JP4464486B2 - High-strength and high-toughness rolled section steel and its manufacturing method - Google Patents

Description

【００３７】
【表２】

【００３８】
【発明の効果】
本発明による合金設計された鋳片と圧延後の温度制御を適用した圧延形鋼は機械試験特性の最も保証しにくいフランジ板厚１／２、幅１／２部においても十分な強度および、優れた靱性を有し大型鋼構造物の信頼性の向上、安全性の確保、経済性等の産業上の効果は極めて顕著なものである。
【図面の簡単な説明】
【図１】図１は、本発明法を実施する装置配置例の略図である。
【図２】図２は、Ｈ形鋼の断面形状および機械試験片の採取位置を示す図である。
【図３】本発明鋼および比較鋼のミクロ組織を示す図である。
【図４】本発明鋼および比較鋼のＭ＊分布を示す図である。
【符号の説明】
１…Ｈ形鋼
２…フランジ
３…ウェブ
４…中間圧延機
５ａ…中間圧延機前後面の水冷装置
５ｂ…仕上げ圧延機後面冷却装置
６…仕上げ圧延機[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-tensile rolled section steel having excellent toughness used as a structural member of a building and a method for producing the same.
[0002]
[Prior art]
Due to the rise in building height and stricter safety standards, steel materials used for building pillars, such as H-shaped steel with a large plate thickness (hereinafter referred to as extra-thick H-shaped steel), are much higher. There is a need for strength, toughness, and a low yield ratio. In order to satisfy such required characteristics, conventionally, a heat treatment such as a normalizing treatment has been performed after rolling. However, the addition of the heat treatment as described above has caused a significant increase in costs such as an increase in energy costs and a decrease in production efficiency, which has a problem in economic efficiency. In order to solve this problem, it is necessary to develop a steel material based on a new alloy design capable of obtaining high-performance material characteristics and a new manufacturing method for manufacturing the steel material.
[0003]
In general, when a shape steel having a flange, for example, an H-shape steel, is manufactured by universal rolling, each of the web, flange, and fillet is restricted due to the limitation of rolling conditions (rolling temperature, rolling reduction, etc.) and the uniqueness of the shape. Differences occur in the rolling finish temperature, rolling reduction, and cooling rate at the site. As a result, variations in strength, ductility, and toughness occur between the portions, and for example, a portion that does not satisfy the standard such as a rolled steel material for welded structure (JIS G3106) occurs. In particular, when rolling and manufacturing extremely thick H-section steel using continuous cast slabs as raw materials, there is a limit to the maximum cast slab thickness that can be produced with continuous casting equipment, and sufficient slab cross-sectional area required for modeling is obtained. Therefore, the rolling is a low pressure ratio rolling. Further, since high temperature rolling is directed to obtain dimensional accuracy of the product by rolling shaping, the thick flange portion becomes high temperature rolling, and the steel material cooling after the rolling is also gradually cooled. As a result, the microstructure becomes coarse and the strength and toughness decrease.
[0004]
There is TMCP (Thermo-Mechanical-Control Process) as a structure refinement method in the rolling process. However, in shape steel rolling, there are restrictions on rolling conditions. Have difficulty. Further, in the field of thick steel plates, techniques disclosed in, for example, Japanese Patent Publication Nos. 62-50548 and 62-54862 have been proposed for producing high-strength and high-toughness steel using the precipitation effect of VN. However, when these methods are applied to the production of a 590 N / mm ² grade steel material, it contains a high concentration of solute N, so that a high carbon island martensite (hereinafter referred to as M *) is formed in the bainite structure to be formed. It was difficult to clear the standard value due to a significant decrease in toughness. Japanese Patent Laid-Open No. 10-147835 discloses accelerated cooling type controlled rolling in addition to low carbonization-low nitrogenization, addition of a small amount of Nb, V, and Mo and refinement of the structure by fine dispersion of Ti oxide and TiN. Has proposed a method for producing a high-strength rolled section steel, but this leads to an increase in production cost and complexity of the production process due to low C and adoption of TMCP.
