he difference between hard and tough alloys??

[Gunslinger]

I've seen this mentioned a few times here, but never seen an explanation of the differences.

Maybe it's just a language barrier for me, but when I hear tough and hard all I can translate this into is the opposite of a soft?!

I understand what you mean when you say brittle, for instance a boolit made from pure lino... but the hard/tough thing is beyond me?!

[felix]

Taffy is tough when soft enough to chew. Taffy approaches the hardness of peanut brittle when ice cold, and is still tough in comparison to peanut brittle at the freezing temperature. A tough metal has a good return to initial dimension when expanded, whereas a hard metal will not contract to the exact starting dimension. Barrel metal should be tough; action/bolt metal should be hard and resist any bending moment whatsoever. However, that is impossible, so the action metal has to be tempered just right to include enough spring as not to shatter when hit with an " instantaneous" 100K psi. ... felix

[outdoorfan]

I imagine it like this.

Hard and brittle: Hard, but brittle. Easily shattering or breaking apart under stress.

Hard and tough: Hard, but not brittle. Easily withstanding much more force than the hard and brittle alloy.

50/50 ww/pure heat treated would be a hard alloy (15-20 bhn) that would still be very ductile. 50/50 ww/lino would be a different story, at least for certain applications.

[sagacious]

...
I understand what you mean when you say brittle, for instance a boolit made from pure lino... but the hard/tough thing is beyond me?!
No worries, it's good to have standard definitions to refer to.

Hardness in this instance means only one thing-- a numerical measurement expression of the BHN level of the alloy; it's resistance to deformation under load. Pure lead demonstrates low hardness.

Toughness in this instance means a capability to generally resist force without breakage. Toughness of metals and alloys is usually measured in the lab by a test that shows the amount of force a sample can resist before breakage under a sudden impact. One can see, for example, that a glass rod would demonstrate both high hardness and low toughness.

Linotype is fairly hard, but not tough. A linotype bullet may be expected to shatter upon striking a hard object.

A bullet cast from ww alloy and air-cooled will be fairly tough, and may be expected to resist breakage or fragmentation better than the linotype example.

A bullet cast from ww alloy and water-quenched will have both the qualities of relatively high hardness and toughness.

I hope this helps shed a little light on those terms. Good shooting! :drinks:

[Gunslinger]

Thanks that really helped, I get it now. Especially the example with glass made it understandable

[montana_charlie]

When hardness is on one side of a comparison, it's only reasonable to have 'softness' on the other side. I think it's misleading to compare 'hardness' with 'toughness'.

Consider two pieces of metal. Both are .25" thick and 2 inches wide.
One is made of cast iron, and the other is a leaf spring (tempered steel).

Both can be so 'hard' that a drill bit will just get dull while trying to drill a hole in them.

A moderate tap with a hammer can break the cast iron, while years of pounding does not break the spring.

One is tough, but the other is 'brittle'...and that is the difference which matters when you compare 'toughness' with something else.

CM

[felix]

The third attribute we care about is the amount of springback. ... felix

[StarMetal]

Tough to me is two fold. First I want an alloy tough enough to take the punishment of the stress put upon it going down the bore. This is especially true when the bullet is going through a bore with a fast rifling twist and at high velocity. Second I want a bullet that when it hits a game target, that it's not going to shatter, not going to pass through the animal like armor piercing, but can expand to a degree. Hardness to me is just a number that helps identify my alloy mix.

Joe

[sagacious]

When hardness is on one side of a comparison, it's only reasonable to have 'softness' on the other side. I think it's misleading to compare 'hardness' with 'toughness'.
As long as both terms are accurately described, it's not misleading to compare any two qualities. That's what the definitions above attempt to remedy.

"Softness" isn't a metallurgical quality. Soft is simply the lack of hardness, much as dark is the absence of light. There is no measurement scale for softness. The scales in use only measure relative hardness.

In actuality, it would be misleading and confusing to suggest that hardness and softness are two separate sides of the comparison. I hope this helps explain that a bit.


Consider two pieces of metal. Both are .25" thick and 2 inches wide.
One is made of cast iron, and the other is a leaf spring (tempered steel).

Both can be so 'hard' that a drill bit will just get dull while trying to drill a hole in them.

A moderate tap with a hammer can break the cast iron, while years of pounding does not break the spring.

One is tough, but the other is 'brittle'...and that is the difference which matters when you compare 'toughness' with something else.

CM
In your example, the analogy is a comparison of toughness in both cases, by the very apt use of an impact test. The accurate conclusion would be, "One (the spring steel) is tough, and the other (the cast iron) is less tough."

The term "brittle" simply describes an absence of toughness. A crust of bread can be brittle, but is neither hard nor tough.

Hope this helps. I applaud the efforts here to seek definitions to the terms commonly used to express the qualities we see in our experiments and handiwork. Cheers all! :drinks: