Table of Content

05 June 2014, Volume 30 Issue 3

Previous Issue    Next Issue

Research and application on dephosphorization pretreatment process in a single converter new doubleslag process

2014, 30(3):  1-4. 

Asbtract ( 250 )  

Related Articles | Metrics

The practice of dephosphorization process with duplex melting with a single converter in Sansteel Minguang Co., Ltd., Fujian was introduced. The average dephosphorization rate was up to 67.3 % in the case of  blowing oxygen intensity 2.0~2.7 m³/(t·min), average blowing time 8.74 min, bottom stirring gas intensity 0.20 m³/t, average temperature 1 328 ℃, average basicity 1.51, and w（T.Fe）=12 %~16 % in early stage dephosphorization of 100 t converter. The carbon mass fraction was 0.113 % and the phosphorus mass fraction was 0.011 % using new double-slag process in one converter. Compared with the conventional smelting process, with the same endpoint carbon content, the phosphorus mass fraction decreased 45 %, and the consumption of slagging material decreased 11.6 kg/t.

Research and application on 65 steel smelting with duplex melting process in two converters

2014, 30(3):  5-8. 

Asbtract ( 264 )  

References | Related Articles | Metrics

The present paper introduced the practice of duplux process in two converters in Sansteel Minguang Co., Ltd., Fujian for 65 steel production. And Dephosphorization and decarburization process parameters and application results were discussed. The process parameters in dephosphorization furnace were blowing oxygen intensity 2.0~2.7 m³/(t•min), blowing time 7~10 min, average lime charge 33.3 kg/t, average basicity 1.51, bottom stirring gas intensity 0.25 m³/(t•min) and end-point temperature 1330~1351℃. The semi-steel average phosphorus mass fraction could be decreased to 0.028 4 % and average carbon mass fraction was 3.04 %. The average dephosphorization degree was 67.7 %. Less slag blowing and catching carbon were used in decarburization furnace with the process parameters of oxygen intensity 4.0 m³/(t•min), bottom stirring gas intensity 0.13 m³/(t•min), average lime charge 13.8 kg/t. At the endpoint of blowing, the average phosphorus mass fraction was 0.013 %, the average carbon mass fraction was 0.21 %, which realized tapping at low phosphorus and high carbon contents. Smelting reduction process with manganese ore was realized in decarburization furnace and manganese ore charge was 4~6 kg/t. The average manganese recovery rate of 46.3 %, and under the catching carbon process the average manganese mass fraction was 0.303 % at the endpoint. The application of high carbon steel production with duplex process in two converters realized the tapping at low phosphorus high carbon contents and manganese ore smelting reduction, and expected blowing results had been obtained.

Practice on low nitrogen controlling technology of Shougang Qiangang

2014, 30(3):  9-11. 

Asbtract ( 247 )  

Related Articles | Metrics

Exploration and research on composition control of nitrogen in high strength IF steel in Shougang qiangang have been introduction in this paper. Production technology and the method of preventing the increasing of nitrogen in high strength IF steel have been summarized also. The production process of low nitrogen steel during converter smelting includes decreasing reblowing numbers and reblowing time, controlling the condition of combined blowing and modifying top slag which contains high nitrogen content. And the production process of low nitrogen steel during RH refining includes improving vacuum degree rapidly, increasing argon circle flow, melting cold steel in vacuum chamber and inert gas protection technology and preventing nitrogen increasing in submerged tube. The average nitrogen content in low nitrogen steel produced by Qiangang is about 15×10^-6 % by using the above technologies.

Research and application of slagadheringresistant spraying mix for gloryhole of converter

2014, 30(3):  12-15. 

Asbtract ( 295 )  

Related Articles | Metrics

The slag-adhering-resistant spraying mix was prepared with recycled material of used Mg-C bricks as main starting material，magnesite clinker as fine aggregate, fused magnesite, SiC, graphite, silicon micro powder and α-Al₂O₃ micro powder as powder lot, alumina cement as firming agent, sodium hexametahposphate as binder, lignin sulfonic acid calcium as water reducing agent, and polypropylene fiber as anti-explosion agent. The prepared spraying mix is low-cost, slag adhering resistance efficiently and easily to clean up. The industrial test and application of the prepared spraying mix showed that the slag-adhering-cleaned frequency reduced from 2~3 times to 1~2 times per shift, and the slag-adhering-cleaned time decreased from 15~30 min to 10~15 min each time. The application of the spraying mix increased the efficiency of slag-adhering-cleaned and decreased the time of non-production.

