Attempt on a hammer; failure

[Jura T]

I wanted to make a hammer, similar to the one Brian Brazeal has demonstrated making. I got the shape to my liking and normalized the hammer. As I had put quite a few hours into making it, I wanted to harden it as well as possible. So I heated it to non-magnetic and quenched in oil. It did not harden. I was using spring steel (~50CrV4), that has hardening temperature slightly higher than normal carbon steel. So next time I heated it a tad past non-magnetic. Still not good. One more heat, again slightly hoter than last time, but this time I only heated the two faces. Now the faces hardened alright. BUT, there was a crack on the other end!

Any guesses whether the crack was caused by the multiple quenches or by the differential heating at the last stage? On the plus side, the grain looks ok.

[pkrankow]

You did not normalize between attempts?
Looks like a good effort, it is a shame about the failure.
Phil

[Jura T]

You did not normalize between attempts?

No. In theory it shouldn't be needed. Quenching is sometimes used for decreasing the grain size, instead of normalizing. However, quenching is always a bigger shock to the steel than normalizing...

[Bentiron1946]

I'm sorry it didn't work out, that would have been a nice hammer. :(

[clinton]

That is a bummer it does look like it would have been a nice hammer the eye looks well centered I think that just hardening the face of the hammer not the whole thing is the way to go
chalk one up for experience

[brianbrazealblacksmith]

What kind of oil did you use? The only problems like that that I have ever experirnced were caused by bad oil.

[ThomasPowers]

Did you remember to remove the decarb layer before testing hardness after your quenching attempts?

I emphasize this to my students as they have often twice as many (or more) heats in than I do when I do a piece and so it's more of a problem for them.

[Jura T]

Brian, the oil is a mixture of hardening oil (that I bought from a steel company) and ATF transmission fluid. I haven't had problems hardening with it before.

Thomas, I ground the faces before hardening. So there shouldn't have been any significantly decarb layer? At the last time the file skated on the faces, at the previous tries it did not.

[bigfootnampa]

So now you know that the secret is to heat the whole hammer to the temp that you last did on the faces only. Then you could draw the temper more on the eye. Remember though that file skating is TOO hard for hammer faces... as finished anyway. Also I think you would find a mid-carbon steel or a mid carbon alloy steel much more suitable for hammers. Hammers are NOT knives and very hard surfaces are NOT desirable... the heat treatment of the mid-carbon steels and alloys is less critical than that of the higher carbon steels (especially as regards hammer sized hunks of steel). Lastly pay attention to your quenching technique... a heavy hunk of metal such as a hammer head needs to be agitated quite energetically as it is quenched, in order to keep cool oil flowing over the faces of the hammer.

For my own purposes I like axle type steels (4140, 4130) or low carbon steels (1035, 1040, 1050) for making striking tooling or hammers. Spring steels might be made to work but would only be chosen if better choices were unavailable (and in such case I would be careful to temper them back aggressively... or leave them unhardened). As an example... spring steels like 5160 would be tempered at 750 to 900 degrees Fahrenheit (for use as springs) and IMO would still be overly hard for hammer purposes. Speaking color-wise I like a blue temper tending toward purple at the eye for hammers... and I believe that mine are harder than most production hammers (this for alloy steels and mid-carbons... spring steels would be different).

[Jura T]

So now you know that the secret is to heat the whole hammer to the temp that you last did on the faces only.

The last time I tried differential hardening was with a wide, japanese style kitchen knife. It cracked as well. So I guess I will use differential tempering only from now on.

I have made a small hammer head from the same steel. I have used it for about two years now and it is my favourite hammer for small work. Cannot remember how I hardened it but I tempered it to darkish yellow. It doesn't seem to be too hard. So based on that, the steel should be ok for hammers.

[pkrankow]

I'm looking at that, and thinking that if you wanted to you could grind the damage out (to prevent crack propagation and cold shuts) then reforge the broken side making a straight peen hammer. Just a thought.
Phil

[Jura T]

Brian, I asked you in another thread that do you harden the whole hammer or just the faces and you replied that just the faces. In one of those Picasa picture series it seemed like if you hardened the whole hammer and then just tempered the eye more than the faces. Which way is it?

