CN111926259A - Low alloy steel for high heat input welding and preparation method thereof - Google Patents

Low alloy steel for high heat input welding and preparation method thereof Download PDF

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CN111926259A
CN111926259A CN202010845048.8A CN202010845048A CN111926259A CN 111926259 A CN111926259 A CN 111926259A CN 202010845048 A CN202010845048 A CN 202010845048A CN 111926259 A CN111926259 A CN 111926259A
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steel
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heat input
input welding
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CN111926259B (en
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李健
师仲然
柴锋
罗小兵
杨才福
柴希阳
王天琪
段美琪
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Zhonglian Advanced Steel Technology Co ltd
Central Iron and Steel Research Institute
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Zhonglian Advanced Steel Technology Co ltd
Central Iron and Steel Research Institute
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium

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  • Organic Chemistry (AREA)
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  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

The invention discloses a steel plate for high heat input welding and a preparation method thereof, belongs to the technical field of high-efficiency welding of ship and marine steel, and solves the problems that the steel plate for high heat input welding in the prior art is high in process cost, low in strength, low in adaptability to high heat input welding, low in post-welding impact power and the like. The steel plate comprises the following components in percentage by mass: 0.05 to 0.16%, Si: 0.04-0.45%, Mn: 0.5-1.5%, P: less than or equal to 0.025%, S: less than or equal to 0.015 percent, Cu: 0.10-0.35%, Cr: 0.05 to 0.18%, Ni: 0.05 to 0.40%, Nb: 0.022-0.035%, V: 0.05 to 0.10%, Mo: 0.02 to 0.07%, Als: 0.001-0.01%, N: 0.001-0.006%, O: 0.002-0.008%, Ti: 0.006-0.018% and Mg: 0.0003 to 0.005%, Zr: 0.0006 to 0.03 percent of one or more than one of the components, and the balance of Fe and inevitable impurity elements. The steel plate has good low-temperature toughness under the condition of 100-DEG-S200 KJ/cm line energy welding, and has good technical economy and wide popularization and application values.

Description

Low alloy steel for high heat input welding and preparation method thereof
Technical Field
The invention belongs to the technical field of low alloy steel for efficiently welding ships and maritime work, and particularly relates to low alloy steel for high heat input welding and a preparation method thereof.
Background
In recent years, China has become the first shipbuilding big country in the world, and the shipbuilding amount accounts for one third of the global shipbuilding industry. With the increasing pace of ocean development in China and the rapid growth of the ship industry, the demand for steel for ocean engineering is rising year by year, and the demand is increasing continuously. The welding cost accounts for 30-40% of the whole manufacturing cost, the welding working hour cost accounts for more than half of the welding cost, and in order to improve the welding efficiency and shorten the engineering manufacturing period, large-linear energy welding is mostly adopted in the fields of ships and ocean engineering. However, due to the increase of the welding line energy, the high-temperature retention time of a welding heat affected zone is prolonged, and when the welding line energy exceeds 50KJ/cm, austenite grains are easy to coarsen seriously; meanwhile, as the cooling speed after welding is slow, coarse side lath ferrite, Widmannstatten structures, upper bainite and other abnormal structures are easily formed in the subsequent phase transformation process, so that the strength and toughness of a welding heat affected zone are seriously deteriorated, and the defects of cracks and the like are easily generated, thereby affecting the safety use performance of the whole structural member. Therefore, how to solve the problem of low-temperature toughness of the large heat input welding steel and improve the large heat input welding adaptability of the marine steel becomes an urgent technical problem to be solved by the steel industry.
Patent document CN102560247A discloses a medium plate high heat input steel and a smelting method thereof, wherein TiO is formed by adding Ti and Al elementsx-MnO-Al2O3-SiO2MnS composite inclusions are precipitated, the precipitation of the composite inclusions is beneficial to inducing acicular ferrite to form in steel and improving the low-temperature toughness of a welding heat affected zone, but the low-temperature toughness is poor, and the impact energy under the condition of 20 ℃ below zero is less than 100J. Patent document CN102839320A discloses a steel plate for high heat input welding and a manufacturing method thereof, which are produced by adding B element and adopting TMCP thermo-mechanical control and rapid cooling process, and are suitable for high-strength and high-toughness steel plates with welding heat input in the range of 100-200KJ/cm, but the microalloying element B is not easy to add and easy to generate segregation during the smelting process, and the production difficulty is high. Patent document CN103031491A discloses a chromium-free micro-aluminum high-strength large heat input steel plate and a manufacturing method thereof, the steel plate has excellent strength, ductility and toughness and welding performance, but the large heat input welding adaptability of the steel plate is only 50-100 KJ/cm. Patent document CN102312173A discloses a steel for high heat input welding structure with tensile strength of 700MPa level and a manufacturing method thereof, wherein oxides of Ti, Zr and the like are formed through reasonable component design, and the welding performance of the steel is improved by matching with TMCP process, but the steel can only adapt to welding heat input of 30-100 KJ/cm. Patent document CN105256095A discloses a method for smelting a steel plate with excellent performance in a large heat input welding heat affected zone, which forms composite inclusions of Mg, Zr and Ti with the size less than 1 μm by controlling the ratio of Ti/O, Mg + Zr to Ti + Al in the steelThe adaptability of high heat input welding of materials is improved, but ferroboron is required to be added into steel, boron is easy to segregate and causes brittleness, and wire feeding treatment is required under the condition of breaking empty and no protection, so that the change of molten steel components is easy to cause to influence the final effect. Patent document CN102839330A discloses a 800MPa grade high-strength thick plate for high heat input welding, which realizes good welding adaptability of steel plate with thickness within 30mm by using low carbon, high Ni, and proper amount of Cr and Mo elements, but the added Ni, Cr and Mo alloy content can reach up to 5%, the cost is high, and the thick plate is only suitable for small welding heat input energy of 40-100 KJ/cm. Patent document CN102286692A discloses a quenched and tempered low-temperature steel and a manufacturing method thereof, which are produced by controlling alloy ratio of Mn/C, Ti/N, Ni/Cu, Ca/S and the like, recrystallization control rolling, online direct quenching and tempering heat treatment processes, can bear large-linear energy welding and obtain good low-temperature performance, but the quenched and tempered low-temperature steel needs quenching and tempering heat treatment and has high process cost.
In general, various research organizations continuously strive to promote the progress of research on steel for high heat input welding, but usually, elements which are easy to segregate, such as B, and the like, or a large amount of expensive alloy elements, such as Ni, Cr, Mo, and the like, are added, and the subsequent quenching and tempering heat treatment is carried out on some materials, however, part of the materials still have the defects of low strength, low adaptability to high heat input welding, low post-welding impact energy, and the like.
