KR101989235B1 - Tmcp typed steel and method of manufacturing the same - Google Patents

Abstract

The present invention relates to a method of manufacturing a semiconductor device, which comprises 0.06 to 0.085% carbon (C), 0.15 to 0.25% silicon (Si), 1.45 to 1.6% manganese (Mn), 0.01% 0.002% or less of sulfur (excluding 0%), 0.015 to 0.05% of aluminum (Al), 0.15 to 0.25% of copper (Cu), 0.025 to 0.035% of niobium (Nb) 0.01 to 0.1% of chromium (Cr), 0.01 to 0.02% of titanium, 0.03 to 0.07% of molybdenum (Mo), 50 ppm or less of nitrogen (exclusive of 0%) and 2.5 ppm or less of hydrogen %) And the remaining Fe (Fe) and unavoidable impurities.

Description

Technical Field [0001] The present invention relates to a TMCP steel material and a method of manufacturing the same,

The present invention relates to a TMCP steel having improved core impact toughness properties and a method for producing the same.

In recent years, the development of shipbuilding capacity in shipyards has led to the construction of super large container vessels, and the requirements for steel to be applied to such super large container vessels are increasing.

For example, the steel material applied to the center portion of the ship due to the structural characteristics of the container ship has been required to have a steel material having excellent structural rigidity and high strength. In addition, as the thickness of the applied steel increases with increasing ship size, there is a demand for improvements in the core impact toughness.

As a prior art, there is Korean Patent Publication No. 2011-0022309 (registered on Mar. 07, 2011, name of invention: method of producing thick plate).

The present invention provides a TMCP steel having improved core toughness characteristics through alloy component control and thermo-mechanical controlled process (TMCP) process control, and a method for manufacturing the same.

In order to achieve the above object, the TMCP steel according to one embodiment of the present invention comprises 0.06 to 0.085% of carbon (C), 0.15 to 0.25% of silicon (Si), 1.45 to 1.6% of manganese (Mn) (P) of 0.01% or less (excluding 0%), 0.002% or less of sulfur (excluding 0%), 0.015 to 0.05% of aluminum (Al), 0.15 to 0.25% ), 0.025 to 0.035% of nickel, 0.65 to 0.75% of nickel, 0.01 to 0.1% of chromium (Cr), 0.01 to 0.02% of titanium, 0.03 to 0.07% of molybdenum and 50 ppm or less of nitrogen (N) 2.5% by mass or less (excluding 0%) of hydrogen (H) and the balance of iron (Fe) and unavoidable impurities.

The TMCP steel may include bainite and ferrite structures in the surface portion and the center portion, and the structure in the center portion may further include at least a portion of the dynamic recrystallized structure.

In order to achieve the above object, the present invention provides a method of manufacturing a TMCP steel material, comprising: (a) 0.06 to 0.085% of carbon (C), 0.15 to 0.25% of silicon (Si) (P) of 0.01% or less (excluding 0%), sulfur (S) of 0.002% or less (exclusive of 0%), aluminum (Al) of 0.015 to 0.05%, copper (Cu) (N), 0.025 to 0.035% of niobium (Nb), 0.65 to 0.75% of nickel, 0.01 to 0.1% of chromium (Cr), 0.01 to 0.02% of titanium, 0.03 to 0.07% of molybdenum, (Excluding 0%), 2.5 ppm or less (excluding 0%) of hydrogen (H), and the balance of iron (Fe) and unavoidable impurities to a temperature of 1125 to 1175 ° C. (b) primary rolling the reheated steel slab at a reduction rate of 4 to 18% by applying a mean flow stress (MFS) of 100 to 150 MPa per pass; (c) secondarily rolling the primary rolled steel at a reduction rate of 2 to 4% by applying a mean flow stress (MFS) of 200 to 400 MPa per pass; And (d) cooling the secondary rolled steel material.

In the method of manufacturing the TMCP steel, the primary rolling is set to gradually increase the rolling rate per rolling pass, and the secondary rolling may be set so that the effective rolling reduction per rolling pass gradually increases.

In the method of manufacturing the TMCP steel, the primary rolling is performed such that the reduction rate per the rolling pass is gradually increased from 18% to the maximum, and the secondary rolling is performed such that the effective rolling reduction stress per rolling pass is gradually increased from 200 MPa .

