Foreword: As we all know, the most frequently searched commodity in March 2022 is nickel, and the "five consecutive breakthroughs" of nickel has shocked the global international financial market. Its industrial chain and supply and demand have attracted much attention and become a hot topic sought after by the market. . There are many varieties of nickel industry chain. The Mysteel team is deeply involved in the research of each link of the nickel industry chain and obtains the most real data information in the industry in time. Mysteel has compiled a special series entitled "Detailed Explanation of Various Species of the Nickel Industry Chain", in order to improve the Good service to the majority of Mysteel customer groups, so as to further understand the various varieties of the nickel industry chain.

This article is a comprehensive introduction to stainless steel in the middle and lower reaches of the nickel industry chain. The full text will focus on five chapters: stainless steel definition, stainless steel classification, smelting process, production capacity and distribution, and stainless steel application. Reference for people from all walks of life.

First, the definition of stainless steel

In my country's iron and steel industry, ordinary carbon steel and special steel coexist. Different from ordinary steel, special steel has higher strength and toughness, physical properties, chemical properties, biocompatibility and process properties, and has a wider range of applications. As an important branch of special steel, stainless steel has relatively more special application fields and higher performance requirements.

From the definition of stainless steel, stainless steel refers to the general term for steel with certain chemical stability in air, water, acid-base salt or other corrosive medium. The good corrosion resistance of stainless steel is due to the addition of chromium to the steel matrix, and the addition of nickel, molybdenum and other elements further improves the corrosion resistance and improves the processing performance.

2. Classification and characteristics of stainless steel

Stainless steel is often divided into: martensitic steel, ferritic steel, austenitic steel, austenitic-ferritic (duplex) stainless steel and precipitation hardening stainless steel according to the structure state. In addition, it can be divided into chromium stainless steel, chromium-nickel stainless steel and chromium-manganese-nitrogen stainless steel according to the composition.

1. Ferritic stainless steel

Generally, it contains 15% to 30% chromium. Its corrosion resistance, toughness and weldability increase with the increase of chromium content, and its resistance to chloride stress corrosion is better than other types of stainless steel. Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28, etc. Because of the high chromium content, ferritic stainless steel has good corrosion resistance and oxidation resistance, but poor mechanical properties and process performance. It is mostly used for acid-resistant structures and oxidation-resistant steels with little stress. This kind of steel can resist the corrosion of the atmosphere, nitric acid and brine solution, and has the characteristics of good high temperature oxidation resistance and small thermal expansion coefficient. .

2. Austenitic stainless steel

Generally, it contains more than 18% chromium, and also contains about 8% nickel and a small amount of molybdenum, titanium, nitrogen and other elements. It has good comprehensive performance and is resistant to corrosion by various media. The commonly used grades of austenitic stainless steel are 1Cr18Ni9, 0Cr19Ni9, etc. This type of steel contains a large amount of nickel and chromium, which makes the steel in an austenitic state at room temperature. This type of steel has good plasticity, toughness, weldability, corrosion resistance and non-magnetic or weak magnetic properties. It has good corrosion resistance in oxidizing and reducing media. It is used to make acid-resistant equipment, such as corrosion-resistant containers and equipment. Linings, conveying pipes, nitric acid-resistant equipment parts, etc., can also be used as the main material of stainless steel watch accessories. Austenitic stainless steel is generally solution treated, that is, heating the steel to 1050-1150 °C, and then cooling it with water or air to obtain a single-phase austenite structure.

3. Austenitic-ferritic duplex stainless steel

It has the advantages of both austenitic and ferritic stainless steels, and has superplasticity. Austenitic and ferritic structures each account for about half of stainless steel. In the case of low carbon content, the chromium content is 18%~28%, and the nickel content is 3%~10%. Some steels also contain alloying elements such as Mo, Cu, Si, Nb, Ti, and N. This type of steel has the characteristics of both austenitic and ferritic stainless steels. Compared with ferrite, it has higher plasticity and toughness, no room temperature brittleness, and significantly improved intergranular corrosion resistance and welding performance. The 475 ℃ brittleness and high thermal conductivity of element stainless steel have the characteristics of superplasticity. Compared with austenitic stainless steel, it has high strength and significantly improved resistance to intergranular corrosion and chloride stress corrosion. Duplex stainless steel has excellent pitting corrosion resistance and is also a nickel-saving stainless steel.

4. Precipitation hardening stainless steel

The matrix is ​​austenite or martensite, and the commonly used grades of precipitation hardening stainless steel are 04Cr13Ni8Mo2Al and so on. It is capable of hardening stainless steel by precipitation hardening, also known as age hardening.

5. Martensitic stainless steel

High strength, but poor plasticity and weldability. The commonly used grades of martensitic stainless steel are 1Cr13, 3Cr13, etc. Due to the high carbon content, it has high strength, hardness and wear resistance, but the corrosion resistance is slightly worse, and it is used for high mechanical properties and corrosion resistance. Some general parts are required, such as springs, turbine blades, hydraulic valves, etc. This type of steel is used after quenching and tempering, and needs to be annealed after forging and stamping.

