Source: As worded by Indian Railways, Government of India

If you have not cancelled the tickets within the prescribed time limits you can approach the Deputy Station Superintendent (Commercial)/Station Manager or Chief Reservation Supervisor of nominated stations. They are authorized to grant refunds up to 30 days from the date of journey on tickets issued from their stations by condoning the delay in surrendering the tickets for cancellation. You must also satisfy the Station Manager that your ticket is not used.