Writing up metallurgy for a campaign

[Fnugus]

I've decided to undertake the humongous task of making a (somewhat) detailed writeup of the available metals (and related materials) in this fantasy world I'm working on. I've hunted the various books and supplements I own without much luck to guide me, and my Google Fu is abysmal (probably I have Incompetence: Google Fu).

Anyway, what I'm looking to do is making a plausible (or at least semi-plausible) stat block for each of the materials, which would include Density, Hardness/HP per inch, cost (this world conveniently has a natural center of trade that could be used to define standard/benchmark prices), and other properties (such as breakage odds, electrical properties, magical properties, availability, refining processes, skills or skill levels required to be able to work with it (if applicable)).

I get from the Basic Set that steel has a hardness of 50-70 DR/inch. Without much else than that to extrapolate from, it's very difficult to go further while still keeping it in touch (and balanced) with already published content.

So, it comes down to this: I seek guidance, either in the form of books and/or supplements that I might find useful, or in the form of helpful advice (or actual help) here. Or links to other useful stuff.

[Dwarf99]

I found this when I was trying to figure out how to work a system for making guns into Metatronic Generators. Since it gives Density in g/cc and lb/ci, you can use it to solve your density issues. For fantasy metals, you can just look to the source and assign a number based on the number it gives relative to teel or iron

[Fnugus]

That's still just arbitrary. For instance, what kind of steel is 50 DR/inch? What is 70 DR/inch? What types of steel are in between (and what are their real world hardness)? How much is iron? Is "hardness" to DR in GURPS an exponential scale? Logarithmic? Linear? It's quite easy to find real world data for hardness and density. It's the conversion to GURPS that gets tricky, as I can't really find any benchmark reference to extrapolate any kind of trend or formula from.

[Polydamas]

Originally Posted by Fnugus

I've decided to undertake the humongous task of making a (somewhat) detailed writeup of the available metals (and related materials) in this fantasy world I'm working on. I've hunted the various books and supplements I own without much luck to guide me, and my Google Fu is abysmal (probably I have Incompetence: Google Fu).

Anyway, what I'm looking to do is making a plausible (or at least semi-plausible) stat block for each of the materials, which would include Density, Hardness/HP per inch, cost (this world conveniently has a natural center of trade that could be used to define standard/benchmark prices), and other properties (such as breakage odds, electrical properties, magical properties, availability, refining processes, skills or skill levels required to be able to work with it (if applicable)).

At least in 3e GURPS, it was canonical that the type of steel called Rolled Homogeneous Armour (RHA) has a DR of 70/inch. One problem in a fantasy setting is that alloys of iron and of copper do not have standardized properties: two lumps of "Spanish iron" or "latten" could be quite different in composition. GURPS “DR” measures resistance to penetration not hardness as engineers use the term. The engineering term hardness is only one factor in resistance to penetration.

The hit points of a solid sheet of material are determined by its mass according to a formula in the Basic Set (4e).

[Fnugus]

Originally Posted by Polydamas

One problem in a fantasy setting is that alloys of iron and of copper do not have standardized properties: two lumps of "Spanish iron" or "latten" could be quite different in composition.

This is exactly the point. How would one go about writing up the differences between ordinary steel (whatever we call it), very fine steel (Damascus steel, maybe?), pig iron, etc.'? Just having some properly grounded baselines for these differnt types of steel could allow for some extrapolation. It'd be even better if one could add the same things for different types of bronze (cornthian bronze, hepatizon, orichalcum, etc.). Then for each other material, it could be compared to these figures.

Originally Posted by Polydamas

GURPS “DR” measures resistance to penetration not hardness as engineers use the term. The engineering term hardness is only one factor in resistance to penetration.

Indeed. And in engineering that is (AFAIK) a combination of hardness, plasticity, elasticity, etc. (tensile strength, ductile strength, w/e). So this is abstracted down into a single figure, and for brittle or semi-brittle materials, we just define them as ablative or semi-ablative, respectively. Big question is, how would the scale for DR go? A material with double the strength have double DR? Or is it quadratic, cubic, or something else entirely?

Originally Posted by Polydamas

The hit points of a solid sheet of material are determined by its mass according to a formula in the Basic Set (4e).

