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ASTM A-574 Carb/Decarb testing

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QAFitz

QAFitz

Materials
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Jul 21, 2005
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Please...
ASTM A-574, Alloy Steel Socket-Head Cap Screws, is not specific in the sequential time for the heat treatment: the pieces could be heat treated either with threads or without threads.
Example: Long socket head blanks are heat treated, then when the specific length is needed for an order the blanks are cut to length, then, ground to roll-body size and roll-threaded. The process of grinding to roll-body size would remove any threaded area carburization or decarburization effects caused by the heat treatment.
Question: Other than "because it's a requirement of the Standard", in this scenario (only) why would the carb/decarb test be required?
 
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How deep is the decarb/carb? What type of grinding process is used? How much is ground off? How straight is the shank? How do you verify that the grinding process does not introduce defects?

Most likely the test would not be required, but you should be able to answer these questions before assuming that grinding definitely removes any defects and does not introduce any new ones.
 
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Question: Why would the carb/decarb test be required?

Answer: To insure that "[t]he process of grinding to roll-body size would remove any threaded area carburization or decarburization effects caused by the heat treatment" and that the parts meet all requirements listed in ASTM A 574.
 
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TVP:
The shanks are straight, we use centerless grinding and we remove more that .025" during the grinding operation.
CoryPad:
ASTM A-370 indicates that to get a good hardness reading, remove a minimum of .025".

FYI: Heat treat is performed in a carbon neutral atmosphere so there is no additional carburization or decarburization, then the shank is ground to roll-body size. The A-574 test is done only on the threaded area at the thread crest, thread root and, at the thread pitch diameter.
 
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QAFitz,

I do not understand why you mentioned ASTM A 370 and a material removal recommendation.

While the heat treating process has been designed to use a neutral atmosphere, there will always be variations in the process and the chemical composition of the incoming parts. You need to perform a check on a part from each lot to verify that the heat treatment has been done correctly.

When you say the A-574 test, do you mean the check for decarburization? Why do you mention the locations?
 
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