Table of Content

05 December 2018, Volume 34 Issue 6

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numerical simulation and optimization practice of high Mach oxygen lance

2018, 34(6):  1-6. 

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Transformation of automatic steel-making was carried out at a steel plant in northern China. In this process, lost of problems had emerged such as low intensity of oxygen blowing , long smelting period, much splashing of molten metal and short lifespan of lance head. According to the fact above, the parameter and operation of oxygen lance have been designed and optimized again and the interaction between the oxygen lance jet and the molten pool has been analogously simulated by Fluent fluid dynamics software. The result shows with the increase of the Mach number of oxygen lance from 1.9 to 2.15 and the change of lance and flow through the L/L0 control, the oxygen lance jet with high Mach number can perform fully and problems mentioned above have been significantly improved as expected.

Study on MHP selection in converter bottom blowing

2018, 34(6):  7-10. 

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After several decades of continuous development，MHP (Multiple Hole Plug) porous plug has become one of the main form of gas supply components. In the current paper，the converter bottom blowing process was calculated theoretically，and the MHP element parameters matching with the gas flow rates were calculated. The results showed that，the MHP bottom blowing had a favorable flow range，which was limited by facility and external pressure. Bottom blowing flow rate was directly proportional to the bottom blowing outlet pressure with clear conversion relationship. Under the certain blowing flow rate，MHP parameters should be selected carefully.

Production process optimization and practice of 150 t LF

2018, 34(6):  11-14. 

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By optimizing the temperature control of LF inlet molten steel, argon blowing control and slagging control, the average temperature of LF inlet molten steel increased from 1 552 ℃ to 1 573 ℃, the roughing slag amount decreases from 60 mm to 45 mm, the stirring energy of molten steel is about 9 000 W/t in LF desulphurization, the average w(FeO) of LF inlet steel slag reaches 1.04 %, and was about 0.5 % in refining process. The basicity of refining slag reached 2.9—3.2, the average first desulfurization rate increased from 59.87 % to 85.54 %, and the refining cycle shortened from 58.3 min to 47.9 min. The production rhythm was accelerated and the production cost was reduced.

Thermodynamic analysis of elemental composition change on the precipitation of sulfides in non-quenched and tempered steel

2018, 34(6):  23-29. 

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The effects of compositional changes on the precipitation of sulfides in non-quenched and tempered steel C38N2 were calculated by Thermo-Calc/DICTRA thermodynamics and kinetics software. It is calculated that the increase of C, Si and Al content can reduce the initial precipitation temperature of MnS in non-quenched and tempered steel. Among them, the change of C content has the most obvious influence on the precipitation temperature, the change of Al content has little effect on the initial precipitation temperature of MnS, and the effect of Si content change on the initial precipitation temperature of MnS is between C and Al. The change of Mn content has a great influence on the equilibrium precipitation of MnS phase. With the increase of Mn content, the precipitation temperature of MnS also increases, and the precipitation of MnS in high temperature zone can be promoted. The change of N content has little effect on the precipitation temperature of MnS, but with the increase of N content, it can promote the precipitation of MnS in high temperature zone. However, when the N mass fraction is increased to a certain extent (0.015%), the change in the N content does not affect the precipitation behavior of MnS. The change in Nb and V content has little effect on the thermodynamics of MnS precipitation in non-quenched and tempered steel, and the initial precipitation temperature of the second phase is lower than the initial precipitation temperature of MnS. However, Ti has a great influence on the precipitation of MnS in non-quenched and tempered steel. When the Ti mass fraction reaches 0.01%, the initial precipitation temperature of TiN is higher than the initial precipitation temperature of MnS, so that TiN is precipitated earlier than MnS. When the Ti mass fraction is more than 0.02%, Ti will suppress the precipitation of MnS in the high temperature region. And this phenomenon also explains the presence of MnS inclusions with (Nb, Ti)N as the core in non-quenched and tempered steel.

Improvement of the refractory materials used in tundish cover

2018, 34(6):  30-33. 

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This paper calculates heat dissipation and the inner and outside surface temperature of three different framework of tundish cover by the related theory of heat transfer, the lining which has small coefficient of thermal conductivity is propitious to preserve heat and to reduce the surface temperature of tundish cover，that would increase the service life of steel structure. The calculating method afford a theoretical basis for choosing lining of tundish cover.

Improving internal quality of 220 mm×260 mm bbearing steel bloom with soft reductin

2018, 34(6):  34-39. 

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This study established a mathematical model of solidification and heat transfer for 220 mm×260 mm bloom, which was verified through the nail-shooting experiments in the narrow side of the bloom. The solidification heat transfer model was calculated for the pull down and soft reduction section and the results were applied to industrial test. The results show that the center segregation and shrinkage cavity significantly improve when the casting speed is adjusted to meet the required soft reduction zone as a matter of priority. Except for the internal crack, the internal quality of the bloom has not been improved obviously because of the unreasonable soft reduction position and distribution of reduction amount.

Evaluation of oxide inclusions in wheel steel by fatigue test method

2018, 34(6):  40-46. 

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In this study, a method was proposed to evaluate the shape, the size and the chemical compositions of oxide inclusions in railway wheel steel. The evaluation method which consists the surface strengthening process and the fatigue test was carefully designed. The ultrasonic inspection was first conducted to CL60 wheel to identity the regions which contains densely-distributed defects and single defect, respectively. The samples were taken from both of the identified regions, and then the shape, the size and the chemical compositions of the defect within the wheel steel were evaluated using the proposed method. The evaluation results show that the single defect is the macro-inclusion with millimeter scale, while the densely-distributed defect is the micro-inclusion with micrometer scale. The macro-inclusion mainly contains Ca, Si and Mg, while the micro-inclusion mainly contains of Al and Ca. Both of the inclusions are in a shape of slender ellipse. According to extreme values method, the largest micro-inclusion which can induces subsurface-initiated fatigue was predicted to be [752 μm，1 168 μm] within 95 % confidence intervals in a wheel.

