KR101185277B1 - Method of manufacturing 500mpa grade for lpg type steel sheet - Google Patents

Abstract

The present invention relates to a method for manufacturing a high strength steel for 500MPa LPG and easy to process, and more particularly, to the addition of Mo to Ni steel to improve the hardening function of the steel, improve the strength by transformation and precipitation strengthening And it relates to a high-strength steel manufacturing method for 500MPa-class LPG and its steel material is easy to workability by reducing the yield ratio by inducing tensile properties to be a continuous yield.

Description

METHOD OF MANUFACTURING 500MPH GRADE FOR LXP TYPE STEEL SHEET}

The present invention relates to a method for manufacturing a high strength steel for 500MPa LPG and easy to process, and more particularly, to the addition of Mo to Ni steel to improve the hardening function of the steel, improve the strength by transformation and precipitation strengthening And it relates to a high-strength steel manufacturing method for 500MPa-class LPG and its steel material is easy to workability by reducing the yield ratio by inducing tensile properties to be a continuous yield.

As the high-strength hot rolled steel for processing, ferrite, martensite structure, ferrite, mixed structure composed of bainite structure, or near single phase structure mainly composed of bainite and ferrite are widely known.

The seismic characteristics of structural steels are most closely related to the yield ratio (ie yield strength / tensile strength ratio) among mechanical properties.

Structural steels are required to be high strength since they must be able to be used as structural materials in the construction of various structures in the future.

In recent years, attention is being paid to the development of securing the toughness at the use temperature of such steels and securing the safety at the strength and working pressure.

According to the present invention, a method of manufacturing high strength steel for 500MPa LPG having easy processability according to the present invention is easy to process 500MPa LPG, which is capable of securing post-processability to a pressure vessel and preventing the reduction in strength by post-processing without a large impact toughness reduction. It is an object of the present invention to provide a method for producing high strength steel for steel.

The method of manufacturing high strength steel for 500MPa LPG easy to process according to the present invention, by adding Mo component to improve the hardening function of the steel to Ni steel to induce the improvement of strength by transformation and precipitation strengthening strength by post-processing It is an object of the present invention to provide a method for manufacturing high strength steel for 500MPa class LPG, which is easy to compensate for degradation.

An object of the present invention is to provide a steel produced through a high strength steel manufacturing method for 500MPa class LPG easy to process.

% By weight to 100% by weight, C: 0.08 to 0.15%, Si: 0.2 to 0.3%, Mn: 0.5 to 1.2%, P: 0.01 to 0.02%, S: 0.004 to 0.006%, Ti: 0.01% or less A heating step of reheating the steel composed of Mo: 0.05 to 0.1%, Ni: 3.0 to 5.0% and the remaining Fe and other unavoidable impurities; A rolling step of hot rolling the reheated steel in the heating step; A soaking step of soaking and heat-treating the steel rolled in the rolling step; And a cooling step of air cooling the steel called in the soaking step.

Subsequently, in the heating step, the reheating of the steel is carried out at 1100 ~ 1200 ℃.

In the soaking step, the soaking heat treatment temperature of the steel is preferably 840 to 880 ° C.

Subsequently, in the rolling step, hot rolling is preferably carried out at a temperature of 900 ~ 1000 ℃.

In addition, in the cooling step, the air-cooling temperature for air cooling the steel is preferably cooled at room temperature after the soaking heat treatment.

Subsequently, in terms of weight% based on 100% by weight, C: 0.08 to 0.15%, Si: 0.2 to 0.3%, Mn: 0.5 to 1.2%, P: 0.01 to 0.02%, S: 0.004 to 0.006%, Ti: 0.01 It is preferably composed of% or less, Mo: 0.05 to 0.1%, Ni: 3.0 to 5.0% and the remaining Fe and other unavoidable impurities.

On the other hand, the steel material, it is preferable that the impact energy (CVN) is 77 to 91 (77) in order to secure the impact toughness.

Subsequently, the steel material, the yield point (YP) is preferably 350 to 400 MPa.

In addition, the steel, the tensile strength of the steel is preferably 520 to 570 MPa.

