CN116200683A - 785 MPa-grade ultra-low carbon bainite steel and preparation method thereof - Google Patents

785 MPa-grade ultra-low carbon bainite steel and preparation method thereof Download PDF

Info

Publication number
CN116200683A
CN116200683A CN202211640904.1A CN202211640904A CN116200683A CN 116200683 A CN116200683 A CN 116200683A CN 202211640904 A CN202211640904 A CN 202211640904A CN 116200683 A CN116200683 A CN 116200683A
Authority
CN
China
Prior art keywords
steel
temperature
rolling
pass
low carbon
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
CN202211640904.1A
Other languages
Chinese (zh)
Inventor
王天琪
柴希阳
柴锋
罗小兵
陈雪慧
师仲然
潘涛
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Zhonglian Advanced Steel Technology Co ltd
Central Iron and Steel Research Institute
Original Assignee
Zhonglian Advanced Steel Technology Co ltd
Central Iron and Steel Research Institute
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Zhonglian Advanced Steel Technology Co ltd, Central Iron and Steel Research Institute filed Critical Zhonglian Advanced Steel Technology Co ltd
Priority to CN202211640904.1A priority Critical patent/CN116200683A/en
Publication of CN116200683A publication Critical patent/CN116200683A/en
Pending legal-status Critical Current

Links

Images

Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • 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
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

The invention relates to the technical field of metal materials, in particular to 785 MPa-level ultra-low carbon bainite steel and a preparation method thereof. 785MPa grade ultra-low carbon bainite steel comprises the following chemical components in weight: c:0.01% -0.03%, si:0.5 to 0.8 percent of Mn:1.0% -2.0%, mo:1.5 to 2.0 percent of Nb:0.03 to 0.07 percent of Ni:4.0 to 6.0 percent of Cr:0.3 to 0.7 percent of Ti:0.01% -0.03%, al:0.01% -0.03%, and the balance of iron and unavoidable impurities. The yield strength of the steel prepared by the method is more than or equal to 785Mpa, the impact energy of a welded joint at minus 40 ℃ is more than or equal to 50J, the CTOD of the welded joint at minus 20 ℃ is more than or equal to 0.17mm, and the yield ratio is 0.77-0.80. Solves the problems of poor matching between the toughness and the weldability and high yield ratio of the existing high-strength hull steel.

