SOME OBSERVATIONS ON ANOMALY SHAPES OF JOMINY HARDENABILITY CURVES

It is usual that a Jominy hardenability curve continuously decreases its hardness as the distance from the water-cooled end increases, however, sometimes abnormal hardness reverse appears especially in Jominy curves on low alloy steels containing carbide-forming elements and also in the case of plain high-carbon steels. The author made a number of observations on the relation between hardenability curves and microstructures along Jominy bars, and also investigated on the continuous cooling transformation and isothermal transformation diagrams of these steels. The results of observations were concluded as follows:1. The anomaly of the hardness curve appeared both in Jominy curves and in the relation curves between hardness of isothermal decomposition products and transformation temperatures, only in the range where the intermediate transformation product and pearlite structure co-existed.2. The hardness reverse was considered to be attributed to the discontinuity of hardness vs. transformation-temperature curves in pearlite and intermediate transformation ranges. And fine pearlite seemed rather harder than coarse bainite, although the formation temperature of the former was higher than that of the latter.3. Alloying of carbide forming elements such as Cr, V, Mo etc. seemed to exaggerate the anomaly probable due to their influences on the shapes of S-curves and nature of carbide in pearlite, however, it could not be considered as essential reason, because plain high carbon steels also had such tendency.4. In the end-quenched structure of plain high-carbon steels, intermediate transformation structure was also observed as well as in the isothermal transformation structure. The author considered that the more accurate study on the S-curves of plain carbon steels, which might indicate pearlite and intermediate transformations separately, would enable to explain the phenomenon.