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The poppet valves of internal combustion engines are exposed
to high temperatures, and they must also be resistant to wear and
erosion. This is the intake valve from an automobile engine. The first photomicrograph at left is of the head of the valve at 500X magnification. The hardness is Rockwell C55. The Nital etch does not bring up the microstructure of this martensitic stainless steel very well. |
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The second image, shown at only 50X at left, is of the
transition zone between the highly alloyed head and the plain carbon
steel stem, whose hardness is Rockwell C34. The valve was
probably heat treated after
the welded joint was made. |
| Specimen 5 is the exhaust valve from the same engine. |