Here is I how I tend to paint anything that looks like metal painted black on my miniatures. I prefer to use a slightly cooler colour palette, as I think it looks more interesting.

1. Basecoat with Abaddon Black .
2. Edge highlight everything with a thick line of Dark Reaper .
3. Highlight everything again, this time with a thin line of Thunderhawk Blue . This colour is a good place to put in some scratches too.
4. With Fenrisian Grey , selectively highlight upward facing edges, corners and prominent edges. Stick primarily to edges where the light would hit and always drag your brush towards the brightest point. If you added scratches previously, reinforce them with a smaller, thinner line underneath.
5. Finally, edge add small highlights to the centre of the previous highlights and corners with Blue Horror . Try to make them very small, dots if at all possible.