EN 8 is only about 0.4% carbon. It shouldn't harden much. However if being red hot means it is exposed to exhaust gasses then carbon monoxide is an excellent carburising agent. That means that any low carbon steel will be a problem.

Titanium would do but is phenomenally expensive. Could you redesign it to cope with lower strength stainless steel? The chromium should prevent hardening.

All the pulse rocket motors tend to be stainless and oh boy do they glow red, might be worth a bash

Don't know about high tensile stainless though, but it does exist

Small quantities are available here, you should be aware there are 3 grades of hardness, 316/80 is the tuff one

Edited By Ady1 on 13/07/2015 22:03:05

4310 chrome moly steel .. you have a pm

Bob

One thing I found when I tried stainless years ago the stainless manifold and the stainless steam line union nut became impossible to unscrew after a run that's why I use dissimilar metals.

The nut is also heated to expand it then tightened onto the manifold I get an extra eighth of a turn from cold.

Also as that manifold is ground with valve grinding paste to the EN24T head I'm a bit concerned about different material expansion rates might cause leakage.

It might be me being too cautious but up to press it has worked.

Thanks for the suggestions and please keep them coming as I am always learning.

Paul

Stainless steel has a nasty habit of galling, been there got the scars from that one trying to remove a stainless steel impeller from a 3" stainless shaft.

One thing I found when I tried stainless years ago the stainless manifold and the stainless steam line union nut became impossible to unscrew

Stainless needs a "contaminant" if it needs to remain mobile, Molybdenum etc, or it cold welds

Colloidal graphite? They use CG in metal and glass moulds because of it's resistance to heat

I've found CG great stuff, it's one of those "1000s of uses" type things

Edited By Ady1 on 14/07/2015 00:45:29

High temperature connections are usually flanged or clamped. A thread will never be the best choice.

Red hot is a challenge. You have to have a steel that doesn't phase change so either it never turns to austenite at high temp, or never turns to ferrite as low temp.

The ferritic steels, to get higher strength, tend to be heat treated to get fine grain. Red hot will probably undo that.

CrMo seems to be good for hot conditions - but will its properties survive red heat? I don't know. I'd like to know the answer

Nickle based alloys are used at really high temps. I guess they will be very difficult to machine.

Or just make a few spares out of low carbon steel and change them regularly?