Grinding Welds?

I use a hard Norzon disc on a 4-1/2 grinder to knock off the top and high spots then a 60 or 80 grit flapper disc on my 4-1/2" grinder to bring it down smooth. Note that everyone has said to not get the metal hot by keeping the disc moving and that is, by far, the most important part of smoothing your welds.