In order to solve the problem of poor mirror polishing effect of steel used in plastic die， the polishing efficiency of die steel is improved by optimizing smelting process. The results showed that the mirror effect was closely related to the purity of steel. From the electric arc furnace burden structure， deoxidization system， LF refining furnace argon blowing control， high vacuum degree cycle of VD vacuum furnace and mold casting process optimization， more comprehensive improvement measures were taken， that is， increasing the use of DRI， using silicon predeoxygenation， optimizing the argon blowing control of steel ladle bottom and improving the high vacuum cycle of VD.The effective size of inclusions decreased from 27.93 μm to 23.65 μm before optimization. The number density of inclusions decreased from 256 / cm ² to 176 / cm ²， and the number density of inclusions decreased by 31.2%. The total amount of B and DS and TiN inclusions was controlled， and the customer satisfaction of polishing performance was recognized.

The development of electric arc furnace （EAF） short process steelmaking is an important way for the iron and steel industry to realize the goal of "double carbon". In recent years， the modern EAF technology has been developing rapidly， and the bottom-blowing stirring technology of EAF is also progressing and being promoted， which makes an important contribution to the high efficiency and energy saving in production with EAF. This paper summarizes the mechanism， process characteristics， system composition， gas type， bottom blowing element type and process arrangement of the electric arc furnace， and summarizes the application of the bottom blowing technology. Simulation calculations shows that the flow 
rate of molten steel is obviously low in the area far away from the bottom blowing device. By arranging the bottom blowingdevice and optimizing the volume of bottom blowing gas in conjunction with the furnace characteristics， it is possible to effectively enhance the dynamic conditions of the molten pool， facilitate the mass transfer of elements within the molten steel， thereby achieving the goal of reducing energy and raw material consumption， and enhancing production efficiency.Therefore， it can be inferred that conducting research， combining different techniques such as blowing， power supply andpowder injection， formulating bottom blowing process system according to the characteristics of different new furnaces， as well as realizing intelligent bottom blowing are important directions for the development of short process steelmaking of modern EAF

The new process of EAF→VOD→LF+VD→ pouring 6 t electrode rod → vacuum consumable remelting （VAR） with lower smelting cost was adopted to produce 15-5PH stainless steel instead of the traditional VIM+VAR process， the causes of point defects were analyzed by scanning electron microscopy and ASPEX detection methods. The results show that calcium aluminate and aluminum spinite exist in the self-consuming electrode， the instability of vacuum consumable remelting process will draw the ingot crown and non-metallic float into the melting pool and remain in the consumable ingot， resulting in point defects after forging.Through process optimization and improvement， the VOD reduction slag is adjusted from 9 kg/t aluminum to 8 kg/t ferrosilicon and 5 kg/t aluminum， the composition of refining slag is adjusted from （mass fraction）CaO 50%-55%， SiO ₂ 10%-15%， Al ₂O ₃ 20%-25% to CaO 45%-50%， SiO ₂ 5%-10%， Al ₂O ₃ 33%-38%， vacuum consumable remelting speed is increased from 4.2 kg/min to 6 kg/min， and the melting drop time is increased from 0.23 s to 0.27 s， the cleanliness of consumable electrode has been greatly improved， the melting speed has been controlled steadily， the non-metal floating matter on the liquid surface of the molten pool has been removed， low and high magnification inspection of the finished material have met the standard requirements， and the inspection pass rate has been increased to more than 98%.

The effects of adding different ratios of DRI （direct reduced iron） to Consteel EAF on smelting technical and economic indicators， molten steel cleanliness， and the ingredients of acr furnace final slag were studied by conducting experiments on all scrap steel and adding 10%， 20%， and 30% ratios of DRI. And based on the experimental results， the key points of smelting control such as adding metal materials， blowing oxygen and carbon， adding slag making auxiliary materials， and slag discharge were analyzed.The results show that as the proportion of DRI added increases， the consumption of electricity， steel material， slag making auxiliary material， and slag amount gradually increase. When the proportion of DRI addition is 30%， due to the large amount of slag， slag overflows from the furnace door in the middle and late smelting process； At the same time， the cleanliness of the molten steel significantly increases after adding DRI to the EAF， and the mass fraction of nitrogen， phosphorus， sulfur and residual elements at the end of EAF smelting is reduced. And as the proportion of DRI added increases， the rate of decrease in nitrogen mass fraction at the endpoint of the electric furnace decreases. In addition， with the increase of DRI addition ratio， the FeO mass fraction of final slag showed a decreasing trend. When DRI is added at a proprotion of 20%， the effect is better， the smelting cycle is lower， the increase in electricity consumption is not high compared to the total scrap steel furnace， and the nitrogen and residual element content is lower， meeting the requirements of most steel grades.

