Combined with the actual situation of X80 pipeline steel production in a factory, the dephosphorization process of combined blowing converter duplex process was tested, and the influence of basicity and oxidizability of converter slag on dephosphorization was studied. The results show that when the phosphorus content of hot metal is 0.118% and 0.116% , the alkalinity of the end slag CaO/SiO ₂ of dephosphorization furnace and decarburization furnace is 1.6-2.0 and 3.3-4.1 respectively ,and the content of T. Fe is 10%-15% and 20%-35% respectively, the dephosphorization rate of the dephosphorization furnace is as high as 50.85% , the average is 38.35% , the end dephosphorization rate is the highest 95.69% , the average is 94.88% , and the phosphorus content of the molten steel at the end of smelting is controlled below 0.007% , the minimum is 0.005% , meeting the production requirements of X80 pipeline steel.

The sulfur content in high-grade non-oriented silicon steel W310 is generally required to be less than 0.002 5%. Based on the manufacturing process of " KR― BOF—>RH—^continuous casting , the mechanism of KR deep desulphurization ,converter smelting and RH powder spraying desulphurization are analyzed and studied in this paper, combined with the working conditions and raw material conditions of the 300 t steel-making system, the thermodynamic and kinetic conditions improvement measures such as optimization of hot metal composition and temperature, composition adjustment of KR and RH desulfurizer, converter heal balance control, strong bottom blowing smelting and process sulfur load control are put forward. Application results show that after optimization, the ratio of sulfur content less than 15 x 10 ^-6 in once KR treatment has increased from 69% to 100%, and the sulfur content after treatment has decreased from 10.48 x 10 ^-6 to 7.07 x 10 ^-6. The average sulfur content at the end point of converter is 20. 10 x 10 ^-6, and sulfur pick-up by 13.03 x 10 ^-6 during process, which are 44. 8% and 49. 8% lower than before optimization, respectively. The sulfur content of RH liquid steel decreases from 19.50 x 10 ^-6 to 8. 65 x 10 ^-6 , the dosage of desulfurizer decreases by 55.9%, and the proportion of sulfur less than 25.00 x 10 ^-6 increases from 90.5% to 100%, good results have been achieved.

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.

In the light of problems of smelting ultra-low phosphorus steel (%/： <0. 03C、<0. 01 OP、<0. 015S、< 0.06Mn、vO. 02Cr、<0.02Ni), the lower liquid temperature at 90 t BOF tapping and serious overoxidation of liquid, led to heating refining by LF, are tested and studied by process optimization. The results show that during BOF (0. 018% - 0. 025% P) tapping process by adding lime and refining slag to produce slag with binary alkalinity 7 and P2O5 <0.5%, the dephosphorization rate of liquid in ladle reaches up to 75%, the phosphorus content of finished products is less than 0.010%, the smelting time is shortened by 3 ~ 4 min. At the same time, the dephosphorization rate of ladle decreases with the increase of liquid steel temperature at the end of converter blowing, the BOF optimum end-point temperature is between 1 630 °C and 1 655 °C. By adopting ladle dephosphorization technology, the smelting process of ultra-low phosphorus steel is shortened to converter blowing—►RH treatment—►continuous casting, and the LF refining process is omitted.

In view of the high silicon and phosphorus content of hot metal in a steel works, a converter slag-retaining double-slag smelting process is used to obtain a stable dephosphorization rate of hot metal. The specific process is to add slag-forming materials such as lime and sludge balls after the start of the blowing process for 3 min. The oxygen supply intensity is 2. 5 m ³ (t ·min) at 0 ~ 3 min, and 3. 2 m ³/( t ·min) at 3 ~ 4. 5 min. The temperature is controlled at about 1320 °C. After the converter has first deslagging, it starts to blow and adds the late slag forming material. When the carbon monoxide in the furnace rises to a stable level, the oxygen lance position is raised appropriately to improve slagging and control the end-point carbon. The test results show that the average dephosphorization rate of hot metal in the dephosphorization period is 58.09% ,and the average dephosphorization rate of molten steel in the decarburization period is 85. 56% ； When the temperature of the semi-steel is 1320 °C ,the basicity of the slag is 2.0,and the TFe content in the slag is 18% ,a better dephosphorization effect can be obtained in the dephosphorization period. When the molten steel temperature of the converter liquid after first deslagging is 1580 °C ,the basicity of the final slag is 3. 5,and the TFe content in the final slag is 20%, a better dephosphorization effect can be obtained in the decarburization period. [P] _e/[P] _r ratio at the end of the converter is 0. 90. The petrographic composition of the slag during dephosphorization and decarburization poriod from the experiment is suitable for dephosphorization of hot metal.

