Role of Precipitates in Recrystallization Mechanisms of Nb-Mo Microalloyed Steel

Mandal, G. K.; Das, Saubhik; Kumar, T. V. Vineeth; Kamaraj, Ashok; Mondal, Kunal; Srivastava, V. C.

doi:10.1007/s11665-018-3711-1

Cited by 14 publications

(6 citation statements)

References 35 publications

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“…The changes in the average size of austenite in the four kinds of steel are presented in Figure 10 , which indicates a pronounced tendency of decreasing in the average size of austenite with the increase of Mo content. This result further supported that the addition of Mo can refine the grain, which may be associated with the pinning effect of the precipitates located in the grain boundaries [ 27 , 28 ].…”

Section: Resultsmentioning

confidence: 53%

Effect of Molybdenum on the Impact Toughness of Heat-Affected Zone in High-Strength Low-Alloy Steel

Ping

et al. 2021

Materials

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The microstructure, precipitates, and austenite grain in high-strength low-alloy steel were characterized by optical microscope, transmission electron microscope, and laser scanning confocal microscopy to investigate the effect of Mo on the toughness of steel. The microstructure was refined and the toughness was enhanced after the addition of 0.07% Mo in steel. The addition of Mo can suppress the Widmanstätten ferrite (WF) formation and promote the transformation of acicular ferrite (AF), leading to the fine transformed products in the heat-affected zone (HAZ). The chemical composition of precipitates changed from Nb(C, N) to (Nb, Mo)(C, N) because of the addition of Mo. The calculated lattice misfit between Nb(C, N) and ferrite was approximately 11.39%, while it was reduced to 5.40% for (Nb, Mo)(C, N), which significantly affected the size and number density of precipitates. A detailed analysis of the precipitates focusing on the chemical composition, size, and number density has been undertaken to understand the contribution of Mo on the improvement of steel toughness.

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Section: Resultsmentioning

confidence: 53%

Effect of Molybdenum on the Impact Toughness of Heat-Affected Zone in High-Strength Low-Alloy Steel

Ping

et al. 2021

Materials

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“…Similar delays in recovery of deformation substructures in Mo containing steels were previously reported by several authors. [21,31,63,64,66] Furthermore, the delay in softening response in the NbMo steel could also explain the existence of predominantly LAB between sub-micrometer-sized ferrite grains. In addition, such regions also act as preferred sites for nucleation of strain-induced NbC precipitates.…”

Section: Grain Size and Gb Charactermentioning

confidence: 99%

Influence of Finish Rolling Temperature and Molybdenum Addition on Strengthening of Low Carbon Niobium Steels—A Computational and Experimental Study

Chakraborty

Primig

2021

steel research int.

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Low C microalloyed steels have widespread applications in contemporary construction and transportation applications owing to their unique combination of high strength and ductility. [1,2] The addition of microalloying elements such as Nb, Ti, and V in the presence of ultralow C contents imparts effective strengthening by precipitation and grain size refinement under controlled thermomechanical processing (TMP) conditions. [3][4][5] Several studies have investigated the role of microalloying and TMP routes on the evolution of harder (nonequilibrium) phases as matrix microstructures, such as acicular ferrite, bainite, and martensite, for high-strength plate and pipeline applications. [6][7][8][9][10][11][12][13] However, a harder phase matrix microstructure suffers from poor stretch flangeability (formability) due to its poor local elongation abilities near higher stress concentration zones along the soft/hard interfaces, leading to premature microvoid crack initiation and failure in thin-sheet applications. [14,15] This explains interest in softer equilibrium phases as matrix microstructures such as ferrite. Ferritic steels offer better stretch formability and are, thus, more suitable for thin sheet applications, e.g., in the automotive industry. Funakawa et al. [16] developed a TiC precipitation-strengthened ferritic steel with a yield strength of 734 MPa, a total elongation of 24%, and a hole expansion ratio around 120% for a 0.047C-0.082Ti-0.2Mo (wt% in the following) hot-rolled steel. A higher ferritic yield strength of 760 MPa in a multicomponent microalloyed 0.04C-0.08Ti-0.011Nb-0.015V-0.18Mo steel was reported by Shen et al. [17] due to a mix of finely dispersed TiC and coarser grain boundary (GB) M 23 C 6 precipitates. Single-hit deformation and aging experiments at 650 C by Mukherjee et al. [18] highlighted the effect of Mo on initiating extremely stable Ti(Mo)C (α/γ) interphase nanoprecipitates in ferrite in a 0.04C-0.05Ti-0.22Mo steel for aging durations between 300 and 3600 s, leading to an average ferrite hardness of 250 vickers hardness number (VHN). In addition, they also observed fine TiC solute clusters during shorter aging periods. The beneficial role of Mo in the presence of Ti in lowering of austenite to ferrite transformation temperature upon continuous cooling and delaying precipitate coarsening while aging during ferritic transformation is also well established. [19][20][21][22][23] While it is evidently clear that microalloying in the presence of Mo improves the yield strength of ferritic steels, deformation at lower temperatures in the two-phase austenite þ ferrite (γ þ α) region, also known as intercritical or warm deformation, [24][25][26][27][28] remains another strategic option to exploit. An average ferrite grain size of 1.3 μm in a C-Mn steel was achieved using large strain warm deformation processing. [28] A comprehensive review by Song et al. [29] examined the influence of both severe plastic deformation and advanced thermomechanical strategies on processing of ultrafine ferrite gr...

