KR101193768B1 - Addition of boron high-carbon steel with hardenability and method of manufacturing the same - Google Patents

Abstract

The present invention relates to a boron-added high carbon hot rolled steel sheet having a hardenability and a method of manufacturing the same, wherein C: 0.32 to 0.34 wt%, Mn: 1.1 to 1.3 wt%, Si: 0.11 to 0.22 wt%, Mo: 0.15 to Hot rolling step of slab plate consisting of 0.25 wt%, Ti: 0.001 to 0.003 wt%, B: 0.001 to 0.0025 wt% and the remaining amount of Fe and other unavoidable impurities at a hot finish rolling temperature (FDT) of 850 to 900 ° C. Winding the hot rolled sheet at a coiling temperature (CT) of 640 to 680 ° C., wherein the slab sheet is made of a composite structure including ferrite and pearlite. P: 0.02% by weight or less, S: 0.01% by weight or less and Cr: 0.15% by weight or less, wherein Mo and Cr are in the range of 0.15 <[Mo] + [Cr] ≤ 0.3 to the hot rolled steel sheet It is characterized by being added.

Description

Boron-added high carbon hot rolled steel sheet and its manufacturing method {ADDITION OF BORON HIGH-CARBON STEEL WITH HARDENABILITY AND METHOD OF MANUFACTURING THE SAME}

The present invention relates to a boron-added high carbon hot rolled steel sheet and a method for manufacturing the same, and more particularly, a tensile strength of 600 MPa or more, elongation of 25% or more, Vickers hardness of 230 Hv or more, and ferrite. And it provides a hot-rolled steel sheet composed of pearlite (Pearlite), to produce a steel pipe using the hot-rolled steel sheet and then to a heat treatment and quenching at 950 ℃ to have a Vickers hardness of 680 Hv or more.

In order to give a high strength and light weight effect to a tool or an automobile, much research is made about the material of the various components which comprise a tool or an automobile.

In particular, hot rolled steel sheets are mainly applied as structural members for automobiles.

Hot rolled steel sheets are usually produced through slab reheating, hot rolling, cooling and winding.

The slab reheating process reheats the slab plate in semifinished form.

Next, in the finishing hot rolling process, the reheated slab is hot rolled using a rolling roll.

Next, in the cooling process, water is sprayed to cool the rolled sheet material in order to wind up the rolled sheet.

Next, in the winding process, the plate is cooled by the cooling process.

The purpose of the present invention is to use boron-added high carbon steel, but in order to minimize the content of Cr, which was previously added in a large amount for quenching, by increasing the content of Mo, the tensile strength is 600 MPa or more, elongation of 25% or more, Vickers The hardness is 230 Hv or more, and to manufacture a hot rolled steel sheet composed of ferrite and pearlite.

In addition, another object of the present invention is to provide a hot rolled steel sheet manufactured by the above-described method, to process the hot rolled steel sheet to produce a steel pipe, and to heat-treat and quench the hot rolled steel sheet having a Vickers hardness having a Vickers hardness of 680 Hv or more To provide a method for producing a boron-added high carbon hot rolled steel sheet for steel pipes.

Boron-added high carbon hot-rolled steel sheet manufacturing method having a hardenability according to an embodiment of the present invention is C: 0.32 ~ 0.34 wt%, Mn: 1.1 ~ 1.3 wt%, Si: 0.11 ~ 0.22 wt%, Mo: 0.15 ~ 0.25 Hot rolling step of slab plate composed of weight%, Ti: 0.001 to 0.003 weight%, B: 0.001 to 0.0025 weight% and remaining Fe and other unavoidable impurities at hot finish rolling temperature (FDT) 850 to 900 ° C. It characterized in that it comprises the step of winding the rolled plate at a coiling temperature (CT) 640 ~ 680 ℃.

