There are many theories about the formation of white spots in forging . But it is more convincing and can be proved by practice: white spots are the result of the interaction of hydrogen and tissue stress in steel. The structural stress here mainly refers to the internal stress formed when austenite transforms into martensite and pearlite. Without a certain amount of hydrogen and more significant tissue stress, white spots cannot be formed. However, if the hydrogen content is high and the tissue stress is not large, white spots will generally not appear. For example, single-phase austenitic and ferritic steels have few white spots due to the absence of phase-change structural stress.
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