Description

785 MPa-grade ultra-low carbon bainite steel and preparation method thereof
Technical Field
The invention relates to the technical field of metal materials, in particular to 785 MPa-level ultra-low carbon bainite steel and a preparation method thereof.
Background
In recent years, steel for hull structures has been developed in the direction of high strength, easy welding, and the like. In general, the strength of a steel sheet is improved by increasing the C content and adding a large amount of an alloy element such as Ni, cr, mo, V. However, the welding difficulty of the steel plate is high due to the high content of C and the high carbon content, and in the actual welding manufacturing process, the welding is performed by adopting the processes of preheating, post-heating and the like, so that the welding construction difficulty is greatly increased, and the welded steel plate is easy to crack due to residual stress, so that potential safety hazard is caused.
In addition, as the strength grade is higher, the steel for the high-strength ship body structure usually adopts a tempering heat treatment mode, the structure is tempered martensite or tempered martensite plus bainite, the yield ratio of the steel plate after the tempering heat treatment is higher (more than or equal to 0.93), and the high yield ratio can reduce the service safety margin of the steel and increase the service risk.
Ultra-low carbon bainitic steel is a large class of high-strength, high-toughness and multipurpose steel grade which is newly developed internationally over 20 years. By greatly reducing the carbon content, the influence of carbon elements on welding performance is eliminated. Moreover, the bainite structure has lower yield ratio due to reasonable distribution of soft and hard phase structures. Therefore, developing an ultra-low carbon bainitic steel with high strength, low yield ratio and easy welding is a direction of searching the steel field for the ship body.
Disclosure of Invention
In view of the analysis, the embodiment of the invention aims to provide 785 MPa-grade ultra-low carbon bainite steel and a preparation method thereof, which are used for solving the problems of poor matching between the toughness and weldability and high yield ratio of the existing high-strength hull structure steel.
The aim of the invention is mainly realized by the following technical scheme:
in one aspect, the embodiment of the invention provides 785 MPa-grade ultra-low carbon bainite steel, which comprises the following chemical components in parts by weight: c:0.01% -0.03%, si:0.5 to 0.8 percent of Mn:1.0% -2.0%, mo:1.5 to 2.0 percent of Nb:0.03 to 0.07 percent of Ni:4.0 to 6.0 percent of Cr:0.3 to 0.7 percent of Ti:0.01% -0.03%, al:0.01% -0.03%, and the balance of iron and unavoidable impurities.
Further, the microstructure of the steel is granular bainite, and the content of the granular bainite is 100%.
On the other hand, the embodiment of the invention provides a preparation method of 785 MPa-grade ultra-low carbon bainitic steel, which is used for preparing the 785 MPa-grade ultra-low carbon bainitic steel and comprises the following steps of:
step 1: heating and forging the steel ingot to obtain a steel billet;
step 2: putting the billet obtained in the step 1 into a heating furnace for heating;
step 3: rough rolling and finish rolling are carried out on the heated steel billet;
step 4: and cooling the finish-rolled steel billet to obtain a finished plate.
Further, in the step 1, the forging heating temperature of the steel ingot is 1190 ℃ to 1210 ℃, the forging opening temperature is 1150 ℃ to 1160 ℃, and the final forging temperature is more than 850 ℃.
Further, in the step 2, the heating temperature is 1190-1210 ℃ and the heating time is 1.8-2.2 h.
Further, in the step 3, the rough rolling is 3-pass rolling, the deformation of the first pass is 15% -17%, the deformation of the second pass is 23% -25%, and the deformation of the third pass is 20% -22%.
Further, in the step 3, the initial rolling temperature of the rough rolling is 1150-1180 ℃ and the final rolling temperature is 960-980 ℃.
Further, in the step 3, the finish rolling is 3-pass rolling, the deformation of the first pass is 19-21%, the deformation of the second pass is 24-26%, and the deformation of the third pass is 33-34%.
Further, in the step 3, the finish rolling start temperature is 950-980 ℃, and the finish rolling temperature is 750-850 ℃.
Further, in the step 4, the cooling rate is 1 to 5 ℃/s.
Compared with the prior art, the invention has at least one of the following beneficial effects:
1. according to the 785 MPa-level ultra-low carbon bainite steel and the preparation method, the low-carbon design is adopted, the strength of the steel is not dependent on the content of carbon and the total amount of alloy elements, but is reinforced by dislocation in a bainite structure, and fine crystals are reinforced; cementite in the base body of the Belleville ferrite is substantially eliminated by controlling the low carbon content, and the toughness, weldability and yield ratio of the steel are further improved.
2. According to the 785 MPa-grade ultra-low carbon bainitic steel and the preparation method, the prepared 785 MPa-grade ultra-low carbon bainitic steel is good in stability, the yield strength is more than or equal to 785MPa (such as 805-831 MPa), the tensile strength is more than or equal to 1030MPa (such as 1031-1072 MPa), and the strength and toughness of the ultra-low carbon bainitic steel obtained under the process window are the same level; according to the preparation method of 785 MPa-grade ultra-low carbon bainitic steel, provided by the invention, the preparation process is simple, the heat treatment after rolling is not needed, and the structure obtained after controlled rolling and controlled cooling is uniform and stable in performance.
3. The ultra-low carbon bainite structure is prepared by a controlled rolling and cooling technology, and 785MPa grade ultra-low carbon bainite steel with low yield ratio is prepared by means of soft and hard coordination in the bainite structure, and the yield ratio is 0.77-0.80.
4. According to the invention, the cementite in the Belleville ferrite matrix is basically eliminated by reducing the carbon content, the elements are controlled to cooperate, the toughness and weldability of the steel are further improved, the impact energy of the welding line center at minus 40 ℃ is more than or equal to 50J, and the CTOD of the welding joint at minus 20 ℃ is more than or equal to 0.17mm.
