KR20220134014A - EH 550 MPa grade quenched and tempered marine steel plate for high heat input welding and manufacturing method thereof - Google Patents

Abstract

C 0.06~0.12%, Si 0.02~0.06%, Mn 0.7~1.2%, Ti 0.006~0.012%, Al 0.002~0.010%, Cr 0.30~0.50%, Mo 0.3~0.4%, V 0.03~0.04%, N 0.0020 An EH 550 MPa grade quenched and tempered marine steel plate for high heat input welding having a weight composition of ~0.0030%, S 0.002~0.010%, P≤0.008% and residual Fe and unavoidable impurities, wherein the steel plate contains Ti-containing oxides. Disclosed are an EH 550 MPa grade quenched and tempered marine steel plate for high heat input welding, characterized in that the particles have an average size of 2 μm to 3 μm and a density of 50 or more particles per mm ² and a manufacturing method. Quenched and tempered marine steel plate has a yield strength EH of 550 MPa or more, a tensile strength of 670 MPa or more, a Charpy impact processing (single value) of the basic raw material at -40°C of 180J or more, and a welding heat input of 50 kj/cm , 100 kj/cm and 150 kj/cm, the Charpy impact processing (single value) of the heat-affected zone at -40°C is 80 J or more.

Description

EH 550 MPa grade quenched and tempered marine steel plate for high heat input welding and manufacturing method thereof

The present invention relates to steel for marine engineering, and more particularly, to an EH 550 MPa grade quenched and tempered marine steel plate for high heat input welding, and a method for manufacturing the same.

Offshore oil and gas is an important energy source in today's world. Advances in the exploration and utilization of oil and gas worldwide have increased the demand for offshore oil and gas engineering equipment such as jack-up drilling platforms, semi-submersible drilling platforms and rigs. are doing The strength grade, toughness grade, thickness, dimensional accuracy and welding performance of steel must be continuously improved to meet the manufacturing requirements of offshore oil and gas engineering equipment.

Because marine steel has many welded parts, it is generally used in harsh environments and has a long service life and high welding performance requirements. By adopting high-temperature input welding technology, the manufacturing cycle of the offshore platform can be shortened and the manufacturing cost can be reduced, which is of great significance to the improvement of the offshore platform manufacturing technology. However, since the marine steel plate has high strength and the alloy content is higher than that of the general marine plate, it is difficult to weld the marine steel plate. After high heat input welding, the cooling rate of the heat affected zone will be relatively slow, the grain size of the heat affected zone will increase rapidly, the microstructure will be greatly coarsened, and the toughness of the weld heat affected zone will be significantly reduced. The loss of toughness in the heat-affected zone compared to the base material can be as high as 80%. Although the weld heat-affected zone width is typically a few millimeters, a large roughness reduction in the coarse grain heat-affected zone is very likely to crack the steel, creating a potential hazard when using offshore platforms.

Chinese patent CN106191659A discloses "a high-temperature input welded steel plate for marine engineering and a manufacturing method therefor", which has successfully developed steel for marine engineering that can be welded with high heat input. The deoxidation process of the smelting process is simple, and ferrosilicon and manganese are mainly used, and no strong deoxidizer is added. After welding simulation with heat input of 100kj/cm and 200kj/cm, impact machining at -60℃ is more than 90J. However, in the present invention, the yield strength of the steel plate is 440 to 460 MPa and the tensile strength is 560 to 580 MPa, so the problem of high-temperature input welding of high-strength marine steel still exists.

Chinese patent CN201410300713.X discloses "High heat input welding 550 MPa grade steel plate and manufacturing method thereof". The alloy composition of ultra-low carbon C, ultra-low Si, high Mn, Nb is adopted, and the Al content of the steel is as low as possible. In the meantime, the TMCP process is optimized. Thus, yield strength of 465 MPa or more, tensile strength of 550 MPa to 650 MPa, Charpy impact work of high heat input welding heat affected zones at -40°C (single value) 100 J The above has been successfully developed. However, the yield strength of the steel plate of the present invention is less than 550 MPa, Ca is used as a deoxidizer, and the smelting process is complicated.

