Minutes Hours

Tempering Time

Fig. 5.21. Tempering Response of Several PH Stainless Steels2'

followed by air cooling. PH during aging at 925° F produces the H-925 condition. The tempering response of a number of PH stainless steels is shown in Fig. 5.21. If stress corrosion is a concern, the PH steels should be aged at the highest temperature that will maintain an adequate strength level.

Some dimensional change are experienced during the heat treatment of the semiaustenitic steels. A dimensional expansion of approximately 0.0045 in./in. occurs during the transformation from the austenitic to the martensitic condition, and, during aging, a contraction of about 0.0005 in./in. takes place. Vapor blasting of scaled parts after final heat treatment is recommended because of the hazards of intergranular corrosion in inadequately controlled acid pickling operations.

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