[0005]
[Problems to be solved by the invention]
In order to solve the above-described problems, it is necessary to produce a low carbon bainite with a small M * production amount in the rolled shape steel to refine the structure. For this purpose, in order to refine the γ grain size during rolling and heating, Ti-O is finely crystallized in advance in the slab during the steelmaking process, and TiN is finely precipitated and added to the core to reduce carbon. Therefore, it is necessary to manufacture a slab containing a small amount of microalloy that can provide high strength in a small amount. Further, the fillet portion of the joint between the flange of the H-shaped steel and the web coincides with the central segregation zone of the continuous cast slab, and MnS in this segregation zone is remarkably stretched by rolling. Here, the high concentration of element segregation zone and stretched MnS significantly reduce the drawing value and toughness in the thickness direction, and may cause lamellar cracking during welding, thus preventing the generation of MnS having this harmful effect. That is also a big issue. As described above, it is difficult for the conventional technique to produce a high-reliability, high-strength, high-toughness rolled steel with high reliability and provide it at low cost.
[0006]
The present invention makes it possible to produce a high-tensile rolled section steel at a low cost without performing a heat treatment such as a conventional normalizing treatment, and is a high-strength, high-toughness 590 N / mm ² class used for a structural member of a building. An object of the present invention is to provide a rolled shape steel and a method for producing the same.
[0007]
[Means for Solving the Problems]
The present invention casts a slab from which a bainite + ferrite + pearlite structure having a low M * content, which is the main cause of toughness deterioration, is obtained, and is rolled into a shape steel shape using this slab, and the cooling rate after rolling In addition, by reducing the M * contained by controlling the temperature history, it is possible to produce a high-tensile rolled section steel at a low cost without performing a heat treatment such as a normalizing treatment. The summary is as follows.
(1) in mass%, C: 0.01~0.10%,
Si: 0.05 to 0.35%,
Mn: 1.0-2.0%,
Cu: 0.3 to 1.2%,
Ti: 0.005 to 0.03%,
Nb: 0.01-0.10%,
N: ≦ 0.010%,
O: 0.001 to 0.007% ,
Al: ≦ 0.05%
And having a chemical composition comprising the balance Fe and inevitable impurities, and the microstructure is composed of bainite, ferrite, pearlite and high carbon island martensite, and the area ratio of the high carbon island martensite is 0.5. tensile strength, characterized in that% or less: 590N / mm ² or more, a yield strength or 0.2% proof stress: 440 N / mm ² or more, 0 Charpy impact absorption energy at ° C.: having 47J or more mechanical properties High-strength, high-toughness rolled steel.
(2) in mass%, C: 0.01~0.10%,
Si: 0.05 to 0.35%,
Mn: 1.0-2.0%,
Cu: 0.3 to 1.2%,
Ti: 0.005 to 0.03%,
Nb: 0.01-0.10%,
N: ≦ 0.010%,
O: 0.001 to 0.007%,
Al: ≦ 0.05%
V: 0.01 to 0.1%, Cr: 0.1 to 1.0%, Ni: 0.1 to 2.0%, Mo: 0.05 to 0.40%, Mg: 0.0001 to A chemical composition comprising any one or more of 0.005%, Ca: 0.0001-0.003%, B: 0.0001-0.003%, the balance being Fe and inevitable impurities And having a microstructure composed of bainite, ferrite, pearlite, and high carbon island martensite, and an area ratio of the high carbon island martensite is 0.5% or less. High strength, high toughness rolled section steel having mechanical properties of mm ² or more, yield strength or 0.2% yield strength: 440 N / mm ² or more, Charpy impact absorption energy at 0 ° C .: 47 J or more.
