Steelmaking

Review on the control of the acicular ferrite in high strength low alloy steels

2022, 38(2): 1-10.

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The formation of volumes of acicular ferrite in high strength low alloy steels is a principal mean to meet high strength and toughness. Several decisive factors affecting the volume fraction of acicular ferrite were reflected in different literatures, and the nucleation mechanism of acicular ferrite and inclusions characteristics conducive to nucleation were summarized by some review, but there was no systematic summary of the effect of variation on apiece factor. In this study, the influence of austenite grain size, cooling rate, inclusion composition, and inclusion size on the volume fraction of acicular ferrite has been summarized. It is concluded that austenite grain size of 100-200 μm, cooling rate of 5-10 ℃/s, inclusion size of 1-2 μm and composition of (Ti、Mg、Zr)O_x are beneficial to promote acicular ferrite nucleation.

Research progress on desulfurization reaction dynamics of hot metal by KR mechanical stirring

2022, 38(2): 11-19.

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KR hot metal desulphurization (also known as mechanical stirring method) has the advantages of high desulfurization efficiency,stable desulfurization effect and low desulfurization cost due to its better reaction conditions. It is widely used in major domestic and foreign steel companies and has gradually become the preferred process for hot metal desulfurization pretreatment. The research results in recent years on improving the dynamic conditions of the KR mechanically stirred hot metal desulfurization were summarized. By understanding the development of the desulfurization reaction at home and abroad，it provides references for the improvement or optimization of KR dynamic conditions.

Application of nickel-containing pig iron in converter smelting of nickel-containing steel

2022, 38(2): 20-24.

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Combined with the practice of a domestic steel plant, the thermodynamic analysis and kinetic research for the application of nickel-containing pig iron in the converter smelting of nickel-containing steels were carried out. Thermodynamic calculations show that, whether in standard state or actual condition of converter smelting, the nickel element dissolved into the molten iron or molten steel through the alloying of the nickel-containing pig iron cannot be oxidized to nickel oxide. The melting rate test of nickel-containing iron block in converter smelting of X80-1 steel showed that the melting rate of nickel-containing iron block with 25 mm thickness was 30 s faster than that of scrap steel. The composition test results of converter semi-steel showed that the nickel-containing iron block could be completely melted after being added into the converter in 5 min. At the same time, through the scanning electron microscopy and X-ray power diffraction of the final slag of the converter, no nickel oxide was found, and the yield rate of nickel in nickel-containing iron block was close to 100 %.

Study on ion migration behavior of lime in dissolution of gasification dephosphorization slag

2022, 38(2): 25-31.

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For converter gasification dephosphorization slag system, the kinetics of static lime dissolution in slag was studied. The research results show that in the temperature range of 1 200～1 500 ℃, as the temperature increases, the melting rate of lime increases, the activation energy of lime melting is E_a=203.1 kJ/mol, the linear equation fitting the relationship between the rate constant and the temperature is ln v_r=-24.43/T-14.62. The limiting link of lime melting is diffusion control. Analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD) the molten slag layer-the boundary layer-the lime layer, the research results show that the migration rate of the slag component Fe²⁺ is faster than the migration rate of SiO₄^4-, from the lime surface to the inside, CaO-SiO₂ composite phase is mainly formed on the lime surface, and more Fe elements will be present inside, forming the main CaO-FeO composite phase.

Study on improving calcium yield of pure calcium wire

2022, 38(2): 32-35.

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The factors affecting the calcium yield of pure calcium wire were studied through theoretical analysis and production practice. The results show that,1) Reducing the diameter of feeding tube can reduce the deflection of and the pilling up of calcium wire；2) The effective absorption range of calcium is from 0.3 m above the bottom to 1.22 m below the liquid level; 3) The feeding speed of calcium wire is affected by the algam thickness of calcium wire, and the calcium wire with different algam thickness has an optimal feeding speed；4) When feeding wire at the downward flow position of argon bubble flow, the calcium yield is better than that at the upward flow position of argon circulation flow；5) The calcium yield of wire packing with seamless is better than that with slit algam tube；6) The composition of molten steel affects the vapor partial pressure of calcium, the effective absorption range of calcium is changed, and then the residence time of calcium in molten steel is different.

