Development history and characteristics of duplex stainless steel in China
I. Development history of duplex stainless steel in China
Duplex Stainless Steel Production: From 2005 to 2007 (the starting period), China's duplex stainless steel production was no more than 10,000 tons, accounting for no more than 0.3%. From 2008 to 2014 (the accumulation period), China's duplex stainless steel production was between 1 and 5 thousand tons. From 2015 to 2018, it grew almost linearly, and from 2018 to 2020, it steadily increased, exceeding 150,000 tons in 2018, reaching 160,700 tons, and nearly 200,000 tons in 2020. In 2021, it leaped to 240,600 tons.
During the continuous growth of duplex stainless steel production in China, significant changes have occurred in its applications, varieties, and specialization:
1.In terms of varieties, plate accounts for more than 70% of duplex stainless steel production, while tubes account for approximately 10-15%.
2.Specialization:
It is divided into three major series: duplex stainless steel plate, duplex stainless steel tube, and duplex stainless steel round steel (tube blank).
Plate is mainly represented by Taigang, with an annual output of approximately 80,000 tons of duplex stainless steel. The production of duplex stainless steel plate by companies such as Jiugang and Qingtuo Group has also increased year by year. Tube production has formed specialized production enterprises, such as Jiuli Special Material Technology and Wujin Stainless, focusing on duplex stainless steel round steel (tube blank). Yongxing Special Stainless Steel, Taigang, and Baowu Special Metallurgy are the main producers, with Yongxing Special Stainless Steel's duplex stainless steel round steel reaching tens of thousands of tons (14,807 tons in 2021).
3.Application expansion:
While consolidating and improving the traditional main application fields of duplex stainless steel in petrochemicals, China's duplex stainless steel has continuously expanded in multiple areas, including oil and gas transportation, chemical shipbuilding, nuclear power, construction, petroleum refining, environmental protection engineering, rail transit, building curtain walls, water conservancy engineering, tanks, plate heat exchangers, pulp and paper making, and food machinery.
II.Characteristics of Duplex Stainless
Steel As the only stainless steel with a dual-phase microstructure, duplex stainless steel has the following characteristics:
1.High alloy content, with high Cr, Mo, and N levels
2.N-alloying
3.Dual-phase microstructure, α-phase/γ-phase: ~1:1
Due to its compositional restrictions, duplex stainless steel is a niche steel in terms of production and application within the stainless steel family. However, its high alloy content, dual-phase microstructure, high strength, and high corrosion resistance make it an indispensable steel in high-end equipment.
Although austenitic stainless steel and ferritic stainless steel are the two most important steel types in terms of usage and have received attention from various production enterprises, duplex stainless steel, as a niche steel with a production volume of less than 1%, has a similar status to super austenitic stainless steel and super duplex stainless steel in high-end equipment applications.
Duplex stainless steel and super austenitic stainless steel are easier to achieve high Cr, Mo, and N alloying, which means that both duplex stainless steel and super austenitic stainless steel are more easily N-alloyed and achieve processable, high PREN values.
Each of the four types of stainless steel has its own characteristics. Martensitic stainless steel has high strength (among which high-carbon martensitic steel is mainly strengthened, but its ductility is relatively poor, while age-hardening and PH steel can achieve high strength and toughness through purity control, and are widely used in the aerospace field); austenitic stainless steel is the largest and most widely used stainless steel due to its excellent corrosion resistance and processing performance; and ferritic stainless steel is basically free of Ni and has excellent stress corrosion resistance.
Duplex stainless steel is the only stainless steel with a dual-phase microstructure. Due to the different effects of alloy elements on the phase ratio and their different distributions in the two phases, duplex stainless steel has a greater range of microstructure and performance control, but it also presents challenges in microstructure and performance control. The difficulties mainly include:
1.Accurate control of N and ensuring purity
2.Thermal plasticity characteristics and difficulties
3.Precipitation sensitivity and precipitation phase characteristics
4.Dual-phase microstructure control and performance improvement
