So I was reading a thread about heat treating and the response from Kevin Cashen made me think I may have the entire process of annealing and normalizing backwards.
My present process is to forge the steel to shape, then perform a slow anneal by heating above critical and cooling overnight in vermiculite. I then grind the blade to final shape. After grinding I normalize three times by heating to
above 1600 then a slow air cool. The next heat is to 1550 and air cool, then 1500 and air cool. I follow the normalizing steps by a heat to just above critical and then into the quench. I perform the heat and quench cycle three times for 5160 and 1095 steels. From reading the thread response by Kevin, it sounded like I should be doing my heat cycling prior to the slow anneal. I thought that heating to above critical during the anneal cycle would cancel all of the prior heat cycling. Leaving you with large grained easy to grind s I thought the steel would need normalizing cycles to refine the grain prior to the quench. Any help on a clear understanding of the proper steps would be greatly appreciated. Most particularly as it relates to 5160. What temp would I use for a stress relieving cycle and where would I put it in the process for 5160?
Lowell, it is quite common for folks such as myself to give advice without first asking for the appropriate details of the process being used, such seems to be the case here, and I apologize.
The anneal you are using is the traditional “lamellar†annealing process of heating to above critical temperature and then slow cooling to allow the formation of pearlite, hence the lamellar label. This will indeed affect grain size to some extent (depending in the maximum temperature used) and redistribute carbon.
I must compliment you however on your choice of initial temperatures for the normalizing cycle. Many start out very low and go even lower, you have opted for the actual industrial normalizing range for the initial heat. This is beneficial for homogenizing all of the internal concerns and the effects of forging. I would still stick with some proper normalizing before the anneal due to the benefits immediately following forging. The idea is to put everything into solution to homogenize and then refine that condition evenly; if there is one thing that is worse that large grain size, it is an uneven grain size and carbide distribution.
Of course one could follow the anneal with other cycles but they would undo the benefits of an anneal, so it is best to put them after the machining and grinding operations. At this point the largest concern is controlling decarburization. If you knife is ground to close to final dimensions and you have decarb from these subsequent operations there will be a skin left over that will result in a knife that will not hold an edge well until it has been re-sharpened several times to expose good carbon steel within. If one employs good methods to avoid decarb and scaling from heat cycles following the grind then you could also dispense with the stress relieving operation and just incorporate it into the cycles.
With a wider array of steels other annealing options could also be incorporated to avoid undoing the effects of the cycling, and while subcritical annealing will work with 5160 it is not as effective as with other steels and I would prefer to adjust one part of the method that you are comfortable with at a time in order to maintain some level of control in a process that has robbed many of us of our sanity long ago.
"One test is worth 1000 'expert' opinions" Riehle Testing Machines Co.
Mr. Cashen-
Am I reading your response correctly that after forging, 3 cycles then the anneal followed by the other 3 reducing heat cycles after grinding is a good way to go? This way there is a more even grain and carbon distribution (although less than optimal due to the following anneal) during the grinding of the blade? Then, what was "messed up" so to speak by the anneal is made better by the final cycling just prior to the heat treat process? Sorry for all the clarification issues.... Sometimes I feel a bit over my head and want to be sure I have the best understanding my little brain will allow <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//smile.gi f' class='bbc_emoticon' alt=':)' />. Thanks for asking a good question, Clay and for your sharing of knowledge, Mr. Cashen.
Jeremy
Jeremy Lindley, Apprentice Smith
Kevin,
No apology needed. Your prior response kicked up a new question in my mind and you have clearly answered the question. I cannot not express clearly enough how much I appreciate this site, the willing help offered, and the in depth explinations you provide.
So my understanding from your answer is that normalizing the steel prior to the lammelar anneal puts the carbon into a proper distribution in the steel. This is the proper step in the process to forge a 5160 blade to shape. Annealing the blade after forging makes the steel machinable and grindable, and messes with the carbon distribution a bit. After you anneal the blade you want to remove the scale and then grind to final shape. At this point the steel needs to be normalized again to refine the grain size and when done properly remove stresses created in the forging process. Another option would be to normalize three times then heat to 1300 and slowly air cool to remove stresses in the steel.
Once you have the steel normalized it is time to run the steel up to just above at or above nonmagnetic and hold it there for a bit. Then into the quench. Repeat two times since I have a simple propane forge and don't want to overheat the steel. I think I have the process down now. Corrections to the process are welcome.