The practical application of particle dephosphorization with compound injection agent on 130 t electric arc furnace is carried out. The composition of dephosphorization slag system in the oxidation period of electric furnace is designed, basicity of slag is controlled between 2.2-2. 8, and the content of iron oxide is controlled between 15% -20%. The composite powder of carbon powder (15% -20%), CaO powder (40% -60%), MgO powder (25% -30%) and CaC powder (5% - 10%) prepared in a certain proportion is injected with nitrogen as the carrier. After adopting the smelting process of injection compound injection agent on EAF steelmaking of 40Cr, 0.45C steel, 20CrMnTi and 60Si ₂Mn etc alloy steels, the reaction area of flux is accelerated, the slag forming speed is improved, and various production indexes are improved. Among them, the power consumption per ton steel is reduced by 90 kWh/t, the steel material consumption per ton steel is reduced by 9. 3 kg/t, the flux consumption per ton steel is reduced by 4. 8 kg/t, the productivity is increased by 5% -6%, and the comprehensive production cost per ton of steel is reduced by 25 yuan/t.

With the gradual improvement of the system science system， the iron and steel production mode has undergone a transformation from the empirical mode to the scientific production mode due to scientific innovation and development， the iron and steel industry with the characteristics of the process system can apply the system engineering approach to think and analyze as a whole， with the technical means of systems science to abstract the complex electric arc furnace steelmaking process description， the complex involving multiple states of matter and energy states of the electric arc furnace The abstraction of the steelmaking process into a unit system with material and energy transformation as constraints， a comprehensive understanding of the energy and material transformation process in the electric arc furnace steelmaking production， the constraints additional process timing factors， you can establish a process model for the simulation of the production process， for the actual working conditions of the electric arc furnace smelting process system analysis and abstraction， to be able to establish a process control model with process operation as the control factor， for the actual production of furnace charge It can analyze the key process factors affecting the technical and economic indexes， solve the problem of "synchronization" of target temperature and carbon content， and achieve the production effect of shortening the smelting cycle of single furnace by 2 minutes.

The technical characteristics of electric arc furnace steelmaking with direct reduced iron as a substitute for scrap steel are analyzed， and the main factors affecting the smelting power consumption are expounded . The results indicate that a large amount of steel left in melting pool （≥ 40%） and intensive mixing such as enhanced oxygen supply， bottom blowing， and electromagnetic stirring are important ways to promote melting and shorten the tap-to-tap cycle （which can be shortened by 8%-10%）. The proportion of direct reducing iron exceeds 30%， continuous feeding should be used. The feeding speed in the early and middle stages of smelting is generally equal to the melting speed of 28-33 kg/min （power supply power is 1 MW）. It is necessary to match lime and dolomite to prevent the erosion of slag line， and the whole smelting process should be sprayed with carbon foam slag to ensure the power supply efficiency. To reduce power consumption of smelting， direct reduction iron with high C content， high metallization rate， low SiO ₂ content， low P content， low S content， and higher temperature should be used as much as possible within a certain suitable range （that is， w［C］ 1%-4.5%， metallization rate ≥ 90%， w［SiO ₂］ ≤ 6%， w［P］ ≤ 0.1%， w［S］ ≤ 0.04%）. The compact short process combining direct reduction iron vertical furnace and electric arc furnace is an important direction for low-carbon， energy-saving， and clean production.