Next, it is preferable that the said steel materials have an elongation 30 to 35%.

In particular, the steel material preferably has a yield ratio (YR) of 65 to 70%.

Subsequently, it is preferable that the microstructure is a complex structure in which the microstructure is a residual acetite (RA) on ferrite bainite.

The method of manufacturing high-strength steel for 500 MPa grade LPG according to the present invention has excellent post-processability because it is possible to secure post-processability to a pressure vessel and to prevent deterioration of strength by post-processing without large impact toughness reduction. There is a technical effect to produce steel with the characteristics of.

500MPa high-strength steel manufacturing method for easy processing according to the present invention, by adding the Mo component to improve the hardening function of the steel to Ni steel induces the improvement of strength by transformation and precipitation strengthening impact characteristics at ultra low temperature There is a technical effect to produce steel that can improve the.

1 is a flow chart schematically showing a process sequence for a high strength steel manufacturing method for 500MPa class LPG easy to process according to an embodiment of the present invention.
Figure 2 is a photograph showing the structure of a high-strength steel for 500MPa class LPG easy processability according to an embodiment of the present invention.

DETAILED DESCRIPTION The following detailed description of the invention refers to the accompanying drawings that show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It should be understood that the various embodiments of the present invention are different, but need not be mutually exclusive. For example, certain features, structures, and characteristics described herein may be implemented in other embodiments without departing from the spirit and scope of the invention in connection with one embodiment. It is also to be understood that the position or arrangement of the individual components within each disclosed embodiment may be varied without departing from the spirit and scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is to be limited only by the appended claims, along with the full scope of equivalents to which such claims are entitled, if properly explained. In the drawings, like reference numerals refer to the same or similar functions throughout the several views, and length and area, thickness, and the like may be exaggerated for convenience.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, so that those skilled in the art can easily carry out the present invention.

In the following detailed description, the high-strength steel for LPG, which is used as an ultra low temperature of -101 ° C, for example, uses Ni alloy steel to which a large amount of Ni is added. In order to compensate for the reduction in strength due to post-processing by inducing the improvement of strength by transformation and precipitation strengthening, and to facilitate post-processability by lowering yield ratio, the processability of the present invention is easy throughout the technical field. Of course, the technical configuration of the high-strength steel for LPG grade [particularly, the steel 30 added with Mo (molybdenum) to the Ni (nickel) alloy steel] can be equally applied.

Steel material 30 using the high-strength steel manufacturing method for 500MPa class LPG having easy hole workability according to the present invention, in a weight% to 100% by weight, C: 0.08 ~ 0.15%, Si: 0.2 ~ 0.3%, Mn: 0.5-1.2%, P: 0.01-0.02%, S: 0.004-0.006%, Ti: 0.01% or less, Mo: 0.05-0.1%, Ni: 3.0-5.0% and the rest of Fe and other unavoidable It may have a steel 30 which is a steel slab composed of impurities.

In particular, 3.0% to 5.0% of Ni (nickel) is added and 0.05% to 0.1% of Mo (molybdenum).

Hereinafter, the role and amount of each component constituting the steel 30, which is a high strength hot rolled steel according to the present invention, will be described.

Carbon (C): 0.08 to 0.15 wt%

Carbon (C) is an element added to improve the hardenability and secure the strength of the steel.

Subsequently, it plays a role of securing strength through precipitation or solid solution strengthening. Such carbon is preferably added in 0.08 to 0.15% by weight of the total weight of the steel 30.

When the added amount of carbon exceeds 0.15% by weight, the yield point and the ductility are deteriorated more rapidly than the positive factor which increases the strength, so that post-processability can be deteriorated, thereby improving post-workability. Since there is a fear of contrary to the characteristics, the significance of the addition of carbon may be lowered.

If the carbon is added in less than 0.08% by weight, the hardenability is less, so that it is difficult to secure the strength of the steel 30.

In addition, it is uneconomical because a relatively large amount of other alloying elements must be added to achieve the same strength.

In addition, it is uneconomical to add a relatively large amount of other alloy elements in order to exhibit the same strength.

silicon( Si ): 0.2 to 0.3 wt%

Silicon increases the strength of steel and is an element necessary for deoxidation.

