.... 12L14 was being recommended as a material to be used in construction on this board. So I express my concern for its use by those of this board.
12l14 is the stuff they make the cheap screws you buy at the local hardware store out of . You know the kind where the head strips at the first use. The 12L14 machines like a dream (The lead helps here) and looks good on paper; it was recommended to me not to use this material as it COULD fracture after having been drawn (such as to octagon)and put under peek pressure's. ....
Let's sort out some of the principles here.
Mild steels (Bessemer conversion process) historically revolutionized (mid 1800's) making of cannons. They were of much greater strength that what was commonly available - cast iron and bronze.
The huge advantage of mild steel was/is the ability to withstand flexing and stressing without fracturing - malleability is closely related to this. It wears better than bronze (hence good for rifled barrels) but not as good for wear than alloy steels (as 4130/4140/4340 and others).
Drawing mild steel (mild steels include 1018, 1020, 1045, 1137, 1144, 1214 and many others) has the advantage of changing the grain structure (lengthening the grain) increasing strength, but has the disadvantage of work-hardening. Hence, cold rolled steels will be stronger, of smoother finish (also related to strength - note the Charpy tests), and a bit more expensive than hot rolled steels which have more scale and are softer, not quite as strong, but less brittle.
Annealing the steel, as in stress proof or stress relieved, reduces the hardness, keeps the strength and increases the cost.
Lead is often added as an inter-molecular lubricant - it greatly increases the ability of steels to be machined at great speed, hence it is loved by machinists that have to produce parts fast.
So the mild steels are good choices for cannon, perhaps they don't have the super strengths of alloy steels, but are tough and withstand repeated firing. There are quite a range of steels that will work.
When you see blackpowder rifles being made of mild steels and modern rifles made of alloy steels it tells you something of the differences in application, notably pressure and wear. Typical pressures for modern high pressure cartridges are in the ranges of 50-55,000 copper units pressure (roughly PSI - but there are a number of issues in comparing them directly as they are measured by different means). Blackpowder loads for the same cartridges (like for example .45-70) are greatly reduced in pressure - more like 1/2 or 2/3.
High velocity rifles run from 3000 to 4000 fps commonly. Modern howitzers (as 105 and 155mm) run something like 2700 and tank cannon (direct fire high velocity) runs close to 4000 if I remember right.
Again applications for two different categories of steel - that is to say, mild steels in general are well suited for what we've been looking at.
