CN111315901A - High-strength low-toughness cold-rolled steel sheet having excellent fracture characteristics and method for producing same - Google Patents
High-strength low-toughness cold-rolled steel sheet having excellent fracture characteristics and method for producing same Download PDFInfo
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- 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
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- 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
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- 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
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- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C21D2211/005—Ferrite
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- 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
The invention provides a method for manufacturing a high-strength low-toughness cold-rolled steel sheet with excellent fracture characteristics. The cold rolled steel sheet of the present invention comprises, in wt%: c: 0.30-0.70%, Mn: 0.2 to 1.0%, Si: 0.005-0.5%, P: 0.005-0.02%, S: 0.01% or less, Al: 0.01-0.1%, Cr: 0.005 to 0.1% and the balance of iron (Fe) and other unavoidable impurities, wherein the fine structure of the steel comprises 50 to 95% of pearlite and the balance of ferrite, the average grain size of the ferrite structure is 10 to 50 [ mu ] m, the average grain size of the pearlite domain is 10 to 50 [ mu ] m, the cold-rolled steel sheet has a thickness of 1.5 to 3.0mmt, and the cold-rolled steel sheet has a room-temperature impact toughness (Charpy absorption energy) of 1.0 to 5.0J (0.05 to 0.35J/cm)2)。
Description
Technical Field
The present invention relates to a method for manufacturing a high-strength low-toughness cold-rolled steel sheet mainly used as a tie bar (nominal tie bar) for a construction panel and also used as a tie bar for various forms, and a high-strength low-toughness cold-rolled steel sheet and a method for manufacturing the same, wherein a hot-rolled material is cold-rolled at a final reduction ratio of 20 to 70% so that the steel sheet has a final thickness of 1.5 to 3.0mmt and a tensile strength of 950MPa or more, and the cold-rolled steel sheet has a room temperature impact toughness (Charpy absorbed energy) of 1.0 to 5.0J (0.05 to 0.35J/cm) based on a thickness of 2.0mmt2)。
Background
The flat tie rods are used as formwork tie rods, also known as nominal wall ties. The flat tie bar is applied to the field of construction, and is a tie member that keeps a certain interval between formworks and finally supports lateral pressure after concrete is poured. The manufacturing process produces a product by cutting and punching a cold rolled material in conformity with the final thickness. Since the required characteristic is to support the lateral pressure, a tensile strength of 950MPa or more is required based on the material of the cold rolled material. In addition, the flat tie bar portion protruding to the outside of the form after construction for different wall thicknesses (intervals between forms) at a construction site should be easily removed with a hammer. Generally, the embedded portion and the protrusion portion can be cut by hitting the protrusion portion of the tie bar once with a hammer, and the fracture surface should also be cut neatly in line. To meet this characteristic, the raw material should have low impact toughness. Due to the unique physical properties required for flat tie rods, the raw materials require unique physical properties of high strength and low toughness rather than the high strength and high toughness required for conventional steels.
Various methods exist for achieving the unique low toughness characteristics of the tie rod, but in the production of hot rolled steel sheets, problems should not occur due to excessively low impact toughness, and smooth production processing without cracking until the final press working is required. Further, the tie rod is a consumable product and a product buried after final construction, and therefore it is required to be able to design/produce at low cost. The characteristics of the flat tie bar requiring such low toughness are not high strength and high toughness required for general steels, and thus there is no specific related art to achieve low toughness.
(Prior Art)
(patent document 1) Korean patent application No. 10-1998-0059176 (application 12/28/1998)
Disclosure of Invention
Technical problem to be solved
Accordingly, the present invention has been made to solve the above-mentioned limitations of the prior art, and an object of the present invention is to provide a high-strength low-toughness cold-rolled steel sheet for a tie rod and a method for manufacturing the same by controlling the composition of steel, a hot rolling process, and a cold rolling process.
Further, the technical problems to be solved by the present invention are not limited to the above-described technical problems, and other technical problems not described may be clearly understood by those skilled in the art through the following descriptions.
