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

Journal Article · Thu Oct 31 23:00:00 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]

---

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, Journal Name: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science Journal Issue: 11 Vol. 27; ISSN MMTAEB; ISSN 1073-5623
• Country of Publication: United States
• Language: English

Related Subjects

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