An object of the present invention is that the yield strength EH is 550 MPa or more, the tensile strength is 670 MPa or more, and the Charpy impact work (single value) of the basic raw material at -40°C is 180J Above, characterized in that when the welding heat input is 50 kj/cm, 100 kj/cm and 150 kj/cm, the Charpy impact processing (single value) of the heat affected zone at -40°C is 80 J or more To provide an EH 550 MPa grade quenched and tempered marine steel plate for high heat input welding, and a method for manufacturing the same.

Charpy impact machining is tested by taking three test samples, measuring three times, and evaluating the samples by taking the average of the results obtained from the three measurements. The Charpy impact processing (single value) of 180 J or more of the basic raw material at -40°C means that each value obtained from three measurements of the Charpy impact processing of the basic raw material at -40°C is 180 J or more. When the welding heat inputs are 50 kj/cm, 100 kj/cm and 150 kj/cm, the Charpy impact machining (single value) of the heat affected zone at -40°C is 80 J The above means that when the welding heat input is 50 kj/cm, each value obtained from three measurements of Charpy impact processing of the heat-affected zone at -40°C is 50 kj/cm, and when the welding heat input is 100 kj/cm - Each value obtained from three measurements of Charpy impact machining of a heat-affected zone at 40 °C is 100 kj/cm, and when the welding heat input is 150 kj/cm, obtained from three measurements of Charpy impact machining of a heat-affected zone at -40 °C Each value is 150 kj/cm.

In order to achieve the above object, the present invention provides the following technical solutions.

By optimizing the alloy composition design, it can be ensured that the alloy composition of the steel plate is within the scope of the present invention, and that the steel plate has sufficient strength, toughness and appropriate basic raw material microstructure. Meanwhile, Ti-containing oxides of appropriate composition and size can be formed on the steel plate by optimizing the type and order of addition of the deoxidizer and controlling the O content in the molten steel and the addition ratio of various deoxidizers. The structure of the high heat input weld heat affected zone can be optimized with a suitable Ti-containing oxide. Therefore, the low-temperature impact performance of EH 550 MPa grade quenched and tempered marine steel plate can be obtained, where EH 550 MPa grade means that the yield strength EH of the quenched and tempered marine steel plate is 550 MPa or more.

Specifically, C 0.06~0.12%, Si 0.02~0.06%, Mn 0.7~1.2%, Ti 0.006~0.012%, Al 0.002~0.010%, Cr 0.30~0.50%, Mo 0.3~0.4%, V 0.03~0.04% An EH 550 MPa grade quenched and tempered marine steel plate for high heat input welding having a weight composition of , N 0.0020 to 0.0030%, S 0.002 to 0.010%, P≤0.008% and residual Fe and unavoidable impurities, wherein the steel plate The average size of Ti-containing oxide particles in , 2 μm to 3 μm, and a density of 50 or more particles per mm ² .

In addition, the quenched and tempered marine steel plate contains at least one selected from Cu≤0.3% by weight, Ni≤1.9% by weight, or B≤0.0015% by weight.

Preferably, [Ti]/[Al] = 2-3 in the quenched and tempered marine steel plate.

The microstructure of the hot-rolled basic raw material of quenched and tempered marine steel plate is martensite tempered to ensure sufficient strength and roughness of the steel.

In the composition design of the steel plate of the present invention:

C is an important element in marine steel plates. Since the increase in the C content of the steel plate leads to an increase in strength and cost reduction of the offshore steel plate, the C content is set to 0.06% or more in the present invention. On the other hand, when the C content increases, the low-temperature toughness and weldability of the marine steel plate decrease. Therefore, the C content is 0.12% or less. In order to obtain the desired effect, the C content in the present invention is 0.06 to 0.12%, preferably 0.06 to 0.09%.

