Need an online source for Stainless??

[CGCINC]

Because it has less carbon, it will help preventing carbide precipitation.

is that rust?

[DaveO]

is that rust?

Here's a quick write-up on carbide precipitation from the ESAB site:
http://www.esabna.com/EUWeb/AWTC/Lesson5_10.htm
Note: "austenitic" refers to the 300 series of stainless steels.

5.4.1 Carbide Precipitation - Many of the austenitic stainless steels are subject to the phenomenon of carbide precipitation. At elevated temperatures in the range of 800-1600°F, the carbon content in excess of 0.02% migrates to the grain boundaries of the austenitic structure where it reacts with chromium to form chromium carbide. If the chromium is tied up with the carbon, it is not available for corrosion resistance. Thus, when the steel with carbide precipitation is exposed to a corrosive environment, intergranular corrosion results, allowing the grain boundaries to be eaten away. Figure 8 shows how intergranular corrosion may take place in a tank holding a corrosive liquid. Notice that the corrosion takes place only in the heat affected zone on the inside where the corrosive media is located, and there is no evidence of failure on the outside.

5.4.1.1 Carbide precipitation has no other effect on the steel, however, other than loss of corrosion resistance in the heat affected zone. During welding, the heat-affected zones along the sides of the weld in austenitic stainless steel are exposed to the temperatures that cause carbide precipitation.