LOW YIELD RATIO AND HIGH TENSION STEEL PLATE EXCELLENT IN LOW TEMPERATURE TOUGHNESS OF WELD HEAT-AFFECTED ZONE AND BASE METAL, AND PROCESS FOR PRODUCING SAME

摘要

The invention discloses a high-tension steel plate with a low tensile ratio, which satisfies the specified chemical composition component, and is composed of following mixed organization: in a microscopic constitution at a position of t/4 (t: thickness of the plate), ferrolity percent in the whole organization is 60-85 surface percent; island shaped martensite percent is 1-5 surface percent; the excess is bainite constitution. Besides, remnant austenite in the island shaped martensite has over 60 surface percent. Based on the composition, low-temperature flexibility of HAZ is still excellent even when welding is carried out through high heat energy input; besides, the low-temperature flexibility of parent metal (steel plate) is also excellent.