Environmental Engineering Reference
In-Depth Information
Figure 3.19
Weld decay of type 304 stainless steel in 25% HNO
3
solution (2
).
that for chromium carbide precipitation. For example, niobium carbide precipi-
tates in the temperature range of 815
C where chromium carbide dis-
solves. During stabilization (i.e., cooling down from melt), niobium carbide
forms in this temperature range leaving no carbon to form chromium carbide at
temperatures below 815
°
C to 1230
°
C, niobium carbide dissolves.
So, when a stabilized steel is heated above this temperature all carbides get dis-
solved. A rapid cooling to room temperature prevents the carbides from reprecipi-
tating. This is exactly the situation faced by the area just adjacent to the weld.
°
C. However, above 1230
°
