KR20120097160A - High strength steel plate and method of manufacturing the same - Google Patents
High strength steel plate and method of manufacturing the same Download PDFInfo
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- KR20120097160A KR20120097160A KR1020110016563A KR20110016563A KR20120097160A KR 20120097160 A KR20120097160 A KR 20120097160A KR 1020110016563 A KR1020110016563 A KR 1020110016563A KR 20110016563 A KR20110016563 A KR 20110016563A KR 20120097160 A KR20120097160 A KR 20120097160A
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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
- C21D8/0221—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
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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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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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
- 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
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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
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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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
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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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
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
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Abstract
Description
The present invention relates to a high tensile steel sheet manufacturing technology, and more particularly to a tensile strength of 45 ~ 55kg / mm class 2 high tensile steel sheet and a method of manufacturing the same excellent tensile aging impact toughness at low temperature through the control of alloy components and process conditions. .
In the case of thick steel pipes manufactured through roll bending, UOE, JOC, etc., steel plates used in shipboard and stern curved parts, and steel plates for general structures, they are processed through presses to form the necessary shapes. Will be As such, when the steel sheet is processed to a desired shape, strain is generated in the material, so that the strength of the material increases, but the elongation and toughness of the material decrease with time, and strain aging occurs. Is called.
Strain aging occurs because invasive elements such as carbon or nitrogen atoms in the steel are stuck to dislocations, which acts as a factor that reduces toughness by impeding the movement of dislocations when deformation occurs. to be. Due to such deformation aging, the strength of the steel sheet is increased, but the impact toughness is greatly lowered. Ductile-Brittle Transition Temperature (DBTT) is increased by approximately 20 to 40 ° C.
One object of the invention to provide a superior strain age impact tensile strength of 45 ~ 55kg / mm 2 class high-strength steel sheet having a toughness at a low temperature of -40 ℃.
Another object of the present invention is to provide a method of manufacturing a high tensile strength steel sheet having excellent strain aging impact toughness through control of alloying components and process conditions.
High tensile steel sheet according to an embodiment of the present invention for achieving the above object is carbon (C): 0.03 ~ 0.10% by weight, silicon (Si): 0.05 ~ 0.50% by weight, manganese (Mn): 1.0 ~ 1.6% by weight , Phosphorus (P): 0.015% by weight or less, sulfur (S): 0.010% by weight or less, aluminum (Al): 0.01-0.05% by weight, niobium (Nb): 0.005-0.030% by weight, titanium (Ti): 0.010- 0.020% by weight, nitrogen (N): 0.005% by weight or less, hydrogen (H): 2.5ppm or less, and ferric (Feicular) with an average grain size of 15 µm or less , Granular Ferrite, Bainite (Bainite) and Perlite (Pearlite) is composed of a complex structure, the needle fraction of the needle-like ferrite and bainite is characterized by having a 50% or more area ratio.
Method for producing a high tensile strength steel sheet according to an embodiment of the present invention for achieving the other object is carbon (C): 0.03 ~ 0.10% by weight, silicon (Si): 0.05 ~ 0.50% by weight, manganese (Mn): 1.0 ~ 1.6 % By weight, phosphorus (P): 0.015% by weight or less, sulfur (S): 0.010% by weight or less, aluminum (Al): 0.01-0.05% by weight, niobium (Nb): 0.005-0.030% by weight, titanium (Ti): Reheating the slab plate consisting of 0.010 to 0.020% by weight and the remaining iron (Fe) and other unavoidable impurities to 1050-1200 ° C .; Primary rolling the reheated plate in a recrystallization zone; Secondary rolling the first rolled sheet using a plurality of rolling passes in a non-recrystallized region; And cooling the secondary rolled plate to 450 to 600 ° C.
At this time, before the slab reheating step, by performing a vacuum degassing process, it is preferable to limit to nitrogen (N): 0.005% by weight or less and hydrogen (H): 2.5ppm or less.
The high tensile steel sheet manufacturing method according to the present invention can form a composite microstructure including acicular ferrite, granular ferrite, bainite and pearlite having an average grain size of 15 μm or less through control of alloying components and process conditions.