Si can be dissolved in ferrite and austenite to improve the hardness and strength of the steel plate, and Si element is an important deoxidizer in the smelting process. However, if the content of Si is too high, the plasticity and toughness of the steel plate are significantly deteriorated, and the formation of M-A islands (martensite-austenite islands) in the high-temperature input welding process is promoted, resulting in high heat The low-temperature toughness of the input weld heat-affected zone is greatly reduced. In the present invention, a low Si content is employed, and the Si content is 0.02 to 0.06%, preferably 0.02 to 0.04%.

Mn is an important deoxidizer in the smelting process, combining with S in the steel to form MnS, eliminating the harmful effects of S in the steel. Since MnS plays an important role in the formation of fine lath bainite in the heat-affected zone of high heat input welding, the lower limit of Mn is 0.7%. If the Mn content is too high, the susceptibility of the marine steel plate to tempering embrittlement increases, so the upper limit of the Mn content is 1.2%. Therefore, the content of Mn in the present invention is 0.7 to 1.2%, preferably 0.8 to 1.0%.

Ti can combine with N and O to form Ti-containing oxides and nitrides. When these Ti-containing oxides and nitrides have an appropriate size, they can promote the formation of fine las bainite in the high-heat input welding heat-affected zone, thereby improving the low-temperature toughness of the marine steel plate. Ti content is 0.006% or more. However, if the Ti content is too high, TiC is formed, which reduces the low-temperature toughness of the basic raw material and the heat-affected zone. The high Ti content of the steel promotes the formation of coarse TiN, which causes cracks in the steel. Therefore, the upper limit of the Ti content is 0.012%. The content of Ti in the present invention is 0.006 to 0.012%, preferably 0.006 to 0.009%.

Al is the most important deoxidizing element in the smelting process. If the Al content is too high, cluster alumina is easily formed, which lowers the purity of the molten steel. If the Al content is too low, the content of free O in the molten steel cannot be well controlled. In addition, since Al plays a refining role, the Al content in the steel is 0.002 to 0.010%, preferably 0.005 to 0.006%.

Cr can increase the hardenability of the steel plate, and is effective for secondary hardening of steel. In the quenching and tempering process, Cr can improve the hardenability after quenching and tempering and make the steel plate exhibit better mechanical properties. The lower limit of the Cr content is 0.30%. However, as the Cr content increases, the tendency of high temperature tempering brittleness increases, so the upper limit of the Cr content is 0.50%. In order to obtain the desired effect, the Cr content in the present invention is 0.30 to 0.50%, preferably 0.35 to 0.50%.

Mo can improve the hardenability of marine steel plates and prevent temper brittleness. In quenched and tempered marine steel plate, Mo can harden the steel plate, improve the tempering resistance or tempering stability of the steel plate, effectively remove the residual stress and improve the plasticity. Therefore, the lower limit of the Mo content is 0.3%. If the Mo content is too high, the carbon equivalent of the steel plate increases significantly, which is detrimental to the welding performance of the steel plate, so the upper limit of the Mo content is 0.4%.

V can refine the structure and grain of the steel plate. In the quenched and tempered steel plate, V can improve the strength and yield ratio of the steel plate, refine the grain, reduce overheating sensitivity, and increase tempering stability, so the lower limit of the V content is 0.03%. If the V content is too high, excess VC is formed, so the upper limit of the V content is 0.04%.

S combines with Mn to form MnS in the steel plate. MnS precipitates on the Ti-containing oxides in the steel plate, promoting the formation of fine las bainite. Therefore, the lower limit of the S content is 0.002%. If the S content is too high, S will segregate in the center of the slab, affecting the Z-direction properties of the thick plate. Therefore, the upper limit of the S content is 0.010%.

P exhibits a strong solid solution strengthening effect, which is advantageous for improving the strength and hardness of the steel plate. However, since P sharply reduces the low-temperature toughness of the steel plate, the upper limit of the P content is 0.008%.

When the N content is high, N is precipitated from the ferrite during quenching, which increases the strength and hardness, and decreases the plasticity and toughness of the steel plate. Therefore, the content of N is 0.0020 to 0.0030%.

Cu can improve the strength and yield ratio of the steel plate, and does not adversely affect weldability. However, the upper limit of the Cu content is 0.3% because hot embrittlement occurs when excessive Cu is present.

