TWI297732B - 490mpa grade high strength weldable structural steel having excellent in high temperature strength - Google Patents

Description

1297732 IX. Description of the invention: [Ming Huji special mussel] Technical field

The present invention relates to a south tension steel for a welded structure excellent in high temperature strength in a short time of about 1 hour in a temperature range of 600 ° C or more and 800 ° C or less, and a method for producing the same, and the high tensile steel is available General welded structures such as construction, civil engineering, marine structures, shipbuilding and various storage containers. The main object of the present invention is a thick plate (thick steel plate), but it also includes a steel pipe or a steel plate. 10 [Prior Art] Background Art 15 20 The strength of a steel material for a general welded structure is lowered from about 350 ° C, and its allowable temperature is about 500 ° C. Therefore, when these steels are used in buildings such as buildings or offices, homes, and three-dimensional parking lots, adequate fire-resistance must be applied to ensure safety during fires; and the construction-related laws also stipulate that the temperature of the steel during fires must not be More than 350 ° C. This is because the endurance (falling strength) of the steel material is about 2/3 times that of the normal temperature at 35 CTC, which is lower than the required strength. In fact, the refractory coating as described above has a significant impact on the cost of construction. In order to solve the problems as described above, a "heat-resistant steel" having a high-temperature endurance has been developed (for example, Japanese Laid-Open Patent Publication No. Hei No. Hei 2-77523, No. Hei 10-68044). The above-mentioned "refractory steel" has an endurance of 600 ° C and 700 ° C, respectively, and can maintain 2/3 or more of the minimum endurance (falling strength) of the specification at normal temperature. However, the term "refractory steel" only indicates the endurance at a specific temperature, and it is completely inconsistent with the endurance of 5 1297732 at a higher temperature than the temperature shown. In particular, when the temperature exceeds 70 (the temperature at rc, there is a fear that the endurance (partition strength) is rapidly degraded due to the temperature field which is partially transformed by the steel component, it is extremely difficult to manufacture a stable steel which reflects the design.

10 The inventors of the present invention have invented the steel which can ensure the high-temperature strength of rc and the manufacturing method thereof (for example, refer to Japanese Patent Laid-Open Publication No. Hei. No. Hei. No. 2-43961) It makes it easier to control the organization, especially to achieve the low drop-to-volt ratio of steel for building structures. However, as is generally known, B also increases the intensity of fire/crush, which is an element of half the work. For example, the fusion input When the heat is small, the heat affected part of the weld will be hardened and the toughness will be deteriorated. Conversely, when the heat input to the weld is too large, B will precipitate at the boundary of the iron grain of the Worthfield, and the hardenability of B cannot be effectively utilized. In order to reduce the heat and toughness of the structure, the heat input range of the welding is limited. As a steel for building structure, the fluctuation ratio must be lower from the viewpoint of vibration resistance. JIS2 "Rolled steel for building structure" specifications It is also required that the ratio of the fluctuation must be less than 80%. The inventor's previous invention was completed in accordance with the above requirements. However, the revision of the building standard, which was implemented in June, 2009, will be revised. For performance regulations, including new technologies and new materials for early use, etc. For construction steels, the first item can be used in Article 37 of the Building Standard 20 Law: JIS material and approved for use as a building structure. And the second item: the performance of the steel is evaluated in accordance with various necessary performances and is recognized by the Minister of the Ministry of the Earth. Therefore, the inventor concentrates on the development of the limit of the fluctuation ratio of the steel for JIS construction and the high temperature strength required so far. And the steel which is excellent in weldability and has excellent toughness of 6 1297732 toughness in a wide range of heat input, finally completed the present invention.

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As described above, when a steel is used as a building, the usual high-temperature strength (endurance = stress) of the steel material is low, and no fire-resistant coating or refractory coating is used, and it is impossible to use it. Moreover, even if it is a newly developed steel, it guarantees that the fire-resistant temperature is only 600~7〇〇°c, and there is a limit. Therefore, research and development can be performed without using a fire-resistant coating at 700~8〇〇°C. Omit the steel for the refractory coating project. SUMMARY OF THE INVENTION An object of the present invention is to provide a high-strength steel for a welded structure excellent in high-temperature strength in a temperature range of 6 ° C or more and 800 ° C or less, and a method for producing the steel industrially and stably. In order to overcome the above problems, the present invention achieves the object of limiting the steel component, the microstructure, and the like to an appropriate range, and the gist thereof is as follows: (1) A high-tensile steel of 49 MPa grade for a welded structure excellent in high-temperature strength %, containing: C: 0.005% or more, less than 〇040%;

