Heat Treating

[thestelster]

I had to make a small part from AISI 4140 steel. A couple of fire bricks, propane torch, and quenching oil (ATF). Heated the part to cherry red (though, I've never seen cherries that colour....maybe maraschino cherries!) In the picture it's a little orange: kind of hard to hand hold the torch in one hand and take a picture with the other. But most of the time it was closer to cherry.

Held it there for 20 minutes, (talk about boring at the end of a long day) and quenched in ATF.

Now to clean it up, polish it bright and temper.

How I wish I could afford a real heat-treat oven like a Paragon or Evenheat!!

 

[thestelster]

So, all polished up to 2,000 grit sandpaper, then degreased. I use a different torch nozzle which gives me less heat and a more pointy flame for tempering. Heated the part very gradually, rotating it constantly, and trying not to stay at the thinner sections for too long, otherwise they'll soften before the rest of the part. Went through the tempering colours until I got a light blue which is app. 640°F, and for 4140 equals app. 43Rc.

And that should be good for this application.

 

[DPittman]

Looks good....what is it, that such a small thing has to be hardened and tempered 4140?

 

[thestelster]

Looks good....what is it, that such a small thing has to be hardened and tempered 4140?

It's an extractor pawl for a Westley Richards single bbl trap shotgun.

 

[PeterT]

How I wish I could afford a real heat-treat oven like a Paragon or Evenheat!!

You and me both. My friend does jewelry casting & was mentioning one of these offshore furnaces. He says they are great value, he no longer messes with gas.
Although not really intended for this purpose, I was wondering out loud if the controller was accurate enough & within required temperature range of typical HT temps. Its not a front loading chamber & not for larger jobs & no inert gas provisions (other than a lid which might minimize air a bit), but maybe for these little parts? This is Amazon price but I've seen them cheaper yet on Ali.

 

[jorogi]

Says 2000f which should be good and digital electric so maybe. Also depending on the size of the crucible you might be able to have the part submerged in flux, ala Chris.
I put forth the motion that you buy one, try it and report back to the group .
Do I have a seconder ?

 

[MrWhoopee]

Twenty minutes?!!
No need to hold the temp that long, that only applies for large parts where you're waiting for the core to heat.
Something that small can be quenched pretty much immediately after reaching critical temp.

 

[YotaBota]

Seconded!

Always happy to help spend another members money. lol

I am also interested to know if or how well these work for small parts.

 

[DPittman]

Twenty minutes?!!
No need to hold the temp that long, that only applies for large parts where you're waiting for the core to heat.
Something that small can be quenched pretty much immediately after reaching critical temp.

I too found that time surprisingly long for a small part however I think some metals require some time at critical temperatures for the molecular changes to happen. I dont think its just a size thing. Possibly @thestelster might explain why his part needed that time at temperature.

 

[thestelster]

Twenty minutes?!!
No need to hold the temp that long, that only applies for large parts where you're waiting for the core to heat.
Something that small can be quenched pretty much immediately after reaching critical temp.

I thought it's 1 hour per inch of thickness.

 

[Darren]

Usually a minute or so after it loses its magnetic attraction ie critical temperature

 

[Aarknoid]

friend does jewelry casting & was mentioning one of these offshore furnaces.

If I had eternity off I just might get around to all the hobbies I think I have. I may have time to give you another review on the slightly upgraded version of that furnace. Will be using for casting into lost wax moulds one day. And it does go cheaper than 399. What might be more useful is finding an old lab oven , there isn't much to them other than a few fire bricks, an element or two, a thermocouple and a controller. Mine may need a refurb as it has a vaccume tube as part of the contoller

 

[thestelster]

Usually a minute or so after it loses its magnetic attraction ie critical temperature

This was a post to a thread started by @Mcgyver at HSM.

 

[thestelster]

I've been scrounging for information on soak time for 4140, and it varies so widely. Anywhere from 30 minutes to 1.5hrs per inch in cross-section.

 

[DPittman]

I've been scrounging for information on soak time for 4140, and it varies so widely. Anywhere from 30 minutes to 1.5hrs per inch in cross-section.

I thought it's 1 hour per inch of thickness

Then you were pretty close with what you did then.

 

[historicalarms]

I agree with MRWoopee. I have made several firing pins and torch heated them very quickly to cherry and then quenched ( ima cheap bastard and didnt want to burn acet unnecessarily), mind you they were all drill rod and not 4140 and all hardened very well. So hard that the first one I did, I dropped on the cement floor before it was tempered down and it shattered like glass into 4 pieces.
I think tempering down is more time critical myself. I use just the bosses kitchen oven to temper and let them soak for an hour at 450 deg. I have no way of telling the brinnel # of the finished product but those pins are still in use and I have never had a home built one fail .

By the way Tels, I have a 1887 lever shotgun that wont extract regularly so I might be building a couple extractors also.

 

[MrWhoopee]

I thought it's 1 hour per inch of thickness.

That's for the real heat treaters with thicker sections and controlled conditions looking for consistent, repeatable results.
A torch and bucket of oil is not that. I'm not heating a 1/4" thick piece for 15 minutes, once it's up to color for a minute or two it's going into the oil.

It's very much like chip load calculations on a manual mill. No manual machinist does that, and with the exception of the old BP power feeds, nobody's power feed is calibrated in IPM anyway. Too many other variables at play.
"Put down that damn calculator and get back to work!"

 

[BaitMaster]

Very cool.

 

[Chris Cramer]

Typically carbon steels are just austenized to temperatures where they bcome non magnetic and quenched in oil, since water will cause cracking. It is tempering that requires more precision when using a forge for heat treatment. Blades are tempered twice for 2 hours if you use a high temperature thermocouple you can measure the temperature fairly accurately.