Technical scheme
The present invention for achieving the above objects relates to a high-strength low-toughness cold-rolled steel sheet comprising, in wt.%: c: 0.30-0.70%, Mn: 0.2 to 1.0%, Si: 0.005-0.5%, P: 0.005-0.02%, S: 0.01% or less, Al: 0.01-0.1%, Cr: 0.005-0.1% and the balance of iron (Fe) and other inevitable impurities, wherein the steel has a fine structure consisting of 50-95% of pearlite and the balance of ferrite, the average grain size of the ferrite structure is 10-50 μm, the average size of pearlite domains is 10-50 μm, the cold-rolled steel sheet has a thickness of 1.5-3.0 mmt, and the cold-rolled steel sheet has a room-temperature impact toughness (Charpy absorbed energy) satisfying 1.0-5.0J (0.05-0.35J/cm)2)。
The cold-rolled steel sheet can satisfy a yield strength of 700 to 950MPa, a tensile strength of 950 to 1200MPa, and an elongation of 2 to 12%.
Further, the present invention relates to a method for manufacturing a high-strength low-toughness cold-rolled steel sheet, the method comprising the steps of:
preparing a steel slab comprising, in weight%: c: 0.30-0.70%, Mn: 0.2 to 1.0%, Si: 0.005-0.5%, P: 0.005-0.02%, S: 0.01% or less, Al: 0.01-0.1%, Cr: 0.005-0.1% and the balance of iron (Fe) and other inevitable impurities;
a reheating step, wherein the steel billet is heated to 1100-1300 ℃;
carrying out rough rolling on the reheated steel billet at the temperature of 1000-1100 ℃, and then carrying out hot finish rolling at the temperature of 850-950 ℃;
cooling the hot-rolled steel plate at the speed of 10-200 ℃/s, and then rolling at the temperature of 550-750 ℃;
the rolled steel sheet is pickled and then cold-rolled at a reduction ratio of 50 to 70% to manufacture a cold-rolled steel sheet, the cold-rolled steel sheet having a fine structure consisting of 50 to 95% of pearlite and the balance of ferrite, the ferrite structure having an average grain size of 10 to 50 μm, the pearlite domain having an average grain size of 10 to 50 μm, and the cold-rolled steel sheet having a thickness of 1.5 to 3.0 mmt.
The cold-rolled steel sheet can satisfy a yield strength of 700 to 950MPa, a tensile strength of 950 to 1200MPa, an elongation of 2 to 12%, and an elongation of 1.0 to 5.0J (0.05 to 0.35J/cm)2) The normal temperature impact toughness (Charpy energy absorption).
The thickness of the rolled hot rolled steel plate can be 2.5-4.5 mmt.
Advantageous effects
The present invention having the constitution as described above can effectively provide high carbon steel having high strength and low toughness for flat tie rods for buildings and other tie rods by optimizing the composition range and manufacturing process conditions of the steel.
Drawings
FIG. 1 is a photograph of a microstructure of invention example 1 in an example of the present invention.
Best mode for carrying out the invention
The present invention will be explained below.
The high-strength low-toughness cold-rolled steel sheet of the present invention comprises, in weight%: c: 0.30-0.70%, Mn: 0.2 to 1.0%, Si: 0.005-0.5%, P: 0.005-0.02%, S: 0.01% or less, Al: 0.01-0.1%, Cr: 0.005 to 0.1% and the balance of iron (Fe) and other unavoidable impurities, wherein the fine structure of the steel comprises 50 to 95% of pearlite and the balance of ferrite, the average grain size of the ferrite structure is 10 to 50 [ mu ] m, the average grain size of the pearlite domain is 10 to 50 [ mu ] m, the cold-rolled steel sheet has a thickness of 1.5 to 3.0mmt, and the cold-rolled steel sheet has a room-temperature impact toughness (Charpy absorption energy) of 1.0 to 5.0J (0.05 to 0.35J/cm)2)。
That is, the present invention is characterized by providing very low toughness to ensure excellent fracture characteristics of the tie rod. Therefore, the fraction of pearlite is 50 to 95%, the average grain size of the ferrite structure is 10 to 50 μm, and the average grain size of the pearlite domain is 10 to 50 μm, based on the final cold rolled material, so that the sizes of very coarse ferrite grains and pearlite domains are secured, thereby realizing low toughness. Specifically, the thickness of the cold-rolled steel plate is 1.5-3.0 mmt, and the yield strength of 700-950 MPa is metA degree, a tensile strength of 950 to 1200MPa, an elongation of 2 to 12%, and 1.0 to 5.0J (0.05 to 0.35J/cm)2) The normal temperature impact toughness (Charpy energy absorption).
The reasons for limiting the alloy components and the contents thereof in the cold-rolled steel sheet of the present invention will be described below.