I think I will have another try with a hammer next weekend. I just need to make a shorter drift to be used with a power hammer first.

[brianbrazealblacksmith]

Brian, I asked you in another thread that do you harden the whole hammer or just the faces and you replied that just the faces. In one of those Picasa picture series it seemed like if you hardened the whole hammer and then just tempered the eye more than the faces. Which way is it?

I think I will have another try with a hammer next weekend. I just need to make a shorter drift to be used with a power hammer first.

I bring the faces up to temp where there are no shadows or dark spots by turning them, and the middle does show colors but it still has shadows or dark spots. You may not be able to see that in the photos. I would consider what the others have posted, also. I prefer to use 1045, but since 4140 is readily availiable for free all around the world, I've used it in most cases.

[Jura T]

Everyone, thanks for the input. Based on that I'm starting to believe that the spring steel I'm using doesn't take differential hardening well (at least not with large cross sections). Then again, it might have been that the temperature across the face wasn't completely uniform. Well, in any case, I'll make another one and see what happens. But first I will do some quenching tests with the steel.

Getting tool steels here in Finland is not easy. I know only one place that sells small quantities of steel. I just checked their www-pages and they don't have any 1050 (or something similar) in their selection . I could probably get 1050/Böhler K950 from another company, but it would mean taking the whole rod (several meters). A bit too much for one hammer...

[Frank Turley]

Several things. You should have normalized between hardenings. You want to get rid of the tempered martensitic structure between the hardening heats. I do one face at a time, heating at the edge of a hot coke fire. After one face is hardened, I remove scale and place the head in the vise vertically with the hardened face upward. I temper with a turned eye tool of 7/8 square stock leaving enough straight for a lengthy shank/handle. I drop the snugly fitting turned eye over the head at a welding heat and temper to a dark straw by heat conduction (on 1045 axle steel). I've quenched this steel in water, quenching VERTICALLY and figure-eighting it in the water to agitate. Bring it out when it quits quivering (making that "cush" sound under water). It will still be a little warm, 150-200ºF. This supposedly helps prevent cracks.

When one face is done, I wrap it with a water wetted rag to protect the temper, and I use large bolt tongs to hold it. The other face or peen is heated at the edge of the fire and quenched. Keep the wet rag on it while tempering the newly hardened face.

The eye is not hardened nor tempered. It remains normalized. If you try to heat the entire head, you'll get the eye hardening and contracting before the heads do, sometimes resulting in a crack on the thin eye cheek(s).

There are other methods, but I've had success with the above.

http://www.turleyforge Granddaddy of Blacksmith Schools

[csciron]

What kind of oil did you use? The only problems like that that I have ever experirnced were caused by bad oil.

[csciron]

Hey Brain, will you please expound on (bad oil) Thanks,, Scott

[brianbrazealblacksmith]

Hey Brain, will you please expound on (bad oil) Thanks,, Scott

I'm referring to oil that has been overheated and broken down, or oil that foams over after putting a large hot piece of metal in it. I would not want to use used motor oil for quenching my hammers either.

[strube1369]

That's not a failure. You successfully learned that THAT didn't work... There's a learning curve to everything and it sometimes feels like I am always on the uphill side of that curve...

[Richard Furrer]

Several things. You should have normalized between hardenings. You want to get rid of the tempered martensitic structure between the hardening heats.
http://www.turleyforge Granddaddy of Blacksmith Schools

Frank,
I am curios...would not the heating to austenite after tempering do the same as the heating to austenite and quenching for another go?
Once the structure forms austenite...its austenite and prior crystalline structure..be it martensite or pearlite..matters little.
I can not think of any metallurgical reason for what you have said.