In the invention, the technical schemes can be mutually combined to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and drawings.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, like reference numerals being used to refer to like parts throughout the several views.
FIG. 1 is a structure of 785MPa grade ultra-low carbon bainite steel in example 1;
FIG. 2 is a structure of 785MPa grade ultra-low carbon bainite steel in example 4;
FIG. 3 shows the structure of 785MPa grade ultra-low carbon bainite steel in example 6.
Detailed Description
Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form a part hereof, and together with the description serve to explain the principles of the invention, and are not intended to limit the scope of the invention.
The invention provides 785 MPa-grade ultra-low carbon bainite steel, which comprises the following chemical components in parts by weight: c:0.01% -0.03%, si:0.5 to 0.8 percent of Mn:1.0% -2.0%, mo:1.5 to 2.0 percent of Nb:0.03 to 0.07 percent of Ni:4.0 to 6.0 percent of Cr:0.3 to 0.7 percent of Ti:0.01% -0.03%, al:0.01% -0.03%, and the balance of iron and unavoidable impurities.
At present, the steel for the high-strength ship body structure in China is usually prepared by adopting a tempering heat treatment mode, the structure is tempered martensite or tempered martensite plus bainite, the yield ratio of the steel plate after the tempering heat treatment is higher, and the matching between the toughness and the weldability is poor; according to the 785 MPa-grade ultra-low carbon bainite steel, cementite in a Belleville ferrite matrix is basically eliminated by reducing the carbon content, the elements are synergistic, the toughness, weldability and yield ratio of the steel are improved by controlling other elements, the yield strength of the prepared steel is more than or equal to 785MPa (such as 805-831 MPa), the tensile strength is more than or equal to 1030MPa (such as 1031-1072 MPa), the elongation after breaking is more than or equal to 16.0% (such as 16.5-18.0%), the reduction of area is more than or equal to 74% (such as 74-80%), the impact power at-40 ℃ is more than or equal to 140J (such as 140J-202J), the impact power at-40 ℃ of a welded joint is more than or equal to 50J, and the CTOD at-20 ℃ of the welded joint is more than or equal to 0.17mm. The problems that the existing high-strength hull structural steel is poor in toughness and weldability matching and high in yield ratio can be solved.
The reason why the casting blank composition of 785MPa grade ultra-low carbon bainitic steel and the method for producing the same in the present invention is limited will be described, and the percentage by mass in the composition will be expressed only in% below.
Carbon (C): the carbon element ensures that a full bainitic structure is formed, C is less than 0.05%, the reduction of carbon content can obviously improve the welding performance of the steel, and researches show that when the carbon content is 0.01% -0.03%, the welding performance is ensured, and meanwhile, the steel with better strength and toughness matching is obtained.
Silicon (Si): silicon is also a solid solution strengthening element as a deoxidizing element, and can improve the strength of steel. When the silicon content is too high, the low-temperature toughness of the steel is lowered, and the weldability is deteriorated. Therefore, the Si content is controlled to be 0.50 to 0.80%.
Manganese (Mn): manganese element is a basic element for bainite formation, so that obvious river bay appears on a supercooled austenite transformation curve, and high-temperature transformation is obviously delayed, so that an upper curve and a lower curve of steel are separated. Mn easily forms MnS impurities with S in steel, and the performance of the steel is damaged. Therefore, the addition amount of Mn is 1.0% to 2.0%.
Molybdenum (Mo): the Mo element can reduce the transformation temperature of bainite, promote the transformation of bainite and shorten the transformation time of bainite. The addition amount of Mo is 1.5% -2.0%.
Niobium (Nb): the Nb element can inhibit the deformation recrystallization behavior of high-temperature austenite, improve the recrystallization temperature, enlarge the non-recrystallization zone, enlarge the deformation accumulation during rolling of the non-recrystallization zone, introduce high-density dislocation and promote tissue refinement. The addition amount of Nb is 0.03-0.07%.
Nickel (Ni): the Ni element mainly reduces the ductile-brittle transition temperature of the steel and improves the strength and toughness. The addition amount of Ni is 4.0% -6.0%.
Chromium (Cr): the Cr element can obviously reduce the transformation temperature of the bainite, influence the C curve of the transformation of the bainite, and improve the strength of the bainitic steel. The addition amount of Cr is 0.3-0.7%.
Titanium (Ti): the titanium precipitate can inhibit the austenite grain growth process during the casting blank heating process and the welding heat cycle process, thereby improving the toughness of the steel plate and the welding heat affected zone. When the Ti content is too low, the action effect is weakened; when the content is more than 0.04%, large-particle TiN is easily formed and the effect is lost. Therefore, the Ti content is controlled to be 0.01 to 0.03%.
Aluminum (Als): acid-soluble aluminum is an excellent deoxidizer for steel, and is an effective element for refining grains. When the Als content is too low, it is difficult to control the oxygen content in the steel; when the content is more than 0.08%, heat cracks of a casting blank are easily generated, and the toughness of steel is reduced. Therefore, the Als content is controlled to be 0.01-0.03%.
The invention also provides a preparation method of the 785 MPa-grade ultra-low carbon bainite steel, which is used for preparing the 785 MPa-grade ultra-low carbon bainite steel and comprises the following steps:
step 1: heating and forging the steel ingot to obtain a steel billet;
step 2: putting the billet obtained in the step 1 into a heating furnace for heating;
step 3: rough rolling and finish rolling are carried out on the heated steel billet;
step 4: and cooling the finish-rolled steel billet to obtain a finished plate.
