KR101499939B1 - Thick plate having high strength and toughness and method of manufacturing the same - Google Patents

Abstract

In one embodiment of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: 0.04 to 0.10% carbon, 0.10 to 0.40% silicon, 1.10 to 1.75% manganese (Mn) (Cu) and nickel (Ni), the balance being at least one selected from the group consisting of iron (Fe) and others Heating the slab containing the impurity to a temperature range of 1100 to 1200 캜; Rolling the slab to a cumulative rolling reduction of 30% or more at a temperature equal to or higher than Ar3 to form a steel sheet; Subjecting the rolled steel sheet to accelerated cooling at a rate of 3 to 30 ° C / sec so as to be in a temperature range of 100 to 400 ° C; The steel plate being reheated from an accelerated cooling end temperature; And a step of cooling the steel sheet having the double heat treatment at a cooling rate of 0.5 ° C / sec or less, wherein the steel sheet has a DS value of 100 ° C or higher and a yield strength of 420 MPa or higher, And a high strength and high toughness steel sheet using the same.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high strength and high strength steel sheet,

More particularly, the present invention relates to a high strength and high toughness steel sheet excellent in low temperature impact toughness and a method of manufacturing the steel sheet.

As depletion of energy resources in the coastal area has led to deep-sea and polar energy development. Especially, as the oil field development in the North Sea is active, the offshore structures are becoming larger, stronger, and cryogenic, and research and development on various steels ensuring toughness and strength in such a harsh environment are actively conducted.

For example, Korean Unexamined Patent Publication No. 2006-0090287 secures the strength and toughness of a steel sheet by using precipitation strengthening of Cu, but since the addition amount of Cu and Ni is large and the aging treatment is required to secure the strength of the steel sheet, There is a problem that occurs.

As another example, Korea Unexamined Patent Publication No. 2002-0070657 proposes a method of manufacturing a high strength steel sheet without complicated cooling process without injecting a high alloy element and the difference between the accelerated cooling stop temperature and the bainite termination temperature is specified in the range of -100 to 50 ° C. High-strength steel sheets are manufactured. However, there is a problem that it is difficult to set the end temperature of the bainite depending on the type of steel and thickness, and precision control must be performed.

In the conventional production of the post-steel plate having high strength and toughness as described above, when cooling is terminated at a temperature not lower than the low-temperature transformation phase production temperature or when the cooling finish is performed at a temperature lower than the low-temperature transformation phase formation temperature, a separate tempering process is performed, The toughness can be improved but the strength is lowered.

In order to solve the above problems, there is provided a high strength and high toughness steel sheet excellent in strength and toughness of a steel sheet and a method for producing the same.

In order to accomplish the above object, an embodiment of the present invention provides a method of manufacturing a semiconductor device, comprising: 0.04 to 0.10% of carbon, 0.10 to 0.40% of silicon, 1.10 to 1.75% of manganese (Mn) , At least one of copper (Cu) and nickel (Ni), 0.01 to 0.05% of Al, Heating the slab comprising iron (Fe) and other impurities to a temperature range of 1100 to 1200 캜; Rolling the slab to a cumulative rolling reduction of 30% or more at a temperature equal to or higher than Ar3 to form a steel sheet; Subjecting the rolled steel sheet to accelerated cooling at a rate of 3 to 30 ° C / sec so as to be in a temperature range of 100 to 400 ° C; The steel plate being reheated from an accelerated cooling end temperature; And a step of cooling the steel sheet having the double heat treatment at a cooling rate of 0.5 ° C / sec or less, wherein the steel sheet has a DS value of 100 ° C or higher and a yield strength of 420 MPa or higher, .

In one embodiment of the present invention, the slab is made of copper (Cu) in an amount of 0.10 to 0.50% and nickel (Ni) in an amount of 0.10 to 0.90% in weight percent of copper (Cu) and nickel (Ni) The CE value of the slab may be 0.40% or less.

