Many moons ago I had to design a demagnetiser for ball races - It consisted of generating a 50Hz alternating magnetic field strong enough to overcome the residual magnetisation of any component to be demagnetised. The field was then allowed to decay slowly over several mains cycles to zero. In your case, you will need to feed an electromagnet with the output of your transformer, hold your component at the point of maximum magnetic field and then slowly withdraw it away from the coil. This reduces the residual magnetism in the component slightly with every mains cycle until it is negligible.
