Failure Analysis of Cylinder Head B
The process conditions used for the second production trial (“Cylinder Head B”) were in general similar to those described in Table 2. Adjustments in the pro- cess parameters considered necessary from the failure analysis of the Cylinder Head A were included, as de- scribed below:
1. The water flow of the cooling system of the perma- nent mold was increased by 30%;
2. The rotation velocity, the gas flux volume and the degassing time were increased to comply with the rotor specification;
3. The cascading height during the transference be- tween ladle and holding furnace was reduced from 250 mm to 100 mm;
4. The water jacket wall thickness in the region pre- senting cracks was increased from 10 to 13mm.
The chemical analysis of the second production trial (“Cyl- inder Head B”) is described in Table 4.
(a)
(b)
(c)
(d)
Figure 3. Cylinder Head A—crack surface of cylinder #3. The crack initiated near the water jacket surface (a); microporosity is seen at the crack origin (b) and (c). Using higher magnification, the characteristic fatigue striation is observed (d). SEM.
International Journal of Metalcasting/Fall 10
23
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