Carbon (C): 0.30 to 0.70% by weight
Carbon is an element that affects strength and toughness. When the content of the carbon is less than 0.30 wt%, it is difficult to secure the target strength. On the other hand, when the content of carbon exceeds 0.7 wt%, formability is lowered due to an excessive increase in strength and the formation of cementite. Further, since it is necessary to form a straight, clean fracture surface at the time of fracture, formation of an excessive amount of carburized body adversely affects fracture characteristics. Therefore, the content of carbon is preferably limited to 0.30 to 0.70% by weight.
Manganese (Mn): 0.2 to 1.0% by weight
Manganese is a solid-solution strengthening element, and is added to prevent red hot brittleness of the slab due to strength increase and formation of FeS. In order to achieve this effect, it is necessary to add 0.2 wt% or more of manganese, and when manganese is contained in an amount exceeding 1.0 wt%, center segregation, micro-segregation, and the like become serious, resulting in coarsening of the final carbide. In the steel material for a tie rod of a flat plate, which is important in low cost design, the cost is increased by excessively adding Mn, and therefore, the content of Mn is limited to 0.2 to 1.0 wt%.
Silicon (Si): 0.005 to 0.5% by weight
Silicon has an effect of improving strength by solid solution strengthening. When the silicon content is less than 0.005 wt%, the effect of improving strength is insufficient, and when a large amount of silicon is added, the surface quality is adversely affected due to the increase of red scale defects. Therefore, the content of silicon is preferably limited to 0.005 to 0.5% by weight.
Phosphorus (P): 0.005 to 0.02% by weight
Phosphorus is an element having a strong solid solution strengthening effect. In order to secure strength, it is necessary to add 0.005 wt% or more of phosphorus, and on the other hand, when the content of phosphorus exceeds 0.02 wt%, workability is impaired due to segregation of P, so the lower limit and the upper limit of the content of phosphorus are limited to 0.005 wt% and 0.02 wt%, respectively.
Sulfur (S): 0.01 wt% or less
Sulfur is an element that easily forms non-metallic inclusions and is an impurity that increases the amount of precipitates, and therefore the sulfur content needs to be controlled to a low level. Therefore, the upper limit of the sulfur content is limited to 0.01 wt%, and the lower the sulfur content, the more excellent the moldability, and therefore the lower limit of the sulfur content is not limited.
Aluminum (Al): 0.01 to 0.1% by weight
Aluminum is added primarily for deoxidation and for AlN formation with nitrogen. When the content of aluminum is less than 0.01 wt%, the above-mentioned addition cannot be achieved, and when the content of aluminum is 0.1 wt% or more, strength excessively increases and slab defects occur during continuous casting, so that the content of aluminum is limited to 0.01 to 0.1 wt%.
Chromium (Cr): 0.005 to 0.1% by weight
For the solid solution strengthening effect, 0.005 wt% or more of chromium needs to be added. On the other hand, when more than 0.1 wt% of chromium is added, center segregation is caused and unnecessary inclusions are formed, and the cost is also increased, and therefore, the upper limit of the chromium content is preferably limited to 0.1 wt%.
The cold rolled steel sheet of the present invention is composed of the above components, and the remaining components not described are iron (Fe). Further, impurities that are inevitably mixed in a general manufacturing process cannot be excluded, but this is well known to those skilled in the art, and therefore, will not be specifically described in the present specification.
The cold-rolled steel sheet of the present invention comprises 50 to 95% pearlite and the balance ferrite. Further, the average grain size of the ferrite structure is 10 to 50 μm, and the average pearlite domain size is 10 to 50 μm, so that the sizes of very coarse ferrite grains and pearlite domains can be secured, and a cold-rolled steel sheet having a low toughness and a thickness of 1.5mmt to 3.0mmt can be effectively provided.
The fine structure of the steel of the cold-rolled steel sheet proposed in the present invention is a mixed structure of pearlite and ferrite. The pearlite has higher strength than ferrite but insufficient toughness, and thus, the formation and propagation of cracks are much easier than ferrite when external impact is applied. Therefore, in the present invention, the low impact toughness of 1 to 5J can be ensured only when 50 to 95% of pearlite is ensured in the microstructure of the final cold-rolled steel sheet. Further, when the average size of the pearlite domain is5 to 40 μm and the average size of the grains of the ferrite structure is as large as 10 to 50 μm, it is more advantageous to realize low toughness.
That is, the steel sheet of the present invention having the above-mentioned fine structure of steel can satisfy the yield strength of 700 to 950MPa, the tensile strength of 950 to 1200MPa, the elongation of 2 to 12%, and the elongation of 1.0 to 5.0J (0.05 to 0.35J/cm)2) The normal temperature impact toughness (Charpy energy absorption).