3. Characteristics of China's stainless steel industry pattern

The development of my country's stainless steel industry is roughly divided into two stages. The first stage is dominated by large state-owned factories, which has created several firsts in the history of stainless steel. During this period, the stainless steel industry has achieved rapid development, and actively built stainless steel under the guidance of the state. Production base, stainless steel output has increased significantly. The second stage is the rise of private giants. Domestic private steel mills account for more than 50% of the domestic production capacity of crude stainless steel, opening a new chapter in the stainless steel industry.

On the other hand, the growth of production capacity and output must be inseparable from the change of equipment and technology. After the growth of domestic production capacity and output has gradually slowed down, more and more companies are optimistic about the raw material advantages of Indonesian nickel mines, and have gone out one after another to build ferronickel production lines and stainless steel plants in Indonesia. In summary, the pattern of my country's stainless steel industry presents the following characteristics:

With the development of China's stainless steel industry and the increasing demand, stainless steel production enterprises have also broken the pattern of two state-owned enterprises, Baosteel in the south and Taigang in the north, and a number of new private stainless steel production enterprises have emerged. Due to the flexibility of the mechanism of private enterprises and the faster innovation and development than traditional state-owned enterprises, they are more able to meet market demands and have become a force that cannot be ignored in China's stainless steel market.

The distribution of steel mills in mainstream production bases shows that in Fujian, Guangdong and Guangxi, Jiangsu, Shandong, Shanxi and other places in my country, the production capacity of stainless steel is relatively concentrated, and the production capacity of steelmaking is relatively large. Private steel mills occupy half of the country.

Under the Belt and Road Initiative, Chinese companies have deployed overseas

In 2013, China proposed the "One Belt, One Road" cooperation initiative. In 2014, Indonesia implemented a ban on the export of nickel ore. Under the "stimulation" of the above policies, the pace of Chinese stainless steel enterprises began to accelerate, and a large number of domestic enterprises went to Indonesia to build ferronickel plants and stainless steel. factory. As of 2021, Indonesia has built a stainless steel crude steel production capacity of 5.5 million tons. In addition, considering the potential new production capacity of stainless steel brought by the industrial chain extension of a number of nickel-iron production enterprises such as Xinxing Casting Pipe, Indonesia Jinchuan, Indonesia Yilian, Indonesia Xinhualian, and Liqin, Indonesia will be another new force for the growth of global stainless steel production in the future. .

Fourth, the main smelting process of stainless steel

At present, the smelting process for producing stainless steel is mainly divided into one-step method, two-step method and three-step method.

4.1 One-step smelting process

The early one-step stainless steel smelting process refers to the completion of scrap melting, decarburization, reduction and refining processes in an electric furnace, and the charge is smelted into stainless steel in one step. This one-step smelting production process that only uses electric furnace to smelt stainless steel is gradually eliminated due to long smelting cycle, low operation rate and high production cost. With the continuous development of the off-furnace refining process and the wide application of AOD furnaces, many stainless steel production enterprises currently use some low-phosphorus or dephosphorized molten iron to replace scrap steel, and use molten iron and alloys as raw materials to enter the AOD furnace for stainless steel smelting. New one-step smelting process.

Compared with the earlier one-step smelting process, the new one-step smelting process eliminates the smelting link of the electric furnace in the production process. Its advantages include: first, lower investment; second, lower production costs; consumption, and improve the purity of molten steel; fourth, the scrap ratio is low, which is suitable for the existing scrap market; fifth, it is especially economical for smelting 400 series stainless steel.

However, the new one-step method has certain requirements for raw material conditions and product solutions: First, the phosphorus content of the molten iron in the AOD furnace is required to be less than 0.03%, so the dephosphorization of the molten iron must be added to the smelting process; second, the alloy is used as the raw material in the new one-step method. It is added to the AOD furnace, and the excessive amount of high-carbon alloy added to the AOD furnace will affect the heat balance of the entire smelting process, and is not suitable for stainless steel varieties with complex compositions and high alloy content.​​

The new one-step stainless steel production process is currently widely used in the production of 400 series stainless steel. As a developing country, China lacks scrap steel resources and is extremely nickel-poor. In addition, 400 series stainless steel is widely used in daily life and industrial production. These objective conditions make the new one-step stainless steel smelting more and more popular. Many manufacturers use it.

4.2 Two-step smelting process

The two-step process route is EAF→AOD, EAF→VOD (electric arc furnace→VOD vacuum refining furnace). The production capacity of the EAF→AOD process accounts for about 70% of the world's stainless steel production capacity. The EAF furnace is mainly used to melt scrap steel and alloy raw materials to produce stainless steel pre-melt, which is then smelted into qualified stainless steel molten steel in the AOD furnace. .