Here, the slab plate is characterized in that it comprises P: 0.02% by weight or less, S: 0.01% by weight or less and Cr: 0.15% by weight or less. At this time, the Mo and Cr is characterized in that it is added to the hot rolled steel sheet in a range satisfying 0.15 <[Mo] + [Cr] ≤ 0.3. (In the above, [] means the weight percent of each component.)

In addition, the Mn and Si are added to the hot rolled steel sheet in a range satisfying 6 ≦ [Mn] / [Si] ≦ 9. (In the above, [] means the weight percent of each component.)

Next, the final structure of the hot rolled steel sheet is characterized in that the composite structure containing ferrite (Ferrite) and pearlite (Pearlite).

In addition, boron-added high-carbon hot rolled steel sheet having a hardenability according to an embodiment of the present invention is C: 0.32 ~ 0.34 wt%, Mn: 1.1 ~ 1.3 wt%, Si: 0.11 ~ 0.22 wt%, Mo: 0.15 ~ 0.25 Weight%, Ti: 0.001 ~ 0.003% by weight, B: 0.001 ~ 0.0025% by weight and the balance of Fe and other unavoidable impurities, characterized in that the microstructure is a composite structure containing ferrite and pearlite (Pearlite) do.

Here, the tensile strength (TS) of the hot rolled steel sheet is 600 MPa or more, elongation (EL) is 25% or more, Vickers hardness is characterized in that 280Hv or more.

In addition, the method for manufacturing a hot rolled steel pipe according to an embodiment of the present invention is C: 0.32 to 0.34% by weight, Mn: 1.1 to 1.3% by weight, Si: 0.11 to 0.22% by weight, Mo: 0.15 to 0.25% by weight, Cr: Providing a slab plate composed of 0.15 wt% or less, Ti: 0.001 to 0.003 wt%, B: 0.001 to 0.0025 wt%, and a balance of Fe and other unavoidable impurities; and hot finishing rolling temperature (FDT) of the slab plate. A hot rolling step at 850 to 900 ° C., winding the hot rolled plate at a winding temperature (CT) of 640 to 680 ° C., pipe forming using the rolled up rolled plate, and heat treating the pipe. It characterized in that it comprises a step of quenching.

Here, the heat treatment temperature is 850 ~ 950 ℃, quenching is characterized in that to perform up to the martensite transformation temperature (Ms).

At this time, the Vickers hardness of the hot rolled steel pipe is characterized in that more than 680Hv.

The boron-added high carbon hot rolled steel sheet having a hardenability according to the present invention and a method for manufacturing the same can contribute to the weight of vehicles and vehicles, such as automobiles, since hardenability suitable for hollow materials is provided.

In particular, when the hot rolled steel sheet according to the present invention uses a round bar as a solid material, weight reduction of about 30% can be realized, and it provides an effect of facilitating the manufacture of steel pipe by providing excellent weldability and pipe joints.

In addition, it provides the deformation preventing properties and excellent elongation required for the durability of the automotive parts when the steel pipe processing as described above, and provides an effect that can simplify the manufacturing process. Therefore, it is possible to reduce the cost of manufacturing the steel pipe and provide an effect of increasing the production efficiency.

1 is a flow chart showing a method of manufacturing a boron-added high carbon hot rolled steel sheet having a hardenability according to an embodiment of the present invention.
Figure 2 is a cross-sectional view showing the microstructure of the boron-added high carbon hot rolled steel sheet according to an embodiment of the present invention.
Figure 3 is a cross-sectional view showing the microstructure of the boron-added high carbon hot rolled steel sheet according to a comparative example of the present invention.

Hereinafter, a boron-added high carbon hot rolled steel sheet having a hardenability according to a preferred embodiment of the present invention and a manufacturing method thereof will be described in detail with reference to the accompanying drawings.

