Effect of carbide phases on crack growth of 0.5 % Mo--B steels under impact, cyclic, and monotonically increasing loading

Journal Article · Fri Mar 01 00:00:00 EDT 1974 · Met. Trans., v. 5, no. 3, pp. 659-666

OSTI ID:4308763

Miller, G A; Stephenson, E T

A study of the influence of carbide phases on the cracking resistance of as-quenched and of quenched and tempered 0.5% Mo-B steels was made using notched or notched and precracked specimens that were subjected to impact, cyclic, and monotonically increasing loading. The carbide influence on fracture, while limited in extent, was found to increase as load, loading rate, volume fraction, and particle size increase. The results for the as-quenched condition showed that the susceptibility of these steels to crack initiation under impact loading at temperatures below --100 deg F is greater when even a small amount of titanium carbide (less than 0.2 vol% of 1 to 5 mu m particles) is present than when none is present. At room temperature, this same carbide concentration has no influence on impact properties, fatigue-crack initiation (in the presence of a notch), fatigue-crack growth rate, or the ductile fracture resistance under monotonically increasing loading at slow strain rate. In the case of the quenched and tempered materials, the alloy containing a large amount of M/sub 23/ C/sub 6/ (2 vol% of 1 to 10 mu m particles) exhibited behavior similar to that observed in the as-quenched materials containing titanium carbide. That is, the presence of M/sub 2/C/sub 6/ was associated with increased susceptibility to crack initiation for impact loading at low temterature. In addition, at room temperature this alloy had a reduced impact energy for crack propagation. For monotonically increasing loading at slow strain rate, this same carbide distribution had no influence on the net section stresses required to initiate stable or unstable crack growth. These stresses fail closely in line with, respectively, the yield stress and tensile strength of the material. Thc alloy containing M/sub 23/C/sub 6/ required less crack opening for a given crack extension--an effect most pronounced after maximum load. Attention is also directed to the use of Charpy test data to assess fracture resistance for modes of loading other than impact. (auth)

• Research Organization: Bethlehem Steel Corp., PA
• NSA Number: NSA-29-024751
• OSTI ID: 4308763
• Journal Information: Met. Trans., v. 5, no. 3, pp. 659-666, Other Information: Orig. Receipt Date: 30-JUN-74
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

N50230* -Metals
Ceramics
& Other Materials-Metals & Alloys-Properties
Structure & Phase Studies
*STEELS- FRACTURE PROPERTIES
BORON ADDITIONS
CARBIDES
CHARPY TEST
CRACKS
FATIGUE
IMPACT SHOCK
LOW TEMPERATURE
MEDIUM TEMPERATURE
MOLYBDENUM ADDITIONS
PARTICLE SIZE
QUENCHING
STRAINS
STRESSES
TIME DEPENDENCE
YIELD STRENGTH