Such silicon plays a role of improving post-workability of the steel by retarding cementite production.

In particular, in the present invention, silicon is added as a deoxidizer for removing oxygen of the steel and is an element that contributes to the solid solution strengthening effect of the steel 30.

Such silicon is preferably added at 0.2 to 0.3% by weight within the carbon content range according to the present invention.

If the silicon content exceeds 0.3% by weight, the weldability of the steel is lowered and red scale is generated during slab reheating and hot rolling, which may cause a problem in surface quality and also may cause a problem of deterioration of plating property after welding. have.

On the other hand, when the content of silicon is added less than 0.2% by weight, the degree of contribution to the solid solution strengthening effect of the steel 30 is insufficient, the effect of improving the strength is insignificant, the deoxidation action of the molten steel is insufficient to clean steel Difficult to get.

manganese( Mn ): 0.5 ~ 1.2 wt%

Manganese is an effective element for increasing strength without deteriorating toughness.

In the present invention, manganese is very effective as a solid solution strengthening element, and is an effective element for securing strength by improving hardening of steel. Manganese also contributes to grain refinement of ferrite by delaying ferrite and pearlite transformation as an austenite stabilizing element.

Such manganese is preferably added in a content ratio of 0.5 to 1.2% by weight in the carbon addition range according to the present invention.

When the amount of manganese exceeds 1.2% by weight, the weldability is greatly reduced, causing inclusions and segregation, thereby acting as a factor that inhibits the toughness of the manufactured hot rolled steel.

In addition, manganese has a problem in that the manufacturing cost increases as it is added as an expensive element.

If the added amount of manganese is less than 0.5% by weight, the effect of strengthening the solid solution is obtained slightly, it may be difficult to secure the strength.

Therefore, in the present invention, it is preferable to adjust the amount of manganese to 0.5 to 1.2% by weight or less in order to reduce manufacturing cost and minimize center segregation and secure strength.

Phosphorus (P): 0.01 to 0.02 wt%

Phosphorus (P) is an impurity element present in steel, and it is advantageous to keep it as low as possible because it can greatly inhibit components and impact toughness that are advantageous for improving strength and corrosion resistance.

In addition, phosphorus (P) plays a role of ensuring the strength without lowering the desired workability or formability.

Such phosphorus (P) is preferably added in an amount of 0.01 to 0.02% by weight of the total weight of the steel 30.

However, when the addition amount of phosphorus (P) exceeds 0.02% by weight, since it may adversely affect the weldability and the like, it is preferable to limit the addition range.

Sulfur (S): 0.004 to 0.006 wt%

Sulfur (S) is an impurity element present in steel similarly to phosphorus (P).

Subsequently, sulfur (S) corresponds to impurities which are precipitated in the form of MnS or the like to increase the amount of precipitates.

In particular, it may inhibit the workability and weldability of the hot rolled steel and cause cracks during processing. Therefore, in the present invention, the addition amount is preferably 0.004 to 0.006% by weight, but preferably limited to the low addition amount ratio.

titanium( Ti ): 0.01 wt% or less

Titanium (Ti) serves to improve the strength while maintaining excellent stretch and stretch flangeability.

In particular, titanium (Ti) can form carbides, nitrides, sulfides, thereby contributing to the improvement of strength and toughness of the hot rolled steel.

Although these effects are recognized as containing 0.001% or more, when it contains exceeding 0.01%, the addition amount of carbon (C) which contributes to plastic hardenability can be reduced.

Therefore, the addition amount of titanium may be 0.01 weight% or less.

When the amount of titanium (Ti) is more than 0.01% by weight, a large amount of coarse titanium (Ti) carbide or nitride may be generated during heating before hot rolling and may impair ductility or processability.

molybdenum( Mo ): 0.05 ~ 0.1 wt%

Molybdenum (Mo) is a very effective element to increase the strength of the material even with a small amount of addition.

Such molybdenum (Mo) can form a fine composite precipitate with titanium (Ti), and can strengthen the steel while maintaining excellent stretch and stretch flangeability.