Disclosure of Invention
In view of the above analysis, the invention aims to provide low alloy steel for high heat input welding and a preparation method thereof, the invention adopts Ti, Mg and Zr oxide metallurgy technology, forms Ti-X-O fine dispersion composite inclusion with reasonable proportion in steel by an oxide metallurgy mode, and is prepared by adopting a controlled rolling and controlled cooling process, thereby refining the grain size of a steel plate, improving the strength and toughness of the steel plate and improving the high heat input welding adaptability of the steel plate. The low-alloy steel plate which has good obdurability matching and is suitable for 100-inch and 200KJ/cm high-heat input welding can be obtained by controlling the microalloying proportion, the internal structure form of the alloy, the grain size and the inclusions based on an oxide metallurgy mode and matching with a proper preparation process.
The purpose of the invention is mainly realized by the following technical scheme:
the invention provides a low alloy steel for high heat input welding, which comprises the following components in percentage by mass: 0.05 to 0.16%, Si: 0.04-0.45%, Mn: 0.5-1.5%, P: less than or equal to 0.025%, S: less than or equal to 0.015 percent, Cu: 0.10-0.35%, Cr: 0.05 to 0.18%, Ni: 0.05 to 0.40%, Nb: 0.022-0.035%, V: 0.05 to 0.10%, Mo: 0.02 to 0.07%, Als: 0.001-0.01%, N: 0.001-0.006%, O: 0.002-0.008%, Ti: 0.006-0.018% and Mg: 0.0003 to 0.005%, Zr: 0.0006 to 0.03 percent of one or more than one of the components, and the balance of Fe and inevitable impurity elements;
C. si, Mn, Cr, Mo, V, Ni, Cu, Als, Ti, Mg and Zr simultaneously satisfy the following relations: c + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15 is more than or equal to 0.21% and less than or equal to 0.38%, Si + Mn + Als is more than or equal to 0.85% and less than or equal to 1.65%, Ti/(Nb + V) is more than or equal to 0.09 and less than or equal to 0.22, and Ti/(Mg + Zr) is more than or equal to 0.42 and less than or equal to 13.5.
The effect of each element in the invention is as follows:
carbon: carbon belongs to interstitial solid solution strengthening elements and is the most main strengthening element in steel, the carbon content in the steel is too low, and the strength of the steel cannot meet the service performance requirement of a steel plate as a structural material, so the addition amount of the carbon is not less than 0.05 percent; meanwhile, carbon is a main element for controlling the structure in steel, and the content of carbon is too high, so that cementite (Fe) in steel is increased3C) The content of the carbon-containing composite can also cause the steel plate to form a brittle phase martensite island under the condition of high heat input welding, the welding crack sensitivity of the steel is increased, the high heat input welding adaptability of the steel is reduced, and in order to avoid the adverse effect of the carbon, the addition amount of the carbon-containing composite is not higher than 0.16%; comprehensively considering, the content of carbon should be controlled within the range of 0.05-0.16%;
silicon: silicon is the main deoxidizing element in steel, and can be dissolved in ferrite to improve the strength and hardness of the steel, so the addition amount of the silicon is not less than 0.04%; however, the excessive content of silicon can reduce the plasticity and toughness of the material and embrittle a heat affected zone under the condition of high heat input welding so as to deteriorate the weldability of the material, and the adding amount of the silicon is not higher than 0.45 percent in order to avoid the adverse effect of the silicon; comprehensively considering, the content of silicon should be controlled within the range of 0.04-0.45%;
manganese: manganese is also an important deoxidizing element in steel, can be used as a desulfurizing agent to eliminate hot brittleness caused by sulfur, and can also improve the strength and toughness of the material, so that the addition amount of the manganese is not less than 0.5 percent; however, too high manganese content easily causes segregation to form a banded structure, so that the plasticity, toughness and weldability of the material are poor, and the addition amount of the manganese is not more than 1.5 percent in order to avoid the adverse effect of manganese; comprehensively considering, the content of manganese should be controlled within the range of 0.5-1.5%;
phosphorus: phosphorus is a harmful element in steel, is easy to form phosphide segregation or regional segregation at grain boundaries as an impurity element, is not beneficial to the plasticity, toughness and welding performance of the material, and therefore the content of phosphorus is not suitable to be too high; comprehensively considering, the phosphorus content should be controlled below 0.025%;
sulfur: sulfur is also a harmful element in steel, sulfide inclusions are easily formed, the plasticity and the toughness of the material are deteriorated, and the sulfide inclusions can also serve as crack starting points in the welding process, so that the sulfur content in the steel is strictly controlled; comprehensively considering, the sulfur content should be controlled below 0.015 percent;
copper: copper can improve the strength of steel and the corrosion resistance of the steel plate while ensuring the toughness of the material, and the copper content is too low to play a necessary reinforcing effect, so the addition amount of the copper is not less than 0.10 percent; but the melting point of copper is low, copper is easy to be brittle and even to cause thermal cracking in the hot working process of the steel plate, and the addition amount of the copper is not higher than 0.35 percent in order to avoid the adverse effect of the copper; comprehensively considering, the content of copper should be controlled within the range of 0.10-0.35%;
chromium: chromium can improve the strength of steel by grain refinement and precipitation strengthening, and chromium also contributes to improving the corrosion resistance of the material, so the addition amount of chromium is not less than 0.05%; but the chromium content is too high, so that the plasticity and toughness level of the material are reduced, the low-temperature toughness of a welding heat affected zone is also obviously reduced under the condition of high heat input welding, and the addition amount of the chromium is not more than 0.18 percent in order to avoid the adverse effect of the chromium; comprehensively considering, the content of chromium should be controlled within the range of 0.05-0.18%;
nickel: the nickel can form a continuous solid solution with austenite, so that the plasticity and the toughness of the material are always kept at a very high level while the strength of the steel is improved, and the improvement effect on the low-temperature toughness of the material is obvious, so that the addition amount of the nickel is not less than 0.05 percent; however, with the increase of the nickel content, the material is easy to form iron scale with larger viscosity in the hot working process, the surface quality of the steel plate is affected, the nickel belongs to precious alloy, the material cost is increased by adding a large amount of nickel, and in order to avoid the adverse effect of the nickel, the adding amount of the nickel is not higher than 0.40%; comprehensively considering, the content of nickel is controlled within the range of 0.05-0.40%;
niobium: niobium can be partially dissolved in steel in a solid solution manner to play a solid solution strengthening role, and simultaneously, the niobium can be matched with a controlled rolling and controlled cooling process to refine austenite grains to generate a fine grain strengthening effect, so that the strength of the steel is improved under the condition of not influencing the toughness and plasticity of the steel, and the addition amount of the niobium is not lower than 0.022%; but too high content of niobium can reduce the plasticity and low-temperature toughness of the material and also can reduce the toughness of a heat affected zone under a high heat input welding condition, and the adding amount of the niobium is not more than 0.035% in order to avoid the adverse effect of the niobium; comprehensively considering, the content of niobium should be controlled within the range of 0.022-0.035%;