In the TMCP steel manufacturing method, the finishing rolling temperature of the secondary rolling may be 730 to 770 캜.

In the method of manufacturing the TMCP steel, the step (d) may include a step of starting cooling at 730 to 700 캜 and ending cooling at 380 to 420 캜.

According to an embodiment of the present invention, a TMCP steel having improved core toughness characteristics and a manufacturing method thereof can be realized through alloy component control and TMCP (Thermo-Mechanical Controlled Process) process control. Of course, the scope of the present invention is not limited by these effects.

1 is a flowchart schematically showing a method of manufacturing a TMCP steel material according to an embodiment of the present invention.
FIG. 2 is a graph showing the reduction rate per pass in the method of manufacturing the TMCP steel according to the experimental example of the present invention.
FIG. 3 is a graph showing effective stresses per pass in a method of manufacturing a TMCP steel according to an experimental example of the present invention.
4 is a photograph showing the microstructure of the TMCP steel according to the experimental example of the present invention.
5 and 6 are graphs showing the results of the low-temperature impact test on the TMCP steel according to the experimental example of the present invention.

Hereinafter, a TMCP steel according to an embodiment of the present invention and a method of manufacturing the same will be described in detail. The terms used below are appropriately selected terms in consideration of functions in the present invention, and definitions of these terms should be made based on the contents throughout this specification.

The TMCP steel has the advantage of obtaining high strength while lowering the CEQ value that affects welding. However, the normal TMCP steel has a relatively low impact toughness at the center (1 / 2t) of the backing material compared to the surface or 1 / 4t. Due to these characteristics, whiskers are used for structural or shipbuilding steels that require 1 / 4t toughness guarantee, but there is a limit in thickness when applied to marine structural steels. In the following embodiments of the present invention, the concept of "Mean Flow Stress" is introduced to improve the toughness of the center portion of the TMCP steel. Through the control of the heat control rolling and rolling pass during rolling, And a method of manufacturing the TMCP steel.

TMCP steel

The TMCP steel according to one embodiment of the present invention comprises 0.06 to 0.085% of carbon (C), 0.15 to 0.25% of silicon (Si), 1.45 to 1.6% of manganese (Mn) (Excluding 0%), 0.002% or less of sulfur (excluding 0%), 0.015 to 0.05% of aluminum (Al), 0.15 to 0.25% of copper, 0.025 to 0.035% of niobium (Nb) (Excluding 0%) of hydrogen (N), 0.20 to 0.75% of chromium (Cr), 0.01 to 0.02% of titanium, 0.01 to 0.02% of molybdenum, 0.03 to 0.07% 2.5 ppm or less (excluding 0%) and the balance of iron (Fe) and unavoidable impurities.

Hereinafter, the role and content of each component included in the TMCP steel according to one embodiment of the present invention will be described.

Carbon (C)

Carbon (C) is added as an interstitial solid element to secure strength of steel. In addition, it can serve to improve the hardenability. However, when it is less than 0.06% by weight, the strength can not be ensured and it is difficult to sufficiently exert the above-mentioned effects. When the content exceeds 0.085% by weight, the toughness of the center portion may be lowered due to an increase in the center portion hardness, and the weldability is deteriorated. Taking this into consideration, the content of carbon (C) in the steel is determined to be 0.06 to 0.085%.

Silicon (Si)

Silicon (Si) can function as a deoxidizer and can help secure the strength of the steel. However, if the content in the steel is less than 0.15% by weight, the effect of deoxidation may not be sufficiently exhibited. If the content is more than 0.25% by weight, the nonmetallic inclusions may be excessively formed, resulting in deterioration in toughness and deterioration in plastic workability. Taking this into consideration, the content of silicon (Si) in the steel is determined to be 0.15 to 0.25%.

Manganese (Mn)

Mn serves as an austenite stabilizing element and contributes to improving the ingot strength and strength at the time of heat treatment. In addition, grain refinement by rolling helps to improve toughness and strength. However, when the content is less than 1.45 wt%, it is difficult to sufficiently exhibit the above effect. When the content is more than 1.6 wt%, inclusions such as MnS may be formed to deteriorate impact toughness and internal quality of the weld. Taking this into consideration, the content of manganese (Mn) in the steel is determined to be 1.45 to 1.6% by weight.

