You probably couldn't replicate this with sigers thin film since it works on IOR's, where this is just a flat plane with the color being produced by oxides when metal gets heated
I made a quick material that replicates the basic premise of your example. I'm sure you can spend quite a bit of time perfecting and making it look tight.
It requires two objects. One object being your metal plate and a separate object representing your weld seams.
1) add a gradient ramp to your refl. colour, switch gradient type to mapped and plop in a corona distance map in the source
2) add in rainbow colour points in the gradient part, starting with red, orange, yellow, green, blue, purple, white (each colour should gradually become whiter and whiter)
2) expand the corona distance map and add the weld seam objects you made with the picker
3) put in a grunge map of your choosing into the distance scale map slot to break up the uniformity of the gradient. To increase or decrease the expansion of the colour tweak the Distance far number for the white value.
4) tweak away! *You can fiddle with the noise parameter in the gradient ramp to break up the uniformity too. Good luck.
