KR20160114915A - Non-heated hot-rolled steel sheet and method of manufacturing the same - Google Patents
Non-heated hot-rolled steel sheet and method of manufacturing the same Download PDFInfo
- Publication number
- KR20160114915A KR20160114915A KR1020150041398A KR20150041398A KR20160114915A KR 20160114915 A KR20160114915 A KR 20160114915A KR 1020150041398 A KR1020150041398 A KR 1020150041398A KR 20150041398 A KR20150041398 A KR 20150041398A KR 20160114915 A KR20160114915 A KR 20160114915A
- Authority
- KR
- South Korea
- Prior art keywords
- steel sheet
- rolled steel
- hot
- weight
- manufacturing
- Prior art date
Links
- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 74
- 239000010959 steel Substances 0.000 title claims abstract description 74
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 21
- 239000011572 manganese Substances 0.000 claims abstract description 25
- 239000010955 niobium Substances 0.000 claims abstract description 21
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 20
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 19
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims abstract description 15
- 239000011651 chromium Substances 0.000 claims abstract description 15
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 15
- 229910052758 niobium Inorganic materials 0.000 claims abstract description 14
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 claims abstract description 14
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 13
- 239000012535 impurity Substances 0.000 claims abstract description 13
- 238000005096 rolling process Methods 0.000 claims abstract description 13
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 13
- 239000010703 silicon Substances 0.000 claims abstract description 13
- 238000001816 cooling Methods 0.000 claims abstract description 12
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 12
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims abstract description 10
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 10
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 7
- 238000004804 winding Methods 0.000 claims abstract description 4
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 28
- 238000005098 hot rolling Methods 0.000 claims description 15
- 238000000034 method Methods 0.000 claims description 15
- 229910052757 nitrogen Inorganic materials 0.000 claims description 14
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims description 12
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims description 12
- 229910052698 phosphorus Inorganic materials 0.000 claims description 12
- 239000011574 phosphorus Substances 0.000 claims description 12
- 229910052717 sulfur Inorganic materials 0.000 claims description 12
- 239000011593 sulfur Substances 0.000 claims description 12
- 229910001562 pearlite Inorganic materials 0.000 claims description 11
- 230000009467 reduction Effects 0.000 claims description 6
- 238000010438 heat treatment Methods 0.000 abstract description 17
- 238000003303 reheating Methods 0.000 abstract description 4
- 235000019362 perlite Nutrition 0.000 abstract 1
- 239000010451 perlite Substances 0.000 abstract 1
- 230000000052 comparative effect Effects 0.000 description 22
- 230000008569 process Effects 0.000 description 9
- 239000008186 active pharmaceutical agent Substances 0.000 description 8
- 239000000203 mixture Substances 0.000 description 7
- 230000009466 transformation Effects 0.000 description 7
- 238000010791 quenching Methods 0.000 description 6
- 230000000171 quenching effect Effects 0.000 description 6
- 238000005496 tempering Methods 0.000 description 6
- 229910001563 bainite Inorganic materials 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 229910001566 austenite Inorganic materials 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 238000005728 strengthening Methods 0.000 description 4
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- 238000009749 continuous casting Methods 0.000 description 3
- 230000007797 corrosion Effects 0.000 description 3
- 238000005260 corrosion Methods 0.000 description 3
- 230000001186 cumulative effect Effects 0.000 description 3
- 230000006866 deterioration Effects 0.000 description 3
- 238000010899 nucleation Methods 0.000 description 3
- 230000006911 nucleation Effects 0.000 description 3
- 238000001953 recrystallisation Methods 0.000 description 3
- 239000006104 solid solution Substances 0.000 description 3
- 238000004781 supercooling Methods 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 238000005204 segregation Methods 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 230000000087 stabilizing effect Effects 0.000 description 2
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 2
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000002950 deficient Effects 0.000 description 1
- 238000005553 drilling Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- UNASZPQZIFZUSI-UHFFFAOYSA-N methylidyneniobium Chemical compound [Nb]#C UNASZPQZIFZUSI-UHFFFAOYSA-N 0.000 description 1
- 238000005065 mining Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000002105 nanoparticle Substances 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 239000003129 oil well Substances 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 230000002250 progressing effect Effects 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 239000011265 semifinished product Substances 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
Images
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
- B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
-
- 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
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Heat Treatment Of Steel (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Abstract
Description
The present invention relates to a hot-rolled steel sheet and a manufacturing method thereof, and more particularly, to a non-heat-treated hot-rolled steel sheet having a composition of a medium carbon low alloy component and a manufacturing method thereof.