(3) in mass%, C: 0.01~0.10%,
Si: 0.05 to 0.35%,
Mn: 1.0-2.0%,
Cu: 0.3 to 1.2%,
Ti: 0.005 to 0.03%,
Nb: 0.01-0.10%,
N: ≦ 0.010%,
O: 0.001 to 0.007% ,
Al: ≦ 0.05%
Rolling, after starting the slab having a chemical composition composed of the remaining Fe and inevitable impurities to a temperature range of 1100 to 1300 ° C., after rolling,
1) The steel material average temperature is accelerated and cooled in the range of 0.1 to 5 ° C./sec to the Ms point temperature represented by the formula (1), and then from the Ms point temperature to 250 ° C., 0.001 to 0.1 ° C. / perform gradual cooling at a cooling rate in the range of sec, then cooling, by performing gradual cooling or accelerated cooling,
2) The steel material average temperature accelerated cooling in the range of 0.1 to 5 ° C. / sec to Ms point temperature or less, after its performs temperature holding of 15 minutes to 5 hours at 250 to 500 ° C., cooled again thing,
The microstructure of the steel material is composed of bainite, ferrite, pearlite, and high carbon island martensite, and the area ratio of the high carbon island martensite is 0.00. 5% or less, a tensile strength: 590N / mm ² or more, a yield strength or 0.2% proof stress: 440 N / mm ² or more, 0 Charpy impact absorption energy at ° C.: high strength and high toughness having the above mechanical properties 47J A manufacturing method of rolled steel.
Ms (° C.) = 539-423 (% C) -30.4 (% Mn) −17.7 (% Ni)
-12.1 (% Cr) -7.5 (% Mo) -54 (% Cu) ···· (1)
(4) in mass%, C: 0.01~0.10%,
Si: 0.05 to 0.35%,
Mn: 1.0-2.0%,
Cu: 0.3 to 1.2%,
Ti: 0.005 to 0.03%,
Nb: 0.01-0.10%,
N: ≦ 0.010%,
O: 0.001 to 0.007%,
Al: ≦ 0.05%
V: 0.01 to 0.1%, Cr: 0.1 to 1.0%, Ni: 0.1 to 2.0%, Mo: 0.05 to 0.40%, Mg: 0.0001 to A chemical composition comprising any one or more of 0.005%, Ca: 0.0001-0.003%, B: 0.0001-0.003%, the balance being Fe and inevitable impurities Rolling is started after heating the cast slab to 1100 to 1300 ° C, after rolling,
1) The steel material average temperature is accelerated and cooled in the range of 0.1 to 5 ° C./sec to the Ms point temperature represented by the formula (1), and then from the Ms point temperature to 250 ° C., 0.001 to 0.1 ° C. / perform gradual cooling at a cooling rate in the range of sec, then cooling, by performing gradual cooling or accelerated cooling,
2) The steel material average temperature accelerated cooling in the range of 0.1 to 5 ° C. / sec to Ms point temperature or less, after its performs temperature holding of 15 minutes to 5 hours at 250 to 500 ° C., cooled again thing,
The microstructure of the steel material is composed of bainite, ferrite, pearlite, and high carbon island martensite, and the area ratio of the high carbon island martensite is 0.00. 5% or less, a tensile strength: 590N / mm ² or more, a yield strength or 0.2% proof stress: 440 N / mm ² or more, 0 Charpy impact absorption energy at ° C.: high strength and high toughness having the above mechanical properties 47J A manufacturing method of rolled steel.
Ms (° C.) = 539-423 (% C) -30.4 (% Mn) −17.7 (% Ni)
-12.1 (% Cr) -7.5 (% Mo) -54 (% Cu) ···· (1)
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
Strengthening of steel is achieved by (1) refinement of ferrite crystal grains, (2) solid solution strengthening by alloy elements, dispersion strengthening by hardened phase, and (3) precipitation strengthening by fine precipitates. High toughness is also achieved by (4) refinement of crystal grains, (5) reduction of solid solution N and C in the parent phase (ferrite), and (6) high carbon martensite in the hardened phase that is the origin of fracture ( M *) and coarse oxides and precipitates can be reduced and miniaturized.
[0009]
In general, toughness decreases with increasing strength, and measures to conflict between increasing strength and increasing toughness are necessary. In particular, in order to ensure the strength of 590 N / mm ² class, which is an object of the present invention, it is essential to use a bainite structure that is a hardened phase. A large amount of high carbon martensite (M *) is contained.
