KR20140042107A - Hot-rolled steel sheet and method of manufacturing the same - Google Patents

Hot-rolled steel sheet and method of manufacturing the same Download PDF

Info

Publication number
KR20140042107A
KR20140042107A KR1020120108423A KR20120108423A KR20140042107A KR 20140042107 A KR20140042107 A KR 20140042107A KR 1020120108423 A KR1020120108423 A KR 1020120108423A KR 20120108423 A KR20120108423 A KR 20120108423A KR 20140042107 A KR20140042107 A KR 20140042107A
Authority
KR
South Korea
Prior art keywords
steel sheet
rolled steel
less
hot
hot rolled
Prior art date
Application number
KR1020120108423A
Other languages
Korean (ko)
Inventor
김형래
박철봉
한성경
Original Assignee
현대제철 주식회사
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 현대제철 주식회사 filed Critical 현대제철 주식회사
Priority to KR1020120108423A priority Critical patent/KR20140042107A/en
Publication of KR20140042107A publication Critical patent/KR20140042107A/en

Links

Images

Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium

Abstract

Disclosed is a hot rolled steel sheet for an oil pipe, which has excellent corrosion resistance and satisfies the API (American Petroleum Institute) 5L X70 standard through the control of alloy components and process conditions, and a method of manufacturing the same.
Method for producing a hot rolled steel sheet according to the present invention by weight, carbon (C): 0.03 ~ 0.06%, silicon (Si): 0.1 ~ 0.2%, manganese (Mn): 1.1 ~ 1.4%, phosphorus (P): 0.01% Sulfur (S): 0.001% or less, Aluminum (Al): 0.02 to 0.05%, Vanadium (V): 0.04 to 0.1%, Niobium (Nb): 0.08 to 0.1%, Titanium (Ti): 0.01 to 0.03% , Molybdenum (Mo): 0.1 to 0.2%, Chromium (Cr): 0.1 to 0.3%, Copper (Cu): 0.2 to 0.35%, Nickel (Ni): 0.1 to 0.3%, Calcium (Ca): 0.001 to 0.004% Reheating the slab plate material consisting of nitrogen (N): 0.006% or less and the remaining iron (Fe) and unavoidable impurities under the slab reheating temperature (SRT) 1150 ~ 1250 ℃; Hot rolling the reheated sheet to a finish rolling temperature (FDT) of 750 to 850 ° C .; And cooling and winding the hot rolled sheet to a winding temperature (CT) of 550 to 620 ° C.

Description

HOT ROLLED STEEL SHEET AND METHOD OF MANUFACTURING THE SAME

The present invention relates to a hot-rolled steel sheet and a method for manufacturing the same, and more particularly, to a pipeline for manufacturing an oil pipe that satisfies the API (American Petroleum Institute) 5L X70 standard having excellent corrosion resistance through controlling alloy components and controlling process conditions, and manufacturing the same. It is about a method.

API (American Petroleum Institute) steel pipes used for oil transportation are used in various ways after heat-combusting materials and heat treatment depending on the purpose of use.The specifications are API 5L AB, API 5L X42, API 5L X46, API 5L X52 , API 5L X56, API 5L X60, API 5L X65, API 5L X70, API 5L X80 and the like.

In recent years, due to global resource depletion, oil and gas mining and transportation work in harsh environments where steel pipes can be corroded by hydrogen sulfide (H 2 S), such as deep seabeds, is increasing, resulting in the construction of large pipelines. have. Accordingly, there is an increasing demand for materials having high strength and corrosion resistance compared to the conventional ones in order to change the use environment or reduce construction costs.

Related prior art documents include Korean Patent Laid-Open Publication No. 10-0770572 (August 26, 2007), which discloses a high carbon steel sheet having excellent hardening heat treatment characteristics and a method of manufacturing the same.

An object of the present invention is to provide a method for manufacturing a hot rolled steel sheet that satisfies the API (American Petroleum Institute) 5L X70 (PSL2) standard and has excellent corrosion resistance through alloy composition control and process condition control.