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

Method for producing a boron-added high carbon hot rolled steel sheet having a hardenability according to the present invention is C: 0.32 to 0.34% by weight, Mn: 1.1 to 1.3% by weight, Si: 0.11 to 0.22% by weight, Mo: 0.15 to 0.25% by weight, Hot rolling step of the slab plate composed of Ti: 0.001 to 0.003 wt%, B: 0.001 to 0.0025 wt% and the remaining amount of Fe and other unavoidable impurities at a hot finish rolling temperature (FDT) of 850 to 900 ° C. and the hot rolled sheet It is prepared by using the winding up temperature (CT) 640 ~ 680 ℃.

At this time, the slab plate is a final structure of the hot-rolled steel sheet may be made of a composite structure including ferrite (Ferrite) and pearlite (Pearlite), P: 0.02% by weight or less, S: 0.01% by weight or less and Cr: 0.15% by weight It further comprises% or less, wherein Mo and Cr are preferably added to the hot rolled steel sheet in a range satisfying 0.15 <[Mo] + [Cr] ≦ 0.3.

That is, in the past, a large amount of Cr was included for the hardenability of the boron-added hot rolled steel sheet, but when the amount of Cr was exceeded, the problem of the hardenability was rather reduced. Therefore, the present invention is characterized by further adding Mo to optimize the quenchability while minimizing the Cr content.

In addition, in the present invention, by using a high carbon steel, while ensuring a high strength of 600 MPa or more, it is possible to manufacture a hot rolled steel sheet having an elongation of 25% or more.

Therefore, the present invention is characterized by adjusting the production conditions and the additive component ratio based on the above results. Hereinafter, the component range of this invention and its manufacturing conditions are demonstrated.

Carbon [C]: 0.32 ~ 0.34 wt%

Carbon is an element that contributes to increasing the strength of steel. Generally, a steel added with less than 0.02% by weight of carbon is called ultra low carbon steel, and a low carbon steel having an addition amount of at least 0.02% by weight and less than 0.08% by weight is a medium having an addition amount of at least 0.08% by weight and less than 0.25% by weight. It is called carbon steel, and it is called high carbon steel which has the addition amount of 0.25 weight% or more and less than 0.6 weight%, and what has the addition amount of 0.6 weight% or more is called ultra high carbon steel.

Among them, since the carbon content range used in the present invention belongs to high carbon steel, the hot rolled steel sheet according to the present invention was referred to as 'boron-added high carbon hot rolled steel sheet having quenchability'.

When the content of carbon in the present invention is less than 0.32% by weight, it is difficult to obtain the strength required to be 600 MPa or more and the Vickers hardness value of 280Hv, which makes it difficult to secure durability. Further, even after the heat treatment, the Vickers hardness value of 680 Hv required for the steel pipe cannot be obtained.

In addition, when the carbon exceeds 0.34% by weight, it is difficult to obtain an appropriate elongation of 25% or more, which may degrade the workability. In particular, the poor weldability due to poor weldability.

Therefore, the content of carbon according to the present invention is preferably limited to 0.32 to 0.34% by weight.

Manganese [Mn]: 1.1 ~ 1.3 wt%

Manganese is added to prevent red brittleness due to FeS formation in which S and Fe are inevitably contained in the steel manufacturing process. Therefore, the addition of manganese generally decreases the ductility at the time of strength increase rather than the addition of carbon.

However, even if the carbon content is high, if the amount of manganese is lower than 1.1 wt%, the strength required by the present invention is not achieved, and if the amount of manganese is excessively increased to an amount exceeding 1.3 wt%, the amount of nonmetallic inclusions is increased. Increasingly, defects such as crack generation may occur during welding of the tube, and segregation phenomenon such as central segregation and micro segregation may become severe, thereby decreasing workability.

Therefore, in the present invention, it is preferable to limit the content of manganese to 1.1 to 1.3% by weight.

Phosphorus [P]: 0.02 wt% or less

Phosphorus is an element that has a high possibility of segregation in the manufacture of steel material, which forms not only the central segregation but also fine segregation, which adversely affects the material, and may also cause delayed fracture, which is destroyed after a certain time after forming.