Ni can strengthen ferrite, refine pearlite, and increase strength without reducing toughness. However, since Ni is an expensive element, the upper limit of the Ni content is 1.9% in consideration of cost.

The main function of B is to increase the hardenability of the steel, thereby saving other expensive elements and reducing costs. Since B has an effect of promoting temper brittleness, the upper limit of the B content is set to 0.0015%. In order to obtain the expected effect, the content of B in the present invention is 0.0015% or less, preferably 0.0010% or less.

In the composition design of the present invention, the content of Si, Al and Ti should be controlled within the scope of the present invention, since these three elements are all deoxidizing elements, different combinations of these elements have a great effect on the kind of oxides formed in the steel. will go crazy When the Al content is low and the Si content is high, a large amount of Si-containing oxide is formed in the steel plate. These oxides easily form chains in the steel plate, greatly reducing the impact toughness. On the other hand, the high Si content promotes the formation of brittle phase MA islands (martensite-austenite islands) in the steel plate and reduces the local toughness. High Al content leads to the formation of large Al ₂ O ₃ oxides. These hard oxides cause cracks in the steel plate, increasing the amount of cracks in the impact process and reducing the impact roughness. If the content of Ti is too high, the formation of TiC is promoted. TiC reduces impact toughness by creating localized brittle regions. On the other hand, the Ti content cannot be too low. If the Ti content is low, the oxygen content of the steel plate cannot be reduced to an appropriate level. If the O content of the steel plate is too high, the oxides formed on the steel plate increase and the impact toughness decreases.

The Ti content is controlled on the premise of controlling the Si content. In order to form an Al ₂ O ₃ -Ti ₃ O ₅ -MnS-based oxide on a steel plate, the content of Ti and Al in the steel plate must satisfy [Ti]/[Al] = 2-3. When the weight percentage ratio [Ti]/[Al] is less than 2, a large amount of isolated Al ₂ O ₃ will be formed in the molten steel. The separated Al ₂ O ₃ serves as a precipitation core that promotes the precipitation of MnS and generates Al ₂ O ₃ -MnS oxide. However, although these oxides have MnS precipitation on the surface, a manganese-poor zone is not formed in the matrix around the oxide, so they cannot serve as a precipitation core that promotes the formation of fine las bainite. Las bainite in the heat-affected zone cannot be induced. When the weight percentage ratio [Ti]/[Al] is greater than 3.0, TiN of a large size is also formed when TiC is formed. TiN of such a large size is precipitated in the molten steel and cracks are easily formed. On the other hand, when the Ti/N ratio is not in the range of 2.0 to 3.0, the amount of Al ₂ O ₃ -Ti ₃ O ₅ -MnS-based oxide is not sufficient to form fine las bainite, so the low-temperature toughness of the heat-affected zone may be improved. can't

The manufacturing method of the EH 550 MPa grade quenching and tempering marine steel plate for high heat input welding of the present invention includes the following steps.

The manufacturing method of the EH 550 MPa grade quenched and tempered marine steel plate for high heat input welding of the present invention includes the following steps.

1) smelting, refining and casting steps, wherein

smelting and refining according to the above-mentioned composition and continuously casting into plate billets; here

In the deoxidation process of molten steel, deoxidizers are added, and the type and order of the deoxidizer is Si->Mn→Al→Ti;

Fe ₂ O ₃ powder and Al are added to the furnace to precisely control the original O content before adding Ti to the molten steel; The amount of Fe ₂ O ₃ can maintain the O content of the molten steel at 0.0040 to 0.01 wt% when the deoxidation process is continued by adding Ti; here

Ti-containing oxide particles in the steel plate have an average size of 2 μm to 3 μm and a density of 50 or more particles per mm ² ;

2) rolling step, where

the plate billet is heated to 1100-1200° C. and held for at least 250 minutes; The starting temperature of rough rolling is 1000-1100°C and the accumulated reduction rate is more than 30%; The starting temperature of finish rolling is 800-900°C, and the cumulative rolling reduction is more than 30%. Optionally, the holding time is 260-280 minutes. If the holding time is too short, the temperature of the steel ingot will be uneven, and the internal temperature of the steel ingot will not meet the requirements. Long holding times lead to energy wastage.

