Rockwell experts

[boyne bowhunter]

I guess what I was most curious about was more about bending versus breaking. Not really worried about the edge. I can determine adequate sharpness in hand. But I cant know if a head is too soft (prone to bend) or too hard (brone to break).

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It's a question that doesn't really have firm answer Tom. Unfortunately the ductility/toughness varies not only with hardness but with metal composition as well. Obviously the higher the harness the more brittle a material will be. However, it is possible that a broadhead made to 57RHC out of 440 stainless may be more ductile than the same broadhead made out of 420 stainless at 55RHC. The bottom line is there are two many unknown variables to give a single response/hardness number. In my completely metallurgically unexpert opinion though, anything above HRC50 is going to win if it hits bone.

 

[Allegheny Tom]

It's a question that doesn't really have firm answer Tom. Unfortunately the ductility/toughness varies not only with hardness but with metal composition as well. Obviously the higher the harness the more brittle a material will be. However, it is possible that a broadhead made to 57RHC out of 440 stainless may be more ductile than the same broadhead made out of 420 stainless at 55RHC. The bottom line is there are two many unknown variables to give a single response/hardness number. In my completely metallurgically unexpert opinion though, anything above HRC50 is going to win if it hits bone.

Thanks.
I wasn't trying to belabor the subject. I just became curious when I saw the (nearly) identical heads on the Grizzlystik site. The Overkill are 40% less expensive than the black label...only 4 Rockwell points difference. I thought that it would be interesting discussion...might save someone a butt load of cash, too.

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[Allegheny Tom]

I just looked at the site again.
The black label are 440C stainless steel 58 Rockwell and the Overkill are AUS4 stainless 54 Rockwell. I have no idea what AUS4 steel is.
Just curious why the Overkill are so much less expensive.


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[Allegheny Tom]

Anything jump out at you guys with these differences?The pic of the Overkill was supposed to also be the 200 gr, but otherwise, the 125 and 200 Overkill are the same.

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[JC3]

I would contact the manufacturer and ask what steel type they are using the the hardness.
Some manufacturers are using 1075 carbon steel, which is a older steel but still very good for broadheads and more easily sharpened that tool steels (D2, A2)
1075 is typically case hardened, but since the cross sectional area is fairly thin, you will get a through hardened effect.
I have also seen S7 tool steel being used now.
S7 is a tool steel used when a "shock load" is applied, such as chisels. punches etc.
I have used it in the past for large dies and punches, where sharpness was not super critical but it still took a good edge with out too much effort.
The 400 series stainless steels (440, 420) are decent steels also, mostly used in cutlery, because of their ease of sharpening and lower chance of staining.

 

[CamoMan]

From my understanding the Aus4 is a lower quality steel that doesn't hold up as well and the 440C is a higher end stainless. So the price difference is purely in the metal going into the blade.

 

[Still Kicking]

I guess what I was most curious about was more about bending versus breaking. Not really worried about the edge. I can determine adequate sharpness in hand. But I cant know if a head is too soft (prone to bend) or too hard (brone to break).

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I don't believe anyone can give you an honest, easy answer to that as there are so many factors to consider. The type of steel, the mass, and the hardening process all contribute to it. For most broadheads you are probably safe from breakage at Rockwell C scale readings below the high 50's. The thinner they are, the easier they will break. If you stay above .045 inch, probably good. Sorry I don't have better answers for you, but most commercial broadheads are made from steels that will bend before breaking.

 

[Still Kicking]

I would contact the manufacturer and ask what steel type they are using the the hardness.
Some manufacturers are using 1075 carbon steel, which is a older steel but still very good for broadheads and more easily sharpened that tool steels (D2, A2)
1075 is typically case hardened, but since the cross sectional area is fairly thin, you will get a through hardened effect.
I have also seen S7 tool steel being used now.
S7 is a tool steel used when a "shock load" is applied, such as chisels. punches etc.
I have used it in the past for large dies and punches, where sharpness was not super critical but it still took a good edge with out too much effort.
The 400 series stainless steels (440, 420) are decent steels also, mostly used in cutlery, because of their ease of sharpening and lower chance of staining.

S-7 is an excellent "shock steel". I worked with it a lot on retainer dies. I made a knife from it for my son and he loves it. D-2 can be hard to edge if the Rockwell is above 56, but it's one of my favorites for edge retention and razor sharpness. I have a couple of the Knives of Alaska D-2 blades that I prefer over anything out there. It makes me sad that all the makers are using 420 now as I feel it is inferior for edged tools.

 

[Still Kicking]

Anything jump out at you guys with these differences?The pic of the Overkill was supposed to also be the 200 gr, but otherwise, the 125 and 200 Overkill are the same.

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The sub zero quench is a bonus if you are concerned with breakage. 440C is a very capable edge and .068 is really thick so the 58 R/C shouldn't be too hard, but will take a little time putting a razor edge on it if it's not already there.

 

[LoadedLimbs]

I just looked at the site again.
The black label are 440C stainless steel 58 Rockwell and the Overkill are AUS4 stainless 54 Rockwell. I have no idea what AUS4 steel is.
Just curious why the Overkill are so much less expensive.

@Allegheny Tom - I'm just reading this thread now. @boyne bowhunter is spot on when he says it's not a simple answer. @Weldabeast was also right when he suggested that looking at knife steel comparisons is informative for folks that desire a good basic understanding of the subject.

I'm an Engineering professional and have some experience with the topic of hardness vs. ductility in steels. Material composition affects the phases of steel and the precipitates that harden and strengthen it. Depending on the type of heat treatment used, the measured properties of hardness and ductility can differ greatly. A really easy to understand explanation of common material properties important for cutting edges is available at the website I'm linking below. It also has easy-to-understand relative comparisons of common tool & knife steels:

https://www.bladehq.com/cat--Best-Knife-Steel-Guide--3368

 

[boyne bowhunter]

@Allegheny Tom - I'm just reading this thread now. @boyne bowhunter is spot on when he says it's not a simple answer. @Weldabeast was also right when he suggested that looking at knife steel comparisons is informative for folks that desire a good basic understanding of the subject.

I'm an Engineering professional and have some experience with the topic of hardness vs. ductility in steels. Material composition affects the phases of steel and the precipitates that harden and strengthen it. Depending on the type of heat treatment used, the measured properties of hardness and ductility can differ greatly. A really easy to understand explanation of common material properties important for cutting edges is available at the website I'm linking below. It also has easy-to-understand relative comparisons of common tool & knife steels:

https://www.bladehq.com/cat--Best-Knife-Steel-Guide--3368

Thanks for the link, nice read!