High-strength high-toughness low-temperature thick-plate structural steel and heat treatment method thereof

A heat treatment method for structural steel, the structural steel being composed of the following components by weight percentage:

• C:
• 0.03-0.08%, Cr:
• 0.8-1.9%, Mn:
• 0.01-1.0%, Ni:
• 3.5-7%, Mo:
• 0.2-0.5%, V:
• 0.15-0.2%, Nb:
• 0.01-0.05%, Cu:
• 1.2-3.8%, Al:
• 0-0.5%, P:
• <0.015%, S:
• <0.010%, and Fe and inevitable impurities as balance;
• wherein the heat treatment method comprises the following steps:
• (1) conducting smelting according to a ratio to form a steel ingot or an ingot blank, and soaking at 1150-1250° C.;
• conducting a total of not less than 12 passes of rough rolling and finish rolling, wherein the final rolling temperature is not lower than 750° C., and a cumulative compression ratio is 4-7;
• and conducting air cooling or water cooling;
• and
• (2) conducting off-line heat treatment, comprising:
• (2-a) quenching, denoted as Q:
• conducting austenization at 870-915° C. for 40-120 min, followed by water cooling;
• (2-b) critical tempering in a two-phase region, denoted as L:
• conducting high-temperature tempering at 625-680° C. for 40-60 min, followed by water cooling;
• or
• (2-c) tempering, denoted as T:
• conducting tempering at 525-575° C. for 30-360 min, followed by air cooling;
• wherein
• when air cooling is conducted after rolling in step (1), the off-line heat treatment comprises step (2-a), step (2-b), and step (2-c) to obtain the structural steel;
• and
• when water cooling is conducted after rolling in step (1), the off-line heat treatment comprises step (2-a), step (2-b), and step (2-c), or sequentially conducting step (2-b) and step (2-c), to obtain the structural steel.