Stainless steel smelting technology advances, especially after the 1960s, refining and continuous casting technology used to further promote the rapid development of stainless steel, and improve the quality of stainless steel to improve the yield and reduce production costs.
China from the early 1950s to begin production of Cold rolled stainless steel, with 3t EAF was no refining and continuous casting equipment, the annual output of only a few hundred tons to thousands of tons, quality, variety, and cost can not meet the requirements. Since the 20th century, 80 years, Taiyuan Iron and Steel Research Institute and other units of the company took the lead in refining technology developed outside China AOD furnace. Subsequently, each special steel has accounted installed outside 18-40tAOD and 15-60tVOD refining equipment, refined than it can be significantly improved. Before 1985, China has been using stainless steel ingot molded behind. TISCO 1280 vertical continuous casting machine into operation after 1985, Steel Factory, Chongqing Special Steel and steel Wuchang there have slab, billet caster cast production. In 1989, Chengdu Seamless Steel Tube Plant production of stainless steel 304 csp caster level, the end of our stainless steel ingot completely molded history. However, due to various reasons, the Chinese steel annual output has been hovering at around 300 000 t, stainless steel smelting technology progress is slow, seriously hampered the development of China's stainless steel. Since 2000, the state of the steel industry structure adjustment, adopted a series of policies and measures to encourage the development of the stainless steel industry, the Chinese stainless steel production by leaps and bounds, from 1999 to 350 000 t in 2003 to grow to 1.778 million t average annual growth rate of about 50 percent, were ranked as the world's four largest producer of stainless steel.
Development AOD furnace equipment and technology
AOD refining furnace is the main equipment of stainless steel, about 1-175tAOD furnace world's 155 units, of which 1/2 in stainless steel plant, the rest of the foundry. AOD refining stainless steel production accounts for more than 80 percent of the world stainless steel.
China's first 18tAOD furnace since September 1983 and put into production, currently about 1-40tAOD furnace more than 20 seats, of which more than 18t AOD furnace total of eight (including TISCO 3x40t, Dalian 1x40t, Pudong 1x30t, the steel Wuchang 1x18t Great Wall 118t and should reach lx18t etc.). In 2004, the steel Wuchang 60tAOD on a steel plant furnaces and furnace production 120tAOD make China AOD furnace equipment level has been significantly improved.
TISCO is China's earliest use of AOD furnace steel production enterprises, the AOD furnace has a total production of stainless steel over 200 million t, accumulated a lot of experience. In order to further expand production capacity, TISCO 18tAOD furnace for implementing transformation twice. After first transformation, AOD furnace volume expanded by 18t 40t, the production capacity increased from 160 000 t to 400 000 t. 2004 implementation of the second reconstruction, the furnace capacity is further expanded to 45t, additional top-blown lance, shortening the smelting time; the introduction of VAI expert automation control system to improve the control precision smelting; reduce ammonia consumption, increased dust dust blower capacity, improve the quality of the environment. After two transformation, TISCO AOD furnace equipment reached the international advanced level. In addition, TISCO also plans to implement environmental projects yen loans, 6 18t of EAF will be transformed into a 90t UHP EAF technology, which not only eliminates the slow pace of steel production bottlenecks, but also to further increase production capacity to 500 000 t, greatly improved the quality of the environment, to achieve a truly clean production.
In recent years, Chinese production operations AOD technology has made significant achievements, major progress as follows:
Improve (1) Lining Life
AOD furnace lining life AOD is the main technical and economic indicators of production, after years of technical research, especially in improving the operation of the process (for example, reducing the furnace when the silicon content of the steel, the improvement AOD slag system, decarbonization of alkalinity increase from 0.5 to 1.0, the reduction of alkalinity increase from 0.8-1.0 to 2.0-3.5 and improve aspects of high quality refractory construction process, and so do a lot of work, AOD lining life in general has improved. TISCO AOD furnace lining life of an average of 110 times the maximum 130 times, including the use of TISCO production of refractories average life expectancy of 92 times.
Improvement (2) desulfurization
China AOD furnace slag mostly single-blowing process. To reduce the S content in steel, using the quick-S process, refining slag basicity of about 2.5, ladle add SiCa, the use of a strong stirring effect desulfurization of steel, the steel in an appropriate amount of residual calcium. The improved AOD process, desulfurization rate of 70%. Currently, TISCO stainless steel sulfur content of 0.005% or less stable at an average of 0.0034%.
(3) N-containing stainless steel smelting
N-containing nitrogen-alloyed stainless steel mainly in two ways: First, the addition of nitrogen and manganese, chromium nitride alloy alloying, the second is the direct alloying with nitrogen, which have lower production costs. AOD furnace can direct alloying with nitrogen, therefore, has the great advantage of stainless steel smelting. TISCO application 40tAOD furnace 18t and dissolved nitrogen in stainless steel, the removal of theory, a nitrogen alloying process model, does not require on-line analysis of steel smelting nitrogen content in the finished product will be able to more precisely control the nitrogen content, control precision ± 0.0135%. Currently, TISCO has applied the model mass OCr19Ni9N directly with nitrogen alloying method, OCr19Ni9NbN, 1Cr17Mn6Ni5N, 00Cr18Ni5Mo3Si2N and 00Cr22Ni5Mo3N and other nitrogen-containing stainless steel. In 2003, the production of various types of stainless steel containing N 35000 t, and achieved significant economic benefits.
