1 Review of steelmaking process
Since the birth of New China in 1949, it has gone through 70 years. During this period, China's steel industry has worked hard on the ruins of the war, and along the way, China's steel industry has made remarkable achievements. In the nearly 30 years since the founding of New China in 1949 to the reform and opening up, China has always taken the development of the iron and steel industry as the central link to realize industrialization. After nearly 30 years of efforts, China has basically formed a relatively complete steel industry system, which has laid the foundation for the rapid development of the steel industry after reform and opening up.
In the 1950s, the focus was on restoring, expanding, and transforming the existing steel production technology and equipment at that time to meet the urgent needs of the new China's economic construction. During the first five-year plan (1953-1957), the Soviet Union assisted China in the construction of 156 industrial projects, including 8 steel projects including Anshan Iron & Steel, Benxi Iron & Steel, Wuhan Iron & Steel, Baotou Iron & Steel, and Qiqihar Steel Plant. 8 Iron and steel projects accounted for nearly half of the total investment of 156 projects. The largest investment was the expansion and transformation of Angang. In addition, during the First Five-Year Plan period, with the help of the Soviet Union, the reconstruction and expansion of nearly 20 iron and steel enterprises, including the Shijingshan Iron and Steel Plant, were started.
The “three big, five middle and eighteen small” planned and started in 1956. The “three big” is to continue the construction of three large iron and steel bases in Anshan Iron and Steel, Wuhan Iron and Steel and Baotou Iron and Steel. Chongqing Iron & Steel, Maanshan Iron & Steel, Shijingshan Iron & Steel Plant, Xiangxi Iron & Steel; "Eighteen Small" refers to eighteen small steel plants such as Jigang, Lingang, and Nangang; In addition, in 1958, a number of local small and medium-sized steel plants were built In the country, a large-scale steelmaking movement was launched nationwide, and more than 30 steel plants were built that year.
The climax of "three-tier construction" started in 1964. At the same time as the iron and steel industry adjusted, it started the construction of the "big three" line, which is dominated by Southwest Pangang and Northwest Jiugang, and the "small third line", which is supported by military industries in the central and western regions. Through this round of new construction and the reconstruction and expansion of other existing steel plants, China has basically formed a basically complete iron and steel industry layout. Since then, most of these enterprises have become the backbone of China's iron and steel industry, and still play an important role and grow. This is of great significance to the development of China's steel industry, and has laid an important foundation for the future development of the new China's steel industry. Table 1 shows the major events of steelmaking in China since the founding of New China in the 70 years.
Table 1: Major steelmaking events in China in the 70 years since the founding of New China
April 25, 1949
平炉成功炼出了新中国第一炉钢水 Ansteel No.1 Steelmaking Plant's No. 2 open hearth successfully smelted the first furnace of molten steel in New China
型枪钢的试制生产任务 Bengang Special Steel Plant completed the first trial production of RS5 gun steel in New China
Xinjiang Bayi Iron and Steel Plant founded by the People's Liberation Army
TISCO successfully smelted the first stainless steel in New China
September 10, 1954
Fushun Special Steel successfully trials the first furnace of chrome stainless steel in New China
类炮钢 Bengang Special Steel Plant successfully developed the first batch of P- type gun steel in China
March 26, 1956
Fushun Special Steel successfully smelted the first furnace of new China
Shougang built the first side-blown converter in China.
