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EP-4215627-B1 - LOW-COST SMELTING METHOD FOR POLAR-USE STEEL USING ULTRA-HIGH PHOSPHORUS MOLTEN IRON

EP4215627B1EP 4215627 B1EP4215627 B1EP 4215627B1EP-4215627-B1

Inventors

  • WANG, Zhongxue
  • LI, YAN
  • MA, HENG
  • HE, Kang
  • WANG, Tengfei
  • ZHANG, PEI
  • SUN, Zhengxu
  • ZHANG, Qingpu
  • WANG, Yuexiang
  • HUO, Xiaoxin

Dates

Publication Date
20260513
Application Date
20210607

Claims (12)

  1. An ultra-high phosphorus molten iron low-cost smelting method for polar steel, comprising successively: a converter smelting step: smelting, deoxidizing and tapping alloying raw materials including molten iron; wherein, in the converter smelting step, in the molten iron as the raw materials, the content of P element is ≥ 0.15 wt%, the content of Si element is 0.15 to 0.6 wt%, the content of S element is ≤ 0.006 wt%, and the content of As element is ≤ 0.006 wt%; the temperature of the molten iron is ≥ 1230°C; in the converter smelting step, when the mass content of silicon in the molten iron as raw materials is ≥ 0.30%, the smelting is carried out by using a double-slag process, wherein the double-slag process specifically includes: step 1): adding a part of slag to the raw materials, wherein the slag includes a slag-forming agent and a coolant, wherein the slag-forming agent is lime and dolomite, and the coolant is sinter ore; then blowing oxygen into the raw materials by using an oxygen lance; and, after a primary slag is completely smelted, taking the oxygen lance out of the converter and pouring the slag; in the step 1), the addition amount of the lime is 20 to 22.5 kg/ton steel, the addition amount of the dolomite is 3.5 to 5.5 kg/ton steel, and the addition amount of sinter ore is 28.5 to 32 kg/ton steel; in the step 1), the time for blowing oxygen is 5 to 6 min; and in the step 1), after the primary slag is completely smelted, the oxygen lance is lifted out of the converter within 15-30 s; step 2): using the oxygen lance to blow oxygen into the molten steel obtained in step 1), then adding the remaining slag in batches, and continuing the smelting, wherein, during the smelting process, the TSC temperature and the content of C of the molten steel are measured, and the lime or the sinter ore is selected to be added according to the measurement results to ensure an alkalinity in the later stage and promote the slag smelting completely; wherein the slag includes a slag-forming agent and a coolant, wherein the slag-forming agent is lime and dolomite, and the coolant is sinter ore; in the step 2), the time from adding the remaining slag to measuring the TSC temperature and the content of C of the molten steel is 70 to 90 s; the total reaction time of step 2) is 240 to 300 s; in the slag of the step 2), the addition amount of the lime is 21 to 25 kg/ton steel, the addition amount of the dolomite is 3.5 to 5.0 kg/ton steel, and the addition amount of the sinter ore is 14 to 20 kg/ton steel; in the step 2), the TSC temperature is controlled to 1540°C to 1590°C, the content of C is controlled to 0.25 wt% to 0.40 wt%; and in the step 2), according to the measured TSC temperature result, the lime or sinter ore is selected to be added to continue the blowing, so as to ensure that the TSO temperature of the converter is controlled to 1600°C to 1650°C, and the content of C is controlled to 0.07 wt% to 0.09 wt%; and spot blowing and temperature increasing are performed if the TSO temperature of the converter is less than 1600°C; in the converter smelting step, when the mass content of silicon in the molten iron as raw material is < 0.30%, the smelting is carried out by using a single-slag process; wherein the single-slag process specifically includes: step a): adding lime, sinter ore and dolomite to the raw materials, in the step a), the lime is added in 2-3 batches, and the addition amount of ton steel is 42.9 to 46.2 kg/t; the sinter ore is added in 3-4 batches, and the addition amount of ton steel is 39.2 to 42.8 kg/t; the dolomite is added in 2-3 batches, and the addition amount of ton steel is 8.57 to 10.7 kg/t; step b): after the slag is completely smelted in the whole process, the TSC is measured, and then lime or sinter ore is selected to be added according to the measured TSC result; in the step b), the addition amount of the lime or sinter ore is 2.15 to 3.57 kg per ton of the molten iron; when TSC ≤ 1540°C, the lime is added and oxygen blowing smelting is continued; when TSC is ≥ 1590 °C, the sinter ore is added; and in the step b), according to the TSO measurement result, if the content of C is ≥ 0.10%, the spot blowing is performed to control the contents of C and P of the molten steel; in the converter smelting step, in the first 7-8 minutes of the smelting, nitrogen is blown at the bottom, wherein the flow rate of nitrogen is 450 to 580 Nm 3 /h in the first 1 to 3min, and the flow rate of nitrogen in the later stage is increased to 800 to 900 Nm 3 /h; after nitrogen is blown at the bottom for 7-8 minutes in the