As with most homogenous objects. This is the easy part.

[DanHoward]

Originally Posted by Fnugus

This is exactly the point. How would one go about writing up the differences between ordinary steel (whatever we call it), very fine steel (Damascus steel, maybe?), pig iron, etc.'? Just having some properly grounded baselines for these differnt types of steel could allow for some extrapolation. It'd be even better if one could add the same things for different types of bronze (cornthian bronze, hepatizon, orichalcum, etc.). Then for each other material, it could be compared to these figures.

You can't do it realistically. If you want to do it for a game then you just pick some arbitrary figures.

[Phantasm]

Various low-tech metals that I'm aware of:

Bronze (copper-tin alloy): low tin content (2%-7%), regular tin content (~8%-12%), high tin content (up to 20%)
Brass (copper-zinc alloy): same zinc contents as tin with bronze
Pewter (tin-lead-antimony alloy)
Electrum (amalgam of gold and silver)
Iron: wrought iron (low carbon content), various grades of steel, cast iron (high carbon content)
Copper
Gold
Silver
Lead
Tin
Zinc
Quicksilver/Mercury

[benz72]

Originally Posted by Fnugus

Indeed. And in engineering that is (AFAIK) a combination of hardness, plasticity, elasticity, etc. (tensile strength, ductile strength, w/e). So this is abstracted down into a single figure, and for brittle or semi-brittle materials, we just define them as ablative or semi-ablative, respectively. Big question is, how would the scale for DR go? A material with double the strength have double DR? Or is it quadratic, cubic, or something else entirely?

The problem with associating DR with a single property is that there are different modes of failure.

e.g. a thin sheet of ductile material used as armor may plasticly deform and transfer the energy (damage) through whereas a thicker sheet may nees to actually be penetrated (exceed toughness and cause rupture) to allow the residual energy to reach the target.

q.v charpy test http://en.wikipedia.org/wiki/Charpy_impact_test

This differs from (but is somewhat related to) hardness. http://en.wikipedia.org/wiki/Hardness

Recall also that good metallic armors (just like the good weapons attempting to defeat them) are not going to be homogeneous. Even a thin tempered plate can have a hardened (and somewhat brittle) surface covering a softer but tougher core. Heat treatment of steel is a VERY complex issue.

If I were to attmept a project such as you are proposing, especially in a fantasy campaign with mystical abilities and materials, I would start by listing properties and then assign processes/names/costs/skill levels/exclusivity to those properties.

Things like the reduced weight, corrosion resistance, supernatural effects, shape memory, magnetism, etc. Make them optional treatments for some materials with specialized skills (probably at high cost or requiring special materials).

I believe there is a good start to this kind of 'power-up' method in the DF series already. Anything that attempts to incorporate more rules out of a materials textbook is likely to fail on the effort/fun*accuracy rating.

[benz72]

Originally Posted by tbrock1031

Iron: wrought iron (low carbon content), various grades of steel, cast iron (high carbon content)

Many people mistakenly believe that steel has a higher C content than Iron. This is inaccurate.
Compare C content listed here
http://en.wikipedia.org/wiki/Carbon_steel
with
http://en.wikipedia.org/wiki/Cast_iron

The trick isn't getting in more Carbon but rather getting Carbon and Oxygen out to leave purer Fe and THEN carefully controlling the additions of alloying agents.

[Polydamas]

Originally Posted by Fnugus

Indeed. And in engineering that is (AFAIK) a combination of hardness, plasticity, elasticity, etc. (tensile strength, ductile strength, w/e). So this is abstracted down into a single figure, and for brittle or semi-brittle materials, we just define them as ablative or semi-ablative, respectively. Big question is, how would the scale for DR go? A material with double the strength have double DR? Or is it quadratic, cubic, or something else entirely?

What do you mean by “strength”?

I think that even trained metallurgists rely heavily on experiments to predict the properties of a new alloy, and the formulas which they have are very complicated and assume a world which does not work the way many fantasy settings do (one without spirits, undead, disintegration rays, or enchantments of unbreakability but with industrial processes which can make identical sheets of metal).

This could be a great excuse to learn some metallurgy, but I don't think you will learn much that is helpful for gaming.