Next, a method for producing a high-strength low-toughness cold-rolled steel sheet according to the present invention will be described.
The method for manufacturing a high-strength low-toughness cold-rolled steel sheet according to the present invention comprises the steps of: preparing a billet having the composition as described above; a reheating step, wherein the steel billet is heated to 1100-1300 ℃; carrying out rough rolling on the reheated steel billet at the temperature of 1000-1100 ℃, and then carrying out hot finish rolling at the temperature of 850-950 ℃; cooling the hot-rolled steel plate at the speed of 10-200 ℃/s, and then rolling at the temperature of 550-750 ℃; the rolled steel sheet is pickled and then cold-rolled at a reduction ratio of 50 to 70% to manufacture a cold-rolled steel sheet, the cold-rolled steel sheet having a fine structure consisting of 50 to 95% of pearlite and the balance of ferrite, the ferrite structure having an average grain size of 10 to 50 μm, the pearlite domain having an average grain size of 10 to 50 μm, and the cold-rolled steel sheet having a thickness of 1.5 to 3.0 mmt.
Reheating and hot rolling of steel slabs
In the present invention, the billet having the alloy composition as described above is first reheated, and in this case, the reheating temperature is preferably between 1100 ℃ and 1300 ℃ which is a normal level. When the reheating temperature is less than 1100 ℃, it is difficult to ensure a sufficient temperature for the slab to pass through a desired slab material, and when the reheating temperature exceeds 1300 ℃, abnormal austenite growth and surface defects due to scale occur, so the reheating temperature of the slab is preferably set to 1100 to 1300 ℃.
Next, in the present invention, the slab reheated as described above is hot-rolled. Namely, a conventional rough rolling process is performed at 1000 to 1100 ℃, and then a hot finish rolling is performed. In this case, in the present invention, the finish hot rolling is preferably performed at 850 to 950 ℃, and more preferably at 900 to 950 ℃. At temperatures above 900 ℃, austenite grains grow, coarsening the size of the final ferrite grains and pearlite domains. The reason why the finish hot rolling needs to be performed at or above the Ar3 transformation point is to prevent the two-phase zone rolling because pro-eutectoid ferrite having no carbide is generated when the two-phase zone rolling is performed. In addition, when the finish rolling temperature is below 850 ℃, a large rolling load is generated, so that the subsequent process is difficult, and when the finish rolling temperature is above 950 ℃, the surface of the steel plate has oxide skin defects, so that the hot finish rolling temperature is limited to 850-950 ℃.
Cooling and winding step
The hot-rolled steel sheet as described above is cooled. In this case, the cooling rate is controlled to be in the range of 10 ℃/s to 200 ℃/s. By performing cooling at the above cooling rate to be maintained longer on a Run-Out Table (ROT), pearlite transformation and domain size and ferrite grain size can be maximized. When the cooling rate is less than 10 ℃/s, the time that can be held on the ROT is insufficient, and therefore it is difficult to secure a pearlite fraction of 50% or more, and when the cooling rate exceeds 200 ℃/s, uniform cooling is difficult due to temperature unevenness in the width direction, and therefore the coil shape becomes very poor. Therefore, the cooling rate is preferably limited to 10 to 200 ℃/s.
Then, the cooled hot-rolled steel sheet is wound at 550 to 750 ℃, and more preferably, a high winding temperature of about 700 ℃ is maintained. The reason why the rolling temperature is limited to 550 to 750 ℃ is that the temperature range is a range in which the pearlite domain size can be maximized. Specifically, this is because when the winding temperature is less than 550 ℃, a bainite or martensite structure, which is a low-temperature transformation structure, occurs, and thus uniform pearlite cannot be obtained, and on the other hand, when the winding temperature exceeds 750 ℃, surface defects such as scale and the like may occur seriously.
Pickling and Cold Rolling step
And pickling the coiled hot-rolled coil. In the pickling, the steel sheet is naturally cooled to a temperature in the range of normal temperature to 200 ℃, and then pickled to remove the scale on the surface layer. At this time, when the pickling temperature of the hot-rolled steel sheet exceeds 200 ℃, the surface layer portion of the hot-rolled steel sheet is excessively pickled, resulting in deterioration of roughness of the surface layer portion, and therefore, the pickling temperature is limited to room temperature to 200 ℃.
