Steelmaking

Production practice for super low phosphorus steel in 260 t converter

2017, 33(6): 1-1.

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Two converter methods (dephosphorization converter + decarburized converter) were used to produce super low phosphorus steel according to the dephosphorization mechanism in the high phosphorus (0.12 %) hot metal conditions of Ansteel Bayuquan steelmaking department. The process parameters in dephosphorization converter and decarburized converter for two converter methods were researched in application process. The pre-smelting dephosphorization rate was controlled above 85 %, and the average phosphorus mass fraction was controlled in 0.018 % in dephosphorization furnace. The average phosphorus mass fraction was controlled in 0.001 2 % at smelting end-point. The average phosphorus mass fraction in the end product was controlled below 0.002 0 %. And the mass production of super low phosphorus steel under the condition of high phosphorus hot metal was realized.

Research and practice of less slag smelting technology in 120 t converter

2017, 33(6): 5-8.

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Converter dephosphorization in Beiying steelmaking plant of Benxi steel group corporation, depended on high basicity, large quantity of slag, high oxidization, low temperature technology in the past. More emphasis on the amount of lime caused high lime consumption, being 40－50 kg/t, and ignoring the slag fluidity and thermodynamic conditions. The plant began to study slag-forming process in 120 t converter in 2016, by reducing slag melting point, changing its liquidity, and improving dynamic conditions. Lime consumption of converter reduced from 42 kg/t to 33 kg/t, decreased by 1/5. And the dephosphorization rate of molten steel in converter endpoint increased form 87 % to 92 %.A large number of production practices show that the converter less slag smelting process was feasible.

Optimization of oxygen lance nozzle for a 100 t top and bottom combined blowing converter

2017, 33(6): 9-14.

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To solve the problems of low service life of oxygen lance and high oxygen consumption, the design of oxygen lance nozzle was optimized for a 100 t top and bottom combined blowing converter. The study includes measuring the pressure loss of oxygen pipeline, water modeling experiment and industrial test. The result of measuring oxygen pipeline pressure loss shows that the resistance loss of oxygen pipeline is 0.08－0.10 MPa during the using pressure 0.8 MPa, leading to an insufficient oxygen pressure for the original lance nozzle. The water modeling experiment shows that, with the new lance nozzle design, the impact depth of metal bath is increased by 7－18 mm, the impact area of metal bath is enlarged by 28－65 mm2 and the mixing time of bath is shortened by 1.9－9.3 s. The industrial test shows that the smelting time is shortened by 0.5 min, the total slagging materials consumption is reduced by about 1 kg/t and the dephosphorization rate is improved by 1.9 %.

Study on steelmaking process with slag conditioner in converter

2017, 33(6): 15-19.

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In order to solve problems of the great fluctuation of hot metal composition, the difficulty on steady-state control during steelmaking and the standardization for steelmaking operation, the slag adjusting process with a slag conditioner was introduced into converter steelmaking. The practice results showed that there were no splashing, no drying and no lance sticking during steelmaking by the slag adjusting process. The slag consumption reduced by 9.3 kg/t, and the metal loss reduced from 11.60 % to 10.01 %. The smelting was smooth during steelmaking and the cost was reduced.

Feasibility analysis on converter dephosphorization process of one step 400 series stainless steel production

2017, 33(6): 20-25.

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The process and advantages of using hot metal smelting 400 series stainless steel were described in this paper. The phosphorus balance of one step 400 series stainless steel production was calculated. The calculation results showed that for ordinary 400 series stainless steel, hot metal dephosphorization converter end point phosphorus mass fraction less than 0.024 % can meet the requirements of end point phosphorus content of the finished product, and for the super pure 400 series stainless steel some higher requirements, hot metal dephosphorization converter end point phosphorus mass fraction should be no more than 0.01 %. Under the condition of reasonable ingredients, the depth of converter dephosphorization can meet the production requirements of all 400 series stainless steels. Based on the actual production data of a steel plant in China, it is further proved that the dephosphorization of converter is a mature and reliable method for the pretreatment of molten iron.

Technology application and comparison on dry mechanical pumps and steam jet pumps

2017, 33(6): 26-29.