Minotaur:
A few thoughts:
1)Was the steel new? If it had been a spring in its past life it may have gotten micro cracks then.
2)It may have cracked in the previous quenches and then let go on the third..as you have suggested BUT then you usually see a black crack where it had heated in the forge in the second or third austenizing heats..I do not see that in the picture
3)Reference 2 above..if it cracked in the temper then you would see the temper oxide in the crack..I do not see that either...no blue crack.
4)The grain is small and good looking in the broken piece so I do not think you are overheating the metal...that or there are rather good grain refiners in it (i.e. vanadium)..in either case I think it is safe to say your heat is ok

however

5) I see a darker border around the broken bit and unless that is due to oil or some other artifact of the photo my guess is that you have removed carbon to a rather large depth and this is why you needed the higher austenizing temps.

Since you have nothing to loose with that hammer head I suggest you grind 3mm off all the surfaces on the other face and do your normal austenizing soak and quench it and see what happens.

Lastly

6) Sometimes you can do everything correct and still have it not work.


Ric

[Larry H]

Minotaur, there is a lot of good advice there, I'm not familiar with that steel but when working with tool steel in general here's a few things
to think about. Don't work it to much, meaning "beat it to death" Don't work it to cool, there is a small window, when you see gray in the steel it's to late for one more hit. I've done many hammers, when they are at a nice even orange I quench in oil, in the center of a full five gallon metal bucket, keep it moving in the oil for ten minutes never take it out to look, hang it in the oil for three or four hours, quench in the morning, go do work when you return, warm hard hammer. I use truck axles, and I learned from 4th gen blacksmith, all four brothers were blacksmiths too ! !

[Frank Turley]

Richard et al, Perhaps a metallurgist could better deal with the question of normalizing between hardenings. As I understand it, normalizing is preferable to annealing on carbon and some low alloy steels, because with annealing, "large carbides are retained," and these carbides are undesirable. This is according to the metallurgist, Quenchcrack, on anvilfire.com.

With that said, I think that proper normalizing refines the grain structure, making it fine and uniform. From that state. the hardening heat is a rising one and the heat treater tends to retain that uniform stucture going into the hardening heat. After hardening, the grains change to a "needle like structure." If a guy reheats to harden from this martensitic structure, yes, he would be undoing previous heat treatments, but he would not be starting from that desired, normalized state.

When I make a tool, I normally use four heat treatments, and here I include forging as a heat treatment.
1. Forging
2. Normalizing or annealing
3. Hardening
4. Tempering

Grain size is important. You shouldn't take a yellow heat on high carbon and let it cool down to hardening heat, or you will retain some coarse grain from the overheating. This makes for a weaker tool which may be subject to spalling, cracking, or breaking.

I offer a quotation from "Modern Steels and their Uses" by Bethlehem Steel.

"Normalizing involves heating to a temperature of about 100 to 150F above the critical temperature, followed by cooling in still air. The uniformly fine-grained pearlitic structure which normally results enhances the uniformity of mechanical properties...Normalizing is also frequently used as a conditioning treatment prior to quenching and tempering. The purpose is to facilitate austenitizing, particularly in grades containing strong carbide-forming elements."

http://www.turleyforge.com Granddaddy of Blacksmith Schools

[Mainely,Bob]

Very well thought out,well stated and well supported post there Ric.
Don`t know about anyone else but I learned some things to look for.
I also look forward to Frank`s reply to Ric`s question.

It`s posts and threads like this that shed real light on heat treating and make it seem like something any reasonable metalworker can understand and do.In doing this it make it seem less like magic and more approachable.
Thanks to all who have posted so far.I`m enjoying this discussion very much.

[thingmaker3]

Data sheet for this steel says to forge at 1050C and not to forge below 840C. Was this adhered to?

[double_edge2]

my 2 cents worth would be, forged at the wrong temp or allowed to get too hot for the alloy.
ive had it with tortion bar alloys if i roll my smoke at the wrong time.
all looks honkey dory till the finnishing or using, the flaw reveals itself.
i love 1045 and 4140 for hammers and anvil tools. too hard a hammer is great for marking up everything when you miss, and chunks of steel in your arm....