We have heard a lot about the influence of titanium on CGI machining. Is this an obstacle for European foundries? Can this cause European foundries to promote grey iron over CGI? What is the source of the titanium and how do the levels differ between European, Asian and American foundries?


Shareholder, name withheld

It is true that titanium is an important factor in the machinability of CGI. However, this is a complex issue that cannot be answered in general terms. We must also consider that the machinability is strongly influenced by the machining technique type of tools, speeds and machines), the length of time that the castings are allowed to cool in the mould before shake-out, and the type of grey iron used in the comparison. For example, is the machinability of CGI being compared to normal grey iron (250 MPa tensile strength, as used in most cylinder blocks) or is it being compared to alloyed grey iron (300 MPa tensile strength, as used in most commercial vehicle cylinder heads). The difference between grey iron and CGI must be quantified for each different circumstance.

Over the past five years, the industry has widely understood and accepted that the titanium level must be as low as possible to optimise machinability. Prior to this, foundries with a naturally low titanium level had an advantage over their competitors because their iron was “easier to machine” … even if the reason for the easier machining could not be explained. Today, however, all car and truck OEMs have included a maximum titanium limit in their CGI specifications (typically 0.015 or 0.020% Ti) and, as every foundry must satisfy the specification, the machinability “advantage” is not as significant as it used to be.

It is also not possible to generally link titanium to the geographical location. As our shareholders may recall, the majority of the machining development was conducted on test pieces produced at the SKF-Mekan foundry in Katrineholm. Initially, the machining researchers could not explain why the SKF test pieces provided longer tool lives than similar test pieces produced at other foundries from Europe, North America and South America. With a typical titanium content of only 0.007%, the SKF test pieces had the lowest titanium and the highest tool life. This provided the initial link between the titanium content and the tool life that was later proven with controlled trials. As the primary raw material for foundry production is steel scrap, rather than iron ore, the titanium issue is accounted for by local steel scrap supply sources, and not by the natural mineral deposits in different geographical regions. For CGI production, the foundries can source low-titanium raw materials from their local suppliers. Although this may be more expensive in some localities, it will always be possible. Ultimately, titanium control is not an impediment to CGI production decisions.