Thermal fatigue - Casting defects

Thermal fatigue - Casting defects

Figure 1: The effect of cast alloy surface and internal defects versus wrought alloy soundness on service performance is illustrated by our old case history, RA330-108. The application was a grid for suspending loads in a gantry furnace at a commercial heat treat shop. The work was neutral hardening from temperatures up to 1850°F (1010°C), quenched in either molten salt, oil or brine.

Defect name: Thermal fatigue
Record No.: 2391
Type of defect (Internal/Surface): Internal, surface
Defect classification: Casting defects
Steel name: Steel
Steel composition in weight %: No data.
Note: When the cast HT (35%Ni 17%Cr) grid was practically new and had been exposed to only a few cycles, a particular job required increased working area for the grid. RA330 allo y plate was formed and welded to the outside of the existing cast grid.
As can be seen in the photo, the cast alloy portion suffered surface attack from soot and the quenching salt, and failed from thermal fatigue. Note the cracks in the center of the cast ribs which occur along the plane of weakness of the dendritic structure. The wrought alloy RA330 exhibited very little surface attack and no fractures.
Reference: Not shown in this demonstration version.