Si: 0.5% or less; Μη: 〇·1 to less than 0.5%; 20 Ρ: 0.02% or less; S: 0.01% or less; Mo ·· 〇·3 to 1.5%;

Nb : 0.03 ~ 〇 · ΐ 5% ; A1 : 0.06% or less; and 7 1297732

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N : 0.006% or less, and defined as ·

PcM=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10 +5B 5 The weld crack sensitivity composition PCM is 0.15% or less, and is substantially not Contains B, and the remainder consists of iron and unavoidable impurities. The microstructure is the mixed structure of the ferrite iron and the toughness steel, and the toughness fraction is 20 to 90%. (2) (1) The high-strength strength of the welded structure is 490MPa grade high tensile steel, which is based on mass%, and further contains:

Cu : 0.05~L0% ; Ni : 0.05 ~ 1.0% ; Cr : 0.05~1.0% ; V · · 0.01 ~ 0.1% ;

Ti : 0.005~0.025% ;

Ca: 0.0005 to 0.004%; REM: 0.0005 to 0·004%; and Mg: 0.0001 to 0.006% of one or more. (3) For the welded structure excellent in high-temperature strength of (1) or (2), the 49 MPa grade high-tensile steel is used, and the old Worthite iron grain of the section parallel to the rolling direction of the plate thickness of 1/4 thick is The average circle is equivalent in diameter and is less than 12 μmηη. (4) A method for manufacturing 49〇Mpa grade high-tensile steel for welding structure with excellent south-temperature strength, which is a steel sheet or cast 8 1297732 piece composed of steel components of (1) or (2), and then heated to After the temperature range of 1100 to 1250 °c, 'lll 〇 (the cumulative reduction ratio below TC is 30% or more and is calendered at a temperature of 850 ° C or more, and then cooled or accelerated by a temperature of 800 ° C or higher to 650. Temperature below °C. [Depletion method] Detailed description of the embodiment of the car father The following describes the invention in detail. For high temperature strength, M析 and Nb can be added by compound to promote high precipitation.

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20 / Li Ri Shou Wending carbonitride, while increasing the differential density of microstructure toughening, and by the solid solution Mo & Nb delay differential recovery. In particular, in order to show the purpose of the present invention, ~8G (the strength at extremely high temperatures of rc, in the prior art, it is necessary to add a larger amount of M〇, but the sputtering and fusion of the structural steel with German welding Contrary to the viewpoint of toughness, it is extremely difficult to coexist with high-temperature strength. From the research of the present inventors, it can be found that the thermal stability and appropriate integration of the mother phase structure at high temperatures are controlled according to the appropriate enthalpy and microstructure control of the alloying elements. The precipitation strengthening effect and the retardation recovery retardation effect make it possible to coexist excellent weldability, weld toughness and high temperature strength. First, the reason why the present invention limits the steel component as claimed in the patent application is that the effect of the steel material is most significant. The element must therefore be controlled within a very small range, and its limited range is _5% or more and less than _〇%. The amount of C is less than 〇·〇〇5%, the strength will be insufficient; if it is more than 0.040%, the amount of Mo will be increased. The larger the invention, the _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Moreover, in order to maintain the thermodynamic stability of the mixed parent phase structure of the tough steel and the ferrite iron, when heating at a high temperature of a fire, the integration of the composite carbonitride precipitates of Mo, Nb, V, Ti is maintained, and the wall is maintained. To ensure the strengthening effect, the amount of C must be controlled to less than 0.040%.

