|
|
|
8th October 2006, 10:30 PM
|
#1 |
|
Member
Join Date: Dec 2004
Posts: 655
|
Thank you Jens.
As far as I remember a lot of steels become brittle at temperatures around 0 centigrade; I doubt that one can fight or even run at minus 40 degrees, so most likely we must look at higher temperatures. Concerning phase transitions - I have no idea about the topic, but 20-30 degrees change in temperature - can it force a fast phase transition ? Or it will take 200 years for the transition to occur ? I think the cause here is a simple brittleness. |
|
|
|
9th October 2006, 04:49 AM
|
#2 |
|
Member
Join Date: Mar 2005
Posts: 116
|
in terms of retained austenite..... .. to make it simple...
1- you bring steel up to a red temperature... which will be about 1475 to 1550 F (say for 1095 steel ).. you approach a temperature where all the carbon in the steel goes into solution ... ( much like table salt goes into solution when you stir it into a glass of water..) -- this state is called austenite ..... 2- the steel is quenched ..... and if cooled quick enough ....it will become untempered martensite ..... this is a very hard but brittle state.... (much like a metal file.... it is very hard to file steel but if you smack it on the side of a table... it may shatter like glass) 3- the steel is put in an oven and tempered to remove some of the hardness and give the steel toughness in return.. now... the higher the alloy steel... the more its tendency to retain austenite... that means.... when the steel is cooled ...some of it will get confused and not transform to untempered martensite... .... now... if you later trip off this retained austenite... it will turn to untempered martensite...... you could end up with an area or a percentage of steel with a very brittle nature do to the heat treatment.... the austenite can be set off by the first tempering... (thats why its good to temper more than once ) -- but more importantly..... it can be set off by undercooling the steel... -- so the cold climate could simple be doing this... -- part of my heat treat cycle is to put my blades in the freezer inbetween oven temperings to reduce this possibility.... heat treaters that work with lots of stainless ....sometimes will use liquid nitrogen to undercool the steel and force the retained austenite to convert.. -- then tempering it to give the steel toughness so far this is the basics of how retained austenite can make things brittle if not taken care of... alloying elements like S and P are some more factors.... as steel is very complex and there can be so many ways it can be altered... -- i heard the S in the titanic steel, when cool was overly brittle.. ? wootz was a very good sword steel.... but all materials have their limits... ...even more importantly.... not all wootz is heat treated the same... some blades were oil quenched..... others edge quenched... others not... -- all this would definitely affect toughness take care Greg |
|
|
|
|
9th October 2006, 10:33 AM
|
#3 |
|
Member
Join Date: Dec 2004
Location: comfortably at home, USA
Posts: 432
|
The Japanese had the same problem with their blades are cold temps during
the Manchurian invasion/occupation in the 1930's-40's. That's why they developed the Koa Isshin Mantetsu blades, to withstand the cold Manchurian winters without breaking. Rich |
|
|
|
|
9th October 2006, 04:28 PM
|
#4 |
|
Member
Join Date: Dec 2004
Location: Europe
Posts: 2,718
|
Thank you for many very interesting mails. You have done well in explaining a rather complicated thing, so that even I have understood it
 thank you very much. When it comes to the quote in my first mail, we must remember that al-Biruni was an observer and a writer, but by no means a sword smith. It seems to me, that making swords in those days, you needed a smith, who was a very good craftsman, and the craftsman needed a good portion of witchcraft, or the blades would bend, break or maybe bothe  . |
|
|
|
 |
|
|
Hybrid Mode
