Replies

1. 
   lwilliams | Nov 19, 2009 02:54am | #1

   Let's see. When I heat treat steel I pull it out of the furnace or out of the flame at 1,500º F and plunge it into oil or water, depending on the steel. I'm trying to drop its temperature around 1,400º as quickly as I can. If I've done that right, the steel is fine and ready to be tempered at 350º to 375º. Lee's book then says I can't raise the temperature of the steel to less than 350º, much less if you're grinding properly, and then quench it in water? This grinding quench, which may drop the temperature of the steel a couple hundred degrees if you've been heavy handed at the grinder, causes too much shock for the steel? Things aren't adding up here for me and I have such serious doubts about the assertion in Lee's book that I ignore the information in the book.

1. 
   user-219305 | Nov 19, 2009 03:14am | #2

   Hmm...I'm inclined to agree with you. Just to play devil's advocate here, I wonder if the very thin nature of the ground edge would cause it to behave differently than a whole iron when quenched...

1. 
   lwilliams | Nov 19, 2009 04:23am | #3

   Rick,Most of the heat treating I do involves profiled molding plane irons and the irons are shaped and beveled before heat treating. If things go right, I have very little work to do other than a little flattening and then final sharpening after heat treating.I think a better argument for Lee's assertion is that the steel going into the quench isn't all that brittle. It's austenite and the quench is what converts it to the more brittle martinsite. The conversion actually takes longer than lowering the temperature. With O-1 or W-1 steel you have a few seconds where you can straighten the steel after the quench if there's been warping. Not many seconds, maybe three or four before the steel is too brittle to try to straighten. Highly alloyed exotic air hardening steels take longer to convert, some up to around six months. That's where cryogenic tempering comes in and will speed the conversion.Still, many heat treating schedules for oil or water hardening steels call for quenching after the temper. At this point the steel is martinsite with almost no retained austenite. The steel is also hotter than you should get it when grinding. If fracturing after tempering was a problem, those heat treating schedules wouldn't include quenching after the temper.I'm not sure what happens to carbides and the powder technology steels if you quench them after heating them. I do it when grinding the steel mounting on carbide tooling but that doesn't necessarily mean it's a good practice. I always grind the steel backing away from carbide bits and other metal working tools to avoid grinding steel on the diamond grinder but avoiding using diamonds on steel or iron is another topic.

1. 
   chscholz | Nov 19, 2009 08:10am | #4

   This all sounds correct. However, I believe what Leonard Lee refers to is an entirely different bowl of fish than the phase diagrams that the previous posters mention (ok, maybe entirely is too strong a term here).

   These days a whole branch of material scientists are trying to figure out what happens before a crack appears, how cracks initiate; when, under what conditions and how microcracks propagate and eventually lead to catastrophic failure. Phrases you might want to Google in this context are fracture mechanism, stress intensity factor, dislocation and others.

   Concerting the original question (can dipping a blade in water increase the amount/size/probability [in fact it is not clear what exactly increases] of microfracture?). It is conceivable that there exists a body of research that shows that this can happen if certain conditions are met. But it is common in the popular literature that scientific findings are taken out of contexts, mis-interpreted or simply mis-understood.

   Not a material scientist, I would give the author the benefit of the doubt, but not enough to change my sharpening habits.

   Chris

   ---

   Chris Scholz

   Dallas/Fort Worth, TX

   Galoot-Tools

2. 
   philip | Nov 19, 2009 12:17pm | #5

   Larry,
   Things are not adding up for you because you are talking about the process of hardening a steel .
   L. Lee is referring to steel already hardened eg as in a chisel- repeated sudden temperature drops as in repeated dipping in water can lead to micro cracking : the steel does not have to anywhere near red hot to encourage this, especially since there is a thin edge involved.
   I have seen two studies of this -one in Machinery Handbook and the other somewhere else. I will try to dig one or the other up.Philip Marcou

2. 
   davcefai | Nov 19, 2009 10:33pm | #6

   Some time back I had a problem where the edge of my chisels was breaking off during use.

   The reason turned out to be that I was overheating the blade then dipping it in water. The blade was hot enough to hiss when it touched the water but not hot enough to change colour.

   I was told that I was making the steel brittle by treating it that way. Now I still cool the blade in water but early and often and no longer have a problem - same chisels, 20 yr old Footprints.

   It is possible that I was also inducing cracking by my ill-treatment.

   My point is that it could be true that quenching causes cracking. However if you keep the blade cool it seems that this will not be a problem.

1. 
   user-219305 | Nov 20, 2009 02:03am | #7

   Your practical experience is bringing focus to this question. The blade hissed when you dipped it in water, the edges broke during use.Because I have an aversion to bluing the steel verging on the paranoid, I haven’t had any problems with edges breaking off...When I grind I stop frequently to check my work and touch the edge. If it’s too hot to touch, I dip it. After the first dip I pay attention to the drops of water on the back of the chisel. The first moments, they just sit there. Then they start to bubble. Then they evaporate quickly. A few moments more of grinding and I dip it again.

3. 
   RalphBarker | Nov 20, 2009 09:11am | #8

   Gosh, I wish someone had told me about this a few decades ago. I've been splashing cold water on my hot face for so long, the micro fractures have turned into major wrinkles! ;-)

1. 
   davcefai | Nov 20, 2009 09:36am | #9

   There's an easy fix for that! An 80 grit sanding disc at about 3000 rpm will smoothen the substrate in no time at all.

1. 
   RalphBarker | Nov 20, 2009 09:55am | #10

   Thanks, Dave. I had thought about using 220 grit, but I can see where the 80 would be much more efficient.