This invention relates to a high-
ductility, high-
toughness, fatigue-resistant X65 grade steel plate for
catenary risers and its production method. The
chemical composition of the steel plate, by weight percentage, is: C: 0.040%–0.060%, Si: 0.10%–0.20%, Mn: 1.50%–1.65%, P≤0.015%, S≤0.0015%, Cr≥0.10%, Cr+Ni: 0.22%–0.33%, Cu: ≤0.20%, Nb: 0.030%–0.050%, Ti: 0.010%–0.025%, Al The
alloy composition is 0.026%–0.050%, with the balance being Fe and unavoidable impurities. Using inexpensive elements such as C, Mn, Cr, and Cu, supplemented with
trace amounts of Nb and Ni, and employing appropriate heating, rolling, and cooling processes, a fine-grained polygonal ferrite +
acicular ferrite
microstructure is obtained. The
alloy addition is low, resulting in low
alloy cost. The steel plate exhibits a transverse yield strength of 476–540 MPa and a tensile strength of 540–640 MPa, achieving X65 strength level. The steel plate has an
impact energy ≥350 J at -30℃, a CTOD ≥1.0 mm at -10℃, and a strength of 10... 7 The fatigue strength after each cycle is ≥350MPa, the longitudinal elongation after fracture of the steel plate is 57%~68%, and the uniform elongation is ≥12%, which meets the technical requirements for manufacturing X65 grade deep-water steel
catenary risers.