However, when molybdenum is excessively added, a hard phase is formed, and thus the stretch flange property may be lowered. If the content is 0.05 wt% or less, the strength increasing effect required by the present invention cannot be obtained.

If the content exceeds 0.1% by weight, the production cost is increased, which is uneconomic.

Therefore, in the present invention, it is preferable to limit the content of molybdenum (Mo) to 0.05 to 0.1% by weight.

nickel( Ni ): 3.0 to 5.0 wt%

Nickel (Ni) is a graphitization promoting element and an element that improves delayed fracture resistance.

In addition, it may be added as an element for preventing the high temperature brittleness generated when the addition of copper (Cu) to increase the strength and to improve the corrosion resistance.

Since the nickel (Ni) is an alloy element capable of improving low temperature toughness, in order to obtain the effect in the present invention, it is preferable to use more than 3.0% by weight.

However, since nickel (Ni) is expensive, it is uneconomical when it contains a large amount of addition, and when the content exceeds 5.0% by weight, the effect may be saturated. It is preferred to limit to 3.0 to 5.0% by weight.

The rest other than the above substantially consists of iron (Fe).

Substantially consisting of iron (Fe) means that the inclusion of other trace elements, including unavoidable impurities, can be included in the scope of the present invention, as long as it does not interfere with the effects of the present invention.

The steel material 30 having such a composition may have a steel material excellent in low temperature toughness for LPG, which is the target of the present invention, and also has a yield point of 350 to 400 MPa and 520 to 570 MPa, which is high in strength and secures post-workability. It can have a tensile strength of.

1 is a flow chart schematically showing a process sequence for a high strength steel manufacturing method for 500MPa class LPG easy to process according to an embodiment of the present invention.

Referring to Figure 1, 500MPa-class high-strength steel manufacturing method for LPG is a heating step (S100) for largely reheating the steel 30, the rolling step of hot rolling the steel 30 heated in the heating step (S100) (S200), the soaking step (S300) called the steel material 30 rolled in the rolling step (S200), the cooling step of air cooling the steel material 30 called in the soaking step (S300) (S400) It includes.

As shown in Figure 1, a high-strength steel manufacturing method for 500MPa LPG according to the present invention will be described below.

Heating stage S100 )

The heating step (S100) for reheating the steel slab is weight percent based on 100 wt%, C: 0.08 to 0.15%, Si: 0.2 to 0.3%, Mn: 0.5 to 1.2%, P: 0.01 to 0.02%, S: 0.004 ~ 0.006%, Ti: 0.01% or less, Mo: 0.05 ~ 0.1%, Ni: 3.0 ~ 5.0% and the heating step of reheating the steel composed of the remaining Fe and other unavoidable impurities (S100).

At this time, the steel slab, which is a steel slab formed as described above, is reheated at a temperature of 1100 to 1200 ° C.

If the reheating temperature is less than 1100 ° C., the precipitates are not sufficiently reusable, and the precipitates are reduced in the process after the hot rolling.

Therefore, by maintaining the reheating temperature of more than 1100 ℃, it is possible to control the re-use of the precipitate, to improve the strength of the material and to ensure a uniform microstructure in the longitudinal direction of the material.

On the contrary, when such a reheating temperature exceeds 1200 ° C., abnormal grain growth of grains may occur. As a result, this may act as a factor against the increase in strength.

Therefore, the reheating temperature of the steel slab in the heating step (S100) is preferably limited to 1100 to 1200 ℃.

Rolling stage ( S200 )

In the rolling step (S200) of hot rolling the steel slab reheated in the heating step (S100), the steel material 30 which is the reheated steel slab is hot rolled.

At this time, it is preferable that hot rolling temperature is 900-1000 degreeC.

As such, when the finish hot rolling temperature exceeds 1000 ° C., brittleness of the steel sheet may increase with a large amount of cooling, and when the finish hot rolling temperature is less than 900 ° C., workability may be deteriorated depending on microstructure unevenness.

Therefore, the finish hot rolling temperature in the rolling step (S200) is preferably limited to 900 to 1000 ℃.