And cold rolling the pickled hot-rolled steel sheet at a reduction ratio of 50 to 70%. Since the tensile strength of a cold-rolled steel sheet is proportional to the reduction ratio, when the reduction ratio is high, the tensile strength of the final cold-rolled steel sheet can be ensured to be 950MPa or more. Therefore, in order to obtain a tensile strength of 950MPa or more, a cold rolling reduction of 50% or more is required. However, since an excessively large reduction increases the load on facilities and makes production impossible, the upper limit of the reduction is set to 70% in consideration of rolling load and production efficiency. In the cold rolled material, the impact toughness has a maximum value at a specific reduction ratio, and shows a characteristic that the impact toughness is reduced at a low reduction ratio or a high reduction ratio. In the 0.3 to 0.7C steel grades, the maximum value of the impact toughness is usually in the vicinity of a cold rolling reduction of about 40%, and the impact toughness is again reduced when the steel grade has a low reduction of 30% or a high reduction of 70%. This is a factor related to the formation of shear-lips and is a common feature of cold rolled materials. In the present invention, it is necessary to ensure high strength and low toughness, and therefore a reduction ratio of 50% or more is advantageous. Preferably, a high compression ratio of 50 to 70% is used in terms of securing strength and low toughness.
In the cold-rolled steel sheet produced by the cold rolling, the microstructure of the steel is composed of 50 to 95% of pearlite and the balance of ferrite. Further, the average grain size of the ferrite structure is 10 to 50 μm, and the average size of the pearlite domain satisfies the range of 10 to 50 μm, so that the ferrite structure has low toughness by securing the sizes of very coarse ferrite grains and pearlite domains.
That is, the cold-rolled steel sheet of the present invention having the above-mentioned fine structure of steel can satisfy the yield strength of 700 to 950MPa, the tensile strength of 950 to 1200MPa, the elongation of 2 to 12%, and the elongation of 1.0 to 5.0J (0.05 to 0.35J/cm)2) The normal temperature impact toughness (Charpy energy absorption).
Detailed Description
The present invention will be described in more detail below with reference to examples.
(examples)
[ Table 1]
| Steel grade | C | Mn | Si | P | S | Al | Cr | Remarks for note |
| 1 | 0.21 | 0.64 | 0.16 | 0.011 | 0.005 | 0.06 | 0.05 | Comparative steel |
| 2 | 0.50 | 0.15 | 0.20 | 0.013 | 0.004 | 0.04 | 0.06 | Comparative steel |
| 3 | 0.82 | 0.59 | 0.23 | 0.012 | 0.004 | 0.03 | 0.07 | Comparative steel |
| 4 | 0.55 | 0.70 | 0.10 | 0.012 | 0.005 | 0.03 | 0.05 | Invention steel |
| 5 | 0.25 | 0.15 | 0.15 | 0.011 | 0.004 | 0.04 | 0.06 | Comparative steel |
| 6 | 0.45 | 1.15 | 0.19 | 0.012 | 0.005 | 0.03 | 0.07 | Comparative steel |
| 7 | 0.82 | 1.20 | 0.21 | 0.011 | 0.004 | 0.03 | 0.05 | Comparative steel |
The content unit of each constituent element in table 1 is weight%.
The thickness of the hot rolled material when the slabs satisfying the alloy composition system described in table 1 were reheated at 1200 ℃ for 2 hours and then hot rolled under the conditions shown in table 2 below is also shown in table 2 below. As shown in table 2, the steel sheet is subjected to a finish hot rolling, cooled to a rolling temperature (CT) at a cooling rate of 20 to 50 ℃/s, and then rolled at the rolling temperature (CT). Thereafter, the rolled hot rolled coil was pickled and then cold rolled under the conditions shown in table 2.
[ Table 2]
The fine structure of the cold-rolled steel sheet test piece manufactured as above was observed, and the average ferrite grain size (μm), pearlite fraction (%), and the size of the pearlite domain (μm) were measured, and the results thereof are shown in table 3 below. In addition, the Yield Strength (YS), Tensile Strength (TS), and elongation (El) of the manufactured cold-rolled steel sheets were measured, and the results thereof are shown in table 3 below. In the present example, the tensile strength was a value obtained by collecting and performing a tensile test according to JIS5 standard with reference to a rolling direction perpendicular to a rolled sheet material, and the impact toughness was a value measured by converting a V-notch Charpy impact test (V-notch Charpy impact test) at normal temperature with reference to a thickness of 1.9 mmt.
