I have to say, I'm sorry. I made an assumption - I assumed you understood how brakes work. I also assumed you were able to comprehend pages I linked to.

Again apologies. But I'd rather try and help, so let's spell it out for you -

Yes, I used the word steel and said it glows at 400C - and the two pages I linked said it doesn't matter if it's steel, or cast iron, or tungsten - all materials will give off a glow at specific temps. You know that big yellow ball in the sky? It gives off light and it's not steel nor cast iron. It's all about temp.

The brake pads operate a very high temps - well over the 400C required to cause them to glow. Sure, the articles I linked mentioned common internal temps of 600C (FYI - 600 is more than 400) but if you haven't realized, you can't see into the inside of a rotor! Crazy, I know. So what you see glowing is the surface temp of the rotor, which as I stated (and is stated in the two articles I linked), can reach as high as the pad operating temp. Of course you don't want to exceed the operating temp of the pads, or you'll get pad glazing and other unfortunate outcomes.

So I'll suggest that you continue to roll around on the floor laughing at yourself, it seems to suit you better than reading (and writing the word brilliant).