KR101400519B1

KR101400519B1 - Steel plate and method of manufacturing the same

Info

Publication number: KR101400519B1
Application number: KR1020120136626A
Authority: KR
Inventors: 임종호; 고상기
Original assignee: 현대제철 주식회사
Priority date: 2012-11-29
Filing date: 2012-11-29
Publication date: 2014-05-30

Abstract

Disclosed are steel material having excellent weather resistance and abrasion resistance and a method for manufacturing the same. According to the present invention, the method for manufacturing steel material includes: (a) a step of quenching a steel material 0.05-0.2 wt% of carbon (C), 1-5 wt% of manganese (Mn), 0.05-1 wt% of silicon (Si), 0.01-1 wt% of titanium (Ti), 0.001-0.003 wt% of boron (B), 0.5-3 wt% of nickel (Ni), 0.2-1 wt% of copper (Cu), 0.01-1 wt% of tungsten (W), 0.01-1.5 wt% of molybdenum (Mo), 0.02-0.1 wt% of niobium (Nb), 0.01-0.1 wt% of vanadium (V), and remaining amount of iron (Fe) and unavoidable impurities; and (b) a step of tempering the quenched steel material at the temperature ranging from 200 to 500°C.

Description

TECHNICAL FIELD [0001] The present invention relates to a steel material and a method of manufacturing the steel material.

The present invention relates to a steel material and a method of manufacturing the same, and more particularly, to a steel material capable of ensuring excellent mechanical properties and chemical resistance through alloy composition and process control, and a method of manufacturing the same.

The container is a container for transporting the contents of long and short distances, and reinforces the function of the steel material as a material for the purpose of reducing the transportation cost or longevity of the container itself.

In order to reduce the thickness of the applied steel, the steel is required to have high strength or weatherability for long-term maintenance.

In recent years, due to the depletion of resources around the world, workload in severe use environments such as deep seawaters has increased, and as containers have become larger in terms of cost reduction, there has been an increasing demand for steel having excellent mechanical properties and weatherability.

Accordingly, studies on quenching & tempering (QT) steels capable of producing steels having high strength, high toughness and high wear resistance properties at a relatively low cost have been actively under way.

However, conventional QT steels are not yet suitable for harsh environments due to the accelerated nature of chemical erosion in marine environments with high internal stress and high salinity or seawater droplets.

A background art related to the present invention is Korean Patent Laid-Open Publication No. 2003-0055534 (published on July 4, 2003), which discloses a method for manufacturing a weather-resistant steel for coasts.

An object of the present invention is to provide a method of manufacturing a steel material capable of realizing excellent mechanical properties and chemical resistance properties through alloy composition and process control, and to provide a steel material manufactured therefrom, which is excellent in mechanical properties and chemical resistance.

(A) 0.05 to 0.2% of carbon (C), 1 to 5% of manganese (Mn), and 0.05 to 0.2% of silicon (Si) in terms of% by weight in order to achieve the above- (B): 0.001 to 0.003%, nickel (Ni): 0.5 to 3%, copper (Cu): 0.2 to 1%, tungsten (W): 0.01 (Fe) and unavoidable impurities is quenched by a quenching process in which the steel material is subjected to quenching treatment at a rate of 1 to 1%, molybdenum (Mo) of 0.01 to 1.5%, niobium (Nb) of 0.02 to 0.1%, vanadium (V) ); And (b) tempering the quenched steel material at 200 to 500 ° C.

In this case, the carbon content is more preferably 0.1 to 0.15 wt%.

In the step (a), the steel material is heated to a temperature of Ac3 or higher and cooled at an average cooling rate of 50 ° C / sec or higher.

In order to achieve the above object, steel according to an embodiment of the present invention includes 0.05 to 0.2% of carbon (C), 1 to 5% of manganese (Mn), 0.05 to 1% of silicon (Si) (Cu), 0.2 to 1% of tungsten (W), 0.01 to 1% of molybdenum (W), 0.01 to 1% of boron (B), 0.001 to 0.003% (Fe) and inevitable impurities, and has a Vickers hardness Hv of 350 or more and a corrosion rate (Vickers hardness: Corrosion Rate) of 1.4 mm / year or less.

In this case, the carbon content is more preferably 0.1 to 0.15 wt%.

The steel has a tensile strength of 485 MPa or more and a yield strength of 345 MPa or more and has an average center absorbed energy of 340 J or more at -60 캜.

