Effect Of Si Content On Microstructure And High Temperature Friction Properties Of FeCrNiCSix Coating By Laser Ladding

Metallurgical equipment is essential to the metallurgical industry. Its working conditions are complex, often in high temperature (500℃), heavy load and other environmental service, high-temperature wear, high-temperature oxidation easily lead to equipment surface damage, and then affect the service safety and service life. Surface coating technology is an important means to protect metallurgical parts. At present, the surface protection technology of metallurgical parts includes spraying technology, arc melting technology, surfacing welding, laser cladding technology and so on. Laser cladding technology uses a high-energy laser beam to melt the powder and form a molten pool on the surface of the matrix at the same time. After rapid cooling, the coating is formed with metallurgical bonding with the matrix. The coating prepared by laser cladding technology has the advantages of metallurgical bonding, low dilute release rate, small heat-affected zone and dense structure, so the protective coating prepared by laser cladding technology has become an effective means of protection for metallurgical parts.

The coating material is the key to the protective effect of laser cladding coating on the surface of metallurgical parts. Among them, Fe-Cr-Si alloy coating can protect the substrate from high-temperature gases, oxides and corrosive media in high-temperature environment, has good oxidation resistance and corrosion resistance, and has high hardness and wear resistance, and is widely used in high temperature, high corrosion, high wear environment of service parts surface protection. The effect of Si content (0.6%-2.5%) on the microstructure and properties of Fe-Cr alloy wear-resisting steel It is found that the addition of Si helps to improve the distribution of the second phase of carbides. With the increase of Si content, the hardness of alloy steel increases, and the wear and corrosion resistance improves. When Si content reaches 2.3%, its toughness decreases.

In summary, Si elements can effectively improve the wear resistance, corrosion resistance and oxidation resistance of the coating. However, at present, the main research focuses on the alloy coating with low Si content (< 5 wt.%), and there are few studies on the alloy coating with high Si content (> 5 wt.%). Therefore, in this paper, FeCrNiCSix coating was prepared by laser cladding technology, and the effect of the change of Si content on the microstructure of FeCrNiCSix coating under high Si content (5 wt.%, 10 wt.%, 15 wt.%) was studied. The influence of hardness and high-temperature wear resistance provides a theoretical basis for the study of high Si alloy coatings, and provides some technical support for the surface protection of metallurgical parts.

The coating powder is made of chromium powder, silicon powder, nickel powder, carbon powder and iron powder with purity ≥99%, and the particle size of the powder is 53~ 150μm after screening. Mixed powders containing 5 wt.%, 10 wt.% and 15 wt.% Si elements were prepared using NX-100 high precision electronic balance. The composition of the mixed powder is shown in Table 1. After configuration, use a planetary ball mill to mix. The rotating speed was 200 r/min, the time was 4 h, and after mixing the powder, the vacuum drying oven was used to dry at 100 ℃ for 2 h. The coatings prepared by powder with different Si content were named 5Si, 10Si and 15Si coatings(Shown in Table 2). The matrix is made of 1Cr11Ni2W2MoV (1Cr11Ni) heat-resistant steel plate.

Tab.1 Composition of heat-resistant steel substrate(wt.%)

Tab.2 Composition ofFeCrNiCSix powder(wt.%)

The laser cladding equipment adopts TruDisk6006 fiber laser, the process parameters are 1600W laser power, 50% bonding rate, spot diameter of 5 mm, scanning speed of 600 mm/min, and powder feeding speed of 5 r/min. After the coating cladding is completed, the sample is cut into a cuboid with a side length of 10 mm with DK7750 wire-cutting equipment. The coating is polished and polished with sandpaper. The corrosion was about 10s in the corrosion solution containing 0.7 wt.% HF, 43 wt.% HNO3, 50 wt.% H2O. The microstructure of the coating was observed by LeicaDM6000M metallographic microscope and FEI-Sirion 200 field emission scanning electron microscope, and the chemical composition of each phase was analyzed by energy dispersive spectrometer (EDS) of the scanning electron microscope. XRD phase analysis was carried out with Miniflex600 X-ray diffractometer. The MC010-HVS-1000 Vickers microhardness tester measures the hardness of the coating cross-section, measuring 10 points, each point 1.5 mm apart, taking the average. The experimental equipment for high-temperature wear performance is MRH-1 wear testing machine. The working diagram of friction and wear is shown in Figure 1. The wear quality loss is measured by DJ1002A high-precision electronic balance. The wear test pattern was cut into cuboid blocks with length, width and height of 20 mm, 10 mm and 10 mm respectively, and polished and polished with sandpaper (600-2000 mesh). After detection by 3D topography profilometer, The average surface roughness of the wear test samples of the three coatings with different Si content is 0.91 μm, and the specific high-temperature wear test parameters are shown in Table 3.

Tab.3 Parameters of high temperature wear test

(1) In the 5Si, 10Si and 15Si coatings prepared by laser cladding, the microstructure of 5Si coatings is mainly dendritic and equiaaxial structure, and the phase composition is mainly composed of γ-Fe and Fe-Cr solid solutions. The microstructure of 10Si and 15Si coatings is mainly equiaxed, and the phase composition is mainly composed of Fe3Si and Fe-Cr solid solution.

(2) With the increase of Si element content, the hardness and wear rate of the coating increase in turn, which is because the Fe3Si phase has a certain brittleness while having a high hardness, and serious spalling occurs during the wear process, and the coating wear rate increases accordingly.

(3) The 5Si coating is mainly characterized by adhesive wear and oxidative wear, and its wear resistance at high temperature is the best, but its oxidation resistance is poor and its hardness is low. 10Si and 15Si coatings are mainly abrasive wear, and the wear rate increases successively. Compared with the three, 10Si coating is judged to be the best Si content coating.

Xi'an Guosheng Laser Technology Co., Ltd. is a high-tech enterprise specializing in R&D, manufacturing and sales of automatic laser cladding machine, high-speed laser cladding machine, laser quenching machine, laser welding machine and laser 3D printing equipment. Our products are cost-effective and sold domestically and abroad. If you're interested in our products, please contact us at bob@gshenglaser.com.