How long was it held at 1560°F? This is a bit high for this alloy. 5160 responds best to 1525°F. This could be an artifact of forging or of heat treatment. Fi the crack is still there you may want to snap the blade for a review of grain. It is more valuable as a broken sample that tells you your grain size than a blade with a crack in it.

One blade soaked at 1560 F for 5 minutes, the other for 10. Is it too long?

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One blade soaked at 1560 F for 5 minutes, the other for 10. Is it too long?

At 1560°F it may be. At 1525°F it seems about right.

Sure it is a crack not just a 60 grit scratch?

Some updates on the issue. It is not a 60 grit scratch, but I found that they are slag inclusions in the steel, not cracks. Besides having the same orientation on both knives, they are very shallow (I could remove one with hand sanding), and when I was polishing, a new one appeared. It was inside the steel (not on any surface) and I don't think a crack would do that.

Another knife maker said that these inclusions were not very rare on 5160.

And thank you Mr. Cashen for the tips about temperature in 5160.

Yes, the tendency towards inclusions in recent batches is around 3 or 4 on my list of reasons not to use 5160. I am just not a big fan of this steel, it is great for an automotive spring, but not so much for my knives. I never really understood how 5160 got to be one of the most overrated steels in bladesmithing.

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Yes, the tendency towards inclusions in recent batches is around 3 or 4 on my list of reasons not to use 5160. I am just not a big fan of this steel, it is great for an automotive spring, but not so much for my knives. I never really understood how 5160 got to be one of the most entirely overrated steels in bladesmithing.

I was using 1080 recently and never had a problem. This 5160 was requested by the client.

I am a bit curious, what are the other main reasons to avoid 5160? And what are the best alternatives?

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This 5160 was requested by the client.

One thing I learned in Home building was that sometimes your job is to protect the client from themselves. I moved away from 5160 a long time ago because it always seemed to have some weirdness in the finish. There was always some sort of spiderweb that would appear in hand finishing and it was never uniform. It was splotchy and detracted from the appearance.

In my opinion (FWIW) the Chrome alloys that make great blades and finish really well, are 52100 or O-1.

I have never used 80CRV2, but some people seem to really like it

Enough folks have the 5160 fetish that I will respect feelings and not dwell on the cons. But there are so many really good steels to choose from that one can always find alternatives. I was very pleased when 80CrV2 hit the scene because it is a excellent alternative that lends itself to a much wider variety of applications. Aldo (NJSB) used to joke that he began offering 80CrV2 as a 5160 alternative just to make me happy. It looks like your knife is a slightly larger one, like in Bowie proportions. Larger knives, by their very nature will require properties in use that smaller knives will not. 5160 would make a great machete but every time I see it used for a hunter or skinner, all I can do is scratch my head and bite my tongue. But even for machetes there are even better steels to work with.

Smaller knives are normally focused on finer cuts, often draw cuts, where long lasting, abrasion resistant edges will be a plus; edges that will work better if they are thinner and higher strength. Steels with less than .8% carbon will not excel in this area. So for smaller knives I would recommend 1095, W-1, W2, O-1 and 52100.

Larger knives have shapes and sizes that will allow for chopping-cleaving type cuts, and most owners of a Bowie will not be able to resist giving something a good whack now and then. This is a different kind of edge with forces applied in a very different way than a smaller knife. Impact toughness plays larger role here than abrasion resistance. Steels with carbon ranges from .6% to .8% have characteristics that naturally align with this type of function. Many makers would ask why not use a higher carbon alloy and just draw the temper more. But why would you handicap a steel to make it perform in way it was not designed? L6, or 80CrV2 will give you excellent large knife performance at surprisingly high Rockwell hardness levels because they were designed to do that, while 1095, W-1, W2, O-1 and 52100, will have to be softened well below their peak performance range to give you anywhere near the same toughness, meaning edge geometries will have to get wonky to compensate.

Proper steel selection, based upon alloy chemistries, is a concept that is long overdue in custom knifemaking, and I have incorporated it into every ABS Intro class I teach now. And speaking of ABS Intro Classes- if you goal is to make a knife that will naturally form well defined hard and soft zones to easily bend to 90°, why do so many people recommend an alloy that is designed to deep harden throughout? Just another thing about 5160 that always had me scratching my head.

Thanks for the detailed answer! I didn't think that much about different steels for bigger and smaller knives, I just changed the temper. But that makes sense, I will start thinking more about it.

Kevin,

Thank you for your your comments above.  You are an authority on metallurgy !

"Steels with carbon ranges from .6% to .8% have characteristics that naturally align with this type of function. Many makers would ask why not use a higher carbon alloy and just draw the temper more. But why would you handicap a steel to make it perform in way it was not designed? L6, or 80CrV2 will give you excellent large knife performance at surprisingly high Rockwell hardness levels because they were designed to do that"

So, can we believe that L6 / 80CrV2 with the right heat treat process or differential heat treat would be better suited for a JS test knife, from a chemistry perspective than 5160?  Effort would be needed to find the right heat treat recipe to obtain 90 degree bend and needed toughness.

I have read much of what you've said and as a newbie, I appreciate the schooling.  I live in Louisiana and don't know when I would have the chance to see your course.  I saw you at the Batson Symposium in June, but you were kind of busy thanks to Airline / "Late Start".

Is there a reference which breaks down an alloys design characteristics, in basic terms, so that smiths could arrive at optimum choices?  Maybe you need to write a book?

Obviously we need to consider our skill, heat treat hardware, etc.

Thanks in Advance >>  JC

Years a go…. When 5160 was a steal used a lot this was happening on lots of blades! At that time the only 5160 that did not have this issue was round bar. I quit using 5160 at is time, I threw away two blades that had the issues that you are seeing and made them out of 1084. I have quit using this steel 15 years a go. 

Thanks Ray