vanadium: the vanadium can refine austenite grains, the strength of the steel is improved through dispersion strengthening and fine grain strengthening, the vanadium can be combined with carbon and nitrogen to form a V (C, N) second phase to be separated out, the strength and toughness of the steel are improved through the separation strengthening and fine grain strengthening, and the welding performance of the steel is improved to a certain extent, so that the addition amount of the vanadium is not less than 0.05%; but too high vanadium content can increase the tempering brittleness of the material and deteriorate the mechanical property of the material, and the addition amount of the vanadium is not higher than 0.10 percent to avoid the adverse effect of the vanadium; comprehensively considering, the content of vanadium should be controlled within the range of 0.05-0.10%;
molybdenum: molybdenum is a solid solution strengthening element, can prevent austenite grains from growing and improve the strength of the material through a fine grain strengthening effect, so the addition amount of the molybdenum is not less than 0.02 percent; however, the material is prone to graphitization due to too high molybdenum content, and the molybdenum also belongs to expensive alloy elements, so that the material cost is increased, and in order to avoid the adverse effect of the molybdenum, the addition amount of the molybdenum is not higher than 0.07%; comprehensively considering, the content of molybdenum should be controlled within the range of 0.02-0.07%;
acid-soluble aluminum: aluminum is a strong deoxidizing element in steel, the content of acid-soluble aluminum is commonly used for representing the deoxidizing level in steel, the content of acid-soluble aluminum is too low, which indicates that the content of oxygen in steel is higher, oxide inclusions are formed to deteriorate the comprehensive performance of the material, and therefore, the content of the aluminum is not lower than 0.001%; but the high content of the acid-soluble aluminum indicates that the content of the aluminum is too high, aluminum nitride is easily formed, the plasticity and the toughness of the material are reduced, the too high content of the acid-soluble aluminum indicates that the content of the oxygen in the steel is too low, the development of an oxide metallurgical process is not facilitated, and in order to avoid the adverse effect of the acid-soluble aluminum, the content of the acid-soluble aluminum is not higher than 0.01%; comprehensively considering, the content of the acid-soluble aluminum is controlled to be in the range of 0.001-0.01 percent;
nitrogen: nitrogen belongs to harmful gas elements in steel, and needs to be controlled at a lower content through a proper smelting process, a certain amount of nitrogen can form a V (C, N) second phase with carbon and vanadium to be separated out, and the mechanical property of the steel is improved, so that the content of the nitrogen is not lower than 0.001%; however, the aging tendency, cold brittleness and hot brittleness of the steel are increased even pores are formed to influence the metallurgical quality when the content of the nitrogen is too high, the weldability of the steel is damaged, and in order to avoid the adverse effect of the nitrogen, the addition amount of the nitrogen is not higher than 0.006%; comprehensively, the content of nitrogen is controlled to be in the range of 0.001-0.006%;
oxygen: oxygen belongs to an oxide metallurgy key element, and reasonable oxygen content control is necessary guarantee for ensuring that a large amount of fine dispersed composite inclusions are formed in steel, pinning austenite grain boundaries and forming ferrite nuclei in coarse grains, so that the content of the oxygen is not lower than 0.002%; however, oxygen is easy to form oxide inclusions with other elements in steel to damage the comprehensive performance of the steel, excessive oxygen can react with key elements Ti, Mg and Zr in the oxide metallurgical process to form coarse oxide inclusions, the low-temperature toughness of a heat affected zone under the condition of large heat input welding is deteriorated, and the content of the excessive oxygen is not higher than 0.008% in order to avoid the adverse effect of the oxygen; comprehensively considering, the content of oxygen should be controlled within the range of 0.002-0.008%;
titanium: titanium can be combined with oxygen to form oxides and nitrogen to form TiN, the two types of particles are typical oxide metallurgical particles, and the titanium oxide which is dispersed and distributed can be used as a subsequent Mg and Zr composite inclusion nucleation point, which is beneficial to improving the heat affected zone structure and refining grains during large heat input welding, so that the toughness is improved, and therefore, the addition amount of the titanium oxide is not less than 0.006%; however, when the content of titanium is too high, coarse titanium compounds can be formed, the low-temperature toughness of a welding heat affected zone is reduced, and in order to avoid the adverse effect of titanium, the addition amount of titanium is not higher than 0.018%; comprehensively, the content of titanium is controlled to be in the range of 0.006-0.018%;
magnesium: the magnesium has stronger high-temperature reducibility than titanium, can be oxidized with titanium oxide inclusions to form composite inclusions, and promotes the nucleation of acicular ferrite in crystal, so that the toughness of a heat affected zone under a large-heat-input welding condition is improved, and therefore, the addition amount of the magnesium is not less than 0.0003 percent; however, the excessive content of magnesium can cause the coarsening of inclusions and is not beneficial to improving the toughness of a welding heat affected zone, and the addition amount of the magnesium is not higher than 0.005 percent in order to avoid the adverse effect of magnesium; comprehensively considering, the content of magnesium should be controlled within the range of 0.0003-0.005%;
zirconium: zirconium also has higher high-temperature reducibility, and zirconia has larger specific gravity and is easier to disperse and distribute in steel, so that the zirconium and the titanium oxide are oxidized to form fine and dispersed composite inclusions, the nucleation of acicular ferrite in crystal is promoted, and the toughness of a heat affected zone under the condition of large heat input welding is improved, so that the addition amount of the zirconium is not less than 0.0006 percent; but the excessive zirconium content can cause the coarsening of inclusions, reduce the mechanical property of the steel plate and the toughness of a heat affected zone after welding, and the addition amount of the zirconium should not be higher than 0.03 percent in order to avoid the adverse effect of the zirconium; comprehensively considering, the content of zirconium is controlled within the range of 0.0006-0.03%;
the total amount of the alloy elements and the proportion of the alloy elements are controlled as follows:
c + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15 is more than or equal to 0.21% and less than or equal to 0.38%: in order to ensure that the strength of the steel meets the use requirement of structural materials, a proper amount of strengthening elements must be ensured in the steel, so that the total amount of elements such as C, Mn, Cr, Mo, V, Ni, Cu and the like in the steel has a lower limit control requirement; however, the addition of the above elements increases the carbon equivalent of the steel sheet to some extent, thereby deteriorating the weldability of the material and reducing the low-temperature toughness of the heat affected zone under high heat input welding conditions, and the total amount of the above elements must be controlled to obtain good high heat input welding suitability. When the C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15 is less than 0.21%, even if controlled rolling and cooling are carried out under the limit condition, the strength of the steel is difficult to meet the application requirement of the structural material due to the fact that the total amount of the strengthening elements is too low; when C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15 is higher than 0.38%, the welding is difficult due to the excessively high carbon equivalent of the steel, and the requirements of 100-200KJ/cm large-linear energy welding process cannot be met. Comprehensively considering the requirements of strength and weldability of the material, the ratio of C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15 should be controlled to be more than or equal to 0.21% and less than or equal to 0.38%; preferably, 0.24% or more C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15% or less 0.35%, or 0.3% or more C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15% or less 0.35%.