Practice on the control of defects in cold rolling of medium and high carbon superior steel

2018, 34(6):  47-50. 

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The peeling defects of 65Mn and 50 cold rolled narrow strip steel were examined in detail by SEM-EDS. Combined with the related quality issues arising from the production process, the main causes of the defects were analyzed, and put forward the improvement measures. After optimization，the defect rate of large peeling was reduced from 1.44 % to 0.015 %，the defect of tiny peeling was eliminated in cold-rolling product，so that the surface quality of products meets the needs of users.

Analysis and quality improvement of low reduction of area in grade 10.9 high-strength bolts

2018, 34(6):  51-56. 

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When producing grade 10.9 high-strength bolts with SCM435 steel hot rolled wire rods, the reduction of area of the finished products was lower than the standard requirements. For this quality problem, the composition of the bolts, microstructure and properties were examined, and the microstructures of the defects were examined by SEM-EDS scanning electron microscopy. The reason for the unacceptable bolt shrinkage rate is that there is an M-belt in the center of the bolt, and at the same time, the core M of the hot-rolling coil breaks due to the cold-drawing process, causing crack defects in the core of the bolt. Based on this phenomenon, in order to improve the performance of bolts, relevant tests have been carried out on the quality control of hot-rolled materials and user processes. It was concluded that by reducing the degree of superheat in the steelmaking process, using hot mill rolling for steel rolling, and adopting reasonable cold working and quenching processes by the user, the segregation of the internal components of the rolled material can be effectively reduced, the state of the organization can be improved, To avoid the influence of the hard-phase structure of the core M on cold work and the performance of finished bolts, So as to achieve the purpose of increasing the bolt shrinkage.

Causes analysis and technology improvement of incompetent properties of HRB500E reinforcing steel

2018, 34(6):  57-60. 

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Based on the statistical results of low strength batches of HRB500E reinforcing steel and the analysis of chemical composition, non-metallic inclusion and weight，the reasons for low strength of reinforcing steel were analyzed in combination with rolling process parameters. The analysis results shows that the reason for HRB500E reinforcing steel low intensity is related to the low heating temperature in the reheating furnace. Based on the analysis results above, with the discussion of vanadium function mechanism for the HRB500E steel，the heating system which influenced dissolution and precipitation were analyzed. On this basis, the heating systems was improved，then the low strength of HRB500E reinforcing steel was eliminated.

Effect of solidification mode of TP304L stainless steel on the inner wall upwarping of pierced billet

2018, 34(6):  61-63. 

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Aiming the upwarping in the inner wall after TP304L stainless steel pierced，the organization of upwarping samples were analysied by high magnification electron microscope. The result shows that the main reasons for the formation of cracks on the inner wall is the lath ferrite, and th elath ferrite is due to solidication mode. The question was solved after the solidification mode was adjusted from FA mode to AF mode.

Research on oxide metallurgy process withTi-Mg-Ca deoxidization system

2018, 34(6):  64-68. 

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In order to further optimize the oxide metallurgy production process withTi-Mg-Ca deoxidization and improve product quality, samples were taken at each process node, and the composition, quantity, size and final effect of oxide metallurgy were analyzed by SEM, OM and Gleeble-3800 dynamic thermal simulation test machine. The type of inclusions was changed from silicon manganese oxide to magnesium aluminum spinel containing titanium, and then to composite inclusions dominated by aluminum titanium calcium oxide. LF and the degassing process of RH had obvious effects of inclusion removal and refinement. Impact work at –40 ℃ of heat affected zone after 150 kJ/cm and 200 kJ/cm welding simulation respectively were 216 J and 208 J. The microstructure of the heat affected zone was mainly acicular ferrite and grain boundary ferrite.

Numerical simulation of twin-fluid atomization characteristic and evaporation characteristic of evaporative cooler

2018, 34(6):  69-74. 

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A comprehensive three-dimensional mathematical model, which adopted Euler-Lagrange approach, was developed to study the liquid membrane broken of twin-fluid atomizer in evaporative cooler. The influence of air-liquid mass ratio on Sauter Mean Diameter (SMD) of droplet and droplet size distribution on evaporation efficiency were analyzed, and the simulation results were compared with the experimental data. The results show that the simulation results coincide with the experimental data. The result shows that the SMD of droplet decreases with the increase of air-liquid ratio. The bestair-liquid ratio is 0.1,the SMD of droplet is 63 μm. Droplet penetration distance are less affected by initial velocity, which is mainly related to particle size. The simulation showed that with the diameter of droplet getting smaller, the complete evaporation time of droplet become shorter. Droplet with diameter less than 250 μm can be completely evaporated in 0.6 s, butthe maximum evaporation time of different drop diameter is 20 times higher.

Analysis and application of steel slag by pressurized hot magnetic separation and purification process in overseas projects

2018, 34(6):  75-78. 

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This paper mainly introduces the application of steel slag in Malaysia “one belt one road” iron and steel project. The regular pattern of combustible gas generation in hot stuffy production of steel slag was analyzed, and the corresponding preventive measures for safety accidents were put forward to ensure the safety in hot stuffy process with pressure.The favorable factors for magnetic separation of steel slag by hot stuffy process with pressure were analyzed. The conclusion can be used for reference in overseas application of steel slag hot stuffing process with pressure and magnetic separation purification line.