Render again and you should have a more defined result (Fig.13).
There are still a fair amount of artifacts, so we need to play around with some render settings to get a better result. Open the Render Setup menu, select the Renderer tab and scroll to the bottom (Press F10) Rendering > Render Setup > Renderer (Fig.14).
The settings here are very important to the quality of the displacement. The important numbers are the Edge Length and Max Displace. The Edge Length controls the number of polygons per pixel in your render, and the Max Displace controls the maximum amount of displacement you get. Since our render is relatively simple; we can set the Max Displace low and speed up our render a bit. To get rid of artifacts in our render, we need to lower the Edge Length value, Try to set it to 1 and do a new render. If you don't like the result then lower it a bit more until you get the desired result. Setting the Edge Length value too low can cause you to run out of memory and mean the render can't complete. It can also increase your render time, so keep that in mind.
Here is a comparison between Edge Length 0,2 and the default 2,0 from our first render (Fig.15).
It might also help here to adjust the strength of the displacement map in your material to get a better effect. When you're happy with the shape of the rendered mesh, it's time to add some metal shading to the result - here are some quick settings you can try (Fig.16).
That should give you a result similar to this, depending on your render scene and light setup (Fig.17).
That's it from me, but keep playing around with the material settings: create a diffuse layer with rust and dirt and add a specular map. The scene setup will be important too since metal is reflective, so maybe you need to add an environment map. There are plenty of ways to improve the look.
Thanks for reading!