SUMMARY
In this case we are faced with a problem of breakage on rings coming from semi-finished products from bars produced by continuous casting.
PROBLEM
During melting, in the continuous casting towing operation, the material comes into contact with the crucible and the graphite die. In-depth analyses show that the alloy has incorporated graphite residues with which it has previously come into contact. In our opinion, this happened during cooling within the die due to the rubbing between the alloy and the graphite. The debris was thus incorporated into the alloy (see photos 1 and 2) and was distributed in the material during rolling. Once the profile of the section desired for the final production of the object was obtained, the resistant section of the profile was impoverished due to the presence of graphite inclusions and therefore showed fragility.
The proof that it is graphite is given by the chemical analysis performed on the inclusions which shows the strong presence of carbon (see analysis 3).
SOLUTION
In this case, the operations to be carried out are different: first of all, it is necessary to verify the origin of the crucibles and the supply chain. Secondly, it is necessary to check their state of wear: very often it is necessary to replace the die with a new one and then evaluate whether it is also necessary to change the crucible.
In some cases, the deterioration of these is due to the poor protection provided by the inert gas blown into the supply chain, which has the function of increasing its life. Make sure that this service is working properly.