[0010]
The present inventors have investigated in detail the influence of various alloy elements on M * generation, which is the main cause of toughness deterioration, and have a strength of 590 N / mm ² and reduced the amount of M * generation. Ingredient system was found. In addition, the present inventors have found a method for dramatically improving toughness by decomposing generated M * by controlling the temperature history after rolling. That is, as the cooling rate after rolling increases, the carbon diffusion is suppressed and M * becomes finer, and the generated M * is also decomposed by maintaining the temperature in the carbon diffusion temperature range after the martensite transformation. I found out.
[0011]
The present invention is characterized by casting a slab from which bainite + ferrite + pearlite structure is obtained, which is a 590 N / mm grade ² steel with a low content of M *, which is the main cause of toughness deterioration. By controlling the cooling rate and temperature history after rolling, the contained M * can be reduced, and high-tensile rolled section steel can be produced at low cost without heat treatment such as normalization. It is what.
[0012]
The reasons for limiting the component ranges and control conditions of the steel of the present invention will be described below. In addition,% means the mass%.
First, C is added to strengthen the steel. If it is less than 0.01%, the necessary strength as a structural steel cannot be obtained, and if it exceeds 0.10%, the amount of M * produced is low. Since the toughness of the base metal is increased and the weld crack resistance, weld heat affected zone (hereinafter abbreviated as HAZ) toughness and the like are significantly reduced, the lower limit is set to 0.01% and the upper limit is set to 0.10%.
[0013]
Next, Si is necessary for securing the strength of the base metal and preliminary deoxidation of the molten steel, but when it exceeds 0.35%, high carbon island martensite is generated in the base metal and the hardened structure of the HAZ. Material and weld joint toughness are significantly reduced. Further, if it is less than 0.05%, the molten steel cannot be sufficiently pre-deoxidized, so the Si content is limited to the range of 0.05 to 0.35%.
[0014]
Mn needs to be added in an amount of 1.0% or more to ensure the strength of the base material, but the upper limit is set to 2.0% from the allowable concentration with respect to the toughness and cracking properties of the base material and the welded part.
Cu precipitates a Cu phase on dislocations in the α phase by holding in the α temperature range and slow cooling, and the normal temperature strength of the base material is increased by precipitation hardening. However, if the Cu phase precipitation in α is less than 0.3%, it is within the solid solubility limit of Cu in α, and no precipitation occurs, so that strengthening by Cu precipitation cannot be obtained. The 1.2% ultra In the precipitation strengthening is limited to Cu0.3～1.2% so saturated.
[0015]
Ti precipitates TiN and controls the generation of M * by reducing the solid solution N. In addition, the finely precipitated TiN contributes to the refinement of the γ phase. By the action of these Ti, the structure is refined and the strength and toughness are improved. Therefore, if the amount is less than 0.005%, the amount of TiN deposited is insufficient, and these effects cannot be exhibited. Therefore, the lower limit of the amount of Ti is set to 0.005%. However, if it exceeds 0.03%, excessive Ti precipitates TiC, and its precipitation hardening causes the toughness of the base metal and the weld heat affected zone to deteriorate, so it is limited to 0.03% or less.
[0016]
Nb is added for the purpose of increasing hardenability and increasing strength. For the expression of this effect, the Nb content needs to be 0.01% or more. However, if it exceeds 0.10%, the precipitation amount of Nb carbonitride increases and the effect as solid solution Nb is saturated, so it was limited to 0.10% or less.
N dissolves in α and increases the strength. However, in the upper bainite structure, M * is generated and the toughness is deteriorated. Therefore, it is necessary to reduce the solid solution N as much as possible, and the upper limit is set to 0.010%. .
[0017]
O (oxygen) is indispensable for the production of Ti-O, and it is necessary to contain 0.001% or more, but if it exceeds 0.007%, the produced Ti-O particles become coarse, In order to reduce toughness, the O content is limited to 0.001 to 0.007%. Al is a strong deoxidizing element and is added to clean steel. However, if it exceeds 0.05%, the amount of M * produced increases and the toughness deteriorates, so the upper limit was made 0.05%. In order to utilize the oxide for refining the structure, Al is required to be 0.007% or less.