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Si is an element which can be used for deoxidation, and has a substitution type solid solution strengthening effect, so that the strength of the base material at normal temperature can be increased, but in particular, when it exceeds 600 ° C, the effect of improving high temperature strength is not obtained. Further, if the addition is too large, the weldability and the toughness of the welded portion are deteriorated, so the upper limit is limited to 0.5%. Further, even if only Ti or Al is contained in the steel, deoxidation can be performed. From the viewpoints of the toughness of the welded portion or the hardenability, the Si amount is preferably as low as possible, and it is not necessary to add it. Μη is an indispensable element for ensuring strength and toughness; the replacement type solid solution strengthening element Μη can effectively improve the strength of the room temperature, but it does not have much improvement effect especially for the high temperature strength exceeding 600 °C. Therefore, as for the steel containing a relatively large amount of Mo in the present invention, it is necessary to limit the amount of Μη to less than 0.5% from the viewpoint of improving the weldability, that is, the pCM is lowered. It is also advantageous to depress the upper limit of the amount of Μη for the center segregation of the continuously cast sheet steel. Moreover, since the lower limit is related to the adjustment of the strength and toughness of the base material, it is necessary to add 〇1% or more. Niobium and S are impurities to the steel of the present invention, and the lower the content, the better. ρ will segregate at the grain boundary of the crystal grain to promote the destruction of the grain boundary, and S will form a sulfide represented by MnS, which will deteriorate the toughness of the base material and the welded portion. Therefore, the upper limit is 002% and 0.01%, respectively.

Mo can visualize and maintain the high temperature strength of the steel of the present invention, and is an essential and indispensable element together with 1^1>. From the point of view of high temperature strength, the more you add 1297732 5

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20

Mo is more advantageous, but considering the strength or weldability of the base metal and the toughness of the welded joint, the amount of addition should be moderate. When the pCM to be described later in the present invention is in the range (0.16% or less), the Mo content can be as low as 5%. The addition of lanthanum and Nb, or the addition of ν and Ή which increase the high-temperature strength described later, can stably ensure the high-temperature strength, so Mo must be added 〇·3% or more. Nb is an element that must be added in combination with Mo. First, the effect of Nb_ is such that the recrystallization temperature of the Worth iron can be increased and the effect of controlling rolling during hot rolling can be maximized. Further, Nb contributes to the fine graining of the Worthite iron when it is reheated before rolling. Further, ]^3 has an effect of increasing the high-temperature strength by precipitation strengthening and suppressing the difference of the recovery, and by adding M〇 in combination, it is helpful to further increase the high-temperature strength. When the Nb content is less than 〇·〇3%, the effect of precipitation strengthening and suppression of poor recovery at 70CTC and 800°C is small; when the content exceeds 〇·15%', the ratio of hardening relative to the added amount is reduced, which is not inconsistent. The economic efficiency will also make the toughness of the welded joint worse. For the above reasons, the content of Nb is limited to the range of 〇·〇3 to 〇15%. A1 is an element which can be used for deoxidation, but deoxidation with Si or Ti is sufficiently sufficient, so the lower limit of the content (including 0%) is not limited in the present invention. However, if too much A1 is used, not only the cleanliness of the steel is deteriorated, but also the toughness of the welded portion is deteriorated, so the upper limit is made 0.06%. Although N is an unavoidable impurity in steel, the addition of Nb and Ti k' N described later can be combined with niobium to form a carbonitride, so that the strength is increased and the properties of TlN steel can be formed. Therefore, the minimum amount of N must contain 〇·〇〇ι%. However, in the case of the crucible, the toughness and weldability of the welded portion are impaired, and the upper limit is 0.006% in the present invention. & The upper limit is not limited by the intangibility of the characteristics, 11 1297732 and is only limited to the extent that the inventors have confirmed. Next, the reason for adding Cu, Ni, Cr, V, Ti, and Ca, REM, and Mg, which are contained as needed, and the range of addition amount thereof will be described. The main purpose of adding the above-mentioned elements to the basic components is to detract from the excellent characteristics of the steel of the invention, and to obtain characteristics such as strength and toughness. Therefore, the amount of these elements added must naturally be limited.

Cu does not cause significant adverse effects on weldability and weld toughness.

It can increase the strength and toughness of the base metal. In order to achieve these effects, at least 0.05% or more must be added. On the other hand, since the addition is excessive, the weldability is deteriorated, and the risk of Cu cracking during hot rolling may increase, so the upper limit is limited to 1.0%. Further, it is known that Cu cracking can be avoided by adding an appropriate amount of Ni corresponding to the amount of Cu, and the weldability is also related to the amount of other alloying elements such as the amount of c, so the upper limit is not limited.