According to the method for producing a steel material according to the present invention, precipitation phases can be generated or controlled by controlling alloying elements such as C, Cu, Ni, Mo, W, and Nb and a quenching and tempering process to impart toughness, It is possible to realize a steel material excellent in weather resistance while satisfying strength limit values such as tensile strength, yield strength, toughness and abrasion resistance.

The steel according to the present invention satisfies a Vickers hardness Hv of 350 or more, a corrosion rate of 1.4 mm / year or less, a tensile strength (TS) of 485 MPa or more, a yield strength (YS) of 345 MPa or more, Thereby having high strength, high toughness and high abrasion resistance and high weather resistance.

1 is a flowchart showing a method of manufacturing a steel material 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.

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

The steel according to the present invention may contain 0.05 to 0.2% of carbon (C), 1 to 5% of manganese (Mn), 0.05 to 1% of silicon (Si), 0.01 to 1% of titanium (Ti) (B): 0.001 to 0.003%, Ni: 0.5 to 3%, Cu: 0.2 to 1%, tungsten (W): 0.01 to 1%, molybdenum (Mo) 0.02 to 0.1% of niobium (Nb) and 0.01 to 0.1% of vanadium (V).

The rest of the above components are composed of iron (Fe) and unavoidable impurities.

Hereinafter, the role and content of each component contained in the steel according to the present invention will be described.

Carbon (C)

In the present invention, carbon (C) is added to secure the strength of the steel.

The carbon is preferably added in an amount of 0.05 to 0.2% by weight based on the total weight of the steel according to the present invention, and more preferably 0.1 to 0.15% by weight in order to ensure curability. If the content of carbon is less than 0.05% by weight, the effect of the addition may be insufficient. On the other hand, when the content of carbon exceeds 0.2% by weight, the weldability, toughness and weatherability may be lowered.

manganese( Mn )

In the present invention, manganese (Mn) is an important element of martensite stabilization, and serves to improve the strength and toughness by making crystal grains finer.

The manganese is preferably added in an amount of 1 to 5 wt%, more preferably 2 to 4 wt%, based on the total weight of the steel according to the present invention. If the content of manganese is less than 1% by weight, it may be difficult to secure strength. On the other hand, when the content of manganese exceeds 5% by weight, the mechanical properties may be deteriorated due to generation of entrained martensite, which is a metastable phase.

silicon( Si )

In the present invention, silicon (Si) functions as a solid solution strengthening element.

The silicon is preferably added in an amount of 0.05 to 1% by weight based on the total weight of the steel according to the present invention. When the content of silicon is less than 0.05% by weight, the effect of the addition may be insufficient. On the contrary, when the content of silicon exceeds 1% by weight, the weldability and toughness are deteriorated.

titanium( Ti )

In the present invention, titanium (Ti) is a main element for improving the incombustibility, and it suppresses coarsening of crystal grains due to the pinning effect of precipitated TiN and contributes to improvement of strength.

The titanium is preferably added in an amount of 0.01 to 1% by weight based on the total weight of the steel material according to the present invention. If the content of titanium is less than 0.01% by weight, the effect of the addition may be insufficient. On the other hand, when the content of titanium exceeds 1% by weight, a coarse precipitate phase is formed to lower strength and toughness.

Boron (B)

In the present invention, boron (B) plays a role of enhancing the strength by blocking segregation of phosphorus (P) as a strong ingot element. If segregation of phosphorus (P) occurs, secondary processing brittleness may occur, so boron (B) is added to block segregation of phosphorus (P) to increase resistance to process embrittlement.

The boron (B) is preferably added in an amount of 0.001 to 0.003% by weight, more preferably 0.001 to 0.002% by weight, based on the total weight of the steel according to the present invention. When the content of boron (B) is less than 0.001% by weight, the amount of boron (B) is insignificant, so that the above effect can not be exhibited properly. On the other hand, when the content of boron (B) exceeds 0.003% by weight, excessive precipitation forms a coarse precipitate phase, thereby lowering strength and toughness.

nickel( Ni )

In the present invention, nickel (Ni) is the most important element for weatherability, and α-FeOOH is formed to densify the green layer. It is also an element which is beneficial for the improvement of nickel (Ni) strength and incombustibility.

The nickel (Ni) is preferably added in an amount of 0.5 to 3% by weight based on the total weight of the steel material according to the present invention. When the content of nickel is less than 0.5% by weight, corrosion resistance may be deteriorated and it may be difficult to secure desired weatherability. Conversely, if the content of nickel exceeds 3% by weight, the production cost may be increased due to high cost.

