Hi Dave-

I can't answer your question, but I will follow the answers. I am trying to understand how to measure the HRc to verify my heat treat and temper without damaging the blade. Do you heat treat and quench the entire blade, measure the HRc on the tang, and then soften the tang and spine? If so, how do you measure the HRc of the tempered blade? If I'm off base, please describe your HRc measurement schedule.

Thank you. Jesse

David, right off the top I would suggest staying with one supplier. In your case 'supplier A' provided the steel that is holding the most consistency & tighter readings. Not all suppliers get their steel from the same foundry so there will be differences in the percentage tolerances in the different 'ingredients' that make up the steel. Begin by finding the supplier that gives the closest and consistent readings in your tests.

On the Rockwell side of the equation, always remember that Rockwell, as a standard, is only held to one point +/- in deviation so when you get a reading that is 1 point off from others, you are still within the margin of error. But I get it, more than .5 makes my teeth itch <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//wink.gi f' class='bbc_emoticon' alt=';)' /> .

Steel making is pretty good in the 21st century, but it is not as exact a science as we would think and this is why most alloy classifications have a range of element percentages that they have to stay within rather than exact numbers. Yes, this means that every new batch of steel could result in you having to adjust your heat treatment procedures. If you find a chemistry that is working very well for you, it is very good advice to buy as much of it as you can afford. A stockpile that will last most of your career would be a hefty investment but would be one of the best things you could do to insure you would be making the best knives possible over the long haul. I did this and have the same chemistry for all of my blades for the foreseeable future, and so I wasn't aware of some problems with our steel supply until I started research into other steels than what I normally work with.

This brings me to a problem that I have more recently become more alerted to, and that is proper steel identification in our community. In most of the testing I am doing now I need to absolutely know what alloy I am dealing with and how it should react to processing. I have lost weeks of work when chemistry turns out to be mismatched. I have the advantage of catching it in lab work but the average knifemaker may never know. Because of this I now insist on getting the certs with all my steel, and I am shocked at how difficult that can be. When I go to the big boys that supply industry they treat a request for certs as perfunctory standard thing. Of course why wouldn't I ask for it? But I am hearing some stories from other makers, about when they ask for certs from smaller suppliers, that shock me. Without the chemistry, or traceable origin, that bar of metal you are being sold could be anything and it should not be a big deal for the seller to provide that information. Just imagine going to buy a car these days and being told that you could not have the history on the vehicle, that the dealer either cannot find the history or prefers to keep it secret. Would you even consider buying the car?

That steel was made somewhere, and any mill out there has to have that information to make the steel. Standard certs will have the precise percentages of chemical elements present, the mill where the steel was made, the number of the heat/batch it came from, and often the internal condition as shipped, i.e. inclusions, carbide condition etc.. Those certs are passed along the chain to be available to any consumer that needs to keep any level of quality control. Even if that chain of communication is broken, for $100 the supplier can have analysis done to ensure the customer at least knows what he has. Yet I am shocked at how hard it can be to find the information on that bar of steel we are buying. I fear that more than a few knives are being made from steel that is not what the maker thinks it is.

This is my understanding:

What happens when a customer orders steel from a foundry goes one of two ways.

Way #1: Customer A says, I'd like some O-1 and here is the specific tolerances in the composition I am willing to accept. Foundry looks at the recipe and quotes a price per ton with a minimum tonnage order. Foundry makes the steel and sends samples of the batch out for whatchamacallit spectrum analysis. If the samples fall within the customer's specified tolerances, the steel ships to the customer. Customer publishes the specific tolerance in their price list to other customers who can be assured that what they buy is going to consistently be of a certain quality.

Way #2: Customer B says I'd like to buy some O-1 and I don't really care what the composition is, as long as it meets the AISI specs for O-1. Foundry quotes a price and a minimum tonnage order and ships this customer all the stuff that didn't meet Customer A's specifications, but still qualifies as O-1 per the AISI specifications.