In one embodiment of the present invention, the 1/4 thickness point of the steel sheet may be made to have an impact absorption energy of-200 J or more at -60 캜.

An embodiment of the present invention provides a high-strength and high-strength post-warp steel sheet produced by a method of manufacturing a high-strength and high-strength post-steel sheet, and a steel sheet having a thickness of 30 to 83 mm.

The effects of the above-described high strength and high toughness steel sheet according to the present invention and its manufacturing method will be described below.

The difference between the double temperature and the accelerated cooling end temperature is 100 ° C or more, and the yield strength is 420 MPa or more and the impact absorption energy is 200 J or more at -60 ° C, thereby making it possible to manufacture a steel sheet having excellent strength and toughness. That is, by controlling the double temperature by self tempering, the strength and toughness of the steel sheet can be secured. Even if the steel sheet is cooled to room temperature, the generation of the low temperature transformation phase is insignificant, and a separate tempering step is unnecessary.

The high strength and high toughness steel sheet is excellent in low temperature impact toughness and can be used for various applications such as shipbuilding, construction, ocean, and pressure boiler. It minimizes the addition of expensive alloying elements to lower the manufacturing cost of steel sheet, It is possible to manufacture a steel sheet having high strength and low temperature impact toughness.

It should be understood that the effects of the present invention are not limited to the above effects and include all effects that can be deduced from the detailed description of the present invention or the configuration of the invention described in the claims.

1 is a graph showing an internal temperature profile of a steel sheet having a thickness of 60 mm in which acceleration cooling is performed.
2 is a graph showing an internal temperature profile of a steel sheet having a thickness of 80 mm in which acceleration cooling is performed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification, when a part is referred to as being "connected" to another part, it includes not only "directly connected" but also "indirectly connected" . Also, when an element is referred to as "comprising ", it means that it can include other elements, not excluding other elements unless specifically stated otherwise.

(C): 0.10 to 0.40%, manganese (Mn): 1.10 to 1.75%, aluminum (Sol. Al): 0.01 (P): 0.0015% or less, and sulfur (S): 0.005% or less, and copper (Cu) and Nickel (Ni), and the remainder is heated in a temperature range of 1100 to 1200 ° C, including a slab containing iron (Fe) and other impurities. At this time, the slab is heated at a temperature of 1100 to 1200 ° C. When the heating temperature is lower than 1100 ° C, hardening of the niobium (Nb) is difficult, The grain size becomes large, and low-temperature toughness can not be ensured. Therefore, the heating furnace heats the slab at a temperature of 1100 to 1200 ° C.

Next, the heated slab can be scaled down. That is, when the slab is heated for a long time in the heating furnace, scale (iron oxide that occurs on the surface) is generated on the slab surface. When the slab is processed in such a scale, the scale of the slab surface is removed through the descaling process because the product is not finished. Such a scale removal operation scales the surface of the slab by various methods such as scaling by spraying high-pressure water on the surface of the slab.

Next, the slab on which the descaling operation is performed adjusts the thickness of the steel after the hot rolling. The steel sheet is a steel sheet with a thickness of 6 mm or more through hot rolling, and is mainly used for large structures such as towers for wind power, ships, pressure vessels, bridges and offshore structures.

The hot rolling operation improves the mechanical properties by controlling the heating temperature, the rolling temperature, and the reduction amount to make the crystal structure of the slab finer. At this time, the hot rolling is cumulatively carried out on the single phase immediately above the Ar3 transformation point, and the hot rolling is carried out at a cumulative rolling reduction of 30% or more, thereby inducing miniaturization of austenite grains by dynamic recrystallization.

In the hot rolling process, rolling is performed on the single-phase region immediately above the Ar3 transformation point, so that the austenite grains are elongated long and at the same time, a deformation band is formed in the grain. Thus, the elongated grain boundaries and the strain-boundary in the crystal grains can obtain fine ferrite grains.

