CN115074618A - FH 550-grade ocean engineering steel plate with low compression ratio and excellent low-temperature toughness and thickness of 150mm and preparation method thereof - Google Patents
FH 550-grade ocean engineering steel plate with low compression ratio and excellent low-temperature toughness and thickness of 150mm and preparation method thereof Download PDFInfo
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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
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/072—Treatment with gases
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- 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
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
-
- 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
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- 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
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
-
- 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
- C22C38/04—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
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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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
- C22C38/18—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
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
Abstract
The invention relates to a FH550 grade ocean engineering steel plate with low compression ratio and excellent low-temperature toughness and the preparation method thereof, which takes Fe as a basic element and also comprises the following chemical components in percentage by mass: c: 0.10 to 0.16%, Si: 0.20 to 0.40%, Mn: 0.9-1.30%, P: less than or equal to 0.007%, S: less than or equal to 0.002%, Cr: 0.30-0.60%, Mo: 0.4-0.6%, Ni: 1.0-2.0%, Cu: 0.2-0.4%, Al: 0.05-0.10%, V: 0.03-0.06%, Nb: less than or equal to 0.005 percent, N: less than or equal to 0.007%, H: less than or equal to 0.00015 percent, B: 0.0008 to 0.002%, Ca: 0.001-0.005% and Ca/S is more than or equal to 1. The method is characterized in that a continuous casting blank is used as a blank, the thickness reaches 150mm, the yield strength is more than or equal to 550MPa, and the tensile strength is as follows: 670-830 MPa, the elongation is not less than 16%, the Charpy impact energy at the position 1/4 of the steel plate is more than 170J at-60 ℃ and at-80 ℃, the Charpy impact energy at the position 1/2 of the steel plate is more than 130J and 90J at-60 ℃ and at-80 ℃, and the mechanical properties of the cross section of the steel plate are uniform.
Description
Technical Field
The invention belongs to the field of preparation of super-thick steel plates, and particularly relates to a 150mm thick FH550 grade ocean engineering steel plate with low compression ratio and excellent low-temperature toughness and a manufacturing method thereof, in particular to a super-thick steel plate with excellent low-temperature toughness at the positions of 1/4 and 1/2 of the thickness of the steel plate and a manufacturing method thereof.
Background
As the development of marine resources extends from shallow sea to deep sea, the service environment of marine equipment develops from conventional temperature to high-cold environment. Particularly, large or ultra-large ocean engineering equipment is required for ocean resource development in cold deep sea areas. Steel plates used to manufacture key parts of large ocean engineering equipment are generally required to have super-thick specifications, high strength and excellent low-temperature toughness. At present, steel ingots or electroslag ingots are generally adopted as blanks in steel mills at home and abroad for manufacturing ultra-thick steel plates for ocean engineering, so that the steel plates have long manufacturing process, low yield and high manufacturing cost, and the manufacturing and upgrading of large ocean engineering equipment are also severely restricted.
The invention ZL201310697653.5 and ZL201310697652.0 discloses a high-toughness extra-thick rack steel plate used at low temperature and a manufacturing method thereof, solves the technical problem of manufacturing the extra-thick maritime work steel plate by using a continuous casting billet, simplifies the process, but the steel grades disclosed by the two patents are 690MPa grade, the tensile strength of the steel grades exceeds the upper limit value of the tensile strength set for FH550 by the classification society regulations, and the steel grades belong to two different steel grades.
CN108517463A discloses a high-ductility FH 550-grade ship plate steel and a preparation method thereof, wherein the thickness range of the steel plate is only 10-30 mm; CN 109112429A discloses a FH550 grade thick plate with excellent low temperature toughness and a manufacturing method thereof, wherein the thickness range of the steel plate is 50-80 mm; the thickness range of the steel plate manufactured by the above patent is far from meeting the requirement of large ocean engineering equipment.