Therefore, in the present invention, while limiting the content of phosphorus to 0.02% by weight or less, it is preferable to adjust so that the minimum amount can be added.

Sulfur [S]: 0.01 wt% or less

Sulfur (S) may combine with manganese to form non-metallic inclusions such as MnS, which may cause defects such as post-cracking during the piping process.

Therefore, it is preferable to completely exclude sulfur (S), but it is expensive to completely remove the sulfur (S), so it is desirable to reduce the content to 0.01 wt% or less as much as possible.

Here, the phosphorus (P) and sulfur (S) is ideally at a minimum content of 0% by weight, but it is preferable to substantially filter out impurities by 0% by weight in terms of cost or efficiency in view of more than 0% by weight. Do.

Silicon [Si]: 0.11 ~ 0.22 wt%

Silicon (Si) serves to improve the formability of the hot rolled steel sheet by delaying pearlite production. If the amount of silicon (Si) is less than 0.11% by weight, the effect of improving formability is inferior, and if it exceeds 0.22% by weight, there is a problem in that the surface characteristics of the hot rolled steel sheet are lowered.

In particular, in the present invention, silicon (S) may be combined with the manganese (Mn) described above to control the electric resistance welding (ERW) characteristics.

When [] means the weight percent of each component, it is preferable to be added to the slab plate according to the present invention in a range satisfying 6 ≦ [Mn] / [Si] ≦ 9.

When the [Mn] / [Si] is less than 6, the use of the Mn-Si-based oxide is lower than the welding temperature, so that a liquid oxide is generated in the tubing process using electric resistance welding (ERW). There is a problem in that the weld is not formed clean because it is submerged out of the weld.

Next, when the [Mn] / [Si] is greater than 9, because the content of Mn is increased, workability may be inferior. Therefore, such silicon (Si) is preferably added in a content ratio of 0.11 to 0.22% by weight of the total weight of the hot rolled steel sheet.

Molybdenum [Mo]: 0.15 ~ 0.25 wt%

Molybdenum (Mo) in the present invention is an essential element for securing the hardenability and room temperature aging resistance of the steel sheet.

Particularly, the molybdenum (Mo) is a main element that provides hardenability to the hot rolled steel sheet according to the present invention in place of chromium (Cr) described below, and when the content thereof is less than 0.15% by weight, the hardenability may be reduced. .

Next, when the content of molybdenum (Mo) exceeds 0.25% by weight, the increase in hardenability compared to the amount of molybdenum added is not large. In other words, the effect of improving the hardenability becomes saturated, resulting in a cost increase, resulting in a decrease in efficiency.

Chromium [Cr]: 0.15 wt% or less

Chromium is generally used as an element to improve the hardenability of hot rolled steel sheets. However, compared with the molybdenum (Mo) there is a problem that the efficiency of increasing the hardenability due to addition. Therefore, it is desirable to limit the maximum content to 0.15% by weight or less.

At this time, in the present invention, chromium (Cr) is 0% by weight, that is, may not be used. However, when added in the range of 0.15% by weight or less, it is preferable to add in a range that satisfies 0.15 <[Mo] + [Cr] ≤ 0.3. Here, [] means weight percent of each component, and may be added up to 0.4 wt% according to the addition range of molybdenum (Mo) and chromium (Cr) according to the present invention. However, 0.4 wt% gives similar results to 0.3 wt% of its effectiveness for increasing hardenability. Therefore, it is preferable to make the maximum addition amount of molybdenum (Mo) and chromium (Cr) 0.3 weight% or less.

Titanium [Ti]: 0.001 ~ 0.005 wt%

In the present invention, titanium (Ti) is combined with carbon (C) or nitrogen (N) in the steel to precipitate in the form of nitrides such as TiN. Therefore, it is an element that can improve the strength through solid solution strengthening in iron (Fe).