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Used in RH vacuum equipment of dry mechanical pump is gradually extended, compared with the traditional steam pump, there are many advantages. Based on the using effects of vacuum pumps in the hotrolled plant and the stainless steel company of Hesteel Tangsteel, the differences of operating characteristics, process effects, cost and environmental impact between steam jet pump and dry mechanical pumps were compared adequately. It was found that the dry mechanical pump running consumption savings of 70 % more than the traditional steam jet pump, and the minimum vacuum degree was 67 Pa, the dehydrogenation capacity was 55 %-80 %,and the denitrification capacity was 10 %-50 %, in the decarburization of vacuum control, cost control and environmental protection was better than three aspects of steam jet pump, compared with the steam jet pump, the effect of degassing and decarbonization was same or even better. By fully excavating the similarities and differences between these two types of vacuum pumps, guidance of choosing vacuum pump is provided for followup production lines.

Structural optimization and industrial tests of single flow tundish

2017, 33(6): 30-36.

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A similar ratio of 1∶2 water model was used to do the orthogonal experiments for the flow control device in slab casting tundishes, to study the influence rules of height and position of lower dam on the flow field, and find the optimal flow control mode. Furthermore, the contrast test between the prototype and optimized tundish was carried out in the steel plant. The results show that retaining a reasonable position and height of lower dam have important influence on the fluid flow behavior of molten steel in the tundish. After lower dam in prototype tundish was moved 1 m toward the injection flow area (scheme No.B15), compared with the prototype tundish, average resident time of optimized tundish was increased of 14.3 %, dead area ratio was decreased of 10.58 %, stagnation time was increased of 11.8 %, and fluid flow state of molten steel in tundish was improved. Meanwhile, T.O mass fraction in tundish was decreased of 47.3 %, the amount of macro inclusions in slab was decreased of 62.3 %, the macro inclusions with size of more than 300 μm were hardly found in the slab, and the total oxygen content in the slab was controlled more stably after optimization, so the removal efficiency of the inclusions was improved obviously.

Mold level fluctuation and submerged entry nozzle clogging control of thin slab continuous casting for nonoriented silicon steel

2017, 33(6): 37-41.

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As distinguished from the level fluctuation caused by bulging for hypo-peritectic steel，aiming at serious mold level fluctuation of thin slab continuous casting for non-oriented silicon steel，by means of researching the effect of the submerged entry nozzle clogging on mold flow field and analyzing the workshop data of accident operation and level curve，it was inferred that the main cause for level fluctuation was the submerged entry nozzle clogging resulted from a great deal of deoxidation products which had not been efficiently removed. The production practice at steelmaking plant of Bensteel indicated that mold level fluctuation range during non-oriented silicon steel casting had been dropped from more than±15 mm to less than±3 mm through some technical measures as controlling accurately blowing end-point oxygen mass fraction of molten steel below 800×10-6，reducing argon flow rate from 150-200 L/min to 40-50 L/min at the later stage of RH，and raising properly superheat to 25-45 ℃ of liquid steel in tundish.

Develop and application of chamfering-mold powder for the boron bearing steel

2017, 33(6): 42-46.

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Facing the serious problem of corner transverse cracks on steel slab while manufacturing SS400B steel in some domestic steel plants, which leads surface up warping on hot rolling, steel plants use chamfering mould instead of right angle mould to solve this. But the longitudinal cracks on slab appear near the chamfering copper plate working face because the different friction and the temperature change the liquid steel flow field and solidified shell. Based three aspect of crystallization, lubricating and carbon composition, a new casting powder was design for chamfering mould casting boron steel. The test shows the cracks on SS400B steel slab have been effective controlled, the crack ratio dropped from 8.2 % to 0.3 %, which meets the customers’ requirement.

Development and application of anhydrous capping technology in CC slab

2017, 33(6): 47-50.

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The traditional capping technology exists the problems of the poor quality of trail billet, the low qualification rate of flaw detection and the long resection length in slab continuous casting. In order to solve the above problem, an anhydrous capping technology was developed and had been applied in a medium and heavy plate company by use of process innovation. “Watering” was changed into anhydrous in casting capping stage. The results showed that, the quality of trail billet was improved，the qualification rate of flaw detection increased from 78.2 % to 98.8 %, and the resection length reduced from 1.5-2.0 m to 0.8 m.

Formation mechanism and control measures of breakout for billet continuous casting

2017, 33(6): 51-56.

