High-strength steel for high-energy welding resistance and manufacturing method thereof

Abstract

The application discloses a high-strength steel for resisting large heat input welding and a manufacturing method thereof. The chemical composition of the steel comprises the following components: C: 0.11-0.15%, Si: 0.15-0.45%, Mn: 1.65-1.95%, Ti: 0.030-0.050%, V: 0.020-0.050%, Als: ≤0.008%, N: ≤0.0050%, Cr: ≤0.10%, P: ≤0.015%, S: ≤0.005%, and the balance of Fe and inevitable impurity elements. The free [O] content is controlled in the smelting process, and the TiOx is better promoted to form the fine and dispersed TiOx composite oxides in the casting blank and the steel plate, so that the original austenite grain growth is prevented in the heating process of the casting blank, and the grain refinement effect is achieved. In the large heat input welding process, the composite oxides promote the formation of acicular ferrite, the grain coarsening in the welding heat affected zone is inhibited, the low-temperature toughness of the large heat input welding heat affected zone is improved, and the steel has the large heat input welding resistance. The long strip-shaped MnS caused by the high Mn content is modified into short rod-shaped or round-shaped by controlling the low S content and the Ti oxide, the morphology, size and distribution of the inclusions are improved by the inclusion modification, and therefore the low-temperature toughness of the steel is improved.

Description

Technical Field

[0001] This invention relates to the field of metal metallurgy, and in particular to a high-strength steel for high heat input welding and its manufacturing method. Background Technology

[0002] With the increasing maturity of gas-electric vertical welding technology, its application in many industries such as high-rise buildings, bridges, large ships, containers, and pressure vessels is becoming more and more widespread, significantly reducing the labor intensity of workers and improving work efficiency. However, with the increasing complexity of the operating environment and the intensification of cost competition, existing steel grades are finding it difficult to simultaneously meet the requirements of high heat input welding and low-temperature toughness. Summary of the Invention

[0003] This invention provides a high-strength steel for high heat input welding and its manufacturing method, which can simultaneously meet the requirements of high heat input welding resistance and low-temperature toughness.

[0004] This invention provides a high-strength steel for high heat input welding and its manufacturing method.

[0005] One or more technical solutions provided in this invention have at least the following technical effects or advantages:

[0006] The high-strength steel for high heat input welding provided by this invention is based on the C+Mn system, with only Ti and V added for microalloying. MnS is modified in a weakly oxidizing atmosphere of molten steel, forming fine TiO₂-containing particles. x High-temperature composite oxides refine grain size, improving the low-temperature toughness and high heat input welding performance of extra-thick structural steel. Specifically, through the rational combination of C and Mn elements, not only is the strength of extra-thick plates improved, but their low-temperature toughness is also controlled, and the weldability caused by excessive carbon equivalent is prevented. Considering performance requirements, the C content is 0.10–0.14%, and the Mn content is 1.65%–1.90%.

[0007] In addition, Si can improve the strength of steel plates and welded joints, but too much Si will affect the low-temperature toughness and surface quality of steel. Therefore, the Si content is 0.10 to 0.45%.

[0008] P, S, and N are unavoidable impurity elements in steel, but they are detrimental to the weldability, low-temperature toughness, and hot workability of steel plates. Therefore, the lower their content, the better. The content of P should be ≤0.015%, the content of S should be ≤0.005%, and the content of N should be ≤0.005%.

[0009] Al is an important deoxidizing element and readily forms a large number of Al2O3 inclusions in steel, affecting the quality and performance of the steel. To avoid affecting the formation of Ti oxides, Al materials are not used for deoxidation. Instead, silicon, manganese deoxidation and secondary deoxidation with titanium are used, and the Al content is strictly controlled to be ≤0.008%.

[0010] V is an important microalloying element. It reacts with C and N to form carbonitride compounds, which precipitate during the slow cooling process of steel plates after rolling and stacking. This is beneficial to improving the strength and low-temperature toughness of extra-thick steel. Therefore, the V content is 0.020 to 0.050%.

