Low-cost ultra-low temperature nickel steel and its manufacturing method

Abstract

Low-cost ultra-low temperature nickel steel and its manufacturing method, the composition weight percent is: C0.04~0.070%, Si≤0.15%, Mn0.80~1.20%, P≤0.010%, S≤0.0020%, Ni5.00~7.00 %, Mo0.05~0.25%, Als0.010~0.030%, Ti0.008~0.018%, N≤0.0040%, Ca0.001~0.004%, the rest is Fe and unavoidable inclusions; the invention adopts ultra-low C -Ultra-low Si-Medium Mn-Low N-Ultramicro + Ti treated low alloy steel composition system, control (%Mn)×[7.33(%Si)+5.16(%Al)]≤1.0, 0.007≤austenite Stability index Au / quenching temperature in two-phase zone T≤0.009, optimized recrystallization controlled rolling and subsequent special combined heat treatment process, so that ultra-low temperature nickel steel can obtain extremely high ultra-low temperature toughness, excellent weldability, and can withstand large heat input welding , has excellent resistance to high tempering parameter SR embrittlement characteristics, and can be manufactured at low cost.

Description

technical field [0001] The invention relates to low-carbon (high-strength) low-alloy steel, in particular to low-cost ultra-low temperature nickel steel and its manufacturing method. Z direction performance ≥ 35%, mainly used for liquefied natural gas storage tanks and marine liquefied natural gas storage tanks. Background technique [0002] As we all know, low-carbon (high-strength) low-alloy steel is one of the most important engineering structural materials, widely used in oil and gas pipelines, offshore platforms, shipbuilding, bridge structures, boiler containers, building structures, automobile industry, railway transportation and machinery manufacturing among. The properties of low-carbon (high-strength) low-alloy steel depend on its chemical composition and the process system of the manufacturing process, among which strength, toughness and weldability are the most important properties of low-carbon (high-strength) low-alloy steel, which are ultimately determined by...

AI Technical Summary

Problems solved by technology

However, the production cost remains high, and the product market competitiveness is low, such as "Pressure Technology", 29(1991), P341

[0005] Secondly, the alloy steel plate undergoes high tempering parameter TP≥18.5×10 3 (TP=T(20+lgt) post-weld heat treatment (SR treatment), the ultra-low temperature impact toughness of the steel plate is seriously deteriorated, and the low-temperature impact energy value is generally lower than 47J, which seriously endangers the safety and reliability of the low-temperature LNG storage tank during service Sexuality, laying hidden dangers of major accidents

[0006] In addition, when welding with large heat input, the low-temperature toughness of the welding heat-affected zone (HAZ) will be severely deteriorated, and the low-temperature ductile-brittle transition temperature of the heat-affected zone (HAZ) is generally difficult to reach -165°C, let alone reach ultra-low temperature- 196°C

[0007] A large number of existing patent documents only explain how to realize the low-temperature toughness of the base metal steel plate at -40°C to -60°C, and explain less about how to obtain excellent low-temperature toughness in the heat-affected zone (HAZ) under welding conditions. How to ensure low temperature toughness at -196°C in the heat-affected zone (HAZ) of ultra-low temperature nickel steel during input welding

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