阅读说明：本技术 大线能量焊接用eh36海洋工程用钢板及其制备方法 (Steel plate for EH36 ocean engineering for high heat input welding and preparation method thereof ) 是由 刘洪波 李建新 孙力 张瑞忠 安治国 李超 信瑞山 于 2019-10-24 设计创作，主要内容包括：本发明属于钢铁冶金领域,涉及大线能量焊接用EH36海洋工程用钢板及其制备方法,包括以下步骤：1)冶炼与铸造,其中钢板以质量百分数计：C：0.05~0.08%、Si：0.12~0.18%、Mn：1.2~1.8%、P：≤0.01%、S：0.003~0.01%、Nb：0.01~0.015%、N：0.004~0.006%、Zr：0.001~0.006%,Ti：0.004~0.02%,其余为Fe及其他不可避免杂质元素；2)轧制；3)冷却。本发明可以显著提高EH36钢焊接热影响区低温冲击韧性,满足海洋工程对大线能量钢的需求。(The invention belongs to the field of ferrous metallurgy, and relates to a steel plate for EH36 ocean engineering for large heat input welding and a preparation method thereof, wherein the preparation method comprises the following steps: 1) smelting and casting, wherein the steel plate comprises the following components in percentage by mass: c: 0.05 to 0.08%, Si: 0.12 to 0.18%, Mn: 1.2-1.8%, P: less than or equal to 0.01 percent, S: 0.003 to 0.01%, Nb: 0.01-0.015%, N: 0.004-0.006%, Zr: 0.001-0.006%, Ti: 0.004-0.02% of Fe and other inevitable impurity elements in balance; 2) rolling; 3) and (6) cooling. The invention can obviously improve the low-temperature impact toughness of the EH36 steel welding heat affected zone and meet the requirements of ocean engineering on large-line energy steel.)

1. The steel plate for the EH36 ocean engineering for the large heat input welding is characterized by comprising the following components in percentage by mass: 0.05 to 0.08%, Si: 0.12 to 0.18%, Mn: 1.2-1.8%, P: less than or equal to 0.01 percent, S: 0.003 to 0.01%, Nb: 0.01-0.015%, N: 0.004-0.006%, Zr: 0.001-0.006%, Ti: 0.004-0.02% of Fe and the balance of inevitable impurities.

2. The steel plate for the EH36 ocean engineering for the high heat input welding according to claim 1, wherein the steel plate has an average Charpy impact energy at-20 ℃ of 239J or more and an average Charpy impact energy at-40 ℃ of 163J or more in a weld heat affected zone at an on-line energy of 200 kJ/cm.

3. The method for producing a steel plate for use in an EH36 ocean engineering for high heat input welding according to claim 1 or 2, comprising the steps of:

step (1): smelting and casting, and mixing the following materials in percentage by mass: c: 0.05 to 0.08%, Si: 0.12 to 0.18%, Mn: 1.2-1.8%, P: less than or equal to 0.01 percent, S: 0.003 to 0.01%, Nb: 0.01-0.015%, N: 0.004-0.006%, Zr: 0.001-0.006%, Ti: 0.004-0.02% of Fe and inevitable impurities as the rest;

firstly, filling a pure iron raw material into a vacuum induction furnace, after melting down, sampling on line to detect the oxygen content in steel, and adding Zr to adjust the oxygen content to 0.002-0.01%; then adding Ti to perform final deoxidation operation, wherein the adding sequence of other elements is Si, Mn, Nb, C and N respectively;

step (2): rolling, namely heating a casting blank with the thickness of 100-300 mm to 1050-1250 ℃, and preserving heat for 1-2 hours to perform two-stage rolling; descaling by high-pressure water before rolling; the thickness of the rolled steel billet is 20-60 mm;

and (3): and cooling, wherein the start cooling temperature is 750-800 ℃, the cooling rate is 10-20 ℃/s, the final cooling temperature is 500-600 ℃, and then air cooling is carried out.