Copper( Cu )

In the present invention, copper (Cu) is an important element for improving the weather resistance. Copper diffuses into the oxidized layer of iron which is formed naturally when the steel is in the atmosphere and forms an oxide film containing copper by substitution with iron. Since this oxide film is amorphous, it is very dense and is known to suppress penetration of oxygen and as a result shows weather resistance.

The copper is preferably added in an amount of 0.2 to 1% by weight based on the total weight of the steel according to the present invention. When the content of copper is less than 0.2% by weight, corrosion resistance may be deteriorated and it may be difficult to secure desired weatherability. On the contrary, when the content of copper exceeds 1% by weight, it may cause hot shortness in which cracks occur during hot working without further improving weatherability.

Tungsten (W)

In the present invention, tungsten (W) contributes to improving the wear resistance by the precipitation phase such as WC. It also contributes to the improvement of weatherability by the formation of WO ₄ ² ^- ions. In the present invention, tungsten is an element for improving abrasion resistance, high strength, and weatherability, which is a substitute for expensive nickel.

The tungsten is preferably added in an amount of 0.01 to 1% by weight based on the total weight of the steel material according to the present invention. If the content of tungsten is less than 0.01% by weight, the effect of the addition may be insufficient. On the contrary, when the content of tungsten exceeds 1% by weight, the steelmaking process is difficult.

molybdenum( Mo )

In the present invention, molybdenum (Mo) contributes to improvement of weatherability by MoO ₄ ² ^- ion formation. Further, it contributes to improvement of abrasion resistance due to precipitation of carbide.

The molybdenum is preferably added in an amount of 0.01 to 1.5% by weight based on the total weight of the steel according to the present invention. If the content of molybdenum is less than 0.01% by weight, the effect of the addition may be insufficient. On the contrary, when the content of molybdenum exceeds 1.5% by weight, the weldability is deteriorated and the manufacturing cost may increase due to the high cost.

Since molybdenum is a high-priced element, it is preferable to simultaneously induce generation of micro precipitates through addition of niobium and vanadium to maximize wear resistance characteristics, and to enhance the weatherability through addition of tungsten.

Niobium ( Nb )

In the present invention, niobium (Nb) effectively works to improve the wear resistance of a steel material by grain refinement and carbide precipitation. At this time, the effect of improving carbide abrasion resistance can be maximized by the addition of tungsten and vanadium.

The niobium is preferably added in an amount of 0.02 to 0.1% by weight based on the total weight of the steel material according to the present invention. When the content of niobium is less than 0.02% by weight, it may be difficult to secure the bending workability of the steel material. Conversely, when the content of niobium exceeds 0.1% by weight, mechanical properties may deteriorate due to the formation of a coarse precipitate phase.

Vanadium (V)

In the present invention, vanadium (V) is an element having a role similar to that of niobium, and the addition of carbides, nitrides, and the like is maximized through compound addition, and grain strength is improved by miniaturization of crystal grains.

The vanadium (V) is preferably added in an amount of 0.01 to 0.1% by weight based on the total weight of the steel according to the present invention. When the content of vanadium (V) is less than 0.01% by weight, the effect of the addition is insignificant. On the contrary, when the content of vanadium (V) exceeds 0.1% by weight, the yield ratio increases.

The steel according to the present invention is characterized by having Vickers hardness Hv of 350 or more and corrosion rate of 1.4 mm / year or less in terms of mechanical properties by the above composition and the process control described below. Which C, Cu, Ni, with the addition of Mo added to the W, Nb, V for maximum wear resistance and control over the generation and secure on the hardenability and _{^{precipitation, α-FeOOH, WO 4 2}} -, MoO ₄ ² ^-, and the like.

It has a tensile strength of 485 MPa or more and a yield strength of 345 MPa or more.

The average center absorbed energy of 340 J or more at -60 캜 is obtained due to the low temperature impact toughness imparted to the steel by tempering at 200 to 500 캜.

The steel material satisfying the yield strength, the tensile strength, the abrasion resistance, the corrosion rate and the toughness of the above-mentioned range can be used for a container ship, a pipeline of an oil pipe, a pressure vessel and the like exposed to a severe use environment such as a marine environment.

Hereinafter, a method of manufacturing a steel material according to the present invention having the above characteristics will be described.

Referring to FIG. 1, the illustrated method of manufacturing steel includes a steel material quenching step S110 and a tempering step S120.

Steel material quenching ( Quenching )

In the steel material quenching step (S110), the steel material having the above composition is quenched.

