Strain-induced precipitation kinetics of Nb(C,N) and precipitates evolution in austenite of Nb–Ti micro-alloyed steels

Chen, Jun; Tang, Shuai; Liu, Zhenyu; Wang, Guodong; Zhou, Yuke

doi:10.1007/s10853-012-6330-5

Cited by 19 publications

(8 citation statements)

References 16 publications

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“…The researchers tracked and monitored the nucleation and growth of precipitate by some approaches like direct observation method, hardness method, resistance method, stress relaxation method, etc. Precipitate–temperature–time (PTT) curve for part of microalloy carbonitride was established accordingly, and strain inducing precipitation behaviors in austenite were scientifically studied 10–12…”

Section: Introductionmentioning

confidence: 99%

Study on Isothermal Precipitation Behavior of Nano‐Scale (Nb,Ti)C in Ferrite/Bainite in 780 MPa Grade Ultra‐High Strength Steel

Wang

Zhao

Liang

et al. 2012

steel research int.

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In order to precisely control the nano-scale (Nb,Ti)C precipitate in hot-rolled 780 MPa Nb-Ti microalloying C-Mn steel, isothermal precipitation behavior of nano-scale (Nb,Ti)C precipitate in the ultra-high strength steel was investigated by the thermal simulation experiments. The results indicated that defects of deformed supercooled austenite became the preferential nucleation sites of nano-scale (Nb,Ti)C precipitate and ferrite, so there was a competition mechanism for austenitic defects between ferritic transformation and precipitate nucleation. Bainitic transformation could effectively freeze austenitic defects, and additional defects are formed because of volume expansion in bainitic transformation process, so bainitic transformation could promote precipitate nucleation. However, precipitate was impacted by both nucleation driving force and atom diffusibility, so the peak temperature of nano-scale (Nb,Ti)C precipitate was 5508C. On the basis of the above theoretical results, hot rolling experiments results showed that when the coiling temperature was 5508C, the yield strength and tensile strength were 710 and 790 MPa, respectively, and the microstructure of hot-rolled steels was mainly bainitic ferrite, and a large number of <10 nm nano-scale (Nb,Ti)C precipitates were obtained. Precipitation strengthening contribution to reached 325 MPa.

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Section: Introductionmentioning

confidence: 99%

Study on Isothermal Precipitation Behavior of Nano‐Scale (Nb,Ti)C in Ferrite/Bainite in 780 MPa Grade Ultra‐High Strength Steel

Wang

Zhao

Liang

et al. 2012

steel research int.

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“…Vanadium is less effective in grain refinement but contributes to strength via precipitation hardening because of higher solubility in austenite as compared to niobium, leading to precipitation at lower temperature. [6] TMCP involving ultrafast cooling (UFC) technology developed by our laboratory is being currently applied to industrial production, [7][8][9] with the aim to reduce the consumption of alloying elements and make the steel making process economically viable, [10][11][12] which can greatly suppress the degree of precipitation in austenite and increase supersaturation in ferrite or bainite, [13] and the precipitation hardening can be enhanced. Thus, it is of practical significance to understand the effect of cooling parameters on the microstructural evolution, precipitation behavior, and mechanical properties in microalloyed steels, such as cooling rate and finish cooling temperature in UFC.…”

mentioning

confidence: 99%

The Determining Role of Finish Cooling Temperature on the Microstructural Evolution and Precipitation Behavior in an Nb-V-Ti Microalloyed Steel in the Context of Newly Developed Ultrafast Cooling