In general, the American Petroleum Institute steel pipes used for oil and gas drilling are used in a variety of applications ranging from API 5CT J55 of about 380 MPa to API 5CT Q125 of about 860 MPa based on the yield strength. Among them, API 5CT J55 and API 5CT K55 require material guarantee on hot-rolled steel sheet. However, in case of API 5CT N80, API 5CT L80, API 5CT P110, API 5CT Q125 QT (Quenching and Tempering) Material after heat treatment Warranted.
In recent years, the demand for high-strength steels has been increasing due to the increase of non-traditional mining, and efforts for lowering the manufacturing cost of the well steel pipes have been steadily progressing in the industry.
As a related prior art, there is Korean Patent Registration No. 0049161 (published on Mar. 29, 1992, entitled "Method for manufacturing a steel tube for oil well with a tensile strength of 70 kgf / mm 2 or more").
An object of the present invention is to provide a hot-rolled steel sheet having a composition of a medium-carbon low-alloy component system, and a heat treatment type hot-rolled steel sheet having high strength without a QT (Quenching & Tempering) heat treatment process.
It is another object of the present invention to provide a method of manufacturing the above-mentioned non-heat-treated hot-rolled steel sheet.
A method of manufacturing a hot-rolled steel sheet according to one aspect of the present invention is disclosed. Wherein the steel sheet comprises 0.15 to 0.19% by weight of carbon (C), 0.3 to 0.3% by weight of silicon (Si), 1.25 to 1.45% 0.02 to 0.03% by weight of niobium (Nb) and the balance of iron (Fe) and other unavoidable impurities is reheated to a temperature of 1180 to 1250 캜. The reheated plate is hot-rolled to a finish rolling temperature of 830 to 870 ° C. The hot-rolled plate is cooled to 550 to 590 캜 and wound. The plate has a pearlite and ferrite structure as a main phase, a yield strength (YS) of 552 to 758 MPa, and a tensile strength (TS) of 670 MPa or more.
In one embodiment, the slab plate includes at least one of sulfur (S), phosphorus (P), and nitrogen (N) as the inevitable impurities, wherein the sulfur (S) The phosphorus (P) may include more than 0 to 0.012 wt%, and the nitrogen (N) may include more than 0 to 0.006 wt%.
In another embodiment, the hot rolling may be carried out at a reduction ratio of 40% to 60%.
In yet another embodiment, cooling of the hot rolled plate may proceed at a cooling rate of 30 to 50 DEG C / sec.
A non-heat treatment type hot rolled steel sheet according to one aspect of the present invention is disclosed. Wherein the non-heat treatment type hot rolled steel sheet comprises 0.15 to 0.19% by weight of carbon (C), 0.3 to 0.3% by weight of silicon (Si), 1.25 to 1.45% by weight of manganese (Mn), 0.02 to 0.40% 0.02 to 0.03% by weight of Nb and balance iron (Fe) and other unavoidable impurities. At this time, the microstructure has a pearlite structure and a ferrite structure as main phases, and has a yield strength (YS) of 552 to 758 MPa and a tensile strength (TS) of 670 MPa or more.
According to the embodiment of the present invention, the yield strength (YS) of 552 to 758 MPa and the tensile strength (TS) of the steel sheet are 670 MPa or more.
1 is a flowchart schematically showing a method of manufacturing a hot-rolled steel sheet according to an embodiment of the present invention.
2 is a microstructure photograph of a specimen according to a comparative example of the present invention.