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“…After the 1 st cold rolling (cold rolling reduction; 50%), the pro-eutectoid ferrite and bainite components are elongated along the rolling direction, as shown in Figure 2 Figure 3 shows TEM bright-field images and energy dispersive spectroscopy maps (EDS) of precipitates present inside a ferrite grain after the 1 st subcritical anneal of the Nbmodified steel. The fine spherical particles were observed as shown in Figure 3, and they were identified to be Nb-Mo complex carbo-nitride particles, i.e., (Nb,Mo)(C,N), by TEM EDS maps of Nb, Mo, C, and N. It is expected that these (Nb,Mo)(C,N) precipitates were present prior to the 1 st subcritical anneal due to the larger size in relation to the usual (< 10 nm) precipitates formed during sub critical tempering or annealing [14].…”

Section: Simulationmentioning

confidence: 99%

Effects of Cold Work on Abnormal Grain Growth During Simulated Carburizing of 4121 Steel Containing Nb

Lee

Seo

Cryderman

et al. 2021

Heat Treating Conference

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Precision cold-forging processes are used to produce near-netshape parts that may then be carburized. During carburization thermal cycles, abnormal grain growth (AGG) after cold forging is known to develop microstructures which limit fatigue strength. In the present study, a small 0.04 wt.% Nb addition was made to a low-alloyed AISI 4121 steel containing 0.3 wt.% Mo. Subcritically annealed specimens were cold rolled (to simulate cold forging) at selected reduction ratios up to 50%, heated according to a simulated gas carburizing cycle at 930 °C, and water quenched to produce a final martensitic microstructure. The number density of abnormally grown grains increased rapidly as the cold rolling reduction ratio increased from 0 to 10%. With a further increase in reduction ratio, the extent of AGG decreased and was absent in samples subjected to the maximum reduction ratio of 50%. The evolution of fine (Nb, Mo)(C,N) precipitates at various stages of processing was characterized by thermodynamic calculations and electron microscopy and compared to the occurrence of abnormal austenite grain growth. The significance of these results for controlling AGG and thus optimizing fatigue performance in commercially-produced cold-forged and carburized components is discussed.

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Role of Precipitates in Recrystallization Mechanisms of Nb-Mo Microalloyed Steel

Cited by 14 publications

References 35 publications

Effect of Molybdenum on the Impact Toughness of Heat-Affected Zone in High-Strength Low-Alloy Steel

Effect of Molybdenum on the Impact Toughness of Heat-Affected Zone in High-Strength Low-Alloy Steel

Influence of Finish Rolling Temperature and Molybdenum Addition on Strengthening of Low Carbon Niobium Steels—A Computational and Experimental Study

Effects of Cold Work on Abnormal Grain Growth During Simulated Carburizing of 4121 Steel Containing Nb

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