Specifically, in the step 1, the forging heating temperature of the steel ingot is 1190-1210 ℃, the forging temperature is 1150-1160 ℃, and the final forging temperature is more than 850 ℃ to obtain the steel billet. The open forging temperature is too high, decarburization is easy, and steel ingots are burnt out; the forging temperature is too low, so that cracks are easy to appear in forging, and the forging is labor-intensive. The final forging temperature is higher than 850 ℃, the final forging temperature is too low, recrystallization cannot be carried out, cold deformation strengthening phenomenon cannot be eliminated, deformation resistance is large, plasticity is reduced, and even cracks are generated on a forging piece, and equipment and tools are damaged; the final forging temperature is too high, and the grains grow up after the blank is deformed to form a coarse structure, so that the mechanical property of the forging is reduced.
Specifically, in the step 2, the heating temperature is 1190-1210 ℃, the heating time is 1.8-2.2 h, and the rolling is carried out after the heating. The steel is heated to generate plastic deformation, and the initial rolling temperature is determined according to 80% of the solidus temperature in the alloy phase.
Specifically, in the step 3, the rough rolling is divided into 3 passes, wherein the deformation of the first pass is 15-17%, the deformation of the second pass is 23-25%, and the deformation of the third pass is 20-22%; the initial rolling temperature of rough rolling is 1150-1180 ℃, and the final rolling temperature of rough rolling is 960-980 ℃; the finish rolling is divided into 3 passes, the deformation of the first pass is 19-21%, the deformation of the second pass is 24-26%, the deformation of the third pass is 33-34%, the finish rolling start temperature is 950-980 ℃, and the finish rolling temperature is 750-850 ℃.
In step 3, rough rolling is performed as recrystallization zone rolling: the steel billet is heated to austenitizing temperature, plastic deformation is carried out, dynamic or static recrystallization is carried out in the deformation process of each pass or between two passes, the recrystallization process is finished, and austenite grains are thinned through repeated rolling and recrystallization. Finish rolling to a non-recrystallized zone: plastic deformation occurs below the austenite recrystallization temperature, dynamic or static recrystallization does not occur after the austenite is deformed, deformed austenite grains are elongated, a large number of deformation bands exist in the grains, nucleation points are more in the phase transformation process, and ferrite grains are further refined.
Illustratively, the rough rolling is divided into 3 passes, wherein the deformation of the first pass is 16.6%, the deformation of the second pass is 24%, and the deformation of the third pass is 21%; the initial rolling temperature of rough rolling is 1150 ℃, and the final rolling temperature of rough rolling is 980 ℃; the finish rolling is divided into 3 passes, wherein the deformation of the first pass is 20%, the deformation of the second pass is 25%, and the deformation of the third pass is 33.3%. The finish rolling temperature is 950 ℃ and the finish rolling temperature is 850 ℃. After 3-pass rough rolling and 3-pass finish rolling, billet grains are well refined.
Specifically, in the step 4, the steel billet after finish rolling is cooled to room temperature, and the cooling speed is 1-5 ℃/s, so that the plate is obtained. Different structure forms of the cooling speed have different, for example, the cooling speed is too fast, the bainite structure of the lath is obtained, the strength of the steel is greatly improved, and the cooling speed is limited to 1-5 ℃/s for obtaining granular bainite steel with similar structure forms and same strength grade.
It should be noted that the invention adopts a low-carbon design, the strength of the steel is not dependent on the content of carbon and the total amount of alloy elements, but is enhanced by dislocation in a bainite structure, and fine crystal is enhanced; cementite in the base body of the belleville ferrite is basically eliminated by controlling the low carbon content; throughregulatingandcontrollingcomponents,theMn-Mo-Nbcontentisincreased,thehardenabilityofthesteelisimproved,andauniformgranularbainiticstructureisobtainedbymatchingwithcontrolledrollingandcooling,whereinthegranularbainiticstructureconsistsofamatrixferritestructure(softphase)andM-Aislands(hardphase)distributedinthematrix. The yield strength is mainly determined by the strength of the soft phase, the tensile strength is mainly determined by the hard phase, the soft and hard phases in the granular bainite are well matched, the strength of the prepared steel plate is ensured, and meanwhile, the yield ratio is reduced.
The preparation method provided by the invention has strong practicability, and can obtain the ultra-low carbon bainite steel with consistent structure types, stable performance and good toughness matching under wider production conditions, wherein the bainite form of the obtained ultra-low carbon bainite steel is granular bainite, and the content of the bainite is 100%.
The yield strength of the ultra-low bainite steel prepared by the method is more than or equal to 785Mpa (such as 805-831 Mpa), the tensile strength is more than or equal to 1030Mpa (such as 1031-1072 Mpa), the elongation after fracture is more than or equal to 16.0 percent (such as 16.5-18.0 percent), the reduction of area is more than or equal to 74 percent (such as 74-80 percent), the impact energy at minus 40 ℃ is more than or equal to 140J (such as 140J-202J), the impact energy at minus 40 ℃ of a welding joint is more than or equal to 50J, the CTOD at minus 20 ℃ of the welding joint is more than or equal to 0.17mm, and the yield ratio is 0.77-0.80.
The advantages of the invention in terms of precise control of the elemental chemistry, content and manufacturing process parameters will be demonstrated in the following specific examples and comparative examples.
Example 1
A785 MPa grade ultra-low carbon bainite steel comprises the following chemical components in weight: c:0.02%, si:0.5%, mn:1.5%, mo:1.8%, nb:0.05%, ni:4.2%, cr:0.5%, ti:0.01%, al:0.02% of iron and the balance of unavoidable impurities. The preparation method comprises the following steps:
step 1: heating and forging the steel ingot with the composition to obtain a steel billet;
the forging heating temperature is 1200 ℃, the forging opening temperature is 1150 ℃, and the final forging temperature is 950 ℃, so that the billet is obtained.
