A kind of high-toughness steel for leg half-chord pipe and its manufacturing method

Abstract

The invention relates to high ductility steel for a semifocal chord pipe for a spud leg and a manufacturing method of the high ductility steel. The high ductility steel comprises the following chemical components in percentage by weight: 0.05-0.08% of carbon, smaller than or equal to 0.10% of silicon, 1.00-1.20% of manganese, smaller than or equal to 0.012% of phosphorus, smaller than or equal to 0.003% of sulfur, 0.70-1.00% of chromium, 0.70-1.00% of nickel, 0.30-0.50% of molybdenum, 0.010-0.030% of titanium, 0.0010-0.0020% of boron and the balance of iron and inevitable impurities. For the high-strength steel plates manufactured from the high ductility steel, the maximum thickness can achieve 85mm, the strength level of the steel is high and achieves 790MPa and above, the steel can bear jug line energy welding of 50-100KJ / cm, the whole thickness directionality is good, and the toughness is excellent.

Description

technical field [0001] The invention relates to a steel for marine engineering and a manufacturing method thereof, in particular to a steel for pile leg semi-chord pipes and a manufacturing method thereof, and belongs to the technical field of iron and steel smelting. Background technique [0002] The half chord is mainly used for the pile leg structure of various types of jack-up drilling platforms such as 300 feet, 400 feet, and 500 feet. Due to the harsh environment, high risk, and high-tech characteristics of marine engineering, it also has its own characteristics in the use of steel. Steel plates must have high strength, high toughness, fatigue resistance, lamellar tear resistance, and seawater corrosion resistance. In addition, to ensure good weldability and good cold working ability, ultra-high-strength steel with a strength of 690MPa is required in some key parts. [0003] At present, the steel for half-chord pipes supplied by Japan, Germany, France, and individual ...

AI Technical Summary

Problems solved by technology

Chinese patent document CN101363101A (application number 200810141457.9) provides a quenched and tempered steel plate with a tensile strength of 800MPa and its manufacturing method, which is characterized in that it is produced by a 26.7-ton flat ingot mold, and the maximum thickness of the steel plate produced is 114mm, and Ni, Cr in the steel , Mo precious alloy composition content is high, resulting in an increase in carbon equivalent and cost

[0007] 1. Poor weldability: it is designed with high carbon content and high alloy content, and there must be hardening and cracking in the welding process

[0008] 2. The conventional deoxidation method is adopted: there is no fine Ti 2 o 3 Or TiN particles are used as nucleation points, which cannot withstand the welding heat input of up to 50-100KJ / cm, and the grains in the heat-affected zone are also easy to become coarse during the welding process, forming upper bainite structure and M-A island, which seriously reduces the toughness after welding

[0009] 3. High alloy content leads to defects such as cracks in billets and steel plates: adding up to 1% of precious alloys such as Cr and Ni is a disadvantage. If effective measures are not taken, it will also bring billets and steel plates. Cracking and other problems, resulting in production failure

[0010] 4. Die-cast steel ingots are used as blanks for production: However, the casting process of steel ingots is long and energy-consuming, and the rate of rolling products is low, which significantly increases the manufacturing cost

At the same time, because of the poor core quality (such as segregation and porosity) of die-cast steel ingots, it is difficult to ensure the core performance of large-thickness steel plates produced with steel ingots

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