TW200925294A - Hot-rolled shape steel for crude oil tanks and process for manufacturing the same - Google Patents

Abstract

A hot-rolled shape steel for crude oil tanks which has a composition containing by mass C: 0.001 to 0.16%, Si: 0.01 to 1.5%, Mn: 0.1 to 2.5%, P: 0.025% or below, S: 0.01% or below, Al: 0.005 to 0.1%, N: 0.001 to 0.008%, W: 0.001 to 0.5% and Cr: 0.06 to less than 0.20% with the balance consisting of Fe and unavoidable impurities and a ferrite/pearlite microstructure containing deformed ferrite in an amount of 10% or above in terms of area ratio based on the whole microstructure and which exerts excellent resistance to uniform or local corrosion independent of coating and exhibits a strength corresponding to YP of 315MPa or above; and a process for manufacturing the steel.

Description

200925294 VI. Description of the Invention: [Technical Field to Which the Invention Is Ascribed] The present invention relates to a hot rolled steel used in a crude oil crucible. In particular, the present invention relates to a local corrosion (i〇cai corrosion) or a comprehensive reduction of a naked state and a primary coated state when used in a longitudinal material of a crude oil tank or the like. Corrosion (generaic 〇 〇 〇 〇 〇 ) gen gen gen gen gen gen gen gen gen gen gen gen gen gen γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ Hot rolled steel and its manufacturing method. The crude oil tank system in the present invention is referred to as an oil tank of an oil tanker or an oil tank for transporting crude oil, a tank for storing crude oil, and the like. Further, 'hot-rolled steel is a steel that is formed into a final shape by hot rolling (relative to this, a thick steel plate is used as a material to cut a thick steel plate into a predetermined size and welded to obtain the final shape of the steel) . Specifically, it refers to the equal leg angle (AB) or the uneqUal leg (ABs) manufactured by hot rolling, and the unequal edge of the mountain type steel (Cong _ Leg _ let (10) hall grab coffee: _), channel steel (Channel beam _ CB), ball plate steel (b): T-bar (T-bar). [Prior Art] In the crude oil tank of the oil tanker, in order to prevent explosion, 97136408 3 200925294 is sealed with an inert gas (〇 2 : 5 vol %, C 〇 2 : 13 vol %, S 〇 2 : 0· 01% by volume, and the residual portion is an exhaust gas of a boiler or an engine such as a representative composition of N2. Therefore, it is known that the inner surface of the upper part of the crude oil tank (the back side of the upper deck) is the rot, such as 〇2, C〇2, S〇2 contained in the blunt gas or H2S volatilized from crude oil. A full-corrosion button occurs with a corrosive gas. Further, the above H2S is oxidized by the catalytic effect of iron rust (rust rust) generated by the rot, and the solid S ′ is formed in an iayered shape in the rust. In addition, the corrosion product (perosi〇n product) is easily peeled off and deposited on the bottom of the crude oil tank. Therefore, the routine inspection of the tanker (d〇c inspecti〇n) carried out every 2.5 years is costly and laborious to repair the upper part of the oil tank or remove the deposit. ❹ m 'The steel used for the crude oil tank bottom plate (bQttQmplate) of the tanker is a protective film derived from crude oil produced by the raw material of the crude oil itself and the inside of the crude oil tank (hereinafter referred to as "crude oil protective film". (〇oil protective film)) The corrosion inhibition effect is considered to be non-corrosive. However, in recent years, it has been known that the steel of the oil sump bottom plate still undergoes local corrosion of a spider type (f〇rm〇f a bowl). The cause of this type of local corrosion can be exemplified by: 97136408 200925294 Condensation (1) High concentration dissolves the salt represented by vaporized sodium (such as lt) condensed water; 骐 detachment (2 ) Peeling off due to excessive washing; high concentration of lals) (3) Sulfide contained in crude oil (sulfidemate degree; (4) 〇 contained in the blunt gas for explosion protection 2, c such as 2 eve < * ^ concentration of 鬲; 〇 (5) the addition of microorganism (microorganism); but the above factors are inference, the clear reason is not clear. As above, the most effective branch, The surface of the riding surface is subjected to a heavy coating to block the steel against the corrosive ring. #凡 corcorive environment. However, if you want to apply paint to a crude oil tank, the construction area is huge, and it takes #1 times to repaint it in about 1Q, so it is pointed out that it takes a lot of labor and expense in construction and inspection. In addition, if the refining of the ® T in the crude oil tank is carried out, it will be promoted to promote the corruption of the damaged part of the film. Therefore, the proposal has steel that is highly corrosive in a corrosive environment such as a crude oil tank. For example, Japanese Patent Publication No. 2003-082435 (Patent Document 1) discloses a corrosion-resistant steel excellent in general corrosion resistance and local corrosion resistance, which is added to a steel of C: 0. 〇1 to 〇. 3 mass%. Si, Mn, p, s, and further added Ni: 〇. 〇 5~3 mass% and selectively added this, (: 11, (^, W, Ca, Ti, Nb, V, B. 97136408 5 200925294 Further, in Japanese Patent Laid-Open Publication No. 2004-204344 (Patent Document 2), there is disclosed that it has excellent resistance to full sulphur, local rot resistance, and can also inhibit the formation of corrosion products containing solid S. Corrosion-resistant steel, which is added with an appropriate amount of Si, Mn, P, S and Cu: 0.001 to 1.2 mass%. /., A1 : 〇. 〇〇卜〇 3质量%, N: 0· 001 〜0. 01% by mass 'and further added Mo: 〇. 〇1~〇. 2% by mass or W: 0. 01~0. 5 mass% of at least one. Ni, Co, Sb, Sn, O Pb, As, Bi, Nb, V, Ti, Ta, Zr, B, Mg, Ca, Y, La, Ce may be selectively added to the steel, and the valley is less than 0. . 1% of Cr. This 'As a ship, which is suitable for use in a ballast tank, etc., is disclosed in International Patent Publication No. WO2007/097142 (Patent Document 3), which has a composition of components. c: 0. 03~0·25 mass%, Si: 〇· 〇5~〇·50% by mass of steel 'containing appropriate amounts of Mn, P, S and A1 : 0.005 to 0.10% by mass, W: 0.01 to 1.0 % by mass, © Cr : 0·01 mass% or more and less than 〇. 2〇 mass%, n: 〇. 〇〇1~〇·〇〇8 mass% 'and selectively contain Sb, Sn, Ni, Mo In the case of Co, Nb, Ti, Zr, V, B, Ca, REM, and Y, the residual portion is composed of {^ and unavoidable impurities. Further, as the steel material, thick plates are exemplified. (Problems to be Solved by the Invention) However, the use of the steels of Patent Document 1 and Patent Document 2 as a steel material for a crude oil tank may give an excellent suppression effect on the overall corrosion of the upper portion of the crude oil tank, 97136408 6 200925294. , but the resistance to localized corrosion caused by the bottom plate of the crude oil tank (hereinafter referred to as It is not sufficient to be "resistance to local rot". The use of Patent Document 3 is different. 'It is not intended to be suitable for the miscellaneous properties of steel for crude oil tanks. 'The steel used in ships' is reduced from the use amount. The cost reduction and security assurance are in the direction of high intensity. For example, the thick steel plate exemplified in Patent Document 3 is used for a high-strength material having a relief stress γρ of ❹315 Mpa or more and preferably a TS of 440 MPa or more. In the case of the thick steel plate, the control of strength and toughness is generally achieved by adjusting the conditions of the TMCP (Thermo-Mechanical Control Process) to an appropriate range. On the other hand, hot-rolled steels used for vertical beam materials (for example, unequal-edge thick steel or T-shaped steel) have a complicated cross-sectional shape and size compared to thick steel plates, so they are controlled as strength and toughness. The method is difficult to use the same TMCP as the thick steel plate. In particular, the hot-rolled steel must be produced in consideration of the bending and warping during the rolling. Therefore, in order to increase the strength, the undulation stress γρ is 3l 5 MPa or more, and it is necessary to review the manufacturing method of the steel itself. Therefore, the object of the present invention is to provide an excellent corrosion resistance to general or local corrosion even if it is not affected by the presence of a coating film even in a corrosive environment such as a crude oil tank of a tanker, and has a YP of Hot-rolled steel for crude oil tank having a strength of 315 MPa or more and a method for producing the same. (Means for Solving the Problem) 97136408 7 200925294 In order to solve the above problems, the inventors first screened the factors related to local corrosion of the tank bottom plate, and the possibility of this test with the crude oil. As a result, the two produced by the bottom plate of the crude oil tank were successfully carried out in various ways: now, a rot (four) - ❹

In fact, the 0K oxygen (4) (sulfurized gas) contained in the spider type that occurs in the bottom of the crude oil tank serves as an important role in the liquid in the rot 2, especially in the coexistence. She has a low rot _ under the environment (specifically, m · 3 = pressure of the two partial pressure. 5 to 20% by volume of the gas saturated aqueous solution in the wide %, H2S rot remaining. That is, in the low 〇 2 Partial pressure and low H2S partial pressure rot

