monty Posted June 7, 2011 Share Posted June 7, 2011 i have heard of double and triple tempering, tempering, shining, re-tempering etc, and have been told that the longer the steel is held at the tempering temp, the more effective it is? has anyone got any more in depth explainations? thanks monty Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted June 7, 2011 Share Posted June 7, 2011 Actually more cycles is more effective than longer time according to the research metallurgist I talked with; but it's rapidly diminishing returns either way. Quote Link to comment Share on other sites More sharing options...
Steve Sells Posted June 8, 2011 Share Posted June 8, 2011 One problem with hardening is that not all the austenite converts to martinsite right away. Leaving us with some retained austenite from the quench. We temper after quenching to reduce brittleness, but after a time the unconverted austenite does convert to martinsite. This is after the first temper cycle so we have some untempered martinsite which is brittle. A second temper cycle helps make sure of tempering this newly converted martinsite. Some steels require a sub zero quench (-170 F and even colder for some SS) after the initial hardening quench to force the retained austenite to convert. As for triple tempering I am not convinced its needed for everything. I only do it if its springs that get a lot of stress. this is a simple explanation, but in the heat treat sticky's in the knife section, I have references for more detailed information. Quote Link to comment Share on other sites More sharing options...
Patrick Nowak Posted June 17, 2011 Share Posted June 17, 2011 It is important to note that not all steels behave in the same way. The higher carbon steels (hypereutectoid, i.e. over 0.77% carbon) are prone to having much more retained austenite than the hypoetectoid grades. The highly alloyed tool steels are in class by themselves. Additionally, the section size of the part and hardenability of the steel used greatly affects the as quenched microstructure. Retained austenite will NOT automatically transform to martensite in low alloy hypereutedtoid grades. It becomes metastable. This can be good or bad depending on the application. For example, some bearings are designed to have a certain amount of retained austenite to promote toughness. Using liquid nitrogen to cool these bearings prior to fitting can force the austenite to transform to untempered martensite which will likely lead to premature bearing failure. When there is a desire to force retained austenite to transform to martensite (as in the case of blades), a sub-zero quench is used and this is followed by a temper. In the case of the low allow, hypoetectoid steels, double tempering at the same or sligtly lower temperature can sometimes help you improve toughness and ductility but it is rare to see this technique result in increased hardness and tensile strength though I'm sure it can happen is some alloys. There are certain grades which have very steep tempering curves, that is the hardness will begin to drop rapidly after a certian temperture is exceeded. This behavior is particularly pronouced in grades containing vanadium. The vanadium forms carbides (good for wear resistance and retention of hardness at higher tempertures) but once those carbides dissolve, the hardness drops quickly. When tempering these grades longer times at lower temps will often offer better control of the final outcome that shorter times at higher temps. For the low alloy steels with carbon up to about 0.50%, most of the time a single temper is sufficient to accomplish the techinical goals. Some grades do require double tempering, but a triple temper is almost never required unless one of the earlier ones was done at the wrong temperture. Patrick Quote Link to comment Share on other sites More sharing options...
monty Posted June 17, 2011 Author Share Posted June 17, 2011 ok, that makes sense, so ideally i should quench once, then do a subzero quench, then double temper? Quote Link to comment Share on other sites More sharing options...
thingmaker3 Posted June 17, 2011 Share Posted June 17, 2011 ok, that makes sense, so ideally i should quench once, then do a subzero quench, then double temper? Ideally you should find out what kind of steel you have and treat it accordingly. If that is not an option, then you can experiment with what you have. See the article by Dave Smucker beginning on page 12: http://www.abana.org/resources/affiliateshare.old/files/ALEX_BEALER_BLACKSMITH_ASSOC/abealer_newsletter_Feb_06%20%28v%2011%29.pdf Quote Link to comment Share on other sites More sharing options...