When the addition amount of the titanium (Ti) is less than 0.001% by weight of the total weight of the slab plate, the above-mentioned strength improvement effect is small, so the lower limit of the addition amount is made 0.001% by weight or more.

In addition, since TiC is precipitated when the added amount of titanium (Ti) exceeds 0.005% by weight, a problem of deteriorating the weld heat affected zone (HAZ) toughness may occur. Therefore, the amount of titanium (Ti) added according to the present invention is preferably limited to 0.001 to 0.005% by weight of the total weight of the slab plate.

Boron [B]: 0.001 ~ 0.0025 wt%

Boron (B) in the present invention serves to improve the hardenability of the hot rolled steel sheet by retarding the ferrite transformation of austenite during the cooling process. Therefore, when added in less than 0.001% by weight it is difficult to obtain sufficient hardenability, when it exceeds 0.0025% by weight may cause segregation may increase the material deviation.

Therefore, the amount of boron (B) added according to the present invention is preferably limited to 0.001 to 0.0025% by weight of the total weight of the slab plate.

In the present invention, the slab formed as described above is hot rolled, then wound and manufactured into a hot rolled steel sheet. In order to secure the strength and ductility of the hot rolled steel sheet, it is essential to control the microstructure, and for this, the setting of the finish rolling temperature (FDT) and the winding temperature (CT) is important.

-Finish rolling temperature (FDT): 850 ~ 900 ℃

In the hot rolling process, if the hot finishing rolling temperature is too high at a temperature exceeding 900 ° C., the pearlite nucleation is delayed due to the coarse grains, and the distance from the winding temperature is large, thereby degrading the temperature controllability.

In addition, when the hot finishing rolling temperature is too low at less than 850 ° C., the increase in the reduction load and the possibility of the formation of the mixed structure at the edge portion increase.

Therefore, in the present invention, it is preferable to adjust the finish rolling temperature at 850 ~ 900 ℃.

-Coiling temperature (CT): 640 ~ 680 ℃

When the coiling temperature is raised to a temperature exceeding 680 ℃, the spacing of the pearlite layer structure becomes wide. The wide spacing of the stratified structures does not effectively prevent dislocation movement, resulting in low strength and concentration of strain at the interface between coarse pearlite and ferrite.

This concentration of deformation leads to void generation at the interface, which eventually grows into cracks, degrading formability.

In addition, even when the coiling temperature is lower than 640 ° C., the carbon solubility in ferrite is increased, so that a degenerated lamellar structure is obtained, not a perfect pearlite structure, and thus it does not effectively prevent dislocation movement, thereby requiring required strength and Hardness value cannot be obtained.

Therefore, in order to secure the mechanical properties required in the present invention, it is desirable to set the winding temperature at 640 to 680 ° C.

In relation to the composition components and the manufacturing method of the present invention described above, Figure 1 is a flow chart showing a method for producing a boron-added high carbon hot rolled steel sheet having a hardenability according to an embodiment of the present invention.

Referring to Figure 1, the step of preparing a boron-added high carbon slab added Mo in accordance with the present invention (S100), and hot finishing rolling the slab at a temperature of 850 ~ 900 ℃ (S110) and hot finishing Performing the step (S120) of winding the rolled plate at 640 ~ 680 ℃.

The boron-added high carbon hot rolled steel sheet thus formed has a tensile strength of 600 MPa or more, and has an elongation of 25% or more and Vickers hardness of 230 Hv or more.

Next, after performing the step (S130) to form the steel pipe to the tube by the hot rolled steel sheet to perform a heat treatment and quenching (S140) process to produce a steel pipe having a Vickers hardness of 680 Hv or more.

Here, the heat treatment step is carried out at 850 ~ 980 ℃, quenching is preferably performed to the martensite transformation temperature (Ms). At this time, the cooling rate is preferably performed at a rate of 100 ℃ / sec or more.

