Is steel austenitic when it is in a full spheroidized annealed state?

[mitch8]

It's all in the title.

 

[mete]

No . Steel is austenitic when it's above the critical temperature . Below that the steel is ferrite with little spheres of carbide .Look at a iron-carbon phase diagram.

http://info.lu.farmingdale.edu/depts/met/met205/fe3cdiagram.html

 

[Stacy E. Apelt - Bladesmith]

As mete says, when steel is fully annealed, it is pearlitic ...which is ferrite and cementite mixed.

 

[mitch8]

Ok thanks that clears things up. I dont see martinsite anywhere on the diagram though? What happened there?

 

[smokey0118]

martinsite happens in quenching. The phase diagram and crystal formation changes dramatically depending on the rate a steel is heated or cooled. Those temperature ranges can be forced up or down. ...read this...
http://www.pdfbook.co.ke/details.ph...y=Technology | Engineering&eid=5759&type=Book

essentially the structure of the steel goes from face-centric to body-centric, (which can't hold as much carbon in between the iron atoms normally). Normally, it would be a bcc(body-centric cubic) structure. Because the carbon got trapped in the structure, it distorts is to an elongated tetragonal structure...which is also what gives martensite it's strength and hardness.

 

[mitch8]

Another question while i have your attention. If i have a piece of perlitic rail steel could i heat it to its critical temp and quench it in water to get martinsite or some microstructure that would work for an axe?

 

[mitch8]

And thanks for the links guys! This is helpful stuff!

 

[Stacy E. Apelt - Bladesmith]

mitch,
I think you have some things mixed up. If you read the stickys on metallurgy, you will get some idea about these structures.

When you HT any blade you convert it to austenite when it gets above 1350F. Then you quench it and if it cools fast enough to miss becoming pearlite, it becomes martensite at 400F.

I can't remember, but I think all RR track is hardened steel. It should make a good axe head. The piece of track you cut will need to be annealed, shaped, hardened ,and tempered.

 

[mete]

The diagram I linked is an Equilibrium diagram.Therefore no martensite ,nor any mention of whether or not it's pearlite or spheroidized.
For an axe or hammer the RR track should work as is without HT.It certainly has the carbon and alloying content to be hardened but you might have great problems findin the composition.