4. The preparation method according to claim 3, wherein in the smelting process in the step (1), after the pure iron raw material is melted down, online sampling is carried out to detect the oxygen content in the steel, Zr is added to adjust the oxygen content to 0.002-0.01%, and the oxygen content in the steel is omega_[O]With Zr addition omega_ZrThe relation of (A) is as follows:

1.25×ω_[O]-0.0125≤ ω_Zr≤1.25×ω_[O]-0.0025

wherein, ω is_[O]And ω_ZrCalculated in mass percent.

5. The production method according to claim 3, wherein the two-stage rolling, i.e., recrystallization zone rolling and non-recrystallization zone rolling; the initial rolling temperature of the rolling stage in the recrystallization zone is 1000-1150 ℃, and the total rolling reduction rate is not lower than 30%; the initial rolling temperature of the rolling stage in the non-recrystallization zone is 800-900 ℃, and the total rolling reduction rate is not lower than 45%.

6. The preparation method according to claim 3, wherein the pressure of the high-pressure water is 14-18 MPa in the process of descaling with high-pressure water.

Technical Field

The invention belongs to the field of ferrous metallurgy, and particularly relates to a steel plate for EH36 ocean engineering for high heat input welding and a preparation method thereof.

Background

With the development of development and utilization of ocean resources in China, EH36 welded structural members are widely used for manufacturing shipbuilding and ocean platform construction, and in order to improve welding quality and efficiency and further achieve the purpose of reducing cost, the requirement on steel for ocean engineering capable of being welded by large heat input is increasingly urgent.

The steel for high heat input welding generally refers to a steel plate with heat input more than 50kJ/cm, and the steel plate is one of the advanced technologies which are pursued by developed countries in the world steel industry.

During large heat input welding, because the high-temperature retention time is long, the phase change cooling rate is slow, austenite grains in a welding heat affected zone of the steel plate grow rapidly, and the impact toughness of the steel plate is poor.

Patent document CN107904504A discloses a normalized delivery EH36 super-thick steel sheet for high heat input welding and a method for manufacturing the same, in which austenite grain size during normalization is refined by adding Nb element, formation of weld heat affected zone grain boundary ferrite is suppressed, formation of intra-grain acicular ferrite is promoted by fine (Ti, V, Nb) (C, N) composite precipitated particles, but the final steel sheet has an average impact work at-40 ℃ in the heat affected zone of only 50J at a heat input of 100 to 200 kJ/cm.

Patent document CN102560247A discloses a high heat input steel of a medium plate with excellent performance and a smelting method thereof, wherein Ti and Al elements are added to precipitate TiO_x-MnO-Al₂O₃MnS can effectively induce acicular ferrite in steel and improve the welding performance of a welding heat affected zone of high heat input steel, but the impact energy is only 90J at the temperature of 20 ℃ below zero.

Patent document CN102839320A discloses a steel plate for high heat input welding and a manufacturing method thereof, wherein B element is added, TMCP thermo-mechanical control and rapid cooling process are adopted for production, but B element is easy to generate segregation, and strict requirements are provided for heat treatment process.

Patent document CN101812639A discloses a high-strength high-heat input welding hull steel and a production method thereof, but the welding input energy applied thereto is only 50 to 100 kJ/cm.

Patent document CN103031491A discloses a chromium-free micro-molybdenum high-strength heat input steel plate and a manufacturing method thereof, wherein precious elements such as Ni and Mo are added to the steel plate, and the production cost is increased.

Patent document CN104404369A discloses a thick steel plate for high heat input welding, which is prepared by adding Mg, Ca, Ti, Al and other elements into steel, and controlling the (Mg + Ca)/(Al + Ti) ratio and the surface density of micron and submicron inclusions with different sizes, so as to obtain a steel plate with tensile strength not less than 510MPa, but the steel plate has an average impact power of only 50J at-40 ℃ under the condition of 200kJ/cm, and active elements such as Ca and Mg are easily oxidized and even combusted, so that the yield of such alloy elements is seriously reduced, the production stability is reduced, and the smelting cost is increased.