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In order to explore the cause of the formation on breakout of the billets for low carbon steel, the characteristics of the breakout shell and the mold tube was investigated by optical microscope and scanning electron microscope. The result shows that the outer surface of the mold was attached with an unknown substance, what was worse, the inner surface plating was detached and the solidification shrink rate of the steel is high. Therefore, the heat transfer effect of the mold was poor, and as a result, the thickness of the shell was uneven and the internal cracks might generate. At last, when the weakest point of the billet shell couldn't withstand the external force, then the breakout would happen. By adjusting the appropriate continuous casting process parameters, and reducing the sulphate content of the mold cooling water, the breakout ratio of the low carbon steel decreased from 1.01 % to 0.30 %.

Research on MgO·Al2O3 spinel inclusions in alloy spring steel 51CrV4

2017, 33(6): 57-61.

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Aiming at the problem of non-metallic inclusions in smelting process, the transformation of inclusions in refining process of alloy spring steel 51CrV4 was studied by sample analysis, SEM and EDS. The origination and formation of MgO·Al2O3 spinel inclusions was analyzed, and the feasibility of inclusion modification by calcium treatment was discussed. The results showed that MgO·Al2O3 spinel inclusions could generate when [Mg] mass fraction between (0.55－30.6)×10-6, and start converted into liquid when [Ca] mass fraction reached 6×10-6. The liquid inclusions content increased rapidly with the improvement of [Ca] content in the steel, and the conversion could be completed when [Ca] mass fraction in the steel reached around 35×10-6.

Discussion on sources of large inclusions in heavy rail steel

2017, 33(6): 62-66.

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Inclusions in the heavy rail smelting process were analyzed statistically by inclusion analyzer. Methods by a ingredient contrast between typical inclusions and large inclusions were adopted to define the source of the large inclusions and take targeted technical measures. Combination with sample of the inclusion overproof and nonconformity in ultrasonic flaw detection analysis, the common type of large inclusions were summed up and the source was discussed. The results showed that greater than 10 μm inclusions in refining process can be removed and typical inclusions contain 5 %-10 % MgO. After refining process, greater than 10 μm inclusions were the secondary oxidation products or mould powder which is characterized by very low content of MgO. The large inclusions which cause the inclusion overproof and nonconformity in ultrasonic flaw detection were the main source of furnace slag, mould powder and nozzle blocking products, the inclusions generally contain the bulk of spinel. To control of large inclusions in heavy rail steel, in addition to the conventional control methods such as to prevent secondary oxidation, prevent slag entrapment and improve nozzle materials, the spinel should be controlled by using of low Al content of alloy and accessories as far as possible, improving refractory quality of tundish zone and suitable for continuous casting furnace number to prevent spinel product gathered in the nozzle.

Industrial testing of high quality converter gas recovery by injecting pulverized coal into the high temperature gas of converter

2017, 33(6): 67-72.

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Based on low calorific value and recovery amount of converter gas from the present various steel mills, a new process on the basis of the industrial trial in a converter with 35 t steel capacity from Echeng Iron and Steel Co.,Ltd. was proposed for preparation of highquality converter gas. By comparing the injecting rate and various carbon materials injected into the converter vaporization cooling flue, the effects of which on the quality and amount of converter gas are therefore investigated. The results show that, with increasing the injection amount of carbon materials, the volume fractions of O2 and CO2 in the gas are decreased, yet CO and H2 in the gas are increased correspondingly. When the rate of pulverized coal injection is 30 kg/min, the volume fractions of O2 and CO2 in the gas are decreased by 63.92 %, 41.19 %, but CO and H2 in the gas are increased by 20.09 %, 240.18 % and the recovery time of gas is increased by 11.40 %, respectively. Therefore, this process is beneficial to improving the quality and amount of converter gas.

Industrial test research on grindability of steel slag by high temperature modifying and air quenching

2017, 33(6): 73-77.

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Industrial trial was carried out by adding 5 % fly ash into molten steelmaking slag and air-granulation process. The experimental results show, compared with the original slag, the content of calcium ferrite, dicalcium silicate and merwinite in the modified slag increase, and the content of Fe, RO and free CaO decreases. The results of grinding test show that the surface area of the powder of the modified steelmaking slag is 22.4 % higher than that of the unmodified steelmaing slag. The theoretical analysis shows that the content of Fe and RO phase can be reduced effectively after the modification and air quenching, which improvies the grindability of the steelmaking slag. The results provide theoretical support and new technical direction for steelmaking slag processing.

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