Disclosure of Invention
The invention aims to solve the technical problem of providing a FH550 grade ultra-thick ocean engineering steel plate with low compression ratio and excellent low-temperature toughness and a manufacturing method thereof by using a continuous casting billet as a blank in the prior art. The thickness of the FH550 steel plate manufactured according to the method is 150mm, the yield strength is more than or equal to 550MPa, and the tensile strength is as follows: 670-830 MPa, the elongation is not less than 16%, the Charpy impact energy at the position 1/4 of the steel plate is more than 170J at-60 ℃ and at-80 ℃, the Charpy impact energy at the position 1/2 of the steel plate is more than 130J and 90J at-60 ℃ and at-80 ℃, and the mechanical properties of the cross section of the steel plate are uniform.
The technical scheme adopted by the invention for solving the problems is as follows: a150 mm thick FH550 grade extra thick ocean engineering steel plate with low compression ratio and excellent low temperature toughness takes Fe as a basic element and also comprises the following chemical components in percentage by mass: c: 0.10 to 0.16%, Si: 0.20 to 0.40%, Mn: 0.9-1.30%, P: less than or equal to 0.007%, S: less than or equal to 0.002%, Cr: 0.30-0.60%, Mo: 0.4-0.6%, Ni: 1.0-2.0%, Cu: 0.2 to 0.4%, Al: 0.05-0.10%, V: 0.03-0.06%, Nb: less than or equal to 0.005 percent, N: less than or equal to 0.007%, H: less than or equal to 0.00015 percent, B: 0.0008 to 0.002%, Ca: 0.001-0.005% of Ca/S, wherein the Ca/S ratio is more than or equal to 1; the carbon equivalent CEV (C + Mn/6+ (Cr + Mo + V)/5+ (Cu + Ni)/15) is less than or equal to 0.65 percent.
The thickness of the steel plate is 150mm, and the microstructure at the thickness of 1/4 and 1/2 is a mixed structure of tempered lower bainite, tempered sorbite and tempered granular bainite.
The detection proves that the yield strength is more than or equal to 550MPa, and the tensile strength is as follows: 670-830 MPa, the elongation rate is more than or equal to 16%, the Charpy impact energy at the position 1/4 of the steel plate is more than 170J at the temperature of minus 60 ℃ and minus 80 ℃, the Charpy impact energy at the position 1/2 of the steel plate is more than 130J and 90J at the temperature of minus 60 ℃ and minus 80 ℃, and the mechanical properties of the steel plate along the thickness section of the steel plate are uniform.
The steel plate of the invention has the following chemical composition design principles:
c: is an element necessary for ensuring the strength of steel, and increasing the carbon content in steel will increase its non-equilibrium structure transformation ability, thereby increasing its strength. However, too high C content is detrimental to the ductility and toughness of the steel and also reduces the weldability and cutting processability of the material. The content of the invention is controlled to be 0.10-0.16%.
Si: is a deoxidizing element in steel, improves the strength of steel in a solid solution strengthening mode, and is beneficial to the corrosion resistance of the steel. Si also reduces the diffusion rate of C in ferrite, so that carbide precipitated during tempering is not easy to aggregate, and the tempering stability of the steel is improved. When the content of Si is less than 0.10%, the deoxidation effect is poor, and when the content of Si is higher, the toughness and welding performance of the steel plate are reduced. The invention controls the content of Si to be 0.20-0.40%.
Mn: is an element for improving the hardenability of steel, and plays a role in solid solution strengthening to make up for the strength loss caused by the reduction of the content of C in the steel. However, too high Mn content increases the carbon equivalent thereof to deteriorate the weldability of the material and to lower the cutting property of the material. The Mn content of the invention is controlled to be 0.9-1.30%.
Ni: is an element for improving the hardenability of steel, improving the low-temperature toughness of the steel and obviously improving the corrosion resistance, particularly the marine atmospheric corrosion resistance. However, when the Ni content is too high, iron scales with strong viscosity are easily generated on the surface of the steel plate and are difficult to remove, and the surface quality of the steel plate is affected. In addition, Ni is also a precious metal, and too high a content increases the cost. The content of the invention is controlled to be 1.0-2.0%.