3) quenching and tempering heat treatment steps;

After being cooled to room temperature by air, the rolled steel plate is subjected to primary heating to 910 to 930° C. for a primary holding time of 40 to 50 minutes; After exiting the furnace and quenching to room temperature, the rolled steel plate is subjected to secondary heating to 650 to 680° C. for a secondary holding time of 115 to 130 minutes; The steel plate is then removed from the furnace and air cooled to room temperature.

In the manufacturing method of the present invention, the deoxidizer should be added in the order of Si→Mn→Al→Ti, and Ti should be added when the oxygen content of the molten steel is appropriate. In the deoxidation process, Si and Mn are first added to reduce the free oxygen content of the steel plate. The deoxidation products of Si and Mn are mainly oxides with low melting points. The oxide having a low melting point floats and dissolves in the slag to be removed, which can significantly reduce the free oxygen content in the molten steel without increasing the oxide amount of the molten steel. Al is then used for deoxidation. Al exhibits a strong deoxidation effect, so that the free oxygen content in the molten steel can be controlled to a low level. Finally, Ti is added to control the formation of oxides. After adding Ti, some free oxygen binds to Ti to form Ti oxide, some Ti and alumina bond together to form Al ₂ O ₃ -Ti ₃ O ₅ composite oxide, and some excess Ti to the steel plate It melts to form free titanium. The core of the oxide control process of the present invention is to control the oxygen content before adding Ti to an appropriate range by adding Al, so that the oxide generated under the oxygen content condition in the steel plate induces the formation of the structure of the heat affected zone after high heat input welding. It plays a role and induces the formation of a fine las bainite structure in the heat-affected zone, thereby improving the low-temperature toughness of the high-heat input welding heat-affected zone.

The Al content of the steel plate should be adjusted to 0.002~0.010%. If the Al content is high, cluster alumina is formed, which affects the purity of the molten steel. The low Al content cannot control the free O content of the molten steel well.

[Ti]/[Al] of the steel plate should be adjusted to an appropriate value. If the value of [Ti]/[Al] is too large, Ti oxide of more than 5 μm is formed in the molten steel and affects the low-temperature roughness. If the value of [Ti]/[Al] is too small, the size and amount of Al ₂ O ₃ in the molten steel significantly increases, so that the Ti-containing oxide Al ₂ O ₃ -Ti ₃ O ₅ -MnS cannot be sufficiently formed in the molten steel. . Therefore, [Ti]/[Al] should be adjusted to 2-3.

When the oxygen content in the molten steel is less than 0.0040%, Ti-containing oxides in the molten steel are not sufficiently formed, and as the temperature of the molten steel increases, Ti combines with N in the steel plate to form TiN precipitates of a large size. Oxides of this kind cannot play a role in inducing the formation of fine las bainite in the heat-affected zone of high heat input welding. When the content of O in the molten steel is greater than 0.01%, there are more oxides with a size larger than 5 μm and fewer oxides with a size of 2 to 3 μm. Oxides of large size can cause cracks when subjected to impact. If the oxide density of a certain size is low, the structure of the heat-affected zone cannot be completely changed or the low-temperature toughness cannot be improved. Therefore, before adding Ti, the O content should be adjusted to 0.0040~0.01%.

