chisel steel theory
Bill Tindall, E. TN
>We put a lot of thought into this topic before we chose CPM 3V for the chisels we made. Our objective was to make a superior chopping chisel. From our conversations with steel manufacturers, most particularly Crucible Steel, it seemed that toughness at high hardness was the most important attribute. If these properties were high then one could make a chisel that would hold up at more acute bevel angles which will result in better penetration and less deflection.
Toughness is the resistance of the steel to breaking under impact. High toughness means that a fine edge will not chip or break in use. The edge will withstand the high impact a chopping chisel encounters and withstand chip prying in mortising operations. Hardness is resistance to deformation. So a hard edge will not bend or crumble upon impact. Often greater hardness results in less toughness.
For a pareing chisel I would expect that about any of the common steels would be fine-O-1, A2, etc. These don't see the forces of a chopping chisel or the abrasion of a plane iron.
At some bevel angle about any steel will work without crumbling or breaking. So the advantage to be gained in what could be called a "high performance chisel" will be mainly in how acute an angle it it can be sharpened and survive.
Some hard tough steels that could be good chisel candidates are S7 and 3V but A2 is a reasonable choice as well. The ever popular carbon steel O-1 is less tough and Japanese carbon steel chisels are reputed to be prone to chipping. Tempering to a lower hardness results in more toughness but then crumbling can be a problem instead. M2 is plenty hard but lacks toughness and chisels made from M2 can chip( in the one case I have tried, hardly statistical).
There is some concern for abrasion resistance in a negative way. The very high abrasion resistance of 3V may be more useful in a plane iron that a chisel. In a chisel it could mean more difficulty sharpening than a less abrasion resistant steel, but we have not found this to be a significant problem in practice. There is certainly a great difference in ease of sharpening between a Marples chisel and one of 3V but much less difference between 3V and an A2 plane iron. ( I need to try chopping with an A2 plane iron and see how this steel does as a chopping chisel)
Note how cautious I have become in these posts over the past year, ever mindful of the critiques that invariably follow. At least you people are more kindly than the turners who I don't deal with any more. (But off in the shadows on Saturday while others are off to flea markets and still others filling out orders to LV and LN there is a growing number of people making their own chisels (and lathe tools) and they are successful.)