The solid s is oxidized and precipitated on the bottom of the crude oil tank and the solid S gate 2S battery, and the local rot is promoted and grown under the acidic environment where the surface of the steel material is partially rotted into a local sub- (β). Yu Yu's inventors investigated the effects of various alloying elements on the local rot caused by the above-mentioned low (1) partial pressure and - knife pressure environment. It has been found that by the addition of Cr and Cr, the rust layer formed on the surface of the steel material in the steel for the crude oil tank is densified, and the local corrosion resistance and the general corrosion resistance are improved. In addition, the addition of Sn Sb or M〇 can help the formation of a dense rust layer containing w, further improving local corrosion resistance and general corrosion resistance. In other words, by mainly making W and Cr and further increasing the contents of Sn, Sb, and M, it is possible to obtain a steel for crude oil tank which is excellent in both local corrosion resistance and overall corrosion resistance. In addition, it has been found that the use of the steel material in the state where the surface is coated with a Zn-containing primer 延长· can extend the coating life • (GC>ating layei* llfe) 'and can also improve the resistance to local rot # Sexual and tolerant. Surface corrosive. In addition, it has been found that high-strength deuteration of hot-rolled steel is required in order not to affect production-tivity and weldabUity, by (α + 2-phase zone rolling) (h〇tr〇1Hngduring) (r + α) region) is effective in introducing a process hardening ferrite. The present invention has been further developed based on the above findings. That is, the present invention is a hot-rolled steel for a crude oil tank, which is provided with C: 0. 00 Bu 0. 16% by mass, Si: 〇· 〇1~1. 5 mass%, Μη: 0·b 2·5 mass%, Ρ: 0_025 mass% or less, s: 〇. 〇1 Mass% or less, A1: ❹ 0.005 to 0.1% by mass, N: 〇.〇〇1 to 0.008% by mass, w: 0.001 to 0.5% by mass, and Cr: 0.06 mass% or more and less than 〇·〇2% by mass And the residual part is composed of Fe and unavoidable impurities; and has a microstructure composed of ferrite iron and pearlite, which contains iron relative to the total tissue system 10% or more of processed fat iron (strain harde) Ning ferrite) The hot-rolled steel for the above-mentioned crude oil tank of the present invention preferably contains at least one of the following groups A to D in addition to the above-mentioned composition 97136408 9 200925294. Sn: 〇. 〇〇5~〇. 3 mass% and sb: 0· 005~0. 3 mass% of one or two selected. Group B: Mo: 〇· 〇〇1~〇. 5 Mass %. C Group. Nb · 〇.00 〇. 1 mass%, V: 〇. 〇〇2~0. 1 mass%, Ti: 〇. 001~0·1 mass% and B mass% or less One or more selected ones. 〇: Ca: 0.0002-0.005 ft〇/〇a REM : 〇. 〇〇〇5~0. 015 mass% of the selected species or two. Preferably, the hot-rolled steel for the crude oil tank has a strength at which the undulation stress YP is 315 MPa or more and the tensile strength Ts is 44 Å or more. Further, the hot-rolled steel for the crude oil tank of the present invention preferably has a zinc base on the surface thereof. Further, the present invention relates to a method for producing a hot-rolled steel for a crude oil tank, which is characterized in that the steel material having the above composition is heated to 1000 to 1350 °. In the method of producing a section steel by C hot rolling, the hot rolling is set to 10 to 80% and the finishing temperature (to 111) at a cumulative reduction ratio (total reduction under a + r region) below the Ar3 transformation point. 1 仂 仂 叶 elbow 11 ^) is defined as (red 3 metamorphosis point -30. 〇~(Ar3 metamorphic point _18(rc) is applied, and then air cooling is performed. Further, the manufacturing method of the present invention is preferably in the above hot rolling, and the position to the steel in the rolling process is (The long-side, short-side, web (_), flange, etc. (refer to the actual implementation of 97136408 200925294), the temperature difference caused by the surface temperature difference is calculated to be within 503⁄4 after the cumulative rolling below the Ar3 metamorphic point The rate is set to ι〇~8〇%, and the finishing rolling temperature is set to (the above-mentioned hot rolling of Ar3 metamorphic point-3(TC)~(Ar3 metamorphic point-l8(rc). [Embodiment] (Composition) For the present invention The reason for limiting the component composition of the hot-rolled steel for the crude oil tank is described as follows: [C: 0. 001 to 0. 16 Mass 〇/〇] The C-based element is the strength of the steel. In the present invention, in order to obtain γρ: μ(10) The above-mentioned required strength must be 〇〇〇1% by mass or more. However, if it is more than 0.16% by mass, the weldability and the fusion heat influence portion are included.

Heat Affected Zone) has reduced toughness. Therefore, [the ratio is in the range of 0.001 to 〇. 16% by mass. Further, in order to have both the strength and the toughness, it is preferably in the range of 0.1% to 15% by mass. [Si : 0. 01~1· 5 mass %]

In the present invention, it is necessary to add 〇 〇 1% by mass or more in addition to the element of the strength of the steel. However, if it is added in excess of 1.5% by mass, the toughness of steel is lowered. Therefore, the 'Si system is set to a range of 0 〇 1 to 15% by mass. In addition, & has an effect of forming an anti-skin film (c〇rr〇si〇n fiim) under the acid brother to improve corrosion resistance. In order to obtain this effect, it is preferred to be in the range of 5 mass 97136408 11 200925294 ° / 〇. [Μη = 0·1 〜2·5 mass%] The rib system is an element which increases the strength of the steel material. In the present invention, in order to obtain the required strength, 〇% or more is added. However, if it is added in an amount of more than 25 mass%, the steel structure and the nature of the n Μη system are added in the range of & In addition, the guarantee of strength and the suppression make _ inferior

From the viewpoint of formation of inclusion, it is preferably in the range of 0.5 to 1.6% by mass, more preferably 〇.8 [P: 0-025 t«.T] P is segregate in the knot. The harmful elements of the 叩tal grain boundary's reduction in the shape of the granules are difficult to reduce as much as possible. In particular, if P contains more than 〇. 〇25 f%, the secret is greatly reduced, so it is determined to be 〇·025 1% by weight or less. In addition, if it is reduced to less than 〇5 贝5, the manufacturing cost will increase, so the lower limit of p is preferably about 0.005 mass%. [S: 0.01% by mass or less] The S system combines with Μη to form MnS belonging to a non-metallic inclusion (n〇n_metaUic inclusion), which is a harmful element for reducing the local rot resistance by causing local corrosion. . Therefore, it is preferable to reduce as much as possible. In particular, the right S contains more than 〇.〇1% by mass, which results in a significant decrease in local corrosion resistance. Therefore, the upper limit is set to 0.01% by mass. In addition, if s is reduced to less than 0.002% by mass, manufacturing may result. The increase in cost is limited to 〇〇2 97136408 12 200925294% by mass. [A1 : 0.005~〇.1 Quality A1 is an element added as deoxidation (4), and the medium age of the present invention is added with 0.005 quality! %the above. However, if the addition of A1 exceeds 〇1% by mass, the steel is lowered, so the upper limit is 〇. i mass%. Preferably, the range of 〇 〇 〇 卯 卯 mass %. [N: 0.001 to 0.008% by mass] © N is an element that reduces the amount of $7, preferably as much as possible.

. In particular, if the N content is more than 0· GG 8% by mass, the upper limit is determined to be 008 mass%. However, it is difficult to reduce the industrial to less than 质量·质量1% by mass. Therefore, the N series is defined as 〇. 〇〇1~〇. 〇〇8 mass% range. [W: 0.001 to 〇.5 mass%] W is an essential element necessary for improving corrosion resistance in the present invention. By adding W, the wot ions formed in a corrosive environment can exhibit a barrier effect on the anion ions such as chloride ions, and form insoluble FeW〇4 to suppress the progress of corrosion. Further, the rust layer formed on the surface of the steel sheet is very deuterated by containing W. The addition of W inhibits the overall corrosion and the growth of local corrosion in the corrosive environment in which niobium and cr are present by such chemical and physical effects. Therefore, a steel material for a crude oil tank which is excellent in local corrosion resistance and general corrosion resistance can be obtained. Further, in the case where the surface of the steel material of the present invention is coated with a primer containing Zn (primary) 97136408 η 200925294, Zn in the primer enters the densified rust layer containing W to form

Fe is a central composite W or Zn composite oxides, so that Zn can persist on the surface of the steel sheet for a long time. Therefore, compared with the steel without double -, the occurrence of local decay can be suppressed for a long time. The effect of improving the durability of the above W is not sufficiently exhibited if the content is less than 0.001% by mass. On the other hand, if it exceeds 5% by mass, the effect is saturated and the cost rises. Therefore, in the present invention, the W system is defined as 〇. 〇〇1 to 〇. 5 © the range of mass%. [Cr: 0. 06% by mass or more and less than 〇. 20% by mass]

The Cr system moves as it progresses to the rust layer, blocks C1-intrusion into the rust layer, and suppresses C1-concentration at the interface between the rust layer and the base iron. Further, in the case of applying a primer containing Zn, Zn can be allowed to exist on the surface of the steel sheet for a long period of time by forming a composite oxide mainly composed of Fe or Zn. As a result, local corrosion can be suppressed for a long time compared to a steel containing no Cr. However, if the effect is less than 0.06 mass%, the effect cannot be fully obtained. On the other hand, if it is 0.20% by mass or more, the toughness of the welded portion is deteriorated. Therefore, the system is in the range of 0.06 mass/s or more and less than 2% by mass. In addition to the age of the silk, the recording coffee of the present invention may further contain one or two kinds and/or Mo selected from the group and the north in the following range in order to improve the corrosion resistance. [Sn ·· 0· 005~〇. 3 mass%]