In the two-step process, if the phosphorus content of the raw materials entering the electric furnace is relatively high, a link of dephosphorization of stainless steel pre-melt needs to be added between the electric furnace and the AOD furnace. The most commonly used pre-melt dephosphorization processes are converter dephosphorization and hot metal tank top spray dephosphorization. When the two-step method uses blast furnace molten iron as the main raw material for stainless steel smelting, if the blast furnace phosphorus content is high, it is also necessary to add a dephosphorization link.​​

The two-step stainless steel smelting process is widely used in the production of various series of stainless steel. 95% stainless steel variety.​​

However, the two-step method still needs to pay attention to the following three points in terms of medium consumption and variety plan: First, with the progress of the smelting process and the improvement of the operation level in recent years, the consumption of argon and other media in the two-step smelting process has been significantly reduced. However, compared with the one-step method and the three-step method, the consumption of argon and other media is still slightly larger; second, when the AOD furnace decarburizes to the end, the oxygen content in the molten steel is relatively high, and ferrosilicon must be added to reduce the oxygen in the molten steel, so the ferrosilicon consumption The third is that it cannot be used to produce ultra-low carbon and nitrogen stainless steel at present, and the gas content in the steel is relatively high.

4.3 Three-step smelting process

The basic process flow of the three-step method is: primary smelting furnace → double blowing converter/AOD furnace → vacuum refining device. The three-step method is an advanced method for smelting stainless steel, and the product quality is good, which is suitable for professional manufacturers and stainless steel production in joint iron and steel enterprises.

The three-step method of stainless steel adds a step of deep decarburization on the basis of the two-step method. The advantages of its smelting process are: first, the division of labor in each link is clear, the production rhythm is fast, and the operation is optimized; The content of oxygen and inclusions is low, and the range of products that can be produced is wide; the third is that molten iron can be used for smelting, the requirements for raw materials are not high, and the selection of raw materials is flexible.​​

However, the three-step stainless steel smelting process realizes the metallurgical function step by step, which will have the following impacts on the production investment: first, the process links are increased, and the investment and production costs are relatively high; second, the vacuum equipment system is complex and the maintenance amount is large.

At present, the smelting process for producing stainless steel in the world mainly adopts the two-step method and the three-step method. Among them, the two-step method of EAF+AOD or EAF+VOD is the most widely used, accounting for about 70%, and the three-step method accounts for about 20%. As low-phosphorus molten iron is widely used in stainless steel production, the new one-step stainless steel smelting process is also adopted by more and more stainless steel production enterprises. In order to adapt to the fierce competition in the stainless steel market, improve product quality and reduce production costs, various enterprises in my country choose appropriate stainless steel smelting processes according to their actual conditions.

4.4 RKEF+AOD double smelting process

Tsingshan Group took the lead in building and putting into operation the first RKEF production line in China in Dingxin, Fujian in 2010. Using the RKEF (rotary kiln + electric furnace) process to produce nickel-containing pig iron (nickel-iron) from nickel-rich and iron-rich nickel oxide ore has significant advantages over the general traditional process (sintering + electric furnace). The entire production process is fully enclosed, and its energy consumption and dust emissions are minimal. The electricity consumption per ton of iron in the production process is reduced by 1500 degrees, and the dust emission is reduced by 80%.

Tsingshan Group has opened up the production of ferronickel and stainless steel smelting process, and created a set of RKEF+AOD dual stainless steel smelting process. →Smelting →Continuous casting →Hot-rolled stainless steel strip, the nickel molten iron is directly sent to the AOD steelmaking furnace without cooling, and hot-loaded and sent twice, which changes the traditional mode of stainless steel production, saves a lot of energy, and greatly improves the The steelmaking speed of stainless steel reduces the loss of raw materials and produces great economic benefits. It has achieved a historic breakthrough in the continuous and integrated production of stainless steel, greatly reduced pollutant emissions, and reduced energy consumption per ton of steel by about 50%. This technology was awarded a national invention patent in 2014, which is the world's first.

5. Application of stainless steel

200 series stainless steel applications
Features: It has the characteristics of acid resistance, alkali resistance, high density, no bubbles and no pinholes in polishing.

Uses: Mainly used for decorative pipes, industrial pipes and some shallow stretched products.

300 series stainless steel applications
Characteristics: As one of the most widely used steel grades, it has good corrosion resistance, heat resistance, low temperature strength and mechanical properties. Good hot workability such as stamping and bending, no heat treatment hardening phenomenon (non-magnetic, operating temperature -196℃~800℃)

Uses: Mainly used for home appliances, tableware, kitchenware, water heaters, boilers, food machinery, etc.; currently in the field of stainless steel decorative welded pipe manufacturing in Guangdong Province, it has also been widely used, such as Haili, Great Wall, Yuehua, Xingzhongcheng, Jian Yuan, Baocheng, Wanjiahong, Lion King, Hongguan, Yunsheng, Minggao and many other member companies of Guangdong Stainless Steel Materials and Products Association are 304 stainless steel products.

400 series stainless steel applications
Characteristics: As a representative steel grade of ferritic steel, it has low thermal expansion rate, excellent formability and oxidation resistance.

Uses: Mainly used for heat-resistant appliances, burners, home appliances, Class 2 tableware, kitchen sinks, exterior decoration materials, bolts, nuts, CD rods, screens, etc.