Cr: the Cr is an element which can improve the hardenability and the tempering stability and is beneficial to improving the strength of the steel, and under the condition of low C content, a proper amount of Cr is added to ensure that the steel plate can reach the required strength. However, since Cr greatly contributes to carbon equivalent, if it is added excessively, toughness, weldability, and flame cuttability of the material are lowered. The content of the invention is controlled to be 0.3-0.6%.
Mo: obviously improves the hardenability and the strength of the steel. The addition of a certain amount of Mo to the low alloy steel will improve its strength without deteriorating its low temperature impact properties. However, Mo is a precious metal, and too high content of Mo increases the cost and also reduces the welding performance and the flame cutting performance of the material. The content of Mo in the invention is controlled to be 0.4-0.6%.
Cu: can improve the hardenability of steel, reduce the hydrogen-induced crack sensitivity of steel and simultaneously is a basic element for improving the corrosion resistance of steel. It promotes anodic passivation of the steel, thereby reducing the corrosion rate of the steel. The enrichment of Cu in the rust layer greatly improves the protective properties of the rust layer. In order to achieve the effect of Cu enrichment in the rust layer, Cu is required to be more than or equal to 0.20%. However, too high a Cu content is disadvantageous in terms of weldability of the steel sheet, and also tends to cause copper embrittlement, thereby deteriorating the surface quality of the steel sheet. In order to meet the requirement that the steel for ocean engineering has certain corrosion resistance, the Cu content is controlled to be 0.2-0.4%.
V: is an element for refining grains and also an element for dispersing and precipitating V (C, N) to obviously improve the strength of the steel. The content of the invention is controlled to be 0.03-0.06%.
Al: mainly plays roles of nitrogen fixation and deoxidation, and is also beneficial to forming a passive film on the surface of steel so as to improve the corrosion resistance. Al is effectively refined by joining with N to form AlN, but if the content is too high, Al-containing inclusions (e.g., alumina, etc.) increase to impair the toughness of the steel. Therefore, the content of the organic silicon compound is controlled to be 0.05-0.10%.
B: is the most obvious element for improving the hardenability of the steel, and is also beneficial to improving the corrosion resistance of the steel. The addition of trace B can inhibit the nucleation of ferrite on austenite grain boundary to obviously improve the hardenability of steel, and has no obvious influence on other properties. The content of the invention is controlled to be 0.0008-0.0020%.
S, P: is a harmful element in steel, and is easy to form defects of segregation, inclusion and the like. Although P significantly improves the atmospheric corrosion resistance of the steel, it significantly reduces both the toughness of the steel and the toughness of the weld heat affected zone, and therefore, its content should be minimized. The invention controls P less than or equal to 0.007% and S less than or equal to 0.002%.
Ca: has obvious effect on the deterioration of the inclusions in the steel, spheroidizes and uniformly distributes the inclusions so as to reduce the adverse effect on the toughness, and simultaneously improves the fluidity of the molten steel so as to improve the problem of nozzle blockage. The content of Ca is controlled to be 0.001-0.005%, and Ca/S is required to be more than or equal to 1.
Carbon equivalent CEV (═ C + Mn/6+ (Cr + Mo + V)/5+ (Cu + Ni)/15): is an important index for evaluating the welding performance of steel. A low CEV is advantageous for the weldability of the steel but is disadvantageous for the formation of a high-strength non-equilibrium structure upon quenching. The high CEV favors the formation of an unbalanced structure, but deteriorates the welding and cutting properties of the steel. Therefore, the CEV is controlled to be less than or equal to 0.65 percent by the method.