Sn is a dense bell layer formed by the combination of W and Cr. 97136408 14 200925294 (4) Acidic Ueidresist嶋) 'Mei, _ The effect of right addition is less than G.GG5 quality f%, then no face, , if Mu Λ π is, ft Λ 上述 上述 上述 于 于 于 于 于 于 于On the other hand, adding ....3 mass to the right will result in a decrease in workability and a reduction in toughness. 〇 力 力 添 ” 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四The acid resistance of Chengzhi Milin has an axis-like effect. However, if the mass is less than 〇%, the above effect cannot be obtained. On the other hand, = add more than U mass%' to shoot the above effect, and The processing uorkability is lowered. Therefore, sb is preferably added in the range of 5%. [Mo : 〇. 〇〇1~〇· 5 mass%]

Mo is added to W or Cr - to improve overall corrosion resistance and resistance to localized lung disease. Moreover, by combining with w, Cr, and/or the like, it is possible to promote the formation of dense _, which has the effect of further improving. The above effects can be obtained by adding 〇1% by mass or more. If it exceeds 0.5% by mass, the effect is saturated and the cost increases. Therefore, in the case of adding Mo, it is preferable to delete the range of 5 mass%. In addition to the above-mentioned components, the hot-rolling of the present invention may be added to the above-mentioned range of two or more selected from the group consisting of Nb, v, Ti and B in the following range. 97136408 15 200925294 [Nb : 0. 001~0. 1 mass%]

The Nb-based element mass %' added for the purpose of improving the strength of steel has a small effect. On the other hand, if it is a case of 'b", it is better to set it as Mq(4)% by mass [V: 0. 〇〇2~〇·1% by mass] V is the strength of steel for material extraction. The lifting effect is small. If it is less than 0.002: _" this, add V two parts of the mass% range. It is 0. 002~0. 1 [Ti : 0· 〇〇1 〇 1. 1% by mass] T:: For the purpose of improving the strength and dynamic properties of steel, the above-mentioned fruit is small. If the constant right is not ❹%, the effect is saturated. Therefore, on the other hand, the right is over the range of 0.1 mass o.ooiii mass%. 4. In the case of adding Tl, it is better to set it to [B: 0.01% by mass or less]. The B system is designed to increase the strength of steel. When it exceeds Ml% by mass, the boring property is lowered/, and 70% is added. 01质量百分比以下。 However, the β is preferably set to 0. 01% by mass or less. In ^,. Therefore, when adding B, it is better to add 〇. 〇匪 above. In the case of adding B under the escaping, in addition to the hot-rolled steel of the present invention, in addition to the ductility, the material of the component can also be ductile 97136408 ^ 'containing one of Ca in the following range and one selected from 200925294 REM Or 2 kinds. [Ca : 0· 0002~0· 005 mass%]

The Ca system has a function of improving the ductility and toughness of the steel by the shape control of the inclusions. However, if Ca is less than 0.0002% by mass, the effect is small. On the other hand, if it exceeds 0.005 mass%, the toughness is lowered. Therefore, the case of adding Ca is preferably determined to be in the range of 〇·〇〇〇2 to 〇. 〇〇5 mass%. ❹[REM : 0. 〇〇〇5~〇. 〇15% by mass] The REM system has a function of improving ductility and toughness by controlling the morphology of the material. However, if the content of REM is less than 〇〇〇·〇〇〇5 mass%, the effect is small. On the other hand, when it exceeds 0.015 mass%, the toughness will fall. Therefore, the case where REM is added is preferably in the range of 15% by mass of 〇5 to 〇 。. In addition, the combination of the particularly preferred elements is % and d. In the hot-rolled section steel of this month, the remainder other than the above components are inevitable impurities. However, the components other than the above are not excluded insofar as they do not impair the effects of the present invention. For example, if 〇 〇〇 8 mass ^, Cu is 〇.05 mass% or less, and Ni is 〇·05 mass% or less,

In the context of sulphur (4) containing hydrogen sulfide, Cu is helpful for the overall rot age. However, the effect of improving local rot is limited. In addition, the addition of CU results in a significant reduction in hot workability. Therefore, the present invention h 97136408 200925294 does not actively add Cu. 0质量质量以下。 In addition, in the form of unavoidable impurities, may be 0. 05% by mass or less. Further, the improvement of the general corrosion resistance and the local corrosion resistance of Ni has not been confirmed, and it has only become a factor of cost increase. Therefore, the steel of the present invention is not actively added. However, in the form of unavoidable impurities, it may contain 〇.〇5 mass% or less. (Microstructure) © λ times, the microstructure of the hot-slurry steel for the crude oil tank having high strength and excellent purity resistance of the present invention will be described. Steel plates for ships (especially high-strength steel plates with a fluctuating stress YP of 315 MPa or more) are generally made of a steel material which suppresses carbon equivalent to a low value and imparts high weldability, and is controlled to be rolled by combination ( Contro 11 ed ro 111 ng) and controlled cooling (c〇ntr〇ii ed c〇〇ii ng) TMCP, introducing hard toughened iron (bainite) into the second phase of the steel plate structure, thereby achieving High strength. Further, when the case of the toughness of the temperature is required, the requirement for the slab is determined by optimizing the conditions of the above-mentioned controlled rolling and controlled cooling. Therefore, in this case, the microstructure of the steel sheet is usually ferrite iron + toughened iron structure. On the other hand, in the case of hot-rolled steel, the width or thickness of the short side and the long side are different. For example, when the wearing surface is not rectangular, the unequal edge of the mountain is not the same as in the case of rolling or cooling. Temperature inequality will inevitably occur. Especially 97136408 18

V 200925294 In the intensity adjustment of application controlled cooling (accelerated cooling), the residual stress becomes uneven, causing twist or bend and curvature, resulting in dimensional accuracy. This is reduced, so that the shape correcting load after rolling is increased. Therefore, it is difficult to apply k to introduce a hard toughened iron structure into the high-strength method of the second phase. This applies to all other hot-rolled sections such as T-beams. © Therefore, in the hot-rolled steel for the crude oil tank, it is required to achieve the lodging stress YP: 315 MPa or more without accelerated cooling after rolling, and it is preferable to further achieve the tensile strength TS: 440 MPa or higher. For this reason, it is necessary to increase the strength by the ferrite iron + wave iron structure belonging to the general hot-rolled structure. As a means for achieving high strength by ferrite iron + wave iron structure, a method of increasing the iron fraction of the second phase wave and a method of grain refining the ferrite iron structure may be considered. Fertilizer iron is solid solution strengthening (s〇iid ❿solution strengthening) or precipitation strengthening (hardening) * hardening method, or (r-cut) 2-phase region Xing Kunzha and a part of the ferrite iron is processed into fertilized iron Method and so on. > Shangfa Fabu will practice the method of raising iron and peak mosquitoes to improve γρ, but since the rise of TS is small, it is impossible to obtain sufficient high strength by this method alone. Moreover, the method of increasing the iron fraction of the Borne must add a large amount of C. However, excessive addition of 'C' leads to a decrease in the solubility, which is not preferable. In addition, the addition of the secret strengthening element or the precipitation strengthening element to strengthen the ferrite-grain iron 97136408 200925294 method will lead to a decrease in the quality of the material due to the addition of a large number of alloying elements, or an increase in the cost of the material. On the other hand, the method of processing the ferrite can suppress the addition of c or alloying elements to a minimum, and raise γρ and Ts - while maintaining the weldability. Moreover, the method of processing the ferrite can be used to obtain high strength without performing controlled cooling (accelerated cooling) after hot rolling, so that it is possible to suppress bending or curling during rolling and cooling when the steel is manufactured. The occurrence of the song, while © to increase the intensity. Therefore, in the present invention, as a means for increasing the strength of the hot-rolled steel for the crude oil tank, a method of forming the microstructure of the steel into a ferrite-rich iron + a ferrite structure containing the processed ferrite is used. The above-mentioned processed ferrite iron must be more than 1% of the entire steel structure in terms of area ratio. If the processed ferrite is less than 10% ‘, the steel reinforcement cannot be fully performed. In addition, although the upper limit is not particularly specified, if it exceeds 70%, the strength rises and saturates. Further, the load of the two-phase region of (α + r) is increased at the time of rolling, and the risk of damage to the roller is increased, so that the area ratio of the processed ferrite is preferably below. 0 The above-mentioned processed ferrite is a differential displacement density (4) μ which is rolled by hot rolling in the (α + r ) 2 phase region below the Ar3 transformation point. (10) 〇η densuy) high fat loss. Adding the age of I silk to the flatness of the money = processing the fertilized iron, and the Wei (four) image of the micro-group shot is determined and determined. Determination of micro-structures The thickness of the thickest part is 1/4. Preferred tie plate thickness 97136408 20 200925294 The remainder is made of ferrite (other than processed ferrite) and the Borne iron structure. The Brilliant structure is preferably 2% or less in area ratio. Further, there may be a structure other than the ferrite iron and the ferritic iron having an area ratio of 20% or less, such as a toughened iron. (Manufacturing Method) Next, a method for producing a hot-rolled steel sheet for a crude oil tank having a ferrite iron + a ferrite structure containing the above-mentioned processed ferrite may be described. © In the production of the hot-rolled steel for the crude oil tank of the present invention, first, it is preferred to melt the steel having the above-described composition into a generally known method such as a converter or an electric furnace. A commonly known method such as continuous casting or ingot casting is used to produce steel materials such as steel slabs or blooms and billets. In addition, after the melting, it is also possible to add ladle refining or vacuum degassing. Next, the steel material is placed in a heating furnace and heated, and then hot-rolled to obtain a hot-rolled steel sheet for a crude oil tank having a desired size and desired microstructure and mechanical properties (mechanical pr〇per1;ies). At this time, the heating temperature of the steel material is set to be in the range of 1,000 to 1,350 Å. If the heating temperature is less than 100 〇 ° C, the deformation resistance becomes large, and it is difficult to perform hot rolling. On the other hand, if the heating exceeds 135 (rc, it will cause the occurrence of surface marks, or increase the scale loss or the original unit of fuel. Preferably, 97136408 21 200925294 is in the range of 1100 to 1300 ° C. For the hot rolling, the cumulative rolling reduction rate below the Ar3 transformation point must be set to 10 to 80%. If the rolling temperature exceeds the Ar3 transformation point, the microstructure of the steel does not contain - processing ferrite, which does not ensure the necessary strength and Resilience. Similarly, if the cumulative rolling reduction rate below the “3 • metamorphic point is less than 10%, the formation of the fertilized iron is less, and the toughening effect is small. Conversely, if the rolling reduction exceeds 8〇% Then, the load of the rolling increases and it is difficult to carry out the rolling or the number of passes of the rolling (number 〇f ❹passes) increases, resulting in a decrease in productivity. Therefore, the cumulative rolling reduction ratio below the Ar3 metamorphic point is set to 1 〇 8 〇. %. It is preferably in the range of 1〇~6〇%. In addition, at least the red 3 metamorphic point below can be passed through i or above, and the cumulative rolling reduction ratio below the 'Ar3 metamorphic point is After the end of the rolling, the area of the roller material (8) relative to the Ar3 Lai Reduction of area (reducti〇n of area) area of the wear material ⑴ packets sheaf of lines represented by the following formula.

