Hardening process

What's your oil quenching temperatures?

Not measured. But could be at 20 deg C.

This is not my specialty, but that doesn't stop me from guessing. I suspect something about your heating process is reacting with carbon in the steel, thus lowering the steel's hardening potential.

Final Hardness depends on Carbon content and proper soaking at quenching temperature as well as of grain size and quenchant agitation. As you know soaking, also is influenced by cross section, shape and size of the part.

35 yrs back I was Works Manager at a large machine building plant for 7 years.

Never did I attempt heat treatment to get HRC45 ++ from EN8.

This 0.35% plain Carbon Steel was good as a medium strength ,easily machined Shafting. Never to be Heat Treated.

It was supplied AS ROLLED-peeled/turned.

Rarely drawn Lightly as Bright Bar.

If you are wanting HRC55+ on the outer skin from EN8 or from lower Carbon/Low alloy Steels, go for Carburizing,Nitriding,Carbonitriding, Chromizing,Borizing-before Induction Heating and quenching.

If you want High Through -Strength then there are 1000 exotic Alloy Steels at fancy prices.

I con cure, I'm only a hobby Blacksmith but the carbon content will have to come up.

Off topic:Beryllium copper is my latest smithing adventure.

BC makes some nice looking machined parts as well.

I am sorry, Iwas out of reach of net.

U r quite right regarding metal. It can be termed asa typographical rerror. I was working with EN -8 for some other job and that just slipped in to this topic. The metal I was referring to was High Carbon High Cromium!

I thank all the respondents. I finally could get required hardness of 60 RC by taking care that the quenching medium was cool with flow of water in radiator pipes.

I also noticed one more flaw. The job which was put in a cage for hardning was quenched half the way so that job only was immersed in oil. Half of the cage was out side oil, which was red hot for more than 5 minutes. Due to this the heat was flowing back to job, thereby retarding the quenching process!

When whole of the cage was immersed, I got required hardness.

Thanks all again.

I can't speak from experience, so I don't want to start an argument with Mukulmahant; but for what it's worth here are a few extracts from a Macreadys data sheet for En8 (BS970 080M40):

"For induction hardening a Carbon content of 0.40 / 0.45% is recommended to achieve maximum hardness.
...Should achieve a surface hardness of 37 - 53 Rockwell C depending on Carbon content.
Temperatures:
Hardening: 830°C Quench in oil.
Tempering: Between 550°C and 660°C
When components made from bright bar are required for induction hardening, removal of material from the surface is recommended to obtain maximum hardness. This stock removal overcomes the effect of surface decarburisation.

The Carbon content that they mention is within the allowable tolerance for this grade.

(Macreadys is (or was) a UK Steel manufacturer/supplier.)

I hope that this is of some help

"required hardness of 60 RC" If I'm reading this correctly. as hard as most files.

also in rereading the question am I missing the temper after the heat treatment or is the problem his heat treatment is not sufficient to warrant tempering?

I'm just a hobby metallurgist and not knowing the trace elements of En8 .40% carbon seems low to make 60 RC.

Brad

YOU r right . I have already replied now.

Thanks anyway.

well, I don't quite agree with, whatever reference you give.

Mukulmahant is right.

Carbon content is not the only cirteria for hardening. The % of other elements Mn, Ni, etc. are also important. Though I don't have it right now, for EN8, it will never give you hardness of 55 to 60 HRC. You will always endup with around 30HRc.

EN8 is medium carbon steel, so it is not recommended for case hardening applications (carburising, nitriding, etc).

If you want to have case hardening of 55-60 HRC, you better go for EN36/353. It will also give you UTS of around 90kgf/sq mm.

I can't comment on whether the Steel manufacturer's data is correct or not, the point I was trying to make (somewhat clumsily) was that the original poster was doing quite well to achieve the hardness that he had managed. I quite agree that an Alloy Steel rather than a Carbon Steel would be more appropriate for his requirements, but perhaps the extra cost is a consideration in his choice?

Drew

I didn't post originally fearing the sensation of own toes in back of throat butat first reading I couldn't believe EN8 would give the required hardness if just quenched. Some carburising or more subtle treatment would be needed from my understanding. Perhaps this just didn't come out clearly from the question.

I'd seriously look at the hardness tester's cal.

Than Q any way for information. Hope u have seen my reply.

IN THE EN8 MATERIAL QUENCH HARDNESS WILL NOT COME ABOVE 45 HRC. PLEASE SELECT THE MATERIAL EN9