[0018]
The amounts of P and S contained as inevitable impurities are not particularly limited, but they should cause a reduction in weld cracking and toughness due to solidification segregation. Therefore, the amounts of P and S should be less than 0.002%, respectively. It is desirable to limit to
Furthermore, depending on the steel type of the section steel according to the present invention, in addition to the above elements, Cr, Ni, Mo, V, B, Mg, and Ca are used for the purpose of increasing the strength of the base material and improving the toughness of the base material. It can contain at least 1 sort (s) of these.
[0019]
Ni is an extremely effective element that enhances the toughness of the base material. To achieve this effect, the Ni content needs to be 0.1% or more. However, addition exceeding 2.0% increases the alloy cost and is not economical, so the upper limit was made 2.0%.
V can refine the rolling structure by adding a small amount, and strengthen it by precipitation of vanadium carbonitride, so that the alloy can be made low in alloy and welding characteristics can be improved. In order to achieve this effect, the V content needs to be 0.01% or more. However, excessive addition of V leads to hardening of the welded part and high yield point of the base metal, so the upper limit of the content was set to V: 0.10%.
[0020]
B is added in a small amount, so that hardenability is increased and strength is increased, so 0.0001% or more is added . However, it has been found that if more than 0.003% B is contained, a large amount of M * is generated in the upper bainite structure and the toughness is significantly reduced, so the upper limit was made 0.003%. Cr is effective for strengthening the base material by improving hardenability. In order to exhibit this effect, the Cr content needs to be 0.1% or more. However, excessive addition exceeding 1.0% is harmful from the viewpoint of toughness and curability, so the upper limit was made 1.0%.
[0021]
Mo is an element effective for ensuring the strength of the base material. In order to achieve this effect, the Mo content needs to be 0.05% or more. In however 0.4 greater than 0%, hardenability improving effect of solid solution Mo precipitates of Mo carbides (Mo ₂ C) is limited to 0.4 0% or less since the saturation.
Mg alloys used for adding Mg are Si-Mg-Al and Ni-Mg. The reason for using the Mg alloy is to reduce the Mg content concentration by alloying, suppress the deoxidation reaction at the time of addition to molten steel, and ensure the safety at the time of addition and improve the yield of Mg. The reason why Mg is limited to 0.0001 to 0.005% is that Mg is also a strong deoxidizing element, and the crystallized Mg oxide easily floats and separates in the molten steel, so it exceeds 0.005%. Even if it is added, no further yield is obtained, so the upper limit was made 0.005%. Further, if the content is less than 0.0001%, the dispersion density of the target Mg-based oxide is insufficient, so the lower limit was made 0.0001%. The Mg-based oxide here is mainly described as MgO. However, according to an electron microscope analysis, this oxide is a complex oxidation with Ti, trace amount Al and Ca contained as impurities. Forming a thing.
[0022]
The reason for limiting Ca to 0.0001-0.003% is that Ca is a strong deoxidizing element, and the crystallized Ca oxide easily floats in the molten steel and is separated as slag. Even if added in excess of%, no further yield is obtained, so the upper limit was made 0.003%. Further, if it is less than 0.0001%, the target Ca dispersion density is insufficient, so the lower limit was made 0.0001%.
[0023]
The rolled steel of the present invention has a microstructure composed of bainite, ferrite, pearlite, and high-carbon island martensite in order to simultaneously secure a tensile strength and toughness of 590 N / mm ² (60 kgf / mm ² ) class, It is necessary to have a microstructure in which the area ratio of the high-carbon island martensite is 0.5% or less.
The reason why the area ratio of the high carbon island martensite in the microstructure is 0.5% or less is that when the high carbon island martensite area ratio exceeds the upper limit, the toughness deteriorates, so the upper limit is less than the upper limit. Limited to concentration range.
[0024]
The above microstructure can be realized by the method of the present invention. That is, the slab having the above chemical composition is reheated to a temperature range of 1100 to 1300 ° C. The reason for limiting the reheating temperature to this temperature range is that the production of the shape steel by hot working requires heating at 1100 ° C. or more in order to facilitate plastic deformation, and sufficient elements such as V and Nb are used. The lower limit of the reheating temperature was set to 1100 ° C. because it was necessary to dissolve the solution. The upper limit was set to 1300 ° C. from the performance and economy of the heating furnace.