❿ (accumulated rolling reduction rate [%] below Ar3 metamorphic point) = _ (") / A Again, the above hot rolling must be set at the finishing rolling temperature (Ar3 metamorphic point _3 〇〇 c) ~ (Ar3 metamorphic point -180. Under the conditions of 〇. If the finishing rolling temperature exceeds (5) the metamorphic point -3G °C), it is not able to fully obtain the strong difference caused by the introduction of the processing fertilizer in the 2-phase rolling. On the other hand, if it is less than (5) metamorphic point -18 () ΐ), the rolling load will increase due to the increase of deformation resistance, making rolling difficult. Before the Ar3 metamorphic point is 97136408 22 200925294, the temperature difference between the various parts of the section steel (long side, short side, web, flange, etc.) during the rolling process (that is, hot rolling during rolling) The temperature difference of the overall steel material is set to be less than 50〇c. For example, for the long side and the short side, there is a difference in plate thickness. If the unequal edge is not equal to the thick mountain steel, it is better to use the long side of the plate thickness thinner than the plate thickness. Thicker • The short side is water-cooled before and after the rolling mill, and the temperature difference between the long side and the short side is suppressed to 5 (within rc. Temperature difference) When the thickness is more than 50 Ό, not only the strength of the short side and the long side, but also the deviation (4) is large, and the bending or the new curve in the cooling step after the rolling becomes large, and the burden of the station consumption is large, and the productivity is high. In addition, the temperature difference between the various parts of the section steel is measured by the radiation thermometer by the surface temperature of each part (flange, web, etc.) of the same section position (length position) of the section steel in the way of the stick, and the highest temperature obtained from The difference between the lowest temperatures is obtained. The means for suppressing the temperature difference between each part of the section (for example, the short side and the long side) within 50 C is preferably used in a rougher rolllng mill. The method of controlling the cooling device before and after. Specifically, 5' is preferably a method of water-cooling the short side of the thicker plate to eliminate the temperature difference by the above-mentioned cooling device. At this time, the water cooling can be performed on the roller. After the rolling mill (1), only the kneading surface, only the back or the front and the back are carried out, and it can also be divided into multiple times according to the size or required precision of the rolled steel. In addition, the water density during water cooling is preferably lm3. /m2.min to The cooling after rolling is air cooling (cooling). This can reduce the shape change such as f curvature or warpage caused by the unevenness of the cold portion after pro-rolling, and can reduce 97136408 23 200925294 after light rolling. The correction burden of the product. The cooling rate during cooling is 0.4 to 1. (TC/S or so. The cooling is accelerated or decelerated within the range of the cooling rate ((4) Cooling, heat preservation, etc.) The implementation is substantially the same as the cooling, and therefore is not particularly excluded. • The hot-milk steel of the present invention obtained as described above can be coated by using a hot-rolled steel as a crude oil tank. The Zn-containing primer greatly improves the resistance to local corrosion and general corrosion. In general, a steel material is subjected to a primer blast treatment after applying a short blast treatment to its surface β. In order to uniformly cover the entire surface of the steel material, a certain thickness or more of the coating thickness is required, and in order to improve the local corrosion resistance and the general corrosion resistance, it is preferable to apply the coating thickness of the Zn-containing primer to 5/Wm or more. . In addition, from the viewpoint of improving the resistance to corrosion = corrosion resistance and general corrosion resistance, the upper limit of the coating amount is not limited, but if the primer is too thick, the cutting property, the weldability, and the economy are deteriorated, so The best is limited to about 100vm. A better coating thickness is applied to the crucible. There is no limit to the type of primer, and a well-known person can be used. Other coating films are also freely achievable depending on the purpose, but economically, a single layer of zinc primer is preferred. [Examples] (Example 1) A steel having the composition shown in Tables 1-1 and 1-2 was melted in a vacuum melting furnace or a converter to obtain a medium steel embryo. The medium steel embryo is placed in a heating furnace, heated to the temperatures shown in Tables 2-1 and 2-2, and then heatd according to the conditions described in Table 3_b 3_2. 97136408 24 200925294, Table 2 - 2-2 The unequal sides of the worn surface dimensions are not equal to thick mountain steel (_) and rolled τ steel. Further, in Table 2_b 2_2, the unequal-edge thick mountain steel (NAB) is represented by a long side as a web and a short side as a flange. / (4) unequal thickness _ from the short side, for the T-shaped steel, remove the (10) tensile test piece from the convex edge, (4) tensile properties (delayed convex ❹ tensile strength TS, elongation E1). In addition, for the unequal edge, the thick mountain, the P, the short side, and the τ steel, the flange is a 2QkJ/cm hot-roll steel system to abut the multi-layer welding (GMAW), and the summer is removed from the central portion of the HAZ. The Minchong film (2mmV incision test piece) was used to measure the absorbed energy by performing a Xia's rush test. In addition, for the samples in which the unequal-edge ridge type steel system is the inspection side, and the τ-type steel system is removed from the flange, the slab is observed at a magnification of 2 GG times. The flattened processing fertilizer granules formed by rolling in the 2-phase region in the observed mirror are tracked, and the area of the processed ferrite iron in the microstructure is determined by the method of the first grade I. In the case of steel with processed ferrite (other than Rolling No. 1Ε), the main phase outside the hair is processed by Bora (rolling N〇.1G) or toughened iron Μ 〇N〇. 1G) Non-processed ferrite iron produced after hot rolling. Further, in the rolling example, the ferrite iron is present in an amount of 3 to 2% by volume. 97136408 25 200925294 (Table 1-1) Steel No_ Chemical composition (% by mass) (1) Remarks C Si Μη Ρ S A1 NW Cr 1 0. 12 0. 18 1. 38 0.018 0.005 0.018 0. 0032 0. 07 0 07 invention example 2 0. 09 0. 35 1. 52 0. 015 0. 004 0. 024 0. 0028 0. 10 0.11 invention example 3 0. 06 0. 48 1. 78 0. 010 0. 002 0. 030 0.0030 0. 22 0. 18 Invention Example 4 0. 10 0. 18 1. 48 0. 008 0. 002 0. 020 0. 0035 0. 08 0. 07 Invention Example 5 0. 10 0. 24 1. 49 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0. 20 0. 94 0. 020 0.010 0. 038 0. 0038 0. 06 0. 10 Invention Example 8 0. 09 0. 25 1. 43 0. 012 0. 006 0. 030 0. 0035 0. 10 0 10 Invention Example 9 0. 12 0. 25 1.42 0. 010 0. 002 0. 031 0. 0028 0. 04 0. 12 Invention Example 10 0. 10 0. 22 1. 38 0. 015 0. 005 0. 028 0. 0037 0. 15 0. 13 Invention Example 11 0. 07 0. 28 1. 56 0. 010 0. 002 0. 028 0. 0035 0. 05 0. 12 Invention Example 12 0. 07 0. 30 1 45 0. 013 0. 005 0. 030 0. 0024 0. 10 0.09 Invention Example 13 0. 07 0.35 1. 38 0. 015 0. 004 0. 0 48 0. 0029 0. 05 0. 10 Invention Example 14 0. 09 0. 15 1. 60 0. 015 0. 004 0. 041 0. 0040 0. 05 0. 12 Invention Example 15 0. 12 0. 20 1.45 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 17 0. 15 0. 08 1. 00 0. 018 0. 007 0. 030 0. 0036 0. 05 0.11 Invention 18 0. 14 0. 20 1. 11 0. 009 0. 003 0. 028 0. 0035 0. 08 0. 13 Invention Example 19 0. 10 0. 30 1. 23 0. 012 0. 004 0. 022 0. 0050 0. 08 0. 15 Invention Example 20 0. 12 0. 31 1. 49 0. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 10 0. 25 1. 45 0. 014 0. 005 0. 031 0. 0025 0. 12 0. 15 Invention Example 23 0. 14 0. 37 1.49 0. 015 0. 005 0. 012 0. 0028 0. 07 0. 19 Invention Example 24 0. 12 0. 35 1. 60 0. 010 0. 004 0. 022 0. 0035 0. 12 0. 15 Invention Example 25 0. 15 0. 29 1. 28 0. 013 0 003 0. 020 0. 0030 0. 02 0. 19 Invention Example 26 0. 05 0. 20 1. 53 0. 012 0. 003 0. 035 0.0028 0. 05 0. 12 Invention Example 27 0. 14 0. 28 1. 35 0. 013 0. 005 0. 022 0. 0031 - 2 Comparative Example 28 0. 15 0. 20 1.40 0. 012 0.003 0. 035 0. 0033 - 0. 09 Comparative Example 29 0. 12 0. 25 1. 53 0. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0. 31 1. 34 0. Oil 0. 003 0. 031 0. 0028 - 0. 05 Comparative example 32 0. 12 0. 22 1. 35 0. 015 0. 004 0. 012 0. 0035 0. 08 0 04 Comparative Example 33 0. 10 0. 25 1. 55 0. 008 0. 005 0. 015 0. 0029 - Two comparative examples 97136408 26 200925294 (Table 1-2) Steel No. Chemical composition (% by mass) 2) Remarks Sn Sb Mo Nb V Ti B Ca REM 1 - Inventive Example 2 Inventive Example 3 - Inventive Example 4 0. 05 Inventive Example 5 0. 05 0. 10 - - 0. 010 - - - Inventive Example 6 0.0015 - Inventive Example 7 0. 07 0. 15 - - - - - _ - Inventive Example 8 - 0. 15 - - - - - - - Inventive Example 9 - - - - - - - - - - - - - - - - - - - - - - - - 0. 12 _ 0. 012 - 0. 008 - one - invention example 11 0. 05 0. 06 - - 0. 070 - - - - invention example 12 0. 04 0. 10 - - - - 0. 0012 - one hair Example 13 0. 05 0. 11 - - - - - 0. 0020 - Invention Example 14 0. 12 0. 21 - - - - - - 0. 0080 Invention Example 15 0. 07 - 0. 10 - 0. 060 0 012 - - - Inventive Example 16 - 0. 05 - - - 0. 014 0. 0015 - - Inventive Example 17 - 0. 11 0. 08 0. 012 - 0.012 - - - Inventive Example 18 - - 0. 05 - - 0. 008 0. 0013 _ - Invention Example 19 - - 0.10 - - - - 0. 0022 - Invention Example 20 - - 0. 06 - - 0. 010 - - 0. 0050 Inventive Example 21 - _ - 0. 012 - 0. Oil - 0. 0015 - Inventive Example 22 - - - - 0. 080 0. Oil - - - Inventive Example 23 - - 0.05 - - - - 0. 0009 0. 0025 Inventive Example 24 0. 10 - 0. 11 - - - - I - Inventive Example 25 0. 06 - - ~ - - - 0. 0015 Inventive Example 26 0. 011 0. 005 0. 10 0. 015 - 0. 012 - 0. 0020 - Inventive Example 27 Comparative Example 28 Comparative Example 29 Comparative Example 30 0. 06 Comparative Example 31 0. 10 0. 08 - - - 0. 012 - - - Comparative Example 32 0. 10 0. 03 - 0. 015 - 0. 010 - 0.0022 - Comparative Example 33 0. 05 0. 10 0.08 - - 0. Oil - - - Comparative Example 27 97136408 200925294 (Table 2-1) Rolling No. Steel No. Ar3 Metamorphic Point (°C) Type Steel Steel billet heating temperature in section size (°C) Remarks web x flange (mmxmm) web thickness (mm) flange thickness (mm) 1A 1 778 NAB 400x100 12. 5 18. 0 1180 Inventive example 1B 1 778 NAB 350x100 12.5 18. 0 1250 Inventive Example 1C 1 778 NAB 300x90 13.0 16. 0 1180 Inventive Example ID 1 778 NAB 250x90 13. 0 16. 0 1280 Inventive Example IE 1 778 NAB 400x100 12. 5 17. 0 1200 Comparative Example IF 1 778 NAB 400x100 13. 0 16. 0 1200 Comparative Example 1G 1 778 NAB 400x100 13. 0 16. 0 1200 Comparative Example 2 2 779 NAB 400x100 13. 0 16. 0 1180 Invention Example 3 3 770 NAB 400x100 12.5 18. 0 1250 Inventive Example 4 4 776 NAB 400x100 12. 5 18. 0 1200 Inventive Example 5A 5 777 NAB 350x100 12. 5 17. 0 1200 Inventive Example 6 6 770 NAB 300x90 13. 0 16. 0 1250 Inventive Example 7 7 803 NAB 300x90 13 0 16. 0 1230 Inventive Example 8 8 784 NAB 250x90 13. 0 16. 0 1280 Inventive Example 9 9 775 NAB 400x100 12.5 18. 0 1250 Inventive Example 10 10 783 NAB 400x100 12. 5 18. 0 1200 Inventive Example 11 11 780 NAB 400x100 12. 5 18. 0 1200 Inventive Example 12 12 789 NAB 400x100 12.5 18. 0 1200 Inventive Example 13A 13 796 NAB 400x100 12 5 18. 0 1230 Inventive Example 14 14 769 NAB 400x100 12. 5 18. 0 1250 Inventive Example 15 15 772 NAB 400x100 12.5 18. 0 1220 Inventive Example 16 16 794 NAB 300x90 13. 0 16. 0 1200 Invention Example 136 97136408 28 200925294 (Table 2-2)