So called S300 )

It is called the steel 30 rolled in the rolling step (S200).

At this time, the temperature called the steel material 30 is preferably 840 to 880 ℃.

Thus, when the soak temperature of the steel 30 exceeds 880 ℃ causes a change in the material.

In addition, when the soak temperature of the steel 30 is less than 840 ° C., the structure may be finely homogenized to reduce strength and toughness.

Therefore, the soak temperature in the soaking step (S300) is preferably carried out at 840 to 880 ℃.

Cooling stage ( S400 )

It is a step of cooling by cooling the steel material 30, which is a steel slab called in the previous soaking step (S300) at room temperature.

The steel material 30 in the present invention is gradually cooled by air cooling, and gradually cools directly above the phase transformation temperature, whereby generation of a supercooled structure can be suppressed.

Therefore, the cooling in the cooling step (S400) is preferably air cooled at room temperature to prevent the occurrence of subcooled tissue.

Figure 2 is a photograph showing the structure of a high-strength steel for 500MPa class LPG easy processability according to an embodiment of the present invention.

Referring to Figure 2 Ni and Mo Mo: 0.05 ~ 0.1% by weight, Ni: 3.0 ~ 5.0% by weight High strength steel 30 for 500MPa LPG according to the present invention, Ferrite (Ferrite) Bainite It can be seen that the composite tissue contains residual acetonitrile (RA) in the phase.

By the manufacturing method as described above, the high-strength steel for 500MPa grade LPG according to the present invention can secure impact toughness while being used for ultra-low temperature of -101, it is easy to workability.

Thus, while being used for the ultra low temperature of -101, the reason why the toughness can be secured and the steel 30 can be easily obtained, as described above, is Mo: 0.05 to 0.1% by weight, Ni: It became possible by containing 3.0-5.0 weight%.

As such, the final structure of the steel material 30 produced by the manufacturing method according to the present invention consists of a tissue containing the residual austenite phase in the two-phase composite tissue in which the ferrite structure is formed on the bainite.

Thus, the steel material 30 produced by the manufacturing method according to the present invention will have a tensile strength corresponding to the range of 520 to 570 MPa.

In addition, the elongation (EL) of the steel material 30 can be seen that the elongation is 30 to 35%.

As can be seen from the experimental results below, Mo (molybdenum) is added to the Ni alloy steel, specifically Mo: 0.05 to 0.1% by weight, Ni: 3.0 to 5.0% by weight, the tensile strength while maintaining the elongation (EL) It shows an excellent characteristic that (TS) becomes high.

In addition, the yield point (YP) of the steel material 30 produced by the manufacturing method according to the present invention has a 350 to 400 MPa, the yield ratio (YR) has a 65 to 70%.

Hereinafter, the present invention will be described in more detail with reference to the following examples.

Example

Hereinafter, the configuration and operation of the present invention through the preferred embodiment of the present invention will be described in more detail.

However, this is presented as a preferred example of the present invention, it should not be construed that the present invention is limited by this in any sense.

Details that are not described herein will be omitted since those skilled in the art can sufficiently infer technically.

One. High elongation  Fabrication of High Strength Steels

The high elongation high strength steel 30 according to the preferred invention material 1 and comparative material 1 of the present invention was prepared under the composition shown in Table 1 and the process conditions described in Table 2.

In Table 1, the addition amount ratio of the components is weight%, and the temperature unit is ° C.

Steel grade C Si Mn P S Ni Mo Ti Soaking temperature Comparative material Ni 0.1 0.25 1.2 0.01 0.005 3.5 - - 870 Invention Ni + Mo 0.1 0.25 1.2 0.01 0.005 3.5 0.1 0.01 870

Table 2 shows the yield point (YP), tensile strength (TS), elongation (EL) and the yield ratio (YR) of high-strength steel for 500MPa class LPG according to the preferred invention material 1 and comparative material 1 of the present invention.

