A new crack for me!

[jonwelder]

Dear Ed, Yesterday while using my torch to heat treat the "edge" of a bowie style knife, 10" blade x 1-1/2" 5160 ,, my torch tip seemed to be taking too long to bring the 10" blade up to critical, so after about 15-20 minutes of struggling, I put on the rosebud, heated it up and did my quench as usual. Today after annealing I ground it out, only to find 2 cracks about 5" apart through the cutting edge up to the quench line! Could this be traced back to the other post about trying to keep a blade hot for a longer period of time than is needed? This has been the only blade I have ever done, and had to stop during the heat and re-start to get it hot enough. It only took me minutes to change heads, and continue the heat to critical, the whole time was probably somewhere around 30 minutes. At no time did it cool down quickly, but it never reached critical until I put the rosebud on it.... any ideas? I did not hear the crack, so I don't know at what point it did it......... another lesson coming, I can feel it! ----Jon

[Ed Caffrey]

What comes to my mind is that you mentioned you hardened it yesterday, and then you mentioned "annealed", but I think you meant to say "tempered"? today.
If the blade sat overnight without tempering it could have very well have cracked from the stress. That happened to me once....I hardened two 52100 blades (edge quenched) and just about the time I was getting ready to turn on the tempering oven, we had a minor emergency and I ran off and left the blades sitting on the bench. I forgot all about them until I walked into the shop the next morning. I turned on the tempering oven to pre-heat it, picked up the blades and found a series of small cracks all up and down the hardened edges of both blades!

[jonwelder]

Yes Ed, I meant tempered,, so many "terms"... Yes, I hardened one day, and tempered the next,,, that's just crazy!! Now I'll have to watch to make sure I can do both operations on the same day. I guess I never noticed, but in the past I have done both in one day. Also, I'm just now starting to make blades 10 inches and longer. I suppose I will also see more problems I have not had with shorter blades. Thanks Ed! --Jon

[B.Finnigan]

I put my blades into temper while they are still smoking from the quench. A quick wipe with a paper towell is the only delay. There have been too many horror stories that I have read over the years on the forums about waiting too long.

[Burke]

More than likely you over heated it with the rosebd. I use a torch on my knives and wait twenty four hours between quenching and tempering. I quench three times and temper three times. I have used this technique on 52100 5160 w2 10xx series and damascuss. I haven't had a blade crack in more than nine years quenching in oil.

[jonwelder]

These longer "bowie" style blades won't fit into the "toaster" oven I have been using. My wife got excited when smoke started rolling out of the top burners on "her" stove the last time I used it!! I had just wiped off the oil and threw them in.

To address the other post,, at no time did any part of the blade go over "non-magnetic",, I don't believe I overheated it. Thanks for sharing your methods! --Jon

[Ed Caffrey]

I had a big smile on my face when I read "her oven". Several years ago, we needed a new kitchen stove, so off to Sears we went. While Cindy (my Mrs.) was going over colors and features with one salesman, I had another one off in a corner whispering "Which one of these ovens will hold the tightest tolerance?"

He pointed out a model that he said would hold the oven temp +/- 10 degrees of the set point. I whispered "Steer her towards that one." We wound up coming home with that model, and wouldn't you know it, on the way home Cindy looked and me and said "YOU are NOT cooking knives in my new oven!"

I knew she would be going to work everyday, and things worked out great, with me tempering blades for the first couple of months....then I screwed up......I didn't do a good job of cleaning the quench oil off one batch, and when she got home from work, the kitchen smelled like burnt oil.

Within a week I purchased a great second hand oven which now resides in my shop.

The moral of the story?..... What she doesn't know can't hurt you....until you get caught! (and sooner or later you will!)

[Crex]

If she can't tell........she can't cook!
My better half of 35 years, let me try it once on a 16" bladed Confederate "D" Guard Bowie (wouldn't even fit in my buddy's store bought HT oven). Emphasis on ONCE.
Now if she catches me in the kitchen with a knife, I'd better be chopping veggies.

What do I do now? I got two toaster ovens, combined the heating components, added a decent lab grade T-stat control (salvaged from an old muffle furnace) and built me a long oven out of recycled soft firebrick. Total cash out was $8-$9 for the thriftstore ovens. The rest being free recycled materials. But we're not going to talk about the time factor here, just call it a recreational science project. WOrks great though.

I practice the "once cool enough to handle and wipe with a rag - into the preheated oven for tempering it goes" group. Why temp the slacktub demons! They cause enough mischief while I'm in the shop as it is.

[Burke]

Originally Posted by jonwelder

To address the other post,, at no time did any part of the blade go over "non-magnetic",, I don't believe I overheated it. Thanks for sharing your methods! --Jon

Jon, I am thinking that you missed writing something here If the blade never got over non magnetic then it should not have got hard. I will take your word that you never over heated the blade but was trying to point out that it would be very easy to do so considering how much heat a rosebud tip puts out. May i suggest that you finish breaking the blade and inspect the grain size in the break.

[jonwelder]

Bill, since it has 2 cracks about 5 inches apart, it's pretty much useless for anything else,, I think I'll do some testing to destruction,, and post the pictures here, Just give me a few days.... Thanks for your input! --Jon

[Steven Kelly]

I have to agree with Bill on this one. I rarely go directly to temper after h/t. I typically let my blades get to room temp and then clean off the oil and scale before putting them into my tempering oven.( I really hate having my small shop full of oil smoke all day. I Don't Think I have ever had a blade crack because of this practice. I have over heated a few blades though and gotten a crack, or more commonly a bad warp. It only takes a second to create a hot spot with a torch... I have found that less heat and more patience works better for me. I just get real comfortable and relax a bit while waiting the 15 or so minutes it takes to get a large blade up to temperature...


Good luk,

Steve

[lenniusmc]

So is using the rosebud to much for 5160 or any steel for torch quenching? I have used the #3 welding tip on my torch and at time found that the rosebud worked better, I just held the blade furhter away. With the wider flame of the rosebud it was easier to get a even temp.

[jonwelder]

When I started this post, I was making a 10" blade knife to do some rope cutting demonstrations with at a show. As Ed pointed out, it may have cracked because I waited overnight to "temper" it...... or little green men entered my shop after I left, and finding nothing better to amuse themselves with, they cracked my blade in 2 places.
After getting Ed's advice, I made another blade the same way, same size, heated it "EDGE FIRST TOWARD THE SPINE" to non-magnetic, with my "rose bud tip",, (just as I did before) which made the whole process a lot faster,, wiped off the oil, and went to the tempering oven. The result: (these are MY findings) no cracks, no warps.. just a great knife! I ground it out, put on a handle, and did over 10 --1" rope cuts (free-hanging) with no problems what so ever. I did not resharpen between cuts, the knife continued to cut with no problems!

As I said before,, these are purely MY findings,, probably not typical at all, probably could never be reproduced even in a laboratory under ideal conditions....in fact, I'm probably the "luckiest" knife maker in the world..............UGH!! !!!-----Jon

[jonwelder]

My forging and rope cutting demo picture.. if I can get it to work!! --Jon

[jonwelder]

I hope this is a little bigger!