Ar3 metamorphic point (.C) Sectional dimension of steel blank rolling No. Steel No. No type of web X-flange (mmxmm) Web thickness (mm) Flange thickness (mm) Heating temperature (t) Remark 17 17 794 NAB 400x100 12. 5 18. 0 1200 Inventive Example 18 18 792 NAB 400x100 12. 5 18. 0 1270 Inventive Example 19 19 796 NAB 400x100 12. 5 18. 0 1300 Inventive Example 20 20 772 NAB 400x100 12. 5 18. 0 1200 Inventive Example 21 21 775 NAB 400x100 12. 5 18. 0 1230 Inventive Example 22 22 779 NAB 400x100 12. 5 18. 0 1250 Inventive Example 23 23 767 NAB 400x100 12. 5 18. 0 1300 Inventive Example 24A 24 764 NAB 400x100 12. 5 18. 0 1210 Inventive Example 25 25 778 NAB 400x100 12. 5 18. 0 1180 Inventive Example 26 26 785 NAB 400x100 12. 5 18. 0 1200 Inventive Example 27 27 779 NAB 400x100 12. 5 18. 0 1210 Comparative Example 28 28 769 NAB 400x100 12. 5 18. 0 1210 Comparative Example 29 29 770 NAB 400x100 12. 5 18. 0 1200 Comparative Example 30 30 783 NAB 400x100 12. 5 18. 0 1250 Comparative Example 31 3i 780 NAB 400x100 12 5 18. 0 1250 Comparative Example 32 32 782 NAB 400x100 12. 5 18. 0 1240 Comparative Example 33 Μ 774 NAB 400x100 12. 5 18. 0 1300 Comparative Example 1H 1 778 T-type 300x125 11.0 19. 0 1300 Inventive Example 11 1 778 T-type 300x125 11. 0 19. 0 1300 Inventive Example 5B 5 777 T-type 300x125 11.0 19. 0 1320 Inventive Example 13B 13 796 T-type 300x125 11.0 22. 0 1280 Inventive example 24B 24 764 T type 300x125 11. 0 25. 0 1300 Inventive example 136 97136408 29 200925294 (Table 3-1) Rolling No. Steel No. Intermediate rolling cooling condition Finishing condition Cooling method Remarks Web _ Flange temperature difference (°C) Cooling position Cooling period Cooling times Ar3 cumulative rolling reduction rate (%) *1 Rolling end temperature (°C) 1A 1 35 Short side roll before and after 2 15 740 Air cooling Inventive Example 1B 1 25 Before and after short-side rolling 2 30 710 Air cooling Inventive example 1C 1 20 Before and after short-side rolling 2 50 710 Air cooling Inventive example ID 1 30 Before and after short-side rolling 2 70 680 Air cooling Inventive example IE 1 30 Before and after short-side rolling 2 0 850 Air cooling Comparative example IF 1 20 Before and after short-side rolling 2 5 770 Air cooling Comparative example 1G 1 70 Short-side, long-side rolling before and after 3 30 720 Water-cooling Comparative example 2 2 30 Short-side roller 1 40 700 air cooling invention before and after rolling 3 3 45 before and after short-side rolling 2 15 740 air cooling invention example 4 4 25 before and after short-side rolling 2 20 720 air cooling invention example 5 5 30 before and after short-side rolling 2 30 700 air cooling invention example 6 6 30 short side 2 50 700 before and after rolling Air cooling Inventive Example 7 7 20 Before short side rolling 2 60 680 Air cooling Inventive example 8 8 40 After short side rolling 2 50 700 Air cooling Inventive Example 9 9 30 Short side roll • After rolling 1 50 700 air cooling invention example 10 10 30 before and after short side rolling 2 30 750 air cooling invention example 11 11 40 before and after short side rolling 2 30 750 air cooling invention example 12 12 30 before and after short side rolling 2 30 720 air cooling invention Example 13A 13 25 Before and after short-side rolling 2 50 700 Air cooling Inventive Example 14 14 25 Before and after short-side rolling 2 30 730 Air cooling Inventive Example 15 15 30 Before and after short-side rolling 2 30 730 Air-cooled invention Example 16 16 45 Short 2 55 750 before air rolling Inventive Example *1 Accumulated rolling reduction rate below Ar3 transformation point 97136408 30 200925294 (Table 3-2) Rolling No. Steel No. Cooling conditions for intermediate rolling Finishing conditions Cooling method RemarksPlate-Flange Temperature Difference (°C) Cooling Position Cooling Period Cooling Times Ar3 Accumulated Rolling Rate (%) Wood 1 Rolling End Temperature (°C) 17 17 30 Short-side Rolling 2 30 710 Air Cooling Invention Example 18 18 30 Before and after short-side rolling 2 70 690 Air cooling Inventive Example 19 19 30 Before and after short-side rolling 3 50 700 Air cooling Inventive Example 20 20 25 After short-side rolling 2 60 700 Air-cooled invention Example 21 21 40 Short After the rolling, 1 20 710 air cooling invention example 22 22 30 before and after short side rolling 2 40 720 air cooling invention example 23 23 30 before and after short side rolling 2 60 730 air cooling invention example 24A 24 25 before and after short side rolling 2 30 730 Air Cooling Inventive Example 25 25 10 Before and after short side rolling 3 30 730 Air cooling Inventive Example 26 26 30 Before and after short side rolling 2 40 720 Air cooling Inventive Example 27 27 20 Before and after short side rolling 2 20 700 Air cooling comparison Example 28 2S 40 Short-side roll before and after 2 30 730 Air-cooling Comparative Example 29 29 40 Before and after short-side rolling 2 30 700 Air-cooling Comparative Example 30 Μ 30 Before and after short-side rolling 2 20 700 Air cooling Comparative Example 31 31 30 Before and after short-side rolling 2 20 710 Air cooling Comparative example 32 32 20 Before and after short-side rolling 2 30 710 Air cooling Comparative example 33 33 10 Before and after short-side rolling 2 30 700 Air cooling Comparative example 1H 1 30 Flange roll Before and after rolling 1 20 730 Air cooling Inventive Example 11 1 60 Flange without 0 20 730 Air cooling Inventive Example 5B 5 30 Before and after flange rolling 3 60 650 Air cooling Inventive Example 13B 13 20 Before and after flange rolling 2 50 650 Air cooling Inventive Example 24B 24 20 Before and after flange rolling 3 50 660 Air cooling invention example *1 Accumulated rolling reduction rate below Ar3 transformation point 97136408 31 200925294 Table 4b shows the above tensile test, Charpy impact test and weaving The result of the investigation. It can be seen from Tables W and 4_2 that the hot-spot steel with composition and microstructure is especially processed relative to the above-mentioned processing _ by the micro-group of the peak-iron surface _ ❹