Aluminum (Al)

Aluminum (Al) can combine with nitrogen to form AlN and contribute to refinement of austenite grains. When the addition amount of aluminum is less than 0.015 wt%, the effect of addition is insufficient. On the contrary, when the addition amount of aluminum exceeds 0.05 wt%, the fatigue strength of the steel can be inhibited. Taking this point into consideration, the content of aluminum (Al) in the steel is determined to be 0.015 to 0.05% by weight.

Nickel (Ni)

It is an effective component to refine the texture of steel and to strengthen its base with austenite or ferrite, and in particular to improve toughness at low temperature to prevent low-temperature embrittlement. In addition, it can prevent the brittleness of the heat of Cu. However, when the addition amount of nickel is less than 0.65, it is difficult to sufficiently exhibit the above effect. When the addition amount of nickel exceeds 0.75% by weight, the manufacturing cost of the component becomes excessively high as compared with the function of nickel, have. Further, the addition of excessive nickel may lower the toughness of the weld heat affected zone. Taking this into consideration, the content of nickel (Ni) in the steel is maintained at 0.65 to 0.75% by weight or less.

Copper (Cu)

Copper (Cu) can contribute to the improvement of the hardness of the steel. On the other hand, when the addition amount of copper is less than 0.15% by weight, it is difficult to sufficiently exert the above-mentioned effects. On the other hand, if it exceeds 0.25% by weight, it may become a factor to hinder the high temperature sedimenting property. Taking this into consideration, the content of copper in the steel is maintained at 0.15 to 0.25% by weight.

Niobium (Nb)

Niobium (Nb) can contribute to the grain refinement and the recrystallization stop temperature to be elevated, thereby enabling high-temperature carburization. When the addition amount of niobium is less than 0.025 wt%, the above-mentioned effect of addition may be insufficient and the strength can not be secured. On the contrary, when the addition amount of niobium exceeds 0.035% by weight, it is present as an inclusion, deteriorating the impact toughness and lowering the toughness of the steel. Taking this into consideration, the content of niobium (Nb) in the steel is determined to be 0.025 to 0.035% by weight.

Molybdenum (Mo)

Molybdenum (Mo) contributes to the improvement of strength and toughness of steel. However, when the content is less than 0.03% by weight, the effect of sintering is not sufficiently exhibited. When the content is more than 0.07% by weight, local toughness may deteriorate the toughness, which may inhibit the machinability and core toughness of the steel. Taking this point into consideration, the content of molybdenum (Mo) in the steel is determined to be 0.03 to 0.07% by weight.

Titanium (Ti) and nitrogen (N)

Titanium (Ti) is an element forming carbonitride, and it can improve the low temperature toughness by fine precipitation of TiC and TiN. In particular, the TiN precipitates have a rectangular parallelepiped shape, and the size thereof is as large as 200 to 1000 nm. Such TiN has a side effect of causing stress concentration where breakage occurs at the corner portion, so that the content of nitrogen (N) is made to be 50 ppm or less. The titanium (Ti) is added in an amount of 0.01 to 0.02% by weight for the grain refining effect of the HAZ portion of the welded portion during welding. When the content of titanium is less than 0.01% by weight, it is difficult to sufficiently exert the above-mentioned effect, and the particle refinement effect is deteriorated. On the other hand, when the content of titanium exceeds 0.02% by weight, the toughness can be deteriorated and the impact toughness is deteriorated due to the formation of coarse TiN. Taking this into consideration, the content of titanium (Ti) in the steel is determined to be 0.01 to 0.02% by weight.

In (P)

Phosphorus (P) enhances the strength of the strength by solid solution strengthening and can function to inhibit the formation of carbide. However, when the content of phosphorus is more than 0.01% by weight, weldability is deteriorated and corrosion resistance is deteriorated due to slab center segregation. Further, phosphorus may be segregated in the austenite grain boundary system and toughness may be lowered. In consideration of this point, the content of phosphorus (P) in the steel material is maintained at 0 to 0.01% by weight or less.