[ Table 3]
As shown in tables 1 to 3, steel type 1 is a steel type having a C content smaller than the composition range of the present invention. The conditions of FDT, CT, cold rolling reduction and the like of comparative examples 1 to 2 manufactured with the component system of Steel grade 1 satisfy the range of the present invention, but the carbon content is outside the allowable range of the present invention, and the tensile strength of the final material is not good, 893MPa and 910MPa, respectively. Further, comparative examples 1 to 2 had impact toughness of 22J and 19J, respectively, and did not satisfy the allowable range of 1.0 to 5.0J, because sufficient strength could not be secured due to a low carbon content, and the lower the carbon, the more excellent the toughness, and thus it was difficult to achieve low toughness.
Steel grade 2 is a steel grade having a Mn content less than the composition range of the present invention. The conditions of FDT, CT and cold rolling reduction of comparative examples 3 to 4 produced by the component system of steel type 2 satisfy the range of the present invention, but the Mn content is outside the allowable range of the present invention, and the tensile strength of the final material is not good, being 920MPa and 931MPa, respectively. This is because the Mn content is low and sufficient strength cannot be ensured.
Steel grade 3 is a steel grade having a C content exceeding the composition range of the present invention. The conditions of FDT, CT and cold rolling reduction of comparative examples 5 to 6 manufactured by using the component system of steel grade 3 satisfy the range of the invention, but the carbon content exceeds the allowable range of the invention, the yield strength of the final material is 980MPa and 976MPa respectively, and the allowable range of the invention is not satisfied 750 to 950 MPa. Further, the tensile strengths of comparative examples 5 to 6 were 1240MPa and 1283MPa, respectively, which were outside the allowable range of 950 to 1200MPa, because the strength was excessively increased by adding too much carbon.
Steel grade 4 is a steel grade satisfying the composition range of the present invention. The FDT, CT, and cold rolling reduction ratios of comparative examples 7 to 10 having the component system of steel type 4 do not satisfy the conditions of the present invention, and thus do not satisfy the finally required material. Specifically, the FDT of comparative example 7 is 830 ℃, and outside the range of 850 to 950 ℃ in the present invention, the impact toughness of the final material is too high, 21J, and thus the low toughness cannot be achieved. The CT of comparative example 8 is 520 ℃ and the impact toughness of the final material is too high to be 18J outside the range of 550 to 750 ℃ in the present invention, so that the low toughness cannot be realized. The cold rolling reduction of comparative example 9 was 16%, and the tensile strength of the final material was 915MPa, which was not within the allowable range of 950 to 1200MPa, under the conditions of the present invention of 50 to 70%. In comparative example 10, the cold rolling reduction was 76%, and the final material, except for the conditions of the present invention of 50 to 70%, had a yield strength of 1030MPa and did not satisfy the allowable range of yield strength of 700 to 950MPa, and had a tensile strength of 1278MPa and did not satisfy the allowable range of 950 to 1200 MPa.
The invention examples 1 to 3 satisfy the hot rolling condition and the cold rolling condition proposed in the present invention, and thus it can be seen that high-strength low-toughness high-carbon steel satisfying the proposed final material requirements can be produced, and fig. 1 shows a final microstructure photograph of the steel grade corresponding to the invention example 1.
Further, steel type 5 is a case where the C and Mn contents are less than the range of the present invention, steel type 6 is a case where the C content satisfies the range of the present invention but the Mn content exceeds the range of the present invention, and steel type 7 is a case where both the C and Mn contents exceed the target content ranges. In comparative examples 11 to 13, which were produced according to the conditions of the production process (hot rolling conditions and cold rolling conditions) of the present invention using steel grades 5 to 7 having steel compositions outside the range of the present invention, respectively, it was found that the strength/toughness targets required in the present invention were not satisfied.
In addition, the value of the room temperature impact toughness (charpy absorbed energy) required for the final product in the present invention is on the level of 1 to 5J, and when the value of the room temperature impact toughness exceeds 5J, the fracture/cutting characteristics become poor. Therefore, in the present invention, the range of the room temperature impact toughness value 1 to 5J, which is superior in fracture/cutting characteristics to the room temperature impact toughness value exceeding 5J, is referred to as low temperature toughness.
In general, when a steel sheet is cut by hammering, the cut surface should not be uneven but should be cut in a straight line for good fracture characteristics of the steel sheet. Therefore, in the present invention, the fracture characteristic means that the steel sheet can be cut by hammering once, and the cut surface is cut into a straight shape as cut with a knife, which is a characteristic obtained when the impact toughness value is between 1 to 5J. If the impact toughness value is higher than 5J, cutting by one-tap is difficult, and the fracture surface increases due to fracture ductility, so that clean cutting cannot be performed.