MattBower Posted June 17, 2011 Share Posted June 17, 2011 ok, that makes sense, so ideally i should quench once, then do a subzero quench, then double temper? Retained austenite is a rather complex subject, and my understanding is simplistic. But I suggest you do some reading on Ms and Mf (martensite start and martensite finish points), soak temperature, and quench speed. There's a lot of good info out there on the Net. (Add "Cashen" to your search terms. Kevin Cashen has written a lot about this, and it tends to be more accessible to us laymen than the discussion you'll find in a metallurgy text.) With that said, with a proper soak and quench (meaning a soak at the right temp, for the right time, and a sufficiently fast quench for your steel), I believe generally it's only the high alloy tool steels that have will have significant amounts of retained austenite. If you're using simple 10xx and other relatively low alloy steels, particularly hypoeutectoid (around 0.8% carbon and below), retained austenite isn't likely to be a problem and a trip to subzero temps probably shouldn't be necessary. But soaking at the wrong temp, or for the wrong time, or quenching too slow (this is where some of the homebrew quench oils can be problematic), can cause RA problems. The best solution to those problems would be to correct your quenching process, rather than trying to make up for earlier mistakes with a cold treatment. I'm not trying to play hide-the-ball by suggesting that you do your own research. I'd give you more specific advice if I could, but as I said this is a complex subject and I don't feel qualified to try to explain it in detail. I do know that there's lots of good information out there; I just haven't fully digested it all myself, yet.Mod note: at teh top of this section there are sticky posts on heat treating including the links Matt just talked about, if you would take the time to read it, you may have your answers Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted June 17, 2011 Share Posted June 17, 2011 Since the blade in "as quenched" state is so stressed and brittle that it can break just laying on the workbench. (Happened to a friend of mine!) I would not then further stress it with a cryo quench. I'd temper it *immediately*; then cryo quench and then temper again. Quote Link to comment Share on other sites More sharing options...
monty Posted June 17, 2011 Author Share Posted June 17, 2011 ok, thanks for the info guys! Quote Link to comment Share on other sites More sharing options...
MattBower Posted June 17, 2011 Share Posted June 17, 2011 Since the blade in "as quenched" state is so stressed and brittle that it can break just laying on the workbench. (Happened to a friend of mine!) I would not then further stress it with a cryo quench. I'd temper it *immediately*; then cryo quench and then temper again. Absolutely. But the recommendation I've seen is for a flash temper to around 300. IIRC, tempering much higher can actually stabilize any retained austenite, which makes it harder to push over the edge into martensite land. (As I said, it's a complex subject. ) So quench, temper at 300, then cryo and temper normally. Or just use simple steels, quench them properly, do at most a double temper, and be happy! Quote Link to comment Share on other sites More sharing options...
monty Posted June 17, 2011 Author Share Posted June 17, 2011 thanks, i think i may stick to simple steel simple hardening option! thanks for all your input! Quote Link to comment Share on other sites More sharing options...
son_of_bluegrass Posted June 17, 2011 Share Posted June 17, 2011 Since the blade in "as quenched" state is so stressed and brittle that it can break just laying on the workbench. (Happened to a friend of mine!) I would not then further stress it with a cryo quench. I'd temper it *immediately*; then cryo quench and then temper again. From my understanding, with simple steels (10XX) a temper between the quench and cryo pretty well negates any benefits the cryo might provide. So if you're using 10XX and want to temper immediately, i wouldn't bother with the cryo. You may get a little more from the steel if you do some form of cryo between the quench and first temper at an increased risk of a cracked blade. Unless you're fanatical about getting absolutely everything possible from the blade, it probably isn't worth cryo-ing simple steels. ron Quote Link to comment Share on other sites More sharing options...
monty Posted June 17, 2011 Author Share Posted June 17, 2011 ok, thanks ron :) Quote Link to comment Share on other sites More sharing options...
Glamuzina Posted November 7, 2012 Share Posted November 7, 2012 Since the blade in "as quenched" state is so stressed and brittle that it can break just laying on the workbench. (Happened to a friend of mine!) I would not then further stress it with a cryo quench. I'd temper it *immediately*; then cryo quench and then temper again. This is called a snap temper, usually 100 degrees below normal temper temp.i.e. 300F before cryo Quote Link to comment Share on other sites More sharing options...
Rich Hale Posted November 7, 2012 Share Posted November 7, 2012 If you know wot steel you have and google heat treat for it...It will say wot to do for temper and will say if it needs a cryo and when. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.