Sulfur (S)

Sulfur combines with manganese to form MnS, which contributes to improvement in machinability. However, when the added amount of sulfur (S) is more than 0.002 wt%, it may cause the room temperature and low-temperature embrittlement of the steel, thereby deteriorating impact toughness. In consideration of this point, the content of sulfur (S) in the steel is maintained at 0 to 0.002% by weight or less.

The final microstructure of the TMCP steel having the above-described alloy composition includes a structure of the center portion including bainite and ferrite structure, and the structure of the center portion may further include at least a part of a dynamic recrystallized structure.

Manufacturing method of TMCP steel

The manufacturing process of TMCP steel which improves impact toughness by 1 / 2t impact toughness because dynamic recrystallization occurs when the effective rolling reduction stress (MFS) is high and the pass count is large in 2-stage rolling, Will be described in detail below.

1 is a flowchart schematically showing a method of manufacturing a TMCP steel material according to an embodiment of the present invention. 1, a method of manufacturing a TMCP steel comprises: (a) 0.06 to 0.085% carbon (C), 0.15 to 0.25% silicon (Si), 1.45 to 1.6% manganese (Mn) (Al) of 0.015 to 0.05%, copper (Cu) of 0.15 to 0.25%, niobium (Nb) of 0.025 to 0.25% (Excluding 0%) of nitrogen (N), 0.35 to 0.75% of nickel (Ni), 0.01 to 0.1% of chromium (Cr), 0.01 to 0.02% of titanium, 0.03 to 0.07% of molybdenum (S100) reheating the steel slab made of 2.5 ppm or less (but excluding 0%) of hydrogen (H) and the remaining iron (Fe) and unavoidable impurities to a temperature of 1125 to 1175 ° C; (b) firstly rolling the reheated steel slab at a reduction ratio of 4 to 18% by applying a mean flow stress (MFS) of 100 to 150 MPa per pass (S200); (c) secondarily rolling the primary rolled steel material at a reduction ratio of 2 to 4% by applying a mean flow stress (MFS) of 200 to 400 MPa per pass (S300); And (d) cooling the secondary rolled steel (S400).

Reheating slabs

In the slab reheating step (SlOO), the slab of the alloy composition is reheated to a temperature of 1125 캜 to 1175 캜. If the reheating temperature is less than 1125 DEG C, the precipitation-type elements can not be sufficiently solidified in the slab, and when it exceeds 1175 DEG C, the austenite grains are coarsened and the grain size increases, The following toughness can not be ensured. According to an embodiment of the present invention, by reheating at a temperature of 1125 ° C to 1175 ° C, the grain size of the initial austenite can be controlled so that the slab has a uniform structure.

Primary rolling

In the primary rolling step (S200), the reheated slab is first rolled. This first rolling step can be rolled at a reduction ratio of 4 to 18% by applying a Mean Flow Stress (MFS) of 100 to 150 MPa per pass.

The effective pressing-down stress may be related to the descending force per pass, the width of the plate material after rolling, the diameter of the rolling roll, the difference in thickness before and after rolling, and the like. That is, the effective down-pressure stress may mean the per-pass stress acting substantially in the rolling process of the sheet material. The effective pressing-down stress can be derived by the following equation.

W is the width (unit, mm) of the steel plate (blade) after rolling, D is the diameter of the rolling roll (unit mm), Ti is the initial thickness of the steel plate ], And Tf is the thickness of the steel sheet after rolling (unit: mm).

In one embodiment, the primary rolling may be set to progressively increase the rolling reduction per rolling pass. This is because as the thickness decreases by rolling, the rolling force is transmitted to the center of the steel by increasing the rolling reduction amount of the next pass. The primary rolling is performed such that the reduction rate per rolling pass gradually increases from 18% to the maximum so that sufficient recrystallization is achieved.

Secondary rolling

In the secondary rolling step S300, the primary rolled steel is rolled at a reduction rate of 2 to 4% by applying a mean flow stress (MFS) of 200 to 400 MPa per pass. The secondary rolling is set to gradually increase the effective pressing-down stress per rolling pass. For example, the secondary rolling may be performed such that the effective pressing-down stress per rolling pass is gradually increased from 200 MPa. The finish rolling temperature of the secondary rolling may be 730 to 770 캜.