Disclosure of Invention

The invention aims to provide a steel plate for EH36 ocean engineering for large heat input welding and a preparation method thereof, and the steel plate can be widely applied to the ocean engineering fields of shipbuilding, ocean platform construction manufacturing and the like.

In order to achieve the purpose, the technical scheme of the invention is as follows:

the steel plate for the EH36 ocean engineering for the high heat input welding comprises the following components in percentage by mass: c: 0.05 to 0.08%, Si: 0.12 to 0.18%, Mn: 1.2-1.8%, P: less than or equal to 0.01 percent, S: 0.003 to 0.01%, Nb: 0.01-0.015%, N: 0.004-0.006%, Zr: 0.001-0.006%, Ti: 0.004-0.02% of Fe and the balance of inevitable impurities.

The preparation method of the steel plate for the EH36 ocean engineering for the large heat input welding comprises the following steps:

(1) smelting and casting

The materials are prepared according to the following mass percentages: c: 0.05 to 0.08%, Si: 0.12 to 0.18%, Mn: 1.2-1.8%, P: less than or equal to 0.01 percent, S: 0.003 to 0.01%, Nb: 0.01-0.015%, N: 0.004-0.006%, Zr: 0.001-0.006%, Ti: 0.004-0.02% of Fe and other inevitable impurity elements in balance; firstly, filling a pure iron raw material into a vacuum induction furnace, after melting down, sampling on line to detect the oxygen content in steel, and adding Zr to adjust the oxygen content to 0.002-0.01%; then adding Ti to perform final deoxidation operation, wherein the adding sequence of other elements is Si, Mn, Nb, C and N respectively;

(2) rolling of

Heating a casting blank with the thickness of 100-300 mm to 1050-1250 ℃, and preserving heat for 1-2 hours to perform two-stage rolling, namely rolling in a recrystallization zone and rolling in a non-recrystallization zone; descaling by high-pressure water before rolling, wherein the rolling temperature in the rolling stage of a recrystallization zone is 1000-1150 ℃, and the total rolling reduction rate is not lower than 30%; the initial rolling temperature of the rolling stage in the non-recrystallization zone is 800-900 ℃, and the total rolling reduction rate is not lower than 45%; the thickness of the rolled steel billet is 20-60 mm;

(3) cooling down

The start cooling temperature is 750-800 ℃, the cooling rate is 10-20 ℃/s, the final cooling temperature is 500-600 ℃, and then air cooling is carried out.

And the pressure of high-pressure water in the high-pressure water descaling is 14-18 Mpa.

The invention has the following components:

the low C content (less than or equal to 0.08%) is beneficial to the low-temperature impact property, the low-temperature strain aging property, the welding property and the corrosion resistance of the steel; 1.2-1.8% of Mn in the steel can play a role in solid solution strengthening so as to ensure that the steel plate has enough strength, and meanwhile, Mn can obviously reduce the starting transition temperature of grain boundary ferrite and promote the formation of acicular ferrite; nb (C, N) formed by 0.01-0.015% of Nb in the steel can generate a nail rolling effect on austenite grain boundaries, so that the steel structure is refined, and the strength and the toughness of a parent metal are improved; since Si element can be dissolved in austenite and ferrite to increase the hardness and strength of steel, the lower limit of Si is 0.12%, but too high Si content promotes the formation of martensite-austenite (MA) islands to significantly reduce the toughness of the weld heat affected zone, and thus the upper limit of Si is 0.18 percent; zr is a main element required by pre-deoxidation in the steelmaking process, the Zr and oxygen form dispersed composite inclusions, the inclusions can limit austenite grain growth by pinning grain boundary movement in a welding heat cycle, acicular ferrite nucleation is induced in the austenite transformation process, excessive Zr can also cause the grains to be coarse and lose the effect of inhibiting grain growth, and the addition amount of the Zr is 0.001-0.006%; ti may form Ti with oxygen₂O₃The lower limit of the Ti content is 0.004%, however, the Ti content in the steel should not be too high, and coarse Ti nitrides and carbides are formed when the Ti content is too high, so that the toughness of the welding heat affected zone is reduced, and the upper limit of the Ti content is 0.02%.