Si + Mn + Als is more than or equal to 0.85% and less than or equal to 1.65%: si, Mn and Al are important deoxidizing elements in steel, wherein Als is the content of acid-soluble aluminum after deoxidation, and can react the oxygen content level in the steel to a certain extent; however, if the amount of the deoxidizing element is excessively added, the oxygen content in the steel is too low, the subsequent oxide metallurgical process cannot be ensured to be smoothly carried out, effective oxide particles cannot be formed, and the nucleation of the acicular ferrite in the crystal cannot be promoted, so that the high heat input welding adaptability of the steel is affected. When the Si + Mn + Als is less than 0.85 percent, even if the refining time or the vacuum degassing time is increased, the total oxygen content in the steel is higher, a large amount of oxide inclusions are formed in the steel, and the comprehensive mechanical property of the steel plate is deteriorated; when Si + Mn + Als is higher than 1.65%, the total oxygen content of the steel is lower after smelting, and the subsequently fed oxide wires are mostly pure alloy particles and can not be used as an effective core for acicular ferrite nucleation, so that the aim of improving the large-heat energy welding adaptability of the steel can not be fulfilled. The overall cleanliness of the steel and the thermodynamic conditions of oxide metallurgy are comprehensively considered, 0.85 percent to 1.65 percent of Si + Mn + Als are controlled, and 1.00 percent to 1.50 percent of Si + Mn + Als are preferably controlled;
Ti/(Nb + V) is more than or equal to 0.09 and less than or equal to 0.22: nb, V and Ti belong to necessary microalloy elements in steel, and are added to be matched with controlled rolling and controlled cooling to precipitate carbonitride to generate a precipitation strengthening effect and coarsen austenite grains of pinning and fixing a grain boundary structure to generate a grain refining effect, and a proper amount of Nb, V and Ti microalloy has an obvious effect of improving the toughness of the steel, but excessive Nb and V cannot form carbonitride, and the microalloying effect can be lost when the Nb, V and Ti exist in a solid solution state, so that the cost is increased; from the aspect of improving the large heat input welding adaptability of steel, the Ti compound has better stability at high temperature, and can play a role of coarsening crystal grains in a structure heat affected zone under the large heat input welding condition, so that the low-temperature toughness of the welding heat affected zone can be improved, and the weldability of the steel is improved, therefore, the Ti/(Nb + V) is required not to be too low; however, if an excessive amount of Ti is added to the steel, coarse titanides are formed under high heat input welding conditions, and the low Nb and V contents do not act as microalloying effects, which is not favorable for improving the overall performance of the steel. When Ti/(Nb + V) is less than 0.09, the Ti content proportion which has the most obvious effect of improving the welding adaptability of the high heat input welding is low, and the structure and the low-temperature toughness of a heat affected zone can not be effectively improved; when Ti/(Nb + V) is higher than 0.22, Nb and V cannot play a role in composite microalloying, excessive Ti forms coarse titanides, and the comprehensive performance of the steel is obviously deteriorated. The comprehensive performance and welding adaptability of the steel are comprehensively considered, and the control value is more than or equal to 0.09 and less than or equal to 0.22 of Ti/(Nb + V), preferably more than or equal to 0.1 and less than or equal to 0.15 of Ti/(Nb + V).
Ti/(Mg + Zr) is more than or equal to 0.42 and less than or equal to 13.5: titanium compounds dispersed in the steel can be used as nucleation points of Mg and Zr composite inclusions, and Mg and Zr are stronger in high-temperature reducibility and combined with Ti to form composite Ti, Mg and Zr inclusions, and can be used as oxide metallurgical particles to promote the nucleation of acicular ferrite in the crystal under the condition of high-heat-input welding; when the content of Ti in steel is low and the contents of Mg and Zr are high, the formed titanides are less, and excessive addition of Mg and Zr can cause impurity content increase and inclusion coarsening in the steel, so that the purpose of improving the weldability cannot be achieved, and the comprehensive mechanical property of the material can be deteriorated, therefore, the Ti/(Mg + Zr) is required not to be too low; however, if the content of Ti in the steel is high and the contents of Mg and Zr are low, excessive Ti can cause the coarsening of the titanide due to the lack of the refining and dispersing effects of Mg and Zr on the titanide inclusions, so that the requirements of controlling the sizes of the inclusions and the proportion of the components required by the implementation of the patent cannot be met, and the improvement of the toughness of a welding heat affected zone is also not facilitated. When Ti/(Mg + Zr) is less than 0.42, the Ti content ratio which has the most obvious effect of improving the welding adaptability of high heat input welding is low, a sufficient amount of oxide metallurgy cores cannot be formed, and the structure and the low-temperature toughness of a heat affected zone are difficult to effectively improve; when Ti/(Mg + Zr) is higher than 13.5, the content of Mg and Zr can not support the control requirements of the quantity, the size and the composition proportion of the composite inclusions, excessive Ti can cause the coarsening of the inclusions, and the comprehensive performance of the steel is obviously deteriorated. Comprehensively considering the requirement of the large heat input welding adaptability of the steel, the temperature should be controlled to be more than or equal to 0.42 and less than or equal to 13.5 of Ti/(Mg + Zr), preferably more than or equal to 3 and less than or equal to 7 of Ti/(Mg + Zr).
Further, the low alloy steel for high heat input welding comprises the following components in percentage by mass: 0.08 to 0.12%, Si: 0.06-0.35%, Mn: 0.8-1.2%, P: less than or equal to 0.015%, S: less than or equal to 0.008 percent, Cu: 0.15-0.25%, Cr: 0.08-0.12%, Ni: 0.08-0.3%, Nb: 0.028-0.032%, V: 0.07-0.09%, Mo: 0.04-0.06%, Als: 0.003-0.008% and N: 0.003 to 0.005%, O: 0.004 to 0.007%, Ti: 0.009-0.016% and Mg: 0.0005 to 0.003%, Zr: 0.001-0.02% of one or more of the following, and the balance of Fe and inevitable impurity elements. C, Si, Mn, Cr, Mo, V, Ni, Cu, Als, Ti, Mg and Zr simultaneously satisfy the relation: c + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15 is more than or equal to 0.24% and less than or equal to 0.35%, Si + Mn + Als is more than or equal to 0.92% and less than or equal to 1.45%, Ti/(Nb + V) is more than or equal to 0.11 and less than or equal to 0.18, and Ti/(Mg + Zr) is more than or equal to 0.55 and less than or equal to 11.5.
