Heat Treating Steel Explained

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Understanding how a crystal formation occurs in volcanic activity is much like what happens in steel. Liquid magma dumped straight into the ocean instantly solidifies, locking in the natural state of the magma. If allowed to cool slowly over thousands of years the different elements begin to clump together forming crystals. Quartz, silver, gold. Cripple Creek Colorado is an excellent geological example of this. This same concept can be applied to heat treating. Instead of thousands of years as a time metric, you’re dealing with seconds.

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The normalizing process I find particularly interesting. If you do several normalization cycles each time lowering the temperature you take it to prior to air cooling you can produce a very fine micro grain structure.

Each time you normalize the crystalline structure has time to grow as it cools. The goal is to take your metal and make the entire piece uniform in its crystalline structure, with the smallest crystal growth possible.

For example, lets say you are working with CPM S110V (my favorite fillet knife material for my personal blades) stainless. This would be the correct heat treatment for the blade.

All steel manufacturers include data sheets for their products. It doesn’t have to be a special alloy steel, you can find these data sheets for many common metals both stainless and non-stainless.

Crucible Industries makes S110V, the data sheet can be found here:
http://www.crucible.com/PDFs/DataSheets2010/Datasheet CPM S110Vv12010.pdf

CPM S110V much be quenched at 2150F. That would be your minimum temperature for normalization cycles. This is the austenitization temperature. It should be non-magnetic, and the lowest temperature that loosens the bonds between the crystalline lattice in the material.

~~Normallization~~

Cycle 1:
Set your soak temp for 2250F and soak for 1hr. This will homogenize – think of it as almost liquidizing the crystalline structures in place, they are still there roughly but are in a state where they will reform during cooling. The bonds that hold them together are broken, but they are still there “thermal memory”. You will never completely get rid of them without melting down the steel. The higher your temp is the longer it takes to cool. You want to start above your quench temperature, but without excessive heat. Go with the closest margin of error your heat treat furnace can achieve. Given the same rate of cooling in air a higher starting temperature will result in larger crystals. This is important to remember. Once you start your normalization cycles you want to make sure you never cycle at a higher temperature than your last cycle. If you do it will continue to improve uniformity, but not so much the grain size. By reducing the temperature a bit on every cycle you both create uniformity of crystalline structure AND force smaller crystals by reducing the time in which the crystals have to grow.

Cycle 2:
Set soak temp for 2225F and soak for 30mins, air cool. This slightly lower temperature will reduce the time it takes for the steel to cool below the austenitization temperature. The crystals that formed in the first cycle will be unable to reform to their original size and the micro-stresses of the crystal formation will force the bigger crystals (thermal memory here) from the previous cycle to break up. This is very good.

Cycle 3:
Set soak temp for 2200F and soak for 20mins, air cool. Again lowering the temperature a bit forces the thermal memory of the previous cycle to break up even smaller.

Cycle 4:
Set soak temp for 2175F and soak for 20mins, air cool.

At this point you have a very uniform crystalline structure throughout your steel and a very small grain structure. By stepping down your temperature each cycle you have forced less of the crystals to homogenize each time, creating an effect that fills in the gaps so to speak between the larger left over crystalline structures that formed during the first 2 or 3 cycles.

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~~Quench~~
At this point you want to go for your quench at 2150F.
Set soak temp for 2150F and soak for 20 minutes. Quench appropriately (interrupted oil quench, I suggest ISO 32 hydraulic fluid)

Note this is below the normalization heats. If you go above your normalization heat temps you ruin the work you have done by the step down cycles. Make sure you never do this – never quench from a heat higher than your normalization heats. While the quenchant will cool much more rapidly than air, you don’t want the small grain structure you built to dissolve. This is an extremely important concept – the longer your steel takes to cool the larger your grain structure will be AND thermal memory (IE achieved crystalline structure size) is affected by temperature. Combine those two concepts and it will hopefully make sense as to why you don’t want to quench above your last normalization cycle’s temp. You want your steel conditioned perfectly by the normalization process so that when you go for a quench you can do it right at the austenitization temperature. If you skip the normalization structure you lock in whatever stresses and non-uniform crystal growth size is in the steel. This is why you see smiths on forged in fire quenching at cherry red end up with high performing blades and those quenching at bright yellow end up with chipping and rolling. Both are hard, but only one is strong. This is also why quenching in water is very dangerous for steels with high rates of crystalline formation. Where pure iron may survive, high carbon alloy steel with very complex crystalline and even carbide micro structures just shatter like glass under that amount of internal stress.

After the quench the uniform/tiny crystal formations are set.

~~Temper ~~
Set soak temp for 975F and soak for 2 hours. Make sure it completely cools to room temp each time. Repeat 2 more times.

Found the Tachi Pics – Blacksmithing

This is just after the differential clay hardening. The hamon is visible in some of the bottom pics.