Ni has substantially the same effect as Cu, and particularly has an effect of greatly increasing the initial properties of the mother material. In order to really enjoy the aforementioned effects, at least 0.05% or more must be added. On the other hand, if the addition is excessive, even if it is seen, the weldability is deteriorated, and since Ni is an expensive element, the economy is impaired. Therefore, in the steel of the present invention, it is considered to be 490 MPa grade steel, and the upper limit is made 1.0%. If you want to increase the strength of the base metal, you can add Cr as needed. If there is a clear distinction between the micro-mixing of cyclic elements from iron scrap and the like, and the effect of Cr is indeed enjoyed, at least 0. 05% or more must be added. When the amount is too much, the adhesion is poor, and the toughness of the refining part is deteriorated like other elements, so the upper limit is limited to 1.0%. 12 1297732 5

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The introduction of i4Cu Νι, Ci* not only helps to strengthen the mechanical properties of the base metal, but also has its effect on weather resistance. For the above purposes, it is preferable to actively add the above elements within the scope of non-destructive splicing and reduction. V contains an effect of enhancing high-temperature strength, and has substantially the same effects and effects as _, but the effect is more versatile. Further, it is also known that V is included in the formula: V has an effect on hardenability and weldability. Therefore, if you want to enjoy the effect of adding V to the parent, set the lower limit and set the upper limit to 0.1% to eliminate the adverse effects of V. Ti can increase the south temperature strength in the same manner as Nb and V. In addition, when the toughness of the base material and the welded portion is particularly required, it is preferable to add Ti. This is because when Ti is less in amount of A1 (for example, 〇·〇〇3% or less), it is combined with ruthenium to form a precipitate containing TiA as a main component, and can be used as a nucleus of metamorphic ferrite iron in the grain to make a fusion portion. Increased toughness. Further, Ti and N are combined and finely precipitated in the steel sheet, and it is possible to suppress the coarsening of the Worthite iron crystal grains during heating and to make the calendered structure finer, and the fine TiN present in the steel sheet can be used to weld the heat affected portion during welding. Tissue fine granulation. In order to achieve the above effects, at least 0.005% of Ti is required. However, when the amount of Ti is too large, TiC is formed, which deteriorates low-temperature toughness, weldability, and the like, so the upper limit is 0.025%.

Ca and REM are combined with the impurity s, and the toughness can be improved or the fracture of the welded portion 20 due to the diffusible hydrogen can be suppressed. However, when the content is too large, the coarse inclusions are formed, which adversely affects the toughness, so both are limited. Within the range of 0.0005 to 0.004%. Since the two elements have substantially the same effect, if at least the above effects are to be added, it is sufficient to add at least one of them. M § has the effect of suppressing the growth of the Worthite iron grains in the heat-affected zone and making the fine particles 13 1297732, and the welded portion can be strengthened. To achieve the above effect, the Mg content must be greater than or equal to 0.0001%. On the other hand, once the amount of addition increases, the effect ratio with respect to the added amount becomes smaller, and the economic benefit is lost, so the upper limit of the content of Mg is set to 〇·〇〇6%. 5

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20 Further, the focus of the present invention is that B is not intentionally added, and if it exceeds the content standard and becomes a contaminant in the private order of steelmaking, then B is not contained in the quality. The addition of a small amount of B can significantly improve the hardenability, and when used in a high-tensile steel, it is advantageous for controlling the structure or increasing the strength, but at the same time, there is a risk that the weldability or the early edge of the welded portion is deteriorated. The present invention achieves the purpose of improving the high-temperature characteristics and the usability of the steel for the welded structure, and avoids the intentional addition of B, and does not substantially have B 〇 even if the components of the steel are as defined above, if the entire component is unsuitable, the invention cannot be obtained. Excellent characteristics of the features. In particular, according to the prior patent of the present inventor (Japanese Patent Application No. 2004-43961), the value of PCM is limited to 〇15% or less in order to greatly improve the weldability and the toughness of the welded portion. Here, the index pCM showing the sensitivity of the weld crack is defined as follows:

PCM=C+Si/30+Mn/20+Qi/20+Ni/60+Cr/20+M〇/15+V>a0+5B In general, the lower the pCM, the better the weldability, and the Pcm is in the 〇 22% or less, that is, preheating when _ is not required (to prevent welding cold cracking). In the high tensile steel 2', especially the high-tensile steel excellent in high-temperature strength according to the present invention, and the element (4) steel which does not contain a significant improvement in hardenability on the male shell, it is extremely low in the range of 〇·15% or less. Yan Ming Yang Ming also defined the microstructure. Only the steel composition is limited. It is also possible to guarantee the excellent splicability of the steel for the welded structure or the sharpness of the welded part. ^ 14 1297732 cannot meet the high temperature characteristics or the basic characteristics (especially strength) of the 490 MPa grade steel. Therefore, for the purpose of the present invention, the microstructure is limited to a mixed structure of ferrite iron and tough steel, and the toughness fraction of the steel is 2〇~90% ° because of the toughness fraction. If it is too low, it is difficult to ensure the strength and south temperature strength of 49 MPa MPa, and if the rate of steel is too high, it will increase the risk of exceeding the strength range of 490 MPa grade steel specified by JIS.