Step 2: putting the billet obtained in the step 1 into a heating furnace for heating;
the heating temperature was 1190℃and the heating time was 2h.
Step 3: rough rolling and finish rolling are carried out on the heated steel billet;
rolling the billet, wherein in the rolling process, the rough rolling is performed for 3 passes, the deformation of the first pass is 16.6%, the deformation of the second pass is 24%, and the deformation of the third pass is 21%; the initial rolling temperature of rough rolling is 1150 ℃, and the final rolling temperature of rough rolling is 980 ℃; 3 passes of finish rolling, wherein the deformation of the first pass is 20%, the deformation of the second pass is 25%, and the deformation of the third pass is 33.3%; the initial rolling temperature of the finish rolling is 950 ℃, and the final rolling temperature of the finish rolling is 850 ℃;
step 4: cooling the finish-rolled steel billet to obtain a steel plate;
the cooling rate of the cooling after finish rolling was 3.0℃per second.
785MPa grade ultra-low carbon bainite steel prepared in the embodiment, wherein the bainite is granular bainite, and the mechanical properties are as follows: the tensile strength is 1042MPa; yield strength is 813MPa; yield ratio 0.78; elongation after break is 17.0%; the area reduction rate is 76%; an impact energy of 189J at-40 ℃; the impact energy of the welding line center is 58J at the temperature of minus 40 ℃, and the CTOD0.18mm at the temperature of minus 20 ℃ of the welding joint. The microstructure diagram is shown in fig. 1.
Example 2
A785 MPa grade ultra-low carbon bainite steel comprises the following chemical components in weight: c:0.01%, si:0.8%, mn:1.8%, mo:1.5%, nb:0.06%, ni:5.8%, cr:0.6%, ti:0.01%, al:0.03%, the balance being iron and unavoidable impurities. The preparation method comprises the following steps:
step 1: heating and forging the steel ingot to obtain a steel billet;
forging heating temperature 1190 ℃, forging opening temperature 1150 ℃ and final forging temperature 860 ℃ to obtain a billet.
Step 2: putting the billet obtained in the step 1 into a heating furnace for heating;
the heating temperature is 1200 ℃, and the heating time is 1.8h.
Step 3: rough rolling and finish rolling are carried out on the heated steel billet;
rolling the billet, wherein in the rolling process, the rough rolling is performed for 3 passes, the deformation of the first pass is 16%, the deformation of the second pass is 23%, and the deformation of the third pass is 22%; the initial rolling temperature of rough rolling is 1180 ℃, and the final rolling temperature of rough rolling is 960 ℃; 3 passes of finish rolling, wherein the deformation of the first pass is 21%, the deformation of the second pass is 26%, and the deformation of the third pass is 33%; the initial rolling temperature of the finish rolling is 950 ℃, and the final rolling temperature of the finish rolling is 750 ℃;
step 4: cooling the finish-rolled steel billet to obtain a steel plate;
the cooling rate of the steel plate after rolling is 5 ℃/s.
785MPa grade ultra-low carbon bainite steel prepared in the embodiment, wherein the bainite is granular bainite, and the mechanical properties are as follows: tensile strength is 1031MPa; yield strength is 825MPa; yield ratio 0.78; elongation after break is 17.5%; the area reduction rate is 78%; impact energy at-40 ℃ is 168J; the impact power of the welding line center is 61J at minus 40 ℃, and the CTOD0.20mm at minus 20 ℃ of the welding joint.
Example 3
A785 MPa grade ultra-low carbon bainite steel comprises the following chemical components in weight: c:0.02%, si:0.8%, mn:1.0%, mo:2.0%, nb:0.03%, ni:6.0%, cr:0.3%, ti:0.02%, al:0.01% of iron and the balance of unavoidable impurities. The preparation method comprises the following steps:
step 1: heating and forging the steel ingot to obtain a steel billet;
the forging heating temperature is 1210 ℃, the forging starting temperature is 1160 ℃, and the final forging temperature is 880 ℃, so that the billet is obtained.
Step 2: putting the billet obtained in the step 1 into a heating furnace for heating;
the heating temperature of the heating furnace is 1200 ℃, and the heating time is 1.9h.
Step 3: rough rolling and finish rolling are carried out on the heated steel billet;
rolling the billet, wherein in the rolling process, the rough rolling is performed for 3 passes, the deformation of the first pass is 15%, the deformation of the second pass is 25%, and the deformation of the third pass is 21.3%; the initial rolling temperature of rough rolling is 1170 ℃, and the final rolling temperature of rough rolling is 980 ℃; 3 passes of finish rolling, wherein the deformation of the first pass is 19%, the deformation of the second pass is 24, and the deformation of the third pass is 34%; the initial rolling temperature of the finish rolling is 950 ℃, and the final rolling temperature of the finish rolling is 850 ℃;
step 4: cooling the finish-rolled steel billet to obtain a steel plate;
the cooling rate of the cooling after rolling is 1 ℃/s.
785MPa grade ultra-low carbon bainite steel prepared in the embodiment, wherein the bainite is granular bainite, and the mechanical properties are as follows: tensile strength is 1065MPa; yield strength is 831MPa; yield ratio 0.78; elongation after break is 17.0%; the area reduction rate is 78%; the impact energy at the temperature of minus 40 ℃ is 173J; the impact power of the welding line center is 52J at minus 40 ℃, and the CTOD0.20mm at minus 20 ℃ of the welding joint.
Example 4
A785 MPa grade ultra-low carbon bainite steel comprises the following chemical components in weight: c:0.03%, si:0.7%, mn:1.2%, mo:1.6%, nb:0.07%, ni:4.0%, cr:0.5%, ti:0.03%, al:0.02% of iron and the balance of unavoidable impurities. The preparation method comprises the following steps:
step 1: heating and forging the steel ingot to obtain a steel billet;
the forging heating temperature is 1200 ℃, the forging opening temperature is 1160 ℃, and the final forging temperature is 950 ℃, so that a rough billet is obtained.
Step 2: putting the billet obtained in the step 1 into a heating furnace for heating;
the heating temperature of the heating furnace is 1210 ℃, and the heating time is 2 hours.
Step 3: rough rolling and finish rolling are carried out on the heated steel billet;
