Table of Content

05 June 2013, Volume 29 Issue 3

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生产实践

Coldmodel simulation and application of slag splashing in 120 t topbottom combined blowing converter

2013, 29(3):  1-5.  doi:

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Coldmodel simulation experiments on slag splashing in a 120 t top-bottom combined blowing converter were carried out. By measuring singer factors (e.g. topblowing gas flowrate, slag viscosity, lance height and slag amount), along with orthogonal test, the optimal parameters were obtained. The order of the factor that affect slag splashing was obtained through the range and variance analysis, which is topblowing gas flowrate > slag viscosity > lance height > slag amount. Finally, the optimized experimental program is that: lance height is 160 mm, topblowing gas flowrate is 51 m³/h, slag amount is 12 %, slag viscosity is 0.000 89 Pa·s，and the splashing density obtained is 23.07 g/(m²·s). It is applied in Tianjin Iron and Steel Group Co.,Ltd., and satisfied result is achieved.

Optimization on metallurgical quality of martensite stainless steel

2013, 29(3):  6-9,18.  doi:

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Based on theory of “decarburization and chromium yield” on smelting of stainless steel and process optimization in AOD refining, the globular oxide inclusion rating is below 2.0 and w(C)=0.02 %～0.04 %、w(Si)=0.49 %～0.53 %、w(Mn)=0.60 %～0.69 %、w(Cr)=12.90 %～13.57 %、w(Ni)=3.95 %～4.34 %、w(S)≤0.015 %、w(P)≤0.028 %、w(O)≤80×10^-6、w(N)≤150×10^-6、w(H)≤3×10^-6 in the high quality steel can be obtained. New process significantly raised martensite stainless steel cleanliness, satisfy the smelting composition and various physical and chemical indicators.

Production practice of lowphosphorus steel grades in PZH steelmaking Plant

2013, 29(3):  10-13.  doi:

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Single slag process and double slag process are used to product low phosphorus steel in Panzhihua Steel & Vanadium Co., Ltd., and single
slag process is primary in actual production. Combined with single slag process low phosphorus steel production of industrial test results, the
ratio of the mass fraction of phosphorus below 0.008 % in molten steel is above 97 %, through controlling the carbon content of the end of converter, temperature and rephosphorization in alloying process. Double slag process can stability control the mass fraction of phosphorus below 0.008 %.

Analyse and improve the intermediate crack in continuous casting slab based on QES

2013, 29(3):  14-18.  doi:

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Aim at the situation that the inner cracks usually appeared in slab of Tangshan Medium Thickness Plate Co., Ltd., threedimensional dynamic cooling system and QES that CCTEC developed were applied online. The slab quality was improved significantly after these two systems ran in normal operation. Based on QES, the impact of production process, composition of molten steel and equipments running status on intermediate cracks were analyzed in the paper. The results showed the main reasons of causing middle cracks were higher content of sulfur, lower ratio of w(Mn)/w(S), the variation of roll gap and the nozzle clogging as well. Finally, the incidence of
intermediate carcks on slab decreased obviously after raising and using the improvement measures.

Improvement of intermediate crack in continuous casting slab with trace boron

2013, 29(3):  19-22.  doi:

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The distribution characteristics of intermediate crack, as well as high temperature mechanical properties of A36 (without boron) and A36B (with boron) slabs are investigated. The result shows that zero ductility temperature decreases after the addition of boron due to the formation of low meltingpoint borides, sulfides and phosphide at the final solidified grain boundary region. On the other hand, the higher strain caused by the mismatch of roll gap during the bending and unbending process will results in the formation and propagation of the cracks along the interdendritic region. Correspondingly, countermeasures to eliminate intermediate crack are put forward, including reducing the content of impurity elements and enhancing the maintenance of roll gap, and then intermediate crack in A36B slabs are decreased.

Formation and control of CaS inclusion in gear steel 20CrMnTiH1

2013, 29(3):  23-27.  doi:

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The themodynamic analysis on formation of (CaO)_m(Al₂O₃)_n and CaS inclusions in gear steel 20CrMnTiH1 using the Factsage.The result shows that when the mass fraction of solute aluminium is 0.035 %,the mass fraction of sulfur is lower than 0.006 7 % and the value of w(Ca)/w(Al) is higher than 0.12,the liquid approximate (CaO)₁₂(Al₂O₃)₇ inclusions will produce in the molten steel. The calcium sulfide inclusions can not be produced inself in molten steel under the condition of this composition experimental steel.The CaS inclusions are precipitated by the reaction of sulfur with CaO of the surface layer of lower melting pointing ((CaO)₁₂(Al₂O₃)₇ inclusions with the temperature of molten steel drop to 1 739.8 K and the sulfide content reached 0.015 9 % at the frontier of solidification.With analysis of the steel sample,it is found that the result is consistent with theoretical calculations. It is obtained by calculation that the mass fraction of sulfur must be controlled below 0.000 318 % when the gear steel 20CrMnTiH1 can not precipitate CaS inclusion in solidification processing.

