Killed steel's grain size 3

[Naruwan]

Dear all,
I know that killed steel will need a content of Aluminum and Silicon as they are strong deoxidizers.

a) Is there a different range (for these elements)for different grades of steel?

b) Aluminum as a deoxidizer and for the control of grain size, then, how fine must the grain size be (in ASTM grain size number)to categorize the steel as killed steel?

c) Am I able to find all these info in ASTM standards?

d) Can I perform a chemical analysis and a grain size check to verify whether this is a killed steel or not?

Thanks!

 

[salmon2]

Good question but I am not an expert on this.

Fully killed steel means the oxygen is removed. So a chemical analysis can tell you the resultant O2 level because you can never completely get rid of it. Also I am not aware of a specific limit to be killed steel.

Grain size dePends on a lot of things so you can't rely on grain size.

My personal experience is that all steel is pretty much fully killed but I am in mechanical field for oil industry.

 

[salmon2]

You can find excellent discussion at below thread:

http://www.eng-tips.com/viewthread.cfm?qid=194837&page=79

 

[swall]

"Killing"causes ingot steel to solidify with uniform grain size, whereas unkilled steels solidify with large columnar grains in the center. So, the killed steel will start out with finer, more uniform grain size than unkilled steel. The aluminum will also prevent grain growth during subsequent high temperature processing, such as rolling, due to the microscopic aluminum nitrides/aluminum oxides which pin the grain boundaries. With the advent of concast steels, the first point is somewhat moot, as the strands, especially those of small section, tend to solidify with finer, more uniform grain than ingot cast steels. But, it is hard to generalize about solidification patterns in concast steels, especially in large section blooms. But, the grain pinning and prevention of grain growth during subsequent processing still holds true.

 

[stanweld]

Dexidizing can be done with aluminum only, silicon only or combinations of Al and Si. I have measured grain sizes as large as 1 on fully sillicon killed as rolled and annealed steels. I have measured typical grain sizes of 4 to 6 on as rolled or normalized silicon killed steels. And I have measured grain sizes as fine as 12 in thermo-mechanically rolled, silicon aluminum deoxidized carbon steels.

 

[swall]

Naruwan--stanweld took care of point a) in your post. The grain size can vary depending on various factors. As for points b) and c), you will need to rely on a mill cert stating the killing practice and grain refinement practice in use. Point d), a chemical analyis may show presence of aluminum, but it does speak directly to what the killing practice was and what the grain refining technique was. Once again, back to the mill cert, which will spell these things out.

 

[metengr]

a) Is there a different range (for these elements)for different grades of steel?

Yes.

b) Aluminum as a deoxidizer and for the control of grain size, then, how fine must the grain size be (in ASTM grain size number)to categorize the steel as killed steel?

There is a difference between fine grain practice and killed steel. One can have both, but killed steel does not equate to fine grained.

c) Am I able to find all these info in ASTM standards?

No. Aluminum additions may not be specified in the material specification but they can be used for deoxidation and to reduce grain size.

d) Can I perform a chemical analysis and a grain size check to verify whether this is a killed steel or not?

Yes, to check the silicon and aluminum contents.

 

[mcguire]

Deoxidzing "kills" steel. This is from old ingot-producing days. It means that the steel doesn't release gas in the solidifying ingot, from the reaction of carbon and dissolved oxygen. Adding silicon reduces oxygen to about 100 ppm. Adding Al reduces it to a couple ppm. BUT!, it also forms aluminum nitride at high temperature which inhibits austenite grain growth, yielding fine grains.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[arunmrao]

Naruwan,in addition to ,the valuable replies,please remember manganese is also added along with silicon, in steel making. However it is the aluminium addition,,which kills the rising metal in the ingot . Hence the term killed steel.

Grain refining is a separate treatment ,and many other additions or treatments are done to grain refine the metal.

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