Easy-welding low-carbon bainitic steel and manufacturing method thereof

Abstract

The invention discloses an easy-welding low-carbon bainitic steel and a manufacturing method thereof, belonging to the technical field of microalloy steel. The steel comprises the chemical components by weight percent: 0.02-0.08% of C, 1.20-1.80% of Mn, 0.10-0.50% of Si, less than or equal to 0.010% of S, less than or equal to 0.015% of P, 0.10-0.30% of Mo, 0.020-0.050% of Nb, 0.03-0.10% of V, 0.005-0.030% of Ti, 0.0050-0.010% of N, 0.0005-0.0020% of B, less than or equal to 0.035% of Al and balance of Fe and inevitable impurities. The proportion between the boron content and the nitrogen content in the steel simultaneously meets the conditions that 3N-10B is more than or equal to 0.005 and less than or equal to 0.015, and Ti+V+10B is more than or equal to 8.525N. The production process of smelting by an electric furnace or a converter, external refining, continuous casting and controlled rolling and cooling is adopted. The invention has the advantages that the yield strength of the steel is more than or equal to 550MPa, the tensile strength is more than or equal to 670MPa, the elongation is more than or equal to 20%, and the charpy impact energy under -40 DEG C is more than or equal to 200J; the charpy impact energy under -40 DEG C in a near weld zone is more than or equal to 100J when the weld heat input is 20-100Kj/cm; and the production process is simple and convenient.

Description

technical field [0001] The invention belongs to the technical field of micro-alloy steel, and in particular provides an easy-to-weld low-carbon bainite steel and a manufacturing method. Background technique [0002] When 5-30ppm boron is added to the steel and segregated at the austenite grain boundary in the form of solid solution boron, the γ→α transformation can be delayed. Compared with delaying the transformation of bainite, the effect of boron on the formation of proeutectoid ferrite is much greater, which is beneficial to the formation of bainite. When boron in the steel interacts with alloying elements such as manganese, molybdenum, chromium, and copper, the effect of promoting bainite transformation is more significant. In a wide range of cooling rates, the continuous cooling transformation of austenite will produce A large number or even all of the bainite structure. In addition, the joint effect of trace amounts of boron and niobium can significantly inhibit the...

AI Technical Summary

Problems solved by technology

[0005] However, the current low-carbon bainite steel has the disadvantages in terms of welding performance: the low-temperature toughness of the heat-affected zone of high-heat input welding is insufficient, so that the steel needs to adopt high-heat-input welding processes such as submerged arc welding and gas-electric vertical welding. The use of thick plate structures is limited

The disadvantage of the above method is that there is no limit requirement on the proportion of boron content and nitrogen content, or it is possible to make the proportion of boron and nitrogen low, so that the role of solid solution boron in promoting bainite transformation in steel is insufficient. Or the proportion of boron and nitrogen is too high, so that VN and BN particles have insufficient effect on promoting the formation of intragranular fine ferrite in the near seam area of ​​high heat input welding

If the steel involved in this patented technology is to be welded, its disadvantage is that the N content is relatively low, and the number of VN and BN particles formed is relatively small, which promotes the formation of intragranular fine ferrite in the high heat input welding zone near the seam, and restricts the formation of shellfish. Insufficient effect of ferrite growth

The disadvantage of this patented technology is that the ratio of boron to nitrogen is low, and sufficient solid-solution boron segregation cannot be produced at the austenite grain boundary in the high heat input welding zone near the seam, and the coarse grain boundary ferrite cannot be effectively suppressed. Formation

The disadvantage of this method is that the ratio of boron to nitrogen is too high. When welding with high heat input, it will still promote the formation of coarse granular bainite and cannot suppress the local embrittlement caused by M-A islands.

[0014] To sum up, the technologies involved in the existing relevant patent documents either do not limit the ratio of boron to nitrogen in steel, or the ratio of boron to nitrogen is improper, or the nitrogen content in steel is low, which is different from that of the present application. Compared with the proposed method of improving the low-temperature toughness of the near-seam area of ​​high heat input welding of boron-containing low-carbon bainite steel by reasonably controlling the range and ratio of boron content and nitrogen content, there are differences.

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