[0011] Ti is added when a certain amount of free [O] element is present in the molten steel, and it forms Ti₂O₃ oxide with the free [O]. Ti₂O₃ has a high melting point and is finely dispersed in the cast billet. During the heating of the billet, it can prevent the coarsening of the original austenite. During the high heat input welding of steel plates, it acts as a nucleation core to promote the formation of acicular ferrite, further refining the grains in the weld heat-affected zone and improving the low-temperature toughness of the weld heat-affected zone. However, excessive Ti and O content both deteriorate the low-temperature toughness of the steel plate and the weld heat-affected zone. Therefore, the Ti content is 0.030–0.050%.

[0012] In summary, the high-strength steel for high heat input welding provided by this invention employs a low-carbon composition design, supplemented with trace amounts of Ti oxide metallurgy, and strictly controls the free [O] content at each stage of the smelting process, as well as the order and nodes of ferrotitanium addition, to better promote TiOx formation. This results in the formation of finely dispersed TiOx-containing composite oxides in both the billet and the steel plate. These TiOx-containing composite oxides not only prevent the growth of the original austenite grains during billet heating, thus refining the grains, but also promote the formation of acicular ferrite during high heat input welding, thereby inhibiting grain coarsening in the weld heat-affected zone and refining the grains in the weld heat-affected zone. This significantly improves the low-temperature toughness of the heat-affected zone at -40℃ during high heat input welding, giving the high-strength steel for high heat input welding provided by this invention high heat input welding resistance characteristics. By strictly controlling the low S content (≤0.005%wt) and Ti oxide metallurgy, the elongated MnS caused by the high Mn content is modified into short rods or round shapes. Inclusion modification is used to improve the morphology, size, and distribution of inclusions, thereby improving the low-temperature toughness of the high-strength steel for high heat input welding provided by this invention. High-strength steel plates with a thickness of 90-100mm are rapidly removed from the line and stacked for slow cooling after ACC weak cooling, ensuring that the surface temperature of the steel plate after the line cooling process is not lower than 400℃. During the slow cooling process of the stacked steel plate, the precipitation of the second phase V(C,N) is promoted, thereby further improving the strength-toughness balance of the extra-thick steel plate. Attached Figure Description

[0013] Figure 1A flowchart illustrating a method for manufacturing high-strength steel for high heat input welding according to an embodiment of the present invention;

[0014] Figure 2 This is a schematic diagram of the surface microstructure of the steel plate obtained by the embodiments of the present invention;

[0015] Figure 3 This is a schematic diagram of the microstructure of the heat-affected zone of a steel plate welded at a high heat input of 200 KJ / cm, obtained from the embodiments of the present invention, and the energy dispersive spectroscopy analysis results of a typical Ti-containing composite oxide. Detailed Implementation

[0016] The present invention provides a high-strength steel for high heat input welding and its manufacturing method, which can simultaneously meet the requirements of high heat input welding resistance and low-temperature toughness.

[0017] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0018] The high-strength steel for high heat input welding provided in this embodiment of the invention comprises the following chemical composition by weight percentage (wt%): C: 0.11-0.15%, Si: 0.15-0.45%, Mn: 1.65-1.95%, Ti: 0.030-0.050%, V: 0.020-0.050%, Als≤0.008%, N≤0.0050%, Cr≤0.10%, P≤0.015%, S≤0.005%, with the balance being Fe and unavoidable impurity elements.

[0019] Specifically, the yield strength R of the steel eL ≥420MPa, tensile strength R m ≥550MPa, yield strength ratio ≤0.80, elongation A≥23%, impact toughness -40℃ KV2≥100J, ≤200KJ / cm high heat-affected zone impact toughness -40℃ KV2≥47J. The thickness range of this steel is 90-100mm.

[0020] See Figure 1 The manufacturing method of high-strength steel for high heat input welding provided in this embodiment of the invention includes:

[0021] Step S110: Smelt and continuously cast a billet according to the chemical composition of the high-strength steel for high heat resistance welding as described above.

[0022] This step is explained in detail. The billet is obtained by smelting and continuous casting according to the chemical composition of the high-strength steel for high heat input welding described above, including:

[0023] The blast furnace molten iron is pretreated to ensure that the [S] content is ≤0.003% before being smelted in the converter. The converter undergoes deep dephosphorization, and the steel is tapped with a [P] content ≤0.012%. Ferrosilicon and ferromanganese are added during tapping to adjust the Si and Mn content and to deoxidize the steel. Aluminum-containing materials such as aluminum granules, aluminum wires, and aluminum ingots are not allowed to be used for deoxidation. During the refining process in the LF ladle furnace, manganese alloy and ferrovanadium are added to adjust the Si, Mn, and V content. When the [O] content is 0.0020% to 0.0040%, Ti alloy is added. Aluminum-containing materials such as aluminum wires are not allowed to be used for deoxidation during the refining process. The steel is then degassed in the RH vacuum furnace. Continuous casting uses argon-protected casting and light reduction technology to cast 450mm thick billets, which are then stacked and slowly cooled for at least 24 hours.

