Pressure vessel steel plate resistant against hydrogen-induced cracking and manufacturing method thereof

Abstract

An anti-hydrogen-induced-cracking pressure vessel steel plate containing, chemical composition of the steel plate according to the weight percentage: 0.16-0.20% of C, 0.15-0.40% of Si, 1.05-1.20% of Mn, less than or equal to 0.008% of P, less than or equal to 0.002% of S, less than or equal to 0.01% of Nb, less than or equal to 0.01% of V, less than or equal to 0.01% of Ti, less than or equal to 0.0005% of B, and the balance being Fe and inevitable impurity elements; carbon equivalent Ceq is less than or equal to 0.42%, and the computational formula for the carbon equivalent is Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15.

1 . An anti-hydrogen-induced-cracking pressure vessel steel plate, characterized by comprising, chemical composition of the steel plate according to the weight percentage: 0.16-0.20% of C, 0.15-0.40% of Si, 1.05-1.20% of Mn, less than or equal to 0.008% of P, less than or equal to 0.002% of S, less than or equal to 0.01% of Nb, less than or equal to 0.01% of V, less than or equal to 0.01% of Ti, less than or equal to 0.0005% of B, and the balance being Fe and inevitable impurity elements; carbon equivalent Ceq is less than or equal to 0.42%, and the formula for calculating the carbon equivalent is
   Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15;   wherein the anti-hydrogen-induced-cracking pressure vessel steel plate is made by the following steps:   (1) smelting technology   continuous casting slabs are adopted for production with following process route of KR pretreatment, converter smelting, LF refining, RH refining, continuous casting, smelting materials are pretreated with KR molten steel, slag-off treatment is conducted after converter steel making, the content of S is strictly controlled to be less than or equal to 0.001% and P less than or equal to 0.006%, each of Group A, Group B, Group C, Group D and Group Ds nonmetallic inclusions has a chart diagram index of less than or equal to 1.0, and their sum is less than or equal to 3.5; low-superheat pouring with whole-course argon protection is adopted for continuous casting, casting slab segregation B is controlled to be under grade 1.0 by means of the dynamic soft-reduction technology, and plate slabs are covered and slowly cooled for over 48 h after exiting the line, so that hydrogen in steel can diffuse sufficiently;   (2) heating and rolling technologies   a segmented heating method is adopted, total heating time is 225-300 min, the temperature of a first heating segment is 1050-1150° C., the temperature of a second heating segment is 1200-1260° C., the temperature of a soaking zone is 1170-1250° C., and the total heating time of the second heating segment and the soaking zone is longer than or equal to 120 min;   a two-stage rolling technology is adopted, the high-temperature large-reduction rolling technology is adopted in the rough rolling stage, and there are at least two longitudinal rolling passes with single-pass rolling reduction greater than or equal to 50 mm; the accumulated reduction ratio of the finish rolling stage is greater than or equal to 60%, finish rolling temperature is controlled between 780 and 820° C., ACC fast cooling is applied after rolling, and steel plates are stacked and slowly cooled for over 72 h after come out of production line, so that sufficient hydrogen diffusion can be realized;   (3) heat treatment technology   the subcritical quenching and tempering technology is adopted, wherein the subcritical quenching has a quenching temperature of 820-850° C. and soaking time factor of 1.8-2.0 min/mm, after that water cooling is conducted; and then tempering, wherein the tempering has a tempering temperature of 640-670° C. and soaking time factor of 3.5-4.5 min/mm.