According to issue of increasing cost and decreasing liquid quality by BOF recarburization process to melt medium and high carbon steel using semi-steel at Pan Gang, the chemical thermal compensating process by increasing silicon content of semi-steel is adopted, and based on dephosphorization thermodynamics in BOF and enrichment regularity of phosphor in slag, it is obtaind that enrichment phase of phosphor in slag is 2CaO • SiO ₂. By using technologic measures such as fast slagging, reduce tapping temperature, it is obtained that the enrichment phase of phosphor in slag is increased, which improve the dephosphorization effect. Results of test indicate that the new thermal compensating process improves the thermal resource of semi-steel as well as shorten the slag forming time from 4. 1 min to 2. 5 min,and the average carbon content of steel at endpoint is of BOF 0.18% , it is obtaind that temperature is 1653 °C ,TFe content of slag is average reduced by 2. 81 percent point,phosphor content of steel is all less than 0.015% .

Through the practice show that, it can be seen the production of bearing steel, the converter tapping temperature ≥1650℃, tapping oxygen ≤300 x 10 ^-6, and 18 kg/t slag can achieve 50% desulfurization efficiency in the tapping process. At the same time, the mode of u slag retaining cone + slide plate slag retaining" is adopted in converter tapping to reduce sulfur by another 0. 000 5% ； the mode of aluminum adding in BOF tapping + LF refining to deoxidize with ferrosilicon powder and controlling the binary basicity of slag to be 5 ~ 6 can achieve more than 50% desulfurization effect and stabilize the casting performance to get finished product sulfur content ≤0.0015% .

Xinggang one-step method (dephosphorization station +60 t AOD furnace +60 t LF furnace) is used in the production of 400 series free cutting stainless steel, in the early stage, in all the sulphur iron was added to the steel in the AOD to fit [S]. The alkalinity of steel slag during the AOD tapping to the upper casting process is always in the low alkalinity range (R = 1.40 ~ 1.95). The consumption of sulphur iron is large, oxygen content in molten steel is high, with the increase of the number of smelting furnaces, the lining erosion is serious, effecting AOD furnace life and billet quality and the steel slag is in a low alkalinity state for a long time, which is easy to cause the increase of [C] content in the steel (especially 430F, 430FR low carbon steel) , which is difficult to achieve multi-furnace continuous pouring. In the later stage, by optimizing the method of adding iron sulphide and the alkalinity of slag at different stages, including iron sulphide in LF late period, AOD slag basicity 2.0 ~ 2.3 and LF slag basicity 1.6 ~ 2.0, the treatment time of low alkalinity slag is shortened, the [S] element loss and the oxygen content of molten steel and the erosion of the furnace lining are reduced. The sulfur element absorption rate was increased from 62% to 75% , the sulphur iron consumption per ton of steel decreased by 2.12 kg, and defects such as subcutaneous bubbles in the slab were controlled.

The production flowsheet of test stainless steel 20Crl3 (/% : 0.20C, 0.37Si, 0.54Mn, 0.030P, 0.002S, 12.22Cr, 0.007Al) is 25 t EAF-VOD-LF-ingot casting. The effect of [Si] and slag basicity on (Cr ₂O ₃ ) content in slag and the desulphurization efficiency of slag by silicon deoxidation process have been analyzed. The calcium yield for stainless steel 20Cr13 by VOD-LF with Si deoxidation refining process is 99. 27% , the [ S] at LF refining beginning is 0. 014% and at end refining [ S] is 0. 007% to meet the requirement of actual production and save the consumption of aluminium ingot and high-carbon ferrochrome and decrease the production cost of stainless steel 20Crl3.
 