Another object of the present invention is manufactured by the above method, while satisfying the API 5L X70 specification having a tensile strength (TS): 600MPa or more and yield strength (YS): 555MPa CLR (Crack Length Ratio): 10% or less, CTR ( It is to provide a hot rolled steel sheet having a crack thickness ratio of 4% or less and a crack sensitivity ratio of 2% or less.

Hot rolled steel sheet manufacturing method according to an embodiment of the present invention for achieving the above object by weight, carbon (C): 0.03 ~ 0.06%, silicon (Si): 0.1 ~ 0.2%, manganese (Mn): 1.1 ~ 1.4 %, Phosphorus (P): 0.01% or less, sulfur (S): 0.001% or less, aluminum (Al): 0.02-0.05%, vanadium (V): 0.04-0.1%, niobium (Nb): 0.08-0.1%, Titanium (Ti): 0.01 to 0.03%, Molybdenum (Mo): 0.1 to 0.2%, Chromium (Cr): 0.1 to 0.3%, Copper (Cu): 0.2 to 0.35%, Nickel (Ni): 0.1 to 0.3%, Reheating the slab plate consisting of calcium (Ca): 0.001 ~ 0.004%, nitrogen (N): 0.006% or less and the remaining iron (Fe) and unavoidable impurities at the slab reheating temperature (SRT) 1150 ~ 1250 ℃; Hot rolling the reheated sheet to a finish rolling temperature (FDT) of 750 to 850 ° C .; And cooling and winding the hot rolled sheet to a winding temperature (CT) of 550 to 620 ° C.

Here, the cooling may be performed at a rate of approximately 5 ~ 100 ℃ / sec.

Hot-rolled steel sheet according to an embodiment of the present invention for achieving the other object by weight, carbon (C): 0.03 ~ 0.06%, silicon (Si): 0.1 ~ 0.2%, manganese (Mn): 1.1 ~ 1.4% , Phosphorus (P): 0.01% or less, sulfur (S): 0.001% or less, aluminum (Al): 0.02 to 0.05%, vanadium (V): 0.04 to 0.1%, niobium (Nb): 0.08 to 0.1%, titanium (Ti): 0.01 to 0.03%, molybdenum (Mo): 0.1 to 0.2%, chromium (Cr): 0.1 to 0.3%, copper (Cu): 0.2 to 0.35%, nickel (Ni): 0.1 to 0.3%, calcium (Ca): 0.001 ~ 0.004%, Nitrogen (N): 0.006% or less and the remaining iron (Fe) and inevitable impurities, CLR (Crack Length Ratio): 10% or less, CTR (Crack Thickness Ratio): 4% And has a crack sensitivity ratio (CSR) of 2% or less, and a tensile strength (TS) of 600 MPa or more and a yield strength (YS) of 555 MPa.

Hot rolled steel sheet and a method of manufacturing the same according to the present invention through the adjustment of the alloy composition and process conditions control, CLR (Crack Length Ratio): 10% or less, CTR (Crack Thickness Ratio): 4% or less and CSR (Crack Sensitivity Ratio): It exhibits 2% or less and excellent corrosion resistance, and satisfies API (American Petroleum Institute) 5L X70 standard having tensile strength (TS): 600 MPa or more and yield strength (YS): 555 MPa.

Accordingly, the hot rolled steel sheet according to the present invention is suitable for use as an oil pipe in a corrosive environment due to hydrogen sulfide (H 2 S), such as a deep sea bottom.

1 is a process flowchart showing a method for manufacturing a hot rolled steel sheet according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a hot-rolled steel sheet according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Hot-rolled steel sheet

Hot rolled steel sheet according to the present invention has a tensile strength (TS): 600 MPa or more while having a crack length ratio (CLR) of 10% or less, a crack thickness ratio (CTR) of 4% or less and a crack sensitivity ratio (CSR) of 2% or less And yield strength (YS): aims to satisfy the API (American Petroleum Institute) 5L X70 specification with 555 MPa.