[0024] Step S120: Heating the billet;

[0025] This step, which involves heating the billet, includes:

[0026] The billet is hot-charged, and the surface temperature of the billet does not exceed 500℃ during hot charging. The temperature of the soaking zone of the heating furnace is 1200~1260℃.

[0027] Step S130: Roll the heated billet, and after the final rolling, use ACC cooling water for weak cooling, with a reddening temperature of 650-700℃;

[0028] Specifically, rolling the heated billet includes:

[0029] A two-stage rolling process is adopted. The first stage is a horizontal rolling to widen the longitudinal rolling to the end, ensuring that the reduction per pass is not less than 45mm during at least two longitudinal rolling passes, and the final rolling temperature is 980~1030℃. The second stage has an initial rolling temperature of 830~860℃ and a final rolling temperature of 800~830℃.

[0030] Step S140: The steel plates are quickly removed from the production line and stacked for slow cooling, which takes at least 48 hours.

[0031] The present invention will be further described in detail below with reference to specific embodiments.

[0032] The high-strength steel plates for high heat input welding provided in this embodiment of the invention have thicknesses of 90 mm and 100 mm and are composed of the following chemical composition (wt%): C: 0.13%, Si: 0.26%, Mn: 1.68%, P: 0.010%, S: 0.001%, Ti: 0.035%, V: 0.032%, Als: 0.004%, N: 0.0036%.

[0033] (1) Smelting and continuous casting process: The blast furnace molten iron is pretreated and [S]≤0.003% is molten iron and then smelted in the converter. The converter is deeply dephosphorized and the steel is tapped to ensure [P]≤0.012%. When tapping the steel, ferrosilicon and ferromanganese are added to adjust the Si and Mn content and deoxidize. Aluminum granules, aluminum wires, aluminum ingots and other aluminum-containing materials are not allowed to be used for deoxidation. When refining in the LF ladle furnace, an appropriate amount of manganese alloy and ferrovanadium can be added to adjust the Si, Mn and V content. When [O]:0.0020%~0.0040%, Ti alloy is added. Aluminum wires and other aluminum-containing materials are not allowed to be used for deoxidation during the refining process. Then it is degassed in the RH vacuum furnace. The continuous casting adopts argon protection casting and light reduction technology and is cast into 450mm thick billets. The billets are stacked and slowly cooled for 36 hours.

[0034] (2) Heated rolling process: The billet is hot-charged, and the surface temperature of the billet is 425℃ during hot charging. The temperature of the soaking zone of the heating furnace is 1240~1250℃. Controlled rolling adopts two-stage rolling. The first stage is a horizontal rolling to widen and longitudinal rolling to the end, ensuring that the single-pass reduction is 46mm~50mm during at least two longitudinal rolling passes, and the final rolling temperature is 990~1010℃. The second stage has an initial rolling temperature of 820~840℃ and a final rolling temperature of 810~830℃, and the steel plate is rolled into steel plates with a thickness of 90mm and 100mm.

[0035] (3) Controlled cooling and stacking cooling process: After the final rolling, ACC cooling water is used for weak cooling, and the red temperature is 660~680℃. The steel plates are quickly removed from the line and stacked for slow cooling for 60 hours.

[0036] A schematic diagram of the surface microstructure of the steel plate obtained from the embodiments of the present invention is shown below. Figure 2 As shown, the microstructure is ferrite + pearlite. A schematic diagram of the microstructure of the heat-affected zone in the steel plate obtained from the embodiments of this invention at a high heat input of 200 KJ / cm² during welding, and the energy dispersive spectroscopy analysis results of typical Ti-containing composite oxides are shown below. Figure 3 As shown, typical Ti-containing composite oxides have a size of approximately 2 μm and exhibit a nucleation state of acicular ferrite in the weld heat-affected zone. This finely distributed Ti-containing composite oxide is conducive to the formation of acicular ferrite, which can refine the grains in the weld heat-affected zone and improve its low-temperature toughness.