The steel is γρ: 3ΐ5Μρ&amp; or more and TS: 440 MPa or more, which is more than the strength required for the present invention. In addition, both of the steel base materials and the dazzling joints exhibit an impact absorption energy of 34 J or more at -20 C, and the impact characteristics are also excellent. On the other hand, even if the composition of the present invention is satisfied and the microstructure is ferrite iron + wave iron, the steel having no processing ferrite (rolling No. 1E) or the steel having a low fraction of processing fertilized iron ( It is not possible to ensure the strength (YP: 315 MPa or more, TS: 440 MPa or more) required for the invention of the present invention. In addition, even if the composition of the present invention is satisfied, the steel is cooled and accelerated after hot rolling, and the ferrite iron + variable iron is used as the microstructure of the microstructure (rolling No. 1G), although high strength, but twisted and warped The shape changes caused by curvature, bending, etc. are large (not shown in the table). It is difficult to carry out engineering production. Further, the rolling No. 11 having a surface temperature difference of more than 50 ° C at the time of hot rolling under the Ar3 transformation point has no problem in terms of mechanical properties, but the steel is stunned or curved. 97136408 32 200925294 (Table 4-1) Rolling No. Steel No. Microstructure Tensile Properties Charpy Impact Characteristics vE(-20°C)(J) Remarks Organizational Structure*1 Processing Fertilizer Iron Fraction Rate (%) YP (MPa) TS (MPa) El (%) Base material welded portion 1A 1 Fsh+P 35 388 441 31 213 150 Invention Example 1B 1 Fsh+P 55 406 452 29 198 - Invention Example 1C 1 Fsb+P 55 432 466 29 200 - Inventive Example ID 1 Fsb+P 75 473 498 26 173 - Inventive Example IE 1 F+P 0 299 347 41 296 - Comparative Example IF 1 Fsh+P 5 335 386 39 288 - Comparative Example 1G 1 Fsh+B 50 446 536 25 196 - Comparative Example 2 2 Fsh+P 65 454 497 30 226 213 Invention Example 3 3 Fsh+P 30 420 477 29 318 256 Invention Example 4 4 Fsh+P 60 401 452 26 250 172 Invention Example 5A 5 Fsh+ P 60 430 478 27 244 203 Inventive Example 6 6 Fsh+P 70 493 532 25 200 160 Inventive Example 7 7 Fsh+P 70 443 475 28 178 130 Inventive Example 8 8 Fsh+P 55 443 479 31 222 186 Inventive Example 9 9 Fsh+P 50 522 563 32 166 155 Inventive Example 10 10 Fsh+P 30 399 441 32 239 186 Inventive Example 11 11 Fsh+P 40 403 446 34 247 222 Inventive Example 12 12 Fsh+P 45 400 451 33 292 201 Inventive Example 13A 13 Fsb+P 60 418 453 30 255 176 Inventive Example 14 14 Fsb+P 30 415 458 35 240 200 Inventive Example 15 15 Fsh+P 30 447 494 35 206 155 Inventive Example 16 16 Fsh+P 50 418 443 33 239 179 Inventive Example *1 F: Fertilizer Granular iron, Fsh: fertilized iron with processed ferrite, P: Boron, B: toughened iron 97136408 33 200925294 (Table 4-2) Rolling No. Steel No. Microstructure tensile properties Charpy impact Characteristic vE(-2(TC)(J) Preparation 5 main organization composition*1 Processing fertilizer granular iron fraction (%) YP (MPa) TS (MPa) El (%) base metal welded joint 17 17 Fsh+P 65 421 468 25 129 123 Inventive Example 18 18 Fsh+P 70 496 522 25 111 116 Inventive Example 19 19 Fsh+P 80 466 504 23 158 170 Inventive Example 20 20 Fsh+P 60 526 559 34 223 171 Inventive Example 21 21 Fsh+ P 30 429 484 28 166 183 Inventive Example 22 22 Fsa+P 60 452 494 30 195 198 Inventive Example 23 23 Fsh+P 50 551 583 31 179 144 Inventive Example 24A 24 Fsh+P 40 502 555 30 200 156 Inventive Example 25 25 Fsh+P 40 460 510 34 166 130 Inventive Example 26 26 Fsb+P 45 425 465 33 318 247 Inventive Example 27 27 Fsh+P 53 422 477 30 129 149 Comparative Example 28 28 Fsh+P 40 451 500 30 132 121 Comparative Example 29 29 Fsh+P 55 441 490 30 177 162 Comparative Example 30 Μ Fsh+P 55 412 466 31 206 170 Comparative Example 31 31 Fsh+P 46 427 483 32 120 160 Comparative Example 32 32 Fsa+P 60 415 461 29 144 162 Comparative Example 33 33 Fsh+P 65 447 497 31 177 175 Comparative Example 1H 1 Fsh+P 40 458 462 35 282 157 Inventive Example 11 1 Fsh+P 40 438 461 33 257 157 Inventive Example 5B 5 Fsh+P 60 441 496 26 187 173 Inventive Example 13B 13 Fsh+P 60 387 446 32 290 188 Inventive Example 24B 24 Fsh+P 50 438 526 30 253 155 Inventive Example *1 F: Fertilizer iron, Fsh: Fertilizer iron containing processed ferrite iron, P: Bora, B: toughened iron 97136408 34 200925294 In addition, for each hot-rolled steel produced, the thickness of the unequal-edge thick steel is from the short side, and for the τ steel, the thickness is cut from the flange (10) A square piece of 50 legs with a width of 50 liters and a length of 50 legs is applied to the surface to give a short burst. Then, the thickness of the inorganic (inGrganie-based) primer is 0/zm (uncoated), 5~1〇_, 15~25/ζιη, 50~70_4 ❹ φ Test piece. Secondly, 'the front end and the back side of the test piece are shielded with a paint with anti-name, and further coated with the crude oil component blown from the actual tanker only as the top surface of the test surface. s (sludge), as a corrosion test piece. Further, in the above-mentioned test of the surface of the rot film, the test piece 2 was coated with the sludge on the test surface. The other is a furnace in which the S 50 mass % furnace is mixed in the central portion of the test surface, and the sulfur-sludge sludge coated on the sulphur of the sulphur is coated with sludge. Test piece (test piece, his heart is only ' Μ 9 rb -jl. The sludge system becomes the starting point of local corrosion and promotes the test result of L mixing", can surely grasp the steel composition to the local rot = thief test piece 2 The influence of the paint and the influence of the combination of the above, the effect of the on-the-job inhibition, the results are known to be compared with the exposure test of the inventor of the inventor and the exposure of the actual vessel: , using the test piece 2, the test &gt; { is attached to the money ^ Guan Zhijia ° test liquid 6 ^ 丨 丨 之 赖 = = = test turf test device test tank 2, strange temperature tank 3 double The type test of the humus test is 腐 韵 97 97 97 97 97 97 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 2009 The liquid 6 system uses the artificial seawater specified by aSTMD1141 as the test mother liquid, and is introduced and adjusted in the night of the Pan Λ Λ 1 茨It is a pure ratio of 5 volumes _ 〇 = product, and the residual portion is a mixture gas 4) composed of (4) gas. Further, the temperature of the test liquid 6 is maintained at _ by adjusting the temperature of entering. The test solution 6 is a system of sputum ❹ 虱 虱 虱 虱 虱 虱 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 Observe the rot state and use the depth gauge (the depth of corrosion of the dip kiss removal/mesh generation part to be resistant to local corrosion corrosion <local corrosion resistance grade) on the basis of the following criteria. No local corrosion money is not deep enough. Lmm The local corrosion depth is above 腿· 〗 〖The leg is less than 〇 2_ 7 The local corrosion depth is 〇.2mm or more and less than 〇6 coffee local corrosion depth is 〇.6mm or more and less than 1〇mm Local corrosion depth is 10 ^The above and less than 15 coffee local corrosion depth is 1.5mm or more. m The results of the above partial corrosion test are shown in Table 5-1, =ΓΓ1' to have the composition of the present invention: n: two: ...', material The local corrosion resistance of hot-rolled steel is 97136408 ^ For grade 36 200925294 卜3, the local brain depth system is suppressed to less than 〇2. In particular, the zinc primer is coated above, and the evaluation of the resistance to local rot is all grade 1, which effectively inhibits local rot. On the other hand, in addition to the hot-drying steel-type steel which is not the steel Να 27~33 which is composed of the invention of the present invention, the local rot is less than the heat of the present invention, and the test is used. The test of the month 2 is even worse. The situation with the test piece 1 is further promoted; 1 the day (four) = the amount of the difference is compared with the difference between the __ 7 steel types in the zinc-coated state, and the steel No. 1~26 is different. That is, in the case of the invented example, the zinc primer of the hot-rolled steel of the material is not coated, and the local corrosiveness, regardless of the toe 27 to 33 as the prime coating state, is compared with the steel of the comparative example. In comparison with the steel, the steel is more restrained. It is worth noting that the test of the film 1 is the hot-rolled steel of the material, and the test is used. However, the use of the test piece 2 ^ 〗 special resistance to local corrosion is poor, the difference is obvious. The resistance to local rot in the test was significantly better than that of the present one. 4° The hot-rolled steel of the present invention is resistant to local rot resistance 97136408 37 200925294 (Table 5-1) Rolling No. Steel No. Example 1 (Test piece 1) Example 1 (Test piece 2) Example 2 Side Thickness (_) Remarks Zinc - Primer Thickness (#01) Reprinter Thickness (//m) Word) 0 5~10 15-25 50-70 0 5~10 15-25 50-70 0 ~ 5-1 〇15-25 50-70 1A 1 3 1 1 1 4 3 2 1 1 - 2 2 1 1 Invention 1 1 2 3 1 1 1 4 3 2 1 2 2 1 1 Invention Example 3 3 3 1 1 1 4 3 2 1 2~~ 2 1 1 invention example 4 4 2 1 1 1 4 3 2 1 2 2 1 1 invention example bA 5 1 1 1 1 3 2 1 1 1 1 1 1 invention you I 6 6 3 1 1 1 4 3 2 1 2 2 1 1 invention example 7 7 1 1 1 1 3 2 1 1 1 1 1 1 invention example 8 8 1 1 1 3 3 2 1 2 2 1 1 invention example 9 9 3 1 1 1 4 2 2 1 2 2 1 1 invention example 10 10 1 1 1 1 3 2 1 1 1 1 1 1 invention example 11 11 1 1 1 1 3 2 1 1 1 1 1 1 invention example 12 12 1 1 1 1 3 2 1 1 1 1 1 1 Inventive Example 13A 13 1 1 1 1 3 2 1 1 1 1 1 1 Inventive Example 14 14 1 1 1 1 3 2 1 1 2 1 1 1 Inventive Example 15 15 2 1 1 1 4 3 2 1 2 2 1 1 Inventive Example 16 16 1 1 1 1 3 2 2 1 2 2 1 1 Evaluation Example of Invention Example <Local Corrosion: Depth Level> 1 : No local corrosion 2 : Less than 0. lmra 3 : 0.1 coffee or more and less than (J. 2 coffee 4 : 0.2mm or more and less than 〇. 6 coffee 5 : 0_ 6mra or more and less than 1 · 〇 mm 6 : 1. 0 or more and less than 1. 5mm 7 : 1.5_ or more <Local corrosion: Depth level> 1 : No local corrosion 2 : Less than 0.1_ 3 : 0.1 or more and less than 0 · 2 face 4 : 0. 2_ or more and less than 0.6_ 5 : 0. 6 coffee or more and less than 1.0 fine 6 : 1. Omm or more and less than 1. 5mm 7 : L 5mra or more <no coating material: corrosion speed grade> 1 : not Full 0.10mm/year 2: 0.1〇_/year or more and less than 0·25_/year 3: 0.25ram/year or more and less than 0. 5Qram/year 4: 0. 50mm/year and less than 1.00mm/ Year 5: 1. 00_/year or more <primer material: rust area rate grade> 1 : less than 53⁄4 2 : 5% or more and less than 15% 3 : 15% or more and less than 25% 4 : 25% or more Less than 50% 5 : 503⁄4 or more