Next, an accelerated cooling treatment is performed on the steel sheet formed through rolling at a cumulative rolling reduction of 30% or more at a temperature of Ar3 or higher. At this time, the cooling end temperature of the steel sheet is accelerated and cooled at a rate of 3 to 30 ° C / sec so as to be in the temperature range of 100 to 400 ° C, thereby increasing the strength and toughness of the product.

Next, the steel sheet subjected to accelerated cooling is recovered by self tempering. FIG. 1 is a graph showing an internal temperature profile of a steel sheet having a thickness of 60 mm in which acceleration cooling is performed, FIG. 2 is a graph showing an internal temperature profile of a steel sheet having an 80 mm thickness in which acceleration cooling is performed, Self Tempering.

The double-heating temperature of the steel sheet has a DS value of 100 deg. C or more in the following formula (1).

DS = double heat temperature - Accelerated cooling end temperature ... (One)

As described above, the DS value of the steel sheet is increased to more than 100 deg. C through the self-tempering to increase the impact toughness of the steel sheet after high strength toughness. In other words, yield strength and impact toughness can be effectively increased even with a small amount of alloying element through a double heat process after accelerated cooling.

That is, the yield strength of the manufactured high strength and high toughness steel sheet is 420 MPa or more and the impact absorption energy is 200 J or more even at a low temperature of -60 캜.

Specifically, the surface temperature increases due to the internal heat of the steel sheet from the temperature at the time of completion of accelerated cooling of the steel sheet, that is, from the accelerated cooling end temperature, and the temperature becomes 100 ° C or more higher than the cooling end temperature. That is, the high-strength and high-toughness steel sheet increases the double heat temperature time during self-tempering to increase the double-heat temperature, thereby imparting impact toughness to the steel sheet having high strength and high toughness.

Next, the steel sheet repaired with the DS value is cooled at a cooling rate of 0.5 DEG C / sec or less. This slow cooling will cool the steel sheet through air cooling.

The alloying elements of the slab charged into the furnace described above are as follows, and the contents of the respective alloying elements are expressed by the weight ratio.

Carbon (C): 0.04 to 0.10%

Carbon (C) is an element effective for increasing the strength of the steel sheet. If the content of carbon (C) is less than 0.04%, desired high strength can not be obtained. If the content is more than 0.10%, the carbon is effective for increasing the strength but deterioration of toughness and ductility There is a problem, and the content of carbon (C) is made to have a weight ratio of 0.04% to 0.10%.

Silicon (Si): 0.10 to 0.40%

The content of silicon (Si) has a weight ratio of 0.10 to 0.40%, and silicon (Si) is a deoxidizing element for removing oxygen in molten steel, which is effective for increasing the strength of a steel sheet.

However, if the content of silicon (Si) is less than 0.10%, a desired high strength can not be obtained. If it exceeds 0.40%, there is a problem that the toughness and ductility decrease sharply. Therefore, the content of silicon (Si) is made to have a weight ratio of 0.10% to 0.40% .

Manganese (Mn): 1.10 to 1.75%

The content of manganese (Mn) has a weight ratio of 0.10 to 1.75%, and manganese (Mn) has an effect of improving the sintering property and increasing the strength at the time of heat treatment.

In particular, it is an essential element added to compensate the strength due to the limitation of the addition amount of carbon (C). If the content of manganese (Mn) is less than 1.10%, the effect of sintering is scarcely exerted. If it exceeds 1.75%, the weldability is lowered and the risk of occurrence of cracks increases. Therefore, the content of manganese (Mn) is 1.10% ~ 1.75% .

Al (Sol. Al): 0.01 to 0.05%

Al (Sol. Al) is an element added as a deoxidizing agent and has an action of fixing nitrogen (N) contained as impurities in the steel. If the content of aluminum (Sol. Al) is less than 0.01%, there is no effect as a deoxidizer. If the content exceeds 0.05%, the weldability may be deteriorated, and the content of aluminum (Sol. .

