Assessment of the effect of the steels structure dispersion on its magnetic and mechanical properties

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 4 2021 Research methodology Samples of 09G2S , St3 , 15KhSND steels with a size of 4.0 x 70.0 x 25.0 mm were laser-cut from the sheets along the direction of its rolling. The chemical composition was determined by the X-MET 7000 analyzer. Table 1 shows the average values obtained during 10 measurements. The heat treatment strongly affects the structural and phase composition of steel. The inhomogenei- ties in the mechanical and magnetic properties of rolled steel, from which samples are made, usually do not exceed 15 % [17]. It is necessary to conduct heat treatment of experimental samples to create distinct variations of the structure and the grain composition. Therefore, before the study conducting, the samples were quenched and then tempered at different temperatures (Table 2). This is done to create variations of the structural-phase state. Ta b l e 1 Chemical composition of the studied steels Steel grade Element content, wt. % С Si P* S* Cr Mn Ni Cu 09G2S 0.11 0.15 0.05 <0.028 0.07 1.91 0.11 0.22 St3 0.16 0.15 0.05 <0.02 0.03 0.45 0.03 0.04 15KhSND 0.16 0.71 0.06 <0.02 0.84 0.79 0.34 0.20 * He indicators of the content of carbon, sulfur and phosphorus are given according to the information speci fi ed in the quality certi fi cates on the steel from which the samples are made. Ta b l e 2 Heat treatment of the test samples Steel grade Heat treatment 09G2S Heating up to 930 ± 20 o С quenching in water. Tempering at 200, 350, 500, 650 o С for 1 hour, air cooling St3 Heating up to 930 ± 20 o С quenching in water. Tempering at 200, 350, 500, 650 o С for 1 hour, air cooling 15KhSND Heating up to 930 ± 20 o С quenching in water. Tempering at 200, 300, 350, 400, 500, 550, 650 o С for 1 hour, air cooling The microstructure of the samples being investigated was studied by the JEOL 6008A scanning electron microscope using a 3% solution of nitric acid as an etchant. The value of the uneven-grained factor is determined by the formulas presented in [18, 19]. The distri- bution of grain severities observed on the micrograph is used. The microphotographs were processed (Figure 1) in the “SIAMS 700” metallographic research software package (Figure 2) to calculate the uneven-grained factor. As an example, Figure 3 shows the distribution of the grain severity of the 15KhSND steel sample. The distributions of the remaining samples have a similar character. The grain severity is determined in accordance with GOST 5639-82 [21]. The calculation of the uneven- grained factor F z is performed by the formula: max max , z i i f Z F f Z = å (1)