 In view of the low free-opening rate of 100 t Electric Arc Furnace （EAF） in a factory， using Fluent software to study the flow characteristics of liquid bath with different deflection angles of oxygen lance. It is found that when the deflection angle of oxygen lance increases from 0° to 30°， the EBT dead zone is virtually eliminated， but the impact strength of molten steel on furnace wall increases by 148.4%. In order to balance the impact strength of furnace wall and liquid bath stirring， the optimization scheme of 1 ^#， 3 ^# and 4 ^# oxygen lance deflection of 10° and 2 ^# oxygen lance deflection of 30° is determined. The practice shows that the free-opening rate increases from 75.2% to 95.6%， the average tapping temperature is reduced by 6 ℃.The application data on ML08Al steel show that the end-point oxygen in molten steel is reduced by 20.9%， and the end-point T.Fe content mass fraction in slag is reduced by 21.6%.

Daye Special Steel trial-produced Ф800 mm diameter high carbon chromium bearing steel GCr15SiMn2 large specification forging material through the process of 70 t electric arc furnace +LF + RH refining-20 t die casting ingot-forging ， the products are used to make ≥5MW high power wind turbine main bearings. By means such as controlling the residual elements ［Ti］≤0.001 6%、high basicity slag refining ［CaO（48%-55%）-SiO ₂（3%-8%）-Al ₂O ₃（30%-40%）-MgO（4%-6%）， basicity R≥6］， RH vacuum treatment，protective casting， reasonable pouring process （pouring temperature and speed） ， two times upsetting and stretching process （comprehensive forging ratio ≥4） and other measures， it can meet the microstructure level of steel 1.0 class， the rating of inclusions for B fine， D fine and Ds in steel were 0.5-1.0 class， carbide banding level CZ7.5， the hardenability J45 mm reach 61.0HRC， all performance meet the standard requirements.

Cr12MoV flat steel mainly adopts the long process of die casting ingot， multi-fire forging and rolling， which has low production efficiency， low yield， high cost and high energy consumption. In order to solve the problems of poor thermal conductivity and ductility of cold working die steel， a short process of 90 t EBT-LF-VD-150 mm×630 mm continuous casting rectangular billet and one-fire heating +15-pass rolling was designed. The rectangular continuous casting billet and rolled 19 mm thick flat steel products of Cr12MoV steel were successfully developed， continuous casting center porosity 1.5 grade， center segregation ≤1.0， the finished flat steel eutectic carbide unevenness level ≤3， the defects inspection quality grade reaches grade A， and the performance indexes meet the standard requirements. Cr12MoV cold working die steel products have achieved mass production and achieved good economic benefits.

In order to achieve the goal of high cleanliness of high-speed gear steel，especially the size of single-Particle D spherical inclusions ≤10 μm， electroslag process was developed to produce high-speed rail gear steel 18CrNiMo7-6 （/%：0.15-0.21C， ≤0.40Si，0.50-0.90Mn，1.50-1.80Cr，1.40-1.70Ni，0.25-0.35Mo，≤0.010P，≤0.010S），Φ250 mm steel billet production process is EBT electric furnace -LF-VD- casting 5.6 t electrode billet - electroslag remelting - forging - annealing - inspection. The electroslag slag system of 5.6 t electroslag ingot is CaF ₂∶Al ₂O ₃∶CaO∶MgO=65∶20∶10∶5 ， in the smelting process the melting rate is controlled at 500-550 kg/h，and the slag amount is 180-200 kg. Compared with the old slag system ，after adopting the new slag system the cleanliness of the produced high-speed gear steel is ［O］≤15×10 ^-6， ［H］≤1.0×10 ^-6，P≤0.008％，S≤0.005％，and non-metallic inclusion rating of A，B，C ，D and Ds series≤1.0 grade ， and the size of single-Particle D spherical inclusions is≤10 μm. Other hardenability and mechanical properties  meet the requirements.

