1084 keeps cracking...

G

gixxer1237

Joined
Mar 10, 2010
Messages
419
Ok. I am not a maker just a hobby hammer swinger. I have made maybe 5 blades that survived HT. They were all produced from 1095 acquired from Admiral several years ago. So my friend asked me to make him a rather large camp knife and I ordered some 1084 from Aldo. Great service. Good guy. So I hammered out some blades. Used my forge to HTC. My process-
Forge blade. Never hammering when color fades below visible in direct light.
Finish forging at just past magnetic.
Normalize 3 times in my forge without Pyro. Use color range and magnetism to determine heat.
Heat up to just past none magnetic. Quench in canola oil heated to 140ish determined with thermometer.
3 blades cracked. One cracked after the first temper of 1 hour at 450. Other two cracked in quench. These where done individually. I paid very close attention to not over heating the steel. Each one the temp I stopped forging got higher. I assumed I was working a little cold and producing cold shuts.
So I made one last try. I did a beautiful 14" harpoon typed blade by stock removal. No way to mess up the forging. I took it to a friend who has access to a evenheat. He did a full annealed and normalization cycle on it. We followed the book. Normalization went 1650, 1550, 1450. Heat treated it to 1475 and quenched in parks 50 heated to 145. Blade came out fine. Tempered 3 times at 500 for 1 hour. I got brave and sanded the scale off after the second temper. Took it to a quick 220, as it was before he, and it was clean. Did not over heat it to color anyplace. After the 3rd temper cycle I pulled it out and about cropped. 1/4" crack almost half way up the blade. What am I doing wrong? He does HTC for machine shops and for the school I work at. I went with the Temps he recommended and pulled my 2nd rate skills out of the equation. Did we mess it up? Any advise welcome.
Oh, edge kept to .075" before he and tempered.
 
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Most likely the cracks were there all the time from your forging.

Any forging below 1500F may cause grain boundary disruption .... which can lead to cracks. I never forge below a full red color. Forging at magnetic is around 1400F.

Is the 1575F you gave as austenitization a typo? It should be 1475 -1500F. 1575 is far too hot.
 
It's hard for me to see what the problem could be, other than perhaps the steel...
Has this happened to you before, with other bars of 1084 or other alloys?
Could the steel have been erroneously sorted/shipped?
Are you sure those cracks were not there earlier than you thought?

Have you called Aldo to see what he thinks?
 
I have made blades out of 1095 without issue excluding when I tried water quenching... I have not contacted Aldo. Maybe I should but I just assumed I was doing something wrong.
I am 9o% sure the crack did not appear until after the 2nd temper.
I have been told before to forge hotter. On the forged blades they never lost color and the last one never got below cherry. I do most of my forging during the day and could still see good color.
 
The only thing I see that could be wrong with the stock removal one is the quench temperature. Parks 50 is used at room temperature and not preheated.
 
It's harder to say with the forged blades just because there are so many things that can go wrong with it, either to hot or to cold. Only thing i see is the parks don't need to be hot. Seems like 70 degrees is ideal. Not sure that would cause the cracks though. I'd call Aldo. When did you buy this steel?
 
Are the cracks in the same place? Possible stress risers? Grind lines running from top to bottom of blade causing stress risers?
 
I don't know how to post pics. Two of the cracks are edge in. One is spine in. If someone PMS me a email and can post pics I'll send em. I only have the last blade. The others, I kind of got angry and broke one, still have the other some place. Figured I'd use it tell failure. I bought the steel in March.
 
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Well, for one, you're at WAY too rough of a grit on your grind before quenching, all of those deep groves are stress risers which WILL form cracks no matter what the steel if you're hardening. Finish the blade to at least 220 before quenching or you'll have cracking problems.
 
I agree, the blade looks like it could have been taken to a finer grit before the HT. However IME most smiths make too big a deal of the surface condition prior to hardening. For example, when I just started knife making at the age of twelve the first blades I quenched never touched sandpaper or a file. They were quenched as finished from a bench grinder running those coarse round discs. So they were a bit rustic if you will. I also suspect overheating of at least some of the blades (IIRC I quenched one from a bright orange-yellow color). Long story short, poor surface prep and temperature control, but no crack. Warping, but no cracks. So what I am saying is there is probably other factors at work too, not just the scratches from the sanding causing cracks to form during the quench. I am not saying they didn't play a part in cracking the blade (they definitely can), I just think something else is likely off too.

Also worth noting, the cracks in those pics are exactly the same as the cracks I got when experimenting with brine quenching, so maybe not 1084 like some have mentioned.

Thats my $0.02 CAD, so adjust its value accordingly.
 
Well, I can say that I've done a whole lot of quenching with a whole lot of alloys, with surface finishes more often than not at 36 grit- and I don't think I've had a crack due to stress risers, ever. Maybe once, and a few of them from water quenching.
I know that it's commonly held to be quite important, to quench from a bit higher of a grit, one thing that helps me is I often finish profiling the edge and spine by grinding lengthwise on the platen (so the grit scratches run with, not across, the edge.) You could try that, but I still suspect the steel.
In the pic it looks as if perhaps your edge is not of an even thickness. If you had very thin edge sections next to thick sections, I could see that promoting cracking.
 
gixxer1237,

1st off, send me a piece of the bar that the knives came off of, if there is any left. Secondly, you might consider using a slower oil. 1084 is a high Manganese steel. Some of you may not agree, but I shy away from using Parks 50 unless I am treating hyper steels with low Mang. such as 1095, W2 and our low Mang. 1075. 1084, 80CrV2, 52100 all get AAA. When I use O-1 I forgo any oil and plate quench with 3/4" aluminum typically to 65/66 RC. Keep in mind that 95% of what we do is Cutlery using 1/8, 3/32 and .072.
 
Aldo I'll see if I have any left. It may just be a scrap from cutting stuff out if that's ok.

If you look at the pic with the pretty colors the blade was hand filed and then lightly cleaned up with a 220 belt. That blade is over 1/4" thick. The ones where it's finished at 60 are because after I found the crack I decided to annealed it and go back and relax heat treat it and do some experimenting with heat treat.
 
It looks as though you took the edge to essentially, sharp. Is that true?

That cross section seems a bit drastic for a fast quench. I used to get "tip dip" or a negative sori when quenching blades with a wedge-shaped heavy spine to thin edge geometry. I started quenching spine first and that helped quite a bit.

Have you inspected the crack? Is it oily, scaly or showing temper oxides? That can give you an idea as to when the cracks occurred.
 
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