10 15 Therefore. The above conditions are the limitations of the inventors' intention to clarify the characteristics of the present invention based on the experimental results, and are not intended to be limiting. In addition, the microstructures are represented by a position where the thickness of the plate is 1/4 thick. In addition, the organization name "tough steel" is a name widely used by the industry, but when the rate is determined by the diversity change, the specific point of the field may cause a blurring ambiguity. At this time, it is also possible to judge according to another organization "fertilizer iron" in the structure of the structure, and the iron content of the fertilizer at this time is 10 to 80%. The ferrite iron referred to here is a lace-like or lace-like ferrite iron (excluding needle-like ferrite iron) which does not contain sulphur carbon. After rolling, the particle size of the Worthite iron crystals is changed. If it is desired to control the sharpness of the Mozhi steel of the Tianli Xi, such as the present invention, it is necessary to appropriately define the 4 Worthian shovel. The finer the grain technique, the finer the final metamorphic structure will be. In order to obtain the Mq_ color which is not lower than the usual one, the Worsfield iron 曰曰 k k 于 于 于 于 于 于 于 于 于 于 于 于 于 于 沃 沃 沃 沃 沃 沃 沃 沃 沃 沃 沃 沃 沃 沃 沃 沃 沃 沃 沃 沃 沃 沃 沃 沃 沃 沃 沃. Depending on the thickness of the plate or the steel-forming knives, there are more than 12 〇 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然 依然Limit the implied meaning. In addition, the particle size of the Worthite iron crystal 15 1297732 is sometimes difficult to discriminate. At this time, it will be centered on the 1/4 thickness of the plate thickness, and the impact is taken at right angles to the final rolling direction of the steel plate. For example, JISZ 2202 2mm V-notch test piece, the source of the brothers, and the field; the unit of the fracture surface when the brittle fracture is defined is defined as the effective crystal grain size of the shirt, and the average diameter of the circle is determined. 9 tablets are only 120 μηη or less. It must be the same as the organization as defined above (organization, organization, ~, sale) 夭 ^ its ^ Tian Ming 巍

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The excellent properties of the present invention, which are the first of the present invention, and the high-temperature characteristics, are easily obtained by the production method defined below. Reheating of steel sheets or slabs with the required steel composition is limited to a temperature range of _~125 generations. The lower limit of the coffee t is for the protection of the product: the thief, the can and the need to add it as needed to ensure the solid solution state of the high-temperature characteristic of the first object. In order to achieve this, the reheating temperature is preferably as high as possible, but since the heated Worthite iron grains are coarsened, it is not preferable from the viewpoint of the base material, so the upper limit is 1250X:. The most direct reason for limiting the rolling conditions is to control the grain size of the Worth W-iron 00 after the rolling is changed to a fine grain as described above. The main reason is to ensure her. Therefore, the delay is delayed by u(8). The cumulative pressure will be more than 30%. In order to precipitate V, Τι, which is added by _, 灿, or the reaction under a low temperature range, the temperature of the rolling is limited to 850 ° C or higher. From the point of view of organizational control, the cooling after calendering should also be limited. Due to the difference in steel composition, the thinner can obtain the structure according to the cooling rate of the cold. However, for thicker people, the cooling rate of the cooling is not fast enough, and 16 1297732 sometimes needs to be accelerated. Accelerated cooling at this time is the most common method of water-cooling when manufacturing thick steel plates, but it is not necessary to adopt water-cooling. Moreover, the purpose of accelerated cooling is to increase the cooling rate of the metamorphic region to control the structure, so it is necessary to accelerate the cooling to a temperature below 650 ° C by a temperature of 800 ° C or higher.