Since the hot rolled steel sheet performed up to the winding step S120 has a composite structure including ferrite and pearlite, the hot rolled steel sheet has characteristics of excellent formability and weldability while having excellent strength. Therefore, it can be easily manufactured in the form of a steel pipe, and then heated to an austenite transformation temperature of 850 ~ 980 ℃ and then quenched, the microstructure is transformed into martensite and has an excellent Vickers hardness of 680 Hv or more .

Therefore, the boron-added high carbon hot rolled steel sheet manufacturing conditions having a hardenability according to the present invention preferably comply with the above-described composition and the range of addition, and will be described with reference to specific embodiments accordingly.

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

1.Manufacture of hot rolled steel sheet

Example 1

Slab plate consisting of C: 0.33 wt%, Si: 0.17 wt%, Mn: 1.2 wt%, Mo: 0.25 wt%, Ti: 0.002 wt%, B: 0.002 wt% and the remaining Fe and other unavoidable impurities After manufacturing using, FDT: hot-rolled finish at 900 ℃, CT: wound at 660 ℃ to prepare a high carbon hot rolled steel sheet.

Example 2

C: 0.33 wt%, Si: 0.17 wt%, Mn: 1.2 wt%, Mo: 0.20 wt%, Cr: 0.10 wt%, Ti: 0.002 wt%, B: 0.002 wt% and the rest of Fe and other unavoidable impurities After the slab plate material was manufactured by using a vacuum melting furnace, the final hot rolled at FDT: 900 ° C, and wound at CT: 660 ° C to prepare a high carbon hot rolled steel sheet.

Example 3

C: 0.33 wt%, Si: 0.17 wt%, Mn: 1.2 wt%, Mo: 0.15 wt%, Cr: 0.15 wt%, Ti: 0.002 wt%, B: 0.002 wt% and the rest of Fe and other unavoidable impurities After the slab plate material was manufactured by using a vacuum melting furnace, the final hot rolled at FDT: 900 ° C, and wound at CT: 660 ° C to prepare a high carbon hot rolled steel sheet.

Comparative Example 1

Slab plate consisting of C: 0.35% by weight, Si: 0.25% by weight, Mn: 1.35% by weight, Cr: 0.31% by weight, Ti: 0.0031% by weight, B: 0.0014% by weight and the remaining Fe and other unavoidable impurities After manufacturing using, FDT: hot-rolled finish at 900 ℃, CT: wound at 660 ℃ to prepare a high carbon hot rolled steel sheet.

Comparative Example 2

Slab plate composed of C: 0.35% by weight, Si: 0.19% by weight, Mn: 1.36% by weight, Cr: 0.19% by weight, Ti: 0.002% by weight, B: 0.0015% by weight and the remaining Fe and other unavoidable impurities After manufacturing using, FDT: hot-rolled finish at 900 ℃, CT: wound at 660 ℃ to prepare a high carbon hot rolled steel sheet.

Comparative Example 3

C: 0.35 wt%, Si: 0.19 wt%, Mn: 1.2 wt%, Mo: 0.14 wt%, Cr: 0.16 wt%, Ti: 0.002 wt%, B: 0.002 wt% and the rest of Fe and other unavoidable impurities After the slab plate material was manufactured by using a vacuum melting furnace, the final hot rolled at FDT: 900 ° C, and wound at CT: 660 ° C to prepare a high carbon hot rolled steel sheet.

Comparative Example 4

C: 0.33 wt%, Si: 0.17 wt%, Mn: 1.2 wt%, Mo: 0.26 wt%, Cr: 0.04 wt%, Ti: 0.002 wt%, B: 0.002 wt% and the rest of Fe and other unavoidable impurities After the slab plate material was manufactured by using a vacuum melting furnace, the final hot rolled at FDT: 900 ° C, and wound at CT: 660 ° C to prepare a high carbon hot rolled steel sheet.

The preparation conditions of the above Examples 1 to 3 and Comparative Examples 1 to 4 are summarized in Table 1, and the values for their respective mechanical properties are summarized in Table 2 below.