试验研究

Research of slagless steelmaking and technology control in converter

2013, 29(3):  28-31.  doi:

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Through thermodynamics and material balance analysis, the relation of slag quantity, silicon content of hot metal, and phoshorus distribution (L_P) was obtained. The higherL_P is, the lower slag quantity and silicon content would be required. On the base of regularity study of the slagging and dephosphorization and desulfurization reaction characteristics at steelslag interface, the less slag steelmaking technology has been proposed. Results show that the lime comsuption has been control 29.01 kg/t, the slag quantity comes up to91.73 kg/t, the dephosphorization rate of steelmaking process reaches 90.08 %，L_P reaches 105.5 and L_S reaches 8.14. By means of influencing factors anlysis of L_P and L_S, the final controlling technology was that the basicity of final salg is controlled not less than3.5, and the mass fraction of T.Fe of final slag is 18 %～20 %, preventing high tapping temperature.

Analysis of the total oxygen content and inclusions in 410S ferritic stainless steel during smelting process

2013, 29(3):  32-35.  doi:

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The total oxygen content and inclusions in 410S ferritic stainless steel produced by the route of hot metal pretreatment→AOD→LF→CC were studied. The results show that the total oxygen content，inclusions quantity and the inclusions size decrease throughout the AOD→LF→CC process. The inclusions after the AOD reduction and are mainly CaO-SiO₂-MgO-Al₂O₃compounds, while in LF refining and tundish. Additionally, the types of inclusions change at the different stage of the process. The variation of the composition of the inclusions during the route of AOD→LF→CC are related to the smelting process. The technology improvement measures in manufacture have been accepted on the basis of the research. The inclusion level of the steel are improved effectively and significantly reduce the occurrence of surface defects of coldrolling plates.

Effects of device shape of RH on characteristics of flow and mixing

2013, 29(3):  36-40.  doi:

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Flow characteristics of RH with enlarged vacuum chamber,ovalshaped snorkel and common type were analyzed and compared by water modeling and numerical simulation. The result shows the RH with ovalshaped snorkel has the best dynamics condition and other models has close result after measurement the circulation flow rate and mixing time. The decarburization in RH with ovalshaped snorkel was promoted by increasing circulation flow rate. The decarburization in hot metal surface of RH with enlarged vacuum chamber was enhanced greatly, which has strict requirement for gas flow and process operation condition. The crucial to improve refining efficiency was optimize geometric and gas parameters of RH system by absorb advantage of two improved models.

Effect of EMBr on the flow field and level fluctuation in CSP funnel type mold

2013, 29(3):  41-44.  doi:

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Through the coupling of turbulence model, multiphase flow model and electromagnetic brake (EMBr) model, the fluid flow and level fluctuation of CSP funnel type mold are simulated in the1 500 mm×90 mm CSP funnel type mold with the casting speed of 5 m/min. The numerical simulation results indicate that the application of EMBr improves the behaviors of fluid flow in the mold significantly. And the flow field inside the mold is more uniform. The maximum fluctuation height is obviously reduced from 15 mm under the condition of without EMBr to 9.2 mm and 2.33 mm when the magnetic flux density is 0.2 T and 0.3 T, respectively. Considering both the braking effect and the production cost, the magnetic flux density which is between 0.2 T and 0.3 T could be reasonable.

Effect of mineralogical structure of flux film on the slab quality for lowalloy steel

2013, 29(3):  45-48,5.  doi:

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In light of the slab quality problems in the production of lowalloy steel Q345B in Tangshan Medium Thickness Plate Company, the mould flux film structure, mineralogical phase and crystal rate have been roundly studied. While combining the quality of slabs, the reasonable mineralogical structure for Q345B steel slab casting is defined by analyzing performance of lubricity and heat conductivity. The results show that, the reasonable solidified film has two layers or more, in which mineralogical phase and glass phase are alternately generated; the mineralogical phase includes cuspidine and akermanite, of which the crystallizing process has a good tendency; with much glass phase, crystal rate of film ranges 35 %～65 %. In order to keep the slab quality well, casting mould powder for lowalloy steel Q345B should be added more bits of MgO and Fe₂O₃, meanwhile pouring crafts and operational conditions should be continually adjusted.

Study on precipitation of microalloyed steel slab in process of hotcharging

2013, 29(3):  49-52.  doi:

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The dynamic precipitation of microalloyed steel slab was investigated through simulating the process of hotcharging and coldcharging performed on Gleeble3500 thermalmechanical simulator in laboratory. The experimental results show that precipitation size increases with the rise of experimental initial temperature, and the cooling rate is the lower, the amount of precipitation is the larger. The austenitic grain was refined by adding titanium, TiN acting as the nucleation of the newly precipitating phases was prevented Nb from being precipitated dispersedly because of the higher formation temperature of TiN and the lower formation temperature of Nb(CN).