(4) the use of AOD dust
Amount of dust AOD furnace smelting of steel production by 0.7% -1.0%, generally AOD dust containing Cr2O315%, NiO4%, CaO26%, Fe27%, MgO15%, and other substances, dust particle ≤20μm, Cr2O3 and dust NiO is precious metal oxides. If recycling is not only a waste of resources, would pollute the environment. So, how to recycle the dust AOD Cr, Ni two things are important issues for each stainless steel mills.
TISCO recovery process is used by the study by sic amount of dust also required mixed oxide forming, after drying 200 ℃ to the medium frequency induction melting furnace reduction, high C cast nickel-chromium alloy (Cr13% -Ni6% ), then returned to the smelting furnace, recovered by this method AOD furnace dust has achieved good economic results.
Progress molten steel smelting technology
China is a developing country. Scrap steel, especially stainless steel scrap savings amount is small, therefore, to develop with all or part of the iron smelting iron stainless steel plant in China's goal is to have three factories with iron smelting steel in the world, including Japan's Nippon Steel Yawata plant, JFE Group Kawasaki and Chiba plant in Brazil Acesita plant. TISCO in China built a molten iron as the main raw material of the three-step process for the production of hot metal in 2003 that desiliconizing dephosphorization pretreatment -30tUHP furnace pre-fluxing -75tK-OBM-S LBE -80tVOD decarbonization refining refining 80tLF - bending Type square slab caster. The key equipment from Japan's JFE Group of hot metal pretreatment Kawasaki introduced, 75tK-B0M-S converter imported from VAI, 80tVOD imported from Danieli, design stainless steel production 55t this production line.
The smelting of stainless steel has the following characteristics:
(1) raw materials and flexible, can be used both pre-fluxing EAF (15-30t) + part dephosphorization of hot metal (30-50t), but also all with hot metal dephosphorization (65t) Stainless steel smelting;
(2) BOF larger capacity can ensure smooth operation without causing splashing;
(3) top lance gun position control, can achieve high speed and after CO decarburization blowing operation, to ensure that the thermal energy required smelting operations;
(4) at the bottom outlet of the cooling gas flow and pressure can be controlled individually, in order to ensure optimal cooling and prolong the service life of the tuyere;
(5) the use of VAI-CON-TEMP continuous temperature measurement devices;
(6) the use of pneumatic slag and slag IRIS measurement system to reduce the excessive amount of steel slag to ensure that the next step along the line VOD operations;
(7) the use of advanced LevelII automatic control systems and software models to ensure automatic control when smelting steel, stainless steel quality improve.
After a year of practice, TISCO basically mastered the K-OBM-S converter steel process, achieved the following results:
(1) K-OBIII-S original design output of 350 000 t / a, put into operation since April 2003, when the production of stainless steel 260 500 t, 2004 was installed K-OBNI-S BOF shell replacement vehicle, shortening the furnace shell replacement time. After the completion of the transformation, stainless steel design production was 550 000 t / a.
(2) lining life continues to improve, up from about the beginning of the current 200 to nearly 700, the bottom is also rising life expectancy, from 50 at the start to the current nearly 300 times (each lining replacement 2- 3 bottom).
(3) a significant reduction in the consumption of hydrogen discharge, the original design of 304 stainless steel smelting hydrogen consumption for 8m3 / t, and now the whole process to the bottom outlet N2 generation Ar, achieved significant economic benefits.
(4) to cancel the alloy melting furnace process, the implementation of 100% hot metal dephosphorization, ferrochrome smelting All 400 series stainless steel two-step production process within the converter added significantly reduce production costs.
(5) As a result of de-P iron smelting stainless steel P content below to scrap as the main raw material of stainless steel smelting, steel, As, Su, Cu and other harmful elements are also greatly reduced.
Baosteel Group, a steel plant with an annual output of 720 000 t of molten iron and chrome water as the main raw material of a stainless steel production line has been put into production. The process route is a pre-melting furnace hot metal pretreatment -100tUHP water and ferrochrome alloy -120tVOD -120tVOD refining refining - continuous casting. The line converter using AOD-L. This production line is put into operation to further improve the Chinese stainless steel with iron smelting technology.
Advances in Continuous Casting Technology
China stainless steel casting technology starting late, until 1985, TISCO production of China's first stainless steel vertical slab caster. Because of this single furnace caster casting off cutting mode, ladle capacity of only 18t, the highest annual output is only 58,000 t, can not achieve full casting production. In 1999, TISCO decided this caster implementation of technological innovation. Its purpose is to increase the transformation of the ladle and tundish capacity, multi-cutting mode using online casting furnace, change two cooling methods, improving the quality of the slab. In 2004, they decided to implement this caster second transformation. The purpose of this transformation is to increase the slab thickness specifications to 200mm, improve casting quality, reduce the slab grinding losses. Its main content is to mold oscillation mode to DYNAFLEX hydraulic vibration, granulated slag secondary cooling system to protect the implementation of dynamic cooling (DYNACS), install a Q VAI quality control expert system, automatic addition of additional devices and printers slab.
After transformation, TISCO has made progress in the casting process following aspects:
(1) stainless steel casting ratio improved significantly. Vertical caster casting ratio increased from 51.4 percent in 1999 to 97.5 percent in 2003.
(2) significantly increased the number of continuous casting furnace. For 304 steel, the even number 6 furnace casting furnace above the slab yield 2.37 percentage increase, on average 96.97%.
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