Next, of the mechanical properties of the hot rolled steel sheet according to the results of Examples 1 to 3 and Comparative Examples 1 to 4, the hardness after heat treatment is quenched to the martensite transformation temperature (Ms) after heat treatment at 950 ℃ Measured.

As can be seen in Table 2, the Vickers hardness of 680 Hv after the heat treatment to the target only for Examples 1 to 4 according to the appropriate composition range and manufacturing method according to the present invention was obtained.

In Comparative Example 1 and Comparative Example 2, when molybdenum (Mo) was not added, it was found that the hardenability was remarkably inferior.

In addition, Comparative Example 3 is a case where molybdenum (Mo) is formed below the reference value according to the present invention, Comparative Example 4 shows a case where molybdenum (Mo) exceeds the reference value according to the present invention, even in both cases It was found that this did not reach the target value according to the present invention.

In addition, the above conditions were also different depending on the range according to the hot finishing rolling temperature and the coiling temperature. Particularly, when compared to the case of Example 2 as an example, the results shown in Table 3 were obtained.

Here, in Comparative Example 5, all other conditions except that the winding temperature was carried out at 580 ℃ was to follow Example 2.

Referring to Table 3, when the coiling temperature is lower than the reference value according to the present invention (580 ℃) it can be seen that the strength is increased, while the elongation is lowered.

The reduced elongation as described above cannot withstand deformation due to external force during steel pipe processing, and thus does not meet the object of the present invention because the processing characteristics are reduced.

The hot rolled steel sheet of the present invention having a suitable winding temperature as described above is shown as a perfect mixture of ferrite and pearlite structure as shown in FIG. 2, while in Comparative Example 5 together with ferrite and pearlite, as in FIG. Low temperature tissue is shown.

As described above, the boron-added high carbon hot rolled steel sheet having a hardenability according to the present invention provides an effect of facilitating the production of steel pipes by providing excellent weldability and tube properties suitable for steel pipe production. In addition, it provides excellent hardenability to increase the hardness after steel pipe manufacturing.

Therefore, the hot rolled steel sheet according to the present invention can replace the round bar with a steel pipe having the same hardness as a solid material. Therefore, weight reduction of 30% of the weight of the round bar can be realized.

In addition, it provides the deformation preventing properties and excellent elongation required for the durability of the automotive parts when the steel pipe processing as described above, and provides an effect that can simplify the manufacturing process. Therefore, it is possible to reduce the cost of manufacturing the steel pipe and provide an effect of increasing the production efficiency.

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 may belong to the present invention without departing from the scope of the present invention. Therefore, the scope of the present invention will be determined by the claims described below.

Claims (18)

