M{sub 2}C precipitates in isothermal tempering of high Co-Ni secondary hardening steel

Journal Article · Fri Nov 01 00:00:00 EST 1996 · Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science

DOI:https://doi.org/10.1007/BF02595438· OSTI ID:413280

Yoo, C H ^[1]; Lee, H M ^[2]; Chan, J W; Morris, Jr, J W ^[3]

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1. POSCO, Pohang (Korea, Republic of). Stainless Dept. Cold Rolling Team
2. Korea Advanced Inst. of Science and Technology, Taejon (Korea, Republic of). Dept. of Materials Science and Engineering
3. Univ. of California, Berkeley, CA (United States)

The effects of isothermal tempering on the coarsening behavior of hexagonal M{sub 2}C precipitates and the secondary hardening reaction in ultrahigh-strength AerMet 100 steel were investigated. The tempering temperatures were 468 C, 482 C, and 510 C, and the tempering time spanned the range from 1 to 400 hours. Experimental studies of the coarsening behavior of the carbides were made by utilizing transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffractometry (XRD). The hardness at the secondary hardening peak was about HRc 55. The average length and diameter of M{sub 2}C carbides were 4 to 8 nm and 1.5 to 2.5 nm, respectively, at all three tempering temperatures; hence, the aspect ratio was almost 3, an equilibrium value in this case. The size of the M{sub 2}C carbides increased monotonically with time, but the growth kinetics did not exactly follow the classical coarsening behavior. The amount of precipitated austenite increased with tempering time and temperature. M{sup 2}C precipitates were still relatively fine even after 200 hours of tempering. This feature seemed to be closely related to the high hardness maintained after prolonged tempering.

• Sponsoring Organization: USDOE
• OSTI ID: 413280
• Journal Information: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Vol. 27, Issue 11; Other Information: PBD: Nov 1996
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
IRON BASE ALLOYS
TEMPERING
MICROSTRUCTURE
COBALT ALLOYS
NICKEL ALLOYS
CHROMIUM ALLOYS
MOLYBDENUM ALLOYS
CARBON ADDITIONS
CHEMICAL COMPOSITION
SAMPLE PREPARATION
TEMPERATURE DEPENDENCE
TIME DEPENDENCE
TRANSMISSION ELECTRON MICROSCOPY
SCANNING ELECTRON MICROSCOPY
X-RAY DIFFRACTION
PARTICLE SIZE
AUSTENITE
CEMENTITE
MORPHOLOGY
HARDNESS