Questions re: normalizing, drawing, quenching

[scdub]

Hi All,

I've completed my first couple of knives and have accumulated more questions. Here are picture links:
http://s211.photobucket.com/albums/bb32/scdub_photos/First Knife - Rescue Entry/
http://s211.photobucket.com/albums/bb32/scdub_photos/Second Knife - Defense Utility/

I'm forging 5160, quenching in canola oil @120 degrees F, and tempering with a toaster oven at 450 (for chopping blades - will probably go down to 400-425 for slicers).

Question #1: Is normalizing necessary? If so, when? Multiple normalizing cycles? Would I lose anything to do all the forging on a blade and anneal it (without normalizing) then bring it home to grind? This is just a question of time management (I don't have enough).

Question #2: With my first knife I used a propane torch to draw down the temper on the handle while keeping the edge in a water bath. I tried for awhile to get the colors to run further down the spine but they didn't want to budge (see photo) and I finally got scared and tipped the blade the rest of the way into the water to stop the reaction. Any thoughts?

Question #3: I'm using about 5 gallons of 120 F canola oil to quench. Seems to be working, but I wanted to know how much gain I could expect to get from using a commercial quenching solution.

Question #4: On my second knife I tried a triple quench. On the third quench the knife twisted on me. I believe it may have been too hot on the third quench - is this the likely cause? Any tips to keep this from happening?(I was able to heat and straighten the blade and after that it only got one more quench.)

Question #5: When quenching, I dip the knife point first into the oil and submirge it about halfway up the handle, then slowly work the knife up and down to keep from forming a "hardness line" on the handle. Since I'm primarily concerned with quenching/hardening the blade, is it necessary to get the entire knife (blade and handle) to critical before quenching, or am I O.K. just bringing up the blade and part of the handle?

Thanks again up front. I can't tell you guys how much I appreciate being able to get specific answers to questions like this. I try to save them up to keep from wasting everyone else's time, and please know that I try to search for answers first.

SCDUB

 

[scottickes]

Question #1: Is normalizing necessary? If so, when? Multiple normalizing cycles? Would I lose anything to do all the forging on a blade and anneal it (without normalizing) then bring it home to grind? This is just a question of time management (I don't have enough).

I'll try to tackle this one for you. I "ALWAYS" normalize. The process of heating steel and then moving it with a hammer puts a lot of stresses in the grain structure of the steel. Think of it as a tower made of toothpicks glued together. You have the tower three feet tall, and you begin to glue a bunch of them on the sides......further and further out....eventually the stress will cause something to give. The steel has stresses in it, pulling in many different directions. When you heat it to normalizing temperature and then let it air cool to ambient, you relieve that stress. It allows the grains to line up nice. I personally normalize three times. Thinking about the tower of toothpicks, normalizing would be like magically lining them all up in the perfect places to keep the tower nice and solid.

I used to have problems with knives warping during anneal, or during hardening. There have been times that I've taken my annealed knife out of the vermiculite and it was nice and straight. I would begin to clean the scale off of it and would notice that it had warped during the clean up process. I get much more consistent results when I normalize.

Another reason to normalize is that if you leave those stresses in the steel and then clean it up, then harden it, those stresses are STILL there! This will result in blades that can crack during hardening.

My advice is to take you time and normalize, anneal, clean it up and get it ready for hardening. Than harden and temper it.

It's even possible that a knife made without a normalizing cycle can make it all the way through the manufacturing process, only to fail (crack or break) when your customer has it. Hopefully, he/she isn't using it in a life threatening situation and counting on it, if it does crack or break.

I personally, would not even consider skipping normalizing.

 

[Kevin R. Cashen]

Begin forging at high temperatures and finish at lower ones. Good and hot for shaping profiles and very heavy reduction, less hot for edge bevels and final smoothing and straightening. This is good for the inside of the steel as well as you technique. The very hot temps will allow you to easily work it, but it will also help homogenize the internal structure, this is very important with some of the things going on in steel that comes from the mill these days and if done right this is indeed one way that our forging can improve things. But forging it all at too low a temp will only segregate things worse, treat forging like a heat treatment and you will do all right.

Normalizing is exactly what its name implies, it is for evening out and refining as much of the inside of the steel as you can. Start out real hot again and then do at least two more at progressively lower heats. Don’t get you panties in a bind over the exact heat as much as the evenness of that heat, this treatment is to make everything as even as possible and you will only defeat that purpose by not heating and cooling as evenly as possible. The first heat may be hot enough to grow grain, don’t sweat it since the idea is to get all the grain the same size on the first heat, after it is all pretty much equal the next two or three will make the grain smaller by cycling through the critical temperatures at lower heat.

The next hang up is the anneal. Annealing can mess with the grain size and possibly undo some of what you did with the normalizing. It is for this reason that I use sub-critical anneals in order to avoid this, but it is a rather more advanced technique that could mess with things if you don’t have the equipment to handle it. In your position I may simply normalize/stress relieve the blade and then heat just the tang to critical for a full anneal. This would be miserable for a much deeper hardening steel but 5160 is less tenacious.

The quench is less critical for 5160 since it is an oil hardening alloy with a more forgiving curve, so the canola may provide the overall speed. However it will not provide that same consistency, evenness or long term reliability of a formulated quenchant dedicated to the task. If you can get it and want to treat yourself to a better quenching experience, you will not regret a good quenching oil. Tough quench may work, Parks AAA would be very good, I believe Chevron makes a good one for this steel and many others.