Cooling

The cooling step (S400) cools the secondary rolled steel. The cooling step (S400) includes the step of cooling being started at 730 to 700 占 폚, cooling at a cooling rate of about 5 占 폚 / s, and ending cooling at 380 to 420 占 폚.

When the cooling end temperature is lower than 380 占 폚, martensite, which is a low-temperature transformed structure, may be formed to deteriorate the low-temperature toughness. If the cooling termination temperature exceeds 420 캜, the material value will not be satisfied.

By performing the above-described process, a TMCP steel material according to an embodiment of the present invention can be manufactured. According to an embodiment of the present invention, the content of the alloying element is controlled, and the TMCP process is performed, but the two-stage rolling process is carried out at different temperatures so that the structure of the surface portion and the center portion includes bainite and ferrite structure, The structure at the center can implement a TMCP steel that further includes at least a portion of a dynamic recrystallization texture.

Hereinafter, preferred examples of the present invention will be described in order to facilitate understanding of the present invention. It should be understood, however, that the following examples are intended to aid in the understanding of the present invention and are not intended to limit the scope of the present invention.

1. Preparation of specimens

As shown in Table 1, the steel specimen having the common composition of the present invention was subjected to the TMCP process using the process conditions according to Comparative Examples and Examples as shown in Table 2, respectively.

ingredient C Si Mn P S Al Cu Ni Nb Ti Cr Mo content
(wt%) 0.07 0.2 1.5 0.005 0.001 0.03 0.17 0.66 0.029 0.018 0.04 0.04

Primary rolling
(Rough rolling) Secondary rolling
(Finish rolling) Comparative Example Reduction rate: 4 to 18%
Effective pressing-down stress: 80 to 120 MPa Reduction rate: 10 to 12%
Effective pressing-down stress: 200 to 250 MPa Example Reduction rate: 4 to 18%
Effective pressing-down stress: 100 to 150 MPa Reduction rate: 2 to 4%
Effective pressing-down stress: 300 to 400 MPa

FIG. 2 is a graph showing the reduction rate per pass in the manufacturing method of the TMCP steel according to the experimental example of the present invention, and FIG. 3 is a graph showing the effective reduction pressure per pass in the manufacturing method of the TMCP steel according to the experimental example of the present invention .

The TMCP steel according to the comparative example of the present invention has the composition shown in Table 1 and the process conditions corresponding to 'Plate A' in FIGS. 2 and 3 are applied. The TMCP steel according to the embodiment of the present invention has the composition shown in Table 1, and the process conditions corresponding to 'Plate B' in FIG. 2 and FIG. 3 are applied.

Referring to FIG. 2, in the method of manufacturing the TMCP steel plate (Plate A) according to the comparative example of the present invention, the primary rolling (passes R1 to R8) shows a gradual increase in the reduction rate per rolling pass, , And then the reduction rate per rolling pass progressively decreased in the secondary rolling (passes F1 to F4). In the method of manufacturing the TMCP steel plate (Plate B) according to the embodiment of the present invention, the primary rolling (passes R1 to R8) is performed such that the reduction rate per rolling pass gradually increases to about 18% In the secondary rolling (pass F1 to F14), the reduction rate per rolling pass was relatively lower than that in the primary rolling.

pass Effective pressing reduction stress
(Example) Effective pressing reduction stress
(Comparative Example) R1 104.19 84.67 R2 154.28 116.03 R3 158.55 115.60 R4 144.14 104.36 R5 149.53 112.46 R6 133.32 98.96 R7 134.72 102.86 R8 129.80 100.46 F1 198.61 170.40 F2 285.37 207.85 F3 306.54 218.62 F4 315.73 224.73 F5 327.14 - F6 330.8 - F7 342.1 - F8 345.87 - F9 353.55 - F10 356.98 - F11 358.80 - F12 371.60 - F13 373.64 - F14 372.01 -

Referring to FIG. 3, in the method of manufacturing the TMCP steel plate (Plate A) according to the comparative example of the present invention, the effective rolling reduction stress applied to the primary rolling passes R 1 to R 8 is maintained at a constant level within a predetermined range The secondary rolling (pass F 1 to F 4) was performed so that the applied effective pressing-down stress gradually increased. In the method of manufacturing the TMCP steel plate (Plate B) according to the embodiment of the present invention, the primary rolling (passes R1 to R8) maintains a predetermined effective stress within a predetermined range, F1 to F14) were performed so that the relatively high effective pressing-down stress gradually increased in comparison with the comparative example. In an embodiment, the secondary rolling was performed such that the effective peeling stress per rolling pass was gradually increased from 200 MPa. Table 3 shows the values of the effective pressing-down stress according to the present experimental example.

