During heat treatment quenching cracks occur due to
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Answer:
1) Improper quenchant. Yes, water, brine or caustic will get the steel harder. If the steel is an oil-hardening steel, the use of these overly aggressive quenchants will lead to cracking.
2) Making an improper selection of steel for the process.
3) Too much time between the quenching and the tempering of the heat-treated parts. A common misconception is that quench cracks can occur only while the piece is being quenched. This is not true. If the work is not tempered right away, quench cracks can (and will) occur.
4) Improper design. This includes sharp changes of section, lack of radii, holes, sharp keyways, unbalanced sectional mass and other stress risers.
5) Improper entry of the part/delivery of the quenchant to the part. Differences in cooling rates can be created, for example, if parts are massed together in a basket. This can result in the parts along the edges cooling faster than those in the mass in the center. Part geometry can also interfere with quenchant delivery and effectiveness, especially on induction lines.
6) Failure to take sufficient stock removal from the original part during machining. This can leave remnants of seams or other surface imperfections that can act as a nucleation site for a quench crack