Effect of niobium on austenite recrystallization and pearlite colony size in a microalloyed eutectoid steel
- PDF / 1,671,427 Bytes
- 4 Pages / 594 x 774 pts Page_size
- 106 Downloads / 239 Views
The authors wish to acknowledge Mr. C.E. Harper and Mr. W.H. Leisler for their help in the heat treatment and metallography. Part of this work was performed on United States Air Force Contract F33615-82-C-5078.
REFERENCES 1. F.H. Froes, J.M. Capenos, and C. E Yolton: Metallography, 1976, vol. 9, pp. 535-37. 2. I. Weiss and E H. Froes: unpublished research, 1984. 3. E. D. Hondros and A. J. W. Moore: Acta Metall., 1979, vol. 7, p. 521. 4. W. B. Morrison: J.I.S.I., 1972, vol. 210, pp. 618-23. 5. R. Winstreads and R. A. Kot: The Recrystallization of Austenite during the Hot RoLling of a Cb-Bearing High Strength Low Alloy Steel, Metallographic Exhibit, Class I, Cleveland, OH, 1976. 6. H. P. Stiiwe: Recrystallization of Metallic Materials, E Haessner and Dr. Riederer, eds., Verlag GMBH, Stuttgart, 1978, p. 16.
Effect of Niobium on Austenite Recrystallization and Pearlite Colony Size in a Microalloyed Eutectoid Steel H.-J. KESTENBACH and G. S. MARTINS For many years, small additions of niobium have been used commercially to refine the ferrite grain size in hotrolled products of low carbon steel. There are several ways in which niobium may lead to ferrite grain refinement.~ The effect, however, is most pronounced when niobium is used to slow down recrystallization kinetics during controlled rolling. 2 In this case, plastic deformation during the final rolling passes is no longer accompanied by recrystallization. As a result, transformation to ferrite during cooling takes place in an elongated and highly dislocated austenite grain structure in which both a larger grain boundary area and a high stored energy of deformation increase the ferrite nucleation rate. In order to retard dynamic or static recrystallization at finish rolling temperatures, niobium has to be taken into solution prior to rolling. This requirement poses no problem in low carbon steel where typical Nb additions in the range of 0.03 to 0.05 pct can readily be dissolved at ordinary soaking temperatures. For high carbon steel, however, the solubility of niobium in austenite is rather low. According to the solubility data of Nordberg and Aronsson, 3 only about 0.01 pct Nb can be dissolved at 1200 ~ in a 0.8 pct carbon steel. The solubility problem may explain why rather limited attention has been paid in the literature to niobium additions in high carbon steel. Such additions, however, appear to have been promising in development work for rail steels,4 and have actually been used on a commercial scale in Brazil. 5 Furthermore, in a deliberate effort to extend microalloying techniques to higher carbon levels, Coladas H.-J. KESTENBACH, Professor, and G. S. MARTINS, Research Student, are with the Departamento de Engenharia de Materiais, Universidade Federal de Silo Carlos, Rodovia Washington Luiz, km 235, 13560 Sgo Carlos-SP, Brazil. Manuscript submitted September 22, 1983. 1496--VOLUME 15A, JULY 1984
shown a strong delaying effect of 0.022 pct Nb dissolved in austenite on the static recrystallization of 0.4 pct carbon steel after hot rolling. The present note
Data Loading...