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In addition, the high-temperature strength of the present invention is targeted at 600 ° C to 800 ° C, and the quantitative target is the ratio of the lodging stress at high temperature to the normal temperature drop stress p (== high temperature drop stress / normal temperature drop stress), in steel The temperature TfC) is in the range of 60 (TC or more and 800 ° C or less, ρ^-0·0033χΤ+2·80. Example: Steel plate (thickness: 12 to 88 mm) of various steel components by converter-continuous casting-thick plate engineering Investigate the HAZ (heat affected zone; Mechanical properties, weldability, and weld toughness evaluation. Table i shows the steel components of the comparative example and the inventive example, Table 2 shows the manufacturing conditions, and Table 3 shows the results of the investigation of the structure and characteristics. The limited range includes various characteristics such as high-temperature strength and reproducible HAZ toughness. In contrast, at least one or more of the steel composition, manufacturing conditions, and structure of the comparative example do not conform to the scope of the present invention. It is understood that the characteristics of the comparative example are inferior to those of the present invention. That is, the amount of c in Comparative Example 19 is low, so the toughness fraction is low, and the room temperature strength and the temperature-to-temperature strength (ratio) are also low. The amount of C is higher, so the fraction of tough steel is higher, and the strength at room temperature is higher. Moreover, the strength of the base material and the early knife of the HAz are also poor. In Comparative Example 21, the amount of Mo is low, and the accelerated cooling start temperature is 17 1297732. It is also lower, so the lower toughness rate is lower, and the high temperature strength (ratio) is also lower. In Comparative Example 22, the lower the Nb amount, the heating temperature, the lower end temperature, and the higher the accelerated cooling stop temperature. The room temperature strength and the high temperature strength (ratio) were low. In Comparative Example 23, when the accelerated addition of B' was applied, the rate of the Weishan steel was higher, the base material of the base material was worse, and the HAZ toughness was also poor. Comparative Example 24 The amount of Μ η is higher, and the PCM is also higher, 11 〇〇. The cumulative reduction below 〇 is also lower, so the tough steel fraction is increased, and the base material of 490 MPa grade steel is excessively strong, and the base material is tough.

10 sex, reproduction of HAZ$i7 is also poor. Further, for example, the PCm of Comparative Example 24 is higher than the limited range of the present invention, but is also only about 0.185%, and the root crack of the oblique y-type fusion crack test is not observed in each of the examples.

18 1297732

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Table 2 Distinguish the heating temperature of the steel (t) The end of the calendering temperature (t) The rate of the K back pressure below the noot (%) [Accelerated cooling start temperature it) Adding the cooling stop temperature (t) Thickness im) 1 11SS m so One VI 1 1200 900 80 - one η 3 1100 culvert so 850 500 50 4 U50 910 TO one one 25 5 1100 m 50 one 50... 6 Π00 900 40 m 480 Τδ 7 ni m 30 mm io this im 1100 950 50 820 m 50 hair ill 1158 reward 60 g:::丨:i 谞ii painting 丨32 I Ming ill 1100 970 so one 32 ill 1250 1000 60 one 1 good 1 ΙΙΙ: camp ΙΙΙ β Ι let 1 discuss II 40 case 12 JI00 9δ0 so ||_|圆议|_ ,...- 4S 13 1)50 920 80 mm 32 I41 noo _ 80 _ 纲 ' 32 15 11S0 m so 120 5 SI3 40 IS 1 just _ 50 m 3 SO 40 17 1 Delete m 50 810 Lai 40 IS 1 Just 980 70 §00 S70 2D 19 ΠδΟ 95 B 5D One 80 20 I1S0 sn 80 S30 S00 32 21 Πδδ §40 50 .m 520 4S Example n 1050 830 35 m 650 75 : n 1250 m 80 850 570 n H im m 20 m ) 4S0 m I 20 1297732 Table 3 Zone ϋ Normal temperature drop stress tensile stress drop stress ratio to normal temperature drop stress P vlrs > Tough steel fraction of the organization Old Worth θ iron crystal grain size (/ / ιη^ IJ) Root split m UK im im Mm .mm 1 W1?T S4I OJ? 5JI l IS, U S0 if » h cracF m S3I in '8JI in -31 η Τ] n 1! fe crack 3 mm til us SI y §1 14 h cxict 4 mmu? “5 δ, n η a? U h crad] ί 40? m o. ai 15S ίο , n 3! Η ί n il U crack S mm iJS t H §§ η jn 1 §S k track jm 54.S e> n UT in s? mn ' il_i h crack This T 413 m Ί. u tu \U1 -3? if w to 88 to crick s 419 mt IS S. S§ tn « 12 H h crack η mmi« fl -n 4S S! n SJ ❻ cr§cf Example 13 mm 0, U tn :.丨i 51 9? unh crack η mm ur 0,S8 lu mti | 4S δδ so nm η 4Si uu 0J8 us u &4 nn Fine cmk !4 mmtu 0 J§ tn -11 s? S! un So cncp ΙΕ mmtul S § m -IS IS SI nn to eraeF ϊί mm Please in Uf -as ss 13 ?4 fc cmi 1? mm please mlunu 5i ST . So crick 13 418 m US 0J1 m -31 nk SB uh cmk IS mm HIS tu n S3 n % fe cracF iL· * 20 51? m §Ji in tn -3 « 12 II 22 lo tuck It antelope - 21 m 5 81 m U4 in -4§丨11 S! ui§ h crick n L η mm 0, IS! MS IU an S3 SI M cracl: η mm Please 1 OJ? 0J3 -3 n it 13 : is So cracF η mm D , S3 fl> 5S 〇> n -fn 13? 33⁄4 I n crack Tensile test piece: JIS Z 2201 1A (full thickness) with a thickness of 40 mm or less, larger than 50 mm JIS Z 2201 No. 4 (1/4 thick) ), the relative pressure is at right angles to the direction

