T91 alloy steel tube elements

T91 alloy steel tube elements
T91 steel alloy elements in solid solution strengthening, dispersion strengthening and improving the oxidation resistance, corrosion resistance of steel, concrete analysis is as follows.
(1) carbon is a solid solution strengthening effect of the most obvious element in steel, with the increase of carbon content of steel rising short-term strength, plasticity and toughness drops, for T91 martensitic steel such, higher carbon content will speed up the carbide spheroidizing and aggregation, accelerate the redistribution of alloy elements, lower steel weldability, corrosion resistance and oxidation resistance, so the heat resistant steel is generally want to reduce the carbon content, but the low carbon, will reduce the strength of steel. T91 steel compared with 12 cr1mov steel, carbon content by 20%, this is a comprehensive consideration of the above factors.
(2) the T91 steel containing trace nitrogen, nitrogen effect is embodied in two aspects. Solid solution strengthening effect on one hand, the room temperature nitrogen solubility in the steel is very small, T91 steel after welding heat affected zone in welding heating and heat treatment after welding process, will be successively appeared.vn solid solution and precipitation process: welding heat affected zone has formed by heating of austenitic organization because of.vn into, nitrogen content, then the degree of supersaturation in normal temperature group increased, in the subsequent heat treatment after welding are tiny.vn precipitation, this increases the organization stability, improved the persistent strength values of heat affected zone. T91 steel, on the other hand, also contains a small amount of A1, the nitrogen to form A1N, A1N in 1 100 ℃ above a lot into the matrix, at lower temperatures and precipitation again, can have better dispersion strengthening effect.
(3) to join the chromium mainly is to improve the oxidation resistance, corrosion resistance of heat resistant steel, chromium content is less than 5%, to 600 ℃ began to severe oxidation, and chromium content of 5% has good oxidation resistance. 12 cr1mov steel under 580 ℃ has good oxidation resistance, corrosion depth is 0.05 mm/a, 600 ℃ when the performance starts to degrade corrosion depth is 0.13 mm/a. T91 chromium content increased to 9%, the use of temperature can reach 650 ℃, the main measure is to make the matrix of dissolve more chrome.
(4) vanadium and niobium are strong carbide forming elements, after joining can form a small and stable alloy carbide and carbon, has a strong dispersion strengthening effect.
(5) join molybdenum is mainly in order to improve the steel hot strong sex, have the effect of solid solution strengthening.
T91 alloy steel tube heat treatment process
The final heat treatment of T91 for high temperature tempering, normalizing + normalizing temperature is 1040 ℃, holding time not less than 10 min, tempering temperature is 730 ~ 780 ℃, holding time not less than 1 h, eventually organization for tempering martensite after heat treatment.
T91 alloy steel pipe mechanical properties
Of T91 steel at room temperature tensile strength of 585 MPa, or room temperature yield strength 415 MPa, or higher hardness HB 250 or less, elongation (50 mm gauge standard circular specimen) 20% or higher, the allowable stress values (sigma] 650 ℃ = 30 MPa.
T91 alloy steel pipe welding performance
According to the carbon equivalent formula is recommended by the international welding T91 carbon equivalent to the weldability of T91 is poorer.

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