3 and 4 are microstructural photographs of a specimen according to an embodiment of the present invention.
Hereinafter, a non-heat treatment type hot-rolled steel sheet according to an embodiment of the present invention and a method of manufacturing the same will be described in detail. The terms used below are appropriately selected terms in consideration of functions in the present invention, and definitions of these terms should be made based on the contents throughout this specification.
Non heat-treated hot-rolled steel sheet
The heat treatment type hot rolled steel sheet according to an embodiment of the present invention has tensile strength (TS) of not less than 670 MPa and yield strength (YS) of 552 to 758 MPa without further heat treatment such as Quenching & Tempering after hot rolling . The non-heat-treated hot rolled steel sheet may have a pearlite structure at room temperature.
The non-heat treatment type hot rolled steel sheet according to one embodiment of the present invention comprises 0.15 to 0.19% by weight of carbon (C), 0.3 to 0.3% by weight of silicon (Si), 1.25 to 1.45% by weight of manganese (Mn) To 0.40 wt.%, Niobium (Nb) 0.02 to 0.03 wt.%, And the balance iron (Fe) and other unavoidable impurities.
As the unavoidable impurities, the non-heat-treated hot-rolled steel sheet may contain phosphorus (P) in an amount of more than 0 and 0.012 wt% or less. The non-heat treatment type hot rolled steel sheet may contain sulfur (S) in an amount of more than 0 and 0.003 wt% or less. The non-heat treatment type hot rolled steel sheet may include nitrogen (N) more than 0 and not more than 0.006 (%) by weight.
Hereinafter, the role and content of each component included in the non-heat treatment type hot-rolled steel sheet according to one embodiment of the present invention will be described.
Carbon (C)
Carbon (C) is added for securing strength and controlling microstructure. In the embodiment of the present invention, when the content of carbon (C) is less than 0.16% by weight, a porosity reaction can not occur at the time of performance, so that sufficient strength can not be ensured and the quality of the hot rolled steel sheet may deteriorate. If the content of carbon (C) exceeds 0.19% by weight, there may be problems such as lowering of strength and toughness or deterioration of weldability. Taking this into consideration, the content of carbon (C) in the steel sheet is determined to be 0.16 to 0.19% by weight.
Silicon (Si)
Silicon (Si) is a ferrite stabilizing element in a steel sheet, which can increase the supercooling degree during ferrite transformation to make fine grains and inhibit carbide formation. This contributes to improvement of the yield strength of the steel sheet. In addition, due to the strengthened ferrite, the crack path can be induced to the grain boundary during fracture.
This effect of adding silicon is possible when the content of silicon in the steel sheet is 0 to 0.3% by weight or less. If the silicon content exceeds 0.3% by weight, the weldability of steel may be deteriorated. Further, in the hot rolling step, the surface quality may be lowered by generating the rolling scale during the reheating step and the hot rolling. Taking this into consideration, the silicon content in the steel sheet is determined to be more than 0 and 0.30% by weight or less.
Manganese (Mn)
Manganese (Mn) is an austenite stabilizing element and is effective for strengthening the solid solution. In addition, manganese (Mn) can increase the hardenability of the steel. The addition of manganese can reduce the equilibrium temperature of the steel, resulting in ferrite reduction and increased pearlite. In addition, the lamellar spacing of the pearlite can be reduced.
If the content of manganese in the steel sheet is less than 1.25% by weight, the effect of strengthening the solid solution can not be sufficiently exhibited. When the content of manganese exceeds 1.45% by weight, the weldability is lowered, MnS inclusions and center segregation are generated, so that ductility of the steel sheet is lowered and corrosion resistance is lowered. Taking this into consideration, the manganese content in the steel sheet is determined to be 1.25 to 1.45% by weight.