To this end, the hot rolled steel sheet according to the present invention in weight%, carbon (C): 0.03 ~ 0.06%, silicon (Si): 0.1 ~ 0.2%, manganese (Mn): 1.1 ~ 1.4%, phosphorus (P): 0.01 % Or less, sulfur (S): 0.001% or less, aluminum (Al): 0.02 to 0.05%, vanadium (V): 0.04 to 0.1%, niobium (Nb): 0.08 to 0.1%, titanium (Ti): 0.01 to 0.03 %, Molybdenum (Mo): 0.1 to 0.2%, Chromium (Cr): 0.1 to 0.3%, Copper (Cu): 0.2 to 0.35%, Nickel (Ni): 0.1 to 0.3%, Calcium (Ca): 0.001 to 0.004 %, Nitrogen (N): 0.006% or less and may be composed of the remaining iron (Fe) and inevitable impurities.

Hereinafter, the role and content of each component included in the hot-rolled steel sheet according to the present invention will be described.

Carbon (C)

Carbon (C) is added to secure the strength and microstructure control, needle-like ferrite having a carbide free lath (Carbide free lath) is possible when forming a low-temperature structure to have a sufficient strength even in the aftermath.

Carbon (C) is preferably added in an amount ratio of 0.03 to 0.06% by weight of the total weight of the hot rolled steel sheet according to the present invention. When the content of carbon (C) is less than 0.03% by weight of the total weight of the hot rolled steel sheet, it may be difficult to secure sufficient strength. On the contrary, when the content of carbon (C) exceeds 0.06% by weight of the total weight of the hot rolled steel sheet, the corrosion resistance may be reduced due to the formation of pearlite by carbon (C).

manganese( Mn )

Manganese (Mn) is a solid solution strengthening element, which improves the hardenability of steel and contributes to securing strength. In addition, as an austenite stabilizing element, retarding pearlite transformation contributes to grain refinement of ferrite.

Manganese (Mn) is preferably added in an amount of 1.1 to 1.4% by weight of the total weight of the hot rolled steel sheet according to the present invention. If the content of manganese (Mn) is less than 1.1% by weight of the total weight of the hot-rolled steel sheet can not exhibit a solid solution strengthening effect properly. On the contrary, when the content of manganese (Mn) exceeds 1.4% by weight of the total weight of the hot rolled steel sheet, not only the weldability is greatly reduced, but also the corrosion resistance of the steel sheet is greatly reduced by the generation of MnS inclusions and the occurrence of center segregation. There is a problem.

silicon( Si )

Silicon (Si) is added together with aluminum (Al) as a deoxidizer to remove oxygen in the steel in the steelmaking process. This is because when the electric resistance welding (ERW) for manufacturing steel pipes, the ratio of Mn / Si falls within a certain range to significantly reduce the occurrence of weld cracking. Silicon (Si) also has a solid solution strengthening effect.

Silicon (Si) is preferably added in a content ratio of 0.1 to 0.2% by weight of the total weight of the hot rolled steel sheet according to the present invention. When the content of silicon (Si) is less than 0.1% by weight of the total weight of the hot rolled steel sheet, the silicon addition effect may not be properly exhibited. On the contrary, the content of silicon (Si) exceeds 0.2% by weight of the total weight of the hot rolled steel sheet, thereby reducing the weldability of the steel, and creating a red scale during the reheating process during hot rolling and hot rolling. It can cause problems with quality. In addition, the plating property may be impaired after welding.

In particular, Al-Si complex deoxidation is performed by adding silicon to control the properties of manganese oxide and silicon oxide due to the characteristics of the hot rolled steel sheet according to the present invention, in which manganese (Mn) of 1.2 wt% or more of the total weight of the hot rolled steel sheet is added.

Niobium ( Nb )

Niobium (Nb) contributes to the improvement of strength of the steel sheet through precipitation of carbonitride precipitates in steel or solid solution strengthening in iron (Fe). In particular, niobium (Nb) improves low temperature toughness by miniaturizing grains of the final microstructure by suppressing recrystallization during rolling.

