Do objects cut through one another based on hardness?

[Mea quidem sententia]

I know if an object like plastic tries to cut through steel, it won't cut through. So I take this to mean that if there are two types of metals, one type (metal-a) will cut through the other type (metal-b) if it is harder. Is it just hardness (and probably toughness) that makes metal-a cut metal-b, or is there some other factors? (I figure there's going to be pressure also.) I suppose I'm just wondering if a harder material will always cut through the other material that is not harder than it.

[chainmailleman]

Yes and no. An Oxy-Acetylene gas mix isn't very hard but "cuts" through almost anything.

In terms of using one object to shape another? Then YES! Case in point, an aluminum cutting bit will not cut steel. It will mar the s**t out of it, but it won't "cut" it. It's all in the definition of cut. Some materials don't cut at all, others love to be cut.

I'm a machinist. As a general rule of thumb, it's ideal to have a tool harder than the material you are working with.

[SylverStar]

In geology there is the Mohs scale for hardness. What I learned in my Geology 101 class is yeah that is basically how it works. Than again 101 classes never give you the whole story.

[PUSS KING]

Enthalpy can also be a factor, particularly if the cutter has a high resistance to extremes of temperature than the cuttee.

[Student]

Cutting is just energy transfer, you need to give enough energy to break apart the bonds holding something together. In most cases mechanical energy (kinetics like knives) or chemical (like the torch mentioned above), other methods can take advantage of the structure of the object you are cutting for example cleavage planes or elastic properties at lower temperatures.

You can cut something harder with something softer if you displace the energy sufficiently (a saw might be warped while quickly cutting a harder material however a rotary saw is better suited to displacing the heat and in some situations a coolant can be used for extended projects.

Also hardness is the property of resisting scratches, Diamonds are a 10 but with sufficient force a softer object can smash it to pieces - the pieces of course would be unscratched. (also resistant to warping or other deformation)

[Flemmes Felares]

Mostly what Student said. It is for the same reason that high pressured water or laser can cut through objects. For example, scissors and knives cut by focusing the energy transfer onto the thin edge of the blades. An edge not as sharp would naturally require more energy to cut the same thing.

How the energy is transferred matters more than just the hardness, but it is a given that the material doing the cutting need to be able to withstand the energy being transferred.