Temper cycles
- Thread starter Gliden07
- Start date
EdCaffreyMS
"The Montana Bladesmith"
Personally, I temper 3 times, 2 hours each time, allowing the piece to cool NATURALLY between tempering cycles. Why? For me it came from 3 years of experimentation, and having far more samples then I'd like to admit, sent off for testing in a professional lab.... and basing my methods on that.
Without writing a book, the resulting grain and elimination of undesirables in the tempered pieces were "best" at 3 cycles of 2 hours at a given temp. After 3, things started to swing the other way. Within certain parameters most folks do what "works" for them.
Time has taught me that subjects of this nature are the ones that always seem to start a firestorm of some type....so I've resigned myself to tell folks what I do, and why I do it....and not argue over it.
Somebody mentioned in another thread about how much info I relay via PM......
Maybe Kevin will swing in and give his input, and a more complete explanation..... but right now I am working on some angle peen hammers!
Without writing a book, the resulting grain and elimination of undesirables in the tempered pieces were "best" at 3 cycles of 2 hours at a given temp. After 3, things started to swing the other way. Within certain parameters most folks do what "works" for them.
Time has taught me that subjects of this nature are the ones that always seem to start a firestorm of some type....so I've resigned myself to tell folks what I do, and why I do it....and not argue over it.
Somebody mentioned in another thread about how much info I relay via PM...... Maybe Kevin will swing in and give his input, and a more complete explanation..... but right now I am working on some angle peen hammers!
Last edited:
Doug Lester
Well-Known Member
Personally, with euticoid or hypoeuticoid steel I think two two hour cycles is enough because these steels are not going to produce much in the way of retained austinite. Hypereuticoid is another matter. Depending on the amount of carbon put into solution retained austinite can be a problem and three two hour cycles could very well help thing by shocking the retained austenite crystals into converting to untempered martensite and then being converted into tempered martensite. That said, if you are dealing with euticoid or hypoeuticoid steel a third three hour cycle is not going to hurt one thing. Just my opinion; not saying that I'm more right than Ed.
Doug
Doug
Kevin R. Cashen
Super Moderator
I don’t go for as long as Ed, but I am also a proponent of more than one tempering cycle. I started out repeating cycles because one thing I learned a long time ago is that there are no set tempering numbers to give you specific HRC numbers, each piece of steel and each heat treatment is different. People still contact me wanting to know what temperature they should temper their steel at to get a certain Rockwell number, and my standard reply is- sorry I’m not in your shop and it’s just not that simple. So, I started doing shorter tempers at lower temperatures followed by Rockwell tests before bumping the temperature up and walking it into the exact HRC I wanted.
After the first two notebooks of HRC numbers, I started to notice a pattern in the data. The groupings of HRC number deviation got tighter with every temper. As Ed also noticed, at 3 cycles the grouping was a tight as it could get. What I mean is this- my first series of numbers may have had a deviation of as much as one point Rockwell between them, the next series was, of course, lower but the deviation tightened to perhaps .5 HRC and on the third there was almost no deviation at all. I didn’t get the same flattening of the numbers with much longer single tempers.
I may go out to 3 or 4 hours total to carefully get the exact HRC numbers I want, but my ideal would be to have the steel behave enough not to go that long. But it is also worth noting that I temper in salts, which almost eliminates the time spent bringing the steel up to temp in an oven. I quench between tempers, to get right to the HRC testing, but since it doesn’t really hurt anything it also give me some peace of mind about arresting some precipitation processes.
Tempering is all about sub-microscopic, like atomic lattice level, movement of carbon atoms, allowing the iron matrix to “relax” a little. At these low temperatures that takes time, like an hour or two, vs a second or two. Eventually these carbon atoms will gather up enough to create tempering carbides, once again too small to see with a light microscope. Where these carbides decide to gather can have differing effects and so you get these little curve balls thrown at you like the topic of this thread.
After the first two notebooks of HRC numbers, I started to notice a pattern in the data. The groupings of HRC number deviation got tighter with every temper. As Ed also noticed, at 3 cycles the grouping was a tight as it could get. What I mean is this- my first series of numbers may have had a deviation of as much as one point Rockwell between them, the next series was, of course, lower but the deviation tightened to perhaps .5 HRC and on the third there was almost no deviation at all. I didn’t get the same flattening of the numbers with much longer single tempers.
I may go out to 3 or 4 hours total to carefully get the exact HRC numbers I want, but my ideal would be to have the steel behave enough not to go that long. But it is also worth noting that I temper in salts, which almost eliminates the time spent bringing the steel up to temp in an oven. I quench between tempers, to get right to the HRC testing, but since it doesn’t really hurt anything it also give me some peace of mind about arresting some precipitation processes.
Tempering is all about sub-microscopic, like atomic lattice level, movement of carbon atoms, allowing the iron matrix to “relax” a little. At these low temperatures that takes time, like an hour or two, vs a second or two. Eventually these carbon atoms will gather up enough to create tempering carbides, once again too small to see with a light microscope. Where these carbides decide to gather can have differing effects and so you get these little curve balls thrown at you like the topic of this thread.