Study on application of composite powder cored wire

2022, 38(2): 36-42.

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Fe-Si+CaO composite powder cored wire was added into molten steel, and its effect on the removing inclusions was studied. The results show that the composite powder cored wire can be added into molten steel，in which the composite powder can diffuse into molten steel and form Si-Ca-Al composite inclusions with the inclusions in molten steel. The appearance of composite inclusions is spherical，which is easy to accumulate and float up. The industrial trial results show that，the composite powder cored wire can remove inclusions and purify molten steel without affecting the control of steel composition. The T.O content，area content and number density of inclusions are decreased significantly，and the sizes of inclusions remaining in the slab are mostly less than 4 μm，and no size larger than 10 μm inclusions.

Numerical simulation of structural optimization and inclusion removal in single strand tundish

2022, 38(2): 43-48.

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To solve the problem of poor flow state in the process of continuous casting and high percentage of the inclusions in molten steel, some improvement schemes regarding the flow control device of single strand tundish were proposed. The flow field and average residence time distribution of molten steel in the tundish under different schemes were comparatively investigated by numerical simulation and water model experiment. The optimal combination of flow control devices was proposed, the distance between the weir and the long nozzle is 1 090 mm, the height of the weir is 180 mm, the distance between of the weir and the dam is 260 mm, the height of the higher dam is 340 mm. Compared with the prototype tundish, the average residence time and plug zone are increased and the dead zone ratio is reduced by 7.14 %.The average removal rate of inclusions reaches 68.7 %, which is 6.6 % higher than the prototype tundish.

Control and improvement for surface quality of peritectic steel billet with high casting speed

2022, 38(2): 49-53.

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For the disadvantages of traditional mold flux of peritectic steel, this paper proposed a novel type of mold flux, which combined both heat transfer and lubrication effects, providing a new solution for the stable highefficiency production of peritectic steel billet. Through the proper decrease of basicity and viscosity of previous mold flux for peritectic steel，introduction of LiO₂ and oxides of transition metallic elements（Fe₂O₃，MnO），as well as the content reduction of fluorine, the applicability and stability of the mold flux for the casting of peritectic steel billet at high casting speed were improved. In view of associrelation and compatibility of series flux properties, as well as service conditions, the qualified ratio of defect-inspection for the peritectic steel billet was highly improved from less than 35 % to more than 93 %，and a continuous high-efficiency and high-quality production way of peritectic steel billet was achieved with the appropriate employment of the novel mold flux for peritectic steel.

Stimulation analysis of volume expansion and application practice for 300 t ladle

2022, 38(2): 54-59.

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In view of steel production capacity improvement and the transformation of big scrap steel ratio production mode, the requirement for ladle volume expansion was put forward. Through modeling and numerical calculation after ladle volume expansion，the temperature field and stress field were analyzed. After the expansion ladle reached the steady-state cycle, the ladle wall surface temperature reached the maximum value of 280 ℃,and the slag line position reached the maximum value of 310 ℃, which was in the safe range. The thickness of the working layer of ladle wall was reduced by 30 mm, the effective capacity of the ladle was increased from 277 t to 286 t, and the monthly production capacity was increased by 18 000 t. While promoting the improvement of steelmaking capacity, the power cost, refractory cost and labor cost were reduced, and the annual economic benefit was about 14 million yuan.

Influence of nozzle aggregated inclusions on fatigue cracks and their control in wheel

2022, 38(2): 60-66.

