Jump to content
I Forge Iron

Embarrassing Lesson in Heat Treating

Recommended Posts

Well, I am a blacksmith with 40 years experience and I still have a lot to learn.

We had a shop fire 5 years ago. I was able to recover nearly all of my tools out of the ashes. One lingering problem was I was not able to successfully retemper my hammers. I retempered my chisels and could easily temper new hammers. The old ones would go through the process and still come out soft. I went on multiple forums and discussed this problem with friends to no avail. I described my process as follows:

Heated them to bright red and let them cool slowly to normalize

Heated them to above magnetic and quench in oil ( tried both Canola and Parks)

They would not harden.

I finally gave up and handled them and just resigned myself to the fact that they were some how negatively affected in the heat of the fire and that was it.

I was playing with tempering some new hammers, out of old drive axles, and got to thinking that I tend to work with mystery tool steel so I use a magnet to let me know when I am at the critical temperature. I realized that for reasons I cannot explain ( I think because I was so worried about saving my favorite hammers and doing it correctly ) when I retempered my old hammers I put them back in the forge after they reached critical temperature, just to soak " a little bit more" to make sure I had it right. 

Well....I have realized that what I was doing was raising them up too high above the critical temperature so that when I quench them, they were not cooling off fast enough to achieve a hardened state, so they stayed soft.

I went back a retempered all of my old hammers, when I reached the non-magnetic state I quenched them and they hardened just as they were supposed to. Tempered to a dark straw and they are perfect.

I was thinking too much, worrying too much, and could have save myself a lot of trouble if I had just followed the directions. 

Link to comment
Share on other sites

On 10/28/2022 at 10:57 AM, Steve Sells said:

correct your usage of the term tempering to hardening

I understand what you are saying. My meaning was I wanted to get to the point that I could retemper my tools. I think if I said I wanted to harden my tools folks would say I forgot that I still needed to temper them. I could have said I wanted to harden and retemper my tools, which is absolutely correct but thought that was implied but I guess not.

Link to comment
Share on other sites

Yes, indeed. The problem arises from how steel behaves when quenched at different speeds. To dramatically oversimplify, steel heated to above the critical temperature needs to be quenched relatively quickly, otherwise the austenite crystals turn into soft pearlite rather than hard martensite. If the workpiece is too hot, it can't lose heat fast enough to keep pearlite from being formed, so it ends up relatively soft.

(Overheating also increases the grain size, so even if the piece does harden successfully, its large grains won't be as strong as a finer grain structure..)

Link to comment
Share on other sites

It's understandable Steven it takes a while to know at a gut level there are more than 60,000 subscribed members spread around the planet, the majority with little or no experience at the anvil let alone heat treating. I ignored your misuse of "tempering" but I've been working metal my whole darned life and blacksmithing as a hobby for close to 50 years. 

We really need to keep in mind people reading our posts may not know steel from aluminum or know heat treating from cooking gumbo. 

Too many people believe the urban myth that people knew more 100+ years ago than we do now so just because someone in 18th century Europe used Temper for virtually all heat treatment doesn't help folk today. We haven't forgotten how it was done back when, mostly it's been supplanted by better materials, equipment, methods and technique. 

We're not really dog piling on you, you seem to be a pretty knowledgeable guy, we're just trying to tailor the forum to a world wide web full of first timers.

Frosty The Lucky.

Link to comment
Share on other sites

  • 4 weeks later...

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...