on_the_edge
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What is the difference between a SR "through hardened" temper and a "differential" temper? Is one generally preferred to the other?
temper difference
- Thread starter on_the_edge
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As I understand it, a through hardened blade is consistently hardened the entire length/width of the blade (e.g., the whole blade is RC 60) while a differentially hardened blade is often softer at the spine to enhance its durability and harder at the edge to enhance its edge retention. The latter is preferable for larger heavy use/abuse blades while the former is good for small knives...and both types of blades may (and often do) have softer tangs.
Cobalt
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Theoretically and in practice I guess, differential temper is done to make a knife as tough as possible. Usually the edge is the hardest, say for example an Rc of 60. Then the steel gets softer as it goes to the spine and ends up at an Rc of whatever the maker feels confortable. Usually the spread I have seen can be 10 Rc points or slightly more. So it may drop to 50 or high 40's.
Every 2 point drop in Rc can show a dramatic increase in impact toughness of a steel, so theoretically the knife should be able to take very hard impacts that the same steel, thru-hardenned could not. Like hitting the spine with a hammer. A knife with a spine at Rc of 46 would take more impact than a knife with a spine at Rc=60 before breaking. For the same steel.
What you loose is lateral strength. A knife who's overal Rc is lower than another will be easier to bend. By the same token, it is less likely to break and more likely to take a set.
So theoretically sR101 differential should be tougher than thru-hardenned SR101. However, thru-hardened SR101 should be much stiffer ad if you ever wanted to sharpen a false edge, you could since the RC is the same all over the knife.
and if you happen to be cliff stamp and grnd off half an inch off a knife edge, you would still have the same Rc.
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You will not have any trouble with it. I beat the hell out of mine, and used it to pry heavily with no problem.
I also threw it A LOT.
Eric Isaacson
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You won't have any problems chopping with it, and there really wasn't a "switch" we just ran the black and tans with the through hardening to keep the price down. In all honesty you probably won't be able to tell any performance difference unless you are really pushing the envelope with them, however, we wanted to put some out at "extravaganza" prices (these were sold through one of the Knob Creek extravaganzas) and this was a way we could cut the cost on them and pass the savings on to the customer
Actually through hardened is better except to collectors. Differential hardening
is the traditional way bowie's and katana's are made and also leave a decorative hamon line where the steel changes that is valued by collectors. Some incredibly good swordsmiths can make a differentialy hardened blade that is stronger than
through hardened. Howard Clark uses the same S7 steel that scrapyard does
to make a sword that has a body of softer but incredibly tough bainite and an edge of hard razor sharp martensite. Bainite and martinsite are the same steel
but with different heat teatments. But it would be incredibly expensive to make knives that were differentially treated and as good or better than through hardened blades. Unless you want differential heat treatments for esthetic reasons you are better of with through hardened blades.
is the traditional way bowie's and katana's are made and also leave a decorative hamon line where the steel changes that is valued by collectors. Some incredibly good swordsmiths can make a differentialy hardened blade that is stronger than
through hardened. Howard Clark uses the same S7 steel that scrapyard does
to make a sword that has a body of softer but incredibly tough bainite and an edge of hard razor sharp martensite. Bainite and martinsite are the same steel
but with different heat teatments. But it would be incredibly expensive to make knives that were differentially treated and as good or better than through hardened blades. Unless you want differential heat treatments for esthetic reasons you are better of with through hardened blades.
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Swamp Rat uses differential heat treat on their larger knives, and that does provide an additional amount of toughness to an already incredibly tough knife.
It does cost more than through-hardening, but it is not an Aesthetic or collector thing. I take it you were responding to the original post and did not read the thread?
Cobalt
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As I stated above, Differential HT will provide increased toughness in most any steel It is much trickier to do than thru hardening and thus usually costs more. Busse gets away with it because his thru hardening system is so complex that there is no literal dfference between the work required to diff Temper and thru harden a blade. The process takes about as long it is just different.
However, a thru hardenned sr101 (52100 modified) blade is still going to be severely tough the way Busse HT's their knife. Their HT is the best in the industry, with the exception of one or two other makers out there. I know that the difference between differential and thru as busse does it is not much. But it is just enough that sr101 does benefit from it.
With differential tempering, the big scare is making sure that there is no stress risers in the hardness transitions of a blade. If you look at differentially tempered blades, when the edge fails it almost always fails near or at the temper line of the edge about 1 to 2 cm's up from the edge. This is a hardness transition in the metal and this change in the matrix can cause stress risers, thereby, causing premature failure. The experienced heat treaters know this and attempt to make the transitions as smooth in the matrix as possible to avoid this "stressfull" situation. Busses HT assures that there will be no issues with the hardness transition and has been proven in serious use.
However, a thru hardenned sr101 (52100 modified) blade is still going to be severely tough the way Busse HT's their knife. Their HT is the best in the industry, with the exception of one or two other makers out there. I know that the difference between differential and thru as busse does it is not much. But it is just enough that sr101 does benefit from it.
With differential tempering, the big scare is making sure that there is no stress risers in the hardness transitions of a blade. If you look at differentially tempered blades, when the edge fails it almost always fails near or at the temper line of the edge about 1 to 2 cm's up from the edge. This is a hardness transition in the metal and this change in the matrix can cause stress risers, thereby, causing premature failure. The experienced heat treaters know this and attempt to make the transitions as smooth in the matrix as possible to avoid this "stressfull" situation. Busses HT assures that there will be no issues with the hardness transition and has been proven in serious use.
As a matter of fact, hitting the pine of a knife with a hammer would end up destroying the knife anyway. This would create micro fractures in the structure of the steel that would eventually lead to breaking. The metallic nature of the hammer would not absorb any of the impact stress generated by hitting the knifes spine, thus causing undue stress / wear on the knife, something that you dont see when using, say, a wooden baton.