Normally the grains used to steep will not convert because they have already been modified in the malting/ kilning process. Most people steep with grains like crystal, Chocolate, and dextrin malts which only add color and flavor to beers.
Partial mash brewers use malts like 2 row and Munich along with their specialty grains and do a rest at about 150- 155 degrees for an hour to convert the starches. The grains are then sparged to extract the sugars.
If you are interested in this process take a look at this thread. It really isn't that much harder to do.