Steelmaking

Development and prospect of calcium treatment process

2018, 34(2): 1-7.

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Theoretical foundation of improving cleanness of steel and modifying inclusions by calcium treatment process were summarized, combined with the physical properties of calcium, evolution of calcium treating method in steel was reviewed, the advantage of wire-feeding process alone with the optimization routine of calcium cored-wire structure and core powder compositionwas emphasically analyzed ,and optimization of wire feeding process was summarized, the problems unsolved in calcium treatment together with the research fields to stabilize calcium yield and realize accurate calcium addition was put forward.

Application and practice on the newly developed refining flux in ladle refining process

2018, 34(2): 8-11.

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The effectiveness of newly developed refining flux in LF refining process was systematically studied based on industrial plant trials. The results show that the newly developed refining flux could not only improve the working environment, reduce the dust pollution, but also bring fast slag formation and excellent foamability due to the high porosity of the refining flux, which is in favour of suberged arc operation, the increase of power transmissionefficiency and heat preservation of liquid steel. The mass fraction of T.Fe in refining slag could be controlled lower than 1.0 % and the slag basicity could be increased larger than 4.5 when using the newly developed refining flux, which is beneficial to the float and removal of inclusions and improve steel cleanliness. It further confirmed the feasibility and reasonability of the newly developed refining fluxin liquid steel refining.

Experiment of bubble behavior in argon blowing through long shroud of continuous casting

2018, 34(2): 12-18.

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Gas bubbles’ size, their distribution and flow behavior in tundish have been investigated at different conditions of argon blowing through long shroud in continuous casting in water model experiments. The experimental results show that in the lower water flowrate range (≤2.4 m3/h), 0.11 mm diameter gas nozzle produces above 60 % proportion of tiny bubbles (0.1－0.5 mm), 0.25 mm diameter gas nozzle 45 %, and 0.58 mm diameter nozzle about 35 %. The proportion of larger bubbles (>1.0 mm) produced with the 0.58 mm diameter gas nozzle is maximal. The proportion of tiny bubbles (0.1－0.5 mm) formed with a 0.25 mm diameter single hole nozzle and a diameter 0.25 mm double-hole nozzle is more than 80 % when the water flowrate is 3.0 m3/h. In the lower water flowrate (≤2.4 m3/h), the proportion of tiny bubbles formed with the two nozzles is similar, but the proportion of larger bubbles (>1.0 mm in diameter) produced with the diameter 0.25 mm double-hole nozzle is smaller than that with the diameter 0.25 mm single hole nozzle and the double-hole nozzle produces larger number of bubbles. The action area of gas bubbles in tundish without a turbulence inhibitor is larger than with a turbulence inhibitor.

Improvement on the SEN clogging of sulfur-bearing Al-killed steel

2018, 34(2): 19-24.

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SEN cloggings of Al-killed resulfurized gearing steel after calcium treatment were analyzed.And the castability of molten steel was improved by optimizing the processe.The results showed that SEN clogging was mainly caused by the CaS and Ca-Al-Mg-O inclusions with high melting-point.The inclusion composition in the Al-killed resulfurized gearing steel wass mainly depended on the ratio of [O] content to [S] content in the steel after Ca-treatment and sulphur addition. By raising the [O] content, CaO contnets in inclusions increased and the castablity of the molten steel was improved. Under the condition of weaker deoxidization process,CaO content increases and CaS content decreases in inclusions. As a result,castability of molten steel improved greatly, with the continuous casting heats increased from 4 to 7 or more.

Research of carbon segregation for high carbon steel billet

2018, 34(2): 25-30.

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Soft reduction is an effective method to improve the carbon segregation of high carbon steel. In this paper, the existing straightening rollers were used to carry out the soft reduction. In order to study the feasibility of soft reduction for the billet continuous casting, the pressing force of straightening machine was analyzed by mechanical calculation, and the billet solidification heat transfer model was established to analyze the solid fraction distribution under different conditions. Meanwhile, the straightening rollers were modified from concave to flat. Through the solidification calculation and the experiments, the research developed the optimal soft reduction process parameters that is suitable for the current billet high carbon steel. The results show that the internal quality of the billet has been significantly improved, and the carbon segregation index dropped below 1.1.