So you see, if you are buying steel from a retailer, what they advertise as the composition becomes important, only if you want a consistent product out of what you are making with the steel you buy. If the retailer advertises the generic composition that qualified per AISI, then you will not get consistent quality steel from that retailer. The specs could be all over the chart. And no, the Customer B retailer doesn't always ask for the specific testing results, they just get something that says the steel meets AISI specs.

Another variable we haven't eliminated yet is the prep treatment you put the blades through post HT before subjecting them to the hardness test. Are you coming straight out of the tempering oven and into the hardness tester?

Thanks everyone for your comments.

Kevin - with respect to the tolerance on the hardness test, I understand +/- 1 is the margin of error. I know at least one major supplier of calibration standards only certifies to +/- 1. Normally I only would discuss hardness to +/- 1, but in this case I went to +/- 0.1 to try to explain that I thought the difference I was seeing was real. From the rest of your answer I am assuming that a difference of 2 HRc between steel lots is not unusual. I had not seen any discussion about this before. I think it is important for new people to know so they don't go in circles trying to perfect their heat treat process when it might be as good as they can get it. Are you aware of any summary of all of the contributors to heat treat variation? Thinking about it now, I suspect the overall margin of error is closer to 2 HRc rather than 1 HRc based on stacking all the tolerances.

Jesse, Joshua - I'll describe my process. If anyone sees room for improvement please let me know! I harden the entire thing (blade + tang) using PBC anti-scale, clean the blade/tang with a scotch brite pad and hot soapy water, and temper. After cooling I observe the color as a sanity check on the temper temperature, and then polish the blade and tang to 220 grit to remove the oxide layer. At that point I am ready for hardness testing. I am very fortunate to have a relationship with a local test lab to bring my blades in for hardness testing. After calibrating the tool, I take 3 - 5 hardness readings on the tang as far front and towards the bottom as I can. This gets my measurement point as close to the cutting edge as possible while ensuring the indentation marks are covered by the scales. I average the readings and round to the nearest 1 HRc number for the hardness value. After that I protect the cutting edge and heat the tang and spine to a blue color before moving on the the next steps.

Kevin, Craig, Joshua - From your discussion points, I am getting the impression we have a supply chain problem (something I thought I left behind when I retired and took up the relaxing hobby of knife making!). With all due respect, even purchasing a large quantity of steel from a single retailer does not ensure it is all from one manufacturing lot. At some point the retailer is going to run low in inventory and place another order from the manufacturer or distributor, and thus have multiple lots in stock. Some user is going to place an order from the retailer and get multiple lots in their shipment, and with my luck it will be me! Also, I don't know if different sizes of the same steel in stock (e.g. 0.125" X 2" 1084 and 0.25" X 1" 1084) would be from the same lot. Some of that will depend on how the steel is sourced by the retailer, and some will depend on the demand (the retailer is going to have to restock the more popular size sooner). As discussed, the only way around this is to get a COA (certificate of analysis) or lot traceability for each piece of steel purchased. I suppose which depends on the user. I am not experienced enough to look at a COA and know how to tweak my heat treat process because the steel I am using today has 0.01% more Cr and 0.05% less Ni than what I used last time. However, from what I am learning I would really appreciate having the lot code on each piece so I can group pieces of the same lot together and check my process before changing lots. I also believe that lot traceability is easier to manage through the supply chain than COA's. Is anyone aware of retailers that provide lot traceability information? As a user, having 2 pcs of steel identical would be ideal, but knowing for certain they are not would be a tremendous help.

Thanks,

Dave

Thank you, David. I see considerable heat treat variations among the Master smiths and am not qualified to comment on your system, but thanks for sharing. Speaking of sharing, we may meet up somewhere, sometime. I, too, am 63 and approaching retirement and I live just off Route 15, 60 miles north of Harrisburg, PA, so we're almost neighbors. - Jesse