Mechanical properties of X70 spiral submerged arc welded steel pipe:
Rating and material: X70
Model: Φ1016mm × 14.6mm spiral submerged arc welded steel pipe
Production requirements: API SPEC 5L X70 acicular iron body, oxygen converter or electric furnace smelting, vacuum degassing, calcium and micro titanium treatment, low carbon microalloyed killed steel; TMCP production steel plate (roll), grain size 10 or less, Non-metallic inclusions ≤ 2.
Tensile properties:
Steel pipe: σs(σt0.5)=485~620 MPaσb≥570 MPa yield ratio ≤0.90
Steel plate (volume): σs(σt0.5)=530~620 MPaσb≥570 MPa yield ratio ≤0.92
According to API Specification 5L, the elongation requirement is calculated to be ≥ 22%.
Weld seam σb≥570 MPa


toughness:
Dwtt: steel plate (volume) (-15 ° C) single Sa% ≥ 70 average Sa% ≥ 85
Steel pipe: (-5 ° C) single Sa% ≥ 70 average Sa% ≥ 85
Charpy impact: pipe transverse (-20 °C) single Sa% ≥ 80 average Sa% ≥ 90 single Cv ≥ 140J average Cv ≥ 190J
Welding and heat affected zone (-20 °C): single Sa% ≥ 30 average Sa% ≥ 40 single Cv ≥ 60 J average Cv ≥ 90


In addition to a small amount of nickel, chromium, copper and molybdenum in the niobium, vanadium, titanium and X70 pipeline steels, the formation of ferrite is delayed to a lower temperature, which is beneficial to acicular ferrite and lower bainite. form. The microstructure of the X70 steel plate is mainly acicular ferrite. A small amount of granular bainite is added, the band structure is less than 2.0, and the crystal grains are fine, which is substantially 11-12. Therefore, X70 pipeline steel is essentially a high-strength, high-toughness acicular ferrite pipeline steel.


The X70 grade coil is deformed and hardened due to its special structure. The degree of influence is high, which greatly reduces the influence of the Bauschinger effect, and the yield strength loss is only about 10 MPa.


Since the tensile strength is mainly determined by the saturation value of the work hardening of the material, after the pipe is made, the tensile strength value is slightly increased, and the post-yield ratio of the pipe is lowered, thereby improving the plastic deformation ability of the steel pipe.