Time : January 31, 2024
In the current era of high-quality development and green and low-carbon development in the steel industry, stainless steel has become a promising steel product due to its high corrosion resistance, long service life, low life cycle cost, and 100% recycling. The acceleration of the localization process of industrial materials such as nuclear power, military, and chemical industries, as well as the expansion of civil markets such as construction engineering and water supply, all indicate that the application prospects of stainless steel pipes are broad. The demand for products from users is constantly moving towards high-end – high, precision, special, fast, specialized, and provincial. At the same time, it will also promote the continuous innovation and progress of high-end stainless steel pipe manufacturing technology, support the stainless steel pipe industry to move towards green, intelligent, and high-quality Development towards service-oriented direction.
At the 2021 (2nd) China Stainless Steel Pipe Summit Forum, Academician Wang Guodong released the research results of high-end stainless steel pipe manufacturing technology by Professor Jiang Zhouhua’s team at the 2011 Steel Common Technology Collaborative Innovation Center of Northeastern University. This article is organized based on the conference report.
According to the data from the Stainless Steel Branch of the China Special Steel Enterprise Association, the crude stainless steel production in China in 2020 was 30.139 million tons, an increase of 2.51%. Among them, Cr Ni steel (300 series) was 14.3796 million tons, accounting for 47.71%; 5.925 million tons of Cr steel (400 series), accounting for 19.66%; Cr Mn steel (200 series) weighs 9.6432 million tons, accounting for 32.007%. Imported stainless steel reached 1.8059 million tons, an increase of 686200 tons year-on-year or 61.33%; The export of stainless steel reached 3.4169 million tons, a year-on-year decrease of 255400 tons and a decrease of 6.95%. The apparent consumption of stainless steel was 25.6079 million tons, an increase of 6.64%.
2.1 High nitrogen stainless steel
High nitrogen steel is a new type of engineering material that has emerged in recent years. It is a steel whose actual nitrogen content exceeds the limit value that can be achieved by preparing materials under atmospheric pressure (0.1 MPa). Among them, the nitrogen content of high nitrogen austenitic stainless steel is above 0.40%, while the nitrogen content of high nitrogen ferritic iron and martensitic stainless steel is greater than 0.08%. The use of nitrogen as an alloying element can not only stabilize the austenite structure, improve strength, and prevent a significant decrease in toughness, but also improve corrosion resistance.
At present, high nitrogen stainless steel has become a major research hotspot, especially high nitrogen austenitic stainless steel. For example, the protective ring made of P900 (18Cr-18Mn-0.6N) has high yield strength and plasticity, good corrosion resistance, especially stress corrosion resistance, and low magnetic permeability. High end non-magnetic drill collars have low magnetic permeability, high mechanical strength, superior corrosion resistance, intergranular corrosion cracking resistance, and superior wear resistance.
2.2 Duplex stainless steel
Dual phase stainless steel is mainly composed of ferrite and austenite phases, and is a type of steel that combines many excellent properties such as excellent corrosion resistance, high strength, and easy processing. The physical properties are between austenitic stainless steel and ferritic stainless steel. Has excellent resistance to chloride stress corrosion and pitting corrosion; Good corrosion fatigue and wear corrosion performance; Excellent comprehensive mechanical properties, with high strength and fatigue strength; Good welding performance; The material has excellent formability and is widely used in fields such as shipbuilding and transportation, petroleum and chemical industry.
Typical varieties of duplex stainless steel:
It belongs to the low alloy type and represents the grade UNS S32304 (23Cr-4Ni-0.1N). The steel does not contain molybdenum and has a PREN value of 24-26. It can replace AISI304 or 316 in terms of stress corrosion resistance.
The second type belongs to the medium alloy type, with a representative grade of UNS S31803 (22Cr-5Ni-3Mo-0.15N, i.e. 2205) and a PREN value of 32-35. Its corrosion resistance is between AISI316L and 6% Mo+N austenite.
The third type belongs to the high alloy type, generally containing 25% Cr, as well as molybdenum and nitrogen, and some also containing copper and tungsten. The standard grade UNS32550 (25Cr-6Ni-3Mo-2Cu-0.2N) has a PREN value of 37-39, and the corrosion resistance of this type of steel is higher than that of 22% Cr duplex stainless steel.
The fourth type belongs to the super duplex stainless steel type, containing high molybdenum and nitrogen, standard grade UNS S32750 (25Cr-7Ni-3.7Mo-0.3N, i.e. 2507), some also contain tungsten and copper, PREN value greater than 40, suitable for harsh medium conditions, with good corrosion resistance and mechanical comprehensive properties, comparable to super austenitic stainless steel.