The control functions of ferrite, pearlite structure, grain size, inclusion size in steel, inclusion surface density and inclusion component proportion in the steel are as follows:
ferrite: ferrite is an interstitial solid solution of carbon in α -Fe, and is the main constituent phase in carbon steels and low alloy steels. The crystal lattice gap in alpha-Fe is very small, so that the carbon dissolving capacity of the alpha-Fe is very poor, the maximum carbon dissolving amount can reach 0.0218% at 727 ℃, the carbon dissolving amount is gradually reduced along with the reduction of the temperature, and the carbon dissolving amount is about 0.0008% at room temperature, so that the low carbon characteristic endows the alpha-Fe with low carbon equivalent and better weldability. When the ferrite content in the steel is less than 65%, the easy-to-weld phase ratio in the structure is too low, and the corresponding hard-to-weld pearlite phase composition ratio increases, and the high heat input welding suitability of the steel deteriorates. Therefore, the content of the ferrite structure in the steel should be controlled to be not less than 65%;
pearlite: pearlite is eutectoid body of ferrite and cementite formed by eutectoid transformation of austenite, the carbon content of the eutectoid body is 0.77%, the eutectoid body is a layered complex phase body formed by alternately overlapping ferrite thin layers and cementite thin layers, and the carbon content in the phase composition is increased, so that the carbon equivalent of the composition phase is correspondingly increased, and the welding difficulty is increased. When the pearlite content in the steel exceeds 35%, the composition ratio of the phase difficult to weld in the structure is high, and the high heat input welding adaptability of the steel is deteriorated. Therefore, the pearlite structure content in the steel should be controlled not to be higher than 35%;
grain size: the crystal grains are basic units of the composition material, the strength of the steel is closely related to the size of the crystal grains according to the Hall-Petch theory, dislocation must overcome the barrier of the crystal grain boundary in the movement process to enable the deformation to be transferred from one crystal grain to another crystal grain, the crystal grains are finer, the crystal grain boundary is more, the barrier is more, the strength of the material is higher, otherwise, the strength is reduced, and in order to ensure the strength of the invented low alloy steel, the size of the crystal grains of the steel cannot be overlarge; however, if the grain size of the base material is too small, the weld joint and the heat affected zone structure of the steel are coarsened under the condition of high heat input welding, and the strength of the steel is greatly reduced by fine grain strengthening, so that the performance of the weld zone is deteriorated. When the average grain size in the steel is less than 3 μm, the steel has a sufficiently high strength, but such fine grains may be coarsened after welding, loss of strength increase due to fine grain strengthening, resulting in deterioration of the welded joint properties; when the average crystal grain size in the steel is more than 25 μm, the strength of the steel is insufficient, and the structural mechanical property requirements necessary for the steel for high heat input welding cannot be satisfied. In general, the average grain size of the steel should be controlled within the range of 3 to 25 μm.
Size of inclusions: the high melting point composite oxide inclusion is an important nucleation point in the oxide metallurgy process, and a large amount of fine and dispersed Ti-X-O inclusion is formed in steel, so that austenite grain boundaries can be pinned, the formation of acicular ferrite in the steel is promoted, and the structure of a heat affected zone is refined under the condition of high heat input welding to improve the toughness. When the size of the inclusions in the steel is less than 0.02 mu m, the high-temperature nucleation particles are too small to play the roles of pinning the grain boundary and refining the grains; when the size of the inclusions in the steel is larger than 4 μm, the size of the inclusions becomes too large to become harmful inclusions in the steel, not only failing to achieve the purpose of improving the toughness due to welding heat, but also deteriorating the mechanical properties of the base metal itself. In combination, the size of the inclusions in the steel should be controlled to be 0.02 to 4 μm.
Areal density of inclusions: the quantity of Ti-X-O inclusions in steel is also an important characteristic parameter influencing the large heat input welding adaptability of the steel, the surface density is taken as an evaluation basis, when the quantity of the Ti-X-O inclusions is too small, the quantity of the formed high-melting-point composite inclusions is insufficient under the large heat input condition of 100-plus-200 KJ/cm, the formation of acicular ferrite with the inclusions as cores cannot be promoted, and finally the beneficial effect of improving the toughness of a heat affected zone under the large heat input welding condition cannot be achieved. Therefore, the area density of Ti-X-O inclusions in the steel should be not less than 1.8X 106Per mm2。
The inclusion component proportion is as follows: the component proportion of Ti-X-O inclusions in steel is an important characteristic parameter influencing the large heat input welding adaptability of the steel, the component Ti oxides in the inclusions are the most important oxide metallurgy core influencing the large heat input welding adaptability, and Mg and Zr in X are important elements capable of effectively refining and dispersing the inclusions so as to disperse and distribute the Ti-X-O inclusions in the steel. Therefore, the Ti-X-O type inclusions in the steel should be controlled to contain not less than 40% by mass of Ti oxides on average, not less than 40% by mass of X oxides, and X is one or a mixture of Mg and Zr.
In one possible design, the structure of the low alloy steel is composed of ferrite and pearlite, and the content of the ferrite structure is not less than 65% and the content of the pearlite structure is not more than 35%.
In one possible design, the low alloy steel has a ferrite average grain size of 3 μm to 25 μm.
In one possible design, the Ti-X-O type inclusions in the low alloy steel have a size of 0.02 μm to 4 μm and an area density of not less than 1.8X 106Per mm2And X is Mg and/or Zr.
In one possible design, the Ti-X-O type inclusions in the steel contain on average not less than 40% by mass of Ti oxides and not less than 40% by mass of X oxides.
In one possible design, the content of ferrite structure is not less than 75%, the content of pearlite structure is not more than 25%; the average ferrite grain size of the steel is more than or equal to 5 mu m and less than or equal to 15 mu m; the size of Ti-X-O type inclusions in the steel is 0.05-2 mu m, and the area density is not less than 2.5 multiplied by 106Per mm2。
The invention also provides a preparation method of the low alloy steel for high heat input welding, which is characterized by comprising the following steps:
s1, adopting an LD-LF-RH/VD smelting process to smelt molten steel;
s2, continuously casting to form a casting blank;
s3, performing multi-stage heating on the casting blank in a heating furnace to perform soaking treatment, and performing high-pressure water descaling treatment on the casting blank after the casting blank is discharged from the heating furnace to ensure that the temperature of the descaled casting blank is more than or equal to 1100 ℃;
s4, performing controlled rolling and controlled cooling after descaling, wherein the initial rolling temperature of rough rolling is not less than 1050 ℃, the initial rolling temperature of finish rolling is controlled at 950 ℃ and 850 ℃ of finish rolling, performing laminar cooling after rolling, and controlling the temperature of red return after cooling at 730 ℃ and 620 ℃ after rolling;
s5, straightening the rolled steel plate, wherein the final straightening temperature is not lower than 550 ℃.