At present,the oxygen content in bearing steel has been controlled at a very low level,and Ds inclusions have become one of the main factors affecting its quality stability.In order to solve this problem,a non-aluminum deoxygenation process is proposed to produce CCr15 bearing steel.Instead of using aluminum as deoxidizer,silicon-manganese pre-deoxidation,slag surface diffusion deoxidation,vacuum final deoxidation and low basicity slag formation in refining process are adopted. Compared with the traditional aluminum deoxidation production process,the main inclusions in the bearing steel of non-aluminum deoxidation process are silicate with a small amount of calcium aluminum-silicon composite inclusions, which reduces the magnesium aluminum spinel and calcium aluminate forming Ds inclusions,and significantly reduces the number of Ds inclusions.Ds inclusions can be stably controlled below grade 0.5 in rolled products,and the proportion of samples graded at grade O is as high as 91.67%.This process can obtain stable production results and product quality, which will provide theoretical and technical guidance for the production of high-quality bearing steel.

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

Through the thermodynamic calculation and analysis of nitrogen solubility in 1Mn18Cr18N protective ring steel， it is found that increasing the content of Cr and Mn elements in the steel can significantly improve the solubility of nitrogen. At the same time， the solubility of nitrogen increases as the molten steel temperature decreases . This paper describes the production process of 1Mn18Cr18N protective ring steel by non-vacuum induction furnace， electric furnace，AOD and LF refining， and alloying treatment with bottom blowing nitrogen， which is shorten the production time， and the composition control is quite stable. When AOD refining bottom blowing nitrogen is used for alloying， the nitrogen content in the molten steel can reach 0. 547% and the nitrogen solubility tends to be saturated. In the LF refining process， when using bottom blowing nitrogen and nitrogen-containing alloys， the nitrogen content in the steel can reach 0.68%.

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 the refining production of LF-RH of 42CrMoA alloy structural steel， the original production process and the industrial test technology of steel inclusion removal by nitrogen addition and release method were carried out， and the good experimental results were obtained. Through systematic sampling， it was found that adding nitrogen through bottom blowing during the LF refining process can increase T［N］ in the steel to 260 × 10 ^-6， and meet the demand of nitrogen release in the form of bubbles during RH vacuum refining process； Nitrogen addition and release method also had good total oxygen removal effects， after RH vacuum treatment， the average T［O］ content reduction can reach 37.4%； Nitrogen addition and release method also had good inclusion removal effect， the number of inclusion per unit area can be reduced from the original 8.771 pieces / mm ² to 3.585 pieces / mm ² after treatment， and the removal rate can reach 34.6%； In all kinds of inclusions， nitrogen extraction method had the highest removal efficiency of alumina inclusion， the proportion of Al ₂O ₃ inclusion in steel can be reduced from 83% to 74% after treatment， which effectively improved the cleanliness of 42CrMoA alloy structural steel.

High carbon steel such as heavy rail steel and bearing steel are smelted by converter， the traditional low-high-low three-stage smelting mode is adopted for oxygen lance control. Because lime is difficult to melt in the early stage， splash intensifies in the middle stage and loses the opportunity of dephosphorization with high alkalinity in the later stage， the splash rate is high in the smelting and the qualified rate of carbon turndown at end-point is low. In order to solve this problem， a new high-low-low-high-low five-stage new smelting model is adopted by analyzing the smelting process. The results show that the splash rate is obviously reduced from 20%～30% to less than 15%， and the qualified rate of carbon turndown at end-point is greatly increased from 69.06% to 93.55%.

The effects of 0.0001%，0.0018% and 0.0037% S content on the solidification characteristics of K417G alloy were studied by isothermal solidification experiment in the temperature range of 1340-1230 ℃. The results show that S can reduce the solidus temperature of the alloy and enlarge the solid-liquid two phase region. When the S content increases from 0.0001% to 0.0037%， the solidus temperature of the alloy decreases from 1255 ℃ to 1245 ℃. During the solidification process， the S element segregates in the liquid phase and precipitates out as the Y phase in the final solidification zone. And S promotes the enrichment of Al and Cr elements at the solid-liquid interface. At the same isothermal temperature， the increase of S content promotes the increase of the volume fraction of MC carbide，γ+γ΄ eutectic and Y phase， and has little effect on the morphology and precipitation temperature of MC carbide and γ+γ΄ eutectic， but the precipitation temperature of the Y phase is increased from 1230 ℃ to 1240 ℃.