Build Log – Hira Zukuri Tachi

Tachi 

Authentic tachi were forged during the Kotō period, before 1596. With a few exceptions katana and tachi can be distinguished from each other if signed, by the location of the signature (mei) on the tang (nakago). In general themei should be carved into the side of the nakago that would face outward when the sword was worn. Since a tachi was worn cutting edge down, and the katana was worn cutting edge up the mei would be in opposite locations on the nakago of both types of swords.

An authentic tachi that was manufactured in the correct time period averaged 70–80 centimeters (27 9/16 – 31 1/2 inches)in cutting edge length (nagasa) and compared to a katana was generally lighter in weight in proportion to its length, had a greater taper from hilt to point, was more curved with a smaller point area.

Unlike the traditional manner of wearing the katana, the tachi was worn hung from the belt with the cutting-edge down, and was most effective when used by cavalry.Deviations from the average length of tachi have the prefixesko- for “short” and ō- for “great or large” attached. For instance, tachi that were shōtō and closer in size to a wakizashi were called kodachi. The longest tachi (considered a 15th century ōdachi) in existence is more than 3.7 meters in total length (2.2m blade) but believed to be ceremonial. In the late 1500s and early 1600s many old surviving tachi blades were converted into katana by having their original tangs cut (o-suriage), the signature (mei) would be lost in this process.

 

Hira Zukuri

Basically a bevel which slopes from the cutting edge of the blade all the way to the back. Rarely seen on full length swords, usually used when making tanto and wakizashi. It forms a lighter and much sharper blade with greatly enhanced cutting ability at the cost of durability. You wouldn’t want to go up against a sword wielding opponent with one of these if you find yourself having to block and parry often. If however one wanted a very light weight but very effective offensive-only sword this is the way to go. In the world of competitive tameshigiri cutting these are often referred to as ‘cheater blades’ due to their cutting effectiveness.

Here is an example of a Hira Zukuri style blade. Note the complete lack of a flat deflecting side edge.

 

 

 

 

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Dagger WIP

Cedar heartwood handle, so pretty.

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Smithing Work Pics

very good pic of a syngas burn, smothered the charcoal with wood chips

Little Smithing Writeup

I’ve been working with hot metal for about a year now. Here’s a little writeup of things I’ve learned along the way.

First some basic one liners of wisdom. All of these have been learned the hard way.

  • Don’t work hot metal while wearing tennis shoes. Use steel toe leather work boots. You will learn new levels of speedy footwork if you ignore this.
  • Always make sure the metal stock is even with the face of the anvil before hitting it. You will save a lot of finger injuries if you keep this in mind.
  • Wood as a fuel source doesn’t work very well, but it works. Chop it up into small chunks or you’ll be waiting for ever for a hot spot.
  • Cold weather can rupture metal slack tubs when the water turns to ice.
  • Yellow/White hot steel is much, much, much easier to work than red. Be patient let the metal heat.
  • 6” wide pipe does not work as a chimney. Order the big stuff the first time (12” works good).
  • Too much air blowing into the forge is bad. If you’re throwing sparks you’re loosing heat.
  • Drill your holes BEFORE you quench… /facepalm
  • Take care not to accidentally bend your blades in the fire when heating to quench, this is especially true for thin blades.
  • Don’t smith without a slack tub nearby. If it breaks go ahead and rig up another one instead of just smithing without it.
  • When in doubt, don’t just take another swing of the hammer. Instead take a closer look and another heat.
  • Fast dry 2 part epoxy is horrible. Don’t use it. Ever. For anything. Use normal slow dry 2 part epoxy. It is crazy awesome.

A little about my shop:

My “anvil” was made pretty cheaply but has been very effective. I used a section from a very large forklift tine cut to size. Four 2′ long sections of rebar are welded to the bottom of it about 8” apart

Blacksmithing: Finished: English Scalping Knife

English Scalping Knife Replica 1750-1790

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Remade the handle, the lanyard tube didn’t fit with the historical accuracy of the peice.eskfinal

This piece was my very first commissioned work, as such I tried my best adhere to the dimensions, look and function of the item.
It’s a very hard blade with great flexibility, and it is very sharp.
This is also the first sheath I’ve ever attempted but I think it turned out ok.

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Specs:
Steel: 9260
Length, Overall: 11.5”
Length, Blade: 7.5”
Length, Handle:4”
Width, Blade Edge: 1/8”
Width, Blade Max Width: 1.25”
Width, Handle: 1”

Taper, Distal: None, until the last .25”
Blade Edge: Taper Grind
Handle Material: Walnut, brass rod/tubing
Finish, Blade: Smithed look(unpolished very light sanding), boiling vinegar bath.
Finish, Handle: Walnut Danish oil
Quench: Vegetable oil full length of the blade and halfway up the handle
Temper: 45mins at 500F, dark yellow and light purple hues visible.
Sheath: Cow leather, black polish, wet soaked to knife shape, cooked in dehydrator.