The influence of stress intensity and microstructure on fatigue crack propagation in ferritic materials

“…The objectives were to test various theoretical and empirical fatigue crack propagation equations' -s' [10][11][12][13][14] and to clarify the relation between fatigue crack propagation rate and metallurgical structure in quenched and tempered steels.…”

mentioning

confidence: 99%

Fatigue crack propagation in 4140 steel

Thielen

Fine

1975

Metall Trans A

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The fatigue crack propagation rates, da/dN, of 4140 steel were measured in dry argon vs tempering temperature. In specimens 3.2 mm thick at a given OK between 15 and 30 MN/ m 3 /2, da/dN decreases with increasing tempering temperature, reaches a shallow minimum for tempering at 400°C. The rate for as-quenched specimens increases with R ratio; this is not the case for the 400, 550 and 650°C tempers. Reducing the specimen thickness to 1.3 mm has little effect on the 650°C temper but causes a large decrease in da/dN for the asquenched condition and 200°C temper. Edge notch specimens tempered at 550 and 650°C are subject to crack arrest from cycling prior to crack initiation. The results are discussed in terms of the metallurgical structures and various fatigue crack propagation equations which have been proposed. The results cannot be explained on the basis of da/dN being determined only by Young's modulus and K.THE fatigue crack propagation rate of vacuum degassed quenched and tempered 4140 steel was investigated vs tempering temperature from 25 to 650°C. The objectives were to test various theoretical and empirical fatigue crack propagation equations' -s' 10-14 and to clarify the relation between fatigue crack propagation rate and metallurgical structure in quenched and tempered steels. EXPERIMENTAL PROCEDURESThe composition of the commercial vacuum degassed AISI 4140 steel supplied by the Inland Steel Company Research Laboratories was (in wt pct):0.38 C, 0.85 Mn, 0.010 P, 0.015 S, 0.25 Si, 0.93 Cr, 0.22 Mo. The as-received rods, 25.4 mm in diam, were hot rolled to 4.2 and 2.5 mm thick sheets, from which blanks 20 x 100 x 3.2 or 20 x 100 x 1.3 mm were machined. These blanks were austenitized for 1 h at 1000°C in an Ar -5 pct H2 atmosphere, oil-quenched and tempered for 1 h at 200, 400, 550 and 650°C respectively, followed by a water-quench. The blanks were then side or center notched by spark machining using a 0.12 mm diam copper wire. For center notching, a hole of 1 mm diam was drilled in the specimen center before heat treatment. The side notches were 1 mm long and 0.18 mm wide. The center notches were 2.5 mm long and 0.18 mm wide. After notching, the faces of the specimens were mechanically polished to facilitate observation of the crack.All fatigue crack propagation tests were conducted on a closed loop electrohydraulic system of 90 KN capacity at room temperature in dry Ar at 30 Hz with a sinusoidal wave form for the applied load. The specimens, contained in a surgical rubber enclosure with a mylar window, were solidly gripped at both ends. The crack length (a) was monitored as a function of the number of cycles (N) with a40 magn. micrometer telemicroscope. Measurements of the crack length were made approximately every 0.15 mm of propagation.Fracture toughness measurements were performed PAUL N. THIELEN is Engineer, Arbed Steel Co.on single edge notched specimens of dimensions identical to those of the fatigue specimens, except that the sparked-in notch was 7 mm long. This initial notch was extended to 9.2 m...

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“…Richards and Lindlev (67) observed that an increase in thickness caused a marked increase in crack growth rate which was in contrast to the result for striation mechanisms. They proposed that the increase in growth rate was caused by the occurrence of miorocleavage in the mechanism of growth.…”

mentioning

confidence: 54%

Fatigue crack initiation and propagation in steels exposed to inert and corrosive environments. Final report, May 1, 1977--December 31, 1977

Youseffi¹,

Finnie²

1978

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The influence of stress intensity and microstructure on fatigue crack propagation in ferritic materials

Cited by 168 publications

References 27 publications

Fractographic and Microstructural Analysis of Fatigue Specimens of A302 Grade B Steel Tested in Air at Room Temperature.

Fractographic and Microstructural Analysis of Fatigue Specimens of A302 Grade B Steel Tested in Air at Room Temperature.

Fatigue crack propagation in 4140 steel

Fatigue crack initiation and propagation in steels exposed to inert and corrosive environments. Final report, May 1, 1977--December 31, 1977

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