Niobium (Nb) is preferably added in an amount ratio of 0.08 to 0.1% by weight of the total weight of the hot rolled steel sheet according to the present invention. This is to increase the carbon solubility in austenite by reducing the content of carbon (C) in the hot-rolled steel sheet to increase the precipitation strengthening effect by the addition of niobium (Nb). When the content of niobium (Nb) is less than 0.08% by weight of the total weight of the hot rolled steel sheet, the addition effect may not be properly exhibited. On the contrary, when the content of niobium (Nb) exceeds 0.1 wt% of the total weight of the hot rolled steel sheet, the precipitation strengthening effect is saturated.

Vanadium (V)

Vanadium (V), like niobium (Nb), contributes to improving the strength of the steel sheet through precipitation of carbonitride precipitates in steel or solid solution strengthening in iron (Fe).

Vanadium (V) is preferably added in an amount ratio of 0.01 to 0.06% by weight of the total weight of the hot-rolled steel sheet according to the present invention in order to secure high strength through the precipitation strengthening effect during the winding. If the content of vanadium (V) is less than 0.01% by weight of the total weight of the hot rolled steel sheet, the addition effect may not be properly exhibited. On the contrary, when the content of vanadium (V) exceeds 0.06% by weight of the total weight of the hot rolled steel sheet, the precipitation strengthening effect is saturated.

titanium( Ti )

Titanium (Ti) prevents austenite grain growth during welding by producing Ti (C, N) precipitates having high temperature stability, thereby minimizing the weld structure and improving the toughness and strength of the hot rolled product.

Titanium (Ti) is preferably added in an amount of 0.01 to 0.03% by weight of the total weight of the hot rolled steel sheet according to the present invention. If the content of titanium (Ti) is less than 0.01% by weight of the total weight of the hot rolled steel sheet, the addition effect may not be properly exhibited. On the contrary, when a large amount of titanium (Ti) exceeds 0.03% by weight of the total weight of the hot rolled steel sheet, coarse precipitates may be generated to reduce corrosion resistance of the steel.

molybdenum( Mo )

Molybdenum (Mo) is a substituted element, contributes to the strength of the hot rolled steel sheet through solid solution strengthening. Molybdenum (Mo) also improves the hardenability of the steel.

Molybdenum (Mo) is preferably added in an amount of 0.1 to 0.2% by weight of the total weight of the hot rolled steel sheet according to the present invention. When the content of molybdenum (Mo) is less than 0.1% by weight of the total weight of the hot rolled steel sheet, the addition effect may not be properly exhibited. On the contrary, when the content of molybdenum (Mo) exceeds 0.2% by weight of the total weight of the hot rolled steel sheet, there is a problem in that the manufacturing cost is increased without any further effect.

nickel( Ni )

Nickel (Ni) is a substitutional element like molybdenum (Mo), and contributes to the strength improvement of hot rolled steel sheet through solid solution strengthening. Nickel (Ni) also improves the hardenability of the steel.

Nickel (Ni) is preferably added in a content ratio of 0.1 to 0.3% by weight of the total weight of the hot rolled steel sheet according to the present invention. When the content of nickel (Ni) is less than 0.1% by weight of the total weight of the hot rolled steel sheet, the addition effect may not be properly exhibited. On the contrary, when a large amount of nickel (Ni) exceeds 0.3 wt% of the total weight of the hot rolled steel sheet, there is a problem in that the manufacturing cost is increased without any further effect.

chrome( Cr )

Chromium (Cr) is an effective element added to secure strength. In addition, chromium (Cr) serves to suppress the central segregation by increasing the diffusion of manganese (Mn) in the slab manufacturing.