Chromium (Cr)
Chromium can affect the steel strength and yield ratio by lowering the equilibrium temperature. In addition, chromium can improve the strength and increase the hardenability. On the other hand, when the content of chromium in the steel sheet is less than 0.2% by weight, the effect of addition can not be sufficiently exhibited. If the content of chromium exceeds 0.4% by weight, chromium may combine with carbon to form a coarse carbide, which may result in a problem of weak toughness. Taking this fact into consideration, the chromium content in the steel sheet is determined to be 0.2 to 0.4% by weight.
Niobium (Nb)
Niobium (Nb) combines with carbon and nitrogen at high temperatures to form carbides or nitrides. Niobium can improve the strength and toughness by delaying the recrystallization during hot rolling to achieve grain refinement. In hot rolling, solid niobium may retard the nucleation and growth of recrystallization, and since such a recrystallization delay does not consume defective sites such as dislocations, it can accelerate nucleation during phase transformation and fine grains. In addition, since the modified organic precipitated carbide during the hot rolling serves as a nucleation site of the ferrite during the phase transformation, the crystal phase can be miniaturized by promoting the phase transformation. Further, while the hot-rolled steel sheet undergoes the ROT (Run-Out Table) or during the phase transformation during winding, the niobium in the solid state forms fine nano-sized precipitates and can contribute to precipitation strengthening.
On the other hand, when the content of niobium in the steel sheet is less than 0.02% by weight, the effect of grain refinement can not be sufficiently obtained. When the content of niobium exceeds 0.03% by weight, excessive precipitation may cause deterioration in performance, rolling property and elongation.
(P), sulfur (S), and nitrogen (N) as inevitable impurities,
Phosphorus (P) enhances the strength of the strength by solid solution strengthening and can function to inhibit the formation of carbide. However, when the content of phosphorus is more than 0.012 wt%, the weldability is deteriorated and corrosion resistance is deteriorated due to slab center segregation. Further, phosphorus may be segregated in the austenite grain boundary system and toughness may be lowered. Taking this into consideration, therefore, the content of phosphorus in the steel sheet is maintained at 0.012 wt% or less.
Sulfur (S) can form precipitates of fine MnS to improve workability. However, if the content of sulfur exceeds 0.003% by weight, toughness and weldability may be impaired and corrosion resistance of steel may be lowered. Therefore, the content of sulfur in the steel sheet is maintained at 0.003% by weight or less.
Nitrogen (N) can be combined with niobium or the like to form carbonitride, thereby making the crystal grains finer. However, when the content of nitrogen is more than 0.006% by weight, the amount of solute nitrogen is increased to lower the impact characteristics and elongation of the steel and to inhibit the toughness of the welded portion. Therefore, the nitrogen content in the steel sheet is maintained at 0.006 wt% or less.
Method for manufacturing a non-heat-treated hot-rolled steel sheet
1 is a flowchart schematically showing a method of manufacturing a hot-rolled steel sheet according to an embodiment of the present invention. Referring to FIG. 1, in step S110, the slab plate of a predetermined composition is reheated. In one embodiment, the slab sheet material may be a semi-finished product material to be subjected to the hot rolling process in the non-heat treatment type hot rolled steel sheet manufacturing method according to an embodiment of the present invention. The slab plate can be manufactured through a continuous casting process after obtaining a molten steel having a desired composition through a steelmaking process.
Wherein the slab plate comprises 0.15 to 0.19% by weight of carbon (C), 0.3 to 0.3% by weight of silicon (Si), 0.15 to 1.45% by weight of manganese (Mn), 0.02 to 0.40% To 0.03% by weight and the balance iron (Fe) and other unavoidable impurities. In addition, as the unavoidable impurities, the slab sheet may contain phosphorus (P) in an amount of more than 0 to 0.012% by weight of the hot-rolled steel sheet. The slab plate may contain more than 0 to 0.003% by weight of sulfur (S). The slab plate may include nitrogen (N) 0 to 0.006% by weight or less.
