Heat Treating help needed

godog,

Go to temperature as I prescribed, regardless of how long it takes, and soak as I prescribed. Test and tweak from there. Eating around the fringes will only cost you more time. I have spent countless hours and dollars doing what you are disregarding me over. Trust me. Your oven may well require you to deviate in timing but you are wise to do as I suggest first.

Pay close attention to what Kit said about tempering your stainless. That is what I was pointing to when I advised not tempering so high (I think you had mentioned 1050 F). It is true that some of our stainless is secondary hardening. Not always is that necessary to HT it properly. There is an exceptional steel, I believe, but for the steels we speak of so far temper as low as possible to achieve the desired hardness without dropping below 400 F for the first - or primary - temper. Kit is the one that taught me not to temper stainless too high. Later you will be down loadig vendor data sheets and will notice on some of those that they warn you about that.

RL
 
Howdy Kit,

Thanks for the advice....yep, I have three test pieces that came with the Rockwell tester, and it either nails it, or is within a half a point, each time...so I suppose the tester is OK. I have no idea if the oven is OK or not, other than the computer on the oven gives me the air temperature, which matches my thermometers, so it is probably OK, at least at room temperatures. As for whether it is dead on a 1850 degrees or so, I don't know.

RLinger, I will pay close attention to your suggestions regarding tempering at lower temperatures....from what I have seen from the data sheets, lower temperatures are the way to go. Got in late from the gym tonight, so I will try your suggestion tomorrow night...I only wish I had read your earlier comments prior to trying that last batch. Thanks again and will let you know what happens.
 
GD you might ask THE MAN that sets the standards, Paul Bos. He will tell you just about anything you need to know, and has been at it since I was in diapers. He dont care if we are at War either. :rolleyes: If you ask him directly he will respond here.
To be honest I dont even try to HT at home I just cant duplicate what Paul does 100% of the time.. Its the best $4 worth of insurance I can buy. Using Paul lets me sleep a bit easier at night.

Here is a shop tour I did on Pauls shop a while back. As you will see he has equipment we can only dream about..

http://www.bladeforums.com/forums/showthread.php?t=226316
 
I've been heat treating ATS34 for years without a problem. Here's my formula, developed from years of history. I keep a file box with 5 x 7 cards in it, and record the results of each heat treating cycle.

I've used both the secondary and primary ranges and they both work fine, but the primary (lower) range gives better resistance to corrosion, as someone has already said. The final working hardness is the same with either method.

50 years ago, steel wasn't as closely refined as it is today, and contained a lot more trash and undesirable elements. For that reason, it was best to start with a cool furnace. Using today's better steels, that isn't necessary.

Here's what I do with ATS34.

Preheat the furnace (by the way, it's a furnace. A low heat furnace for tempering is an oven) ;) to around 1200 degrees and let it sit at temp. for a few minutes to dry out the moisture in the bricks, if yours has bricks. Then take it up all the way to 1920. When it reaches temp, put your foil wrapped steel in. The temp will drop while the steel soaks up heat. When the furnace reaches 1920 again, soak the blade for about 16 to 20 minutes. Leaving it at temp longer than that will start decarbing the steel. That's a bad thing. ;)

After soaking, remove the blade, then quickly remove the foil pkg. Lay the blade on a large piece of steel, and place another large piece of steel on top. The steel will soak the heat out faster than an air quench. That's a good thing. :) and keep the blade straight. Another good thing.

Within 3 to five minutes, after the blade has cooled (you can handle it with bare hands). put it in your wife's kitchen oven heated to 50 degrees less than your desired tempering temp. This is a "snap" temper, just to keep the blade from cracking due to the quench stresses. Leave the blade in for 2 hours. Turn off your furnace and let it cool with the door closed if it has a brick liner. After the furnace cools, put the blade back in and temper it at 375 to 390 degrees, depending on what you want for the final hardness.