As a result, the high tensile steel sheet according to the present invention can secure the strain aging impact toughness: 260 ~ 310 J at -40 ℃ with tensile strength: 480 ~ 580 MPa, yield strength: 400 ~ 530 MPa.
1 is a flow chart schematically showing a method of manufacturing a high tensile strength steel sheet according to an embodiment of the present invention.
Figure 2 is a schematic diagram showing a control rolling (CR) / acceleration cooling (ACC) process applied to the present invention.
Figure 3 is a photograph showing the final microstructure of the high tensile strength steel sheet produced by the method according to the present invention.
Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and only the present embodiments are intended to complete the disclosure of the present invention, and the general knowledge in the art to which the present invention pertains. It is provided to fully convey the scope of the invention to those skilled in the art, and the present invention is defined only by the scope of the claims. Like reference numerals refer to like elements throughout the specification.
Hereinafter, a high tensile steel sheet and a method of manufacturing the same according to preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
High tensile steel sheet
High tensile steel sheet according to the present invention is carbon (C): 0.03 ~ 0.10% by weight, silicon (Si): 0.05 ~ 0.50% by weight, manganese (Mn): 1.0 ~ 1.6% by weight, phosphorus (P): 0.015% by weight or less, Sulfur (S): 0.010 wt% or less, Aluminum (Al): 0.01 ~ 0.05 wt%, Niobium (Nb): 0.005 ~ 0.030 wt%, Titanium (Ti): 0.010 ~ 0.020 wt%, Nitrogen (N): 0.005 wt% % Or less, hydrogen (H): 2.5 ppm or less and the remaining iron (Fe) and other unavoidable impurities.
In addition, the high tensile strength steel sheet according to the present invention is one or more of boron (B): 0.0005 to 0.0015% by weight, copper (Cu): 0.35% by weight or less, and nickel (Ni): 0.40% by weight or less for the purpose of improving strength. It may further include.
Hereinafter, the role and content of each component included in the high tensile steel sheet according to the present invention will be described.
Carbon (C)
In the present invention, carbon (C) is added to secure the strength of the steel sheet.
The carbon (C) is preferably added in a content ratio of 0.03 to 0.10% by weight of the total weight of the steel sheet according to the present invention.
If the content of carbon (C) is added to less than 0.03% by weight of the total weight of the steel sheet may be difficult to secure strength. On the contrary, when the content of carbon (C) exceeds 0.10% by weight of the total weight of the steel sheet, the strength of the steel sheet is increased, but there is a problem that low-temperature impact toughness and weldability are deteriorated.
Silicon (Si)
In the present invention, silicon (Si) is added as a deoxidizer for removing oxygen in the steel in the steelmaking process. Silicon (Si) also has a solid solution strengthening effect.
The silicon (Si) is preferably added in a content ratio of 0.05 to 0.50% by weight of the total weight of the steel sheet.
If the content of silicon (Si) is less than 0.05% by weight of the total weight of the steel sheet, the effect of adding silicon is insignificant. On the contrary, when the content of silicon (Si) exceeds 0.50% by weight of the total weight of the steel sheet, there is a problem in that an oxide is formed on the surface of the steel sheet to lower the weldability of the steel sheet.
Manganese (Mn)
Manganese (Mn) is an austenite stabilizing element, and serves to refine the grains to improve strength and toughness.
The manganese (Mn) is preferably added in a content ratio of 1.0 to 1.6% by weight of the total weight of the steel sheet.
If the content of manganese (Mn) is added less than 1.0% by weight, the effect of securing strength and refining grains is insufficient. On the contrary, when the content of manganese (Mn) exceeds 1.6% by weight, there is a problem in that sulfur dissolved in steel is precipitated with MnS to lower low-temperature impact toughness.
Phosphorus (P)
Phosphorus (P) contributes to the improvement in strength in part, but the lower the content, the lower the content is a representative element to lower the low-temperature impact toughness. Therefore, the content of phosphorus (P) is preferably limited to 0.015% by weight or less of the total weight of the steel sheet.