Inclusions in the heat-affected zone are studied and the composition, size and amount of inclusions are determined in the present invention. The composition of the inclusions was analyzed based on SEM-EDS images taken with a Zeiss EVO18 scanning electron microscope. The size and density of inclusions were detected and analyzed by an automatic inclusion analyzer. SEM and EDS can be used to collect data, and analysis software can be used to automatically detect and analyze inclusions in an automated inclusion analyzer to accurately identify the composition, size, quantity and other information of inclusions in the steel plate. When analyzing inclusions in a steel plate using the method described above, when the average size of Ti-containing inclusions in the steel plate is 2 μm to 3 μm and the density has a density of 50 or more particles per mm ² , the steel plate exhibits low-temperature roughness. was confirmed to be high. Meanwhile, the Ti-containing inclusion should be an Al ₂ O ₃ -Ti ₃ O ₅ -MnS composite oxide. This kind of Al ₂ O ₃ -Ti ₃ O ₅ core and oxides with MnS precipitates on the surface of Al ₂ O ₃ -Ti ₃ O ₅ core play an important role in the formation of fine las bainite in the heat-affected zone. It is generally believed that the formation of the Al ₂ O ₃ -Ti ₃ O ₅ -MnS composite oxide is due to the local saturation of Mn and S elements around the Al ₂ O ₃ -Ti ₃ O ₅ oxide. However, MnS is generally not precipitated in molten steel because of its high solubility in molten steel. However, since the solubility of MnS is reduced during the solidification and cooling process and the element S is easy to segregate, MnS is easily precipitated on the surface of the Al ₂ O ₃ -Ti ₃ O ₅ oxide formed in advance. Al ₂ O ₃ -Ti ₃ O ₅ -MnS composite oxide can serve as a nucleus for nucleation of fine las bainite. A manganese-deficient region is formed near the interface between the Al ₂ O ₃ -Ti ₃ O ₅ -MnS composite oxide and the steel plate matrix, promoting the formation of fine las bainite. As a result of ESD analysis of oxides in the heat-affected zone, it was confirmed that Al ₂ O ₃ -Ti ₃ O ₅ -MnS composite oxide with a size of 2 μm to 3 μm could induce the formation of fine las bainite in the heat-affected zone.

In the rolling and heat treatment process of the present invention, the heating temperature before rolling is 1100 to 1200° C., and the holding time is 250 minutes or more to ensure complete austenitization. The starting temperature of rough rolling is 1000~1100℃, and the cumulative rolling reduction is 30% or more. If the steel billet is rolled within this temperature range, recrystallization may occur to refine the austenite grains. If the reduction ratio is less than 30%, more coarse austenite grains remain, reducing the strength and toughness of the basic raw material.

The starting temperature of finish rolling is 800-900°C, and rolling is possible in a dual-phase region. Dislocations formed during rolling can act as nuclei for ferrite nucleation to improve the strength and toughness of the basic raw material. In the present invention, the cumulative reduction ratio exceeds 30%, because when the reduction ratio is less than 30%, a small dislocation is formed and sufficient acicular ferrite nucleation cannot be induced.

In the quenching and tempering heat treatment process, the rolled steel plate is air-cooled to room temperature, then first heated to 910-930°C for a holding time of 40-50 minutes, and then the rolled steel plate is taken out of the furnace and water is quenched to room temperature. This quenching process allows the structure of the marine steel plate of the present invention to be transformed into martensite with minimal cooling rate. The rolled steel plate is then heated secondary to 650-680°C for a secondary holding time of 115-130 minutes. After that, the steel plate is taken out of the furnace and air-cooled to room temperature. The steel structure after quenching is mainly martensite, which tends to transform into metastable and stable ferrite and cementite at room temperature. Therefore, the steel plate must be tempered to remove the internal stress to prevent deformation and cracking. Tempering at 650~680℃ and holding for 115~130 minutes, supersaturated carbon is precipitated in the martensite of the quenched marine steel plate, and the main structure of the basic raw material is transformed into tempered martensite, so that the quenched and tempered marine steel plate has a high to have strength and toughness.

According to the requirements of the classification society, the composition of EH 550 is C≤0.18, Mn 0.9~1.6, Si≤0.5, S≤0.035, P≤0.035, Al≥0.015, Nb=0.02~0.05, V=0.05~0.1, Ti ≤0.02, Cu≤0.35, Cr≤0.2, Ni≤0.4, Mo≤0.08.