smelting, switch to argon, and the flow rate of argon is increased to 1000 to1100 Nm 3 /h; in the converter smelting step, when carbon-oxygen equilibrium of the converter is > 0.0032, the TSO composition of the converter needs to be determined as C: 0.06 to 0.09 wt%, P ≤ 0.006 wt%, S ≤ 0.020 wt%, then the steel can be tapped; when the carbon-oxygen equilibrium of the converter is between 0.0021 and 0.0032, the carbon at the measuring end point of the converter needs to be ≤ 0.045%, otherwise, spot blowing is performed; in the converter smelting step, the deoxidizing is carried out by using ferro-manganese-aluminum, and the addition amount of the ferro-manganese-aluminum is 1.7-2.5 kg/t steel; in the converter smelting step, after the smelting and before the deoxidizing, slag splashing for converter protection is preformed by using a 2000 mm lance level - 1500 mm lance level - 500 mm lance level with nitrogen, wherein the lance is repeatedly lifted during the process of slag splashing, and after the slag splashes dry, the nitrogen is closed and the lance is lifted, and the time of the slag splashing is 140 to 200 s; a LF refining step: performing slag adjusting and refining on molten steel obtained in the converter smelting step to obtain a refined molten steel, wherein, in the LF refining step, the mass ratio of the slag used for the slag adjusting is: lime : fluorite : calcium carbide : aluminum slag = (3-5) : (3-5) : 1 : (1-2); and after the slag adjusting, an aluminum wire is fed for aluminum enrichment, and a titanium wire is fed for titanium enrichment; and the time of the refining is 30 to 45 min; a RH degassing step: vacuum degassing the refined molten steel; a continuous casting step: performing continuous casting on the molten steel obtained after the RH degassing step to obtain a cast billet, wherein the content of P in the steel component obtained by the smelting method is less than 0.007 wt% by mass percentage.
  2. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, characterized in that , in the converter smelting step, the raw material further comprises scrap steel; wherein the mass of scrap steel / (mass of molten iron + scrap steel) ≤ 8%.
  3. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, characterized in that , in the converter smelting step, blowing nitrogen and argon at the bottom of the converter during the whole smelting process.
  4. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, characterized in that , in the converter smelting step, when carbon-oxygen equilibrium of the converter is ≤ 0.0021 and the carbon at the measuring end point of the converter is ≤ 0.045%, taping the steel directly.
  5. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, characterized in that , in the converter smelting step, the alloys used in the alloying include: metal manganese, ferrosilicon, ferroniobium, ferrovanadium and nickel plate.
  6. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, characterized in that , in the LF refining step, the slag is adjusted to a final slag alkalinity of ≥ 2.2, and a top slag before leaving the station must be a yellow-white slag or a white slag, and the retention time of the yellow-white slag or the white slag is not less than 10 minutes.
  7. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, characterized in that , in the RH degassing step, when the vacuum degassing is performed, the degree of vacuum is ≤ 133Pa, circulation time is not less than 15 minutes, and degassing time is greater than 5 minutes.
  8. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, characterized in that , in the RH degassing step, after the vacuum degassing, a calcium aluminum wire is fed at 80-100 m/converter, and blow softly is not less than 10 minutes.
  9. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, characterized in that , in the continuous casting step, the superheat degree of the molten steel is controlled < 25°C.
  10. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, characterized in that , in the continuous casting step, for 175 section, the pulling speed during continuous casting is 1.25-1.35m/min; for 200 section, the pulling speed during continuous casting is 1.2-1.4m/min; for 250 section, the pulling speed during continuous casting is 1.1-1.3m/min; for 300mm section, the pulling speed during continuous casting is 0.85-0.95m/min.
  11. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, characterized in that , in the continuous casting step, a crystallizer is made of peritectic steel to protect slag; the middle ladle is covered with a covering agent combined with carbonized rice husks to ensure good coverage of the liquid surface of the middle ladle: the long nozzle of the large ladle is sealed with argon, and the flow rate is 90-120L/min.
  12. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, characterized in that , in mass percentage, the steel composition obtained by the smelting process comprises: C: 0.06-0.10%, Si: 0.20-0.35, Mn: 1.5-1.65%, Nb: 0.010-0.030%, V: 0.010-0.035%, Ti: 0.010-0.035%, Al: 0.015-0.040%.