Titanium (Ti): 0.005 to 0.03%

Titanium (Ti) forms Ti nitride to prevent the austenite from becoming coarse during heating of the slab and fine tune the ferrite structure to improve toughness. In order to obtain such an effect, titanium (Ti) should be added in an amount of 0.005% or more. However, if it is added excessively, the upper limit is limited to 0.03% because the Ti nitride is coarsened during the steelmaking process and it can not effectively prevent the coarsening of austenite that occurs during heating. Therefore, the content of titanium (Ti) is made to have a weight ratio of 0.005 to 0.03%.

Niobium (Nb): 0.005 to 0.03%

Niobium (Nb) is an element which greatly improves the toughness of a steel by making the structure of the steel finer. However, when the content is less than 0.005%, the toughness effect of steel is not obtained. The content is made to have a weight ratio of 0.005 to 0.03%.

Copper (Cu): 0.10 to 0.50%

Copper (Cu) is an element which improves the strength of a steel sheet without significantly deteriorating toughness. The effect is shown at 0.10% or more, and when it exceeds 0.50%, it helps to improve strength and corrosion resistance, So that the content of copper (Cu) is made to have a weight ratio of 0.10 to 0.50%.

Nickel (Ni): 0.10 to 0.90%

Nickel (Ni) is useful as an element for improving strength without deteriorating toughness, similar to copper (Cu). However, since it is an expensive element, the content of nickel (Ni) is 0.10 to 0.90% by weight.

Here, the slab is made to contain at least one of copper (Cu) and nickel (Ni). That is, the alloy element of the slab may include only one element of copper (Cu) and nickel (Ni), or may contain both elements of copper (Cu) and nickel (Ni) .

At this time, carbon (C), manganese (Mn), copper (Cu) and nickel (Ni) contained in the slab have a CE value of 0.40% or less by the following formula (2).

CE = carbon (C) + manganese (Mn) / 6 + {(copper (Cu) + nickel (Ni)) / 15} (2)
The values of carbon (C), manganese (Mn), copper (Cu), and nickel (Ni) substituted in the above formula (2) are substituted with values indicating the content of each alloy component in weight%.

In addition to the alloying elements described above, the remainder is made of iron (Fe) and other impurities, and impurities such as phosphorus (P) and sulfur (S) are finely contained.

Phosphorus (P): 0.015% or less (excluding 0%)

Phosphorus (P) is an element that inhibits the impact toughness of steel. It is preferable to reduce the amount added to cause internal brittleness and processability by accumulating in the center segregation part during playing and minimize hydrogen embrittlement. However, P (P) is limited to 0.015% or less considering the facility capability.

Sulfur (S): 0.005% or less (excluding 0%)

Sulfur (S) is an element harmful to ductility and impact toughness as in phosphorus (P). It causes high temperature cracking and center segregation during continuous casting and is formed of inclusions such as MnS, ) Is limited to 0.005% or less.

The slab made of the above-described alloying element is made of a high-strength high-tensile steel sheet having a yield strength of 420 MPa or more through a process of producing a steel sheet with high strength and high toughness and having an impact absorption energy of 200 J or more at a low temperature of -60 ° C .

Table 1 below shows the constituents of the slab (post-steel plate) charged into the furnace.

Specifically, the slab composition shown in the examples and comparative examples in Table 1 contains 0.04 to 0.10% of carbon (C), 0.10 to 0.40% of silicon (Si), 1.10 to 1.75% of manganese (Mn) (Al): 0.01 to 0.05%, titanium (Ti): 0.005 to 0.03%, niobium (Nb): 0.005 to 0.03%, copper (Cu): 0.10 to 0.50% and nickel And the remainder contains other impurities of 0.015% or less (excluding 0%) of iron (Fe) and phosphorus (P) and 0.005% or less (exclusive of 0%) of sulfur (S).

At this time, copper (Cu) and nickel (Ni) were contained as an alloy element of the slab, and one kind thereof was contained. In Example 2 and Comparative Example 3, copper (Cu) And nickel (Ni) were not contained in Comparative Example 2. In all other examples and comparative examples, an experiment was conducted in which the alloy elements of copper (Cu) and nickel (Ni) were contained.

