National standards, grades and chemical composition of duplex stainless steel filter screens

National standards, grades and chemical composition of duplex stainless steel filter screens

Many duplex stainless steel grades have been added to the new Chinese standard GB/T 20878-2007 "Stainless Steel and Heat Resistant Steel Grades and Chemical Composition". For example: 14Cr18Ni11Si4AlTi, 022Cr19Ni5Mo3Si2N, 12Cr21Ni5Ti. For more grades, see the standard. In
addition: the famous 2205 duplex steel is equivalent to China's 022Cr23Ni5Mo3N.
Finally, it is wrong for some web pages and even papers to write duplex stainless steel as duplex stainless steel. Duplex refers to the presence of two metallographic structures, not the "direction".

After normal solution treatment (heating at 1020℃～1100℃ and water cooling), duplex stainless steel contains about 50%～60% austenite and 50%～40% ferrite. With the increase of heating temperature, the ratio of the two phases does not change significantly.
Duplex stainless steel has good low-temperature impact toughness. For example, the impact absorption energy of a 20mm thick plate transverse specimen at -80℃ 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℃, due to the precipitation of σ phase, its stress corrosion resistance will be significantly deteriorated. Due to the appropriate ratio of Cr equivalent to Ni equivalent of this steel, a large amount of primary austenite structure is still retained after high-temperature heating, and secondary austenite can be generated during the cooling process. As a result, the total amount of austenite phase in the steel is not less than 30% to 40%, so that the steel has good intergranular corrosion resistance.
In addition, as mentioned above, the crack tendency is very low when welding this steel, and preheating and post-weld heat treatment are not required. Due to the high content of N in the base material, a single-phase ferrite zone will not be formed in the near-seam area of welding, and the austenite content is generally not less than 30%. Applicable welding methods include tungsten inert gas arc welding and electrode arc welding. Generally, in order to prevent the coarsening of grains in the near-seam area, low line energy welding should be used as much as possible during welding.

chemical composition

Mechanical behavior