Steelmaking

The practice of low nitrogen steel in Less Slag Steelmaking

2015, 31(2): 1-4.

Asbtract ( 167 )

Related Articles | Metrics

The factors influencing nitrogen content in BOF were analyzed in less slag steelmaking. The results showed that the good equipments of top The factors influencing nitrogen content in BOF were analyzed in less slag steelmaking. The results showed that the good equipments of top oxygen blowing were very important. The nitrogen mass fraction of blowing end in steel could be within 12×10-6 using FeSi for raising temperature. The argon stirring at the BOF bottom in the whole blowing process could decrease nitrogen mass fraction of 3.3×10-6. The nitrogen content would decrease when some coolant were added to the BOF with the carbon mass fraction of 0.3%－0.4%. Reblowing and long tapping time would increase nitrogen content in steel. Through optimized measures the nitrogen mass fraction could be within 15×10-6 at the ladle and meet the demand of low nitrogen steel.

Optimization of RH produce technics for extra-low carbon steel

2015, 31(2): 5-8.

Asbtract ( 150 )

Related Articles | Metrics

Combining theory and produce practice in Qian’an Steel and basing on the principle of RH decarburization and production data, the decarburization process was divided into three stages：rapid stage, slow stage and sluggish stage. The influence of vacuum pressure, lift gas flow rate, opportunity of oxygen blowing and scrape or alloy mixing， the immersion depth of snorkel，the stick slag on hot offtake on decarburization were researched. The importance of vacuum equipment accuracy control was emphasized. It is concluded that the forward vacuum process can increasing decarburization rate, the lowhigh control mode of lift gas flow rate are suitable，and exhausting rate in tube can be increased by cleaning slag in hot offtake regularly. After process optimization，the success rate of extralow carbon was increased from 50 % to more than 90 % and average carbon mass fraction in steel at the end of RH treatment was controlled below 0.001%.

Critical technology of improving cleanliness of 20Mn2 steel

2015, 31(2): 9-12.

Asbtract ( 151 )

Related Articles | Metrics

Through analyses of samples and plant data, critical steps of improving cleanliness of 20Mn2 steel were obtained, and it included control of endpoint of converter, refining process and calcium treatment. Based on integrating thermodynamics and theoretical analyses with practical process, optimized scheme including control of peroxidation at endpoint of converter by governing w(C)≥0.08%, w(P)≤0.015%, modification of refining slag by adding bauxite and adjusting amount of CaO to limit composition of slag in the range of w(CaO)=50 %－60 %, w(Al2O3)=20%－40%，w(SiO2)=5%－10%，w(MgO)=5%, and domination of reoxidation and length of CaSi wire within 145－216 m was obtained. Industrial trials of optimized scheme showed that continuous casting heats increased from 5.9 heats to 14 heats，oxygen content in steel declined dramatically, amount and dimensions of inclusions diminished.

Study of controlling-sulfur technique in ultra low-carbon and ultra low-sulfur steel

2015, 31(2): 13-16.

Asbtract ( 129 )

Related Articles | Metrics

Some experience of the process and operation on refining ultralow carbon ultra low sulfur steel were introduced. Through the comparison of low sulfur and ultra low sulfur steel production, control routing of sulfur content was obtained，and process capability index of w(S)≤0.003 5 % in slab was increased from 0.85 to 1.13. By pretreatment of hot metal, material quality control，production plan optimization，desulfuration in RH, heats produced by ordinary process, the sulfur mass fraction within 0.003 % proportion can reach more than 90 % in slab. Heats produced by desulfuration process, the sulfur content within 0.002 % proportion can reach 100 % in slab. The control of sulfur element ability received a significant improvement.

Optimization on the flow distribution of 20 t three strand T shape tundish

2015, 31(2): 17-20.

Asbtract ( 170 )

Related Articles | Metrics

Based on the similarity principle，RTD curves of different testing schemes were investigated in 20 t three strand T shape tundish by using water model test. By analyzing of the scheme of RTD curves and the mixed model calculation results, the best optimization solution was concluded for the tundish retaining wall. After the flow optimization, mixing evenly time of liquid steel decreased from nearly 250 s to about 100 s, mean residence time increased from 500 s to 1 000 s, package dead volume decreased from nearly 60 % to about 20 %, every flow liquid steel temperature difference decreased from 5.33 ℃ to 1.17 ℃. The large inclusions (more than 50 μm) was not more than 6.5 mg/10 kg in slab, the small diameter inclusion size was less than 6 μm in steel. The production practice shows that the new tundish retaining wall is beneficial to the uniform temperature of molten steel and the probability of collision removal rate of inclusions.

Control on surface longitudinal crack of billet for 410 stainless steel

2015, 31(2): 21-25.