Chromium (Cr) is preferably added in an amount of 0.1 to 0.3% by weight of the total weight of the hot rolled steel sheet according to the present invention. When the content of chromium (Cr) is less than 0.1% by weight of the total weight of the hot-rolled steel sheet, the effect of addition thereof can not be exhibited properly. On the contrary, when the content of chromium (Cr) exceeds 0.3% by weight of the total weight of the hot rolled steel sheet, there is a problem of deteriorating the weldability or the heat affected zone (HAZ) toughness.

Copper( Cu )

Copper (Cu) is an element that shows excellent corrosion resistance when added together with nickel (Ni) to suppress the permeation of H.

Copper (Cu) is preferably added in an amount of 0.2 to 0.35% by weight of the total weight of the hot rolled steel sheet according to the present invention. The copper (Cu) content is required at least 0.2% by weight of the total weight of the hot-rolled steel sheet in order to exhibit the effect of suppressing the permeation of H, but when contained in a large amount, the content of copper (Cu) shows hot shortness during rolling. It was limited to 0.35% by weight or less of the total weight of the hot rolled steel sheet.

calcium( Ca )

Calcium (Ca) is added for the purpose of improving the electrical resistance weldability by forming CaS inclusions and hindering the production of MnS inclusions. That is, since Ca (Ca) has a higher affinity with sulfur (S) than manganese (Mn), CaS inclusions are generated when calcium is added, and MnS inclusions are reduced. Such MnS is stretched during hot rolling to cause hook defects and the like in electrical resistance welding (ERW), so that electrical resistance weldability can be improved.

Calcium (Ca) is preferably added in an amount of 0.001 to 0.004% by weight of the total weight of the hot rolled steel sheet according to the present invention. When the calcium (Ca) content is less than 0.001% by weight of the total weight of the hot rolled steel sheet, the MnS control effect may not be properly exhibited. On the contrary, when the content of calcium (Ca) exceeds 0.004% by weight of the total weight of the hot-rolled steel sheet, generation of CaO inclusions is excessively generated, which deteriorates performance and electrical resistance weldability.

Nitrogen (N)

Nitrogen (N) is an inevitable impurity. When it is contained in an amount exceeding 0.006% by weight of the total weight of the hot-rolled steel sheet according to the present invention, the amount of nitrogen employed is increased to lower the impact property and elongation of the steel sheet, . Therefore, in the present invention, the content of nitrogen (N) was limited to 0.006% by weight or less of the total weight of the hot rolled steel sheet.

In (P)

Phosphorous (P) is added to inhibit cementite formation and increase strength.

However, phosphorus (P) has a problem of deteriorating weldability and deteriorating corrosion resistance by slab center segregation. Therefore, in the present invention, the content of phosphorus (P) was limited to 0.01% by weight or less of the total weight of the hot rolled steel sheet.

Sulfur (S)

Sulfur (S) inhibits the toughness and weldability of steel. In particular, the sulfur (S) is combined with manganese (Mn) to form a MnS non-metallic inclusions may deteriorate the resistance to stress corrosion cracking to generate cracks during processing of the steel, as a result can reduce the corrosion resistance of the steel .

Accordingly, in the present invention, the content of sulfur (S) is limited to 0.001% by weight or less based on the total weight of the hot-rolled steel sheet.

Hot-rolled steel sheet manufacturing method

1 is a process flowchart showing a method for manufacturing a hot rolled steel sheet according to an embodiment of the present invention.

Referring to FIG. 1, the method for manufacturing a hot rolled steel sheet according to an exemplary embodiment of the present invention includes a slab reheating step S110, a hot rolling step S120, and a cooling / winding step S130. At this time, the slab reheating step (S110) is not necessarily performed, but it is more preferable to carry out the step to derive effects such as reuse of precipitates.