Judging tempering solely by color is a treacherous game since the colors are determined as much by exposure to oxygen as the heat. If you so much as touch the blade your finger oils can give an entirely different tempering color. Use a good oven that you have checked the temperature accuracy on and forget about the colors, this will be easy once you see the wide array of colors your blades will have at the exact same temperature in the exact same oven. You will also notice that the blades will develop a richer color as they are cooling after they have been removed from the oven when they are exposed to more fresh oxygen, the inside of the steel only cares about the heat and doesn’t give a rip about oxygen or colors. After the temper draw the other parts back with a torch, but be aware the in order to get that rich blue in just few seconds you are having to go much higher in temp than if you had set it on there for two hours. Time + temperature, time + temperature…

 

[scdub]

Thanks guys.

I'm convinced re: normalizing. I'll also be in the market for a good quench oil when I've sold a few more knives.

I have this feeling that all my questions may have in fact been answered but I'm just not smart enough to fully understand the answers...

Normalizing: Kevin, when you talk about lower temps for 2nd, 3rd normalizing cycles, are you talking sub-critical? Or, alternatively, should the first one be somewhere above critical? (Critical to me meaning non-magnetic). Is it best to do all normalizing after knife has been forged to shape or should I do them along the way?

After the temper draw the other parts back with a torch, but be aware the in order to get that rich blue in just few seconds you are having to go much higher in temp than if you had set it on there for two hours.

I'm not sure what you mean here. Is this a warning about killing the edge temper? If so, is a water bath for the edge sufficient protection or is there something else you'd recommend. FYI: I'm only using the torch to draw back temper. I'm tempering in an oven @ 450 twice for two hours.

Last one again: Is it O.K. not to have the handle reach critical before quenching?

Thanks again. Let me know where to send the beer.

SCDUB

 

[Kevin R. Cashen]

To be honest there is way too much sub-critical heating among bladesmiths, the erroneous concept of if a little bit is good then a whole lot has to be even better has us segregating our steel and sacrificing strength in a lot of areas. When I say “hot” for the first one, industry starts many normalizing operations at around 1600F, and since we will have the ability to refine the grain in subsequent operations I wouldn’t hesitate to go with it in order to very effectively homogenize the steel. Forget red on the first heat go for an even and proper orange. This is why I say the next two heats will be cooler. The next could be at around 1500F and followed by the neighborhood of 1400F. (1414F. is the point at which the magnet will stop sticking) for insurance it could be followed by another at just above 1300F, not only would this create very fine sub-grains but it would be an excellent stress relieve and possible prep for grinding without a full anneal.

The reliance on the magnet for an accurate temperature for all operations is fine for the beginner but one really needs to advance beyond it eventually in order to maximize various heat treating operations. As mentioned the Currie point is 1414F., and the proper solution temperatures for many simple steels can be over 100 degrees higher, not to mention that actual changes from the room temperature state start occurring almost 100 degrees cooler.

If one approaches forging with a healthy mindset, every heating and cooling will be a normalizing operation with hammering thrown in, but that hammering will introduce random energy into the equation that will need to be dealt with in the end by a good normalization.

My warning about the higher temperatures to get the blues when drawing back the spine and tang was to illustrate one more case of the oxide colors not being all that accurate for judging temperature, I had assumed that you were protecting the edge with water.

It is o.k. not to have the handle up to temp. before quenching if you have no intention of hardening the handle, however if you have the handle prepared for it and want to be very thorough, a quenched and heavily drawn tang will beat an un-heat treated one in strength and even in toughness if drawn sufficiently. For this reason I like to quench as much of the tang as possible, leaving just the threads at the tip (if present) untouched to avoid stress risers. This also allows me a great place to do all the Rockwell testing I want without touching my carefully placed finish.

 

[scdub]

Excellent.

Thanks so much once again. I hope others reading this have gained as much as I have.

One last question before I dive into my next batch of blades. It seems that most literature suggests quenching at just above non-magnetic - say 1500 degrees. Does this sound about right?

 

[Kevin R. Cashen]

1500F is a very good number for many steels. 5160 would do very well at 1525F however. I wouldn't be so picky about those 25 degrees except if you are not soaking the steel for extended periods every little degree higher you can get away with will help make up for it.

 

[Allan Molstad]

scdub,
Thats a nice bit of knife testing you shot there...
However if I were to suggest a few changes for your next filmed blade test, I would say that a better shirt that covered the wrist would be helpfull .
You did do a little blade bending test in the car door, but Im not sure where you were headed with that test?...Can a door be popped open like that?
A vise could have helped show the abliity of the blade to bend/flex and not snap too.

I did like the blade test where you drove the blade into the car top, then started hitting it with a hammer to open up a bigger cut.

Thats a knife that can take battoning like a pro.

 

[scdub]

I thought I'd share the fact that I share this laptop with my wife who is in law school. In other words - I don't get it much.

Allan - thanks for the tip about a long sleeved shirt.

I didn't think I'd be able to pop the door but wanted to try. (I was with a couple of fire fighters that day and they said it's often hard to do even with a halligan tool.) The main point of that test was to see if the knife could take my full body weight without breaking or setting a bend.

I liked the baton cutting through the roof the best too. Since I actually carry a baton on duty I figured it's something I could actually do in the field if the need should arise (knock on wood).

As I make more knives I plan to do some test blades and use a cheater bar in a vise to see what they can really take - maybe after I get a real belt grinder...