High-toughness hot-rolled high-strength steel with yield strength being 800 MPa and manufacturing method of high-toughness hot-rolled high-strength steel

Abstract

The invention discloses high-toughness hot-rolled high-strength steel with the yield strength being 800 MPa and a manufacturing method of the high-toughness hot-rolled high-strength steel. The chemical components of the high-toughness hot-rolled high-strength steel comprise, by weight, 0.02-0.05% of C, 0-0.5% of Si, 1.5-2.5% of Mn, 0-0.015% of P, 0-0.005% of S, 0.02-0.10% of Al, 0-0.006% of N, 0.01-0.05% of Nb, 0.01-0.03% of Ti, 0.03-0.06% of Nb and Ti, 0.1-0.5% of Cr, 0.1-0.5% of Mo, 0.0005-0.0025% of B, and the balance Fe and inevitable impurities. According to the high-toughness hot-rolled high-strength steel, the design thinking of ultra-low carbon martensite is adopted, the grain size of austenite is refined through compound addition of Nb and Ti, the hardenability and the temper hardening resistance are improved through compound addition of Cr and Mo, and by utilizing the hot continuous rolling technique, ultra-low carbon martensite structures are obtained through direct quenching or the low-temperature coiling technique; the yield strength of the high-strength structural steel can reach 800 MPa, quite excellent low-temperature impact toughness can still be achieved within the temperature range from minus 80 DEG C to room temperature, and the ballistic work can reach over 100 J at the temperature of minus 80 DEG C.

Description

technical field [0001] The invention belongs to the field of structural steel, and in particular relates to a high-toughness hot-rolled high-strength steel with a yield strength of 800 MPa and a manufacturing method thereof. Background technique [0002] In the construction machinery industry such as truck cranes, concrete pump trucks, and concrete mixer trucks, more and more companies are gradually increasing the use of high-strength structural steel, adopting high-strength thinning in the design of new models, and accelerating product upgrades. At present, high-strength steels with a yield strength of 600 and 700 MPa have been widely used. However, the application of high-strength steel with a yield strength above 800 MPa is still relatively limited. The composition design of 600 and 700MPa grade hot-rolled high-strength steel mostly adopts the addition of high titanium for precipitation strengthening, and the structure is mostly granular bainite. The ductile-brittle tra...

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Problems solved by technology

[0004] Chinese patent 03110973.X discloses an ultra-low carbon bainitic steel and its manufacturing method, because the cooling stop temperature after water cooling is between the bainite transformation temperature Bs and the martensite transformation temperature Ms or below the Bs point. In the range of -150°C, its strength is low. Even if a relatively high content of Cu and Ni is added and tempered at a medium-high temperature, the highest yield strength of the steel plate does not reach 800MPa, and its structure is mainly ultra-low carbon bainite; and After the Cu content exceeds 0.4%, tempering treatment must be carried out, which increases the process flow and manufacturing cost. Therefore, using this patent can only produce a series of high-strength steels with low strength, which cannot reach a yield strength of 800MPa or more.

As we all know, when the Mn content reaches more than 3%, although the mechanical properties of the steel plate are better, for steel mills, such a high Mn content is extremely difficult in steelmaking, especially in continuous casting, and the billet is prone to cracks during continuous casting , and cracks are prone to occur during hot rolling, and the practicability is poor; moreover, the carbon content in Example 4 reaches more than 0.07%, which does not belong to the ultra-low carbon category in the usual sense

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