A quenched and tempered low temperature steel and its manufacturing method

Abstract

The invention relates to hardened and tempered low-temperature steel, which comprises the following chemical ingredients by weight percentage: 0.040 percent to 0.080 percent of C, at most 0.15 percent of Si, 1.20 percent to 1.60 percent of Mn, at most 0.015 percent of P, at most 0.003 percent of S, at most 0.010 percent of Als, 0.05 percent to 0.35 percent of Cu, 0.10 to 0.40 percent of Ni, 0.10 percent to 0.30 percent of Mo, 0.007 percent to 0.012 percent of Ti, 0.020 percent to 0.050 percent of V, 0.0055 percent to 0.0085 percent of N, 0.0008 percent to 0.0020 percent of B and 0.001 percentto 0.004 percent of Ca. In addition, the element contents meet the following relationship that: Mn / C is greater than or equal to 15 but smaller than or equal to 30; the equivalent weight of Ni is greater than or equal to 0.25 percent; Ti / N is between 1.0 and 2.0; B is greater than 0.714(N-0.292Ti-0.518Als); Ni / Cu is greater than or equal to 1.0; Ca / S is between 1.0 and 3.0, and in addition, the Ca(percentage)*S(percentage)0.28 is greater than or equal to 1.0*10<-4> but smaller than or equal to 1.5*10<-3>; and the rest are iron and unavoidable impurities. The steel is manufactured through combining processes of recrystallization control milling, on-line direct quenching, tempering heat treatment, the excellent low-temperature performance can be obtained, and in addition, a steel plate can bear large-line energy welding and is particularly suitable for being used for making liquefied petroleum gas (LPG) low-temperature storage tanks.

Description

technical field [0001] The present invention relates to a low temperature steel, in particular to a low C-high Mn-ultra-low Als-medium N-a small amount (Cu+Ni+Mo) alloying-ultrafine (Ti+B) treatment of low Quenched and tempered low-temperature steel with yield strength ≥ 490MPa, tensile strength ≥ 610MPa, Charpy transverse impact energy (single value) ≥ 100J at -50°C in the composition system of alloy steel, which can be welded with large heat input, mainly used for low-temperature storage tanks , cryogenic pressure steel pipes, and manufacturing materials for offshore platforms in ice sea areas. Background technique [0002] When adopting the prior art related to the present invention to manufacture -50 ℃ low-temperature transverse impact toughness (single value) ≥ 100J quenched and tempered high-strength thick steel plate, generally a certain amount of precious alloying element Ni will be added in the steel to ensure The base metal steel plate has excellent low-temperatur...

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Problems solved by technology

[0002] When adopting the prior art related to the present invention to manufacture -50 ℃ low-temperature transverse impact toughness (single value) ≥ 100J quenched and tempered high-strength thick steel plate, generally a certain amount of precious alloying element Ni will be added in the steel to ensure The base metal steel plate has excellent low-temperature toughness. In addition to high manufacturing costs, the low-temperature toughness of the heat-affected zone (HAZ) is severely deteriorated during welding with high input energy, and the low-temperature toughness of the heat-affected zone (HAZ) is difficult to reach low temperature. Requirements for steel [EP0288054A2, US Patent 4851052, EP 0839921A1, EP0168038]; Japanese steel companies used the direct quenching and tempering process (ie DQT) to produce high-strength and high-toughness steel plates in the 1980s, and achieved certain results [ Japanese Laid-Open Patent Publication No.153730 / 1983, Japanese Laid-Open Patent Publication No.77527 / 1983, Japanese Post-Exam Patent Publication No.3011 / 1983], the main technical solution is above Ar3, from recovery / recrystallization structure direct quenching + tempering heat treatment, but the low-temperature toughness of the steel plate is poor, showing that the low-temperature crack resistance of the steel plate is insufficient, and cannot meet the requirements of low-temperature steel; a large number of patent documents only explain how to realize the low-temperature toughness of the base steel plate. Under welding conditions, there are few explanations for obtaining excellent low-temperature toughness of the heat-affected zone (HAZ), especially how to ensure the low-temperature toughness of the heat-affected zone (HAZ) when welding with large input energy [Zhao 63-93845, Zhao 63-93845, Zhao 63-79921, Zhao 60-258410, special flat 4-285119, special flat 4-308035, flat 3-264614, flat 2-250917, flat 4-143246, US Patent4855106, US Patent5183198, US Patent4137104]

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