The invention also aims to provide a FH550 grade ocean engineering steel plate with 150mm thickness and excellent low-temperature toughness and low compression ratio and a manufacturing method thereof, wherein the manufacturing method comprises the following steps:
smelting and continuous casting: smelting raw materials are sequentially subjected to KR molten iron pretreatment, converter smelting, LF refining, RH refining and continuous casting of a straight arc-shaped continuous casting machine to smelt high-purity molten steel; and then a high-quality continuous casting slab with the thickness of 450mm is obtained through a dynamic soft reduction technology, a secondary cooling water dynamic control technology and a low superheat degree control technology by further continuous casting, and the center segregation of the continuous casting slab is as follows: class C0.5 or better, center porosity: equal to or better than 0.5 grade, no shrinkage cavity, no central crack, no corner crack and no triangular area crack, and provides high-quality continuous casting blank for low-compression ratio rolling in the subsequent process.
Slab slow cooling: after the casting blank is off line, the casting blank is required to be stacked into a pit or covered, and high-temperature slow cooling hydrogen diffusion treatment is carried out to ensure that hydrogen in the core of the casting blank can be fully diffused, so that the H content in the casting blank is further reduced, the hydrogen induced cracking of a steel plate is further avoided, and the performance of the steel plate 1/2 at the thickness position is ensured.
Heating and rolling a plate blank: and heating the continuous casting plate blank to 1160-1280 ℃, and preserving heat for 2-4 hours to fully dissolve alloy elements in the steel, play the strengthening and toughening role of the alloy elements and ensure the uniformity of the components and the performance of a final product.
After the heat preservation is finished, high-pressure water descaling treatment is carried out, and then two-stage rolling is carried out: the rolling initial rolling temperature of the first stage is 1050-1200 ℃, the total reduction rate is more than or equal to 50%, and more rolling deformation occurs in the high-temperature stage by increasing the total reduction rate of the rough rolling stage, namely: the deformation is carried out in the state of lower deformation resistance, thus being beneficial to the deformation and permeation to the core of the continuous casting billet and effectively welding the looseness of the core of the continuous casting billet. Meanwhile, the steel plate is rolled under strong pressure, the maximum single-pass reduction rate is more than or equal to 18 percent, so that the core defects of the continuous casting billet are fully closed, and the performance of a FH550 steel plate with large thickness at the position of 1/2 thickness is ensured. And the rolling start temperature of the second stage is 850-940 ℃, the total compression ratio is more than or equal to 25%, strong descaling water is adopted for cooling treatment before each rolling, the steel plate is rolled to the thickness of a finished product, and the steel plate is air-cooled and straightened after the rolling is finished.
On the premise of 450mm large-thickness high-quality continuous casting billets, the effect of large-compression-ratio rolling by adopting the die-cast steel ingots is obtained by innovatively designing reasonable distribution of total reduction rate in two-stage rolling and matching single-pass strong reduction, even under the condition of low compression ratio with the compression ratio of only 3. Straightening the rolled steel plate, then performing air cooling on the steel plate to 550-650 ℃, then performing covering stack slow cooling for more than or equal to 72 hours to fully reduce or remove the H content in the rolled steel plate so as to ensure the performance of the thickness of the finished steel plate 1/2, and discharging the steel plate from a furnace for air cooling.
Heat treatment of the steel plate: and (3) carrying out quenching and tempering treatment after the steel plate is air-cooled to room temperature to obtain a finished FH550 steel plate, wherein the quenching and heating of the quenching and tempering process are carried out by using a continuous furnace, and the quenching and heating temperature is as follows: 880-930 ℃, in-furnace time: 1.8-2.0 min/mm, quenching the steel plate by using a quenching machine until the surface temperature of the steel plate is less than or equal to 100 ℃, and then cooling the steel plate to room temperature by air; the tempering treatment was also carried out using a continuous furnace, tempering temperature: and (2) at 620-680 ℃, in-furnace time: 2.5-4.0 min/mm, and air cooling to room temperature after discharging.