Charpy impact test piece: JlSZ 2202 2mmV slit, rolling direction still temperature tensile test piece: round bar (8mm or ΙΟιηπιφ), 1/4 thick position, calendering direction and right angle thermal history 1: 1400° Cxl seconds, 800»500°C cooling time 8 seconds Thermal history 2: 1400°Cx30 seconds, 800-500°C cooling time 330 seconds 10 Industrial use possibility Manufactured by the steel component and manufacturing method of the present invention The steel, the microstructure can meet the limited scope of the present invention, and the high temperature 21 1297732 can be confirmed by the embodiment.

Strength, weldability, and weld toughness are all excellent. That is, the steel for the welded structure having the high-temperature characteristics of the fire-resistant steel which can only guarantee the high-temperature characteristics of about 600 ° C, which is far superior to the conventional one, can be stably produced in a large amount industrially, and can be expanded, for example, as a building application. Or no fire resistance by 5 or so. I: Simple description of the figure 3 None [Explanation of main component symbols] 22

Claims (1)

1297732 X. Patent application scope: L—The 490MPa grade high tensile steel with welded structure with excellent high temperature strength, whose steel composition is in mass%, contains: C: 0·〇〇5% or more, less than 0.040%; Si: 0.5 % below; Μη : 0.1 ~ less than 0.5% ; Ρ : 0·02% or less; 10 15 S: 0.01% or less; Mo: 〇·3~1.5%; Nb: 〇.〇3~0.15%; A1 ··0.06% or less; and N: 0.006% or less, and defined as: PCM=C+Si/30 +Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10 +5B The weld crack sensitivity composition Pcm is 〇·15% or less, and substantially does not contain Β, and the remaining part It is composed of iron and inevitable impurities. Further, the microstructure is a mixed structure body of ferrite iron and tough steel, and the toughness fraction is 20 to 90%. 20 2. The 490 MPa grade high tensile steel for the welded structure with excellent high temperature strength as in the first paragraph of the patent application is in mass %, and further contains: Cu: 0.05-1.0% ί Ni : 0.05-1.0% ; Cr : 0.05 —1.0% ; 23 1297732 10 15 V : 0.01 to 0.1% ; Ti · 0.005 to 0.025% ; Ca : 0.0005 to 0.004% ; REM : 0.0005 to 0.004% ; and Mg · · 0.0001 to 0.006% of one or more. 3. For the 490 MPa grade high tensile steel of the welded structure excellent in high temperature strength according to the first or second patent application, the average circle of the old Worthite iron grains in the section parallel to the rolling direction of the 1/4 thick position of the plate thickness Quite a diameter, below 120μηη. 4. A method for producing a 490 MPa high-strength steel for a welded structure having excellent high-temperature strength, which is a steel sheet or a cast piece composed of a steel component of claim 1 or 2, and further heated to 1100 to 1250 ° C. After the temperature range, the cumulative reduction ratio at 1100 ° C or lower is 30% or more, and the temperature is rolled at a temperature of 850 ° C or higher, and then cooled or cooled from a temperature of 800 ° C or higher to a temperature of 650 ° C or lower. twenty four