Specifically, in S1, the LD converter is used for smelting molten steel to perform silicon-manganese-aluminum deoxidation, the content of dissolved oxygen after the converter is controlled to be less than or equal to 180ppm, the content of acid-soluble aluminum is controlled to be 5-130ppm, and the content of phosphorus is controlled to be less than or equal to 0.025%, so that high-quality molten steel is provided for an LF refining stage; white slag is produced for desulfuration by LF refining, the white slag desulfuration retention time is more than or equal to 15min, the low S content in steel is ensured, the sulfur content is controlled to be less than or equal to 0.015 percent, harmful sulfide impurities in steel are reduced, the LF end point oxygen content is determined to be less than or equal to 100ppm, a foundation is laid for the oxygen content control in the RH or VD refining stage, and the accurate regulation and control of each alloy component of steel is realized; the molten steel is conveyed to RH (vacuum circulation degassing) or VD (vacuum degassing) for refining, the vacuum degree is less than or equal to 120Pa, the pressure maintaining time in a refining furnace is more than or equal to 15min, the soft argon blowing treatment time is more than or equal to 10min, so that the gas content in the steel is reduced, meanwhile, the contents of other alloy elements except Ti, Mg and Zr are adjusted according to the component requirements of the steel plate, oxygen is determined before discharging, the oxygen content is controlled to be 0.002-0.008%, a component basis is provided for oxide metallurgy operation in the subsequent continuous casting process, and then, the molten steel is tapped and cast into a continuous casting blank.
S2, controlling the superheat degree of the tundish to be not higher than 25 ℃, controlling the section size of the continuous casting billet to be 230 multiplied by 1510mm, controlling the specific water amount of a secondary cooling zone to be 0.4-0.7L/Kg, the cooling water amount of a narrow-face crystallizer to be 460-; controlling the continuous casting billet withdrawal speed to be 1.0-1.3m/min, matching the continuous casting billet with the wire feeding treatment of a subsequent crystallizer, and ensuring that each part of the continuous casting billet obtains high-melting-point composite inclusions which are distributed in a dispersed manner and are used as oxide metallurgy nucleation cores; electromagnetic stirring and soft reduction are adopted to ensure that the continuous casting billet obtains low segregation degree and better metallurgical quality; after molten steel is poured, a Ti-X alloy wire is fed at the position of a water gap of a crystallizer by adopting a special wire feeding device, wherein X can be single Mg, Zr or a mixture of Mg and Zr, the wire diameter of the alloy wire is controlled to be phi 3-phi 8mm according to the type and filling rate of the added alloy, and the wire feeding speed is controlled to be 5-35m/min, so that good manufacturability and high yield of the wire feeding process are ensured.
In S3, the casting blank is subjected to soaking treatment by adopting multi-stage heating temperature rise in a heating furnace, wherein the temperature of a preheating section is 700-. Through the heating control, the steel billet is ensured to be completely hot and fully austenitized, the crystal grains are not coarsened, and all alloy elements are fully dissolved in solid solution, so that a good foundation is provided for the subsequent rolling control. And (3) taking the casting blank out of the heating furnace, and then carrying out high-pressure water descaling treatment to ensure that the temperature of the descaled steel blank is more than or equal to 1100 ℃ so as to ensure the control requirement of rolling and cooling temperature.
In S4, performing controlled rolling and controlled cooling after descaling, wherein the initial rolling temperature of rough rolling is more than or equal to 1050 ℃, the initial rolling temperature of finish rolling is controlled at 900-; the finishing temperature is controlled to be 800-850 ℃, and the mechanical property control requirement of the steel is ensured through reasonable finishing temperature control; carrying out laminar cooling after rolling, controlling the temperature of red return after cooling after rolling to be 620-730 ℃, increasing the phase change supercooling degree through controlled cooling, increasing the ferrite nucleation rate, forming fine dispersed precipitated phases and further improving the toughness matching of the steel; and straightening the rolled steel plate, wherein the final straightening temperature is not lower than 550 ℃, and ensuring the good plate shape quality of the steel plate.
Furthermore, in S1, the content of dissolved oxygen in the smelting stage of the LD converter is less than or equal to 150ppm, the content of acid-soluble aluminum is 8-100ppm, and the content of phosphorus is controlled to be less than or equal to 0.02%; the white slag desulfurization retention time in the LF refining stage is more than or equal to 20min, the fixed oxygen content of the LF end point is less than or equal to 90ppm, and the sulfur content is less than or equal to 0.01 percent; in the RH or VD refining stage, the vacuum degree is less than or equal to 100Pa, the pressure maintaining time in the refining furnace is more than or equal to 20min, the soft argon blowing treatment time is more than or equal to 15min, and oxygen is determined before discharging, wherein the oxygen content is 0.003-0.007%.
Further, in S2, the superheat degree of the tundish is not higher than 20 ℃, the specific water amount of the secondary cooling zone is 0.5-0.7L/Kg, the cooling water amount of the narrow-face crystallizer is 480-500L/min, the cooling water amount of the wide-face crystallizer is 3200-0L/min, the throwing speed of the continuous casting billet is 1.1-1.2m/min, and the wire feeding speed of the Mg, Zr or the mixed alloy wire of Mg and Zr is controlled at 8-30 m/min.
Further, in S3, the preheating section temperature is 750-.
Further, in S4, the initial temperature of rough rolling is not less than 1080 ℃ in the controlled rolling and controlled cooling stage, the initial temperature of finish rolling is controlled at 920-; the final correction temperature of the rolled steel plate is 560 ℃ to 580 ℃.
Compared with the prior art, the invention can at least realize one of the following technical effects:
1) the method provides the low alloy steel for large heat input welding and the preparation method thereof, and the low alloy steel for large heat input welding with good obdurability matching and good low-temperature toughness under 100-grade 200KJ/cm heat input welding can be obtained by micro-alloying proportion, alloy internal structure form, grain size and inclusion control based on oxide metallurgy mode. The thickness of the steel plate reaches 15-70mm, the yield strength is 350-750MPa, the tensile strength is 400-850MPa, and the impact energy of the V-shaped notch at-40 ℃ is 180-300J; the impact energy of the V-shaped notch at the temperature of minus 40 ℃ in the heat affected zone of the welding joint of the steel plate is 150-250J under the welding line energy of 100-200KJ/cm, and the steel plate has good technical economy and wide popularization and application values.
2) The casting blank is subjected to soaking treatment by adopting multi-stage heating temperature rise in a heating furnace, so that the steel blank is completely hot and fully austenitized, crystal grains are not coarsened, and all alloy elements are fully dissolved in solid solution, thereby providing a good foundation for subsequent rolling control.
