Modeling of CCT Diagrams and Ferrite Grain Size Prediction in Low Carbon Nb–Mo Microalloyed Steels

Abstract

In this paper a multi-linear regression analysis is developed to predict continuous cooling (CCT) diagrams in low carbon Nb and Nb-Mo microalloyed steels. The inputs to the analysis include the weight percentage of alloying elements, the prior austenite grain size, the retained strain and the cooling rate. To develop the model, 11 steels with different combinations of Nb and Mo were considered. In some cases, the resulting equations have been validated with external data from the literature. Additionally, the model was also employed to predict hardness and ferrite grain size with the aim of providing a tool to link microstructural features with mechanical property predictions. Both Nb and Mo additions promote a reduction of ferrite and bainite start temperatures, where the effect is more pronounced for Nb in the bainitic region. Both microalloying elements contribute to an increase in hardness and a refinement of the microstructure.

Continuous cooling transformation diagrams of HSLA steel for seamless tubes production

“…The transformation diagrams obtained for the steel investigated were confronted with CCT/DCCT diagrams of similar steel grades available in the literature [6,7]. Figure 19 shows the CCT diagram of the steel containing 0.13 C -1.53 Mn -0.25 Si -0.01 V -0.043 Nb (in weight %) based on a combination of dilatometer tests and HAZ tests performed on the Gleeble 3800 simulator [7].…”

“…The results of extensive work related to the design and modeling of the CCT/DCCT diagrams of HSLA steels with varying contents of Nb and Mo were published by Isasti et al [6]. The experiments were carried out on the deformation dilatometer Bähr DIL805D after the annealing of the specimens at the temperatures of 1473 -1523 K, ensuring the dissolution of niobium rich MX precipitates.…”

“…The final cooling rate makes it possible to control the austenite softening processes, and phase transformations during decomposition of austenite and grain growth. The published results [4][5][6][7][8][9][10][11][12], and our experiences gained in the laboratory conditions using the hot deformation simulator Gleeble 3800 [13][14], as well as the semi-continuous hot rolling mill [15][16] prove the crucial role of the cooling parameters after hot forming. This can be deduced from the continuous cooling transformation diagrams, especially when considering the previous deformation history.…”

“…CCT diagram of the 28NbHC steel grade; black points and curves[6] superimposed with the CCT diagram presented inFig. 14 -blue curves…”

Alloying Effects of Molybdenum and Niobium on Chromium Bearing Low Alloy Steel for Water Ballast Tank

“…Both the Mo and Nb additions were proved as effective in the lowering of the transformation temperatures, and a greater effectiveness was observed regarding the Mo and the Nb in the ferritic and bainitic regions, respectively. 44) Especially, the Nb is particularly effective in the retardation of the recrystallization, thereby ef cient for grain re nement. 45) Mo is also known as an alloying element for the retardation of the ferrite formation, and this is ef cient for lowering bainitic transformation temperature, and especially in terms of its assistance of the Nb for the recrystallization retardation.…”