Analysis of cold bending crack on Q345B direct rolling thick plate

2014, 30(3):  16-19. 

Asbtract ( 217 )  

References | Related Articles | Metrics

Cold bending crack appeared on Q345B thick plate after using direct rolling process. The metallographic structure, inclusions, precipitates in hot charging rolling and direct charging slab were studied, and the results showed that banded structure and MnS inclusions in thick plates were the mainly reasons which caused cold bending crack in direct charging plates. Precipitates in direct charging plate were less which could not give enough strengthening effect. Carbon and other elements generated dendritic segregation during solidification process, and then dendritic segregation transformed into banded structure during rolling process. MnS inclusions were generated during solidification process, which formed in Al-killed steel without other deoxidation elements according to the appearance and chemical composition of inclusions. The banded MnS inclusions have been reduced, and segregation has also been improved accordingly throught sulfur content controlling, electromagnetic stirring application and chemical composition adjustment.

Study on nozzle clogging behaviour of Ti-IF steel

2014, 30(3):  20-23. 

Asbtract ( 267 )  

Related Articles | Metrics

The nozzle clogging of Ti-IF steel were analyzed by SEM, through the study of nozzle clogging is divided into two layers, including near the nozzle refractory material part reaction layer for Ti-Al-O composite inclusion and Al₂O₃ inclusion mixture, near steel accumulation horizon for Al₂O₃ inclusion and cold steel mixture. The inclusions of steel in tundish were analyzed by SEM, through the analysis found that a lot of Ti-Al-O composite inclusion and Al₂O₃ inclusion in the tundish steel. The Ti-Al-O composite inclusion and Al₂O₃ inclusion is the main reason for the nozzle clogging.

Decarburization process optimization of 180 t RH vacuum degasser

2014, 30(3):  24-27. 

Asbtract ( 293 )  

Related Articles | Metrics

Optimizations of initial carbon and oxygen condition，blowing oxygen time, exhausting system, and liftgas flowrate pattern were conducted to develop an effective decarburization process for 180 t RH degasser. The initial carbon mass fraction was kept between (250-500)×10^-6，and oxygen mass fraction between )=（300-650）×10^-6；the pressure in the vacuum chamber quickly decreased to less than 150 Pa；when the initial condition w(C)/w(O)>0.66，oxygen was blew to force decarburization at eaaly；the lift gas was 1.0G m³/h（0~4 min），0.8G m³/h（4~6 min），1.0G m³/h（after 6 min）.With the new process largescale industrial production results indicated that a majority of final mass fraction of carbon could be reach to less than 15×10^-6 in 15 min.

Application of aluminum deoxidation process in vanadium microalloyed steel

2014, 30(3):  28-32. 

Asbtract ( 276 )  

References | Related Articles | Metrics

A production practice of aluminum deoxidation process combining with a stopper tundish was introduced in this paper. Aluminum ferromanganese was added as deoxidizer into the converter and calcium wires were introduced for inclusions calcium treatment into ladle furnace before the refining ending. Stopper tundish was applied to avoid casting accident of nozzle clogging caused by inclusions gathering around the nozzle so as to ensure the steady of casting process. Through the application of optimized process, the steelmaking and casting operations were stale and highly effective, and the test results of final product showed that the aluminum deoxidation could improve the steel deoxidation ratio remarkably with oxygen mass fraction less than 20×10^-6 and the inclusion level in the microstructure lowered evidently.

Analysis and countermeasures on bearing failure of continuous caster segment

2014, 30(3):  33-36. 

Asbtract ( 298 )  

Related Articles | Metrics

To improve the service life of segment bearing of WISCO’s slab continuous caster and decrease the accident of foreign body rolled defect in slab by bearing damage, the reasons of the bearing failure were comprehensively analyzed, and the design and the process parameter optimization of the segments were studied. The results showed that the main reason for the bearing failure of the segments is abnormal overload. Then the improvement measures, such as adjusting soft reduction parameters, optimizing end slab output mode and using soft clamping function, were proposed. After caster segments process optimized, the ratio of segments failure caused by the bearing damage was decreased from 89.7% to 62.5%, the average life cycle of segments was increased from 122 days to 140 days, and the foreign body rolled defect in hot rolled coil was basically eliminated.

