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Question on heat treatin A-2

Krutch

Stainless
Joined
Feb 11, 2010
Location
somewhere in Illinois
I hardened a piece of A-2 and it cooled in air overnight. Am tempering it this morning and can't see why the delay between hardening and tempering would be detrimental. Any thoughts on this would be appreciated. I am a novice to heat treating though I understand the process somewhat.
Thanks for any advice and smart ass answers are also appreciated.
Krutch
 
Most sources recommend not ever letting the part get below 125F.. Keeps stresses down. I usually set it on top of the furnace after it is fairly cool. I have done the same as you, though.. Letting part sit all night, never had any problems.
 
It REALLY is better to put the part in a PRE HEATED tempering oven when it gets to where you can BARELY hold it with juggling(about 140º). The tool will last longer and perform better. If you are making an important tool or part,better heed this advice.
 
I have made a lot of parts out of high carbon mystery steel (plow shares, leaf springs etc.) The only problem I have ever had is not tempering the steel in a timely manner and having it crack overnight. I never do that any more but if it doesn't crack then I don't see a problem with the tempering being effective or anything.
 
Depends what the part is used for, and if/how many/where the stress concentrations are. But in generally, you probably have invisible micro cracks that can lead to problems down the line, or not, again depending on what the part is used for.

The carbides (which is what makes the steel hard) are larger than the sum of the particles they form from, & expand quite a bit in the steel. As it cools they try to crack the surface. Annealing changes the matrix to somewhat smaller particles & allows them to rearrange with less stress in the material. This is a vast over- simplification, you can (& should) read about the process if you are going to be doing much steel hardening.

smt
 
I have not seen A2 or any of the other tool steels crack from not being tempered promptly, but I have seen high carbon steel bars just sitting on a table suddenly explode.

Tom
 
Just because you do not see any difference does not mean that there is no improvement in immediate tempering. There IS. Read about it. It makes your tools last longer.

And,it is not about fully hardened tools left overnight to crack or explode,though that can be a problem. It has to do with improving the micro structure of the tool steel.

I use an ordinary toaster oven,but with a long shanked hi temp thermometer stuck inside it through a slot in the back side of the oven. Don't trust the oven's own temperature control. They can be way off,and there is a 25º window in both hardening and tempering in order to get the most out of your tool steel. Doubt this and you are not doing the best job.

Using mystery metal is very poor practice. We had a hard headed gunsmith in the museum who thought he was more macho if he could make something out of nothing. He made some mainsprings out of some car springs he found. After hours of work,they broke when he tried to cock the locks. Turned out the springs were actually made of some kind of air hardening steel. He wasted a lot of labor trying to save 50 cents worth of known alloy spring steel. And,he didn't look too smart in the end after all.

This guy was a great craftsman,but he never did learn diddly about steels. He had an anvil cast from steel,but it turned out to be too soft. When he went back to the shipyard that cast it,the foundry man asked him how hard he wanted the anvil to be. He could not answer the question. He came back and messed around for several days. Finally found a knife blade and took that to the shipyard. The foundry man said "Oh,you want it as hard as a knife?(Which didn't sound too swift either!). They ended up hard facing the anvil,and to this day the face of the anvil is a little bumpy,and you can see the swirls that the hard facing sticks left in it. Needs to be ground smoother,at least. Fortunately,the relatively light pounding from gunsmith work has not caused the thin hard facing to get pounded into the softer steel beneath it.

Fortunately,when I made anvil patterns for the blacksmith shop(18th. C. patterns,of course),they sent the pattern off to Texas,where they cast anvils from 4140 and hardened them. These anvils look good,and in 30 years+ have not gotten sway backed from hard daily pounding.
 
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Thanks guys for your opinions and knowledge.
The part I made is a roll for a hand crank beading machine. Looking a little like a mushroom with a radius of 1/8" at the edge of the 3.280" OD where the rolls will meet the work. Meant to bend sheet metal with hand pressure used to force the bend. I know the end user and he will not be abusing it. Of course I can't see any micro cracks but no other obvious defects were apparent. I have no scientific way to check the actual hardness. File skids, not cuts. Will tell end user to be wary of chipping when using. Should be OK for the service he will put it through.
I had a nice book on heat treating but it was lost when an old car was taken to the scrap yard before I cleaned it out.
I have an old toaster oven which I use to heat Harley castings and other such items to remove and install press fit bushings & etc. It claims 450+ setting but I will have to see how accurate the setting are. I tempered with the oven I hardened with. Temp reading is more believable and steady on it.
This is the second time I used the HT oven to harden something. The first was S-7 for a rivet anvil and it worked as I hoped. I will take the info here and use it to do better work. Need to get another book on HT, too.
 








 
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