5160

T

thunderbolt5

Joined
Aug 23, 2012
Messages
6
Hi all,

I'm new here, but not so new to metalworking. I'm a machinist as my day job, and have an entire shop at my disposal, including cnc's, grinders, manual mills and lathes, etc.

Anyway, I'm making a big meaty wacker of a knife and have a couple questions.

After referencing my Machinery's handbook, I'm normalizing some blanks of 5160 that is 12"x2"x .323" thick. I did say they were going to be meaty...

However, here's my questions; I'm normalizing @ 1600°F, but for how long? I figured about an hour soak would be fine? They are pretty thick...

Anyway, after this, I'll put then in the hardness tester and see where they're at. I might not even have to draw them back to work them. We'll see.

T.
 
When I normalize after forging, I bring it up to temperature (doing this by eyeball and with a magnet), then pull it out and let it air cool until there's no more heat color visible in dim light. Then I do that two more times. Makes a nice, fine grain. At soaking for an hour, you're probably looking at some large grain growth, and all else being equal, the larger grain will be weaker.
 
Maybe you're confusing some terms and procedures. No need to normalize if you're doing stock removal. Depending on the steel, you may want to anneal the steel by heating it to non-magnetic (1475) and then putting in vermiculite to cool very slowly and leaving the steel soft. As Storm Crow says, after forging you do want to normalize several times to refine the grain structure before heat treat. This is a very basic description of things, but the procedures work. Check the stickies at the top for more good info.
 
Whether you are forging or not, unless you are sure the steel has been normalized/annealed, it is a good idea to normalize... anything else, would be a gamble.

Do as Stormcrow says. Bring up to 1500-1600F let air cool(no vermiculite needed). The trick is to do three normalizing cycles, each at a lower temperature, ending with a final cooldown from just past non-magnetic (which is 1418F). If you want it softer(annealed), heat until it just begins to show color in a dark room and let it cool. Using vermiculite is okay for simple hypoeutectoid steels (5160 is actually in that range) but I avoid it due to the fact it can really muck up steels with higher cabron content(1095, O1, 52100, etc) It doesn't help all that much so I don't see the sense in using it unless your shop is in the frigid North.
 
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Excellent replies, thank you.

I left the blanks in for about an hour. Then cracked the door and let them cool, it took several hours.

I took of the blanks, scaled it, and put it in the Rockwell tester and it came out @ 22rc. Awesome. I'm not even going to worry about annealing right now.

A file cuts them like butter. Now I'm going to surface grind them, then rough profile with a band saw, then grind the beveling, rough sharpen, then harden.

I'm not sure about what my final temper will be. This steel is capable of 63 rc. Is that too hard? It will end up near 5/16" thick, so should I be concerned about brittleness? Or should i draw it back to 58 or so? Or will 5rc make any difference?

T.
 
The idea is to quench for maximum hardness, then temper back to the desired range. 58HRC is good for a chopper. That would most likely be around 425F if everything went well in the quench.
 
thunderbolt5 said:
If 63rc is fine for this steel/application, then maybe save a step and not bother drawing it back....?

T.
Click to expand...
Tempered martensite is tougher than untempered martensite. Even if your quench only yielded a 58HRC count, it would be very brittle. That is why we go for maximum hardness and temper back. It makes a better, stronger and tougher blade. Once you get a better grasp of metallurgy, it will all make sense bud.

I would avoid cracking the door of your kiln to let things cool. Firstly, it makes little difference to the steel but more importantly, it can shorten the life of the elements your kiln.(if it is electric, that is.)
 
Gotcha, makes sense.

I followed the advise of a fellow in my shop that does our other heat treating with the door. We shut the power off and let the temp fall a few hundred degrees, the door was propped open about a half inch or so. Still took several hours for it to get to ~400°.

Thanks for the advise.
 
Storm Crow said:
When I normalize after forging, I bring it up to temperature (doing this by eyeball and with a magnet), then pull it out and let it air cool until there's no more heat color visible in dim light. Then I do that two more times. Makes a nice, fine grain. At soaking for an hour, you're probably looking at some large grain growth, and all else being equal, the larger grain will be weaker.
Click to expand...

Speaking of that...

If I wanted to generate finer grain structure, what would be the process fire this? Say, if I wanted to make sure that the finer structure was present.

It is simply repeatedly normalizing? Or would there be a specific process for this?
 
Thermal cycling at the proper temperatures refines grain. As I understand it, refinment is a product of nucleation and recrystalization. Nucleation begins to occur at points of strain(dislocations and former grain boundries) Repeated cycling into the recrystalization realm allows the steel to do this on it's own. That said, grain can only be refined so much, which is why after 2-3cycles, you aren't gaining anything but more chances to screw up. We use reducing austenization heats for each cycle to avoid grain growth. There is no sense in undoing what you've done.
 
Ok, so I've got the knife almost done. Next step will be heat treating. But, a couple questions.

I can either harden the knife with a torch, then oil quench, or, I can use the oven, then oil quench. Which would be the best option?

Secondly, with tempering, I'm wondering the best way to do this.

I can, again, either temper in the oven, which would give the most even results, or, I can temper with the torch.

The knife is 5160, 12" long, the blade is 1.750" wide, and the knife is full-tang and 5/16" thick.

Would differential tempering be better? If so, what would be the best method?

Obviously, this is a big, hard-use knife, I need durability first, then toughness.


Ideas?
 
Harden using your oven(1525F) and oil quench(130F).

Temper with your oven, twice at 425F.

With 5160, you shouldn't have to torch back the spine but if it makes you feel better, put the edge in 3/8" of water and slowly blue the spine about 2/3rds of the width. Quench right away in water.

Obviously, this is a big, hard-use knife, I need durability first, then toughness.
Click to expand...
Durability is toughness, brother. I think you mean toughness first, then strength.

Toughness is the ability of the steel to deform before breaking. Not enough toughness, the steel is brittle... too much, it loses all strength and bends/rolls.
Strength is the ability of the steel to resist deformation. Too much strength, it's brittle... too little, it bends/rolls.

There is a special relationship between the two. For example, if the geometry and strength are up to the task, you won't be able to flex the knife enough to deform it... so having a higher HRC is not a problem. Your blade is pretty thick. That's why I suggest to not bother with a differential temper.... but it's up to you.
 
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