The development trend of duplex stainless steel varieties is economic, super, and super. Among them, LDX 2101 (UNS S32101) is a low nickel and high nitrogen duplex stainless steel that has been successfully developed as an economical Z. It has high strength and good resistance to chloride stress corrosion cracking. It has been widely used in special chemical environmental equipment such as papermaking industry equipment, food processing equipment, offshore oil platforms, desalination (seawater desalination) equipment, etc. SAF 3207HD has extremely high tensile strength, ranging from 980 to 1180MPa, with a PREN of 50 and a critical point corrosion (CPT) of 90 ℃. It can be used for oil and gas production in deeper water, higher temperature and pressure environments, making it an ideal material for deep water projects. DP-3W high corrosion resistant super duplex stainless steel plate is mainly used in salt production, soy sauce brewing equipment containing high chloride in the food industry, as well as in environments with severe chloride ion corrosion such as pumps for underwater oil extraction.
2.3 Super austenitic stainless steel
Super austenitic stainless steel is a special type of stainless steel. Compared with ordinary austenitic stainless steel, the content of alloying elements such as Ni, Cr, Mo, N is higher than the general value, especially Mo, which can reach 4.5% to 7%. Its main characteristics are:
Super austenitic stainless steel is mainly used for manufacturing seawater treatment equipment, wet flue gas desulfurization absorption towers, flue gas purification equipment, heat exchangers, and pharmaceuticals? Bleaching equipment in industries such as industry and papermaking.
2.4 Special stainless steel
Special stainless steel products are mainly used in corrosion-resistant plastic molds (such as 4Cr13, 4Cr13Mo, 4Cr13MoN); Nuclear power main pipelines, high-pressure boiler pipes, blades, retaining rings, turbine guide vanes and blades in the energy field (nuclear power, thermal power, hydropower); Oil and gas extraction (such as super 13Cr, 15Cr, duplex stainless steel); High temperature and corrosion-resistant components (pipelines, valves) in petrochemical industry; Marine engineering (seawater desalination, deep sea oil extraction, construction) (such as super duplex stainless steel, super austenitic stainless steel, duplex stainless steel reinforcement); In the aviation industry (such as high-strength stainless bearing steel (CSS-42L, X30CrMoN152), high-strength fasteners PH13-8Mo, 15-5PH); In the field of environmental protection (such as super stainless steel NAS 254N and NAS 354N for flue gas desulfurization).
In addition, there are stainless steel materials used in thermal fusion experimental reactors, stainless steel materials used in nuclear power – main pipelines, and ultra high strength stainless steel used in aviation.
3.1 High end stainless steel smelting technology – electroslag remelting
The high-end high-quality special steel produced by electroslag remelting accounts for more than 90% of the total output of special metallurgy in China. Electroslag remelting is the main method for producing high-end special steel and alloys. It is a special metallurgical method in which the consumable electrode is remelted and refined through slag resistance heat in a water-cooled crystallizer, and sequentially solidified into steel ingots. It has significant characteristics such as slag washing and refining, sequential solidification, no large inclusions in the ingot, small macroscopic and microscopic segregation, and uniform composition and structure. Suitable for large steel ingots with harsh production and service conditions (high temperature, high pressure, high speed, heavy load, corrosion), severe segregation during solidification, and high alloy ingots that are prone to segregation and precipitation of brittle phases. Mold casting and continuous casting (large inclusions and segregation) cannot be replaced.
Traditional electroslag remelting has problems such as high power consumption, severe pollution, high cost, low cleanliness, poor solidification quality, and shortage of high-quality large ingots. It is urgent to develop a new generation of electroslag remelting technology to meet the needs of high-end equipment upgrading, harsh service conditions, extremely high performance requirements, and unit parameter upgrading.
The Innovation Center for Common Technology of Steel at Northeastern University innovatively adopts the Constant State of all Parameters (CSP) theory, which achieves low permeability slag, fully enclosed inert gas protection, constant slag temperature and composition, molten pool, and slag steel oxidation properties; The innovation adopts the Super Cooling Optimal Melting Rate Shallow Pool (SCOM-SP) homogenization control theory under ultra fast cooling and Z-optimal melting rate. While considering surface forming quality, Z maximizes the reduction of LST (local solidification time), reduces macroscopic and microscopic segregation of steel ingots, and achieves homogenization solidification in the electroslag process.
Innovatively developing a complete set of technology and equipment for semi continuous electroslag remelting of solid and hollow steel ingots. Compared with the traditional electroslag remelting process, the innovative process reduces processes, improves quality, and lowers costs, achieving continuous, efficient, and low-cost production; The material yield of semi continuous solid steel ingots produced through innovative processes has increased by 10%, production efficiency has increased by 60%, and costs have been reduced by 15% -20%; The quality of semi continuous hollow steel ingots has significantly improved, with a 10% increase in material yield, a 60% increase in production efficiency, and a 30% -60% reduction in costs. This technology has been evaluated by the expert group of the China Iron and Steel Industry Association as having reached a leading level in overall technology.