Compared with the prior art, the invention has the advantages that:
1. the extra-thick FH550 steel plate manufactured by the invention has the thickness of 150mm, and can meet the design requirements of large-scale or extra-large-scale marine equipment manufacturing.
2. The extra-thick FH550 steel plate manufactured by the invention directly uses a continuous casting blank without any other processing (for example, a plurality of plate blanks are processed into a composite blank by composite processing) as a rolling blank, thereby omitting the cogging process of using a die-cast steel ingot as the blank in the rolling process, namely, omitting the cogging heating, the cogging rolling and the intermediate blank cutting and cleaning processes, and simplifying the production process. Compared with the FH550 steel plate made of the die-cast steel ingot, the yield of the steel plate is obviously improved by using the continuous casting billet, the production process is simplified, and the production time is shortened, so that the manufacturing cost of the large-thickness rack steel plate is reduced, the defects of the prior art are overcome, and the steel plate has obvious advantages in industrial production.
3. The ultra-thick FH550 steel plate manufactured by the invention has tensile strength within 670-830 MPa and excellent low-temperature toughness: the Charpy impact energy at the steel plate 1/4 and the Charpy impact energy at the steel plate 1/2 and the Charpy impact energy at the steel plate 1/4 and the steel plate 3580 are respectively greater than 130J and 90J. This strength and low temperature toughness match is very difficult for FH550 steel grades.
Drawings
FIG. 1 is a microstructure of a steel sheet manufactured in example at a thickness of 1/4;
FIG. 2 is a microstructure of a steel sheet manufactured in example at a thickness of 1/2;
FIG. 3 shows the variation of Brinell hardness of the steel sheet in a cross section along the thickness of the steel sheet produced in the example.
Detailed Description
The present invention will be further described with reference to examples.
The FH550 grade extra thick ocean engineering steel plate with low compression ratio and excellent low temperature toughness related to the embodiment has the thickness of 150mm, and comprises the following components in percentage by mass: c: 0.12%, Si: 0.25%, Mn: 1.10%, P: 0.005%, S: 0.0009%, Cr: 0.50%, Mo: 0.48%, Ni: 1.37%, Cu: 0.22%, Al: 0.070%, V: 0.038%, N: 0.0026%, B: 0.0015%, the balance being iron and inevitable impurity elements, and 0.61% of carbon when Ceq (C + Mn/6+ (Cr + Mo + V)/5+ (Cu + Ni)/15).
The production process of the extra-thick FH550 steel plate comprises the following steps:
preparing smelting raw materials according to the chemical composition, and sequentially performing KR molten iron pretreatment, converter smelting, LF refining, RH refining, continuous casting of a straight arc continuous casting machine (continuous casting billet thickness: 450mm), covering and slow cooling of the continuous casting billet, cleaning of the continuous casting billet, heating, high-pressure water descaling, two-stage controlled rolling, straightening, air cooling and tempering.
Further, the specific process of the heating, controlled rolling and cooling stages comprises the following steps: carrying out center segregation on the produced continuous casting billet: class C0.5, loose center: 0.5 grade, no shrinkage cavity, no central crack, no corner crack and no triangular region crack, heating to 1230 ℃, preserving heat for 3 hours, taking out of the furnace, performing high-pressure water descaling treatment, and performing two-stage full longitudinal rolling. In the first stage, the rolling start temperature is 1180 ℃, the thickness of the intermediate billet is 220mm, the total rolling reduction rate is 51.1 percent, the maximum single-pass reduction rate is 18.5 percent, and strong descaling water is adopted to cool the billet between every two rolling passes; the rolling start temperature of the second stage is 900 ℃, the final plate thickness is 150mm, the total reduction rate is 31.8 percent, and strong descaling water is also adopted to cool the plate blank among each rolling pass. Straightening after rolling, and then slowly cooling in air (heating the steel plate to 600 ℃, keeping the temperature for 72 hours, cooling the steel plate to 200 ℃ along with the furnace, taking the steel plate out of the furnace, and air-cooling the steel plate to room temperature). The steel plate after slow cooling enters a continuous furnace for quenching and heating, and the heating temperature is as follows: 900 ℃, in-furnace time: 1.8min/mm, water quenching by using a quenching machine until the surface temperature of the steel plate is 90 ℃ below zero, and then air cooling to room temperature. The quenched steel sheet is tempered in a continuous furnace. Tempering and heating temperature: 670 ℃, in-furnace time: 3.5min/mm, and air cooling to room temperature after discharging.