Start with 375 for 2 hrs., check the hardness, and if you're satisfied, temper it again at the same temp. If you want to drop the hardness a point, raise the temp to 390 and temper it again for 2 hrs.

This formula will give you about 60 to 61 Rc at 375, and 59 to 60Rc at 390.

The final hardness will vary a little between batches of steel, because the steel mill has to keep within a tolerance band. They mix the chemistry with each batch just like you do baking a cake. A little of this, a little of that, and it will vary slightly with each batch. So temper a few degrees low, check the result, then temper again at a slightly higher temp. to get exactly what you want.

For ATS34, it's best to double or triple (counting the flash) temper 2 hrs. each time.

Now if you want to cryo quench, do that after the first flash temper.

I'll help you with the formula for any tool steel if you email me at donwrobinson@earthlink.net.

I'll also send you the Hitachi TTT chart by email if you want.

By the way, I don't deal with people who use aliases or refuse to reveal who they are either. If you become a famous knifemaker, how will people know who you are?

I don't care who knows where I live. If they bother me, I'll just shoot them. :)
 
Kit is on the money.
I have a portable that I check the big oven with to make sure its dead on.
I send the portable in every year for calibration.
The ASM heat treater's guide is a good reference book for most materials.
Use the manufactures spec sheets for materials not listed in it.
 
Godog,

I beg you re-read my reasons for pre-heating. Equalizing the steel cross section at pre-heat prevents or minimizes distortion and also helps insure a consistant soak at austenitizing temperature. I can see or understand no reason a steel's purity in chemsitry would have any bearing on whether or not to pre-heat. A pre-heat for such thin parts as our blades is probably not as important as for larger parts but I have noticed an improvement by pre-heating and therefore always do it regardless of steel type. I do adjust the ramp rate to pre-heat according to blade thickness.

In testings I have gotten better grain structure with air quenching deep hardening steel than I have oil quenching or plate quenching. I do not choose to air quench as a matter of convenience. If I get a blade in to heat treat that has not been ground (no bevel) I may plate quench it. Most blades are ground before HT and I do not plate quench those because there is no way the plates will contact the bevel. The only part of blade that contacts the quench is the flat of the blade and not even much of that because of the distal taper. The ricasso would get a wonderful quench. Of course I can not argue with success either so anyone getting good results with plates; that's great. I just don't do it unless the blade has not been ground.

It sounds like your Rockwell tester is as close as you could hope to get it, especially if one of your test blocks is close to the hardness you want your blades to be.

I fold my foil three times on each of the two sides and twice on the length wise folds. I place about 1 or 2 sq. inches of brown paper bag stock in the packet (on top of the tang). As explained by Kit, it will expire the oxygen. I have never YET had any decarburation even when soaking for up to 30 minutes.

RL
 
" expire the oxygen" ? I didn't teach you that. The paper or machining chips acts as a "getter" that is it readily oxidizes from the oxygen in the foil packet so the blade doesn't oxidize. When you are using foil ,that slows down heat transfer so preheat and soak times are more important.
 
Thank you ol'master of the heat waves. :) I'm from West Virginia so if I spelled it correctly that should be worth a point.
 
I guess thats why I still smoke. Gotta have those butts for the foil pouches. Works better than anything I ever tried.
Mete, does nicotine make for a better heat treat? :rofl:
 
Thanks again for all your help....guess I'm gonna have to take up smoking now so I can use the butts in the foil wrap.

Will be cranking up the Furnace this weekend and give you an update.

Take care
 
rlinger
I,m new to heat treating too and you said to "place in the heated tempering oven immediately before the steel falls below hand warm" this is the first time I have heard this. What happens if you let it cool and do it the next day?
 
I believe it has to do with grain structure and that the grain structure will be more refined if not allowed to drop below hand warm (about 125 - 150 F) before placing in temper. It may be more critical to low alloy steels but I practice it with all steels I have so far heat treated.

RL
 
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