[0025]
Next, after rolling and rolling the steel slab heated as described above,
(1) The steel material average temperature is accelerated and cooled within the range of 0.1 to 5 ° C./s to the Ms point temperature, and then cooled within the range of 0.001 to 0.1 ° C./s from the Ms point temperature to 250 ° C. Slow cooling at a speed, and then cool down or slow cooling or accelerated cooling
(2) The steel material average temperature is accelerated and cooled within the range of 0.1 to 5 ° C./s to the temperature below the Ms point temperature, and then the temperature is maintained at 250 to 500 ° C. for 15 minutes to 5 hours, and then cooled again. These are produced by combining at least one or a plurality of methods.
The reason for carrying out such a manufacturing method is that, in (1) , the steel material average temperature is heated and cooled within the range of 0.1 to 5 ° C./s up to the Ms point temperature after rolling. ° C. / is less than s many diffusion of carbon, coarse M * is produced in large quantities, is because the toughness is reduced in order to obtain a cooling rate of 5 ° C. / s greater is strong accelerated cooling This is because it requires a device and is economically difficult.
[0026]
Further, after that , the reason for slow cooling from the Ms point temperature to 250 ° C. at a cooling rate in the range of 0.001 to 0.1 ° C./s is that at a cooling rate of more than 0.1 ° C./s, M by slow cooling is used. * This is because the decomposition effect cannot be obtained, and at a cooling rate of less than 0.001 ° C./s, it takes a long time to lower the steel material temperature, and the production efficiency is lowered. Preferably, it is 0.01-0.1 degree-C / s.
[0027]
Next, in (2) , when the steel material average temperature is from 0.1 to 5 ° C./s up to the Ms point temperature or less after rolling, the accelerated cooling is less than 0.1 ° C./s. many of the diffusion quantity, coarse M * is produced in large quantities, is because the toughness is reduced in order to obtain a cooling rate of 5 ° C. / s greater requires powerful accelerated cooling device, economically It is difficult.
[0028]
The reason why the temperature is maintained at 250 to 500 ° C. for 15 minutes to 5 hours is that the diffusion rate of C is slow in the temperature range below 250 ° C., and it takes a long time to decompose M *. There, the raised to the temperature range of 500 ° C. greater, because the heating cost is increased.
[0030]
【Example】
Prototype steel is melted in a converter, alloy is added, preliminary deoxidation treatment is performed, oxygen concentration of the molten steel is adjusted, Ti and Mg are added in some cases, and a thick cast slab of 250 to 300 mm is obtained by continuous casting. Casted. The cooling of the slab was controlled by selecting the amount of water in the secondary cooling zone below the mold and the drawing speed of the slab. The slab was heated at 1300 ° C., and the rough rolling process was not shown, but was rolled into an H-section steel by a universal rolling mill shown in FIG. Water cooling between rolling passes is provided with water cooling devices 5a before and after the intermediate universal rolling mill 4, and is performed as necessary by repeating spray cooling and reverse rolling of the outer surface of the flange, and accelerated cooling after rolling is performed on the rear surface of the finishing universal rolling mill. The flange outer surface was spray-cooled as necessary with the installed cooling device 5b. In the cooling floor, the cooling rate was controlled by a method in which the steel material was brought into close contact or a method in which the steel material was covered with an iron plate. Further, if necessary, the temperature was maintained for a certain time using a heat treatment furnace.
[0031]
The mechanical characteristics shown in FIG. 2 are collected from the center part (1 / 2t2) of the plate thickness t2 of the flange 2 from the 1/4 width and 1/2 width (1 / 4B, 1 / 2B) of the flange width overall length (B). The obtained test piece was used. In addition, the characteristic about these places was obtained because the flange 1 / 4F part shows the average mechanical characteristics of the H-section steel, and the flange 1 / 2F part has the most deteriorated characteristics. This is because it was determined that the mechanical test characteristics of the H-section steel can be represented by
[0032]
Table 1 shows the chemical component values of the steel of the present invention and the comparative steel.
