The invention discloses a manufacturing method of an X70 large-deformation steel fire-bent
pipe. The manufacturing method comprises the following steps of 1, utilizing a straight seam submerged-
arc welding steel
pipe made by steel plate controlled-rolling and controlled-cooling as a base
pipe, 2, carrying out medium-frequency
induction heating bending of the main pipe by an integral heating
quenching bending technology under the conditions of an
induction heating temperature of 950 to 1050 DEG C and a feeding rate of 40 to 80mm / min, and cooling at a
cooling rate greater than or equal to20DEG C / s by an external
spray cooling method, and 3, putting the fire-bent pipe obtained by the step 2 into a
heating furnace, carrying out integral heating at a temperature of 700 to 850 DEG C, carrying out heat preservation for 1.0 to 2.0 hours, carrying out
quenching, and carrying out integral
tempering under the conditions of a
tempering temperature of 350 to 550 DEG C and
tempering heat preservation time of 1.5 to 2.5 hours. The X70 large-deformation steel fire-bent pipe obtained by the manufacturing method has bent pipe strength and
toughness satisfying X70 standard requirements, a high longitudinal tensile
stress ratio, a high uniform elongation percentage, and a good
longitudinal deformation capability.