Sulfur (S)
Sulfur (S) is an element inevitably contained in the production of steel together with phosphorus (P) and forms MnS to lower low-temperature impact toughness. Therefore, the content of sulfur (S) is preferably limited to 0.010% by weight or less of the total weight of the steel sheet.
Aluminum (Al)
Aluminum (Al) serves as a deoxidizer to remove oxygen in the steel.
The aluminum (Al) is preferably added in 0.01 to 0.05% by weight of the total weight of the steel sheet. If the content of aluminum (Al) is added less than 0.01% by weight, the deoxidation effect is insufficient. On the contrary, when the content of aluminum (Al) exceeds 0.05% by weight, there is a problem in that Al 2 O 3 is formed to lower the low temperature impact toughness.
Titanium (Ti)
In the present invention, titanium (Ti) forms a TiN upon slab reheating, thereby inhibiting austenite grain growth, thereby miniaturizing the structure of the steel sheet.
The titanium (Ti) is preferably added in 0.010 ~ 0.020% by weight of the total weight of the steel sheet. If the content of titanium (Ti) is less than 0.01% by weight, the titanium addition effect may not be properly exhibited. On the contrary, when the content of titanium (Ti) exceeds 0.02% by weight, TiN precipitates are coarsened and the effect of suppressing grain growth is reduced.
In addition, the titanium (Ti) is in addition to the above content range, so that the weight ratio of titanium (Ti) to nitrogen (N) ([Ti] / [N], where [] is the weight% of each component) is 3.0 to 4.0. It is preferred to be added. If the weight ratio of titanium (Ti) to nitrogen (N) is less than 3.0, TiN precipitate may not be sufficiently formed. Conversely, when the weight ratio of titanium (Ti) to nitrogen (N) exceeds 4.0, the TiN precipitate may be coarse.
Nitrogen (N)
Nitrogen (N) in the present invention forms AlN, TiN and the like to play a role to refine the grain.
Nitrogen (N) is preferably added in a content ratio of 0.005% by weight or less of the total weight of the steel sheet. If the content of nitrogen (N) exceeds 0.005% by weight, there is a problem of lowering the internal quality of the steel sheet by generating inclusions in the steel.
Niobium (Nb)
Niobium (Nb) combines with carbon (C) and nitrogen (N) at high temperatures to form carbides or nitrides. Niobium-based carbides or nitrides suppress grain growth during rolling to refine grains, thereby improving strength and low temperature toughness of the steel sheet.
The niobium (Nb) is preferably added at 0.005 to 0.030% by weight of the total weight of the steel sheet according to the present invention.
If the content of niobium (Nb) is added at less than 0.005% by weight, the niobium addition effect may not be properly exhibited. On the contrary, when the content of niobium (Nb) is added in excess of 0.030% by weight, not only the weldability of the steel sheet is lowered, but also the strength and low temperature toughness due to the increase in niobium content are not improved any more and remain in solid solution in the ferrite. Rather, there is a risk of lowering the impact toughness.
Boron (B)
Boron (B) is a strong hardenable element and may only contribute 0.0005% by weight or more of the total weight of the steel sheet to contribute to the improvement of the strength of the steel sheet.
However, when the addition amount of boron (B) exceeds 0.0020% by weight of the total weight of the steel sheet, there is a problem that the low-temperature impact toughness is sharply lowered, causing material variation due to grain boundary segregation.
Copper (Cu)
Copper (Cu) together with nickel (Ni) serves to improve the hardenability and low temperature impact toughness of the steel.
The copper (Cu) is preferably added to 0.35% by weight or less of the total weight of the steel sheet. If the content of copper (Cu) exceeds 0.35% by weight, there is a problem of lowering the surface quality of the steel.
Nickel (Ni)
In the present invention, nickel (Ni) is refined to solid crystals and dissolved in austenite and ferrite to strengthen the matrix. In particular, nickel (Ni) is an effective element for improving low temperature toughness.
The nickel (Ni) is preferably added to 0.40% by weight or less of the total weight of the steel sheet. If the content of nickel (Ni) exceeds 0.40% by weight, there is a problem of causing red light brittleness.
