Composition of BS materials

[will123]

Please consider a titanium alloy to BS TA 56. This calls for a composition of:
Al 5.5 - 6.75%
V 3.5 - 4.5%
Fe 0.30% max
O+N 0.25% max
H 0.0125% max
Ti remainer

However the certificate sent with the material we order, says it is to TA 56, but has a typical composite of: -
Al 6.2%
V 4.1%
O 0.177%
Fe 0.18%
C 0.006%
N 0.007%
H 0.002%
Y Lt.005%
Each Lt.10
Total 0.135%
Ti remainder.

Firstly, what is Lt? And secondly, the composition of the alloy received contains additional elements not mentioned in the standard. Admittedly they are trace elements, but I wqould have thought they would be mentioned in the standards. Or is there a different standard that deal with acceptable limits of trace elements.

 

[CoryPad]

Lt stands for less than. I am not familiar with this specific standard, but I am sure it contains information regarding trace elements. Most standards have a statement like: all others total 0.30% max.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Carburize]

Trace elements are often reported because other industry-specific or user-specific specifications require them to be controlled. I don't know the particular alloy but if it is also used in aerospace applications then user specifications probably contain limits to the trace elements. The supplier typically carries out an analysis which satisfies as large a number of users as is economically possible.