Table 2 shows the production methods of the steels of the present invention and comparative steels shown in Table 1, the mechanical test characteristic values of these H-shaped steels, and the area ratio of M *. In addition, it is well known that the rolling heating temperature is set to 1300 ° C., in general, the γ grains are made finer by lowering the heating temperature and the mechanical test characteristics are improved. This is because it was judged that this value can represent the mechanical test characteristics at a heating temperature lower than that. As for the cooling conditions after rolling was performed at the following conditions (1) to (3).
[0033]
(1) The steel material average temperature is accelerated and cooled within the range of 0.1 to 5 ° C./s to the Ms point temperature, and then cooled within the range of 0.001 to 0.1 ° C./s from the Ms point temperature to 250 ° C. Slow cooling is performed at a speed, and then cooling or slow cooling or accelerated cooling is performed.
(2) The steel material average temperature is accelerated and cooled within the range of 0.1 to 5 ° C./s to the Ms point temperature or lower, and then the temperature is kept at 250 to 500 ° C. for 15 minutes to 5 hours, and then cooled again.
[0034]
(3) Allow to cool after rolling.
FIG. 3 shows the microstructure and FIG. 4 shows the M * distribution. In FIG. 4, the white part is M *. In either figure, (a) is a comparative steel No. No. 8 and (b) is a steel No. of the present invention. Three.
As shown in Table 2, any rolling shape steel produced by the present invention tensile strength 590N / mm ² or more, a yield strength or 0.2% proof stress 440 N / mm ² or more, Charpy impact absorption energy at 0 ℃ A mechanical property of 47 J or more was exhibited.
[0035]
On the other hand, all the comparative steels have a large M * area ratio, and the standard of Charpy impact absorption energy of 47 J or more cannot be cleared.
[0036]
[Table 1]

[0037]
[Table 2]

[0038]
【The invention's effect】
Rolled section steel with alloy-designed slab and temperature control after rolling according to the present invention has sufficient strength and excellent strength even at 1/2 part of flange plate thickness and width 1/2, which are the most difficult to guarantee mechanical test characteristics. Industrial effects such as improvement of reliability, securing of safety and economic efficiency of large steel structures having excellent toughness are extremely remarkable.
[Brief description of the drawings]
FIG. 1 is a schematic illustration of an example device arrangement for carrying out the method of the present invention.
FIG. 2 is a diagram showing a cross-sectional shape of an H-section steel and a sampling position of a mechanical test piece.
FIG. 3 is a view showing microstructures of the steel of the present invention and a comparative steel.
FIG. 4 is a view showing M * distributions of the steel of the present invention and a comparative steel.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... H-section steel 2 ... Flange 3 ... Web 4 ... Intermediate rolling mill 5a ... Water cooling device 5b of the front and rear surfaces of the intermediate rolling mill ... Finish rolling mill rear surface cooling device 6 ... Finish rolling mill

Claims (4)

In mass%,
C: 0.01 to 0.10%,
Si: 0.05 to 0.35%,
Mn: 1.0-2.0%,
Cu: 0.3 to 1.2%,
Ti: 0.005 to 0.03%,
Nb: 0.01-0.10%,
N: ≦ 0.010%,
O: 0.001 to 0.007% ,
Al: ≦ 0.05%
And having a chemical composition composed of the balance Fe and inevitable impurities, and the microstructure is composed of bainite, ferrite, pearlite and high carbon island martensite, and the area ratio of the high carbon island martensite is 0.00. tensile strength, characterized in that 5% or less: 590N / mm ² or more, a yield strength or 0.2% proof stress: 440 N / mm ² or more, Charpy impact absorption energy at 0 ° C.: the 47J or more mechanical properties Has high strength and high toughness rolled section steel. In mass%,