Study on factors affecting the disqualification of heavy and medium plate by ultrasonic detection

2014, 30(3):  37-41. 

Asbtract ( 179 )  

Related Articles | Metrics

On the basis of statistical analysis of qualified ratio for ultrasonic detection, the qualified and unqualified samples of heavy and medium plates by ultrasonic detection were analyzed through macrostructure examination，metallographic examination and SEM analysis etc. Results showed that the main factor affecting the disqualification of heavy and medium plate by ultrasonic detection were the small cracks in the center of steel plates, which resulted from the combined action of center segregation and the hydrogen of steel. The qualified ratio of steel plates 25 mm or above by ultrasonic detection were increased evidently by reducing the content of hydrogen in steel, improving the center segregation of slabs simultaneously and optimizing the production plan and process flow for different steel grades with different thickness, and then the qualified ratio of heavy steel plates（25 mm or above） and sheet steel by ultrasonic detection were increased from 88.61 % to 96.27 % and from 97.08 % to 98.44 %.

Key technologies of smelting high cleanliness bearing steel with EAF

2014, 30(3):  42-45. 

Asbtract ( 220 )  

Related Articles | Metrics

The bearing steel was smelted using 100 t EAF in the domestic steel factory, and it is difficult to control of the total oxygen mass fraction less than 10×10^-6. After a system of the research, the improvement measures were proposed as followed: the end-point carbon mass fraction was above 0.1 %; the addition of Al-deoxidizer and the slagging were advanced to the LF refining; the slag basicity was controlled in 5-8, and w(CaO)/w(Al₂O₃) of the slag was controlled in 1.5-1.7, and w(MgO) was controlled in 5 %-8 %; the electromagnetic stirring intensity was reduced in order to prevent mold slag entrapment. The industrial test showed that the total oxygen mass fraction of the bearing steel could be controlled below 10×10^-6 by using the improvement measures.

Studies on re-utilization of LF cold steel making slag

2014, 30(3):  46-49. 

Asbtract ( 192 )  

Related Articles | Metrics

Based on the experiments on briquette of LF carbon steel slag, the reasonable parameters were presented on briquette by comparing briquette properties with the use of different binder. The industrial trials were conducted and differential scanning calorimeter(DSC) were also employed to determine the cooling methods on LF cold steelmaking slag, the results provided technical support for the reasonable utilization of LF cold steelmaking slag.

Application of thermal simulation on design and analysis of RH vacuum tank

2014, 30(3):  50-53. 

Asbtract ( 235 )  

Related Articles | Metrics

In this paper, the design and analysis of a new process technology which is lifting the vacuum tank to the work position with a original temperature 1 300 ℃ by off-line heating was performed using the thermal simulation module of SolidWorks Simulation. The finite element model of the vacuum tank including the shell and refractory lining was established. Three types of boundary conditions, in which the vacuum tank were preheated to 1 300 ℃ for 96 hours transiently，for 20 hours transiently and preheated to the steady state, were considered in the performed simulations. Then, the vacuum tank was left to cool naturally in 30 minutes. Finally, the temperature drop characteristics of the vacuum tank was analyzed. Results showed that the heat storage of the factory lining in the vacuum tank was obvious insufficient with the temperature condition in which the tank was preheated to 1 300 ℃ in 20 hours transiently. And the temperature of the top area was less than 800 ℃ after the cooling process. So it could not meet with the production requirements. For the other two temperature boundary conditions for the preheating, all parts of the vacuum tank exhibited a higher temperature than 800 ℃ after the cooling process, which could meet with the production requirements. Also, a good correlation was obtained between the temperature distribution of vacuum tank after preheating in 96 hours and cooling naturally in 30 minutes with the actual temperature distribution. From the economic point of view, the preheating solution in which the tank was preheated in 96 hours should be used in practical production. Computational results provided some theoretical guidance for the engineering application of RH vacuum furnace.

Study on heat transfer behavior of mold copper plate during high speed continuous casting of steel slabs

2014, 30(3):  54-59. 