The key materials for CRP1000 and CAP1400 nuclear power plants and 700 ℃ demonstration power plants provided by Baowu Special Metallurgy contribute to the first lunar exploration project, including the Chang’e satellite, the Long March 3A carrier rocket, and the Shenzhou-6 manned spaceflight and carrier rocket. The 20MnNiMo electroslag steel plate produced by Wugang is used for supporting components of 80000 ton molding machines, with a maximum thickness of 390mm; SXQ500D and other hydroelectric steel plates, with a maximum thickness of 305mm, meet the requirements of key components for Baihetan and Wudongde hydroelectric power stations, fill the domestic gap, replace imports, and reduce the import price from 60000 yuan/t to 20000 yuan/t.
The 100 ton level large electric slag steel produced by Tongyu Heavy Industry has become the world’s first key material for the main pipeline of the AP1000 nuclear power plant, filling the gap and being exported abroad; We have provided thick electric slag steel plates for the fourth generation nuclear power demonstration project in Xiapu, Fujian, China, and achieved the localization of the fourth generation nuclear power steel. Daye Special Steel has become a global top supplier of electric slag materials for bearing manufacturing enterprises such as SKF, FAG, TIMKEN, etc. Its supply share accounts for over 60% of China’s quasi high-speed railway (160km/h) bearing material supply. The electric slag cold rolling rolls of China Steel Xingji have a domestic market share of 70% in the plate and strip market, and are exported to more than 50 countries around the world.
3.2 High end stainless steel smelting technology – pressurized metallurgy
Pressure not only enhances the metallurgical process by increasing element solubility, improving thermodynamic and kinetic conditions, but also improves the solidification structure by changing the phase transition of the solidification process, enhancing cooling effectiveness, and shortening local solidification time.
Pressure electric slag remelting (PESR) is currently an effective method for producing high nitrogen steel commercially. There are currently two typical alloying methods: alloy addition devices (Germany) and manufacturing composite electrodes (Japan). The German Z large pressure electric slag furnace has a capacity of 20 tons, and the operating pressure of the smelting chamber is 4.2 MPa. The Z large production ingot has a diameter of 1 meter and weighs 20 tons.
In order to promote the development of industries such as aviation and new materials in Liaoning, the Steel Common Technology Innovation Center of Northeastern University has reached cooperation intentions with Fushun Special Steel, 601 (Shenyang Aircraft Design and Research Institute), 606 (Shenyang Engine Research Institute), 410 (Dawn), 112 (Shenyang Aircraft), Liaoning Zhongwang, and others, From 2023 to 2024, the industrialization of high nitrogen stainless bearing steel (X30-NEU) will be achieved in the Shenfu Demonstration Zone using 10 ton industrial equipment (10 ton pressurized ladle furnace, 10 ton pressurized electric slag furnace), and the products will be expanded to high-end molds, medical equipment, military cutting tools, and other fields.
3.3 Special alloy smelting technology
For the metallurgical quality control technology of difficult to deform high-temperature alloy GH4151 ingots, the Iron and Steel Common Technology Innovation Center of Northeastern University has conducted research from the aspects of ingot structure analysis, alloy solidification behavior, alloy segregation characteristics, crack formation mechanism, and homogenization process research. The ingot quality control criteria have been formulated. After extrusion opening, near isothermal forging forming, and Z-final heat treatment, the Z-final effect on the microstructure of the disc is studied γ’ Evaluate the phase and mechanical properties.
By controlling the metallurgical quality of GH4151 alloy ingots, the GH4151 discs prepared have excellent mechanical properties such as tensile performance, durability, and fatigue performance, all of which exceed the technical specifications provided by the engine design manufacturer. Compared with other disc alloys, GH4151 alloy has similar tensile and durability properties to typical deformation and powder disc levels abroad; Exceeding the mechanical properties such as tensile and durability of domestic deformable disk alloys and powder high-temperature alloys; The fatigue performance of GH4151 alloy exceeds that of domestic powder high-temperature alloys.
The superior performance of the disc has been verified by controlling the ingot size, hot charging and annealing, crack control, homogenization process, and element segregation control γ’ The correctness and rationality of organizational control. The next step will be to conduct pilot testing and industrial transformation at the Shenfu New Area Industrial Research Institute.
2024 January 4th Week XZBRG Product Recommendation:
Stainless Steel Ball Bearings:
Stainless steel ball bearings can resist corrosion caused by moisture and other individual medium. 316 stainless which provides superior corrosion resistance when compared to conventional 440 stainless balls.
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