In one embodiment, the slab plate may be reheated for at least 2 hours at a temperature of 1180 to 1250 占 폚. When the slab plate is reheated at the above-mentioned temperature, the segregated components in the continuous casting process can be reused. When the reheating temperature is lower than 1180 ° C, the niobium carbide is not sufficiently solidified, and there may be a problem that the segregated components are not distributed evenly in the continuous casting process. When the reheating temperature is higher than 1250 ° C, very coarse austenite grains are formed and it may be difficult to secure strength. If the temperature is higher than 1250 占 폚, the heating cost is increased and the process time is increased, resulting in an increase in manufacturing cost and a decrease in productivity.
In step S120, the reheated sheet material is hot-rolled. The hot rolling is performed such that the Finishing Delivery Temperature (FDT) is 830 to 870 ° C. If the finish rolling temperature is lower than 830 캜, there is a problem that a blister structure occurs due to an abnormal reverse rolling. When the finish rolling temperature exceeds 870 캜, the austenite grains are coarsened, Can be.
The hot rolling may be carried out so that the cumulative rolling reduction is 40 to 60%. If the cumulative rolling reduction is less than 40%, it is difficult to obtain a uniform but fine structure, and the deviation of the strength and impact toughness may be severely generated. If the cumulative rolling reduction exceeds 60%, there is a problem that the rolling process time is prolonged and the fishy property is deteriorated.
In step S130, the hot-rolled plate is cooled and wound. In a specific embodiment, the hot-rolled plate is cooled to a temperature of 550 to 590 캜 and wound. When the coiling temperature is lower than 550 캜, sufficient strength can be secured, but it may be difficult to secure ductility. On the other hand, when the coiling temperature exceeds 590 占 폚, sufficient strength can not be ensured.
In order to control the amount of pearlite, phase transformation must be intensively generated at the coiling temperature. The cooling after hot rolling in this embodiment can be carried out at a cooling rate of 30 to 50 DEG C / sec. If the cooling rate is less than 30 占 폚 / sec, the fraction of ferrite increases more than necessary, thereby making it difficult to secure sufficient strength. If the cooling rate exceeds 50 DEG C / sec, locally subcooling occurs, pearlite transformation does not occur on the surface or inside of the steel sheet, and bainite may be formed. Such a bainite-formed portion may cause poor roundness when the steel sheet is subsequently worked with a product such as a pipe.
The non-heat treatment type hot rolled steel sheet according to one embodiment of the present invention can be manufactured through the above-described manufacturing method. The yield strength (YS) of 552 to 758 MPa and the tensile strength (TS) of 670 MPa or more can be ensured through a quenching & tempering heat treatment process through the alloy composition of the hot-rolled steel sheet and the hot- . The final microstructure of the non-heat-treated hot-rolled steel sheet produced in this process is predominantly composed of pearlite and ferrite.
Example
Best Mode for Carrying Out the Invention Hereinafter, a preferred embodiment of the present invention will be described in more detail. It should be understood, however, that this is a preferred embodiment of the present invention and that the spirit of the present invention is not limited to the following embodiments.
1. Preparation of specimens
The specimens of Comparative Examples 1 to 3 and Examples 1 and 2 were prepared according to the main composition of Table 1 and the process conditions of Table 2.
In the case of Comparative Example 1, the content of manganese and niobium was higher than that of the present example, and vanadium (V) was added as an alloying element, which is a low carbon type having a lower carbon content than the hot rolled steel sheet of the example of the present invention. In the case of Comparative Example 1, the coiling temperature is lower than the coiling temperature of this embodiment. In the case of Comparative Example 2, the carbonaceous steel sheet has a carbon content higher than that of the hot-rolled steel sheet of the embodiment of the present invention. Although not shown in Table 2, the steel sheet is subjected to tempering at 850 ° C or higher and quenching to room temperature . In the case of Comparative Example 3, the hot rolled steel sheet was wound at a temperature lower than that of the hot rolled steel sheet of the embodiment of the present invention, and the cooling rate was also increased. Examples 1 and 2 proceeded with the composition and process conditions of the examples of the present invention. In the case of Example 1, the coiling temperature was higher than that of Example 2 by 10 ° C.