2. Tissue and property evaluation

The microstructure of the above Comparative Examples and Examples was observed.

4 is a photograph showing the microstructure of the TMCP steel according to the experimental example of the present invention. The upper photographs of FIG. 4 relate to the microstructure of the TMCP steel plate (Plate A) according to the comparative example of the present invention, and the lower photographs of FIG. 4 show the microstructure of the TMCP steel plate (Plate B) The left photographs of FIG. 4 relate to the microstructure of the 2 mm area of the surface portion of the TMCP steel, and the photographs of the right side of FIG. 4 relate to the central microstructure of the TMCP steel.

Referring to FIG. 4, in the TMCP steel plate (Plate A) according to the comparative example of the present invention, the surface structure is bainite and acicular ferrite, and the central structure is bainite, ferrite and acicular ferrite. Organization can be confirmed. Meanwhile, in the TMCP steel plate (Plate B) according to the embodiment of the present invention, the surface structure is bainite and ferrite structure, the center structure includes bainite, ferrite and acicular ferrite structure, (Partial DRX) < / RTI >

The low-temperature impact test was conducted on the comparative examples and the examples, and the results are shown in Figs. 5 and 6. Fig.

5 and 6, in the TMCP steel plate (Plate A) according to the comparative example of the present invention, the difference in the low temperature impact property values between the surface portion and the center portion of the steel is relatively large in the 0 ° C region, , The difference in low-temperature impact property values between the surface portion and the center portion of the steel is relatively small at 0 ° C in the TMCP steel plate (Plate B).

It is to be understood that the invention includes various modifications and equivalent embodiments that can be derived from the disclosed embodiments as well as those of ordinary skill in the art to which the present invention pertains. Accordingly, the technical scope of the present invention should be defined by the following claims.

Claims (7)

delete delete (a) from 0.06 to 0.085% of carbon (C), 0.15 to 0.25% of silicon (Si), 1.45 to 1.6% of manganese (Mn), 0.01% or less of phosphorus (excluding 0% (Ni), 0.65 to 0.75% of nickel (Ni), 0.1 to 0.25% of copper (Cu), 0.025 to 0.035% of niobium (Nb) (Excluding 0%), hydrogen (H) 2.5 ppm or less (however, 0% or less) of nitrogen (N), 0.01 to 0.1% of chromium (Cr), 0.01 to 0.02% of titanium, 0.03 to 0.07% of molybdenum Reheating the steel slab consisting of the remaining iron (Fe) and unavoidable impurities to a temperature of 1125 to 1175 캜;
(b) primary rolling the reheated steel slab at a reduction rate of 4 to 18% by applying a mean flow stress (MFS) of 100 to 150 MPa per pass;
(c) applying a mean flow stress (MFS) of 300 to 400 MPa per pass to the primary rolled steel material, followed by secondary rolling at a reduction ratio of 2 to 4%; And
(d) cooling the secondary rolled steel material;
≪ / RTI > The method of claim 3,
Characterized in that the primary rolling is set such that the reduction rate per rolling pass gradually increases, and the secondary rolling is set so that the effective pressing down stress per rolling pass gradually increases.
Method of manufacturing TMCP steel. 5. The method of claim 4,
Characterized in that the primary rolling is carried out such that the reduction rate per rolling pass gradually increases to a maximum at 18% and the secondary rolling is carried out such that the effective rolling reduction stress per rolling pass gradually increases from 200 MPa.
Method of manufacturing TMCP steel. The method of claim 3,
Wherein the finish rolling temperature of the secondary rolling is 730 to 770 占 폚.
Method of manufacturing TMCP steel. The method according to claim 6,
Wherein step (d) comprises: starting cooling at 730 to 700 < 0 > C and ending cooling at 380 to 420 &
Method of manufacturing TMCP steel.

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