Non comparable Ni steel Invention Ni + Mo Steel YP [MPa] TS [MPa] EL [%] YR [%] CVN YP [MPa] TS [MPa] EL [%] YR [%] CVN After heat treatment
407 519 36 78 137 380 558 33 68 77 394 520 33 76 102 379 558 33 68 91

Referring to Table 1 and Table 2, Mo (molybdenum) is added to the Ni alloy steel, specifically, Mo: 0.05 to 0.1% by weight, Ni: 3.0 to 5.0% by weight, while maintaining the elongation (EL) Excellent tensile strength (TS) is exhibited.

In addition, it can be seen that the inventive material 1 has a higher elongation (EL) but a higher tensile strength (TS) R than the comparative material 1.

Therefore, the high-strength steel for 500 MPa grade LPG produced in accordance with the present invention, while maintaining the elongation (EL) to improve the tensile strength (TS), it is possible to increase the post-workability while increasing the impact toughness.

In the above described a preferred embodiment of the steel produced according to the high-strength steel manufacturing method for 500MPa class LPG according to the present invention.

The foregoing embodiments are to be understood in all respects as illustrative and not restrictive, the scope of the invention being indicated by the following claims rather than the foregoing description, and the meaning and scope of the claims and All changes or modifications derived from the equivalent concept should be interpreted as being included in the scope of the present invention.

30: steel
S100: heating stage
S200: rolling step
S300: soak stage
S400: Cooling stage

Claims (12)

By weight%, C: 0.08 to 0.15%, Si: 0.2 to 0.3%, Mn: 0.5 to 1.2%, P: 0.01 to 0.02%, S: 0.004 to 0.006%, Ti: more than 0% to 0.01% or less, Mo : 0.05 ~ 0.1%, Ni: 3.0 ~ 5.0% and the heating step of reheating the steel composed of the remaining Fe and other unavoidable impurities (S100);
A rolling step of hot rolling the reheated steel in the heating step (S200);
A soaking step (S300) of soaking and heat-treating the steel rolled in the rolling step; And
500MPa-grade LPG high-strength steel manufacturing method comprising a; cooling step of air cooling the steel called in the soaking step (S400).
The method of claim 1,
In the heating step,
Reheating of the steel is a method for producing high strength steel for 500MPa LPG, characterized in that carried out at 1100 ~ 1200 ℃.
The method of claim 1,
In the soaking step,
The soak heat treatment temperature of the steel is 840 to 880 ℃ high strength steel manufacturing method for 500MPa class LPG, characterized in that.
The method of claim 1,
In the rolling step,
Hot rolling is a high-strength steel manufacturing method for 500MPa-class LPG, characterized in that carried out at a temperature of 900 ~ 1000 ℃.
The method of claim 1,
In the cooling step,
The air-cooled temperature of the steel material air-cooled is 500MPa class LPG high strength steel manufacturing method, characterized in that the cooling at room temperature after the soaking heat treatment.
% By weight to 100% by weight, C: 0.08 to 0.15%, Si: 0.2 to 0.3%, Mn: 0.5 to 1.2%, P: 0.01 to 0.02%, S: 0.004 to 0.006%, Ti: more than 0% To less than 0.01%, Mo: 0.05 ~ 0.1%, Ni: 3.0 ~ 5.0% and the remaining high strength steel for 500MPa LPG characterized in that it is composed of other inevitable impurities.
The method according to claim 6,
The steel,
High strength steel for 500MPa class LPG, characterized in that the impact energy (CVN) is 77 to 91 (Ｊ) to secure impact toughness.
The method according to claim 6,
The steel,
Yield point (YP) is a high strength steel for 500MPa class LPG, characterized in that 350 to 400 MPa.
The method according to claim 6,
The steel,
High strength steel for 500MPa class LPG, characterized in that the tensile strength of the steel is 520 to 570 MPa.
The method according to claim 6,
The steel,
High strength steel for 500MPa class LPG, characterized in that the elongation is 30 to 35%.
The method according to claim 6,
The steel,
Yield ratio (YR) is a high strength steel for 500MPa grade LPG, characterized in that 65 to 70%.
The method according to claim 6,
The steel,
The high-strength steel for 500MPa LPG, characterized in that the microstructure is a composite structure containing residual austenite (RA) on the ferrite bainite (Bainite).

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