C: 0.32 to 0.34 wt%, Mn: 1.1 to 1.3 wt%, Si: 0.11 to 0.22 wt%, Mo: 0.15 to 0.25 wt%, Ti: 0.001 to 0.003 wt%, B: 0.001 to 0.0025 wt% and the balance Hot rolling the slab plate composed of Fe and other unavoidable impurities to a hot finish rolling temperature (FDT) of 850 to 900 ° C .; And
Winding the hot rolled sheet at a coiling temperature (CT) of 640 to 680 ° C .; a method of manufacturing a boron-added high carbon hot rolled steel sheet having a hardenability, comprising: a hot rolled sheet.
The method of claim 1,
The slab plate is P: 0.02% by weight or less and S: 0.01% by weight or less, characterized in that the hard boron-added high carbon hot rolled steel sheet manufacturing method characterized in that it comprises.
The method of claim 1,
The slab sheet material is Cr: 0.15% by weight or less, characterized in that it comprises a hardenable boron-added high carbon hot rolled steel sheet characterized in that it comprises.
The method of claim 3, wherein
The Mo and Cr are added to the hot rolled steel sheet in a range satisfying 0.15 <[Mo] + [Cr] ≤ 0.3, characterized in that the boron-added high carbon hot rolled steel sheet having a quenchability. (In the above, [] means the weight percent of each component.)
The method of claim 1,
Mn and Si are added to the hot rolled steel sheet in a range satisfying 6 ≦ [Mn] / [Si] ≦ 9, wherein the boron-added high carbon hot rolled steel sheet having a hardenability. (In the above, [] means the weight percent of each component.)
The method of claim 1,
The final structure of the hot rolled steel sheet is a method for producing a boron-added high carbon hot rolled steel sheet having a hardenability, characterized in that the composite structure containing ferrite and pearlite (Pearlite).
C: 0.32 to 0.34 wt%, Mn: 1.1 to 1.3 wt%, Si: 0.11 to 0.22 wt%, Mo: 0.15 to 0.25 wt%, Ti: 0.001 to 0.003 wt%, B: 0.001 to 0.0025 wt% and the balance Consisting of Fe and other unavoidable impurities,
Hardened boron-added high-carbon hot rolled steel sheet, characterized in that the microstructure is a composite structure containing ferrite and pearlite (Pearlite).
The method of claim 7, wherein
The hot rolled steel sheet is boron-added high carbon hot rolled steel sheet having a hardenability, characterized in that P: 0.02% by weight or less and S: 0.01% by weight or less.
The method of claim 7, wherein
The hot rolled steel sheet is boron-added high carbon hot rolled steel sheet having a hardenability, characterized in that it comprises Cr: 0.15% by weight or less.
The method of claim 9,
The Mo and Cr is boron-added high carbon hot rolled steel sheet having a hardenability, characterized in that included in the hot rolled steel sheet in a range satisfying 0.15 <[Mo] + [Cr] ≤ 0.3. (In the above, [] means the weight percent of each component.)
The method of claim 7, wherein
The Mn and Si are boron-added high carbon hot rolled steel sheet having a hardenability, characterized in that included in the hot rolled steel sheet in a range satisfying 6 ≤ [Mn] / [Si] ≤ 9. (In the above, [] means the weight percent of each component.)
The method of claim 7, wherein
Tensile strength (TS) of the hot rolled steel sheet is boron-added high carbon hot rolled steel sheet having a hardenability, characterized in that more than 600 MPa.
The method of claim 7, wherein
Elongation (EL) of the hot rolled steel sheet is a boron-added high carbon hot rolled steel sheet having a hardenability, characterized in that 25% or more.
The method of claim 7, wherein
Vickers hardness of the hot rolled steel sheet is boron-added high carbon hot rolled steel sheet having a hardenability, characterized in that more than 280Hv.
C: 0.32 to 0.34 wt%, Mn: 1.1 to 1.3 wt%, Si: 0.11 to 0.22 wt%, Mo: 0.15 to 0.25 wt%, Cr: 0.15 wt% or less, Ti: 0.001 to 0.003 wt%, B: 0.001 Processing a slab plate composed of 0.0025% by weight and the remaining amount of Fe and other impurity impurities;
Hot rolling the slab plate to a hot finish rolling temperature (FDT) of 850 to 900 ° C .;
Winding the hot rolled sheet at a winding temperature (CT) of 640 to 680 ° C .;
Tightening using the wound rolled sheet; And
Heat-treating and quenching the corrugated steel pipe; a method of manufacturing a hot-rolled steel pipe comprising: a.
The method of claim 15,
The Mo and Cr are added to the hot rolled steel sheet in a range satisfying 0.15 <[Mo] + [Cr] ≤ 0.3. (In the above, [] means the weight percent of each component.)
The method of claim 15,
The heat treatment temperature is 850 ~ 980 ℃, quenching method of producing a hot rolled steel pipe, characterized in that performed to the martensite transformation temperature (Ms).
The method of claim 15,
Vickers hardness of the hot rolled steel pipe is a method of producing a hot rolled steel pipe, characterized in that more than 680Hv.

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