The high tensile strength steel sheet according to the present invention may further contain hydrogen (H) in addition to the alloying components described above. At this time, hydrogen (H) is an inevitable impurity, it is preferable to limit the addition amount to a very small amount through vacuum degassing treatment. Thus, in the present invention, the content of hydrogen (H) was limited to 2.5 ppm or less of the total weight of the steel.
Method of manufacturing high tensile steel sheet
1 is a flow chart schematically showing a method of manufacturing a high tensile strength steel sheet according to an embodiment of the present invention.
Referring to FIG. 1, the method of manufacturing a high tensile strength steel sheet includes a slab reheating step S110, a first rolling step S120, a second rolling step S130, and a cooling step S140.
Reheat slab
In the slab reheating step (S110), carbon (C): 0.03 to 0.10% by weight, silicon (Si): 0.05 to 0.50% by weight, manganese (Mn): 1.0 to 1.6% by weight, phosphorus (P): 0.015% by weight or less, Sulfur (S): 0.010 wt% or less, Aluminum (Al): 0.01 ~ 0.05 wt%, Niobium (Nb): 0.005 ~ 0.030 wt%, Titanium (Ti): 0.010 ~ 0.020 wt% and the rest of iron (Fe) and others The slab plate made of unavoidable impurities is reheated.
At this time, titanium or nitrogen, the weight ratio of titanium to nitrogen ([Ti] / [N], where [] is the weight percent of each component) to satisfy the 3.0 ~ 4.0 in order to improve the strength and secure low-temperature impact toughness desirable.
In addition, the slab plate further includes one or more of boron (B): 0.0005 to 0.0020% by weight, copper (Cu): 0.35% by weight or less, and nickel (Ni): 0.40% by weight or less for the purpose of securing strength. There may be.
At this time, in the slab reheating step (S110), it is preferable to reheat the slab plate at slab reheating temperature (SRT): 1050 to 1200 ° C.
If the slab reheating temperature (SRT) is less than 1050 ° C., there is a problem that the reheating temperature is low to increase the rolling load. On the contrary, when the slab reheating temperature exceeds 1200 ° C., niobium (Nb) and titanium (Ti) precipitates are dissolved to prevent austenite grain growth and coarsening of austenite grains ensures strength and low temperature toughness. There is a difficult problem.
Although not shown in the drawings, before the slab reheating step (S110), the vacuum degassing treatment is preferably limited to nitrogen (N): 0.005 wt% or less and hydrogen (H): 2.5 ppm or less.
Such vacuum degassing may be performed using a vacuum degassing facility (RH or VDOB), which is a secondary refining facility of the steelmaking process. At this time, the vacuum degassing facility serves to remove gases such as nitrogen (N), hydrogen (H) of molten steel.
1st and 2nd rolling
Figure 2 is a schematic diagram showing a control rolling (CR) / acceleration cooling (ACC) process applied to the present invention.
Referring to FIG. 2, after the primary rolling is performed in the austenitic recrystallized region to manufacture a high tensile strength steel sheet, fine structures may be formed through the secondary controlled rolling and accelerated cooling in the austenitic non-recrystallized region. Through this, the high tensile strength steel sheet can secure both target strength and low temperature toughness.
In the primary rolling step (S120), in order to control the reduction ratio of the secondary rolling in the austenite uncrystallized region described later, the reheated slab plate is rolled at a temperature of 930 ° C. or more, which is a temperature higher than the austenite recrystallization stop temperature. More specifically, the primary rolling may be carried out at a temperature of 930 ~ 1050 ℃ corresponding to the austenite recrystallization region.
The reduction ratio of the primary rolling may be determined according to the cumulative reduction ratio of the secondary rolling. For example, if the thickness of the sheet before hot rolling is 100 mm, the thickness after the end of control rolling is 40 mm, and the cumulative rolling rate of the secondary rolling is 50%, the sheet thickness after the primary rolling should be 80 mm (80 mm to 40 mm). ). Therefore, the reduction ratio of the primary rolling is 20% (100 mm to 80 mm).