Zhonggang completed the first domestic vertical billet continuous caster and the first arc slab continuous caster put into operation
顶吹转炉 Shougang completes China's first 30t top-blown converter
型钢包精炼炉，开始推广钢包精炼 Baotou Steel introduced two ASEA-SKF ladle refining furnaces in Sweden and began to promote ladle refining
Baosteel begins construction, the largest steel industry introduction project since the founding of New China
炉在太钢建成投产 New China's first 18t AOD furnace completed and put into operation at TISCO
WISCO's No. 2 steelmaking plant achieved full continuous casting, becoming China's first full continuous casting steelmaking plant
New China's first stainless steel vertical slab caster put into operation
油井管项目，是继宝钢之后，我国引进的重点钢铁项目 Signed for the preparation of TPCO oil well pipe project in Tianjin. It is the key steel project introduced by China after Baosteel
TISCO's first vertical bending special steel slab continuous casting machine introduced by Austria from New China put into production
负能炼钢” ，达到国际先进水平 Baosteel converter starts “ negative energy steelmaking ” , reaching international advanced level
Wugang's first 90t in China introduced from Austria 1.9m大型板坯连铸机投产 Ultra-high-power electric arc furnace and China's first 1.9m large-scale slab caster put into operation
竖式电弧炉，德国福克斯公司制造 Jiangsu Shagang Completed the First 90t Vertical Electric Arc Furnace in China
亿吨，达到1.0124亿吨，成为世界第一产钢大国 China's steel output exceeded 100 million tons, reaching 10124 million tons, becoming the world's largest steel producer
Tangshan Iron and Steel Company stopped production of side-blown converters, so far China has eliminated side-blown converters
Using the three-step method to make the first converter stainless steel in China
All open hearth furnaces in China are discontinued and eliminated
顶吹转炉停产 Shougang's last 30t top-blown converter ceased production
China's stainless steel output surpasses Japan, ranking first in the world
管线钢 Baosteel successfully developed X120 pipeline steel
管线钢，也是国内首次 Ansteel develops X100 pipeline steel for the first time, which is also the first time in China
电渣重熔炉，是目前世界上最大的电渣炉 The 450t electroslag remelting furnace officially put into operation by Shanghai Heavy Machinery Plant is currently the largest electroslag furnace in the world
Φ 1000mm 连铸圆坯在兴澄特钢投产 The largest specification Φ 1000mm continuous casting round billet was put into production in Xingcheng Special Steel
康斯迪（ Consteel ）电炉成功投产，也是目前我国最大的电弧炉 Jiangsu Heavy Industry 220t Consteel electric furnace was successfully put into production, and it is also the largest electric arc furnace in China at present.
最厚板坯连铸机投产，设计最大铸坯宽度为2600mm Xingcheng Special Steel's 450mm thickest slab continuous casting machine was put into production, and the designed maximum slab width was 2600mm
The world's first vertical two-machine two-flow large round billet continuous casting machine was completed and put into production in Zhongyuan Special Steel
The state requires that all the strip steel produced by industrial frequency and intermediate frequency induction furnaces be removed
The first quantum electric arc furnace in China was completed and put into production at Guilin Pinggang Company
Baowu one-key converter intelligent steelmaking success
When the People's Republic of China was established in 1949, China had only 158,000 tons of steel, accounting for 0.1% of the world's steel output. In 1978, China's crude steel output was only 31.78 million tons, which accounted for 4.4% of the world's crude steel output. After the reform and opening up in 1986, The annual output exceeded 50 million tons, and the annual output of crude steel exceeded 100 million tons in 1996, becoming the world's largest steel producer and consumer. It exceeded 200 million tons in 2003 and will increase by about 100 million tons every two years. In 2018, crude steel output reached 928 million tons, accounting for more than 50% of the world's crude steel output in that year. The status of the steel industry in the world has been significantly improved; the import and export pattern of steel products has also undergone a fundamental change, which has completely ended the history of China's steel “supply in short supply”. This has strongly promoted China's industrialization and modernization process, significantly enhanced its comprehensive national strength, and supported the status of a world power. It must be seen that China has become a major manufacturing country, and the steel industry has played an important role in supporting the defense industry, petroleum industry, shipbuilding industry, infrastructure construction, and equipment manufacturing.
2 Progress and development of steelmaking technology
The scientific and technological progress of steelmaking in New China has achieved world-renowned achievements, and scientific and technological achievements have continuously emerged. To a large extent, some technical bottlenecks restricting the development of steelmaking have been resolved. China has made significant progress in the localization and modernization of steelmaking technology and equipment. The quality of varieties has been optimized and improved, and the overall level has been significantly improved. Great strides have been made in energy conservation and environmental protection, bringing the overall level of steelmaking to a new level. New modernized zones including large-scale old enterprises such as Anshan Iron and Steel and Baotou Iron and Steel have been completed and put into production, and a number of modern coastal steel bases are also emerging.
