best way to straghten a katana before heat treatment

[mack79]

I am making my first katana and would like to know if there are any tricks to straghten it an easier way before I heat treat?:

 

[mete]

Make sure it's annealed .You can do a sub-critical anneal , 1200 F for two hours . Then use some muscle to straighten and it should be OK after you HT.

 

[mack79]

Thx for the info I just got into blade making and have do e a lot of reading on things I have a two burner gas forge could you tell me the best way to anneal with what I have?

 

[Matt River]

Forge anneal is simple. Heat up, cool slow. Heat to near critical preferably, stick into a can of wood ash or vermiculite. For a katana, a large heated plate or bar with lots of residual heat should be nested alongside the blade to slow the cooling.

Making a large slightly curved blade straight can be difficult, many smiths use very precise, counted, symmetrical hammer work. Every single heat I end by straightening, every time. Trying to straighten at the end, to me, is the primary reason for breakage, cracks, and a return to the initial crooked shape.

Boards with a notch like a wrench can be used to take out twist. Sacrificial beater stick can be used immediately after quench during brief plastic stage. Tempering can be done with the blade braced against bending, or for existing bend tweak a little past, then brace and temper. After tempering cold forging the blade on a concave stump with wooden mallet may work, traditional technique. On a large blade grind removal can also effect symmetry, the blade should be planished and smooth at the forging stage, no lumps, this will create uneven stresses in the steel after quench, when you grind, it will warp. Good luck

 

[Mecha]

Great stuff right there, Matt River! :thumbup:

 

[samuraistuart]

If the steel is hypereutectoid, I would not do the slow cool vermiculite thing (unless a solid normalizing were to follow this at some point). This puts pro-eutectoid cementite in grain boundaries, making for a brittle structure. If it's steel like 1050, 1065, 5160, 1075, a eutectoid....then there isn't excess carbide to go to grain boundary, so it's a non issue. Not advised with 1095, W1, W2, and the hypereutectoid steels, which aren't the "best" alloys for a sword anyway.

 

[mete]

I'm glad you added that ! Often the advice is to SSLLOOWW cool but then you may get continous grain boundary carbide ! That can be extremely brittle .That means someday the customer drops the blade and it shatters !

 

[samuraistuart]

Shatters? I hope not! I hear that, and may have been guilty of saying it myself! What actually happens when you take a very brittle steel, say as quenched 52100, and drop it? It will likely break in half or a few pieces, but not shatter. Is that correct? I've never dropped or thrown a hardened untempered piece of steel before, and I've heard some say it will shatter....but that isn't really true, right?

 

[hank_rearden]

i watched a luis mills video of him making a longish tanto. after the the first quenching, he simply reheated and tapped it with his hammer.

 

[mack79]

Thanks for all the help the sword has come out very well for me for my first attempt I'll post some pics.