That's the tricky question. For TMT rebars which are medium carbon steel, rebend test is carried out for seeing the effect of strain aging but for wire rod no such test is there in the standard I think. It has been seen in plants that after 2-3 days, if the retest is carried out, UTS values are reduced. This reduction will be more in high carbon wire because already their UTS is very high i.e. upto 1200 MPa. This happens due to strain aging and residual stress release. There is no fix optimization of time is available but to avoid any reduction in UTS below the minimum requirement, people try to achieve 30-50 MPa more than the limit value.

Thanks for taking interest in it.

This can be attributed to the release of molecular hydrogen which increases the cohesive strength resulting in clevege fracture.

Yes, it happens for high carbon steels. The ductility i.e. %R.A increases from 25-30 to approximately 40 after some days.However, the UTS do not show any marked change.

Can you put more light upon this phwnomena.

Yes..I did not think about it from Hydrogen point of view. That's certainly can be the reason. Strain aging is mostly related to diffusion of Nitrogen into interstitial position which releases locked stress which we call residual stress. Literature is available on this. If YS is decreasing but UTS is not, hence it may due to the reduction of upper yield point. I think in order to find out the answer, we need to study the strain aging behavior. Please let me know if you find any answers.

The maxima in the %RA appears after certain number of days. I want to fix the number of days for different section of wire rods.

Then you have to collect lot of data for each and every grade. However, if it is possible to model it using the known empirical relation. I think you should collect data and use ANN for prediction.

Thank you very much for the suggestion. Ofcouse i will try.

ANN with respect to composition, properties and process parameters. We can do something together.

It will be my pleasure.