Crucible steel blades

Rivkin · 8th October 2006, 07:31 PM

I am by far no specialist, and know absolutely 0 about the field, but I would see it this way:

Imagine that you have a metall at a very high temperature. Atoms move randomly with large amplitudes. Now we introduce a defect - a few atoms are moved away from the equilibrium configuration. Because of random motion the rest of the atoms is likely to adjust to the dislocation - kind of like water does not fall into pieces if you stir it - randomly moving molecus fill the empty space. So is the metall it is plastic - it is actually softer than at small temperatures, but more crack resistant. Now at low temperatures if you move an atom so far away it effectively looses contact with one of its neighbours (the lattice "breaks"), the neighboring atoms can not readjust to maintain the stability, the crack forms and propagates in the material (again, the material can not adjust).

This process obviously depends on how much energy one has to spent to adjust/change the configuration of atoms, so I would expect the "brittleness" being given by energy structure calculations. It is going to greatly depend on the material and its composition, it is quite possible that wootz was more brittle than other steels, however I think it especially relates to the wootz that Biruni was talking about, not some other wootz - I would expect a significant variations depending both on chemistry and on geometry of the wootz (since wootz is essentially two types of lattices in one material).

Battara · 8th October 2006, 09:35 PM

At risk of repeating what has been said and in hopes of adding to it, carbon stiffens the steel in other ways by stiffening the crystaline structure. Brittleness implies that something is not as flexible and as temperatures drop, the molecules vibrate less and "stiffen" more. Flexibilty drops and the piece, or any metal for that matter becomes more rigid, thus being more prone to snap off. IN warmer temperatures, metal molecules vibrate more, become more "fluid" and thus a piece can bend more, including bending upon impact.

Jens Nordlunde · 8th October 2006, 09:41 PM

Well Rivkin, you may not be a specialist - but neither am I - you do however know far more about this than I do

.
Hi Jeff,
You write: ‘Carbon makes steel brittle in general, not just at cold temperatures. Over 1 % C, the amount of carbide increases and the carbides form at grain boundaries, reducing the strength of the grain boundary. Wootz blades are heat treated in such a way as to minimize the bad effects of having a lot of excess carbide, to take advantage of their excellent edge enhancing properties.’

Now it is easy to test, but how did they test it in the early days, the carbon, and all the other things being in the ore? Besides the quality must have differed from where the iron was mined – or from where the iron ore was imported from.

Rivkin · 8th October 2006, 10:30 PM

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.

Gt Obach · 9th October 2006, 04:49 AM

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

Rich · 9th October 2006, 10:33 AM

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

Jens Nordlunde · 9th October 2006, 04:28 PM

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

.

9th October 2006, 04:28 PM	#7
Jens Nordlunde 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.

8th October 2006, 07:31 PM	#1
Rivkin Member Join Date: Dec 2004 Posts: 655	I am by far no specialist, and know absolutely 0 about the field, but I would see it this way: Imagine that you have a metall at a very high temperature. Atoms move randomly with large amplitudes. Now we introduce a defect - a few atoms are moved away from the equilibrium configuration. Because of random motion the rest of the atoms is likely to adjust to the dislocation - kind of like water does not fall into pieces if you stir it - randomly moving molecus fill the empty space. So is the metall it is plastic - it is actually softer than at small temperatures, but more crack resistant. Now at low temperatures if you move an atom so far away it effectively looses contact with one of its neighbours (the lattice "breaks"), the neighboring atoms can not readjust to maintain the stability, the crack forms and propagates in the material (again, the material can not adjust). This process obviously depends on how much energy one has to spent to adjust/change the configuration of atoms, so I would expect the "brittleness" being given by energy structure calculations. It is going to greatly depend on the material and its composition, it is quite possible that wootz was more brittle than other steels, however I think it especially relates to the wootz that Biruni was talking about, not some other wootz - I would expect a significant variations depending both on chemistry and on geometry of the wootz (since wootz is essentially two types of lattices in one material).

8th October 2006, 09:35 PM	#2
Battara EAAF Staff Join Date: Dec 2004 Location: Louisville, KY Posts: 7,280	At risk of repeating what has been said and in hopes of adding to it, carbon stiffens the steel in other ways by stiffening the crystaline structure. Brittleness implies that something is not as flexible and as temperatures drop, the molecules vibrate less and "stiffen" more. Flexibilty drops and the piece, or any metal for that matter becomes more rigid, thus being more prone to snap off. IN warmer temperatures, metal molecules vibrate more, become more "fluid" and thus a piece can bend more, including bending upon impact.

8th October 2006, 09:41 PM	#3
Jens Nordlunde Member Join Date: Dec 2004 Location: Europe Posts: 2,718	Well Rivkin, you may not be a specialist - but neither am I - you do however know far more about this than I do . Hi Jeff, You write: ‘Carbon makes steel brittle in general, not just at cold temperatures. Over 1 % C, the amount of carbide increases and the carbides form at grain boundaries, reducing the strength of the grain boundary. Wootz blades are heat treated in such a way as to minimize the bad effects of having a lot of excess carbide, to take advantage of their excellent edge enhancing properties.’ Now it is easy to test, but how did they test it in the early days, the carbon, and all the other things being in the ore? Besides the quality must have differed from where the iron was mined – or from where the iron ore was imported from.

8th October 2006, 10:30 PM	#4
Rivkin 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	#5
Gt Obach 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	#6
Rich 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