Asbtract ( 114 )

Related Articles | Metrics

To control longitudinal surface crack of 410 stainless steel billet，a few measures were employed such as composition optimization of molten steel, water flow rate adjustment of mould, chemical and physical properties improvement of mold powder and casting speed optimization，which was following the formation mechanism of surface longitudinal cracks of 410 stainless steel. As a result, the longitudinal surface cracks of 410 stainless steel was effectively controlled, production accidents as breakout were mainly avoided.Surface quality of slab was greatly enhanced，the surface longitudinal cracks in slab was decreased from 11.24 % to 2.18 %，the recondition rate of casting slab was reduced by 3.4 %.

Theoretical analysis and pilot production of two stepdeoxidization process for Q235 steel

2015, 31(2): 26-29.

Asbtract ( 155 )

Related Articles | Metrics

Based on the thermodynamic calculation of complex deoxidization with Al-Si-Mn, a two-step deoxidization process was proposed for Q235 steel. The first deoxidization step was carried out during BOF tapping, with suitable amounts of silicon, manganese and small amounts of aluminum; and the final deoxidization step was carried out during LF refining with aluminum wire feeding. The equilibrium state of the liquid steelslag system was calculated by the thermodynamic software Thermo-Calc. The results show that the dissolved oxygen mass fraction of the molten steel is 1×10-6 and the sulfur mass fraction of the molten steel is 1.5×10-6at LF end. The experiment results show that when the total aluminum mass fraction is 0.004 %～0.015 %, the total oxygen mass fraction is (20－35)×10-6 in steel and the sulfur mass fraction is less 0.012 % in steel at the end of LF refining, and the cost of deoxidized alloys can save 4.2 yuan/t.

Effect of calcium treatment on change behavior of inclusionsin sulfur-containing nonquenched and tempered steel

2015, 31(2): 30-35.

Asbtract ( 124 )

Related Articles | Metrics

The industrial test of inclusions modification by calcium treatment in sulfurcontaining non quenched and tempered steel was carried out. The effect of calcium treatment on inclusions evolution was obtained by the qualitative study in which inclusions changing with the development of process was analyzed by using SEM and EDS. In order to control sulfides morphology, the type，quantity and size of sulfides before and after calcium treatment were quantitatively analyzed by INCA Feature with automatically scanning inclusions function. It is found that calcium treatment can increase the quantity of compound sulfides, especially the calciumcontaining compound sulfides, and then in favor of reducing the proportion of long strip sulfides by forming more globular or spindle sulfides, finally improve the anisotropy of steel. The mechanism of sulfides modification by calcium treatment was further analyzed, it is concluded that under the premise that does not affect mechanical properties of steel, calcium treatment is advantageous to the control of sulfides morphology in sulfurcontaining non quenched and tempered steel through properly lowering molten steel cleanliness. It is feasible to use calcium treatment for sulfides morphology control in industrial production.

Comparison of Cleanness of Low Carbon Aluminium Killed Steel with Different RH Refining Process

2015, 31(2): 36-39.

Asbtract ( 166 )

Related Articles | Metrics

The process characteristics and steel cleanness of lowcarbon aluminum killed steel under different RH process routes were discussed. The results showed that: the w(T.Fe+MnO)of route 1 was 5 %-12 %, while route 2 was under 2 %, besides the lost of acidsoluble aluminium for route 1 was 54×10-6 more than route 2. Effective removal time of inclusion under route 2 was 64 min more than 45 min of route 1, and the total oxygen at mold through process route 1 was 13×10-6 higher than that of route 2. The total inclusion ratio of route 1 was higher than that of the route 2, and for rout 1, it has 10.6 % of the inclusions bigger than 5 μm,while only 3.6 % for route 2.The optimization measures were put forward respectively according to the different RH refining process.

Physical-mathematical simulation and application of flow field of molten steel in four-strand tundish

2015, 31(2): 40-43.

Asbtract ( 153 )

Related Articles | Metrics

Based on the prototype of a tundish for fourstrands symmetrical casting 360 mm×480 mm bloom, the effect of different flow control devices on flow field of liquid in tundish were studied by using geometric similarity raito 1∶3 water model to get optimum baffle. Results show that average residence time in tundish without flow control device is rather small, and dead area volume fraction was 50.09 %; with using the optimum new Ytype baffle, piston flow zone in tundish increased by 14.22 % and dead area volume fraction decreased by 32.49 %, the standard deviation of average residence time of two nozzle is small. Onsiteexperiment shows that T.O mass fraction in liquid in tundish is decreased by 45.61 % and total inclusions are reduced from 0.46 mg/kg to 0.17 mg/kg.

Study of the effect of EMS on the bubble distribution in slab surface layer

2015, 31(2): 44-48.

Asbtract ( 175 )

Related Articles | Metrics

The distribution of over 50 μm bubbles in slab surface layer with or without EMS was studied by using metallographic analysis method. The results show that the bubbles of the two processes cluster at a certain distance from the inner arc of the slab as the accumulation zone, but the bubbles distribution with EMS has no obvious symmetry about the centerline of the broad face. Numerical results from a flow analysis in the mold show that the main difference between the two processes is that EMS can improve flow distribution of the nozzle impact area. A more stable transverse flow appears the nozzle impacting area with EMS, which is helpful to the removal of the bubbles; while without EMS, there is a large longitudinal vortex area at the quarter of the broad face, which leads to the bubbles clustering and easily to be captured by the shell. The influence on the bubbles distribution with or without EMS was studied by combining the experiment with the simulation, it's important for the purity of the IF steel casting slab.