In the smelting and casting process, in the smelting process in the step (1), after the pure iron raw material is melted down, online sampling is carried out to detect the oxygen content in steel, Zr is added to adjust the oxygen content to 0.002-0.01%, and the oxygen content in the steel is omega_[O]With Zr addition omega_ZrThe relation of (A) is as follows:

1.25×ω_[O]-0.0125≤ ω_Zr≤1.25×ω_[O]-0.0025

wherein, ω is_[O]And ω_ZrCalculated in mass percent.

In the rolling process, the main reason for controlling the heating temperature of the casting blank to be 1050-1250 ℃ is that Nb (C, N) in the steel cannot be completely dissolved when the heating temperature before rolling is less than 1050 ℃; when the heating temperature is more than 1250 ℃, the austenite grain size of the casting blank can grow rapidly.

The starting rolling temperature of the rolling stage in the recrystallization zone is 1000-1150 ℃, the total rolling reduction rate is not less than 30%, so that the steel plate is fully recrystallized in the austenite zone, and austenite grains can be refined.

The initial rolling temperature of the rolling stage of the non-recrystallization zone is 800-900 ℃, so that flattened austenite grains are obtained in the low-temperature austenite zone; the total reduction rate is not less than 45 percent, which is to increase the deformation energy storage of austenite and provide position and energy for the subsequent refinement of ferrite grains by utilizing the formed dislocation.

The invention has the following beneficial effects:

zr and Ti form a large amount of fine and dispersed high-melting-point composite oxide inclusions in the smelting process, acicular ferrite nucleation can be effectively induced in a steel plate welding heat affected zone, crystal grains are refined, the low-temperature impact toughness of the EH36 steel welding heat affected zone can be remarkably improved, the requirement of ocean engineering on large-line energy steel is met, and the welding structural member can be widely used for manufacturing ships and ocean platform construction. Under the condition that the welding energy of the steel plate is 200kJ/cm, the average Charpy impact energy of a welding heat affected zone at the temperature of minus 20 ℃ is more than or equal to 239J, and the average Charpy impact energy of the steel plate at the temperature of minus 40 ℃ is more than or equal to 163J.

Drawings

FIG. 1 is a structural diagram of a welding heat affected zone under an optical microscope at an input line energy of 200KJ/cm in example 1;

FIG. 2 is a structural diagram of a welding heat affected zone under an optical microscope at an input line energy of 200KJ/cm in example 2;

FIG. 3 is a tissue diagram under an optical microscope of a welding heat affected zone of example 3 at an input line energy of 200 KJ/cm;

FIG. 4 is a tissue diagram under an optical microscope of a welding heat affected zone of example 4 at an input line energy of 200 KJ/cm;

FIG. 5 is a tissue diagram under an optical microscope of a welding heat affected zone of example 5 at an input line energy of 200 KJ/cm;

FIG. 6 is a tissue diagram under an optical microscope of a welding heat affected zone of example 6 at an input line energy of 200 KJ/cm;

FIG. 7 is a structural diagram of a welding heat affected zone under an electron microscope at an input line energy of 200KJ/cm in example 1;

FIG. 8 is a structural view under an electron microscope of a weld heat affected zone in example 2 at an input line energy of 200 KJ/cm;

FIG. 9 is a structural diagram of a welding heat affected zone under an electron microscope at an input line energy of 200KJ/cm in example 3;

FIG. 10 is a structural view under an electron microscope of a weld heat affected zone of example 4 at an input line energy of 200 KJ/cm;

FIG. 11 is a structural view under an electron microscope of a weld heat affected zone of example 5 at an input line energy of 200 KJ/cm;

FIG. 12 is a structural view under an electron microscope of a weld heat affected zone in example 6 at an input line energy of 200 KJ/cm.