The 45Mn2R steel Φ40-50 mm rolled product is developed by ≥ 40% hot metal- 50 t EAF-LF-VD-180 mm x 220 mm cast billet-rolling flow sheet. The cleanliness and casting ability are improved by controlling EAF end [C] ≥ 0.10% ,[P] ≤ 0.015% , tapping temperature 1 620-1 660 °C , preliminay deoxidation using " recaburizing agent + (15%Ca-12%Al-45%Si) compound deoxidation reagent + (50%CaO-34%A1 ₂O ₃-4%MgO) synthetic slag" during tap ping, S content in metal ≤ 0.010% before Ca treatment, feeding S wire after Ca treatment for 20 min, soft blowing for 20 min after VD etc process measure. Results show that produced 45Mn2R steel (/% : 0.43-0.46C, 0.22-0.27Si, 0.009-0.017P, 0.065-0.086S, 0.32-0.36Cr, 0.003-0.010Ti, 0.013-0.034AIs) has better comprehensive properties to meet user requirement.

Quality stainless steel 1. 4104 ( /% ：0. 16C,1. 23Mn,16. 40Cr,0. 41Ni,0. 43Mo,0. 023Ca ) for electro-hydraulic controller has been first melted at Daye Special Steel Co Ltd by 20 t electronic arc furnace and refined in ladle furnace and vacuum degassing unit, cast 1. 2 t ingot and forged into products. The transverse mechanical properties and machinability have been enhanced significantly by feeding bismuth cored wire（Bi：0. 036% ) and adding rare earth nodulizer (Ce： 0.054% ). Comparing with that of the free Bi-Ce steel, the total number of inclusion of the containing Bi-Ce steel decreases by 84. 4% and the number of MnS inclusion decreases by 85. 5% , average size of inclusion increases from 4. 5 μm to 13. 7 μm and cut force lower by 70～80 N with thicker and more easily broken chips, the transverse reduction of area increases from 3% to 17% .

The experimental data of 400 heats of steel produced by 110 t EAF + LF/VD refining + continuous casting + hoi rolling in a special steel plant are statistically analyzed. The hardenability [at (920 ± 10) °C for 50 min and then air cooling to room temperature,followed by holding at (880 ±5) °C for 30 min water quenching] and chemical composition of 20CrMnTiH steel are obtained by means of Jominy test and spectral analysis to get a linear relationship between the hardenability and the content of residual boron. By each steelmaking practice analysis it is found that the main source of B in steel is EAF tapping slag. The content of B in steel can be effectively controlled by controlling the amount of tapping slag in EAF tapping. In addition, when the amount of Al ₂O ₃ in the refining slag decreases from 30 % to 15% ~20% ,the content of B in steel can be controlled below 0. 000 2%.

The Φ219 mm x 20 mm seamless tube of 09MnNiD steel (/% ；0.07 ~ 0.10G,0. 25 ~ 0.35Si, 1.35〜1.40Mn,0.49 〜0.51Ni,0.020 ~O.O35A1, ≤0. 02Nb, ≤0.015P, ≤0.006S) has been produced by 20 t EAF—LF + VD→ ingot casting —► rolling Φ270 mm round billet—► cross piercing → CPE rolling tube—► online normalization. By con trolling EAF endpoint [C] ≤ 0.04% and [ P] W≤ 0. 008% , LF refining [S] ≤ 0.005% ,VD≤67Pa, 15 min, ingot cast steel overheating ≤ 45 °C , cooling rate of hot rolled piercing shell 30 ~70 P/min, and steel tube normalizing at 910 °C. The test results show that the microstructure is F + P, grain size grade 10, —70 °C impact energy KV2 3257 J, tensile strength 503 〜508 MPa,yield strength 354~356 MPa,and the chemical composition, mechanical properties, nondestructive testing meet the requirements of GB 150.2-2011 standard.

The evolution of inclusions in gear steel 18CrNiMo7-6 produced by 70 t EAF + LF + RH process is systematically analyzed and studied by means of whole process sampling and ASPEX test. The test results show that sampling after adjusting the composition during LF refining the removal rate of inclusions with size 1 ~ 10 μm is 89% , with > 10 μm is 97% , from adjusting the composition during LF refining to the end of soft blowing, and the removal rate of size 1 ~ 10 μm inclusions reaches 54% removal rate of inclusions > 10 μm is 66% , and the inclusions > 20|im are basically removed. The inclusion completes the transformation from Al ₂O _3 → Al ₂O _3 · MgO →Al ₂O ₃ · CaO.