ASTM A213 T91 alloy steel pipes for boilers, superheaters and heat exchangers

T91 steel pipe is a new type of martensite heat resistant steel pipe.It is based on 9Cr1MoV steel to reduce the carbon content, strictly limit the sulfur, phosphorus content, add a small amount of vanadium, niobium elements for alloying.The German steel number corresponding to T91 is X10CrMoVNNb91, the Japanese steel number is HCM95, and the French steel number is TUZ10CDVNb0901.

 

Chemical Composition of T91 alloy steel pipe

C

Mn P S Si Cr Mo V Nb N

Ni

0.08-0.12

0.30-0.60 ≤0.02 ≤0.01 0.20-0.50 8.00-9.50 0.85-1.05 0.18-0.25 0.06-0.10 0.03-0.07

≤0.40

 

Performance analysis:

  1. solid solution strengthening effect of carbon is very strong, 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.Compared with 12Cr1MoV steel, the carbon content of T91 steel is reduced by 20%, which is decided by taking the above factors into consideration.
  2. T91 steel contains trace nitrogen, the role of nitrogen reflected 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.VNsolid solution and precipitation process: welding heat affected zone has formed by heating of austenitic organization because of VN, 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.On the other hand, T91 steel also contains a small amount of A1, and nitrogen can form A1N with it. A1N will dissolve into the matrix in large quantities only when the temperature is above 1,100 ℃, and then precipitates out again at a lower temperature, which can play a good dispersion strengthening effect.
  3. The addition of chromium is mainly to improve the anti-oxidation and anti-corrosion ability of heat-resistant steel, when the chromium content is less than 5%, 600℃ began to violent oxidation, and when the chromium content is up to 5%, it has a good anti-oxidation.12Cr1MoV steel has good oxidation resistance below 580℃, corrosion depth is 0.05mm /a, performance begins to deteriorate at 600℃, corrosion depth is 0.13mm /a.The chromium content of T91 is increased to about 9%, and the service temperature can reach 650℃. The main measure is to dissolve more chromium in the matrix.
  4. Vanadium and niobium are both strong carbide forming elements, which can form fine and stable alloy carbides with carbon, and have a strong dispersive strengthening effect.
  5. The main purpose of adding molybdenum is to improve the thermal strength of steel and strengthen the solid solution.

 

Heat treatment process:

The final heat treatment of T91 is normalizing + high temperature tempering, the normalizing temperature is 1040℃, the heat preservation time is not less than 10 min, the tempering temperature is 730~780℃, the heat preservation time is not less than 1h, and the structure after the final heat treatment is tempered Martensite.

 

Mechanical properties:

T91 steel has tensile strength ≥585 MPa at room temperature, yield strength ≥415 MPa at room temperature, hardness ≤250 HB, elongation (a standard circular sample with a standard distance of 50 mm)≥20%, allowable stress value 650℃=30 MPa.

 

T91 alloy steel pipes are widely used in manufacturing boilers, superheaters and heat exchangers.Please contact us to get a quotation if you need T91 steel pipes.

 

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