Effect of chamfer structure on temperature of slab corner and industrial test for controlling transverse corner crack

2018, 34(2): 31-37.

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Aiming at controlling slab transverse corner crack of microalloyed steel containing niobium or titanium,the chamfered mould technology has been developed and applied on the Masteel slab continuous caster. The effect of chamfer structure on temperature of slab corner has been studied by establishing three dimensional steady heat transfer model and using the method of numerical simulation. The control effect for corner transverse cracks of slabs with different angle shape has been compared and analyzed through the industrial tests. The numerical simulation results showed that the corner temperature was obviously increased when the slab angle was changed from a right angle to an obtuse angle. The slab corner temperature will be increased from 788 ℃ to 1 091 ℃ above at a place where the distance from meniscus was 900 mm. The slab width corner temperature was 1 091 ℃, 1 128 ℃ and 1 110 ℃ when the slab width angle was 120°,125°and 125°respectively. Accordingly, the temperature of the slab narrow face angle was 1 254 ℃, 1 240 ℃ and 1 209 ℃respectively. Industrial test results showed that transverse corner cracks has been effectively controlled by using chamfered mould and soft secondary cooling process. The transverse corner crack ratio was the lowest when the angle of the slab width chamfer was 125° and the slab quality could meet the need of hot charging and direct rolling.

Optimization on F-EMS position and casting parameters of billet caster

2018, 34(2): 38-43.

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In order to improve the macrostructure and center segregation of billet, heat transfer model of solidification of billet with 200 mm×200 mm section was established. The best position of F-EMS was analyzed considering both steel grade and casting speed. And finally, the F-EMS was moved to 9.85 m away from the mold level. After optimization on casting parameters and constant speed casting, the macro structure defects such as white band and central porosity were eliminated, and center segregation of low carbon steel and medium carbon steel was controlled about 1.05, center segregation of high carbon steel was controlled about 1.10. Moreover, experiment result shows that decreasing cooling water quantity of crystallizer from 130 m3/h to 110 m3/h can prevent the growth of columnar grains and increase the proportion of equiaxed grain.

On-line inspection technology of continuous casting slab liquid core

2018, 34(2): 44-50.

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Accurately measuring the liquid fraction and the solidification end of the slab is of great significance to reduce internal defects such as central segregation and shrinkage porosity of the slab, and it is also great significance to improve the quality of slabs and productivity. In this paper, a new method is proposed to detect the liquid core thickness and the solidification end of the casting, which is achieved by controlling the low amplitude and low frequency vibration of the arc in the fan section, and at the same time extracting the fluctuation amplitude of the liquid level under the corresponding vibration frequency. According to the coupling relationship between the reduction efficiency and the thickness of the liquid core, as well as the rheological behavior of the slab in the solid-liquid coexistence zone under the periodic vibration of the inner arc of the segment, the mathematical relationship between the liquid core thickness and the liquid level fluctuation in the mold is deduced theoretically. The liquid core thickness and solidification end of the slab with different amplitude and different casting speed were tested in a steel plant, and the feasibility of the method was verified by comparison with the theoretical values. The results provide guidance and reference for the on-line detection of the liquid core thickness and the solidification end of the slab in the solidification process of continuous casting.

Analysis on the rhythm of billet in CC- rolling section based on queuing theory

2018, 34(2): 51-54.

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CC-rolling section as one of the components of the interface model，have an important influence on steel production process.With the hot charging technology in-depth application,the matching between the process devices is by the quantity、production capacity, etc. to theproduction rhythm. The billet rhythm of heating furnace decided to roll the rolling rhythm,thus affecting the rhythm of the entire section. The paper analysis the time interval of CC-Rolling section of YanchangYongxin Steel Mill,guided by queuing theory,optimize the time interval that the billet enters the furnace,put forward reasonable time value, which provides a theoretical support for the management.

