WOW, the old ABS heat treating forum is really rocking today. Yes! This is how it should be.

Hello Steve, chefs knives are cool because they can be used at those fantastic high hardness and one can get the joy of using an extremely sharp and high performing cutter, and as a maker you get the pleasure of putting such a knife into the hands of somebody who appreciates it and knows how to use it. To answer your question a little bit more information is required if the 60HRC after temper. I very often get requests to troubleshoot heat treatments but only have the final Rockwell to work with. With just the final number, there is really no reference point to go from in determining the entire heat treatment. By far the as quenched hardness is the most important to the heat treater while the post temper number is useful to the end user.

For 1095 an as-quenched HRC of 66 is very possible and very desirable for such a knife. Moreover, if that level of hardness is obtained in the quench, the tempering will be a greater task as it will require much more time and temperature than most bladesmiths are used to in order to get things in the 59-60 range. Fortunately for a chef’s knife you don’t have to draw it back that far and the higher you can leave it, without chipping in normal use, the better.

Your 1475F soak is very good, but you may want to add a couple minutes to it if these blades are ground from mill stock. Aldo has some suppliers that really know how to spheroidized (I have done micrographs that show that when they say 95% spheroidal, they mean it!) and it takes a bit to get things back into solution. With using Parks #50 with this blade thickness, I am confident that we can rule out the quench and focus on the heat. By far the quickest and most logical adjustment would be the soak time, slowly bump it up in the direction of 10 minutes and see which time is the shortest and yields the best hardness. If you get beyond 15 minutes with no improvement, I would grudgingly bump up your temperature to 1500F. But I may better consider a good normalizing heat from 1500F to 1550F and then a 1475F soak for the quench.

I am certain it was a typo, but you really want retained martensite! <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//wink.gi f' class='bbc_emoticon' alt=';)' /> I shoot for as much retained martensite as possible. But fun aside- retained austenite is the threat you mean, fortunately there is much less of that threat with 1095. If you were to heat above 1500F you would then need to worry about it, but keeping things around 1475F is the best defense against RA. With a simple steel like this I tell folks who use liquid nitrogen to bump up Rockwell to save their time and money and just drop their soak temperature.

If you get the soak temp and time balanced out I would expect to see some really sweet 63HRC chef’s knives without a problem.

Thanks Kevin, I will make several pieces and try at different soak times. Let you know how it goes.

That could be a T-shirt! <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//laugh.gi f' class='bbc_emoticon' alt=':lol:' />

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<img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//wink.gi f' class='bbc_emoticon' alt=';)' /> I shoot for as much retained martensite as possible.

Ok, had time to run a little test. Not sure my small sample size will bear fruit but here it is. I cut 5 pieces of 1095 into 1"x2" stock (all 3/32). I then soaked each pice for 10min separately

at varying temps quenched in parks 50, finally I tested with a rockwell tester...twice( the RC tester was said to be 1 point low so my results reflect the adding of 1 point to each result). These are the temps and my results.

Degrees

1) 1530 66.5 66.5

2) 1515 67 66.5

3) 1500 67 66.5

4) 1475 66 65

Result 5 was a different process 10min soak then air cool followed by another 10min soak and quench.

5) 1475 67 68

Sooo what did I learn? Are my samples appropriate size? My knives are typically 3/32x 2"x8'-10" Do I need more samples?

Thanks in advance.

One more question, should I drop this in the topic of the month as well?

|quoted:

Ok, had time to run a little test. Not sure my small sample size will bear fruit but here it is. I cut 5 pieces of 1095 into 1"x2" stock (all 3/32). I then soaked each pice for 10min separately

at varying temps quenched in parks 50, finally I tested with a rockwell tester...twice( the RC tester was said to be 1 point low so my results reflect the adding of 1 point to each result). These are the temps and my results.

Degrees

1) 1530 66.5 66.5

2) 1515 67 66.5

3) 1500 67 66.5

4) 1475 66 65

Result 5 was a different process 10min soak then air cool followed by another 10min soak and quench.

5) 1475 67 68

Sooo what did I learn? Are my samples appropriate size? My knives are typically 3/32x 2"x8'-10" Do I need more samples?

Thanks in advance.

Steve, from your post this is what I would give for input-

Your samples are fine, your stock is not very friendly to it but when I do these type of tests I grind to a blade cross section and then use special water cooled sectioning saw to slice off samples from the hardened stock so that I can take my Rockwell readings on the core of the sample. But your stock is so thin that not only will it be difficult to properly Rockwell without going to a micro-hardness test, I wouldn't expect much of a deviation from outside to center thin this thickness.

What I can draw from your data is the following- your 1095 is very effectively spheroidized and will benefit from a soak but higher temps show you that retained austenite becomes an issue. Your hardness curve fits a very accurate profile for this steel, although the readings are all well within the margin for errors in Rockwell testing. Without preparation by previous thermal treatments the carbide is very segregated and requires a little over 1500F to go into full solution, but this is a bit on the high side for this steel and the next step up to 1530F suggest too much carbon in solution with a stabilization of that parent austenite, resulting in lower percentages of martensite. Number 5 with its normalization has the carbide dissolved and evenly dispersed for efficient solution at the proper temperature of 1475F yielding maximum hardness.

Although I would double check your tester for accuracy, while 68 HRC may be possible with 1095 I would find 67 HRC a bit more likely. The thing about calibrating a tester is that it needs to be done as close to your target range as possible. I have seen many a tester that read dead on at 55HRC but was two points off at 65HRC, but more often the reverse. Also I would suggest more than just two test in this sort of research. In this type of testing one can overcome some error and variables through sheer quantity of data samples and averaging. Try to take no less than five readings and them average them out. This will also give you insights into consistency at the same time, it would be common for steel with these conditions to have a wider Rockwell spread over the 5 readings, and this would then narrow with more refinement if he carbide.

Thanks Kevin,

I was felt I was having trouble get the steel in to full solution and my results were inconsistent. I was hopeful the normalization step would cure this. Typically my 1095 is either 1/8 or 3/32, when I forge I use 1084 o5 5160 in thicker cross sections. With the other steels my results have been much more consistent.

Thanks again

Steve