3) The initial rolling temperature of rough rolling is more than or equal to 1050 ℃, the initial rolling temperature of finish rolling is controlled at 900-; the finishing temperature is controlled to be 800-850 ℃, and the mechanical property control requirement of the steel is ensured through reasonable finishing temperature control; and carrying out laminar cooling after rolling, controlling the temperature of red return after cooling after rolling to be 620-730 ℃, increasing the phase change supercooling degree through controlled cooling, increasing the ferrite nucleation rate, forming fine dispersed precipitated phases and further improving the toughness matching of the steel.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and drawings.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.
FIG. 1 is a metallographic structure of a material of comparative example 1 enlarged by 100 times;
FIG. 2 is a 100-fold enlarged morphology of inclusions for the composition of comparative example 2;
FIG. 3 is a metallographic structure of a comparative example 3 component material magnified 500 times;
FIG. 4 is a metallographic structure of a material of comparative example 4 enlarged by 100 times;
FIG. 5 is SEM morphology of inclusions for a 5000 x magnification of example 6 component material;
FIG. 6 is a plot of areal density scans of ASPEX inclusion inclusions of the component material of example 7;
FIG. 7 is a plot of acicular ferrite at 100 times magnification after high heat input welding for the example 9 component material.
Detailed Description
A low alloy steel for high heat input welding and a method for manufacturing the same will be described in further detail with reference to specific examples, which are provided for comparison and explanation purposes only and to which the present invention is not limited.
Comparative examples 1 to 5 and examples 1 to 9 are given to illustrate the composition and the effect of the low alloy steel for high heat input welding prepared by the present invention. The specific chemical compositions of the comparative examples and examples are shown in Table 1, and the alloy element ratios, the structure compositions, the grain sizes, the inclusion areal densities, and the inclusion component ratios are shown in Table 2.
TABLE 1 comparative and various examples chemical compositions
Figure BDA0002642757060000181
TABLE 2 alloy element ratios, structures, crystal grains and inclusions of comparative examples and examples
Figure BDA0002642757060000182
The room temperature tensile property and the impact property of the material are tested according to GB/T228.1-2010 metal material tensile test and GB/T229-.
TABLE 3 mechanical Properties of the comparative and various examples
Figure BDA0002642757060000191
Comparative example 1: the carbon content in the steel is 0.04 percent, the carbon content requirement of 0.05 to 0.16 percent which does not meet the invention requirement is not met, and other elements, alloy proportion, structure, grain size and inclusions all meet the invention requirement; influenced by carbon content, although the test steel has better high heat input welding adaptability, the tensile strength of the steel is 255MPa, the yield strength is 218MPa, which is mainly caused by coarser ferrite structures in the steel due to low carbon, and the strength requirement of the steel for high heat input welding as a structural material is not met, and the structures in the steel are shown in FIG. 1;
comparative example 2: the value of Ti/(Mg + Zr) in the steel is 18.89, the requirement of 0.42-13.5 of the invention requirement is not met, the components of the inclusions are 72 percent of Ti +13 percent of Mg +15 percent of Zr, wherein the specific gravity of the Mg + Zr is only 28 percent, the requirement of the invention requirement is not less than 40 percent, and other elements, alloy proportion, structure, grain size and inclusions all meet the invention requirement; influenced by Ti/(Mg + Zr), the proportion of Mg + Zr in the inclusion components is low, the size of the inclusion in the steel is large, although the test steel has good tensile property, the-40 ℃ impact work value of the parent metal is only 131J, the-40 ℃ impact work after large-heat-input welding is lower to 65J, the low-temperature toughness of the parent metal and a welding heat affected zone is poor, the mechanical property requirement of the large-heat-input welding steel is not met, and the inclusion in the steel is shown in figure 2;
comparative example 3: the contents of ferrite and pearlite structures in the steel are respectively 54% and 46%, the requirements of 65% + 35% which do not meet the invention requirements are not met, and other elements, alloy proportion, structures, grain sizes and inclusions all meet the invention requirements; influenced by the structure composition, the hard phase pearlite structure content in the steel is higher, although the test steel has higher strength, the elongation is as low as 18 percent, the plasticity is poor, the-40 ℃ impact energy of the base metal and the base metal after large heat input welding is respectively as low as 164J and 142J, the low-temperature toughness of the base metal and the welding heat affected zone is poor, the mechanical property requirement of the large heat input welding steel is not met, and the microstructure in the steel is shown in figure 3;
comparative example 4: the grain size in the steel reaches 33 mu m and does not meet the requirement of 3-25 mu m of the invention requirement, and other elements, alloy proportion, structure, grain size and inclusions all meet the invention requirement; the yield strength of the steel is as low as 339MPa under the influence of coarse grain size, the-40 ℃ impact energy of the base metal and the welded steel subjected to high heat input welding is as low as 129J and 55J respectively, the low-temperature toughness of the base metal and the welded heat affected zone is poor, the comprehensive mechanical property of the steel does not meet the mechanical property requirement of the high heat input welded steel, and the microstructure in the steel is shown in figure 4;
comparative example 5: the components of the inclusions in the steel are 27% of Ti, 36% of Mg and 37% of Zr, the requirements that the components of Ti oxides are not less than 40% are not met, and other elements, alloy proportion, structure, grain size and inclusions meet the invention requirements; influenced by inclusion components, although all mechanical properties of the base metal of the steel meet the structural application requirements, the-40 ℃ impact energy after the high heat input welding is as low as 116J, the high heat input welding adaptability of the steel is poor, and the high heat input welding requirement of 100-200KJ/cm is not met;
the SEM morphology of inclusions, the areal density of ASPEX inclusions and the morphology of acicular ferrite in the tissues after the heat simulation of high heat input welding of the materials in examples 6, 7 and 9 are respectively shown in figures 5, 6 and 7.
As can be seen from Table 2, the steel for high heat input welding in each example has good mechanical properties, and the comprehensive mechanical properties of the steel, particularly the low-temperature toughness after high heat input welding, are remarkably improved along with the optimization of the alloy proportion in the steel, the increase of the ferrite proportion in the structure, the reduction of the grain size, the reduction of the size of Ti-X-O type inclusions, the increase of the surface density of inclusions and the improvement of the contents of Ti, Mg and Zr in the inclusion components; the tensile strength is 641-847MPa, the yield strength is 502-744MPa, the elongation is 35-56%, the reduction of area is 46-77%, and the base material-40 ℃ impact energy is 194-298J, so that the composite material has excellent comprehensive mechanical properties; meanwhile, after the steel is subjected to 100-200KJ/cm high heat input welding thermal simulation, the-40 ℃ impact energy reaches 162-247J, and excellent high heat input welding adaptability is shown.
