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The influence of niobium and molybdenum on the structure and properties of low-alloy wear-resistant steel

Time: 2021-04-03 Views: 3

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Aiming at the actual working conditions of the low-alloy wear-resistant steel liner, on the basis of reasonable chemical composition design, the influence of the alloying elements niobium, molybdenum and heat treatment process on the structure and performance of the low-alloy wear-resistant steel is studied to obtain the hardness and The good match of impact toughness meets the use requirements of the liner.
Using DTA differential thermal analysis and metallographic microscope, X-ray diffractometer, scanning electron microscope, Rockwell hardness tester, impact testing machine, abrasion testing machine and other experimental equipment, through the microstructure and impact fracture morphology of steel Observation, Rockwell hardness, impact toughness, hardenability and wear resistance and other properties of the test, the systematic in-depth study of the effects of different contents of niobium and molybdenum and heat treatment process on the microstructure and mechanical properties of multi-element low-alloy wear-resistant steel.
The experimental results show that with the addition of niobium, most of the niobium exists in the form of carbide (NbTi) C in the as-cast state, which can refine the grains; after heat treatment, the niobium in the sample is partially dissolved into austenite In, it can inhibit the growth of crystal grains and improve the hardenability of steel. At the same time, as the niobium content increases, the hardness and impact toughness continue to increase, and the niobium content is 0. At 0.6%, 900 has passed. After C quenching and tempering at 250℃, the hardness reaches 54.5HRC, and the impact toughness reaches 28.5J/cm2. The niobium content is O. When the thickness of 0.6% of the sample is 120mm, it can be quenched completely at 900℃ and has good hardenability. The wear resistance of the samples increased significantly with the increase of niobium content. The wear resistance of the samples with a niobium content of 0.06% after heat treatment increased by 32.67% compared with that without niobium.

After the addition of molybdenum, the grains are refined and the mechanical properties are also significantly improved. Part of the molybdenum is dissolved in austenite, and part of it exists in the form of carbide (CrMo Fe) 7C3. The hardness of the sample in the as-cast state increased from 38.5HRC to 42.6HRC with the increase of the molybdenum content. After the sample was quenched at 900℃ and tempered at 250℃, the sample with a molybdenum content of 0.8% had a higher content of molybdenum. For 0.4% of the sample, 3.3 HRC was added, showing a significant strengthening effect. With the increase of the molybdenum content, the sample exhibits good hardenability and hardenability, and has a higher resistance to temper embrittlement.
The heat treatment research shows that the test material is passing through 900. The structure after C quenching and tempering at 250°C is tempered martensite + a small amount of retained austenite + a very small amount of carbides, and high strength and toughness are obtained. After heat treatment, the fracture of the impact specimen was fibrous fracture with a large number of dimples, which has the characteristics of ductile fracture.
According to the research results of this subject, the liner is trial-produced, the size is about 320×200×120mm, the chemical composition is C0.40"-0.45%, Si 1.0~1.5%, Mn 0.8~1.2 %, Cr 1.8-2.2%, Mo 0.45-0.65%, abstract Nb 0.05"-'0.07%, and the heat treatment process is the quenching temperature 900. C, the holding time is 3h, the quenching medium is No. 10 engine oil, and the tempering temperature is 250. C, the holding time is 6h. The structure is tempered martensite + a small amount of retained austenite. The hardness value obtained by sampling on the liner body is 52"-'56HRC, and the impact toughness is 35"-'45J/cm2.

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