What is the cause of discrepancy in the hardness of specimen that used for Rockwell hardness test ?
Answer:
Its possible as well that this is a heat treated material... Are you saying the center is softer than the outside? If thats the case then heat treatment is a very valid option...
Look at the microstructure of the material and see what type of grains are formed...
A possible solution to this would be crystallinity. Throughout your material, you have a structured arrangement of atoms, known as crystallinity, and each material has a different arrangement of atoms. Since the center's crystallinity is undisturbed as opposed to the outter edge of your material, it is 'harder'. The outer edge is considered 'soft' b/c of the voids in bonding and abrasions it has incurred during forming.
Hope this helps...
I assume that the parts do not meet the specifications? Sounds like the heat treating process was not the proper one for the material type, shape and size. Your best bet is to consult with a good heat treating company to have the job done correctly.
If the parts are to specifications there will be slight differences in the different areas of the part. Lots of factors play in to this such as material type, shape and size to name a few.
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