Properties and Welding of 2507 duplex stainless steel
Duplex stainless steel has become an important engineering material, which is widely used in petrochemical, offshore and coastal facilities, oilfield equipment, paper-making, ship-building and environmental protection. 2507 duplex stainless steel is developed on the basis of the second-generation duplex stainless steel 2205. At present, there are SAF2507, UR52N+, Zeron100, S32750, 00Cr25Ni7Mo4N, etc. The 2507 structure is composed of austenite and ferrite, and both The dual characteristics of stainless steel and ferritic stainless steel have a lower thermal expansion coefficient and higher thermal conductivity than austenitic stainless steel. Its pitting corrosion coefficient (PREN) is greater than 40, and it has high resistance to pitting and gaps. Corrosion, chloride stress corrosion cracking resistance, high strength, high fatigue strength, low temperature and high toughness at the same time, is a widely used duplex stainless steel. In recent years, with the continuous expansion of the application fields of duplex stainless steel pipes, the demand for welding technology has increased, which has accelerated the development of welding technology. Therefore, summarizing and discussing the research results on the weldability of 2507 stainless steel at home and abroad has important engineering practical significance for the application of 2507 duplex stainless steel.
The very low Carbon content in the chemical composition of 2507 duplex stainless steel can improve the weldability of the steel and reduce the precipitation tendency of carbides at the grain boundary during heat treatment, increase the intergranular corrosion resistance, high chromium, high molybdenum and higher nitrogen content , Can improve the corrosion resistance, make it have a good resistance to formic acid, acetic acid, nitride and other uniform corrosion, pitting corrosion, stress corrosion resistance. Nitrogen is added as an alloying element to stainless steel, which can improve the stability of austenite, balance the phase ratio of duplex steel, increase the strength of the steel without affecting the plasticity and toughness of the stainless steel, and can partially replace the Ni in the stainless steel. Cost, N has the effect of delaying the dispersion of intermetallic compounds and stabilizing austenite in duplex stainless steel.
The structure of 2507 duplex stainless steel is composed of ferrite and austenite. The austenite is distributed on the ferrite matrix and is distributed in strips. The interface between the austenite and ferrite is not smooth when observed at higher magnifications, but is jagged. , Which shows that during the cooling process after rolling, austenite is formed by nucleation and growth at the ferrite interface. The presence of austenite in the structure of duplex stainless steel can reduce the brittleness and grain growth tendency of high chromium ferrite, improve weldability and toughness, and chromium-rich ferrite can increase the yield strength of austenite in stainless steel. Resistance to intergranular corrosion and stress corrosion, that is, the ferrite dual-phase structure has high strength and high toughness, while maintaining high resistance to stress cracking, pitting and crevice corrosion, especially chloride and sulfide It has high resistance to stress corrosion cracking, so it can effectively solve the long-standing failure problem of austenitic stainless steel caused by local corrosion.
The 2507 duplex stainless steel welding method has a wide range of applicability. It can be welded by a variety of methods. The welding heat input and cooling rate affect the phase balance of ferrite and austenite and the performance of the welded joint. In order to ensure that the weld has a suitable structure Comparative example and good mechanical properties and corrosion properties. When welding, avoid too small or too large heat input, and control it at 5～20kJ/cm. Remove the lower limit when welding thin-walled parts, and increase the heat appropriately when welding thick-walled parts. Enter, the temperature between tracks should not exceed 100°C.
