[TheForge] No need to temper this blade

[Andy Vida]

Barking Crow wrote:
> 
> Yesterday at our FABA meeting in Sneads Fl. John Butler demonstrated the
> steeling of wrought and mild steel tools.  It was a great demo and he made
> it look easy as all the welds took first time. 

	The great talents always seem to do that.  It's maddening. :)

> On the chisel blank that
> John forged he welded a piece of old file to a piece of mild steel and in
> the later discussion said that he would quench it in oil and that there was
> no need to temper this chisel blade as the tool steel  was forge welded to
> the mild steel backer everywhere and therefore he didn't have to worry about
> tempering the tool steel to keep it from being too brittle and breaking as
> the mild steel would be dead soft and tough.  This was an interesting  new
> concept for me. 

	This is, as you pretty much observe below, common practice on
	good Japanese chisels.  The really expensive ones will show
	the welded pattern in alternating layers of hard steel and 
	dead soft iron.  I think that is more for art's sake than anything
	else.  I do know that the Japanese tend to leave their chisels
	in a full hard state, making them a bit tougher to sharpen, but
	also they hold their edges better.  I also believe that the 
	generally anal quality of Japanese craft (and I mean that as a
	compliment, not an insult) is such that you are not likely to
	see a wood joiner using his chisel as a prybar.  This being the
	case, it is also less likely that he will damage his edges.

	The comparatively large body of soft steel/iron provides all the
	support that is needed to prevent breakage with proper use.
	Also, the bottoms are hollow ground to facilitate sharpening
	and I would not be surprised if this provided some relief of
	stress, but I could be wrong on that account.  The only real
	chunk of serious steel is right up at the front where it is
	needed.  It's usually about an inch long in new chisels and
	when used properly should last pretty well a lifetime and
	even beyond before you will grind away all the useful bit
	steel.  Even then one ca in some cases flatten the hollow and
	gain a few more sharpenings.  I've seen this demonstrated, but
	I don't know how well it really works.

>  It would end up sort of like the expensive Japanese
> chisels.  So, I'm wondering what experience or thoughts you guys have on
> this decidedly apolitical subject.  Do you think there's an advantage to
> having a mild or wrought backer to a steel blade?  Why?

	It's the old yin/yang thing... hard and soft in this case.
	Look at how sharp and tough a pattern welded blade can be.
	And the thinner the hard sections, the more able they are
	to deform without damage.  But a thin section alone has no
	strength to resist bending, so a nice fat chunk of iron is
	used to do that and to support the thin, very hard, and
	somewhat more flexible bit.