In the method for manufacturing a hot rolled steel sheet according to the present invention, the slab sheet material in the semi-finished state, which is the target of the hot rolling process, is% by weight, carbon (C): 0.03 to 0.06%, silicon (Si): 0.1 to 0.2%, manganese (Mn): 1.1 to 1.4%, phosphorus (P): 0.01% or less, sulfur (S): 0.001% or less, aluminum (Al): 0.02 to 0.05%, vanadium (V): 0.04 to 0.1%, niobium (Nb): 0.08 to 0.1%, titanium (Ti): 0.01 to 0.03%, molybdenum (Mo): 0.1 to 0.2%, chromium (Cr): 0.1 to 0.3%, copper (Cu): 0.2 to 0.35%, nickel (Ni): 0.1 to 0.3%, calcium (Ca): 0.001 ~ 0.004%, nitrogen (N): 0.006% or less and the remaining iron (Fe) and inevitable impurities.

At this time, the slab plate having the above composition can be obtained through a continuous casting process after obtaining a molten steel having a desired composition through a steelmaking process.

Reheating slabs

In the slab reheating step S110, the slab plate having the above composition is reheated to a slab reheating temperature (SRT) of 1150 to 1250 ° C. Through the reheating of the slab plate, re-use of the segregated components and re-use of precipitates may occur during casting.

If the slab reheating temperature (SRT) is less than 1150 DEG C in this step, the segregated components in casting may not be sufficiently reused. On the other hand, when the SRT exceeds 1250 ° C, the austenite grain size increases and the ferrite of the final microstructure is coarsened, which may make it difficult to secure strength. In addition, can do.

Hot rolling

In the hot rolling step (S120), the reheated sheet is finished hot rolled in a finishing rolling temperature (FDT): 750 to 850 ° C. corresponding to the austenite uncrystallized region.

In this step, when the finish rolling temperature (FDT) is less than 750 ° C., abnormal reverse rolling occurs to form a mixed structure, thereby greatly reducing low-temperature impact toughness. On the contrary, when the finish rolling temperature (FDT) exceeds 850 ° C., the ductility and toughness are excellent, but there is a problem that the strength is sharply lowered.

In this case, the hot rolling may be performed so that the cumulative rolling reduction in the non-recrystallized region is 40 to 60%. If the cumulative rolling reduction of the hot rolling is less than 40%, it is difficult to obtain a uniform and fine structure, which may cause a significant variation in strength and impact toughness. On the other hand, when the cumulative rolling reduction of the hot rolling exceeds 60%, there is a problem that the rolling process time is prolonged and the fishy property is deteriorated.

Cooling/ Coiling

In the cooling / winding step (S130), the hot rolled sheet is wound while cooling. If winding is performed simultaneously with cooling, the cooling end temperature may be a coiling temperature (CT).

In this step, the winding may be carried out at a coiling temperature (CT) 550 ~ 620 ℃. In this case, the strength of the steel sheet can be maintained by forming the appropriate precipitated phase.

If the coiling temperature CT is less than 550 ° C., the strength may be insufficient due to the coarsening of the crystal grains. On the other hand, when the coiling temperature (CT) exceeds 620 ℃ low temperature impact toughness can be greatly reduced.

On the other hand, the cooling is preferably carried out at a cooling rate of approximately 5 ~ 100 ℃ / sec. If the cooling rate is less than 5 ℃ / sec, it may be difficult to secure the strength due to the coarsening of precipitates. On the contrary, when the cooling rate exceeds 100 ° C / sec, the structure is hardened, the low-temperature toughness can be lowered, and only the steel sheet manufacturing cost can be increased by excessive cooling without any further effect.

Hot-rolled steel sheet manufactured by the above process (S110 ~ S130) is a low carbon-based carbon content of 0.03 ~ 0.06% by weight of the alloy component control and process conditions control Tensile strength (TS): 600MPa or more and yield strength (YS) ): Satisfies API 5L X70 specification with 555 MPa and has a CLR (Crack Length Ratio): 10% or less, CTR (Crack Thickness Ratio): 4% or less and CSR (Crack Sensitivity Ratio): 2% or less In addition, it has excellent corrosion resistance properties.

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.

The contents not described here are sufficiently technically inferior to those skilled in the art, and a description thereof will be omitted.