At present, domestic traditional steel products are mainly based on converter steelmaking. The production advantages of electric furnace steelmaking have been compressed to a limited production range of high-alloy steel and tool steel (of course, popular steel types can also be produced, but in terms of output, Cost competitiveness is low), and its market competitiveness has dropped significantly. At present, there are mainly three types of steelmaking production processes:
1) Converter process: blast furnace-hot metal pretreatment-converter-secondary refining-continuous casting-rolling.
2) Electric furnace process: electric furnace-secondary refining-continuous casting-rolling.
3) Special metallurgy: electroslag remelting, vacuum induction melting, vacuum arc remelting, electron beam melting, plasma melting, etc. (such as titanium alloy production)-forging or rolling.
2.1 converter steelmaking
The oxygen top-blown converter was first proposed in 1952, and has developed rapidly in the past seventy years. As users have become increasingly demanding of the properties and quality of steel, the scope of application of steel has become wider and wider. Yield and quality, more and more attention to expanding varieties. In this case, the converter production process has changed a lot. The development of hot metal pretreatment, double-blown converter, external furnace refining, and continuous casting technologies has broken the traditional converter steelmaking model. It has been developed from converter smelting to hot metal pretreatment → double blowing converter smelting → furnace refining → continuous casting. This process is characterized by large-scale, modern and continuous equipment. At present, the largest converter in China has reached 350t. The oxygen converter has changed from the original leading process to a process link of the new process, which mainly assumes the tasks of decarburization and heating of molten steel. Negative energy steelmaking, energy conservation, converter steelmaking have become the mainstream of contemporary steelmaking.
With the continuous progress of steelmaking technology, the traditional production process (blast furnace → converter → ingot) has gradually been replaced by a new process (blast furnace → hot metal pretreatment → converter → external refining → continuous casting). Out-of-furnace refining already occupies an important position in modern steel production. Take stainless steel smelting as an example: stainless steel can adopt one-step method, two-step method and three-step method.
1) One-step method refers to the completion of all metallurgical tasks in the electric arc furnace, including melting of scrap steel and alloys, decarburization refining, steel slag reduction and alloying. At present, the one-step process has been eliminated due to long smelting cycles, severe burnout of refractory materials, and high costs;
2) Two-step method refers to the primary furnace
(Such as converter, electric arc furnace) melting scrap steel and alloy materials to produce stainless steel mother liquor, and then refining into qualified stainless steel molten steel in the converter (electric furnace) refining furnace;
3) The three-step method is based on the two-step method, adding deep decarburization equipment to produce ultra-low carbon or ultra-low carbon nitrogen stainless steel.
2.2 Electric furnace steelmaking
Prior to the 1970s, China's electric arc furnaces were generally ordinary electric furnaces of less than 30t.
In the 1980s, the construction of 50-75t ordinary power and high-power electric furnaces was started. At the same time, 50-150t high-power and ultra-high-power electric furnaces were introduced and constructed. Equipped with different types of out-of-furnace refining devices, the steelmaking process is changed from the traditional electric furnace one-step steelmaking method to the two-step steelmaking method in which the electric furnace and external furnace refining. . The technological process has evolved from the traditional electric furnace steelmaking → die casting production process to a new process using high-power or ultra-high-power electric furnace → outside furnace refining → continuous steel casting.
In the 70 years, the development of electric furnace steelmaking is not as fast as that of converters after the 1960s. However, with the advancement of electric furnace steelmaking technology, the development of large-scale ultra-high-power electric furnace technology and refining technology outside the furnace The adoption of EAF has made great progress in electric furnace steelmaking technology, and the output of electric furnace steel and its proportion have increased. At present, China's largest electric furnace has reached 220t (the largest electroslag remelting furnace has reached 450t; the largest vacuum induction melting furnace has reached 13t), which has guaranteed the demand for special materials such as nuclear power stations, high temperature alloys, aerospace materials in China.