38 97136408 200925294 (Table 5-2) Rolling No. Steel No. &gt; Example 1 (Test piece 1) Example 1 (Test piece 2) Example 2 Remarks Primer thickness (#m) Zinc primer thickness (/ΖΠ1) Resin primer thickness (//in) 0 5-10 15-25 50-70 0 5~10 15-25 50-70 0 5~10 15-25 50-70 17 17 1 1 1 1 3 3 2 1 2 2 1 1 Inventive Example 18 18 3 1 1 1 4 3 1 1 2 2 1 1 Inventive Example 19 19 2 1 1 1 4 2 1 1 2 2 1 1 Inventive Example 20 20 3 1 1 1 4 3 2 1 2 1 1 1 Inventive Example 21 21 3 1 1 1 4 3 2 1 2 2 1 1 Inventive Example 22 22 3 1 1 1 4 3 1 1 2 2 1 1 Inventive Example 23 23 3 1 1 1 4 3 1 1 2 2 1 1 invention example 24A 24 2 1 1 1 3 2 1 1 2 1 1 1 invention example 25 25 2 1 1 1 4 3 2 1 2 2 1 1 invention example 26 26 1 1 1 1 3 2 1 1 1 1 1 1 Inventive Example 27 27 6 5 5 4 7 7 6 5 5 5 5 4 Comparative Example 28 28 6 5 5 3 7 5 4 3 5 5 4 4 Comparative Example 29 29 6 5 4 4 7 7 5 5 5 5 5 4 Comparison Example 30 30 6 5 4 4 7 7 5 5 5 5 4 4 Comparative Example 31 31 6 5 4 3 7 6 5 5 5 5 4 4 Comparative Example 32 32 3 2 1 1 5 4 3 2 4 3 3 2 Comparative Example 33 33 6 4 2 2 5 4 4 3 4 4 3 3 Comparative Example 1H 1 3 1 1 1 4 3 2 1 2 2 1 1 Inventive Example 5B 5 1 1 1 1 3 2 1 1 1 1 1 1 Inventive Example 13B 13 1 1 1 1 3 2 1 1 1 1 1 1 Inventive Example 24B 24 2 1 1 1 3 2 1 1 2 1 1 1 Evaluation Example of Invention Example <Local Corrosion: Depth Rating 〉 1 : No local corrosion 2 : Less than 0.1 coffee 3: 0.1_ or more and less than 0.2 coffee 4: 0.2_ or more and less than 〇. 6mm 5: 0.6mm or more and less than 1. 〇mm 5:1.0 And less than 1.5 coffee 7: 1.5 coffee or more <local corrosion: depth level> 1: no local corrosion 2: less than 0. lram 3:0 · 1 coffee and not full. 2mm 4: 0.2 or more and less than full 〇.6咖5: 0.6 coffee or more and less than 1. 〇 1 i: 1· 0 round or more and less than 1,5 turn 7 : 1.5mm or more <no coating material: like 1: less than 0.10u 2 : 0.10mm / year and less than 0. 2 3 : 0. 25iran / year and less than 0.5 4 : 0.50mm / year and less than 1.0 5 : 1. 00_ / year < primer material: rust δ 1 : not full 53⁄4 2 : 5% or more and only 3: 15% or more and 4 : 253⁄4 or more and 5 : 503⁄4 or more ί Silver speed book / year or more 5mm / year or more 0mm / year or more 0_ / year or more 积 rate etc. '15 % Table full 25 Table full 50 L level> - Level > % % 39 97136408 200925294 (Embodiment 2) By the same as the user of Embodiment 1 No. 1~33 steel as hot-rolled steel material having a thickness of the cut length of 48mm 25mmx 4mmx width of small rectangular pieces, the surface thereof is administered to a short burst. Then, a corrosion test piece of the inorganic zinc primer having a coating film thickness of 0/zm (uncoated), 5 to 10/ζι, 15 to 25_, and 5 Å to 7 Å was prepared. Next, in order to accelerate the corrosion test, the X-shaped cut to the surface of the steel material is applied to the surface of the coating film in such a manner that the scratch area rate is ί ο %, for the following comprehensive rot test. The general corrosion test was carried out using the corrosion test apparatus shown in Fig. 2. The corrosion test apparatus is composed of a corrosion test tank 9 and a temperature control plate 1〇, and the corrosion test tank 9 is kept at a temperature of 4 (TC water 13). Further, in the water 13, by introducing 12% by volume. C〇2, 5 vol% 〇2, 〇〇1 volume 〇2, 〇. 1 vol% HzS, the residual gas is a mixture of N2 (introduced gas 11), and the supersaturated water vapor is filled with the corrosion test tank 9 Inside, the corrosive environment in the crucible plate on the crude oil tank is reproduced. Then, the corrosion test piece 8 attached to the back surface of the test tank is passed through the temperature control panel 10 of the built-in heater and the cooling device, and is repeated for 20 days. Ϊ́χ 4 hours + 5 (rcx 4 hours as a change in the enthalpy cycle / m degree, the formation of dew condensation water on the surface of the test piece, thereby causing general corrosion. In Figure 2, the symbol 12 indicates the exhaust gas discharged from the test tank. After the evaluation of the overall corrosion resistance of each test piece in the following manner: 0 97136408 40 200925294 <zinc primer uncoated material> Determination of corrosion in the thickness of the plate before and after the test (decrease in Plate thickness) It is converted to every! The corrosion plate thickness is evaluated by the following classification to evaluate the general corrosion resistance. 1 'The residual speed is not full. l〇mm/year 2 · The corrosion rate is 〇. l〇mm/year and above and less than 〇. 25mm/year 3 The corrosion rate is 〇. 25mm/year and above and less than 〇·5〇_/year 4 · Corrosion speed is 〇. 50mm/year and above and less than 1. 〇〇mm/year 5: rotted rice speed is 1. 00mm /year or more <zinc primer coating material> The area ratio of the rust generated on the surface of each test surface and under the coating film was measured, and the general corrosion resistance was evaluated by the following classification.

