Ultra-high toughness, excellent weldability ht550 steel plate and manufacturing method thereof

Abstract

Ultra-high toughness, excellent weldability HT550 steel plate and its manufacturing method, based on the composition system of ultra-low C-high Mn-Nb microalloying-ultrafine Ti treatment, controlling Mn / C at 15-30, (%Si) ×(%Ceq)≤0.050, (%C)×(%Si)≤0.010, (%Mo)×[(%C)+0.13(%Si)] at 0.003~0.020, Ti / N=2.0~4.0, (Cu+Ni+Mo) alloying, Ni / Cu≥1.0, Ca treatment, Ca / S ratio between 0.80 and 3.00, by optimizing the TMCP process, the microstructure of the steel plate is fine ferrite + self-tempered bainite , the average grain size is less than 15μm, the yield strength is ≥460MPa, the tensile strength is 550MPa~700MPa, the yield ratio is ≤0.85, and the Charpy impact energy (single value) at -60°C is ≥60J; in obtaining uniform and excellent toughness and strong plasticity While matching, the steel plate can withstand large heat input welding, especially suitable for cross-sea bridge structures, offshore wind tower structures, offshore platform structures and hydropower structures.

Description

Technical field [0001] The invention relates to an ultra-high toughness, excellent weldability HT550 steel plate and a manufacturing method thereof. The Charpy impact energy with a yield strength of ≥460MPa, a tensile strength of 550MPa to 700MPa, and a yield ratio of ≤0.85 at -60°C is obtained through a TMCP process. (Single value) ≥60J, excellent weldability steel plate, the microstructure of the steel plate is fine ferrite + self-tempered bainite, the average grain size is below 15μm. Background technique [0002] As we all know, low-carbon (high-strength) low-alloy steel is one of the most important engineering structural materials, which are widely used in oil and gas pipelines, offshore platforms, shipbuilding, bridge structures, boiler vessels, building structures, automobile industry, railway transportation and machinery manufacturing. in. [0003] The performance of low-carbon (high-strength) low-alloy steel depends on its chemical composition and the process system of th...

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Problems solved by technology

In this way, the alloy content of the steel plate is high, which not only leads to high manufacturing cost of the steel plate, but also high carbon equivalent Ceq and welding cold crack sensitivity index Pcm, which brings great difficulties to on-site welding. Preheating is required before welding. After heat treatment is required, the welding cost increases, the welding efficiency decreases, and the working environment of the welding site deteriorates; the existing large number of patent documents only explain how to realize the strength and low-temperature toughness of the base metal steel plate, so as to improve the welding performance of the steel plate and obtain an excellent welding heat-affected zone HAZ has few instructions on low-temperature toughness, and does not involve how to ensure the hardenability of the central part of the quenched and tempered steel plate to ensure the strength and toughness of the steel plate and the uniformity of strength and toughness along the thickness direction of the steel plate (Japanese patents Sho 63-93845, Sho 63-79921, Zhao 60-258410, Special Flat 4-285119, Special Flat 4-308035, Flat 3-264614, Flat 2-250917, Flat 4-143246, USPatent4855106, USPatent5183198, USPatent4137104)

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