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Effect of Vanadium on Austenite Grain
Refinement and Martensite Structure
T.Jing,Y.T.Ning,H.L.Liu
(B), B. Yang, and Y. Chen
R&D Institute of Benxi Steel Plates Co., Ltd., Benxi 117000, Liaoning, China
daliang_lhl@hotmail.com
Abstract. The original austenite and quenched martensite structures of press
hot steel with vanadium have been investigated by means of optical microscope
and scanning electron microscope. The results show that V exists in the form of
dispersed nanoscale VC or (V, Ti) C complex carbide in austenite, which has a
significant effect on the refinement of the original austenite grain size. When the
heating temperature is higher than 900 °C, the V(C, N) decomposition results
in the rapid decrease of austenite grain refinement, however, the austenite grains
are still refined due to the drag effect of Ti(C, N) on V(C, N). The combination
of vanadium and carbon in austenite can reduce the content of C in quenched
martensite, which could promote the formation of strip martensite and avoid the
formation of twinned martensite, so as to improve the toughness of materials and
improve the problem of hydrogen-induced cracking.
Keywords: Grain size ·Vanadium carbonitride ·Microstructure
1 Introduction
With the rapid growth of automobile exhaust emissions and the use of passenger cars,
collision safety standards are strict year by year, and it is imperative to improve the
strength and stiffness of the car body and optimize the structure. In view of this demand,
more and more high strength steel and ultra-high strength steel are applied to automobile
components [1]. High strength steel has good strength and hardness, but poor plasticity
and toughness. In order to improve the overall performance, refining the size of proto-
austenite grain is one of the most effective methods [2,3]. V is one of the rich elements
in China. With high solubility in steel, V is one of the most commonly used and effective
strengthening elements in micro alloyed steel [4]. Adding a certain amount of V to steel
can precipitate carbides of V in austenite, refine the grain size of austenite, and play
a great role in improving the strength and toughness of finished products [5]. In this
paper, by comparing with V and not add V two kinds of test steel original austenitic
organization, and by using electron microscope (TEM), and transmission electricity to
its microstructure and precipitation particle morphology observation, the precipitation
of VC or (V, Ti) C content to the original austenite grain size refinement effect and its
influence to the martensite after quenching organization [6,7].
© The Author(s) 2023
Y. Zhang and M. Ma (Eds.): ICHSU 2022, AHMST 2, pp. 36–41, 2023.
https://doi.org/10.2991/978-94-6463-114-2_5
Effect of Vanadium 37
Table 1. The chemical composition of 22MnB5 hot stamping steel.
Sample CSi Mn V
No. 1 0.25–0.35 0.2–0.4 1.0–1.5 0
No. 2 0.25–0.35 0.2–0.4 1.0–1.5 0.1–0.3
2 Materials and Procedures
Two kinds of high-strength steel plates were designed in the experiment. The specific
composition is shown in Table 1.
The samples were heated to 850 °C and 900 °C, respectively, held for 5min, and
quenched. Take after quenching specimen made of metallographic specimen after grind-
ing and polishing. The morphology of primitive austenite was observed by optical
microscope. Will add V steel specimen using the line cut into 600 µm, punching after
sand paper finely ground to 45 µm, electrolytic double injection preparation into TEM
specimen, the precipitation phases and martensitic matrix form.
3 Results and Analysis
The optical micrograph of the original austenite morphology of samples No. 1 and No.
2areshowninFig.1and Fig. 2. The original austenite grain size under different heating
temperatures was determined by using the straight-line cut-off method and Image-Pro
software. The specific size is shown in Table 2. It can be seen that under different heating
temperature, the original austenitic grain size of added V steel is smaller than the one
without V.
The precipitation of the v-added steel after hot rolling was analyzed from the micro-
scopic point of view by transmission electron microscopy. The image of transmission
electron microscopy is shown in Fig. 3(a). It can be seen that there are nano V and Ti
carbides in the steel plate, and the precipitate size is 20–50 nm. The specific morphol-
ogy was shown in Fig. 3(b). Scattered small nano-scale precipitates can not only refine
austenite grain, improve the product strength and toughness, and precipitation of VC or
(V, Ti) C consumes carbon in austenite, reduce the carbon content of martensite after
quenching, the phase change after plate strip produced by the dislocation martensite for-
mation, avoid twin martensite formation, improve the identity of the hydrogen induced
cracking problem, The morphology of martensite after quenching is shown in Fig. 3(c).