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The characteristics of rim cracks and inclusions in the wheel were analyzed,it was shown that the type of fatigue cracks was caused by the aggregated large-size inclusions in the steel.These inclusions originated from the aggregated attachments on the inner wall of the nozzle. In the casting process, the endogenous inclusions in the molten steel aggregated and adhered on the inner wall of the nozzle, the inclusions would fall off randomly and remained in the billets during solidification.These large inclusions were distributed at the position of 20-40 mm from the surface of the continuous casting billet, which were distributed in the wheel rim area after wheel rolling, located at 10-20 mm below the tread. The sizes of inclusions generally exceeded 500 μm, and the main composition was calcium aluminate. For the process optimization of calcium treatment and electromagnetic stirring and shielding casting in the overall process of continuous casting, the aggregation and attachment of inclusions on the inner wall of nozzle have been effectively controlled. The stability of continuous casting and the wheel quality have been significantly improved. The total number of large-sized inclusions was reduced by more than 76 % and the number of inclusions larger than 1 mm was greatly reduced to 8 % from 35 %.

Analysis of influencing factors of surface linear defects of non-oriented electrical steel

2022, 38(2): 67-74.

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Combining scanning electron microscopy and large sample electrolysis, the composition and source of inclusions in the surface linear defects of W800 grade non-oriented electrical steel in the CSP process were studied. SPSS software was used to regress and analyze the main factors which affected the surface linear defects in the steelmaking process. Research shows that the content of large inclusions in the steady state casting process is 5.39 mg/10 kg. The large inclusions which cause linear defects on the surface of non-oriented electrical steel are mainly deoxidized products, magnesia-aluminum spinel and ladle top slag, and the main types are Al₂O₃, MgO-Al₂O₃, CaO-Al₂O₃-MgO and CaO-Al₂O₃-SiO₂. The cleanliness of steel in the unsteady casting process reduces significantly, and the proportion of linear defects on the surface of the hot-rolled sheet increases. The main factors affecting the surface linear defects are w(CaO)/w(Al₂O₃) at the top slag of RH exit, oxygen level at the end of RH deoxidation and minimum tonnage of tundish in continuous casting process.

Influence of excess air coefficient on operation of converter waste heat boiler

2022, 38(2): 75-82.

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The safe operation of the converter waste heat boiler is affected by factors such as blowing time, excess air coefficient, flue gas velocity, etc. Among them, the excess air coefficient is most closely related to practical production. Based on the thermal calculation process of the converter waste heat boiler, a thermal calculation program was compiled, and change rules of theoretical combustion temperature, heat transfer and exhaust gas temperature were obtained based on the program when the excess air coefficient changed. To the 180 t converter waste heat boiler, under the conditions that the primary furnace gas temperature is 1 600 ℃ and gas volume composition is 90 % CO and 10 % CO₂, the result shows the theoretical combustion temperature increases by 286.1 ℃, the proportion of CO in flue gas decreases from 72.468 % to 41.052 %, the heat transfer increases significantly, and the exhaust gas temperature increases by 139.12 ℃ as the excess air coefficient increases from 0.08 to 0.3.

Study on the mechanical properties of carbonation of steel slag bricks

2022, 38(2): 83-88.

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In order to find a new method of utilizing steel slag, the steel slag aggregate from Jinan Iron and Steel Plant was placed in an airtight container and carbonated with 100 % CO₂. Experimental results showed that steel slag could absorb CO₂ under a certain pressure, and the strength of steel slag specimen after carbonation was greatly improved compared with that without carbonation. When the water-cement ratio of steel slag powder was 14.5 % by gravimetric method, the weight gain rate of carbonation of steel slag brick was 15.05 %, and the corresponding compressive strength and flexure strength were 36.88 MPa and 9.69 MPa respectively. According to XRD and FE-SEM microscopic test methods, the reason for the improvement of mechanical properties of specimens was that the Ca²⁺in steel slag, the water added with CO₂ carbonated to generate CaCO₃, resulting in a denser microstructure and reducing pore diameter.

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