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Study on the role of vanadium in high toughness wear-resistant steel.

Author: LiXiaoXian
Tutor: YuLan
School: Kunming University of Science and Technology
Course: Materials Science
Keywords: Vanadium hardenability mechanical properties mechanisms ofstrengthening and toughening wear-resistant steel
CLC: TG142.72
Type: Master's thesis
Year: 2013
Downloads: 86
Quote: 0
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Abstract


In the development of high-strength low alloy steel, Vanadium is usually added in steels to improve strength and toughness of the steel through refining grains and the second phase precipitation hardening as well as the technology of controlled rolling and cooling process. The fundamental reason of performance instability of wear-resistant steel is its strength and toughness is insufficient, In this thesis, we adjust Vanadium content to study the effect of Vanadium to hardenability and strength and toughness of wear-resistant steel.The Jominy end quench test was carried out, to research the effect of V and austenitizing temperature on the hardenability of steel. Based on the relationship of hardenability and hardness and other researchers’empirical formula, the influence coefficient of solid solution Vanadium on the hardenability was investigated. In addition, the effect of Vanadium on CCT curve were determined on Formastor-F Ⅱ automatic transformation measuring apparatus. It further verify the influence of Vanadium on the hardenability of steel. The effect of Vanadium content on the microstructure and mechanical properties of direct quenching steel was disscussed. What’s more, we investigated the influence of reheating temperature on the microstructure and mechanical properties of the steels without V and containing0.30%V, and explored the strength mechanism of steel.The results showed that in the Jominy test, when austenitizing temperature is880℃, with the increase of V content in steel, the critical diameter of the steel is increased, and then its hardenability is improved. Meanwhile, vanadium addition leads to CCT curve shifts to the right, decreases the cooling velocity of austenitic transformation of martensitie, expand the cooling speed range of martensitic transformation。Consistent with the experimental results of Jominy end quench test, hardenability of steel is improved. The results of different austenitizing temperature for the steel containing0.30%V in the Jominy test indicated that, its hardenability was gained at austenitizing temperature before960℃. The hardenability of steel gradually dcreased as the rising of the temperature over960℃. Combining with the experience formula, the multiplying for vanadium is increased with the increase of the concentration of V in solution, and the relationship can be expressed as: fv(%V)=0.96964+3.226[V]+12.4917[V]2.Through the direct quenching process, with the increase of V content in steel is up to0.30%, the average thickness of pancaked prior-austenite is reduced to about6.99μm, which resulted in a good combination of strength and toughness. The yield strength is up to1301MPa and tensile strength is1746MPa, and-40℃impact energy is40J, elongation and area reduction remaining basically unchanged. In experimental steel, V mainly exist in solid solution state, when the V content was more than0.30%in steel, VC particles precipitated. Along with the change of vanadium content in steel, the microstructure morphology is characterized using electron backscattered diffraction (EBSD) technique and transmission electron microscopy (TEM). In addition, the strengthening mechanisms were preliminarily analyzed.During the process of reheating+low-temperature tempering, the prior-austenite grain size of steel without V and steel containing0.30%V is increased. When reheating temperature rises from880℃to920℃, the prior-austenite grain size of steel without V and steel containing0.30%V grow from12.12μm4.06μm to17.56μm、10.76μm respectively. Compared with steel without V, the effect of vanadium grain refinement is obvious. The mechanical properties of steel without V and steel containing0.30%V is decreased with reheating temperature increasing. The yield strength is1238MPa and-40℃impact energy is57.3J at880℃of steel containing0.30%V. The strengthening and toughening analysis of steel containing0.30%V showed that grain refinement is the main reason to strength enhancement and the effective size controlling strength is the bloke width.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallic materials > Steel > Special performance of steels > Wear-resistant steel
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