1. Preparation of specimens

Specimens according to Examples 1 to 3 and Comparative Examples 1 to 2 were prepared under the compositions shown in Table 1 and the process conditions described in Table 2. Then, after reheating, hot rolling, cooling, and winding the hot rolled specimens according to Examples 1 to 3 and Comparative Examples 1 to 2, tensile tests and HIC (Hydrogen induced cracking) tests were performed on each.

[Table 1]

Figure pat00001

[Table 2]

Figure pat00002

2. Evaluation of mechanical properties

Table 3 shows the mechanical property results for the specimens prepared in Examples 1-3 and Comparative Examples 1-2.

[Table 3]

Figure pat00003

Referring to Tables 1 to 3, in the case of the specimens prepared according to Examples 1 to 3, it can be seen that both the tensile strength (TS): 600 MPa or more and the yield strength (YS): 555 MPa corresponding to the target value are satisfied. have.

In addition, in the case of specimens prepared according to Examples 1 to 3, a crack length ratio (CLR): 10% or less, a crack thickness ratio (CTR): 4% or less, and a crack sensitivity ratio (CSR): 2 corresponding to a target value It can be seen that all the% or less is satisfied.

On the other hand, in the case of specimens prepared according to Comparative Examples 1 and 2, both the tensile strength (TS) and the yield strength (YS) met all the target values, but CLR, CTR and CSR did not all meet the target values. Compared with the specimen prepared according to Examples 1 to 3, the carbon (C) content, which lowers the corrosion resistance when added in a large amount, exceeds 0.06% by weight of the total weight of the steel sheet, and in addition, phosphorus (P) or sulfur ( It can be said that it is due to the high content of S).

As can be seen from the above experimental results, the specimens prepared according to Examples 1 to 3 that satisfy the conditions presented in the present invention are compared with Comparative Examples 1 to 2 that do not, carbon (C), phosphorus (P), By lowering the sulfur (S) content, the API 5L X70 specification can be satisfied while significantly improving the corrosion resistance.

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: Hot rolling step
S130: cooling / winding step

Claims (4)

By weight%, carbon (C): 0.03 to 0.06%, silicon (Si): 0.1 to 0.2%, manganese (Mn): 1.1 to 1.4%, phosphorus (P): 0.01% or less, sulfur (S): 0.001% Aluminum (Al): 0.02 to 0.05%, Vanadium (V): 0.04 to 0.1%, Niobium (Nb): 0.08 to 0.1%, Titanium (Ti): 0.01 to 0.03%, Molybdenum (Mo): 0.1 to 0.2 %, Chromium (Cr): 0.1 to 0.3%, Copper (Cu): 0.2 to 0.35%, Nickel (Ni): 0.1 to 0.3%, Calcium (Ca): 0.001 to 0.004%, Nitrogen (N): 0.006% or less And reheating the slab plate made of the remaining iron (Fe) and inevitable impurities at a slab reheating temperature (SRT) of 1150 to 1250 ° C.
Hot rolling the reheated sheet to a finish rolling temperature (FDT) of 750 to 850 ° C .; And
And hot-rolling the cold rolled sheet to a winding temperature (CT) of 550 to 620 ° C .; hot rolled steel sheet manufacturing method comprising a.
The method of claim 1,
The cooling
Hot rolled steel sheet manufacturing method characterized in that carried out at a cooling rate of 5 ~ 100 ℃ / sec.
By weight%, carbon (C): 0.03 to 0.06%, silicon (Si): 0.1 to 0.2%, manganese (Mn): 1.1 to 1.4%, phosphorus (P): 0.01% or less, sulfur (S): 0.001% Aluminum (Al): 0.02 to 0.05%, Vanadium (V): 0.04 to 0.1%, Niobium (Nb): 0.08 to 0.1%, Titanium (Ti): 0.01 to 0.03%, Molybdenum (Mo): 0.1 to 0.2 %, Chromium (Cr): 0.1 to 0.3%, Copper (Cu): 0.2 to 0.35%, Nickel (Ni): 0.1 to 0.3%, Calcium (Ca): 0.001 to 0.004%, Nitrogen (N): 0.006% or less And the remaining iron (Fe) and inevitable impurities,
CLR (Crack Length Ratio): 10% or less, CTR (Crack Thickness Ratio): 4% or less, and CSR (Crack Sensitivity Ratio): Hot rolled steel sheet characterized in that it has 2% or less.
The method of claim 3,
The hot-
Hot rolled steel sheet characterized by having a tensile strength (TS): 600 MPa or more and a yield strength (YS): 555 MPa.
KR1020120108423A 2012-09-27 2012-09-27 Hot-rolled steel sheet and method of manufacturing the same KR20140042107A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
KR1020120108423A KR20140042107A (en) 2012-09-27 2012-09-27 Hot-rolled steel sheet and method of manufacturing the same