In the smelting process, the order of addition of the deoxidizer is very important and should be added in the order of Si→Mn→Al→Ti, and the O content in the molten steel is 0.0040~0.01wt% before adding Ti. Under these deoxidation process conditions, a micron-scale Al ₂ O ₃ -Ti ₃ O ₅ -MnS composite oxide having an average size of 2 μm to 3 μm and a density of 50 or more particles per mm ² may be formed. Changing the deoxidation sequence changes the oxide type of the steel plate, forming a brittle phase in the heat-affected zone and affecting the impact toughness.

Advantages of the present invention are as follows.

In the present invention, the composition design of the high-strength marine steel plate is optimized. In the refining process, by controlling the free oxygen content of the steel plate to an appropriate range, optimizing the type and addition sequence of the deoxidizer, _and adjusting the ratio of _{the deoxidizer} Al/Ti, _the size, composition and Positive control can be realized. Therefore, Al ₂ O ₃ -Ti ₃ O ₅ -MnS oxide can improve the formation volume of fine las bainite in the heat-affected zone during solidification and phase transformation and the low-temperature roughness of the heat-affected zone after high-heat input welding of marine steel plates.

In the present invention, strong deoxidizers such as Ca, Mg, Re are avoided, and the smelting process is simplified to avoid disadvantages of using strong deoxidizers, for example, the disadvantages of not being easy to store and use of such deoxidizers.

The invention is further described below with reference to examples.

In an embodiment of the present invention, the alloy composition is adjusted during the refining process, and the alloy for deoxidation is added in the order of Si→Mn→Al to deoxidize. While securing the alloy composition, Fe ₂ O ₃ powder is added to adjust the oxygen content of the steel plate, and then ferro-titanium is added, and the weight% of Ti in ferro-titanium is 69.8%.

Chemical compositions of Examples and Comparative Examples are shown in Table 1. In the comparative example, the Al content is 0.045% and 0.051%, respectively; In Comparative Example, the Ti/Al ratio and/or the density of the Ti-containing oxide having a size of 2 to 3 μm may not satisfy the conditions of the present invention.

Table 2 shows the manufacturing method of the steel plate of Examples and Comparative Examples of the present invention. Table 3 shows the strength, low-temperature toughness, and low-temperature toughness of the heat-affected zone of the basic raw materials of Examples and Comparative Examples. The yield strength, tensile strength, and area reduction rate of the basic raw material are the average values of the two detection values, and the Charpy impact processing of the basic raw material at -40°C and the Charpy impact processing of the heat-affected zone at -40°C is the average value of the three detected values. .

Here, tensile tests such as yield strength, tensile strength and area reduction of the basic raw material were performed in accordance with GB/T 228.1-2010 "Metal materials - Tensile test - Part 1: Test method at room temperature" and SCL233200kN tensile tester was adopted. . The test conditions were as follows: temperature: 25°C; Test rate: 2 mm/min before yield: Humidity: 56%, test rate: 20 mm/min after yield. The impact test is performed according to GB/T 229-2007 "Metallic materials-Charpy pendulum impact test method", an instrument impact tester (SCL112) is used, and the impact energy is 60 J.

From the data in the table, it can be seen that the yield strength and tensile strength of the basic raw materials of Examples are slightly higher than those of Comparative Examples. After thermal simulation tests of 50 kj/cm, 100 kj/cm and 150 kj/cm, the Charpy impact processing at -40° C. of the heat-affected zone of the example is all greater than 80 J. The Charpy impact machining at -40°C of the comparative example is relatively low after thermal simulation tests for three heat inputs. Therefore, the low-temperature toughness of the heat-affected zone of the embodiment can be greatly improved by an oxide control process and an appropriate composition design to satisfy the requirements of the marine steel plate for high heat input welding.

The present invention adopts an optimized composition design, provides an appropriate Ti/Al ratio, optimizes the type and sequence of deoxidation alloy in the refining process, and adds Fe ₂ O ₃ powder to the size, composition, and amount of Ti-containing oxide And by controlling the density, it is possible to induce a fine lath bainite structure in the heat-affected zone. Finally, EH550 high-strength marine steel plate for high-temperature input welding can be obtained.

