Stacy E. Apelt - Bladesmith
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Posting this in parts due to length:
W2 gets a lot of talk, but to most it is a bit of a mystery.
Some comments from those who use it will help others with learning and working this steel. I will link this thread to the HT sticky.
If you are an experienced maker who uses W2 and are proficient with forging and HT, post your advice and observations.
If you are still learning - and we are all still learning - and have specific questions, post them here, too.
I'll start off with some basics:
W2 isn't an exact content description. The "W" means it is a water quench steel, and the "2" designates it as a little different from W1.
Generally, W2 has high carbon content, but that is not a guarantee. If bought from a knife supplier, or using a known and analyzed batch, then the carbon content can be relied on. If you just buy W2 from a steel supplier, it can range from .80% to nearly 2% carbon.
Most knife grade W2 has around 1.5% carbon. Manganese is usually around .40%, but it can be lower. It is the batches with the lower Mn content, that knifemakers love. There are various small amounts of chromium, nickel, tungsten, and vanadium in W2. W1 has less vanadium. In many cases, both steels get called, and sold as, W2. This is why you want an analysis of the exact batch you are buying.
Because of this variability, and the tricky nature of HT for W2, when you find a batch you like, it is a really good idea to buy as much of it as you can. This is why guys like Don Hansen, and formerly Bill Moran, bought it in thousand pound batches. Label it and keep it separate from other batches of W2. You will read and hear about makers hoarding Don's W2 like it was gold bullion. To many makers, that is close to what perfect W2 is. I never thought of it before now, but I have hundreds of dollars worth of expensive steel sitting openly in the smithy. Don's W2 stash is locked in the storage building with the HT ovens and valuable stuff.
Because of the makeup, W2 is very shallow hardening, and must have a very rapid cooling rate in quench. It must drop from 1450°F to below 1000°F in less than one second. This requires either a fast oil, like Parks #50, or water. Water/brine will certainly harden W2, but the risk of cracked and broken blades is high. Most makers use the fast oil. Alternate oils and concoctions just won't work for W2.
The shallow hardening and rapid quench rate make W2 great for attaining an active hamon. It may take dozens to hundreds of trial and error attempts, but once you zero in on the HT and clay application (some makers use no clay), you can attain amazing hamon patterns. This is because the steel exposed to the quenchant will miss the pearlite nose and go on as super-cooled austenite (until it converts to martensite at the Ms) while the steel under the clay and near it will change into pearlite. The boundaries of these two structures creates the hamon.
W2 forges well.
Like most high carbon steels, use lower austenitization temps. A forge can be used, but an oven is far better for W2. You may end up picking a very exact temperature that creates a hard edge and amazing hamon. It isn't unusual for numbers like 1437 degrees F (eg.) to be used by some makers. Since all equipment reads and operates a bit different, you will have to find your own magic number, Just because Don or Chuck get good results with 14XY° doesn't mean you will get their results. You may have to use 14YZ°.
W2 isn't a magic steel, and it has not particular attribute ... beyond being good for hamon. It will harden to Rc 65-66 as quenched. And can be used at Rc 64-65 for slicers. Lower hardness down to Rc 62 is used for more rugged knives. If just getting started, shoot for Rc 63-64. Edge retention and toughness are not why you pick W2, so if they are of prime importance, another steel would be a better choice. One of the main advantages of W2 is that it is cheap and readily available.
W2 gets a lot of talk, but to most it is a bit of a mystery.
Some comments from those who use it will help others with learning and working this steel. I will link this thread to the HT sticky.
If you are an experienced maker who uses W2 and are proficient with forging and HT, post your advice and observations.
If you are still learning - and we are all still learning - and have specific questions, post them here, too.
I'll start off with some basics:
W2 isn't an exact content description. The "W" means it is a water quench steel, and the "2" designates it as a little different from W1.
Generally, W2 has high carbon content, but that is not a guarantee. If bought from a knife supplier, or using a known and analyzed batch, then the carbon content can be relied on. If you just buy W2 from a steel supplier, it can range from .80% to nearly 2% carbon.
Most knife grade W2 has around 1.5% carbon. Manganese is usually around .40%, but it can be lower. It is the batches with the lower Mn content, that knifemakers love. There are various small amounts of chromium, nickel, tungsten, and vanadium in W2. W1 has less vanadium. In many cases, both steels get called, and sold as, W2. This is why you want an analysis of the exact batch you are buying.
Because of this variability, and the tricky nature of HT for W2, when you find a batch you like, it is a really good idea to buy as much of it as you can. This is why guys like Don Hansen, and formerly Bill Moran, bought it in thousand pound batches. Label it and keep it separate from other batches of W2. You will read and hear about makers hoarding Don's W2 like it was gold bullion. To many makers, that is close to what perfect W2 is. I never thought of it before now, but I have hundreds of dollars worth of expensive steel sitting openly in the smithy. Don's W2 stash is locked in the storage building with the HT ovens and valuable stuff.
Because of the makeup, W2 is very shallow hardening, and must have a very rapid cooling rate in quench. It must drop from 1450°F to below 1000°F in less than one second. This requires either a fast oil, like Parks #50, or water. Water/brine will certainly harden W2, but the risk of cracked and broken blades is high. Most makers use the fast oil. Alternate oils and concoctions just won't work for W2.
The shallow hardening and rapid quench rate make W2 great for attaining an active hamon. It may take dozens to hundreds of trial and error attempts, but once you zero in on the HT and clay application (some makers use no clay), you can attain amazing hamon patterns. This is because the steel exposed to the quenchant will miss the pearlite nose and go on as super-cooled austenite (until it converts to martensite at the Ms) while the steel under the clay and near it will change into pearlite. The boundaries of these two structures creates the hamon.
W2 forges well.
Like most high carbon steels, use lower austenitization temps. A forge can be used, but an oven is far better for W2. You may end up picking a very exact temperature that creates a hard edge and amazing hamon. It isn't unusual for numbers like 1437 degrees F (eg.) to be used by some makers. Since all equipment reads and operates a bit different, you will have to find your own magic number, Just because Don or Chuck get good results with 14XY° doesn't mean you will get their results. You may have to use 14YZ°.
W2 isn't a magic steel, and it has not particular attribute ... beyond being good for hamon. It will harden to Rc 65-66 as quenched. And can be used at Rc 64-65 for slicers. Lower hardness down to Rc 62 is used for more rugged knives. If just getting started, shoot for Rc 63-64. Edge retention and toughness are not why you pick W2, so if they are of prime importance, another steel would be a better choice. One of the main advantages of W2 is that it is cheap and readily available.
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I tempered at 440 to get Rc63/64 with the brine. I did a 1095 knife the same day, and can't get consistent readings on the tang. The 1095 knife was ground before heat treatment where the W2 knife was thin, and austentized after profile. I broke the last two blades in brine, so I added a 1400f extra cycle after the 1450. I quench after the last cycle cools to magnetic in medium oil. For brine I use a wash of clay over the whole blade, then clay up for the hamon. 