C: 0.01 to 0.10%,
Si: 0.05 to 0.35%,
Mn: 1.0-2.0%,
Cu: 0.3 to 1.2%,
Ti: 0.005 to 0.03%,
Nb: 0.01-0.10%,
N: ≦ 0.010%,
O: 0.001 to 0.007%,
Al: ≦ 0.05%
V: 0.01 to 0.1%, Cr: 0.1 to 1.0%, Ni: 0.1 to 2.0%, Mo: 0.05 to 0.40%, Mg: 0.0001 to A chemical composition comprising any one or more of 0.005%, Ca: 0.0001-0.003%, B: 0.0001-0.003%, the balance being Fe and inevitable impurities It has, and will microstructure bainite, ferrite, pearlite and high-carbon island-like martensite, the tensile area ratio of the high carbon island martensite being not more than 0.5% strength: 590N / mm ² or more, a yield strength or 0.2% proof stress: 440 N / mm ² or more, 0 Charpy impact absorption energy at ° C.: high strength having the above mechanical properties 47J high toughness rolled shape steel. In mass%,
C: 0.01 to 0.10%,
Si: 0.05 to 0.35%,
Mn: 1.0-2.0%,
Cu: 0.3 to 1.2%,
Ti: 0.005 to 0.03%,
Nb: 0.01-0.10%,
N: ≦ 0.010%,
O: 0.001 to 0.007% ,
Al: ≦ 0.05%
Rolling, after starting the slab having a chemical composition composed of the remaining Fe and inevitable impurities to a temperature range of 1100 to 1300 ° C., after rolling,
1) The steel material average temperature is accelerated and cooled in the range of 0.1 to 5 ° C./sec to the Ms point temperature represented by the formula (1), and then from the Ms point temperature to 250 ° C., 0.001 to 0.1 ° C. / perform gradual cooling at a cooling rate in the range of sec, then cooling, by performing gradual cooling or accelerated cooling,
2) The steel material average temperature accelerated cooling in the range of 0.1 to 5 ° C. / sec to Ms point temperature or less, after its performs temperature holding of 15 minutes to 5 hours at 250 to 500 ° C., cooled again thing,
The microstructure of the steel material is composed of bainite, ferrite, pearlite, and high carbon island martensite, and the area ratio of the high carbon island martensite is 0.00. 5% or less, a tensile strength: 590N / mm ² or more, a yield strength or 0.2% proof stress: 440 N / mm ² or more, 0 Charpy impact absorption energy at ° C.: high strength and high toughness having the above mechanical properties 47J A manufacturing method of rolled steel.
Ms (° C.) = 539-423 (% C) -30.4 (% Mn) −17.7 (% Ni)
-12.1 (% Cr) -7.5 (% Mo) -54 (% Cu) ···· (1) In mass%,
C: 0.01 to 0.10%,
Si: 0.05 to 0.35%,
Mn: 1.0-2.0%,
Cu: 0.3 to 1.2%,
Ti: 0.005 to 0.03%,
Nb: 0.01-0.10%,
N: ≦ 0.010%,
O: 0.001 to 0.007%,
Al: ≦ 0.05%
V: 0.01 to 0.1%, Cr: 0.1 to 1.0%, Ni: 0.1 to 2.0%, Mo: 0.05 to 0.40%, Mg: 0.0001 to A chemical composition comprising any one or more of 0.005%, Ca: 0.0001-0.003%, B: 0.0001-0.003%, the balance being Fe and inevitable impurities Rolling is started after heating the cast slab to 1100 to 1300 ° C, after rolling,
1) The steel material average temperature is accelerated and cooled in the range of 0.1 to 5 ° C./sec to the Ms point temperature represented by the formula (1), and then from the Ms point temperature to 250 ° C., 0.001 to 0.1 ° C. / perform gradual cooling at a cooling rate in the range of sec, then cooling, by performing gradual cooling or accelerated cooling,
2) The steel material average temperature accelerated cooling in the range of 0.1 to 5 ° C. / sec to Ms point temperature or less, after its performs temperature holding of 15 minutes to 5 hours at 250 to 500 ° C., cooled again thing,
The microstructure of the steel material is composed of bainite, ferrite, pearlite, and high carbon island martensite, and the area ratio of the high carbon island martensite is 0.00. 5% or less, a tensile strength: 590N / mm ² or more, a yield strength or 0.2% proof stress: 440 N / mm ² or more, 0 Charpy impact absorption energy at ° C.: high strength and high toughness having the above mechanical properties 47J A manufacturing method of rolled steel.
Ms (° C.) = 539-423 (% C) -30.4 (% Mn) −17.7 (% Ni)
-12.1 (% Cr) -7.5 (% Mo) -54 (% Cu) ···· (1)

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