rolling the billet, wherein in the rolling process, the rough rolling is performed for 3 passes, the deformation of the first pass is 17%, the deformation of the second pass is 24.3%, and the deformation of the third pass is 20.6%; the initial rolling temperature of rough rolling is 1160 ℃, and the final rolling temperature of rough rolling is 980 ℃; 3 passes of finish rolling, wherein the deformation of the first pass is 19%, the deformation of the second pass is 25%, and the deformation of the third pass is 33%; the initial rolling temperature of the finish rolling is 950 ℃, and the final rolling temperature of the finish rolling is 800 ℃;
step 4: cooling the finish-rolled steel billet to obtain a steel plate;
the cooling rate of the cooling after rolling is 1 ℃/s.
785MPa grade ultra-low carbon bainite steel prepared in the embodiment, wherein the bainite is granular bainite, and the mechanical properties are as follows: tensile strength is 1072MPa; yield strength is 805MPa; yield ratio 0.78; elongation after break is 16.5%; the area reduction rate is 74%; the impact energy at the temperature of minus 40 ℃ is 140J; the impact power of the welding line center is 50J at the temperature of minus 40 ℃, and the CTOD0.17mm at the temperature of minus 20 ℃ of the welding joint. The microstructure diagram is shown in fig. 2.
Example 5
A785 MPa grade ultra-low carbon bainite steel comprises the following chemical components in weight: : c:0.02%, si:0.7%, mn:1.4%, mo:1.6%, nb:0.05%, ni:3.2%, cr:0.5%, ti:0.02%, al:0.02% of iron and the balance of unavoidable impurities. The preparation method comprises the following steps:
step 1: heating and forging the steel ingot to obtain a steel billet;
the forging heating temperature is 1200 ℃, the forging opening temperature is 1150 ℃, and the final forging temperature is 900 ℃, so that a rough billet is obtained.
Step 2: putting the billet obtained in the step 1 into a heating furnace for heating;
the heating temperature was 1190℃and the heating time was 2.1h.
Step 3: rough rolling and finish rolling are carried out on the heated steel billet;
rolling the billet, wherein in the rolling process, the rough rolling is performed for 3 passes, the deformation of the first pass is 15.3%, the deformation of the second pass is 24%, and the deformation of the third pass is 22%; the initial rolling temperature of rough rolling is 1150 ℃, and the final rolling temperature of rough rolling is 980 ℃; 3 passes of finish rolling, wherein the deformation of the first pass is 20%, the deformation of the second pass is 24.6%, and the deformation of the third pass is 34%; the initial rolling temperature of the finish rolling is 960 ℃, and the final rolling temperature of the finish rolling is 750 ℃;
step 4: cooling the finish-rolled steel billet to obtain a steel plate;
the cooling rate of the steel billet after finish rolling is 2 ℃/s.
785MPa grade ultra-low carbon bainite steel prepared in the embodiment, wherein the bainite is granular bainite, and the mechanical properties are as follows: tensile strength is 1066MPa; the yield strength is 821MPa; yield ratio 0.77; elongation after break is 16.5%; the area reduction rate is 78%; an impact energy of 195J at-40 ℃; the impact energy at the center of the welding line is 57J at the temperature of minus 40 ℃, and the CTOD0.18mm at the temperature of minus 20 ℃ of the welding joint.
Example 6
A785 MPa grade ultra-low carbon bainite steel comprises the following chemical components in weight: c:0.02%, si:0.5%, mn:2.0%, mo:1.7%, nb:0.05%, ni:3.8%, cr:0.4%, ti:0.02%, al:0.02% of iron and the balance of unavoidable impurities. The preparation method comprises the following steps:
step 1: heating and forging the steel ingot to obtain a steel billet;
forging heating temperature 1190 ℃, forging starting temperature 1160 ℃ and final forging temperature 850 ℃ to obtain a rough billet.
Step 2: putting the billet obtained in the step 1 into a heating furnace for heating;
the heating temperature is 1200 ℃, and the heating time is 2.2h.
Step 3: rough rolling and finish rolling are carried out on the heated steel billet;
rolling the billet, wherein in the rolling process, the rough rolling is performed for 3 passes, the deformation of the first pass is 17%, the deformation of the second pass is 23%, and the deformation of the third pass is 20%; the initial rolling temperature of rough rolling is 1150 ℃, and the final rolling temperature of rough rolling is 960 ℃; 3 passes of finish rolling, wherein the deformation of the first pass is 19%, the deformation of the second pass is 25%, and the deformation of the third pass is 33.6%; the initial rolling temperature of the finish rolling is 950 ℃, and the final rolling temperature of the finish rolling is 800 ℃;
step 4: cooling the finish-rolled steel billet to obtain a steel plate;
the cooling rate of the cooling after rolling was 4 ℃/s.
785MPa grade ultra-low carbon bainite steel prepared in the embodiment, wherein the bainite is granular bainite, and the mechanical properties are as follows: the tensile strength is 1047MPa; yield strength is 817MPa; yield ratio 0.80; elongation after break is 18.0%; the area reduction rate is 80%; impact energy at-40 ℃ is 202J; the impact power of the welding line center is 53J at the temperature of minus 40 ℃, and the CTOD0.22mm at the temperature of minus 20 ℃ of the welding joint. The microstructure diagram is shown in fig. 3.
Table 1 shows the chemical compositions and the contents of the steel of the examples; table 2 shows the process parameters of the preparation process of the example steel; table 3 shows the mechanical properties of the example steels; table 4 shows the welding properties of the example steels.
Table 1 chemical composition (wt.%)
Numbering device C Si Mn Mo Nb Ni Cr Ti Al
Example 1 0.02 0.5 1.5 1.8 0.05 4.2 0.5 0.01 0.02
Example 2 0.01 0.8 1.8 1.5 0.06 5.8 0.6 0.01 0.03
Example 3 0.02 0.8 1.0 2.0 0.03 6.0 0.3 0.02 0.01
Example 4 0.03 0.7 1.2 1.6 0.07 4.0 0.5 0.03 0.02
Example 5 0.02 0.7 1.4 1.6 0.05 3.2 0.5 0.02 0.02
Example 6 0.02 0.5 2.0 1.7 0.05 3.8 0.4 0.02 0.02
Table 2 example and comparative example preparation process
Figure BDA0004008909460000141
TABLE 3 mechanical Properties of example and comparative steels
Figure BDA0004008909460000152
Table 4 weldability of example and comparative steels
Figure BDA0004008909460000151
The present invention is not limited to the above-mentioned embodiments, and any changes or substitutions that can be easily understood by those skilled in the art within the technical scope of the present invention are intended to be included in the scope of the present invention.