Asbtract ( 258 )  

Related Articles | Metrics

Based on high speed continuous casting process of low carbon steel in SGJT，a three-dimensional finite-element heat-transfer model was established by ANSYS to predict temperature distribution of mold copper during high speed continuous casting. The results showed that the effect of backup plate could be neglected. An increase of temperature occurred around mold bottom and the extent of growth increased as casting speed rises. Increasing casting speed leaded to higher temperatures, but the increment decreased. The highest center temperature of hot copper surface at casting speed 2.3 m/min was 328.0 ℃, occurring just 10 mm below the meniscus. Nickel layer bringed a higher temperature and had a positive relation to thickness and casting speed. Increasing water flow rate could reduce the temperature of copper plate within a certain range.

Study on microstructure of slag films and properties of the mold powder for Q235B steel

2014, 30(3):  60-63. 

Asbtract ( 217 )  

Related Articles | Metrics

In light of the slab quality problems in the production of Q235B steel, the chemicophysics properties of the mold powder were analyzed; and then combining the quality of slabs, the microstructures of slag films were roundly studied. The results showed that, the melting temperature, viscosity of this flux was lower than the theoretical value of fluxes casting for peritectic steel, and the microstructures were different between reasonable films and unqualified films. The mineralogical phase of reasonable films for Q235B steel slab casting, of which crystal rate could reach 90 %～95 %, include akermanite, cuspidine and wollastonite. The outstanding characteristic of unqualified films with longitudinal cracks accidents was that crystal rate could be only 65 %～70 %. As to unqualified films with sticking breakout accidents, the biggest difference comparing with reasonable films was the mass formation of cuspidine, while crystal rate could anomaly reach 95 % or more. Combining the parameters of casting technics and chemical components of the mold powder casting for Q235B steel, the causes of abnormal film structures and quality defects of slab surface were finally given.

The quality control process optimization research of the ultra low carbon steel M2A1 head slab

2014, 30(3):  64-68. 

Asbtract ( 225 )  

Related Articles | Metrics

Combined with the actual production of a certain factory，analyzed the number，pattern，component of head slab，normal slab and different processing stages for ultra low carbon steel M2A1，found out the main reasons of the high inclusion content in the head slab. By optimizing the cast starting preparations，cast starting tonnage，Ar control，using stopper instead of common steel cast-starting pipe，optimizing the cast-starting speed curve in the tundish，and setting emergence time according to different sections，the quality of the head slab was improved. T[O]，[N] and inclusions contents was decreased along with the casting direction. T[O] content decreased from 0.0036% to 0.0025% at the position of 2.5m along head slab. And the total amount of inclusions decreased from 11.50mg/10kg to 8.26mg/10kg，inclusion number per unit area decreased from 8.73 mm^-2 to 6.26 mm^-2，and are close to those of normal slab after the position of 2.5m along head slab.

Influence of low temperature brittle zone on surface transverse crack of S355J2 steel

2014, 30(3):  69-73. 

Asbtract ( 204 )  

Related Articles | Metrics

On account of current status quo of S355J2 steel’s cracks in the production process, surface transverse cracks were analyzed by SEM and EDS, and low temperature brittle zone was detected by Gleeble-1500 test. The morphology and size of precipitates were analyzed by using TEM, and thermo dynamical calculations of precipitates were counted. The results indicated that the sulphur segregation at the grain boundary formed sulfides and increased the brittleness of grain boundary when γ→α transformation occurred which lead to rise the susceptibility of transverse cracks in steel. The low temperature brittle zone was 750—910 ℃, and the temperature of transverse crack susceptibility range was 745—903 ℃, which was in correspondence with the former. The ductility of steel decreased while the size of precipitates decreased, so did the thickness of ferrite film increased.

Improvement of surface sliver defect for hot rolled SPHC strip

2014, 30(3):  74-78. 

Asbtract ( 272 )  

Related Articles | Metrics

The reason of sliver defect on the surface of hot-rolled SPHC strip was investigated. The results showed that mold powder entrapment caused by the clogging of submerged entry nozzle was the predominant reason in the process of continuous casting. Calcium treatment thermodynamics and tundish flux chemistry were optimized based on the thermodynamic calculation and industrial experiments. After the optimized processing parameters were used, the clogging issue of submerged entry nozzle was resolved effectively, mold level fluctuation could be steadily controlled at less than ±3 mm, and surface sliver defect of hot-rolled SPHC strip was significantly reduced.