As described above, although the preferred embodiments of the present invention have been described in the detailed description of the present invention, those skilled in the art can make various modifications without departing from the scope of the present invention. Therefore, the scope of the claims of the present invention should not be limited to the above-described embodiments, but should be defined by the appended claims and equivalents thereof.
Claims (4)
1. A high-strength low-toughness cold-rolled steel sheet, comprising, in wt.%: c: 0.30-0.70%, Mn: 0.2 to 1.0%, Si: 0.005-0.5%, P: 0.005-0.02%, S: 0.01% or less, Al: 0.01-0.1%, Cr: 0.005-0.1% and the balance of iron (Fe) and other unavoidable impurities, and the fine structure of the steel is composed of 50-95% of pearlite and the balance of ferriteThe average grain size of the structure is 10-50 μm, the average size of the pearlite domain is 10-50 μm, the cold-rolled steel sheet has a thickness of 1.5-3.0 mmt, and the impact toughness (Charpy absorption energy) at normal temperature satisfies 1.0-5.0J (0.05-0.35J/cm)2)。
2. A high-strength low-toughness cold-rolled steel sheet as claimed in claim 1, wherein said cold-rolled steel sheet satisfies yield strength of 700 to 950MPa, tensile strength of 950 to 1200MPa and elongation of 2 to 12%.
3. A method for manufacturing a high-strength low-toughness cold-rolled steel sheet, comprising the steps of:
preparing a steel slab comprising, in weight%: c: 0.30-0.70%, Mn: 0.2 to 1.0%, Si: 0.005-0.5%, P: 0.005-0.02%, S: 0.01% or less, Al: 0.01-0.1%, Cr: 0.005-0.1% and the balance of iron (Fe) and other inevitable impurities;
a reheating step, wherein the steel billet is heated to 1100-1300 ℃;
carrying out rough rolling on the reheated steel billet at the temperature of 1000-1100 ℃, and then carrying out hot finish rolling at the temperature of 850-950 ℃;
cooling the hot-rolled steel plate at the speed of 10-200 ℃/s, and then rolling at the temperature of 550-750 ℃;
the rolled steel sheet is pickled and then cold-rolled at a reduction ratio of 30 to 70% to manufacture a cold-rolled steel sheet having a fine structure consisting of 50 to 95% of pearlite and the balance of ferrite, the average size of grains of the ferrite structure is 10 to 50 μm, the average size of pearlite domains is 10 to 50 μm, and the cold-rolled steel sheet has a thickness of 1.5 to 3.0 mmt.
4. The method of manufacturing a high-strength low-toughness cold-rolled steel sheet as claimed in claim 3, wherein said cold-rolled steel sheet satisfies the yield strength of 700 to 950MPa, the tensile strength of 950 to 1200MPa, and the elongation of 2 to 12%A ratio of 1.0 to 5.0J (0.05 to 0.35J/cm)2) The normal temperature impact toughness (Charpy energy absorption).
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| KR1020170147450A KR102010053B1 (en) | 2017-11-07 | 2017-11-07 | High strength and low toughness cold-rolled steel sheet having good fracture characteristics, method for manufacturing same |
| PCT/KR2018/012596 WO2019093689A1 (en) | 2017-11-07 | 2018-10-24 | High-strength, low-toughness cold-rolled steel sheet having excellent fracture properties, and method for producing same |
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| CN114540700A (en) * | 2020-11-24 | 2022-05-27 | 上海梅山钢铁股份有限公司 | Cold-rolled steel plate for precision stamping chain saw guide plate with tensile strength of 1050MPa |
Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1598032A (en) * | 2003-08-28 | 2005-03-23 | 杰富意钢铁株式会社 | High-carbon hot-rolled steel plate,cold-rolled steel plate and making method thereof |
| CN101410544A (en) * | 2006-03-28 | 2009-04-15 | 杰富意钢铁株式会社 | Hot-rolled ultra soft high-carbon steel plate and process for production thereof |
| JP2011219845A (en) * | 2010-04-14 | 2011-11-04 | Nippon Steel Corp | Sn-Zn PLATING HIGH-STRENGTH STEEL SHEET FOR PRESS WORKING EXCELLENT IN CORROSION RESISTANCE, AND MANUFACTURING METHOD THEREFOR |