Claims (10)

1. A 785MPa grade ultra low carbon bainitic steel characterized by comprising the chemical components by weight: c:0.01% -0.03%, si:0.5 to 0.8 percent of Mn:1.0% -2.0%, mo:1.5 to 2.0 percent of Nb:0.03 to 0.07 percent of Ni:4.0 to 6.0 percent of Cr:0.3 to 0.7 percent of Ti:0.01% -0.03%, al:0.01% -0.03%, and the balance of iron and unavoidable impurities.
2. The 785MPa ultra-low carbon bainitic steel according to claim 1, wherein the microstructure of the steel is granular bainite with a granular bainite content of 100%.
3. A method for preparing 785 MPa-grade ultra-low carbon bainitic steel, which is used for preparing 785 MPa-grade ultra-low carbon bainitic steel according to claim 1 or 2, and is characterized by comprising the following steps:
step 1: heating and forging the steel ingot to obtain a steel billet;
step 2: putting the billet obtained in the step 1 into a heating furnace for heating;
step 3: rough rolling and finish rolling are carried out on the heated steel billet;
step 4: and cooling the finish-rolled steel billet to obtain a finished plate.
4. A method according to claim 3, wherein in step 1, the forging heating temperature of the ingot is 1190 ℃ to 1210 ℃, the forging temperature is 1150 ℃ to 1160 ℃, and the final forging temperature is > 850 ℃.
5. The method according to claim 3, wherein in the step 2, the heating temperature is 1190 ℃ to 1210 ℃ and the heating time is 1.8h to 2.2h.
6. The method according to claim 3, wherein in the step 3, the rough rolling is 3 passes, the deformation amount of the first pass is 15% -17%, the deformation amount of the second pass is 23% -25%, and the deformation amount of the third pass is 20% -22%.
7. The method according to claim 6, wherein in the step 3, the initial rolling temperature of the rough rolling is 1150-1180 ℃ and the final rolling temperature is 960-980 ℃.
8. The method according to claim 3, wherein in the step 3, the finish rolling is performed in 3 passes, the deformation amount of the first pass is 19-21%, the deformation amount of the second pass is 24-26%, and the deformation amount of the third pass is 33-34%.
9. The method according to claim 8, wherein in the step 3, the finish rolling start temperature is 950 to 980 ℃, and the finish rolling finish temperature is 750 to 850 ℃.
10. The method according to claim 3, wherein in the step 4, the cooling rate is 1 to 5 ℃/s.
CN202211640904.1A 2022-12-20 2022-12-20 785 MPa-grade ultra-low carbon bainite steel and preparation method thereof Pending CN116200683A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN202211640904.1A CN116200683A (en) 2022-12-20 2022-12-20 785 MPa-grade ultra-low carbon bainite steel and preparation method thereof