The slag-making material addition system of Q355 steel was optimized， from the traditional "three-batch feeding" mode to the "eight-batch feeding" mode， and 100 kg steel slag modifier was added in the first and third batches respectively. At the same time， the oxygen blowing system of Q355 was changed from the traditional "constant flow， high-low-low lance position" control to "variable pressure， high-low-high-low lance position" control. Base above， a converter economical smelting process suitable for the actual production of Q355 steel was developed. The practice results show that compared with the original smelting process， the total oxygen supply time of the improved process is shortened by 1 min， the hit rate of phosphorus at the end point of smelting is 100%， the average value of phosphorus removal rate at the end point is increased by 4.24%， and the average value of lg L _p is increased by 0.35. Compared with the consumption of slagging materials in the original process， the average consumption of steel lime per ton in the improved process is 34.01 kg， a decrease of 8.73 kg， and the average consumption of total slag material per ton of steel is 43.95 kg， a decrease of 9.13 kg. In addition， the average iron and steel material consumption of the improved process is 1078.02 kg/ton steel， which is 0.60 kg/ton steel less than that of the original process. The economic smelting of Q355 steel converter is realized， the consumption of slagging material and steel material is reduced， and the production cost of Q355 steel smelting is effectively reduced.

This article presents the smelting practice of 9Ni steel for ultra-low-temperature pressure vessel in a certain steel plant by the "BOF → LF → scraping slag/fetching slag → LF → VD → CC" process. The decarburization and desulfurization in the BOF + LF process require that the steel produced by the converter has a low phosphorus （w［P］） ≤ 0.009%） and carbon content （w［C］） ≤ 0.05%）， with an average desulfurization rate of 74.3% and an average decarburization rate of 51.2%. The control of phosphorus content is more difficult than carbon content in the production process. In the scraping slag process， the average phosphorus reversion rate in the molten steel is 16.89%， while in the fetching slag process， it is 22.61%. Although the scraping slag process results in a lower phosphorus reversion rate in the molten steel， the processing time is increased by 15 to 20 minutes， and the average molten steel loss is increased by 3.1 t per heat. After adjusting the addition of nickel plates from the converter to the ladle furnace， the average nickel recovery rate increases by 3.74%. Through optimizing the production process， the molten steel in the tundish meets internal control requirements for phosphorus（ P）， sulfur （S）， nitrogen N， total oxygen （T.O）， and carbon （C）， ensuring high purity of the molten steel， the macrostructure center segregation of the cast slab reaches 1.0～1.5 grade in class C， the internal and surface quality of the cast slab are good. The rolled steel plate exhibits excellent performance at -196 ℃.

 During the process of non-protective atmosphere electroslag remelting of 9CrMoCoB steel， Iron oxide scale generated from the oxidation of the electrode surface are introduced into the slag pool ， as a result the oxygen potential of the slag pool increases and easily oxidized elements in the metal melt pool burns seriously. In order to reduce the oxygen potential of the slag pool and improve the yield rate of easily oxidized elements， appropriate deoxygenation agent should be added to the steel during the smelting process. Firstly， the high-temperature oxidation behavior of 9CrMoCoB steel at different temperatures was studied by using a thermogravimetric analyzer， and corresponding oxidation kinetics were established； Secondly， XRD and SEM-EDS analyses were conducted on the oxide scale of the sample； Finally， based on the above experiments and the temperature distribution on the electrode surface in the process of ESR in non protective atmosphere， a better deoxidation system was proposed. The results indicate that the weight gain at low-temperature oxidation （500-700 ℃） can be ignored； The weight gain at medium temperature oxidation （900-1 000 ℃） consists of two stages： the linear law stage of rapid oxidation period and the parabolic law stage of diffusion control； The weight gain during oxidation at high temperatures （1 100-1 200 ℃） follows a parabolic pattern. At different temperatures， the high-temperature oxidation rate of 9CrMoCoB steel is k=exp(44.1317-\frac{40163.707}{{46}^{(h+0.33)}+723.15}. The oxide skin has a layered structure， with an outer layer of iron oxide and an inner layer of iron chromium composite oxide phase. During the smelting process， the 9CrMoCoB electrode （diameter 75 mm） is introduced into the slag pool with a FeO content of 9.02 g every 5 minutes. To completely reduce the introduced FeO ， the addition of pure Si is 1.75 g， which can avoid readily oxidizing elements burning and obtain qualified chemical composition of the electric slag ingots.