Claims (9)

C 0.06~0.12%, Si 0.02~0.06%, Mn 0.7~1.2%, Ti 0.006~0.012%, Al 0.002~0.010%, Cr 0.30~0.50%, Mo 0.3~0.4%, V 0.03~0.04%, N 0.0020 An EH 550 MPa grade quenched and tempered marine steel plate for high heat input welding having a weight composition of ~0.0030%, S 0.002~0.010%, P≤0.008% and residual Fe and unavoidable impurities, the marine steel plate comprising:
Here, the average size of Ti-containing oxide particles in the steel plate is 2 μm to 3 μm and the density is EH 550 MPa grade for high heat input welding, characterized in that it has a density of 50 or more particles per mm ² Quenched and tempered marine steel plate.
The EH 550 MPa grade quenched and tempered marine steel plate for high heat input welding according to claim 1, further comprising at least one selected from Cu≤0.3% by weight, Ni≤1.9% by weight, or B≤0.0015% by weight.
3. EH 550 MPa grade quenched and tempered marine steel plate for high heat input welding according to claim 1 or 2, characterized in that [Ti]/[Al] = 2-3 in steel.
3. An EH 550 MPa grade quenched and tempered marine steel plate for high heat input welding according to claim 1 or 2 having a microstructure of tempered martensite.
3. The Charpy impact work of the base material according to claim 1 or 2, wherein the yield strength EH is at least 550 MPa, the tensile strength is at least 670 MPa, and at -40°C ( Charpy impact processing (single value) of the heat affected zone at -40°C when the single value) is 180J or more and the welding heat input is 50 kj/cm, 100 kj/cm and 150 kj/cm EH 550 MPa grade quenched and tempered marine steel plate for high heat input welding, characterized in that it is 80 J or higher.
The EH 550 MPa grade quenched and tempered marine steel plate for high heat input welding according to claim 1, wherein the Ti-containing oxide is Al ₂ O ₃ -Ti ₃ O ₅ -MnS composite oxide.
A method for producing an EH 550 MPa grade quenched and tempered marine steel plate for high heat input welding according to any one of claims 1 to 6, comprising the steps of:
1) smelting, refining and casting steps, wherein
smelting and refining according to the composition of any one of claims 1 to 3 and continuously casting into plate billets; here
In the deoxidation process of molten steel, deoxidizers are added, and the type and order of the deoxidizer is Si->Mn→Al→Ti;
Fe ₂ O ₃ powder and Al are added to the furnace to precisely control the original O content before adding Ti to the molten steel; The amount of Fe ₂ O ₃ can maintain the O content of the molten steel at 0.0040 to 0.01 wt% when the deoxidation process is continued by adding Ti; here
Ti-containing oxide particles in the steel plate have an average size of 2 μm to 3 μm and a density of 50 or more particles per mm ² ;
2) rolling step, where
the plate billet is heated to 1100-1200° C. and held for at least 250 minutes; The starting temperature of rough rolling is 1000~1100℃, and the accumulated reduction rate is more than 30%; The starting temperature of the finish rolling is 800-900° C., and the cumulative reduction ratio is 30% or more;
3) quenching and tempering heat treatment steps;
After being cooled to room temperature by air, the rolled steel is subjected to primary heating to 910 to 930° C. for a primary holding time of 40 to 50 minutes; After exiting the furnace and quenching to room temperature, the rolled steel plate is subjected to secondary heating to 650 to 680° C. for a secondary holding time of 115 to 130 minutes; The steel plate is then removed from the furnace and air cooled to room temperature.
8. The method of claim 7, wherein the quenched and tempered marine steel plate has a microstructure of tempered martensite.
9. The Charpy impact work of the base material according to claim 7 or 8, wherein the yield strength EH is at least 550 MPa, the tensile strength is at least 670 MPa, and at -40°C ( Charpy impact processing (single value) of the heat affected zone at -40°C when the single value) is 180J or more and the welding heat input is 50 kj/cm, 100 kj/cm and 150 kj/cm Method of manufacturing EH 550 MPa grade quenched and tempered marine steel plate for high heat input welding, characterized in that 80 J or more.