Phosphorus and carbon segregation: Effects on fatigue and fracture of gas-carburized modified 4320 steel

Journal Article · Wed Jun 01 00:00:00 EDT 1994 · Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States)

DOI:https://doi.org/10.1007/BF02652297· OSTI ID:7029370

Hyde, R S; Krauss, G; Matlock, D K ^[1]

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1. Colorado School of Mines, Golden, CO (United States). Advanced Steel Processing and Products Research Center

Phosphorus and carbon segregation to austenite grain boundaries and its effects on fatigue and fracture were studied in carburized modified 4320 steel with systematic variations, 0.005, 0.017, and 0.031 wt pct, in alloy phosphorus concentration. Specimens subjected to bending fatigue were characterized by light metallography, X-ray analyses for retained austenite and residual stress measurements, and scanning electron microscopy (SEM) of fracture surfaces. Scanning Auger electron spectroscopy (AES) was used to determine intergranular concentrations of phosphorus and carbon. The degree of phosphorus segregation is directly dependent on alloy phosphorus and carbon content. The degree of carbon segregation, in the form of cementite, at austenite grain boundaries was found to be a function of alloy phosphorus concentration. The endurance limit and fracture toughness decreased slightly when alloy phosphorus concentration was increased from 0.005 to 0.017 wt pct. Between 0.017 and 0.031 wt pct phosphorus, the endurance limit and fracture toughness decreased substantially. Other effects related to increasing alloy phosphorus concentration include increased case carbon concentration, decreased case retained austenite, increased case compressive residual stresses, and increased case hardness. All of these results are consistent with the phosphorus-enhanced formation of intergranular cementite and a decrease in carbon solubility in intragranular austenite with increasing phosphorus concentration. Differences in fatigue and fracture correlate with the degree of cementite coverage on the austenite grain boundaries and the buildup of phosphorus at cementite/matrix interfaces because of the insolubility of phosphorus in cementite.

• OSTI ID: 7029370
• Journal Information: Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States), Vol. 25:6; ISSN 0360-2133
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CARBON
SEGREGATION
PHOSPHORUS
STEELS
FATIGUE
FRACTURE PROPERTIES
CEMENTITE
EXPERIMENTAL DATA
ALLOYS
CARBIDES
CARBON COMPOUNDS
DATA
ELEMENTS
INFORMATION
INTERMETALLIC COMPOUNDS
IRON ALLOYS
IRON BASE ALLOYS
IRON CARBIDES
IRON COMPOUNDS
MECHANICAL PROPERTIES
NONMETALS
NUMERICAL DATA
TRANSITION ELEMENT COMPOUNDS
360103* - Metals & Alloys- Mechanical Properties