Ultra-thick, ultra-high-toughness and excellent-weldability 1000 MPa-grade steel plate and manufacturing method thereof

Abstract

The invention discloses an ultra-thick, ultra-high-toughness and excellent-weldability 1000 MPa-grade steel plate and a manufacturing method thereof. A component system of ultra-low C-ultra-low Si-medium Mn-(Ti+Nb+V+B) microalloyed steel is adopted as the basis, the content of acid-soluble Als in the steel is properly increased, metallurgical methods that Als / [(%N)-0.292(%Ti)] is larger than or equal to 23, (%C)*(%Si) is smaller than or equal to 0.016, Ca treatment is performed, a Ca / S ratio is 1.00-3.00, and (%Ca)*(%S)0.18 is smaller than or equal to 2.5*10<-3> are adopted, TMCP plus off-linequenching and tempering process (QT) is optimized, [H*(t<relaxation>)*xi] / [(T<finish rolling>-T <cooling stopping>)*(Ceq*V<cooling rate>)] is controlled to be larger than or equal to 40 and smaller than or equal to 550, (T<quenching>)*[lg(t<quenching maintenance>)] / [(%Mo)+0.73(%Cr)+1.67(%V)+311(%B)] is controlled to be larger than or equal to 730 and smaller than or equal to 1050, and [(T<tempering>)*[lg(t<tempering maintenance>)] / DI is controlled to be larger than or equal to 320 or smaller than or equal to 120, the microstructure of the finished steel plate is fine low carbon tempered martensite plus little tempered lower bainite, the average crystal size is less than 20[mu]m, and the excellent plasticity and toughness HT950 steel plate is obtained.

Description

technical field [0001] The invention relates to a 1000MPa grade steel plate with ultra-thickness, ultra-high toughness and excellent weldability and a manufacturing method thereof. 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, hydropower engineering, bridge structures, boiler containers, building structures, automobile industry, railway transportation and In mechanical manufacturing; the performance of low-carbon (high-strength) low-alloy steel depends on its chemical composition and manufacturing process, among which strength, toughness, plasticity, weldability and the matching between them are the most It is an important performance, which ultimately depends on the microstructure of the finished steel; with the continuous development of metallurgical technology, people put forward higher requiremen...

AI Technical Summary

Problems solved by technology

[0003] Existing high-strength steel plates with tensile strength ≥ 980MPa are mainly produced by off-line quenching and tempering process (i.e. RQ+T); however, for steel plates with thickness ≤ 60mm, they can also be produced by on-line quenching and tempering process (i.e. DQ+T); in order to obtain For ultra-high strength, the steel plate must have sufficiently high hardenability and hardenability, that is, the hardenability index of the steel plate DI≥3.50×the thickness of the finished steel plate〖DI=0.311(%C) 1 / 2 [(1+0.64(%Si)]×[(1+4.10(%Mn)]×[(1+0.27(%Cu)]×[(1+0.52(%Ni)]×[(1+2.33( %Cr)]×[(1+3.14(%Mo)]×25.4(mm)〗and the carbon content of the steel plate should exceed 0.12%, or even reach more than 0.15%, to ensure that the steel plate has sufficient strength and excellent low-temperature toughness And the uniform microstructure and properties along the thickness direction of the plate, so it is inevitable to add a large amount of alloying elements such as C, Cr, Mo, Ni, Cu, V to the steel, resulting in high carbon equivalent and cold crack sensitivity index of the steel plate, serious Affect the weldability of the steel plate; in addition, the surface (sub) surface layer of the steel plate with high carbon and high alloy content is prone to over-quenching, forming a coarse martensitic structure, which makes the low temperature toughness and elongation of the surface (near) surface layer of the steel plate serious. Deterioration 【Electric Civil Engineering (Japanese), 1986, Vol.201, P33; Iron and Steel, 1986, Vol.72, S612; Iron and Steel, 1986, Vol.72, S614; Iron and Steel, 1985, Vol.71, S1523; Iron and Steel, 1986, Vol.72, S615; Iron and Steel, 1986, Vol.73, S1398; Kawasaki Iron and Steel Technical Report (Japanese), 1988, Vol.20, P233; Iron and Steel Research (Japanese), 1986, Vol.322, P99; CAMP-ISIJ Japanese), 1989, Vol.3, P207; NKK Technical Report (Japanese), 1990, Vol.133, P37; Electric Power Civil Engineering (Japanese), 1994, Vol.249, P1 ; Sumitomo Metals (Japanese), 1995, Vol.47, P1; Nishiyama Memorial Technical Lecture 191-192, 2008, P162]; lower elongation and low temperature toughness are not only detrimental to the cold and hot workability of steel plates, but also to the resistance of steel plates Fatigue performance, stress concentration resistance sensitivity, crack resistance and structural stability are greatly affected; fatigue heavy-duty structures such as pressure steel pipes, steel branch pipes and volutes in hydropower projects, thermal power turbine generators and offshore oil production platform structures Therefore, when using ultra-high-strength steel for large-scale fatigue and heavy-duty steel structures, it is generally expected that 1000MPa-grade high-strength steel not only has excellent strength and toughness, strong plasticity matching and weldability, but also has an elongation rate of 14 % or more to ensure the processing performance and fatigue resistance of the steel plate

A large number of existing patents and technical documents only explain how to realize the strength and low-temperature toughness of the base steel plate, improve the weldability of the steel plate, and obtain excellent welding heat-affected zone HAZ low-temperature toughness. At the same time, it improves the tensile elongation of the steel plate and the uniformity of the mechanical properties in the thickness direction, and it does not point out how to prevent the surface (sub) surface layer of the steel plate from over-quenching (Japanese patents Zhao 63-93845, Zhao 63-79921, Zhao 60-258410, Special Opening 4-285119, Special Opening 4-308035, Flat 3-264614, Flat 2-250917, Flat 4-143246, US Patent 5798004, EP 0288054A2, Nishiyama Memorial Technical Lecture No. 159-160, P79~P80)

[0004] Chinese Patent No. ZL201010227961.8 discloses "960MPa quenched and tempered steel plate with excellent toughness and strong plasticity and its manufacturing method". 60°C Charpy transverse impact energy (single value) ≥ 47J, but the steel plate manufacturing technology of the invention can only produce a maximum steel plate thickness of 80mm

[0005] Chinese Patent No. ZL201110071217.8 discloses "a kind of excellent ductility and toughness HT960 steel plate and its manufacturing method". It is produced by TMCP+off-line tempering process, which fully exerts the quenching potential of alloy elements, and the alloy content, manufacturing cycle and manufacturing cost of the steel plate are large. The comprehensive mechanical properties and weldability of the steel plate are also greatly improved, but the production thickness of the steel plate is still limited, the maximum thickness can only reach 70mm, and it is still impossible to produce thicker steel plates.

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