Description

Technical Field The invention belongs to the field of ferrous metallurgy, relates to an ultra-high phosphorus molten iron low-cost smelting method for polar steel. Background With the increasing shortage of energy in the world, countries have successively increased the development of polar oil and gas energy and built many offshore platforms, and the demand for ultra-low temperature resistant steel for polar use has soared. Due to the extremely low polar temperature, the content of phosphorus in steel is very important to the toughness of steel, however, the content of phosphorus in domestic molten iron varies greatly, some steel mills are affected by ore raw materials, and the ultra-high phosphorus molten iron produced is not suitable for the production of low phosphorus steel, which seriously slowed down the pace of production. With the increasing demand for low-phosphorus high-quality steel by users, how to use converters to achieve such ultra-high phosphorus hot metal smelting polar low-phosphorus steels at the lowest cost is the focus of research at this stage. At present, some enterprises at home and abroad widely use converter duplex method to produce low-phosphorus steel, such as LD-NRP method of JFE, H converter of Kobe steel, BRP method of Baosteel, etc. Such processes have high requirements for equipment, and in the process of converter molten iron transferring, the heat loss is large and the production efficiency is low. There is also a double-slag method that continuously performs dephosphorization and decarburization of molten iron on the same converter, which is simple to operate and does not require new equipment, and has been widely used at home and abroad. Although there are many patents on smelting low-phosphorus steel with high-phosphorus molten iron, such smelting process has the disadvantages of long process flow and high cost. Several similar patents are briefly described below: Patent document CN 109593907A discloses "a method for smelting low-phosphorus steel", which produces finished products of qualified billet with P≤0.005% by controlling the converter blowing lance position, oxygen supply intensity, bottom blowing flow, and slag control under tapping , but this method is only applicable to molten iron with phosphorus content less than or equal to 0.10%. Patent document CN 109897933A discloses "a high-efficiency smelting process for producing low-phosphorus clean steel in a converter", which smelts low-phosphorus steel by a converter double-slag method, but the phosphorus content of molten iron used in the smelting method is all less than 0.13%, and the residual slag treatment is easy to produce phosphorus back phenomenon, which is not suitable for ultra-high phosphorus hot metal smelting. Patent document CN 109402323A discloses "a method for smelting ultra-low phosphorus steel with ultra-high phosphorus molten iron". This patent optimizes the ratio of lime ash and slag modification agent in the LF refining process, and adjusts the composition of the steel slag to increase the phosphorus content of the steel slag capacity, thereby increasing the distribution ratio of phosphorus in steel slag and molten steel, providing favorable conditions for dephosphorization. However, the smelting method does not describe the converter smelting process in detail, and the P content in the molten steel in the LF converter is at a low level, and the LF refining process takes too long, which is not conducive to high-efficiency and low-cost batch industrial production. Document CN112048665 reveals a method for preparing a steel board for polar marine engineering. In terms of mass percentage, the steel plate components are: C: 0.06~0.09%, Si: 0.20~0.35%, Mn: 1.48~1.63%, Nb: 0.020%~0.035%, Ti: 0.010%~0.020%, V: 0.020 %~0.035%, Ni: 0.08%~0.17%, Als: 0.015%~ 0.040%, P: ≤0.013%, S: ≤0.005%. The preparation method of the steel plate includes: primary smelting, refining, and casting to obtain a cast slab, which is then slowly cooled for not less than 48 h. The slowly cooled cast slab is heated and then rolled to obtain a steel plate; the steel plate is then cooled for not less than 60 hours. This steel type has excellent comprehensive properties such as high strength, low temperature resistance, easy welding, corrosion resistance, and good low temperature aging impact toughness. The method requires slow cooling steps, which substantially slow down the process. SUMMARY In view of the deficiencies of the prior art, the purpose of this application is to provide an ultra-high phosphorus molten iron low-cost smelting method for polar steel, which can realize the requirement of using molten iron with a phosphorus content higher than 0.150% to smelt steel with a phosphorus content of less than 0.007%, and can significantly reduce the ductile-brittle transition temperature of steel, and meet the requirements of polar and extremely cold working conditions. To achieve the above object, the present invention inventi