38 T. Jing et al.
Fig. 1. Morphology of the original austenite at 850 °C.
Fig. 2. Morphology of the original austenite at 900 °C.
Table 2. The original austenite grain size at different heating temperatures.
Sample 850 °C 900 °C
No. 1 5.9 7.5
No. 2 3.4 5.9
The percent of grain refinement 42 21
Effect of Vanadium 39
Fig. 3. TEM images of sample.
4 Discussion
Theoretically, the strength of quenched martensite increases with the increase of carbon
content, but the increase of carbon content will lead to the formation of twin martensite,
reducing the toughness of the material. Meanwhile, twin martensite has a ridge, which
is easy to enrich hydrogen on this ridge, causing hydrogen cracking of the material.
Thermo-calc software was used to calculate the amount of VC precipitation in the test
steel with V changing with temperature. According to theoretical analysis, almost all the
martensite after quenching is martensite, and the proportion of twin martensite is very
small. In order to prove this conclusion, transmission electron microscopy was used to
observe the microstructure of martensite obtained by quenching V test steel, and the
results are consistent with theoretical calculation.
5 Conclusion
(1) V exists in the form of VC or (V, Ti) C complex carbides in austenite. The size of V
is small and nanoscale, and the distribution of V is dispersed, which has an obvious
effect on the refinement of the original austenite grain size.
40 T. Jing et al.
(2) When the heating temperature is higher than 900 °C, the effect of V(C, N) on the
refinement of austenite grain decreases rapidly due to the increasing amount of
V(C, N) resolution, and the effect of Ti on the refinement of austenite grain is still
certain due to the drag effect of V resolution.
(3) V can consume C in austenite, reduce the content of C in quenched martensite,
promote the formation of strip martensite, avoid the formation of twin martensite,
improve the toughness of materials, improve the problem of hydrogen-induced
cracking.
Acknowledgments. The work is supported by National Natural Science Foundation of China
(No. U1908224), National Natural Science Foundation of China (No. U1708252), and Liao Ning
Revitalization Talents Program (No. XLYC2007066). The Project is also sponsored by “Liaoning
BaiQianWan Talents Program”.
References
1. S. Liu, M. Long, S. Y. Zhang, Y. Zhao, J. Zhao, Y. Feng, D. F. Chen and M. T. Ma, Study
on the prediction of tensile strength and phase transition for ultra-high strength hot stamping
steel, Journal of Materials Research and Technology 9, 14244 (2020).
2. Z. X. Gui, W. K. Liang and Y. S. Zhang, Enhancing ductility of the Al-Si coating on hot
stamping steel by controlling the Fe-Al phase transformation during austenitization, Science
China 57, 1785 (2014).
3. W. K. Liang, W. J. Tao, B. Zhu and Y. S. Zhang. Influence of heating parameters on properties
of the Al-Si coating applied to hot stamping, Science China 60, 1088 (2017).
4. Y. F. Li, Y. Chen and S. H. Li, Phase transformation testing and modeling for hot stamping
of boron steel considering the effect of the prior austenite deformation, Materials Science &
Engineering A 821, 141447 (2021).
5. N. Li, J. Lin, D.S. Balint and T.A. Dean, Modelling of austenite formation during heating
in boron steel hot stamping processes, Journal of Materials Processing Technology 237, 394
(2016).
6. N. Li, J. Lin, D.S. Balint and T.A. Dean, Experimental characterisation of the effects of ther-
mal conditions on austenite formation for hot stamping of boron steel, Journal of Materials
Processing Technology 231, 254 (2015).
7. C. N. Jing, D. M. Ye, J. R. Zhao, T. Lin, C. Wu and Q. T. Lei, Effect of hot stamping and
quenching & partitioning process on microstructure and mechanical properties of ultra-high
strength steel, Materials Research Express 8, 036506 (2021).
Effect of Vanadium 41
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