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Gt Obach · 10th April 2005, 03:43 PM

Hi Jens
It puzzles me why some concider wootz brittle in the northern climes... I live in northern ontario where much of the winter is -20 to -30 cel..... and my work knives that I use in the forrest are made of wootz.... none has been brittle ... yet !

but .... you must remember that wootz is a highly alloyed steel !
-these kinds of steels can be a risk to retained austenite: I'll explain further,how this is bad-
- quench procedure: 1) heat blade to non-mag/cherry red- steel becomes austenitic (carbon is in solution)
2) quench blade - this cools the steel quickly enough so as to avoid producing pearlite structure ( and favour producing Martensite.... begining at MS/martensite start)
3) once steel has reached temp for MS.... it can now only produce martensite...
4) it must cool completely to MF/ martensite finish to produce the most martensite and get rid of almost all the austenite
5) if you do not undercool the steel enough... you may have remaining austenite called " retained austenite"
- this is notorious in stainless steels.... this is why you cryoquench these steels, in order to under cool it enough and convert the retained austenite... by reaching MF

6) now you temper your steel..... to produce a tempered martensite....which is not as hard but much tougher..... ( temper cycles can no trip of some austenite to become untempered martensite -- which is brittle--)
7) this is why you should temper 2 to 3 times....to minimize this phoenomena

this is just inna nutshell.... theres more to it...

anyhow......if the steel matrix in the wootz blade has some retained austenite...and its brought into a cold climate.... you could possibly reach MF and produce some untempered martensite in the blade..... which is a brittle structure... (the cure would be another temper cycle)

hope that helps a little...
-have abit of the flu... so i'll proof read it later... :-(
Greg

10th April 2005, 03:43 PM	#2
Gt Obach Member Join Date: Mar 2005 Posts: 116	Hi Jens It puzzles me why some concider wootz brittle in the northern climes... I live in northern ontario where much of the winter is -20 to -30 cel..... and my work knives that I use in the forrest are made of wootz.... none has been brittle ... yet ! but .... you must remember that wootz is a highly alloyed steel ! -these kinds of steels can be a risk to retained austenite: I'll explain further,how this is bad- - quench procedure: 1) heat blade to non-mag/cherry red- steel becomes austenitic (carbon is in solution) 2) quench blade - this cools the steel quickly enough so as to avoid producing pearlite structure ( and favour producing Martensite.... begining at MS/martensite start) 3) once steel has reached temp for MS.... it can now only produce martensite... 4) it must cool completely to MF/ martensite finish to produce the most martensite and get rid of almost all the austenite 5) if you do not undercool the steel enough... you may have remaining austenite called " retained austenite" - this is notorious in stainless steels.... this is why you cryoquench these steels, in order to under cool it enough and convert the retained austenite... by reaching MF 6) now you temper your steel..... to produce a tempered martensite....which is not as hard but much tougher..... ( temper cycles can no trip of some austenite to become untempered martensite -- which is brittle--) 7) this is why you should temper 2 to 3 times....to minimize this phoenomena this is just inna nutshell.... theres more to it... anyhow......if the steel matrix in the wootz blade has some retained austenite...and its brought into a cold climate.... you could possibly reach MF and produce some untempered martensite in the blade..... which is a brittle structure... (the cure would be another temper cycle) hope that helps a little... -have abit of the flu... so i'll proof read it later... :-( Greg