2. Evaluation of mechanical properties
Table 3 shows the evaluation results of the mechanical properties of the specimens according to Comparative Examples 1 to 3 and Examples 1 and 2.
Referring to Tables 1 to 3, the specimens prepared according to Examples 1 and 2 satisfy the target yield strength (YS) of 552 to 758 MPa and tensile strength (TS) of 670 MPa or more. At this time, in Example 2 in which the coiling temperature was 10 占 폚, yield strength and tensile strength were high.
In the case of Comparative Example 1, a low carbon steel sheet having a carbon content lower than the carbon content of the present embodiment was selected to have a lower coiling temperature than the present embodiment, in which manganese and niobium contents were increased and vanadium was added, The target values of the yield strength and the tensile strength were achieved. In the case of Comparative Example 2, the target values of the yield strength and the tensile strength were achieved through quenching and tempering (QT) after winding. In the case of Comparative Example 3, the cooling rate was also the fastest under the condition of the lowest coiling temperature. At this time, yield strength and tensile strength were also measured the highest. However, as described below, it may have disadvantages in the microstructure.
FIG. 2 is a microstructure photograph of a specimen according to a comparative example of the present invention, and FIGS. 3 and 4 are microstructure photographs of a specimen according to an embodiment of the present invention. 2 is a photograph of the microstructure of Comparative Example 3, FIG. 3 is a photograph of the microstructure of Example 1, and FIG. 4 is a microstructure photograph of Example 2. FIG.
Referring to FIG. 2, it can be confirmed that, in the case of the specimen produced according to the condition of Comparative Example 3, the microstructure is a mixed phase of pearlite and bainite. As described above, the bainite is generated by local supercooling at the time of cooling in the hot rolling process, and may cause a poor roundness at the time of casting. In addition, the bainite may cause deterioration of the weldability of the steel. On the other hand, referring to Figs. 3 and 4, no bainite structure was found in the specimens of Examples 1 and 2. Therefore, according to the manufacturing method of the present embodiment, it is possible to prevent the roundness failure due to the local supercooling of the steel.
It is to be understood that the invention includes various modifications and equivalent embodiments that can be derived from the disclosed embodiments as well as those of ordinary skill in the art to which the present invention pertains. Accordingly, the technical scope of the present invention should be defined by the following claims.
-
Claims (6)
(b) hot rolling the reheated plate to a finish rolling temperature of 830 to 870 캜;
(c) cooling the hot-rolled plate to 550 to 590 DEG C and winding,
After the step (c), the plate has a pearlite and ferrite structure as a main phase, a yield strength (YS) of 552 to 758 MPa, a tensile strength (TS) of 670 MPa or more
A method of manufacturing a non-heat-treated hot-rolled steel sheet.
(a)
The slab plate
At least one or more of sulfur (S), phosphorus (P) and nitrogen (N) is contained as the unavoidable impurities,
Wherein the sulfur (S) is greater than 0 and less than or equal to 0.003 wt%, the phosphorus (P) is greater than 0 and 0.012 wt%, and the nitrogen (N) is greater than 0 and less than or equal to 0.006 wt%
A method of manufacturing a non-heat-treated hot-rolled steel sheet.
In the step (b)
The hot rolling is carried out at a reduction ratio of 40% to 60%
A method of manufacturing a non-heat-treated hot-rolled steel sheet.
(c)
Lt; RTI ID = 0.0 > 50 C / sec < / RTI >
A method of manufacturing a non-heat-treated hot-rolled steel sheet.
The microstructure has a pearlite structure and a ferrite structure as main phases, a yield strength (YS) of 552 to 758 MPa, a tensile strength (TS) of 670 MPa or more
Non - heat treated hot rolled steel sheets.