In the secondary rolling step (S130), the primary rolled plate is secondarily rolled in the austenite non-recrystallized region. At this time, the secondary rolling uses a plurality of rolling passes so that control rolling is applied.
It is preferable to perform the finishing temperature (FDT) of secondary rolling at 750-850 degreeC. If the finishing temperature of secondary rolling exceeds 850 ° C, strength cannot be sufficiently secured. Conversely, when the secondary rolling finish temperature is less than 750 ° C., abnormal reverse rolling may occur to significantly lower the low temperature impact toughness.
Secondary rolling may be carried out so that the cumulative reduction in the unrecrystallized region is 40 to 70%. If the cumulative reduction ratio of the secondary rolling is less than 40%, it is difficult to secure low-temperature impact toughness due to insufficient control rolling. On the other hand, when the cumulative reduction ratio of secondary rolling exceeds 70%, the steel sheet manufacturing cost may increase excessively. In addition, the average rolling reduction per each pass can be carried out to 10 to 20% so that sufficient rolling can be made for each pass.
The number of rolling passes may be determined according to the cumulative reduction ratio of the secondary rolling and the average reduction ratio for each pass. Similarly, the average reduction ratio for each pass may be determined according to the number of rolling passes and the cumulative reduction ratio of the secondary rolling. Can be.
Cooling
In the cooling step (S140), grain growth is suppressed by cooling the plate member on which the secondary rolling is completed to the cooling end temperature by an accelerated cooling method or the like.
At this time, it is preferable that cooling completion temperature is 450-600 degreeC. If the cooling end temperature exceeds 600 ℃ there is a problem of insufficient strength due to the formation of coarse microstructure. On the contrary, when the cooling end temperature is less than 450 ° C., a large amount of low temperature transformation tissue is formed, and thus low temperature impact toughness is insufficient.
On the other hand, the cooling rate in the cooling step (S140) is preferably 5 ~ 15 ℃ / sec. If the cooling rate is less than 5 ° C / s, it may be difficult to secure a microstructure consisting of acicular ferrite, granular ferrite, bainite and pearlite. On the contrary, when cooling rate exceeds 15 degree-C / s, a structure becomes hard and it is difficult to ensure target low temperature impact toughness.
After the cooling step (S140), air cooling may proceed to room temperature.
The high tensile strength steel sheet produced through the manufacturing process (S110 ~ S140) is a composite of acicular ferrite, granular ferrite, bainite and pearlite having an average grain size of 15 μm or less. Can be organized. The tissue fraction of the needle-like ferrite and bainite may have 50% or more of area ratio.
Through this, the high tensile strength steel sheet can secure tensile strength: 480 to 580 MPa and yield strength: 400 to 530 MPa, and can secure an average impact toughness of 260 to 310 J at a low temperature of -40 ° C.
Example
Hereinafter, the configuration and operation of the present invention through the preferred embodiment of the present invention will be described in more detail. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.
Details that are not described herein will be omitted since those skilled in the art can sufficiently infer technically.
1. Specimen Manufacturing
Specimens according to Examples 1 to 4 and Comparative Examples 1 to 3 were prepared under the compositions shown in Tables 1 and 2 and the process conditions described in Table 3.
[Table 1] (unit:% by weight)
[Table 2] (unit:% by weight)
[Table 3]
2. Evaluation of mechanical properties
Table 4 shows the mechanical property evaluation results of the specimen prepared according to Examples 1 to 4 and Comparative Examples 1 to 3.
[Table 4]
Referring to Table 4, the specimens prepared according to Examples 1 to 4 exhibited a tensile strength (TS) of about 480 to 580 MPa, and a strain age impact toughness of about 260 to 310J at -40 ° C., at high strength and low temperature. The strain aging impact toughness of all was excellent.
In particular, in the case of Example 3 to which boron (B) was added, the tensile strength (TS) showed the highest value of 562 MPa. In addition, in the case of Example 4 to which copper (Cu) and nickel (Ni) were added, it was confirmed that the strain-aging impact toughness had the highest value of 305J at -40 ° C, while having a relatively high value at an elongation of 32.1%. It was.