At present, among the steelmaking enterprises in China, converter steelmaking still occupies a dominant position, while electric furnace steelmaking only accounts for about 11% of total steelmaking, which is far below the world average. With the increase of China ’s scrap steel output and the reduction of electricity costs, China ’s EAF steelmaking output has a lot of room for growth. However, China really began to vigorously develop electric arc furnaces from the 1980s to the early 1990s, and electric furnaces were becoming a competitor for converter steelmaking. At present, in addition to the energy provided by the electrode, the electric arc furnace can also be supplemented by an oxygen lance and a fuel burner (such as secondary combustion technology). The electric arc furnace is the most effective scrap melting furnace (the preheating technology of the scrap can be used to reduce the energy demand). In order to reduce carbon emissions, in view of the increase in steelmaking capacity of electric arc furnaces, society also requires reduced carbon emissions and more flexible operation methods. Therefore, electric furnaces still have potential and development prospects.
As early as the 1950s and 1960s, some special steel plants such as the No. 5 Steel Plant, Dalian, Fushun, and Taigang in China used high-synthetic synthetic slag in steelmaking to desulfurize bearing steel and ladle during the tapping process. Initial refining technology such as static degassing, but without refining equipment, the effect was not ideal due to the limitations of the process technology at that time. In 1967, Daye Steel Plant introduced the first-generation RH (circulation method) vacuum processing equipment from West Germany, and took the lead in adopting refining technology outside the furnace in China's special steel enterprises.
In the late 1970s, China introduced a variety of external furnace refining equipment from Sweden, West Germany, and Japan, and independently developed refining furnaces such as LF, VOD, VD, and AOD. Each special steel plant according to its own varieties and Quality requirements and specific conditions, have built various forms of refining equipment outside the furnace. For example, Taiyuan Iron and Steel uses electric furnace → AOD to produce stainless steel, and the economic benefits are significant; the production of stainless steel by VOD at Shanggang No.3 Plant and Great Wall Steel Plant is also very good; LFV and VHD / VOD (actually used at Shanggang No.5 Plant and Daye Steel Plant) Use according to LF / VD) to produce bearing steel, gear steel, etc., reduce the gas content in steel to [H] ≤ 2ppm, [O] ≤ 10ppm, [N] ≤ 20ppm; [S] ≤ 0.005% in molten steel, [P ] ≤ 0.008%, reaching the level of international bearing steel.
Capable of producing high-quality varieties, refining outside the furnace has become an indispensable means, and the efficiency of refining outside the furnace has been fully exerted in production. The "Trinity" short-flow process with refining technology outside the furnace as the core is widely used in domestic steel companies and has achieved good results. Primary refining (converter or electric furnace) → refining → continuous casting has become a typical short process of modernization.
However, China's true possession of ladle refining technology began with the introduction of two ASEA-SKF ladle refining furnaces from Sweden in 1975.
In 1979, China designed the first 40t LF / VD ladle refining furnace, and its matching 200kg / h six-stage steam jet pump was also designed and manufactured in China. Since then, ladle refining furnaces below 50t have been promoted by various steel mills, but large-scale ladle refining furnaces still rely on imports.
In June 1991, Tianjin Steel Pipe Company introduced a set of 150t LF / VD large-scale ladle refining furnace (vacuum degassing) and put it into production; in 1996, China had the ability to design and manufacture large-scale ladle refining furnaces. Shanghai Pugang, Shanghai No. 5 Steel Plant, Wuhan Iron and Steel Other steel mills have put into operation large-scale domestic LF / VD ladle refining furnaces. In this way, China's ladle furnace design technology and equipment level can completely replace imports.
Since the 1980s, China ’s off-furnace refining technology has developed rapidly, and iron and steel enterprises have made rapid progress in the construction of refining furnaces. Especially key iron and steel enterprises have been generally equipped with off-furnace refining, and they have comprehensively turned to steelmaking (converter, electric furnace) → refining outside the furnace → company Cast direction development.
After the successful development of the first 40t LF refining furnace at the No. 5 Steel Plant in China in 1983, most electric furnace steelmaking plants began to be equipped with LF furnaces, and the production capacity could be increased by 15% -30%. The vacuum required for refining outside the furnace of the steel plant The functions of degassing (vacuum decarburization) and precise fine-tuning of components are realized by the refining device.