Analysis of inclusions in 42CrMoA crankshaft steel by the mold casting

2018, 34(2): 55-60.

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To improve the cleanliness of 42CrMoA crankshaft steel ,and reduce the gap between 42CrMoA crankshaft products and imported products，the inclusion type, composition, size, quantity and distribution in different parts of 42CrMoA were analyzed. The evolution of inclusions in steel during refining and solidification process was analyzed. Inclusion distribution in crankshaft steel ingot was determined. The result showed that the inclusions in refining process were mainly composed of CaO, Al2O3 and MgO, while the chemical composition of inclusions were mainly CaS, CaO, Al2O3, MgO in the ingot. Most of inclusion morphology were spherical and block. The number of inclusion in the lateral direction was less external and more internal, and decrease gradually from the head to the tail.

The origin and control of blister defects on slabs of boron-bearing low-carbon steel

2018, 34(2): 61-66.

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In order to control the blister defects on the slab of boron-bearing low-carbon steels in Meishan steel, gas chromatograph, Heraeus hydrogen gauge, SEM and method of electrochemistry were used to analyze the cause and effect factors of blister defects on the slab. High temperature plasticity of slabs with and without Mg treatment were tested with Gleeble-3500 thermal simulation test machine. Then improvement measures were proposed in accordance with Meishan Steel. The results showed that big Al2O3 inclusions were found in the blisters, the mass fraction of CH4 and H2 were 45.86 % and 51.79 % respectively inside the blisters, and positive segregation of B in the center of slab was the important effect factors of blister defects. Mg treatment was used to improve the quality of the slab, resulting in that the center segregation reduced to 1.8 and the number of inclusions larger than 50 μm reduced to 0.63%. Coolant addition in converter and addition of ladle slag modifier were also optimized. In sunny days, the coolant addition was all iron ore; and in rainy days, less than 31 kg/t pellets and complemental iron ore were added to converter as coolant. The addition of ladle slag modifier was less than 1.5 kg/t and complemented by lime. After process optimization, the frequency of blister defects in month average reduced from 5 to 0.78 in Meishan Steel.

Surface cleanliness control of automobile panel steel slab

2018, 34(2): 67-72.

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In this study, the distribution of inclusions at different depths beneath the shell surface was analyzed by auto-SEM. Water simulations and numerical simulation measurements were conducted to reveal the mechanism of inclusions captured by hooks. The results show that the inclusions are maximizing at 1－3 mm depths from the slab surface. Three kinds of inclusion movements in hook region were found: captured by the meniscus, captured below the meniscus and some of captured inclusions return to liquid steel. Most of the inclusions were captured near the meniscus which may lead to the highest inclusions amount near the surface of slab. Additionally, the number of inclusions captured by hooks will reduce with increasing the casting speed and casting temperature.

Investigation on the deformability of inclusions in tire cord steels during processes of hot-rolling and cold-drawing

2018, 34(2): 73-78.

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The deformability of inclusions in tire cord steels during the processes of hot-rolling and cold-drawing and the related influencing factors were analyzed and discussed in the current work. It was found that the deformation index of inclusions during the hot-rolling process first increased and then decreased with an increase in the contents of Al2O3 and (MgO+Al2O3) in inclusions. It was also generally inversely proportional to the solidus temperature of inclusion.Young’s modulus was used to evaluate the low-temperature deformability of the inclusions during the cold drawing process of tire cord steels. It was proposed that the deformabilities of inclusions during cold drawing are inversely proportional to their Young’s moduli. In order to reduce the fracture ratio of tire cord steel wires during cold drawing, the inclusions were proposed to be controlled to the regions of low Young’s modulus, those with high SiO2 content and extremely low Al2O3 content.

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