After normal solution treatment (heating and water cooling at 1020℃～1100℃), the duplex stainless steel contains about 50%-60% austenite and 50%-40% ferrite. With the increase of heating temperature, the change of the two phases is not obvious.
Duplex stainless steel has good low-temperature impact toughness, such as 20mm thick transverse specimens at -80 ℃ impact absorption work can reach more than 100J. In most media, its uniform corrosion resistance and pitting corrosion resistance are good, but it should be noted that when this type of steel is heat treated below 950°C, its stress corrosion resistance will be significantly deteriorated due to the precipitation of σ phase. Since the ratio of Cr equivalent to Ni equivalent of the steel is appropriate, a large amount of primary austenite structure remains after heating at high temperature, and secondary austenite can be generated during the cooling process, resulting in the total amount of austenite phase in the steel Not less than 30% to 40%, so that the steel has good resistance to intergranular corrosion.
In addition, as mentioned earlier, the tendency to crack when welding this steel is very low, and preheating and post-weld heat treatment are not necessary. Due to the high N content in the base material, the single-phase ferrite area will not be formed in the weld near-seam area, and the austenite content is generally not less than 30%. Applicable welding methods include tungsten electrode argon arc welding and electrode arc welding. Generally, in order to prevent coarsening of the grains near the seam area, low linear energy welding should be used when welding.
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