On the other hand, in the case of Comparative Example 1 in which the contents of carbon (C), niobium (Nb), and titanium (Ti) were outside the ranges proposed in the present invention and air-cooled without finishing rolling in the uncrystallized region after finishing rolling, The elongation was 28.5%, which was somewhat lower than that of Examples 1-4, but the strain aging impact toughness at -40 ° C was only 25J. In addition, in the case of Comparative Example 2 in which the content of carbon (C) is out of the range suggested in the present invention, the strain aging impact toughness at −40 ° C. was only 63J.
In addition, except for copper (Cu) and nickel (Ni), the alloy components are the same as in Example 4, but in the case of Comparative Example 3 in which the process conditions deviate from the range suggested by the present invention, the tensile strength (TS) is relatively 532 MPa. Although high, the strain aging impact toughness at -40 ° C was only 105J.
Figure 3 is a photograph showing the microstructure of the high tensile strength steel sheet produced by the method according to the invention, more specifically the microstructure of the specimen prepared according to Example 1.
As shown in Figure 3, the average grain size is composed of a complex structure of acicular ferrite (Gicularular ferrite), granular ferrite (Bainite) and pearlite (Pearlite) having an average grain size of 15㎛ or less.
In addition, it can be seen that the microstructure of the steel sheet produced by the method according to the present invention has a tissue fraction of acicular ferrite and bainite having 50% or more as an area ratio.
As described above, the high tensile steel sheet produced by the method according to the present invention has a tensile strength (TS): 480 to 580 MPa and a yield strength: 400 to 530 MPa, and a strain aging impact toughness at -40 ° C: 260 to 310 J. It can be secured.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Such changes and modifications are intended to fall within the scope of the present invention unless they depart from the scope of the present invention. Accordingly, the scope of the present invention should be determined by the following claims.
S110: Slab reheating step
S120: Primary rolling step
S130: Secondary rolling step
S140: cooling step
Claims (12)
Primary rolling the reheated plate in a recrystallization zone;
Secondary rolling the first rolled sheet using a plurality of rolling passes in a non-recrystallized region; And
Cooling the secondary rolled plate to 450 ~ 600 ℃; manufacturing method of high tensile steel sheet comprising a.
Prior to the slab reheating step,
A vacuum degassing treatment is performed to limit nitrogen (N) to 0.005% by weight or less and hydrogen (H) to 2.5 ppm or less.
The slab plate is
The weight ratio of the titanium (Ti) to the nitrogen (N) ([Ti] / [N], where [] is the weight percent of each component) is 3.0 to 4.0, characterized in that the manufacturing method of high tensile strength steel sheet.
The slab plate is
Boron (B): 0.0005 to 0.0020% by weight, copper (Cu): 0.35% by weight or less and nickel (Ni): 0.40% by weight or less of the manufacturing method of a high tensile strength steel sheet characterized in that it further comprises.
The secondary rolling is
A method for producing a high tensile strength steel sheet, which is carried out so that the finishing temperature is 750 to 850 ° C.
The secondary rolling is
A method of manufacturing a high tensile strength steel sheet, wherein the cumulative reduction ratio in the unrecrystallized region is 40 to 70% and the average reduction ratio per pass is 10 to 20%.
The cooling rate is
A method for producing a high tensile strength steel sheet, which is performed at 5 to 15 ° C / sec.
It consists of a complex structure of acicular ferrite, granular ferrite, bainite and pearlite, with an average grain size of 15 μm or less, and the tissue fraction of the acicular ferrite and bainite. It has 50% or more by this area ratio, The high tensile strength steel plate characterized by the above-mentioned.
The steel sheet
The high strength steel sheet, characterized in that the weight ratio of the titanium (Ti) to the nitrogen (N) ([Ti] / [N], where [] is a weight% of each component) is 3.0 to 4.0.
The steel sheet
Boron (B): 0.0005 to 0.0015% by weight, copper (Cu): 0.35% by weight or less and nickel (Ni): high tensile steel sheet, characterized in that it further comprises at least one.