Analysis and control of inclusions in spring steel used in fastener of highspeed railway by the electrolytic method in nonaqueous solution

2013, 29(3):  53-57.  doi:

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The inclusions in spring steel used in fastener of highspeed railway were extracted without any damage by the electrolytic method in nonaqueous solution. The morphology, size and shape of inclusions were observed by SEMEDS and the influences of these factors on performance of fastener in highspeed railway were also analyzed. Based on the composition of this spring steel, thermodynamic equilibrium among molten steel, inclusions and refining slag was calculated, and the iso [O] and iso [Al] in CaO-SiO₂-Al₂O₃ system were obtained, which could provide theoretical basis for oxygen and inclusions control in steelmaking process.

Analysis on compositions and microstructure of the sulfur containing freecuttingnonquenched and tempered steels from domestic and abroad

2013, 29(3):  58-61.  doi:

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The comparative study about the sulfur containing freecutting nonquenched and tempered steels from domestic and abroad is done in this paper. The results show that the sulphur content from domestic samples is higer than that from abroad, and the Al_S and nitrogen contents are a bit lower, the total oxygen content of both from home and abroad samples are basically consistent, about 11×10^-6; The microstructures of the samples both from home and abroad consist of intergranular ferrite and pearlite, but the grain size for the foreign samples is coarser, compared to the domestic samples. The sulphides in foreign samples are dispersed distribution, their shapes tend to be spindlelike; but the sulphides in domesic samples are in uneven distribution, their shapes tend to be elongated.

Relationship of converter capacity and nonorder slab ratio

2013, 29(3):  62-64.  doi:

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Aim at the many specifications and small order quantity, it has been predicted by order that the nonorder slab ratio is respectively 28 %，34 %，38 % corresponding to converter capacity of 260 t，300 t，350 t. It has been predicted by actual production that the nonorder slab ratio is respectively 28 %，31 %，36 % corresponding to converter capacity of 260 t，300 t，350 t. The converter capacity is more, the nonorder slab ratio is more. Compared the converter capacity of260 t with300 tand 350 t, the spot contracts are separately less than 40 000 t and more than 50 000 t on 10 million ton steelmaking mill. The proper converter capacity can reduce nonorder slabs and the production loss.

辅助技术、材料及设备

Analysis and practice about dealing the dust and mud pellet containing iron with torpedo

2013, 29(3):  65-68,7.  doi:

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Through thermodynamic analysis of the torpedo deal with dust and mud pellets containing iron by ferric oxide direct reaction equation, the torpedo whether has enough heat to make the dust and mud pellet deoxidize itself after pouring hot metal have be investigated . Calculation shows that, the dust and mud pellet can be warmed up by torpedo after pouring hot metal, and hot metal can offer enough thermodynamics and dynamics conditions for selfreduction of the dust and mud pellet. Industrial test prove with dealing dust and mud ball with torpedo is feasible.

Research and application on process of disposal ironcarbon pellet in converter

2013, 29(3):  69-72.  doi:

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In this paper, the application experiment of ironcarbon pellet in converter was introduced. The selfreduction reaction carried out by the heat in converter, and the iron was recycled in this process. The influence of some parameters in converter and the beneficial results were analyzed. The best method of using ironcarbon pellet is that adding the pellet oneoff after accepting the hot metal. The yield of iron is 92.66 %. The quantity of sulfur element has the trend to raise by 0.000 38 % on average per ton of the ironcarbon pellet. 309.45 yuan could be saved by using ironcarbon pellet in producing one ton steel.

Effect of temperature on the evaporation of zinc from EAF dust reduced using silicon

2013, 29(3):  73-77.  doi:

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The effect of temperature on the evaporation of zinc from electric arc furnace dust (EAFD) by silicon was investigated. The experiments were carried out in a conductive furnace and the samples collected were analyzed with Xray Fluorescence (XRF), Xray Diffraction (XRD) and Scanning Electron Microscope (SEM) equipped Energy Dispersive Spectroscopy (EDS). The results show that when the mixture of silicon and EAFD was heated, the oxides of ferrum and zinc are reduced simultaneously. The evaporation amount of zinc increases with the temperature rising, and 95.90 % of zinc volatilizes from the furnace in the form of zinc fume at 1 300 ℃. The reduction of EAFD belongs to solidsolid reaction, and the formation of iron is conducive to the evaporation of zinc. The part of zinc remaining in the mixtures mainly forms the spinel solid solution (Mg,Fe,Zn) (Cr,Fe)₂O₄.