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202211640904.1A CN116200683A (en) 2022-12-20 2022-12-20 785 MPa-grade ultra-low carbon bainite steel and preparation method thereof

Publications (1)

Publication Number Publication Date
CN116200683A true CN116200683A (en) 2023-06-02

Family

ID=86516314

Family Applications (1)

Application Number Title Priority Date Filing Date
CN202211640904.1A Pending CN116200683A (en) 2022-12-20 2022-12-20 785 MPa-grade ultra-low carbon bainite steel and preparation method thereof

Country Status (1)

Country Link
CN (1) CN116200683A (en)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH08276286A (en) * 1995-04-04 1996-10-22 Nippon Steel Corp Laser welding method for steel plate superior in toughness of welded joint
CN101213316A (en) * 2005-08-15 2008-07-02 株式会社神户制钢所 Thick steel plate excelling in toughness of large heat input welded joint
CN102260825A (en) * 2010-05-27 2011-11-30 株式会社神户制钢所 High-strength Steel Board And Manufacturing Method Thereof
CN110846594A (en) * 2019-11-28 2020-02-28 钢铁研究总院 Copper-containing ultra-low carbon bainite steel and preparation method thereof

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH08276286A (en) * 1995-04-04 1996-10-22 Nippon Steel Corp Laser welding method for steel plate superior in toughness of welded joint
CN101213316A (en) * 2005-08-15 2008-07-02 株式会社神户制钢所 Thick steel plate excelling in toughness of large heat input welded joint
CN102260825A (en) * 2010-05-27 2011-11-30 株式会社神户制钢所 High-strength Steel Board And Manufacturing Method Thereof
CN110846594A (en) * 2019-11-28 2020-02-28 钢铁研究总院 Copper-containing ultra-low carbon bainite steel and preparation method thereof

Similar Documents

Publication Publication Date Title
US9394579B2 (en) High-strength steel material having outstanding ultra-low-temperature toughness and a production method therefor
US10378073B2 (en) High-toughness hot-rolling high-strength steel with yield strength of 800 MPa, and preparation method thereof
JP6048626B1 (en) Thick, high toughness, high strength steel plate and method for producing the same
CN113862558B (en) Low-cost high-toughness high-strength tempered steel with yield strength of 700MPa and manufacturing method thereof
JP5741260B2 (en) Cryogenic steel material excellent in CTOD characteristics after imparting strain and method for producing the same
CN108342655B (en) Quenched and tempered acid-resistant pipeline steel and manufacturing method thereof
KR20240099374A (en) High-strength steel with excellent weather resistance and its manufacturing method
JP7016345B2 (en) Microalloy steel and its steel production method
CN112813344A (en) High-strength high-toughness easy-to-weld structural steel plate with yield strength of 620MPa and preparation method thereof
JP5194572B2 (en) Method for producing high-tensile steel material with excellent weld crack resistance
JP2008075107A (en) Method for manufacturing high-strength/high-toughness steel
CN113166901B (en) Chromium-molybdenum steel plate with excellent creep strength and preparation method thereof
CN111051555B (en) Steel sheet and method for producing same
CN115572901B (en) 630 MPa-grade high-tempering-stability low-carbon low-alloy steel plate and manufacturing method thereof
JPH09137253A (en) High tensile strength steel excellent in stress corrosion cracking resistance and low temperature toughness and its production
JP4123597B2 (en) Manufacturing method of steel with excellent strength and toughness
KR20160014998A (en) Steel sheet and method of manufacturing the same
CN110846594B (en) Copper-containing ultra-low carbon bainite steel and preparation method thereof
JP2002363685A (en) Low yield ratio high strength cold rolled steel sheet
US12134801B2 (en) High strength hot rolled steel sheet having excellent elongation and method for manufacturing the same
CN116200683A (en) 785 MPa-grade ultra-low carbon bainite steel and preparation method thereof
CN114134387A (en) 1300 MPa-tensile-strength thick-specification ultrahigh-strength steel plate and manufacturing method thereof
JPH11131177A (en) Steel plate for medium-or ordinary-temperature pressure vessel, capable of omitting post weld heat treatment, and its production
CN114480949A (en) 690 MPa-grade low-yield-ratio weather-resistant welding structural steel, steel plate and manufacturing method thereof
CN116179956B (en) Super thick ship plate steel based on same component and achieving different strength levels of 420-890 MPa and production method thereof

Legal Events

Date Code Title Description
PB01 Publication
PB01 Publication
SE01 Entry into force of request for substantive examination
SE01 Entry into force of request for substantive examination