Research on formation of internal cracks by soft reduction in billet continuous casting

2015, 31(2): 49-53.

Asbtract ( 157 )

Related Articles | Metrics

To investigate the formation of internal cracks in steel billets during soft reduction with liquid core, fully coupled thermomechanical finite element models were developed by Abaqus/Explict, and sensitive temperature range of internal crack was calculated by solidification phase transition model. With the finite element models, the temperature distribution, the stress and strain states in the billet were calculated. The relation between internal cracks and equivalent plastic strain, as well as maximal principal stress was analyzed. The results indicate that internal cracks will be initiated when the accumulated strain exceeds the critical strain or the applied tensile stress exceeds the critical fracture stress during solidification. The results can provide references for the optimization of soft reduction in strand deformation distribution and improving the internal quality of the strand.

Study on the precipitation behavior of MnS and the formation of intragranular ferrite in low sulfur micro-alloy steel

2015, 31(2): 54-58.

Asbtract ( 146 )

Related Articles | Metrics

Low sulfur micro-alloy steel with Al-Si-Mn-Ti complex deoxidation was produced by vacuum induction furnace. Precipitation regularity of MnS was analyzed by thermodynamic calculation. The morphology, size and composition of inclusions and precipitation morphology of MnS on multiple oxide were studied by using FE-SEM with EDS. The results showed that the precipitation of MnS is mainly controlled by Mn and S contents and temperature of the steel. Mn-Si, Mn-Ti, Al-Mn-Ti and Al-Mn-Si complex oxides are all effective to be nucleation site for MnS. MnS takes on mosaiclike precipitation at Si-Mn oxides surface and is encapsulated at TiMn oxides surface. MnS can also be dissolved in Al-Ti-Mn and Al-Si-Mn oxides. The size of complex oxides that can induce formation of IGF is 2－3 μm.

Research on the corrosion mechanism magnesiachrome brick of RH snorkel

2015, 31(2): 59-61.

Asbtract ( 134 )

Related Articles | Metrics

The factors affecting the RH snorkel magnesiachrome brick erosion rates were researched. By controlling argon flow rate, developing a standard baking flames, changing the order of adding alloy, improving RH snorkel utilization, the common average life of the RH snorkel has been increased from 78 heats to 86 heats, increased by 10.25 %, and steelmaking costs are reduced effectively.

Industrial test on online detoxification of EAF stainless steel slag by silicothermic reduction process

2015, 31(2): 62-66.

Asbtract ( 188 )

Related Articles | Metrics

As chromium content in stainless steel EAF slag is very high, there is a certain leaching risk of Cr6+ from the slag. Silicothermic reduction process was adopted for reducing and detoxifying of liquid layer of the slag during the end of stainless steel smelting in this study. It is found that heavy metal oxide contents of the slag can be effectively reduced, of which Cr2O3 mass fractionis reduced from 6.10 % to 0.79 %, and the maximum detoxification rate can be upto 87.1 %. After detoxification, the phase of CaCrO4, which is the main phase containing Cr6+, was disappeared. According to the leaching toxicity test, the leaching of total Cr was reduced to 0.08 mg/L, while the leaching of Cr6+ was reduced to below 0.01 mg/L, and both of them were obviously far below the national standard's value. Thus, safe discharging and resource utilization of the treated EAF stainless steel slag can be realized.

Present situation and prospect of fine gas bubbles formation in the ladle shroud

2015, 31(2): 67-72.

Asbtract ( 166 )

Related Articles | Metrics

The small inclusions is hard to removal by buoyancy during continuous casting. The method of using highspeed liquid steel to break gas into fine gas bubbles to removal small inclusions in liquid steel is an alternative measure. Fine gas bubbles formation in the ladle and the existing problems was reviewed，and the formation process of small bubbles in the ladle shroud was analyed by the chemical industry’s relevant research results on bubble breakup and coalescence in turbulent liquid. It was found that the constriction of fine gas bubbles formation is the short residence time of initial bubble in the high turbulent region. At the same time, the method of controlling fine gas bubbles in the ladle shroud has been prospected.

the Resource Recycling of LF Refining Slag

2015, 31(2): 73-78.

Asbtract ( 201 )

Related Articles | Metrics

Because of the stacking covers and environment pollution problems increasingly prominent, the research of refining slag recycling is most great significance to enterprise's energy conservation and emissions reduction. The research status of recycling LF spent slag and the major problems were analyzed. It is considered that the focus of future research to the LF spent slag is the desulfurization. LF refining slag contains a lot of useful components, as long as the slag removes the harmful elements, LF refining slag can be recycled. Scholars have conducted extensive research on desulfurization in order to promote the LF refining slag recycling, and have made many achievements. It has great significance for achieving energy conservation.

Table of Content