Jiang M.,University of Science and Technology Beijing |
Chen B.,Shougang Institute of Technology
ISIJ International | Year: 2010
Laboratory study was carried out to discuss evolution mechanisms of non-metallic inclusions in high strength alloyed steel refined by high basicity slag, aiming at formation of lower melting temperature inclusions to improve anti-fatigue properties of steel. It is found that steel/slag reaction time had great effect on inclusion types, compositions and shapes. With reaction time extended from 30 to 180 min, solid MgO-Al2O3 and MgO-based inclusions were finally changed into CaO-MgO-Al2O3 system inclusions lower melting temperature (<1 773 K). While shapes of inclusions varied in the route blocky/angular → near spherical → spherical. Al2O3/MgO·Al2O3/MgO and MgO/MgO · Al2O3/CaO · 2Al2O 3 stability diagram were obtained by thermodynamic calculation. The results indicated that MgO and MgO·Al2O3 inclusion would be formed at early stage of steel-slag reaction because activity of Mg is much larger than that of Ca in steel. However, with increase of Ca activity, solid MgO Al2O3 and MgO inclusions would be inevitably and gradually transferred into complex liquid inclusions even dissolved [Ca] is as low as 0.0002%. Thus, SEM-EDS mappings of CaO-MgOAl2O3 system inclusions are characterized by high melting temperature solid MgO · Al2O3 or MgO-based inclusion cores surrounded by lower melting temperature CaO-Al2O3 outer surface layers, which would be softer during hot rolling and therefore be helpful to improve anti-fatigue properties of steel. Model was established to elucidate change mechanisms of inclusions. Transferring kinetics of inclusions was discussed qualitatively to analyze velocity controlled steps. It is found that diffusion of Mg and Ca in solid inclusion core and the formed CaO-Al2O 3 outer surface layer would be probably the limited step during evolution of inclusions. However, further work should be done to discuss evolution kinetics of inclusions quantitatively.
Liang X.,Shougang Institute of Technology
Yejin Fenxi/Metallurgical Analysis | Year: 2015
The following analytical conditions were obtained by experiments: the excitation voltage was 1150 V, the excitation current was 45 mA, the pre-combustion time was 180 s and the integral time was 10 s. Moreover, the photomultiplier voltage of elements was adjusted, realizing the optimal output relationship between elemental content and excitation intensity. The simultaneous determination method of twelve elements in cast iron (including carbon, silicon, manganese, phosphorus, sulfur, nickel, chromium, molybdenum, copper, titanium, vanadium and boron) by direct current glow discharge optical emission spectrometry was established. The matrix iron element was used as internal standard. Six standard samples of alloyed white cast iron for spectral analysis were used to prepare calibration curves based on the relative content and intensity of analytical element to matrix. The correlation coefficients for all elements were higher than 0.9940. The precision test results indicated that the relative standard deviations (RSD) were between 0.24% and 2.5%. The certified reference materials of grey cast iron were determined according to the proposed method, and the found results were consistent with the certified values. The analysis of white cast iron samples was compared with the spark source atomic emission spectrometry, and the results were consistent. ©, 2015, Central Iron and Steel Research Institute. All right reserved.
Chu R.-S.,Shougang Institute of Technology
Kang T'ieh/Iron and Steel | Year: 2015
The size, area, composition, type and distribution of non-metallic inclusions with high-melting point (CA2 and CA6, which C:CaO, A:Al2O3) in inspection substandard samples were analyzed by aspex explorer automated scanning electron microscope. To analyze the reason that why the center is the concentrated area of the large-size inclusions, three aspects for the causes of calcium aluminate with high-melting point causing the aggregation behavior for flaw substandard is focused on: features of non-metallic inclusions, the characteristics of continuous casting machine and the behavior of nonmetallic inclusions during the process of solidification. The results show that calcium aluminate with high-melting point gathered together, and is easy to aggregate. The casting speed is slow for the curved continuous casting machine compared with the average arc caster. The thickness of slab is thin and the molten steel solidifies rapidly, which makes the solidification end generate early, and form an easy gathering area near the center during the steel solidification. The inclusions are pushed and engulfed in the shell and will aggregate. While the space and time of floatation is reduced, combined with the effect of promoting the capture, the center forms a concentrated area of the large-size inclusions. ©, 2015, Chinese Society for Metals. All right reserved.
Xu Y.-L.,Shougang Institute of Technology
Yejin Fenxi/Metallurgical Analysis | Year: 2015
When tinplate sample was ablated layer by layer by glow discharge spectrometry(GDS), formula integral was set according to glow discharge integral spectrum from sample surface to its center for the purpose of calculating the thickness and mass of tinplate coating and passivation layer, substrate component, harmful elements in the coating, etc. The depth-time diagram was curved by GDS, and it showed that the depth resolution of tin coating was lower than that of substrate iron layer. The method has been applied to determine the mass of tinplate coating and passivation layer, substrate component(carbon, silicon, manganese, phosphorus, sulfur, nickel, chromium and copper), and the relative standard deviation was not higher than 2.3%(n=10), 3.0%(n=10) and 4.3%(n=5). The results were consist with those obtained by X-ray fluorescence spectrometry(XRF), spectrophotometry and inductively coupled plasma atomic emission spectrometry(ICP-AES). The harmful elements in the tinplate coating were determined by this method. The method could realize the simultaneous determination of multi testing items in tin plate. ©, 2015, Central Iron and Steel Research Institute. All right reserved.
Chu R.,Shougang Institute of Technology
Proceedings of the 6th International Congress on the Science and Technology of Steelmaking, ICS 2015 | Year: 2015
In the current paper, size, area, composition, type and distribution of non-metallic inclusions with high-melting point (CaO2Al2O3 and CaO E6Al2O3) in inspection substandard samples were analyzed by aspex explorer automated scanning electron microscope. The distribution of inclusions in the thickness direction of slab produced in Pretreatment of hot metal → LD → LF → Calcium treatment → RH → CC process was stuied, indicating that the number of inclusions inner arc is the maximum, and the inclusions at the center is minimum. Whereas, the number of less than 10 Êm inclusions is the maximum in loose side, and that of larger than 10 Êm inclusions is the maximum in the center. The causes of the aggregation behavior of calcium aluminate in highmelting point were investigated in the nature of non-metallic inclusions, the characteristics of continuous casting machine and behavior of nonmetallic inclusions during solidification. The results show that calcium aluminates with high-melting point are easier to gathered and aggregate. When the Al2O3 content of calcium aluminate inclusions is 80%, the aggregation ability is the strongest. The casting speed of the curved continuous casting machine is slower compared with the average arc caster. The smaller thickness of slab and rapid solidification lead to the earlier solidification end, and formation of an easy gathering area near the center during the solidification. The inclusions are pushed, engulfed and aggregated in the solidification. Since floating in space and time reduced, and promoting of the capture, there is a concentrated area of the large-size inclusions formed in the center of slab.