The finished steel plate manufactured by the manufacturing process has high strength, good plasticity, high low-temperature toughness and high Z-direction performance, has excellent comprehensive performance, and the mechanical properties of the finished steel plate are shown in Table 1.
TABLE 1 mechanical Properties of the steel sheets produced in the examples
As can be seen from the table 1, the Z-direction performance (reduction of area) of the FH550 steel plate manufactured by the invention exceeds the highest requirement of ocean engineering on the Z-direction reduction of area of the steel plate being more than or equal to 35%, and the lamellar tearing resistance of the FH550 steel plate with large thickness is ensured. The Z-direction performance also reflects the compactness of the steel plate along the thickness direction, so that the extra-thick FH550 steel plate directly manufactured by the continuous casting blank has high compactness, and the strict performance requirement of the core part of the FH550 steel plate is ensured.
The uniformity of the mechanical properties of the steel sheet was further evaluated by testing the distribution of the brinell hardness HB of the steel sheet along the thickness section, and the results are shown in fig. 3. It can be seen that the brinell hardness of the steel sheet is almost constant throughout the thickness section within the allowable range of experimental error, that is, the 150mm thick steel sheet manufactured accordingly has high overall mechanical property uniformity in the thickness section.
Although preferred embodiments of the present invention have been described in detail hereinabove, it should be clearly understood that modifications and variations of the present invention are possible to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (8)
1. The utility model provides a low compression ratio is good at low temperature toughness FH550 level ocean engineering steel sheet that 150mm is thick, its characterized in that: the steel plate takes Fe as a basic element and also comprises the following chemical components in percentage by mass: c: 0.10 to 0.16%, Si: 0.20 to 0.40%, Mn: 0.9-1.30%, P: less than or equal to 0.007%, S: less than or equal to 0.002%, Cr: 0.30-0.60%, Mo: 0.4-0.6%, Ni: 1.0-2.0%, Cu: 0.2-0.4%, Al: 0.05-0.10%, V: 0.03-0.06%, Nb: less than or equal to 0.005 percent, N: less than or equal to 0.007%, H: less than or equal to 0.00015 percent, B: 0.0008 to 0.002%, Ca: 0.001-0.005% of Ca/S, wherein the Ca/S ratio is more than or equal to 1; the carbon equivalent CEV (C + Mn/6+ (Cr + Mo + V)/5+ (Cu + Ni)/15) is less than or equal to 0.65 percent.
2. The FH550 grade ocean engineering steel plate with low compression ratio and excellent low temperature toughness as claimed in claim 1, wherein the FH550 grade ocean engineering steel plate comprises: the maximum thickness of the steel plate can reach 150mm, and the microstructure at the thickness of 1/4 and 1/2 is a mixed structure of tempered lower bainite, tempered sorbite and tempered granular bainite.
3. The FH550 grade ocean engineering steel plate with low compression ratio and excellent low temperature toughness of claim 1, wherein: the yield strength of the steel plate is more than or equal to 550MPa, and the tensile strength is as follows: 670-830 MPa, the elongation is not less than 16%, the Charpy impact energy at the position 1/4 of the steel plate is more than 170J at-60 ℃ and at-80 ℃, the Charpy impact energy at the position 1/2 of the steel plate is more than 130J and 90J at-60 ℃ and at-80 ℃, and the mechanical properties of the cross section of the steel plate are uniform.