[0037] In this embodiment of the invention, longitudinal samples were taken 10 mm below the surface of the steel plate and mechanical properties were tested, including tensile and impact properties, as shown in Table 1.

[0038] Table 1

[0039]

[0040]

[0041] Therefore, it can be seen that the steel plate provided in the embodiments of the present invention meets the requirements of yield strength R. eL≥420MPa, tensile strength R m The requirements are: ≥550MPa, yield strength ratio ≤0.80, elongation A ≥23%, and impact toughness -40℃ KV2 ≥100J.

[0042] In this embodiment of the invention, steel plates were longitudinally sampled and processed into 11mm×11mm×90mm welding thermal simulation specimens. Welding thermal simulation tests with different line energies were then conducted on a Gleeble-3500 thermo-mechanical simulation testing machine. After the tests, tensile and impact specimens were processed for tensile and low-temperature impact tests. Table 2 shows the low-temperature impact data of the weld heat-affected zone at -40℃ under different line energy conditions in this embodiment of the invention.

[0043] Table 2

[0044]

[0045] As can be seen from the test results in Table 2, the steel plates provided in the embodiments of the present invention meet the standard requirement of KV2≥47J at -40℃ in the weld heat-affected zone, and have a large margin.

[0046] The steel plate provided in this invention has the characteristics of high strength, excellent low-temperature toughness and excellent resistance to high heat input welding, and the production process is short, the production cost is low and the operation is highly operable, thus having a good market prospect.

[0047] Any aspects of this invention not described in detail in the embodiments are well-known techniques to those skilled in the art. Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this invention and not to limit it. Although this invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this invention without departing from the spirit and scope of this invention, and all such modifications and substitutions should be covered within the scope of the claims of this invention.

Claims

1. A method for manufacturing high-strength steel resistant to high heat input welding, characterized in that, include: The billet was obtained by smelting and continuous casting according to the chemical composition of high-strength steel for high heat resistance welding. The chemical composition of the high-strength steel for high heat input welding includes, by weight percentage: C: 0.11~0.15%, Si: 0.15~0.45%, Mn: 1.65~1.95%, Ti: 0.030~0.050%, V: 0.020~0.050%, Als≤0.008%, N≤0.0050%, Cr≤0.10%, P≤0.015%, S≤0.005%, with the balance being Fe and unavoidable impurity elements; The process of smelting and continuously casting a billet according to the chemical composition of high-strength steel for high heat resistance welding includes: The blast furnace molten iron is pretreated to ensure that the [S] content is ≤0.003% before being smelted in the converter. The converter undergoes deep dephosphorization, and the steel is tapped with a [P] content ≤0.012%. Ferrosilicon and ferromanganese are added during tapping to adjust the Si and Mn content and to deoxidize the steel. During the LF ladle furnace refining, manganese alloy and ferrovanadium are added to adjust the Si, Mn, and V content. When the [O] content is 0.0020%~0.0040%, Ti alloy is added. The steel is then degassed in an RH vacuum furnace. Continuous casting uses argon-protected casting and light reduction technology to cast 450mm thick billets, which are then stacked and slowly cooled for at least 24 hours. The billet is heated; The heated billet is rolled, and after the final rolling is completed, it is cooled with cooling water at a temperature of 650~700℃. The steel plates are quickly removed from the production line and stacked for slow cooling, which takes at least 48 hours.

2. The method for manufacturing high-strength steel for high heat input welding as described in claim 1, characterized in that, The heating of the cast billet includes: The billet is hot-charged, and the surface temperature of the billet does not exceed 500℃ during hot charging. The temperature of the soaking zone of the heating furnace is 1200~1260℃.

3. The method for manufacturing high-strength steel for high heat input welding as described in claim 1, characterized in that, The rolling of the heated billet includes: A two-stage rolling process is adopted. The first stage is a horizontal rolling to widen the longitudinal rolling to the end, ensuring that the reduction per pass is not less than 45mm during at least two longitudinal rolling passes, and the final rolling temperature is 980~1030℃. The second stage has an initial rolling temperature of 830~860℃ and a final rolling temperature of 800~830℃.

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