Table 2 shows the yield strength and impact absorption energy according to the manufacturing method of the steel sheet after high strength and high toughness.

In Examples and Comparative Examples, a slab having a composition ratio according to the present invention was prepared as a steel sheet having high strength and toughness according to the above-described method of manufacturing a high strength and high toughness steel sheet. However, The yield strength and the impact absorption energy of the steel sheet produced by varying the recuperation temperature - accelerated cooling end temperature) were measured. In other words, in the case of the embodiment, the slow cooling process was carried out while the temperature range of the DS was 100 ° C or more, while in the comparative example, the slow cooling process was performed under the DS temperature range of less than 100 ° C .

In Examples 1 to 6, the slow cooling treatment was carried out in a state in which the temperature range of the DS was 100 ° C or higher, so that the yield strength of the steel sheet after high strength and high toughness was 420 MPa or more, the impact absorption energy at low temperature of- Or more, and shows excellent properties in terms of strength and toughness.

On the other hand, in Comparative Examples 1 to 3, the slow cooling treatment was carried out under the temperature range of DS lower than 100 ° C, and the yield strength of the steel sheet after high strength and high toughness satisfied 420 MPa or more, It is understood that the impact toughness is lower than that of Examples, with an absorption energy of 98 J or less.

Here, the stiffness and toughness of the steel sheet were measured by taking the specimen at 1/4 of the steel sheet thickness and then measuring the yield strength of the steel sheet. The impact test energy was measured through the impact test at the test temperature of -60 ° C Respectively.

As described above, the present invention increases the double-temperature temperature time during which the self tempering is performed to increase the double heat temperature, thereby imparting impact toughness to the steel sheet after high strength and high toughness. Such high strength and high toughness steel sheet has a high impact toughness even at a low temperature of -60 ° C, and can be used for structures used in deep sea and polar regions. Through the manufacturing process of the high strength and high strength steel sheet, it is possible to manufacture a high strength and high strength steel sheet having a yield strength of 420 MPa and a thickness of steel sheet having a shock absorption energy of 200 J or more at a low temperature of -60 ° C. of 30 to 83 mm .

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

Claims (4)

(Ti), 0.01 to 0.05% of aluminum (Al), 0.1 to 0.40% of carbon (C), 0.10 to 0.40% of silicon (Si) : 0.005 to 0.03%, and niobium (Nb): 0.005 to 0.03%, and at least one of 0.10 to 0.50% of copper (Cu) and 0.10 to 0.90% of nickel (Ni) ) And other impurities in a temperature range of 1100 to 1200 캜;
Rolling the slab to a cumulative rolling reduction of 30% or more at a temperature equal to or higher than Ar3 to form a steel sheet;
Subjecting the rolled steel sheet to accelerated cooling at a rate of 3 to 30 ° C / sec so as to be in a temperature range of 100 to 400 ° C;
The steel plate being reheated from an accelerated cooling end temperature; And
The steel sheet having the double heat treatment is subjected to cooling at a cooling rate of 0.5 DEG C / sec or less,
Wherein the steel sheet has a DS value of 100 deg. C or more and a yield strength of 420 MPa or more according to the following formula (1).

DS = double heat temperature - Accelerated cooling end temperature ... (One) The method according to claim 1,
The slab is made of carbon (C), manganese (Mn), copper (Cu), and nickel (Ni) substituted into the following formula (2) Is a value representing the content of each alloy component in weight%.

CE = carbon (C) + manganese (Mn) / 6 + {(copper (Cu) + nickel (Ni)) / 15} (2) The method according to claim 1,
Wherein a 1/4 thickness point of the steel sheet has an impact absorption energy of 200 J or more at -60 캜. A high strength steel sheet produced by the manufacturing method according to any one of claims 1 to 3, wherein the steel sheet has a thickness of 30 to 83 mm.

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