Abstract
The microstructures and mechanical properties of a series of vacuum melted Fe/(2 to 4) Mo/(0.2 to 0.4) C steels with and without cobalt have been investigated in the as-quenched fully martensitic condition and after quenching and tempering for 1 h at 673 K (400°C) and 873 K (600°C); austenitizing was done at 1473 K (1200°C) in argon. Very good strength and toughness properties were obtained with the Fe/2 Mo/0.4 C alloy in the as-quenched martensitic condition and this is attributed mainly to the absence of internal twinning. The slightly inferior toughness properties compared to Fe/Cr/C steels is attributed to the absence of interlath retained austenite. The two 0.4 pct carbon steels having low Mo contents had approximately one-half the amount of transformation twinning associated with the two 0.4 pct carbon steels having high Mo contents. The plane strain fracture toughness of the steels with less twinning was markedly superior to the toughness of those steels with similar alloy chemistry which had more heavily twinned microstructures. Experiments showed that additions of Co to a given Fe/Mo/C steel raisedM S but did not decrease twinning nor improve toughness. Molybdenum carbide particles were found in all specimens tempered at 673 K (400°C). The Fe/Mo/C system exhibits secondary hardening after tempering at 873 K (600°C). The precipitate is probably Mo2C. This secondary hardening is associated with a reduction in toughness. Additions of Co to Fe/Mo/C steels inhibited or eliminated the secondary hardening effect normally observed. Toughness, however, did not improve and in fact decreased with Co additions.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
References
S.K. Das and G. Thomas:Tram. ASM, 1969, vol. 62, p. 659.
M. Raghavan and G. Thomas:Met. Trans., 1971, vol. 2, pp. 3433–39.
D. H. Huang and G. Thomas:Met. Trans., 1971, vol. 2, pp. 1587–98.
J. McMahon and G. Thomas: Third International Conf. on Strength of Metals and Alloys,Microstructure and Design of Alloys, vol. 1, pp. 180–84, Cambridge, England, 1973.
G. Thomas:Iron and Steel International, 1973, vol. 46, pp. 451–61.
R. S. Archer, J. Z. Briggs, and C. M. Loeb, Jr.:Molybdenum: Steels-Irons-Alloys, Climax Molybdenum Co., 1948.
L. Colombier:Molybdenum in Stainless Steels and Alloys, Climax Molybdenum Co., Ltd., 1967.
K. J. Irvine:J. Iron Steel Inst., 1962, vol. 200, p. 820.
K. J. Irvine:Heat Treatment of Metals, ISI Special Report No. 95, p. 37, The Iron and Steel Institute, London, 1966.
F. B. Pickering:Precipitation Processes in Steels, ISI Special Report No. 64, p. 23, The Iron and Steel Institute, London, 1959.
R. W. K. Honeycombe:Trans. Iron Steel Inst. of Japan, 1966, vol. 6, p. 217.
P. Payson:Trans. ASM, 1959, vol. 51, p. 60.
P. Wilkes:Metal Sci. J., 1968, vol. 2, p. 8.
R. G. Baker and J. Nutting:Precipitation Processes in Steels, ISI Special Report No. 64, p. 1, The Iron and Steel Institute, London, 1959.
R. W. K. Honeycombe:Proceedings of the National Research Institute of Metals, Tokyo, p. 44, 1966.
K. J. Irvine and F. B. Pickering:J. Iron Steel Inst., 1960, vol. 194, p. 137.
R. Goolsby:Relationships Between Microstructure and Fracture Toughness in a Secondary Hardening Steel, Ph.D. Thesis, University of California, Berkeley, Lawrence Berkeley Laboratory Report-405, 1971.
K. Kuo:J. Iron Steel Inst., 1953, vol. 173, p. 363.
R. W. K. Honeycombe:Low Alloy Steels, ISI Publication No. 114, p. 65. The Iron and Steel Institute, London, 1968.
D. J. Dyson, S. R. Keown, D. Raynor, and J. A. Whiteman:Acta Met., 1966, vol. 14, p. 867.
Annual Book of ASTM Standards, Designation E399-72, p. 960, 1972.
K. J. Irvine, F. B. Pickering, and J. Garstone:J. Iron Steel Inst., 1960, vol. 196, p. 66.
C. R. Simcoe and A. E. Nehrenberg:Trans. ASM, 1965, vol. 58, p. 378.
C. R. Simcoe, A. E. Nehrenberg, V. Biss, and A. P. Coldren:Trans. ASM, 1968, vol. 61, p. 834.
B. R. Banerjee:J. Iron Steel Inst., 1965, vol. 203, p. 166.
P. M. Kelly and J. Nutting:J. Iron Steel Inst., 1961, vol. 197, p. 199.
A. J. Baker, P. M. Kelly and J. Nutting:Electron Microscopy and Strength of Crystals, G. Thomas and J. Washburn, eds., p. 899, John Wiley and Sons, New York, 1963.
J. R. Low, Jr.:Engineering Fracture Mechanics, 1968, vol. 1, p.47.
T. Tom:Microstructural Variables and Fracture Toughness of High Strength Mo and Mo-Ni Steels, D. Eng. Thesis, University of California, Berkeley, Lawrence Berkeley Laboratory Report-1856, 1973.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Clark, R.A., Thomas, G. Design of strong tough Fe/Mo/C martensitic steels and the effects of cobalt. Metall Trans A 6, 969–979 (1975). https://doi.org/10.1007/BF02661349
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF02661349