During quenching, the steel material can be cooled to an Ac3 temperature of approximately 800 to 900 ° C or higher, and then cooled to an average cooling rate of 50 ° C / sec or higher.

At this time, when the temperature at the time of quenching is less than Ac3, the ferrite may not be sufficiently transformed into austenite, and it may become difficult to secure the desired strength. In addition, when the average cooling rate during quenching is less than 50 DEG C / sec, unwanted transformation may occur during cooling.

Tempering Tempering )

In the tempering step S120, the quenched steel material is tempered to impart toughness to the steel material.

In the present invention, the tempering is preferably performed at 200 to 500 ° C. for 1 to 5 hours. When the tempering is carried out at less than 200 DEG C or when the tempering time is less than 1 hour, it may become difficult to obtain a desired low temperature toughness. Conversely, when the tempering is carried out at a temperature exceeding 500 캜 or when the tempering time exceeds 5 hours, it may become difficult to obtain strength and low-temperature toughness due to carbide precipitation and crystal grain coarsening.

Example

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. 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

A steel specimen of 70 mm × 150 mm × 3 mm in height according to Examples 1 to 3 and Comparative Example 1 was manufactured under the composition shown in Table 1 and the process conditions shown in Table 2.

[Table 1]

[Table 2]

2. Property evaluation

Table 3 shows the tensile test, the corrosion rate evaluation result, the Vickers hardness and the impact absorption energy measurement results of the steels produced according to Examples 1 to 3 and Comparative Example 1.

The rate of corrosion was evaluated by a neutral salt spray test according to KS D 9502. The neutral salt spray test was carried out for 45 days at a slope angle of 30 ° at a pH of 6.5 to 7.2 (25 ° C) and a 5% sodium chloride solution at 35 ° C.

The impact absorption energy was expressed by the average impact absorption energy obtained by performing the Charpy impact test based on KS B 0810 three times at -60 ° C against the center portion in the thickness direction of the steel material produced according to Examples 1 to 3 and Comparative Example 1.

[Table 3]

Referring to Table 3, tensile strength, yield strength, bark hardness and impact absorption energy of the specimens according to Examples 1 to 3 were higher than the target values, and the corrosion rate also satisfied the desired physical properties.

In particular, the specimen according to Example 3 having a carbon content of 0.15 wt% exhibited the lowest corrosion rate and the highest bark hardness.

The tensile strength, the yield strength and the impact absorption energy of the specimens according to Comparative Example 1 in which Ni, Cu and Nb were not added all exceeded the target values, while the corrosion rate and the Burr's hardness were less than the target values and the weatherability and abrasion resistance were inferior Could know.

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: Steel material quenching step
S120: Tempering step

Claims

(A) 0.05 to 0.2% of carbon (C), 1 to 5% of manganese (Mn), 0.05 to 1% of silicon (Si), 0.01 to 1% of titanium (Ti) ), 0.001 to 0.003% of nickel, 0.5 to 3% of nickel, 0.2 to 1% of copper, 0.01 to 1% of tungsten, 0.01 to 1.5% of molybdenum, ): 0.02 to 0.1%, vanadium (V): 0.01 to 0.1%, and remaining iron (Fe) and inevitable impurities; And
(b) tempering the quenched steel material at 200 to 500 占 폚.

The method according to claim 1,
The content of carbon
0.1 to 0.15% by weight.

The method according to claim 1,
The step (a)
Wherein the steel material is heated to a temperature not lower than the Ac3 temperature and then cooled at an average cooling rate of not less than 50 DEG C / sec.

(C): 0.05 to 0.2%, manganese (Mn): 1 to 5%, silicon (Si): 0.05 to 1%, titanium (Ti): 0.01 to 1%, boron (B): 0.001 (Ni): 0.5 to 3%, Cu: 0.2 to 1%, tungsten (W): 0.01 to 1%, molybdenum (Mo): 0.01 to 1.5%, niobium (Nb): 0.02 To 0.1%, vanadium (V): 0.01 to 0.1%, and the balance of iron (Fe) and unavoidable impurities,
A Vickers hardness Hv of 350 or more and a corrosion rate of 1.4 mm / year or less.

5. The method of claim 4,
The steel
And the content of carbon is 0.1 to 0.15% by weight.

5. The method of claim 4,
The steel
A tensile strength of 485 MPa or more and a yield strength of 345 MPa or more.

5. The method of claim 4,
The steel
And an average center absorbed energy of 340 J or more at -60 캜.