| KR20130110634A (en) * | 2012-03-29 | 2013-10-10 | 현대제철 주식회사 | High strength steel sheet and method for manufacturing the same |
| CN103509997A (en) * | 2013-09-25 | 2014-01-15 | 马钢(集团)控股有限公司 | 440MPa-class cold-rolled high-intensity automobile structural steel and manufacturing method thereof |
| CN104313483A (en) * | 2014-10-31 | 2015-01-28 | 武汉钢铁(集团)公司 | High-carbon cold-rolled automobile diaphragm spring steel and production method thereof |
| EP2975150A1 (en) * | 2013-03-14 | 2016-01-20 | Nippon Steel & Sumitomo Metal Corporation | High strength steel plate with excellent delayed destruction resistance characteristics and low temperature toughness, and high strength member manufactured using same |
| CN106062231A (en) * | 2014-03-07 | 2016-10-26 | 新日铁住金株式会社 | Medium-/high-carbon steel sheet and method for manufacturing same |
| CN106119495A (en) * | 2016-08-19 | 2016-11-16 | 武汉钢铁股份有限公司 | A kind of manufacture method of cold rolling medium high carbon structural steel |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR100218693B1 (en) | 1996-12-31 | 1999-09-01 | 유기범 | Subscriber module normality testing method of a keyphone system |
| KR100370474B1 (en) * | 1998-12-28 | 2003-03-17 | 주식회사 포스코 | Manufacturing method of hot rolled steel sheet for high strength construction scaffold |
| JP4995109B2 (en) * | 2008-02-07 | 2012-08-08 | 新日本製鐵株式会社 | High-strength cold-rolled steel sheet excellent in workability and impact resistance and method for producing the same |
| KR101344651B1 (en) * | 2011-10-28 | 2013-12-26 | 현대제철 주식회사 | Manufacturing method of steel-sheet |
| KR101412311B1 (en) * | 2012-06-28 | 2014-06-25 | 현대제철 주식회사 | Method for manufacturing high strength cold rolled steel sheet |
-
2017
- 2017-11-07 KR KR1020170147450A patent/KR102010053B1/en active IP Right Grant
-
2018
- 2018-10-24 CN CN201880072180.0A patent/CN111315901B/en active Active
- 2018-10-24 WO PCT/KR2018/012596 patent/WO2019093689A1/en active Application Filing
Patent Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1598032A (en) * | 2003-08-28 | 2005-03-23 | 杰富意钢铁株式会社 | High-carbon hot-rolled steel plate,cold-rolled steel plate and making method thereof |
| CN101410544A (en) * | 2006-03-28 | 2009-04-15 | 杰富意钢铁株式会社 | Hot-rolled ultra soft high-carbon steel plate and process for production thereof |
| JP2011219845A (en) * | 2010-04-14 | 2011-11-04 | Nippon Steel Corp | Sn-Zn PLATING HIGH-STRENGTH STEEL SHEET FOR PRESS WORKING EXCELLENT IN CORROSION RESISTANCE, AND MANUFACTURING METHOD THEREFOR |
| KR20130110634A (en) * | 2012-03-29 | 2013-10-10 | 현대제철 주식회사 | High strength steel sheet and method for manufacturing the same |
| EP2975150A1 (en) * | 2013-03-14 | 2016-01-20 | Nippon Steel & Sumitomo Metal Corporation | High strength steel plate with excellent delayed destruction resistance characteristics and low temperature toughness, and high strength member manufactured using same |
| CN103509997A (en) * | 2013-09-25 | 2014-01-15 | 马钢(集团)控股有限公司 | 440MPa-class cold-rolled high-intensity automobile structural steel and manufacturing method thereof |
| CN106062231A (en) * | 2014-03-07 | 2016-10-26 | 新日铁住金株式会社 | Medium-/high-carbon steel sheet and method for manufacturing same |
| CN104313483A (en) * | 2014-10-31 | 2015-01-28 | 武汉钢铁(集团)公司 | High-carbon cold-rolled automobile diaphragm spring steel and production method thereof |
| CN106119495A (en) * | 2016-08-19 | 2016-11-16 | 武汉钢铁股份有限公司 | A kind of manufacture method of cold rolling medium high carbon structural steel |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114540700A (en) * | 2020-11-24 | 2022-05-27 | 上海梅山钢铁股份有限公司 | Cold-rolled steel plate for precision stamping chain saw guide plate with tensile strength of 1050MPa |
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| KR20190051609A (en) | 2019-05-15 |
| KR102010053B1 (en) | 2019-08-12 |
| CN111315901B (en) | 2022-02-25 |
| WO2019093689A1 (en) | 2019-05-16 |
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