4. A method for manufacturing FH550 grade steel plate having a thickness of 150mm and excellent low-temperature toughness at a low compression ratio according to claim 1, comprising the steps of: the method comprises the following steps:
1) smelting and continuous casting: smelting raw materials are sequentially subjected to KR molten iron pretreatment, converter smelting, LF refining, RH refining and continuous casting of a straight arc-shaped continuous casting machine to smelt high-purity molten steel; then, a high-quality continuous casting plate blank with the thickness of 450mm is obtained through further continuous casting by a dynamic soft reduction technology, a secondary cold water dynamic control technology and a low superheat degree control technology;
2) slab slow cooling: after the casting blank is off line, the casting blank is stacked in a pit or a cover, and high-temperature slow cooling hydrogen diffusion treatment is carried out to ensure that hydrogen in the core of the continuous casting blank can be fully diffused, so that the H content in the continuous casting blank is further reduced, the hydrogen induced cracking of a steel plate is further avoided, and the performance of the steel plate 1/2 at the thickness part is ensured;
3) heating the plate blank: heating the continuous casting plate blank to 1160-1280 ℃, and preserving heat for 2-4 hours to fully dissolve alloy elements in the steel, play the strengthening and toughening role of the alloy elements and ensure the uniformity of the components and the performance of a final product;
4) rolling a plate blank: after the heat preservation is finished, high-pressure water descaling treatment is carried out, and then the steel plate is air-cooled and straightened after the two-stage rolling is finished;
5) heat treatment of the steel plate: and (4) performing air cooling on the steel plate to room temperature, and then performing quenching and tempering treatment to obtain a finished FH550 steel plate.
5. The method for manufacturing FH550 grade steel plate with low compression ratio and excellent low temperature toughness as claimed in claim 4, wherein the FH550 grade steel plate has a thickness of 150mm, and is characterized in that: in the step 4), the rolling start temperature of the first stage is 1050-1200 ℃, the total reduction rate is more than or equal to 50%, the rolling start temperature of the second stage is 850-940 ℃, the total reduction rate is more than or equal to 25%, and strong descaling water is adopted for cooling before each rolling, so that the finished product is rolled to the thickness.
6. The method for manufacturing FH550 grade steel plate with low compression ratio and excellent low temperature toughness as claimed in claim 5, wherein the FH550 grade steel plate has a thickness of 150mm, and is characterized in that: straightening the rolled steel plate, then performing air cooling on the steel plate to 550-650 ℃, then performing covering stack slow cooling on the steel plate for more than or equal to 72 hours to fully reduce or remove the H content in the rolled steel plate so as to ensure the performance of the steel plate 1/2 at the thickness part, and discharging the steel plate from a furnace for air cooling.
7. The method for manufacturing FH550 grade steel plate with low compression ratio and excellent low temperature toughness as claimed in claim 5, wherein the FH550 grade steel plate has a thickness of 150mm, and is characterized in that: the steel plate is rolled under strong pressure in the first stage of rolling, the maximum single-pass reduction rate is more than or equal to 18 percent, so that the core defects of the continuous casting billet are fully closed, and the performance of the FH550 steel plate with large thickness at the position of 1/2 thickness is ensured.
8. The method for manufacturing FH550 grade steel plate with low compression ratio and excellent low temperature toughness as claimed in claim 4, wherein the FH550 grade steel plate has a thickness of 150mm, and is characterized in that: quenching and heating in the hardening and tempering process are carried out by using a continuous furnace, and the quenching and heating temperature is as follows: 880-930 ℃, in-furnace time: 1.8-2.0 min/mm, quenching the steel plate by using a quenching machine until the surface temperature of the steel plate is less than or equal to 100 ℃, and then cooling the steel plate to room temperature in air; the tempering treatment was also carried out using a continuous furnace, tempering temperature: and (2) at 620-680 ℃, in-furnace time: 2.5-4.0 min/mm, and air cooling to room temperature after discharging.
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