TEM STUDY OF MICROSTRUCTURES OF STEEL Ni9

The microstructures of martensite and austenite in steel Ni9 treated under 800℃1 h, WQ+670℃1 h, WQ+585℃1 h, WQ were investegated with TEM. Most of tempered austenite particles do not precipetate according to theoritical K-S or N-W orientation relationship (OR) with martensite martrix, but have small deviation from these two ORs. In a martensite lath packet, the different austenite variants with the above approximate ORs are pricipetalted. The lath-like tempered austenite precipetates along martensite boundaries with habit plane (335)γ'∥(341)α. Martensite twins form when austenite transformed into martensite. These twins disappear during tempering.