Wang

Deng

et al. 2016

Metall Mater Trans A

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We have studied here the impact of finish cooling temperature on the microstructural evolution and precipitation behavior in Nb-V-Ti microalloyed steel through thermo-mechanical simulation in the context of newly developed ultrafast cooling system. The microstructural evolution was studied in terms of morphology and crystallography of precipitates using high-resolution transmission electron microscopy. At finish cooling temperature of 933 K and 893 K (660°C and 620°C), the microstructure primarily consisted of polygonal ferrite, together with a small amount of wedge-shaped acicular ferrite and lamellar pearlite, while, at 853 K and 813 K (580°C and 540°C), the microstructure consisted of lath bainite with fine interlath cementite and granular bainite with martensite/ austenite (M/A) constituent. In all the finish cooling temperatures studied, the near-spherical precipitates of size range~2 to 15 nm were randomly dispersed in ferrite and bainite matrix. The carbide precipitates were identified as (Nb,V)C with NaCl-type crystal structure. With a decrease in the finish cooling temperature, the size of the precipitates was decreased, while the number density first increased with a peak at 893 K (620°C) and then decreased. Using Ashby-Orowan model, the contribution of the precipitation strengthening to yield strength was~149 MPa at the finish cooling temperature of 893 K (620°C).In the last few decades, high-strength low-alloy (HSLA) steels have been widely used in buildings, bridges, and ships because of their potential to obtain high strength-toughness combination. [1] Superior mechanical properties were obtained through optimization of alloy design in conjunction with thermo-mechanical processing (TMCP). [2][3][4][5] The improvement in mechanical properties was a consequence of grain refinement together with microstructural control and precipitation strengthening. The carbide-forming elements include titanium and niobium that facilitate grain refinement and contribute to dispersion hardening through carbide precipitation in the matrix. The relative contribution of the microalloying elements is determined by the solubility of carbides in the microstructure. Titanium is beneficial because it combines with nitrogen at relatively high temperature, preventing grain growth, while niobium can effectively retard recovery and recrystallization during hot rolling leading to grain refinement. Moreover, these two elements can precipitate as carbides from the supersaturated ferrite solid solution or precipitate as interphase precipitates during austenite-to-ferrite transformation increasing strength. Vanadium is less effective in grain refinement but contributes to strength via precipitation hardening because of higher solubility in austenite as compared to niobium, leading to precipitation at lower temperature. [6] TMCP involving ultrafast cooling (UFC) technology developed by our laboratory is being currently applied to industrial production, [7][8][9] with the aim to reduce the consumption of alloying elements and make the s...

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“…In fact, the progress of transformation for the lowest cooling rate of 0.5°C/s is markedly retarded. Although the stored energy of deformation for lower deformation temperature is further higher than that for higher one, on the basis of Chen et al's report, 20) the temperature range of strain-induced precipitation of Nb(C,N) for lower deformation temperature is much lower than that for higher one during continuous cooling. For lower deformation temperature, on the one hand, the driving force for precipitation of Nb(C,N) is higher due to higher supersaturation ratio, on the other hand, the density of precipitates nucleation sites is also higher due to higher dislocation density, resulting in the formation of a great number of fine precipitates, which can effectively pin γ /α interfaces due to higher pining force, so the transformation kinetics is lowered.…”

Section: Transformation Behaviormentioning

confidence: 96%

Influence of Deformation Temperature on γ-α Phase Transformation in Nb–Ti Microalloyed Steel during Continuous Cooling

Chen¹,

Li²,

Liu³

et al. 2013

ISIJ Int.

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The dynamic continuous-cooling-transformation (CCT) diagrams of Nb-Ti microalloyed steel for four different deformation temperatures of 850, 900, 950 and 975°C were plotted by means of a combined method of dilatometry and metallography. The influence of deformation temperature on continuous cooling transformation behavior and transformation microstructure was elucidated. The reason that the polygonal ferrite transformation field is shifted to the right and moved down as the deformation temperature is increased and the progress of transformation for lowest continuous cooling rate of 0.5°C/s was obviously retarded at the lowest deformation temperature of 850°C was discussed in details based on transformation kinetics and strain-induced precipitation kinetics, respectively. Moreover, the polygonal ferrite grain size for lowest continuous cooling rate of 0.5°C/s can be significantly refined from approx. 15.4 μm to 9.4 μm as the deformation temperature is reduced from 975°C to 850°C. In addition, the empirical equation to calculate γ-α phase transformation start temperature was established, and the calculated Ar3 temperatures are in good agreement with measured ones.

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Strain-induced precipitation kinetics of Nb(C,N) and precipitates evolution in austenite of Nb–Ti micro-alloyed steels

Cited by 19 publications

References 16 publications

Study on Isothermal Precipitation Behavior of Nano‐Scale (Nb,Ti)C in Ferrite/Bainite in 780 MPa Grade Ultra‐High Strength Steel

Study on Isothermal Precipitation Behavior of Nano‐Scale (Nb,Ti)C in Ferrite/Bainite in 780 MPa Grade Ultra‐High Strength Steel

The Determining Role of Finish Cooling Temperature on the Microstructural Evolution and Precipitation Behavior in an Nb-V-Ti Microalloyed Steel in the Context of Newly Developed Ultrafast Cooling

Influence of Deformation Temperature on γ-α Phase Transformation in Nb–Ti Microalloyed Steel during Continuous Cooling

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