The inevitable impurities include at least one or more of sulfur (S), phosphorus (P), and nitrogen (N)
Wherein the sulfur (S) is greater than 0 and less than or equal to 0.003 wt%, the phosphorus (P) is greater than 0 and 0.012 wt%, and the nitrogen (N) is greater than 0 and less than or equal to 0.006 wt%
Non - heat treated hot rolled steel sheets.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR1020150041398A KR20160114915A (en) | 2015-03-25 | 2015-03-25 | Non-heated hot-rolled steel sheet and method of manufacturing the same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR1020150041398A KR20160114915A (en) | 2015-03-25 | 2015-03-25 | Non-heated hot-rolled steel sheet and method of manufacturing the same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| KR20160114915A true KR20160114915A (en) | 2016-10-06 |
Family
ID=57164615
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| KR1020150041398A KR20160114915A (en) | 2015-03-25 | 2015-03-25 | Non-heated hot-rolled steel sheet and method of manufacturing the same |
Country Status (1)
| Country | Link |
|---|---|
| KR (1) | KR20160114915A (en) |
-
2015
- 2015-03-25 KR KR1020150041398A patent/KR20160114915A/en not_active Application Discontinuation
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| KR100957970B1 (en) | High-strength and high-toughness thick steel plate and method for producing the same | |
| KR101758497B1 (en) | Steel Plate For Pressure Vessel With Excellent PWHT Resistance And Manufacturing Method Thereof | |
| KR101799202B1 (en) | High-strength steel sheet having excellent low yield ratio property and low temperature toughness and method for manufacturing the same | |
| KR101778406B1 (en) | Thick Plate for Linepipes Having High Strength and Excellent Excessive Low Temperature Toughness And Method For Manufacturing The Same | |
| KR101940872B1 (en) | Hot rolled steel sheet for use in oil well pipe, steel pipe using the same and method for manufacturing thereof | |
| KR20170143415A (en) | Steel reinforcement and method of manufacturing the same | |
| KR101917451B1 (en) | Low-yield ratio steel sheet having excellent low-temperature toughness and method for manufacturing the same | |
| CN108474089B (en) | Thick steel plate having excellent low-temperature toughness and hydrogen-induced cracking resistance and method for manufacturing same | |
| KR101546154B1 (en) | Oil tubular country goods and method of manufacturing the same | |
| KR20190036028A (en) | Non-heated type hot-rolled steel sheet, method of manufacturing the same, steel pipe, and method of manufacturing steel pipe using non-heated type hot-rolled steel sheet | |
| KR101714929B1 (en) | Austenitic steel having excellent wear resistance and method for manufacturing the same | |
| KR20190045453A (en) | Hot rolled steel sheet and method of manufacturing the same | |
| KR101546138B1 (en) | Hot-rolled steel sheet and manufacturing method of the same | |
| KR101505299B1 (en) | Steel and method of manufacturing the same | |
| KR101797367B1 (en) | High carbon hot-rolled steel sheet and method of manufacturing the same | |
| KR101675677B1 (en) | Non-heated hot-rolled steel sheet and method of manufacturing the same | |
| KR101246466B1 (en) | METHOD OF MANUFACTURING EXCELLENT FORMABILITY HOT ROLLED STEEL SHEET HAVING 1000MPa GRADE AND HOT ROLLED STEEL SHEET FABRICATED USING THEREOF | |
| KR101787256B1 (en) | Non-heated type hot-rolled steel sheet and method of manufacturing the same | |
| KR102495181B1 (en) | High strength hot rolled steel sheet for steel pipe having excellent impact toughness and method of manufacturing the same | |
| KR20160114915A (en) | Non-heated hot-rolled steel sheet and method of manufacturing the same | |
| KR102407420B1 (en) | High strength hot rolled steel sheet for steel pipe and method of manufacturing the same | |
| KR20190058046A (en) | Steel reinforcement and method of manufacturing the same | |
| KR102560057B1 (en) | High yield ratio and high strength steel sheet having excellent bendability and the method for manufacturing the same | |
| KR101443445B1 (en) | Non-heated type high strength hot-rolled steel sheet and method of manufacturing the same | |
| KR20180138297A (en) | Steel reinforcement and method of manufacturing the same |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A201 | Request for examination | ||
| E902 | Notification of reason for refusal | ||
| E601 | Decision to refuse application |