The steel sheet
Tensile strength (TS): 480 ~ 580 MPa and Yield strength: 400 ~ 530 MPa characterized by having a high tensile strength steel sheet.
The steel sheet
High tensile steel sheet, characterized in that the strain aging impact toughness at -40 ℃ is 260 ~ 310 J.
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| Application Number | Priority Date | Filing Date | Title |
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| KR1020110016563A KR20120097160A (en) | 2011-02-24 | 2011-02-24 | High strength steel plate and method of manufacturing the same |
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| Application Number | Priority Date | Filing Date | Title |
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| KR1020110016563A KR20120097160A (en) | 2011-02-24 | 2011-02-24 | High strength steel plate and method of manufacturing the same |
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| KR20120097160A true KR20120097160A (en) | 2012-09-03 |
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| KR1020110016563A KR20120097160A (en) | 2011-02-24 | 2011-02-24 | High strength steel plate and method of manufacturing the same |
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| KR (1) | KR20120097160A (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR101467050B1 (en) * | 2012-10-31 | 2014-12-02 | 현대제철 주식회사 | Steel plate and method of manufacturing the same |
| WO2016105002A1 (en) * | 2014-12-24 | 2016-06-30 | 주식회사 포스코 | Low-temperature steel sheet with excellent surface processing quality and method for manufacturing same |
| KR101726082B1 (en) * | 2015-12-04 | 2017-04-12 | 주식회사 포스코 | Steel having superior brittle crack arrestability and resistance brittle crack initiation of welding point and method for manufacturing the steel |
| WO2017095190A1 (en) * | 2015-12-04 | 2017-06-08 | 주식회사 포스코 | High-strength steel having excellent brittle crack arrestability and welding part brittle crack initiation resistance, and production method therefor |
| KR102218423B1 (en) * | 2019-08-23 | 2021-02-19 | 주식회사 포스코 | Thin steel plate having excellent low-temperature toughness and ctod properties, and method for manufacturing thereof |
-
2011
- 2011-02-24 KR KR1020110016563A patent/KR20120097160A/en not_active Application Discontinuation
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR101467050B1 (en) * | 2012-10-31 | 2014-12-02 | 현대제철 주식회사 | Steel plate and method of manufacturing the same |
| WO2016105002A1 (en) * | 2014-12-24 | 2016-06-30 | 주식회사 포스코 | Low-temperature steel sheet with excellent surface processing quality and method for manufacturing same |
| CN107109602A (en) * | 2014-12-24 | 2017-08-29 | Posco公司 | The excellent steel plates for low temperature service of suface processing quality and its manufacture method |
| KR101726082B1 (en) * | 2015-12-04 | 2017-04-12 | 주식회사 포스코 | Steel having superior brittle crack arrestability and resistance brittle crack initiation of welding point and method for manufacturing the steel |
| WO2017095175A1 (en) * | 2015-12-04 | 2017-06-08 | 주식회사 포스코 | High-strength steel having excellent brittle crack arrestability and welding part brittle crack initiation resistance, and production method therefor |
| WO2017095190A1 (en) * | 2015-12-04 | 2017-06-08 | 주식회사 포스코 | High-strength steel having excellent brittle crack arrestability and welding part brittle crack initiation resistance, and production method therefor |
| KR102218423B1 (en) * | 2019-08-23 | 2021-02-19 | 주식회사 포스코 | Thin steel plate having excellent low-temperature toughness and ctod properties, and method for manufacturing thereof |
| WO2021040332A1 (en) * | 2019-08-23 | 2021-03-04 | 주식회사 포스코 | Thin steel plate having excellent low-temperature toughness and ctod properties, and method for manufacturing same |
| CN114245831A (en) * | 2019-08-23 | 2022-03-25 | 株式会社Posco | Steel sheet having excellent low-temperature toughness and CTOD characteristics and method for manufacturing the same |
| JP2022544044A (en) * | 2019-08-23 | 2022-10-17 | ポスコ | Thin steel material with excellent low-temperature toughness and CTOD properties, and method for producing the same |
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