Detailed Description

In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following detailed description is made with reference to specific drawings and examples, but the scope of the present invention is not limited to these examples.

The chemical compositions of the steel plates corresponding to the examples are shown in table 1, wherein the data in the table are the mass percent of each element, and the balance is Fe and other inevitable impurities.

Table 1: main chemical component (wt%) of steel in inventive examples 1 to 6

The production process of the steel plate comprises the following steps:

step 1: smelting and casting, and mixing according to target components shown in table 1; firstly, filling a pure iron raw material into a vacuum induction furnace, after melting down, sampling on line to detect the oxygen content in steel, and adding Zr to adjust the oxygen content to 0.002-0.01%; then adding Ti to perform final deoxidation operation, wherein the adding sequence of other elements is Si, Mn, Nb, C and N respectively;

step 2: rolling, namely heating a casting blank with the thickness of 100-300 mm to 1050-1250 ℃, preserving heat for 1-2 hours, and performing two-stage rolling, namely rolling in a recrystallization zone and rolling in a non-recrystallization zone, wherein phosphorus is removed by high-pressure water before rolling, the initial rolling temperature in the rolling stage of the recrystallization zone is 1000-1150 ℃, the total reduction rate is not lower than 30%, the initial rolling temperature in the rolling stage of the non-recrystallization zone is 800-900 ℃, the total reduction rate is not lower than 45%, and the thickness of the rolled billet is 20-60 mm;

and step 3: and cooling, wherein the start cooling temperature is 750-800 ℃, the cooling rate is 10-20 ℃/s, the final cooling temperature is 500-600 ℃, and then air cooling is carried out. The specific rolling process of each example is shown in table 2.

The tensile properties and weld heat affected zone impact properties of the steel sheets obtained by the processes of melting and casting, rolling and cooling according to the above examples are shown in Table 3. From the tensile property results of the examples, the yield strength of the steel plate is 388-404 MPa, the tensile strength is 490-533 MPa, and the elongation is better than or equal to 24 percent; under the condition that the input line energy is 200KJ/cm, the average Charpy impact energy of a steel plate welding heat affected zone at the temperature of minus 20 ℃ is more than or equal to 239J, and the average Charpy impact energy at the temperature of minus 40 ℃ is more than or equal to 163J.

Table 2: steel plate rolling process in embodiments 1-6 of the invention

Table 3: examples 1-6 of the invention include tensile properties of steel plates and impact properties of weld heat affected zone

FIGS. 1 to 6 are the structure diagrams of the welding heat affected zone observed under an optical microscope in examples 1 to 6 under the condition that the input line energy is 200kJ/cm, respectively, and it can be clearly seen in the diagrams that the structure of the heat affected zone in examples 1 to 6 is composed of a large amount of intra-crystalline acicular ferrite, a small amount of grain boundary ferrite and fine bainite, the acicular ferrite can effectively divide the original austenite grains into a plurality of fine independent areas, and the bainite formed at a slightly lower temperature is limited in the fine areas, so that a mixed structure of the acicular ferrite and the bainite with fine grains is obtained, the effective grain size of the mixed structure is far smaller than the original austenite grain size, and the generation of the fine grains can obviously improve the impact toughness of the welding heat affected zone of the steel plate.

FIGS. 7 to 12 are structural views of the weld heat affected zone observed under an electron microscope in examples 1 to 6 under an input line energy of 200kJ/cm, respectively, and it is apparent that inclusion particles precipitated in examples 1 to 6 were observedImpurities can be used as a core to induce acicular ferrite to be precipitated; the chemical composition of the inclusion particles is shown in Table 4, and it can be seen that the inclusions are MnS-Al₂O₃-ZrO₂-Ti₂O₃The composite inclusion of (3).

Table 4: in the examples 1-6 of the invention, the content of inclusions in the welding heat affected zone is wt%

。