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
KR1020120108423A KR20140042107A (en) 2012-09-27 2012-09-27 Hot-rolled steel sheet and method of manufacturing the same

Publications (1)

Publication Number Publication Date
KR20140042107A true KR20140042107A (en) 2014-04-07

Family

ID=50651355

Family Applications (1)

Application Number Title Priority Date Filing Date
KR1020120108423A KR20140042107A (en) 2012-09-27 2012-09-27 Hot-rolled steel sheet and method of manufacturing the same

Country Status (1)

Country Link
KR (1) KR20140042107A (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2022045648A1 (en) * 2020-08-26 2022-03-03 주식회사 포스코 Hot-rolled steel plate having excellent impact toughness of welded zone and method for manufacturing same

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2022045648A1 (en) * 2020-08-26 2022-03-03 주식회사 포스코 Hot-rolled steel plate having excellent impact toughness of welded zone and method for manufacturing same

Similar Documents

Publication Publication Date Title
KR101467049B1 (en) Steel sheet for line pipe and method of manufacturing the same
KR20150124810A (en) High strength steel sheet and method of manufacturing the same
KR101505279B1 (en) Hot-rolled steel sheet and method of manufacturing the same
KR101505262B1 (en) High strength steel plate and method for manufacturing the same
KR101546132B1 (en) Extremely thick steel sheet and method of manufacturing the same
KR101546138B1 (en) Hot-rolled steel sheet and manufacturing method of the same
KR20150124811A (en) Steel sheet for line pipe and method of manufacturing the same
KR20140042107A (en) Hot-rolled steel sheet and method of manufacturing the same
KR20140130324A (en) Hot-rolled steel sheet for pipe and method of manufacturing the same
KR20150002956A (en) Steel sheet for line pipe and method of manufacturing the same
KR101546124B1 (en) Hot-rolled steel and method of manufacturing the same
KR20150076888A (en) Extremely thick steel sheet and method of manufacturing the same
KR101443445B1 (en) Non-heated type high strength hot-rolled steel sheet and method of manufacturing the same
KR101185222B1 (en) Api hot-rolled steel sheet with high strength and method for manufacturing the api hot-rolled steel sheet
KR101235944B1 (en) High strength api hot-rolled steel sheet with low yield ratio for american petroleum institute and method of manufacturing the api hot-rolled steel sheet
KR20140042108A (en) Hot-rolled steel sheet and method of manufacturing the same
KR20140119898A (en) Hot-rolled steel and method of manufacturing the same
KR101377890B1 (en) High strength hot-rolled steel sheet and method of manufacturing the same
KR20150002955A (en) Steel sheet and manufacturing method of the same
KR101586883B1 (en) High strength steel and method of manufacturing the same
KR101412372B1 (en) Hot-rolled steel sheet and method of manufacturing the hot-rolled steel sheet
KR101505290B1 (en) Steel sheet for line pipe and method of manufacturing the same
KR101443446B1 (en) Non-heated type hot-rolled steel sheet and method of manufacturing the same
KR101435319B1 (en) Method of manufacturing steel sheet
KR20150076991A (en) Steel sheet for line pipe and method of manufacturing the same

Legal Events

Date Code Title Description
A201 Request for examination
E902 Notification of reason for refusal