Inspection of the Metal Microstructure in Laser-Surfaced Rollers
Tóm tắt
The microstructure and crystalline structure of laser-surfaced 9Kh2MF and 8Kh3SMFA steel samples are studied. Samples are taken from the working rollers of the reversible rolling mill at PAO Uralmashzavod. Sealing of surface cracks in the rollers by means of a laser is regarded as an effective repair method in small-scale production. The goal of the research is to monitor the quality of laser-surfaced steel components. The inspection focuses on metallurgical defects (nonmetallic inclusions, gaps, regions with nonuniform chemical composition) in the surfacing zone and the surrounding thermal influence zone. An ultrasound method is employed. Metallographic study of the microstructure and crystalline structure of laser-surfaced steel samples is necessary in order to develop an ultrasonic monitoring method. Metallurgical defects in steel are mainly found by means of a scanning electron microscope capable of X-ray spectral microanalysis (EDS analysis) and electron back-scattering diffraction (EBSD analysis). The present work employs a Carl Zeiss Auriga Crossbeam scanning electron microscope with EDS analysis of the surface’s elemental composition and EBSD analysis of the surface’s crystalline structure. The metallographic data for the laser-surfaced steel samples from the rollers reveal metallurgical defects along the boundary of the surfacing zone. The microheterogeneities measure 10–50 and 1–3 μm for 9Kh2MF and 8Kh3SMFA steel, respectively. The elements present include Mn, Si, and O for 9Kh2MF steel and Mn, Cr, and Mo for 8Kh3SMFA steel. The surface metal is found to be less textured than the basic metal and has more uniform acoustic characteristics. That must be taken into account in ultrasound monitoring of laser-surfaced steel components. In the ultrasound monitoring of laser-surfaced working rollers, signal recording with reflectivity equivalent to a flat-bottomed hole of 1.5-mm diameter is recommended.
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