Fatigue resistance of laser heat-treated 1045 carbon steel
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400
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a: o z w o
300
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I N 1OO
o
IN
792
H. B. SINGH, S. M. COPLEY, A N D M. BASS
-24
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100
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I 10
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SOLIDIFICATION SPEED,
I o 100 R
I -6
(t4etres/sec, x l o )
Fig. 2--Dependence of the primary dendrite spacing on the growth speed of DS IN-100.
directionally solidified alloy as a function of growth speed. The primary dendrites are present in the form of regular arrays. Dendrite spacing measurements were done along straight lines containing large number of those dendrites. The primary dendrite arm spacing can be seen to decrease with increasing R. Figure 2 shows the dendrite spacings measured as a function of crucible withdrawal speed R. Solid line is the least squared straight line fit through these data points and can be represented by log d = - 4.705 - 0.2393 log R where d is expressed as m and R as m/s. The data show an excellent fit as per the relationship, d oc ( g ) -~ which agrees very well with the relationship predicted by Hunt. 6 Primary dendrite spacing data obtained in a similar experiment on superalloy IN-792 s are also plotted in Fig. 2 as a function of growth speed, R and can be represented by log d = 4.931 - 0.2647 log R These data also follow the relationship, d oc ( R ) -~ in a good agreement with the predicted relationship of d cc (R)- 0.25. This investigation was conductd as part of a project funded by Aeronautical Research and Development Board of the Ministry of Defence, Government of India.
1. Aerospace Structural Metals Handbook, vol. 5, Code 4212 p. 21. (AFML-TR-68-115), 1977 (Dept. of Defense). 2. M. C. Flemmgs: Solidification Processing, p. 147, McGraw Hill Inc., 1974. 3. J. A. Howarth and L. F. Mondolfo: Acta Metall., 1962, vol. 10, p. 1037. 4. J. O. Coulthard and R. Elliott: J. Inst. Met., 1967, vol. 95, pp. 21-23. 5. P. K. Rohatgi and C. M. Adams, Jr.: Trans. TMS-AIME, 1967, vol. 239, pp. 1737~,6. 6. J. D. Hunt: Solidification and Casting of Metals, pp. 3-9, The Metals Society, London, 1979. 7. S. N. Tewari: Trans. lndian Inst. Met. 1978, vol. 31, pp. 480-83. 8. L. S. Lasak: M.S. Thesis, Rensselaer Polytechnic Institute, Troy, New York, 1976. 138--VOLUME 12A, JANUARY 1981
It has been demonstrated that rapid heating and cooling produced by scanning a laser beam across a metallic surface can be employed to harden ferrous alloys. ] However, only preliminary information has been reported relating the details of the irradiation treatment to the resultant changes in microstructure and mechanical properties such as hardness and fatigue life.2,3 In this investigation, we have determined the changes in microstructure, hardness and fatigue life of a 1045 carbon steel produced by irradiating the reduced section of rotating beam fatigue specimens with a continuous wave, carbon dioxide laser of moderate power (475 W). The experimental arrangement for irradiating specimens is shown in Fig. 1. The specimen was mounted between centers on a lathe and the optical path of the laser beam was arranged so that the lens (L) focussing the beam on the surface of the spe
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