ELONGATION PROBLEMS IN STEELS 2

[mw1st]

Despite chemistry being OK, we experience poor elongation in our plain carbon steels and low alloy steel castings (stainless is OK).
IE. 4140 normalized 4% - 5% annealed 8% - 10%
Can get higher elongations, but on the expense of Tensile and Yield strengths.
Melting - coreless induction furnace. Steel is deoxidized by ladle addition of .02% Al and .05%Ti.

Thank you
Mark

 

[salmon2]

What is your current strength level?

Any hot working between casting and heat treatment?

Current elongation seems low to me.

 

[arunmrao]

Have you used any grain refiners .It appears no from your post It helps to add. Also the role of tramp elements will have a significant effect on ductility. Please check.

What is the section thickness of the casting. Is the test bar prepared from a keel block or removed from the casting. If it is later,check for microporosities and other inhomogenities.

Finally I hope the test bar preparation is satisfactory.

_____________________________________
"The richer we have become materially, the poorer we have become morally and spiritually." Martin Luther King Jr

 

[mw1st]

The strength levels vary from batch to batch.
YS 70 - 90KSI TS 120-140 KSI

There's no preliminary processing before casting.
The charge is made up of foundry returns, steel scrap, purchased certified ingots and ferro alloys for chemistry adjustment.

Test bar is prepared from the keel block. Section thickness average from .5" to 3". P and S levels less than .015, Al .005%.
We did some trial with Vanadium to refine grain size hoping to improve toughness - no success. And other than Ti for deoxidation and to fix Nitrogen, no other refiners are used.

Ps. In the past we used Al as a final deoxidizer (.1% ladle addition). For a couple years now, that's been changed to .02%Al and .05%Ti. As a result CO and N related defects has been greatly reduced and filter blockage was also reduced. (Probably less Al2O3 to clogged filter pores). Maximum flow, before filter blockage almost doubled!

Thanks
Mark

 

[arunmrao]

You have done almost all the right things,try some FeSiZr,CaSi and misch metal as grain refiners only for the keel block metal and observe.Please recheck for tramp elements and test bar fracture surface. Finally,the heat treatment cycle if you could let us know,though you must be doing it right is my assumption.

_____________________________________
"The richer we have become materially, the poorer we have become morally and spiritually." Martin Luther King Jr

 

[arunmrao]

How are you separating the test bar round from the keel block,by flame cutting or machining. Also are you providing any stress relief treatment before removal?

_____________________________________
"The richer we have become materially, the poorer we have become morally and spiritually." Martin Luther King Jr

 

[mw1st]

Thanks arunmrao, you're good man

Regarding FeSiZr and CaSi, what rate of addition should I use?
Also, should I use these alloys together, or separately?
And finally, what granulation should I request upon ordering these alloys?

Mark

 

[mw1st]

arunmrao

Test bar is removed (cut) using cut off saw, and no stress relived treatment is applied neither before or after cutting.

 

[stanweld]

Asvise deox with Si, addition of Al for primary fine grain melting.

 

[TVP]

I agree with the others that the as-cast grain size is likely too large, especially with section sizes > 0.5 inch. You should separate deoxidation from grain refinement, using the suggestions by arunmrao or stanweld. Deoxidizing with Si followed by ~ 0.2% Al should produce a fine grain structure.

 

[mw1st]

Thank you all
We do deoxidize melt with Si. FeSi is added to the furnace shortly before tapping out, as a final Si chemistry adjustment, than Al and Ti is added to the tap stream into the ladle.

TVP - your suggestion adding .2% Al is probably to much.
May end up with final Al to high leading to further embrittlement, and also to much aluminium nitride precipitation causing "rock candy" type cracking when we quench and temper.

Thanks
Mark

 

[arunmrao]

One last suggestion,at what temperature are you pouring the metal. Can there be a problem of high pouring temperature. Try adding only calciumsilicide alongwith aluminium into the ladle before tapping. Else,I cannot find any answer for your problem. What casting are you pouring in this alloy?


_____________________________________
"The richer we have become materially, the poorer we have become morally and spiritually." Martin Luther King Jr

 

[mw1st]

Thanks arunmrao
We pour variety of parts in this alloy, ranging from 1 lb to 600 lb. Temperature range: from 2800F to 3000F depending on casting modulus. Regardless of alloy, we try to pour at the lowest temperature that will provide soundness.

Mark

 

[arunmrao]

Your pouring temperature is high and you are pouring between 1540 and 1640 C, (based on section thickness)definitely a very high range. Also do you find difference in test bar poured at 1540C and 1640C,please check.

_____________________________________
"The richer we have become materially, the poorer we have become morally and spiritually." Martin Luther King Jr

 

[mcguire]

Arumrao
You sharing of specific knowledge is extremely valuable and generous. I look forward to coming to India some day to meet you.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[TVP]

I meant 0.02% Al, not 0.2%. Sorry for the error.

 

[mw1st]

arunmrao, there's no difference in mechanical properties regardless if test bar was poured hotter or cooler.
And I must disagree, 1540 C - 1640 C are typical pouring temperatures for plain carbon or low alloy steel castings ie. 1030 or 4130. High alloy steels castings ie. 310 or 316 generally are poured cooler.

Mark