At present, the most widely used refining devices in China are LF, RH, VD, AOD, VOD, etc. (VOD is mainly used for refining of ultra-low carbon stainless steel). From the perspective of the overall process of the steelmaking plant and the quality of its varieties, it can meet the quality requirements for dehydrogenation, deoxidation, and removal of inclusions in most molten steels, and it can smelt ultra-low carbon steel through a vacuum decarburization reaction, which is beneficial to remove inclusions and promote desulfurization Reaction, composition fine-tuning function, steel grades with strict composition control requirements (such as power stations, oil well pipe steels, etc.), fine-tune the composition accurately under vacuum or reducing atmosphere. When refining ultra-low sulfur steel grades, It has fast and efficient desulfurization function, and changes the sulfide inclusion form through calcium treatment, thereby improving the quality of steel.
2.4 Continuous casting
In the 1990s, the technical level and equipment level of newly-built steelmaking and continuous casting projects in China continued to improve, and the starting point of the technical level and equipment level of newly-built continuous casting projects was relatively high. During continuous casting, molten steel flows from the ladle and flows into the mold through the tundish. During the whole process, the molten steel is easily in contact with the air, causing secondary oxide inclusions, affecting the quality of the continuous casting slab, and directly affecting the product quality of the steel.
In order to improve the quality of continuous casting slabs, many process technologies are used to improve product quality and increase economic benefits, such as molten steel protection casting, mold hydraulic vibration, electromagnetic stirring device, secondary cooling dynamic model control technology, casting slab dynamic light reduction, ladle Slag detection, mold breakout prediction and other technologies.
In 2010, China has steadily developed and made breakthroughs in the continuous caster technology of various models in terms of improving the level of independent continuous casting equipment and product grades. In particular, domestic continuous casters and oversized continuous casters using independent technology have successively set new records. At present, the thickest slab caster in China has reached 450mm and the maximum slab width is 2600mm; the cross section of the largest round slab caster has reached Φ1000mm; and the cross section of the domestic billet continuous caster has also reached more than 400mm. Super-sized slabs, round slabs, and square slabs replace die casting, which greatly improves the yield rate and greatly improves production efficiency. Domestic continuous casting equipment has not only the strength to compete with foreign companies on the same platform in China, but also has achieved complete export.
In short, the promotion and application of scientific and technological innovation achievements in the steel industry are obvious. Steelmaking has focused on promoting a large number of advanced technologies such as technology, equipment, energy conservation, environmental protection, and comprehensive utilization of resources. It has ensured the research and development and production of a large number of high-end products, and has contributed to the upgrading and development of the major downstream industries of steel. For example, X100 and X120 steel for long-distance natural gas pipelines in the energy industry; steel plates for ultra-low-cooled LNG (liquefied natural gas) storage tanks; steel plates for LNG transport ships have been localized; domestic steel for 700 ° C ultra-supercritical boilers in the energy industry; Take steel pipe as an example. Inconel 690U nickel-based alloy steel pipe is used in the power station. In the petroleum industry, the drilling depth of Well Tashen 1 in July 2006 was 8408m; in July 2019, the drilling depth of Well 1 was 8882m. These achievements are inseparable from the progress of steelmaking technology. The reform and opening up of China's iron and steel industry has achieved remarkable results, greatly promoting the changes in the technological structure of steelmaking processes, and reducing the gap with the world's advanced level.
While making remarkable achievements in steelmaking process technology, equipment and product quality, great progress has been made in energy saving and emission reduction. Optimize steelmaking production process, reduce steelmaking energy consumption, strengthen fine management and operation, make full use of chemical energy generated by chemical reaction in molten steel and physical energy in exhaust gas, such as secondary combustion technology and preheating technology of scrap steel; meanwhile, develop New type electric arc furnace, efficient use of electrical energy, green environmental protection electric arc furnace smelting; meanwhile, long process steelmaking minimizes and avoids environmental pollution, develops green smelting, such as smoke and dust collection, preheating and utilization technologies, converter "negative energy steelmaking" ". The average energy consumption per ton of steel has decreased, new water consumption per ton of steel has continued to decrease, and sulfur dioxide emissions per ton of steel have been significantly reduced; these indicators mean that the current comprehensive energy consumption for smelting 1t of steel is only equivalent to 1 / 4-1 / 5. In addition, industrial dust emissions have also dropped significantly, promoting green production, green manufacturing, and intelligent manufacturing in the industry. A large number of garden-type factories and cleaner production environment-friendly steel companies have emerged one after another.
(This article is reproduced from the World Metal Herald)