On the basis of good comprehensive mechanical properties, the high heat input welding adaptability of the low alloy steel for high heat input welding in the embodiment of the invention is greatly improved compared with the traditional steel, the maximum impact power value at minus 40 ℃ after 100-inch and 200KJ/cm high heat input welding thermal simulation can reach 250J, and the low alloy steel for high heat input welding has excellent high heat input welding adaptability. Meanwhile, the steel plate which has good obdurability matching and good low-temperature toughness under the condition of 100-plus-energy 200KJ/cm linear energy welding can be obtained only by controlling the microalloying proportion and matching with a proper preparation process, controlling the internal structure form and the grain size of the alloy and controlling the inclusion based on an oxide metallurgy mode, has excellent comprehensive performance and large linear energy welding adaptability, is very easy to realize industrial production, and has good technical economy and wide popularization and application values.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.

Claims (10)

1. The low alloy steel for high heat input welding is characterized by comprising the following components in percentage by mass: 0.05 to 0.16%, Si: 0.04-0.45%, Mn: 0.5-1.5%, P: less than or equal to 0.025%, S: less than or equal to 0.015 percent, Cu: 0.10-0.35%, Cr: 0.05 to 0.18%, Ni: 0.05 to 0.40%, Nb: 0.022-0.035%, V: 0.05 to 0.10%, Mo: 0.02 to 0.07%, Als: 0.001-0.01%, N: 0.001-0.006%, O: 0.002-0.008%, Ti: 0.006-0.018% and Mg: 0.0003 to 0.005%, Zr: 0.0006 to 0.03 percent of one or more than one of the components, and the balance of Fe and inevitable impurity elements;
c, Si, Mn, Cr, Mo, V, Ni, Cu, Als, Ti, Mg and Zr simultaneously satisfy the following relations: c + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15 is more than or equal to 0.21% and less than or equal to 0.38%, Si + Mn + Als is more than or equal to 0.85% and less than or equal to 1.65%, Ti/(Nb + V) is more than or equal to 0.09 and less than or equal to 0.22, and Ti/(Mg + Zr) is more than or equal to 0.42 and less than or equal to 13.5.
2. The low alloy steel for high heat input welding according to claim 1, wherein the composition is, in mass percent, C: 0.08 to 0.12%, Si: 0.06-0.35%, Mn: 0.8-1.2%, P: less than or equal to 0.015%, S: less than or equal to 0.008 percent, Cu: 0.15-0.25%, Cr: 0.08-0.12%, Ni: 0.08-0.3%, Nb: 0.028-0.032%, V: 0.07-0.09%, Mo: 0.04-0.06%, Als: 0.003-0.008% and N: 0.003 to 0.005%, O: 0.004 to 0.007%, Ti: 0.009-0.016% and Mg: 0.0005 to 0.003%, Zr: 0.001-0.02% of one or more of Fe and inevitable impurity elements as the rest;
c, Si, Mn, Cr, Mo, V, Ni, Cu, Als, Ti, Mg and Zr simultaneously satisfy the following relations: c + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15 is more than or equal to 0.24% and less than or equal to 0.35%, Si + Mn + Als is more than or equal to 0.92% and less than or equal to 1.45%, Ti/(Nb + V) is more than or equal to 0.11 and less than or equal to 0.18, and Ti/(Mg + Zr) is more than or equal to 0.55 and less than or equal to 11.5.
3. The low alloy steel for high heat input welding according to claim 1 or 2, wherein the structure of the low alloy steel is composed of ferrite and pearlite, and the content of the ferrite structure is not less than 65%.
4. The low alloy steel for high heat input welding according to claim 3, wherein the ferrite average grain size of the low alloy steel is 3 to 25 μm.
5. The low alloy steel for high heat input welding according to claim 3, wherein the Ti-X-O type inclusions in the low alloy steel have a size of 0.02 μm to 4 μm and an area density of not less than 1.8X 106Per mm2And X is Mg and/or Zr.
6. The low alloy steel for high heat input welding according to claim 5, wherein the Ti-X-O type inclusions in the steel contain Ti oxides not less than 40% by mass and X oxides not less than 40% by mass on average.
7. The method for producing a low alloy steel for high heat input welding according to claims 1 to 6, characterized by comprising the steps of:
s1, adopting an LD-LF-RH/VD smelting process to smelt molten steel;
s2, continuously casting to form a casting blank;
s3, performing multi-stage heating on the casting blank in a heating furnace to perform soaking treatment, and performing high-pressure water descaling treatment on the casting blank after the casting blank is discharged from the heating furnace;
s4, performing controlled rolling and controlled cooling after descaling, wherein the initial rolling temperature of rough rolling is not less than 1050 ℃, the initial rolling temperature of finish rolling is controlled at 950 ℃ and 850 ℃ of finish rolling, performing laminar cooling after rolling, and controlling the temperature of red return after cooling at 730 ℃ and 620 ℃ after rolling;
s5, straightening the rolled steel plate.
8. The method for preparing a low alloy steel for high heat input welding according to claim 7, wherein in S1, the molten steel smelted by the LD converter is deoxidized by silico-manganese-aluminum, the content of dissolved oxygen after the converter is controlled to be less than or equal to 180ppm, the content of acid-soluble aluminum is controlled to be 5-130ppm, and the content of phosphorus is controlled to be less than or equal to 0.025%; white slag is produced and desulfurized in LF refining, the white slag desulfurization retention time is more than or equal to 15min, the fixed oxygen content of the LF end point is less than or equal to 100ppm, and the sulfur content is controlled to be less than or equal to 0.015 percent; and (2) carrying the molten steel to RH or VD for refining, wherein the vacuum degree is less than or equal to 120Pa, the pressure maintaining time in the refining furnace is more than or equal to 15min, the soft argon blowing treatment time is more than or equal to 10min, the contents of other alloy elements except Ti, Mg and Zr are adjusted according to the component requirements of the steel plate, oxygen is determined before discharging, and the oxygen content is controlled to be 0.002-0.008%.
9. The method for manufacturing a low alloy steel for high heat input welding according to claim 7, wherein the slab casting speed of the slab is controlled to be 1.0 to 1.3m/min in S2;
after molten steel is poured, Ti-X alloy wires are fed at the position of a crystallizer water gap by adopting wire feeding equipment, wherein X is single Mg, Zr or a mixture of Mg and Zr, and the wire feeding speed is controlled to be 5-35 m/min.
10. The preparation method of the low alloy steel for large heat input welding according to claim 7, wherein the heat soaking treatment in S3 comprises a preheating section, a first heating section, a second heating section and a heat soaking section, wherein the temperature of the preheating section is 700-.
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CN113046649A (en) * 2021-03-10 2021-06-29 南京钢铁股份有限公司 Steel for large heat input welding ship structure and manufacturing method thereof
CN113046639A (en) * 2021-03-11 2021-06-29 南京钢铁股份有限公司 460 MPa-grade hot-rolled steel for ship structure and manufacturing method thereof
WO2023097979A1 (en) 2021-12-02 2023-06-08 莱芜钢铁集团银山型钢有限公司 Corrosion-resistant high-strength steel sheet weldable with high heat input and used for ocean engineering, and preparation method therefor

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