How much do you know about the details of 12Cr1MoVG alloy steel pipe

12Cr1MoVG alloy steel pipe is a low-alloy heat-resistant steel. Vanadium is an element that shrinks the V-phase region; when dissolved in V-Fe, it inhibits the transformation of austenite to pearlite, which is beneficial to the formation of austenite. The total alloy content in this steel is only half that of 2.25Cr-1Mo steel, but its creep strength (580℃) is 1.4 times that of 2.25Cr-1Mo. The maximum operating temperature of 12Cr1MoVG alloy steel pipe: 12Cr1MoVG/GB5310 is mainly used for boiler superheaters, reheaters, and other heating surface piping systems with metal wall temperatures not exceeding 580℃, and boiler headers and main steam pipelines with metal wall temperatures not exceeding 565℃.

Chemical composition of 12Cr1MoVG alloy steel pipe: Carbon: 0.08~0.15, Silicon: 0.17~0.37, Manganese: 0.40~0.70, Molybdenum: 0.25~0.35, Chromium: 0.90~1.20, Vanadium: 0.15~0.30

Mechanical properties of 12Cr1MoVG alloy steel pipe:

Tensile strength (σb/MPa): ≥490,

Yield point (σs/MPa): ≥245

Elongation after fracture (δ5/%): ≤22,

Reduction of area (ψ/%): ≥50,

Impact energy (Aku2/J): ≥71,

Impact toughness value αkv (J/cm2): ≥88(9) Brinell hardness (HBS100/3000) (annealed or high-temperature tempered state): ≤179

Process properties of 12Cr1MoVG alloy steel pipe:

(1) Forging and rolling details of 12Cr1MoVG alloy steel pipe: initial forging temperature 1180~1145℃, final forging temperature greater than 850℃, followed by stacking and cooling.

(2) Cold and hot working of 12Cr1MoVG alloy steel pipe: small diameter steel pipes can be cold-bent, and no heat treatment is required after bending. Large diameter thin-walled pipes can be cold-bent, and high-temperature tempering heat treatment is required after bending. Large-diameter thick-walled pipes need to be hot-bent. The heating temperature for hot-bent pipes is 980℃, the final bending temperature is >800℃, and normalizing and tempering heat treatment are required after bending.

(3) Heat treatment of 12Cr1MoVG alloy steel pipe: finished steel pipes should undergo normalizing + tempering heat treatment. The heat treatment specifications have a relatively sensitive impact on the properties of the steel. Recommended normalizing temperature: 980~1020℃. Holding time: 1 minute per millimeter of wall thickness, but not less than 20 minutes; Tempering temperature: 720~760℃, holding time: greater than 2 hours. For wall thicknesses greater than 30mm to 40mm, forced cooling should be performed; for wall thicknesses greater than 40mm, quenching and tempering treatment should be performed. Quenching temperature: 950~990℃; Tempering temperature: 720~760℃, holding time: greater than 2 hours. When the final rolling temperature of the 12Cr1MoVG alloy steel pipe is the normalizing temperature of 980~1020℃, hot rolling can replace normalizing. The normal microstructure of finished 12Cr1MoVG alloy steel pipe after heat treatment is ferrite + pearlite + bainite. Excessive tempering temperature after normalizing will result in undesirable interphase transformation products—blocky martensite; low tempering temperature easily leads to embrittlement.

(4) Welding materials for 12Cr1MoVG alloy steel pipes: manual welding, gas shielded tungsten inert gas (GSIG), and metal inert gas (MIG) automatic welding, or submerged arc welding can be used. For small-diameter, thin-walled pipes with excessive height, argon arc welding can be used for the root pass, followed by manual or automatic welding for the cover pass. For circumferential welds of large-walled, large-diameter pipes with excessive height for boiler headers, argon arc welding can be used for the root pass, followed by submerged arc welding for the cover pass. For welds of 12Cr1MoVG alloy steel pipes, internal argon arc welding can be used for the root pass, followed by manual welding for the cover pass. E5515-B2-V (R317) welding rods are used for manual arc welding, and H08CrMoV welding wire is used for automatic welding. Although this steel has good weldability, it tends to cold crack and be brittle. It should be preheated to 200~250℃ before welding (preheating is not required for small-diameter, thin-walled steel). After welding, it should be subjected to stress relief heat treatment at 700~740℃.