Microstructure-mechanical property relationships of martensite and lower bainite in a 0. 3%C-3%Cr-2% Mn steel

Technical Report · Fri Apr 01 04:00:00 EST 1983

OSTI ID:6063439

Tokushige, H

In the as-quenched condition, martensite of a 0.3%C-3%Cr-2%Mn steel consists of heavily dislocated laths containing fine autotempered carbides and bounded by thin films of retained austenite. Similarly, lower bainite after 10 minutes of isothermal holding at 360/sup 0/C consists of dislocated bainitic ferrite laths, unidirectional intralath carbides, and interlath films of retained austenite. However, when the isothermal holding is prolonged to one hour, retained austenite has decomposed into interlath carbides in a similar manner to that observed in martensite tempered at 240 to 400/sup 0/C. Crystallographic studies have revealed that bainitic ferrite laths are related to adjacent laths as well as to parent austenite through the same orientation relationships as those found for martensite laths, which strongly confirms the shear aspect in the bainite transformation. Bainitic carbides, identified as cementite, are found to have the Isaichev orientation relationship with ferrite, which supports the idea that cementite has formed directly from austenite. The lower bainitic structure is more similar to that of martensite tempered on the tempered martensite embrittlement (TME) range rather than as-quenched martensite. The as-quenched martensite exhibits a high strength and toughness, the latter being greatly enhanced by tempering at 200/sup 0/C. The strength and toughness of lower bainite are substantially lower than those of as-quenched martensite, and they remain relatively unchanged upon tempering up to 400/sup 0/C. Fractographic examinations indicate the similarities in the fracture mode between TME and lower bainite; in both cases, the absence of retained austenite films and the presence of coarse carbides appear to cause brittle fracture. 104 references, 52 figures.

• Research Organization: Lawrence Berkeley Lab., CA (USA)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 6063439
• Report Number(s): LBL-15956; ON: DE83012437
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102* -- Metals & Alloys-- Structure & Phase Studies
360103 -- Metals & Alloys-- Mechanical Properties
ALLOYS
AUSTENITE
BAINITE
CARBON ADDITIONS
CHROMIUM ALLOYS
CHROMIUM STEELS
CRYSTAL STRUCTURE
DATA
EXPERIMENTAL DATA
FRACTURE PROPERTIES
HEAT TREATMENTS
INFORMATION
IRON ALLOYS
IRON BASE ALLOYS
MANGANESE ALLOYS
MANGANESE STEELS
MARTENSITE
MECHANICAL PROPERTIES
MICROSTRUCTURE
NUMERICAL DATA
STEELS