Calcium treatment for A350 LF2 and content of S < 0,003% 1

[rado74]

We are forged valve manufacture and an end user is requesting for carbon steel calcium treated and with content S less than 0,003%.
Our forging companies are saying that the calcium treatment is a very old treatment and in the last years it has been replaced by the use of vacuum during the production of the material (in this case A350 LF2). Does anybody know any reference to this point to demonstrate to our end-user ?

Thank you in advance for any help
Corrado

 

[metengr]

You might want to re-consider what your client wants because calcium treatment is still being used today regardless of sulfur content to provide desired mechanical and notch toughness properties. You might want to check the information below, yes, this applies to plate steels but the same concept would apply to forgings.

http://pc.arcelormittal.com/NA/plat...ts/ProductBrochure/ARCELORMITTAL FINELINE.pdf

 

[TVP]

I'm not sure that your forging companies are understanding what is being asked. Ca modification is frequently used on Al-deoxidized steels in order to modify the aluminum oxides that cause submerged entry nozzle clogging during continuous casting. This can be done either in the ladle furnace or as part of a vacuum degassing procedure where the steel is first vacuum treated, then treated with Calcium Silicide wire, and then possibly dosed with sulfur wire to create an optimum balance of sulfide inclusion for enhanced machinability. Here is one reference on the subject:

http://webcache.googleusercontent.c...um+treat+steel+cold+heading+Saarstahl&ct=clnk

 

[SJones]

Would the material be for sour service by any chance?

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[rado74]

Yes carbon steel is for sour service
Corrado

 

[rado74]

Actually it seems that the Ca treatment is made for castings, is it valid the same for forgings?

 

[metengr]

Yes, it is for forgings as well.

 

[rado74]

Can we say that the calcium treatment is done in order to obtain a low percentage of Sulphur? or just to obtain a better mechanical strenght of the material?

 

[SJones]

Not really. The intent of the specifier is to have the calcium treatment for sulphide shape modification as a barrier to HIC and SSC. Sadly, the specifier is confusing specification requirements that are applied to rolled plates for subsequent forming into line pipe with the necessary requirements for forgings that, in general, are not susceptible to HIC. A not uncommon mistake, hence the reaction of the forge masters.

ISO 15156-2, Clause 8 states:
"The probability of HIC/SWC is influenced by steel chemistry and manufacturing route. The level of sulfur in the steel is of particular importance, typical maximum acceptable levels for flat-rolled and seamless products are 0,003 % mass fraction and 0,01 % mass fraction, respectively. Conventional forgings with sulfur levels less than 0,025 % mass fraction, and castings, are not normally considered sensitive to HIC or SOHIC."

Naturally, the steelmaker is going to have to cast a good clean steel to achieve the Charpy requirements of A350 LF2. This, in itself, should be reassurance as to H2S service performance.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04