The rust area ratio is less than 5%. The rust area ratio is 5% or more and less than 15%. The rust area ratio is 15% or more and less than 25%. The area ratio is 25% or more and less than 50%. The rust area ratio is 50% or more. The results of the above comprehensive corrosion test are also shown in Tables 5_丨 and 5_2. It can be seen from Tables 5 to 1, 5-2 that the heat-resistance steel of the steel N〇.b% which is in accordance with the composition of the present invention is a good grade for the non-coating material. . On the other hand, the hot-rolled steel of the comparative example of steel shame. 27 to 33 is not coated with an inorganic primer, and even if it is coated with 97136408 200925294 ::: comprehensive plum is still hotter than the invention. (Industrial Applicability) Cloth low-cost provides high-intensity and is not only exposed, but also excellent in resistance to aging and resistance to local oil sump. The use of steel is used as the original, (4, the situation has greatly reduced the upper part of the crude oil tank (the upper deck and the ❹ =1 surface light and the (four) Wei board clock _, so it can be extended during the period of painting - can reduce the repair work And the cost of repairing the cost of the ship. The hot-rolled steel for the crude oil tank of the present invention shows excellent performance in the environment of seawater. It can also extend the life of the ship by extending the repair period of the ship. It can also be used in A hot-rolled steel sheet used in other fields similar to those used in the environment of the rot. [Simplified description of the drawings] Fig. 1 is a view showing a test apparatus used in the local corrosion test used in the embodiment 1. Fig. 2 is a diagram showing the second embodiment. Used for general corrosion Diagram of the test device. [Explanation of main component symbols] 1, 8 test piece 2, 9 corrosion test bath 3 constant-temperature bath 97136408 42 200925294 4, 11 5 ' 12 6 7 ' 13 10 s introduced gas exhaust gas test liquid water temperature control board (temperature-control plate) ❹ 97136408 43

Claims (1)

200925294 VII. Application for Patent Fan Park: 1.- Type of hot-rolled steel for crude oil tank, which is equipped with 〇 〇 〇 mu mu mu mu mu mu mu mu mu mu mu mu mu mu mu mu mu mu Mn Mn Mn Mn Mn Mn Mn Mn Mn Mn Mn Mn Mn Mn : 〇 Η Η Η 暑 4 4 '% by mass, AI: 0. 〇〇 5 ~ 〇. 1% by mass, N: 〇. 001 0. 008 质质%, w: 〇〇〇1~〇. 5 mass% And 〇〇 6 mass % or more and less than 2. 2 () f amount %, and the residual part is composed of &amp; and unavoidable impurities; ❹ 、 ',,, and The micro-structure composed of the wire iron, the fertilizer grain contains the processed ferrite iron in the area of the total structure, and the hot-rolled steel for the crude oil trough according to the i-th item of the patent application scope. In addition to the above-mentioned component composition, it further contains ι or 2 selected from %: please 5 to 〇3 = and Sb:(K(K)5 to 〇.3 mass%. The hot-rolled steel for the crude oil tank of the item has the above-mentioned composition and further contains M〇: _~Q 5 mass / 4. For the hot-rolled steel for crude oil tank according to item 2 of the patent application, wherein: In addition to the above-mentioned component composition, the following steps include: g gqi~g 5 mass / 5 · For the hot-rolled steel for crude oil tanks of the first item (4), the above-mentioned composition is included, and the step contains Delete, V: 〇· 002~0 1 皙吾〇/, τ..η 4, • 1 quality /. Ti . 〇.0〇1~〇. i mass% and Β mass% or less selected 1 or more or more. 6·For example, in the hot-rolled steel for crude oil tanks in the second paragraph of the patent application, in which the composition of the above components is further included, Nb: G. (10) is a mass%, , 97136408 44 200925294 V: 0·002~Ο.1 mass%, Ti: 〇·0〇b 0.1 f quantity % and B: 0.01% by mass or less, one or more selected ones. The hot-rolled steel for the crude oil tank, wherein, in addition to the above-mentioned component composition, further contains Nb: 〇. 〇〇 〇 〇 j mass%, 'v · 〇. 002~0.1 mass%, Ti: 〇. 〇〇 1 to 1% by mass and B: 〇. 01% by mass or less selected one or more. 8. For hot-rolling type of crude oil tank according to item 4 of the patent application重量质量质量和B, In addition to the composition of the above components, further containing from Nb: 0. 001~0. 1% by mass, v. 〇. 002~〇. 1% by mass, Ti: 001~0. 1% by mass and B One or two or more selected from the group consisting of 0% by mass or less. 9. The hot-rolled steel sheet for a crude oil tank according to any one of the above-mentioned claims, wherein, in addition to the above-mentioned component composition, further contains ca: 0002. 0002~0. 〇〇5 mass% and rem : 〇. 0005~〇. One or two selected from 15% by mass.热 ίο. The hot-rolled steel for crude oil tanks according to any one of the above-mentioned claims, which has a strength of a relief stress of 31.5 MPa or more and a tensile strength of 440 MPa or more. • 11. For hot-rolled steels for crude oil tanks according to item 9 of the patent application, the system has a strength of 315 MPa or more and a tensile strength of 44 MPa or more. 12. A method for producing a hot-rolled steel for use in a crude oil tank, which is obtained by heating a steel material having a composition of any one of the patents No. 1 i 9 to 1000 to 1350 ° C, and then hot rolling Method for forming steel; 97136408 45 200925294 wherein, in the above-mentioned hot rolling, the cumulative rolling reduction rate below the transformation point of Ar3 is set to 10 to 80%, and the finishing rolling temperature is determined as (Ar3 metamorphic point, 3 (TC)~ (Ar3 metamorphosis) The condition of -180 ° C is applied, followed by cooling. - 13. The method and method for producing hot-rolled steel for crude oil tank according to claim 12, wherein the hot rolling is carried out during rolling The temperature difference caused by the location of the section steel is determined to be 5 以 by the surface temperature difference. After 〇, the cumulative rolling reduction rate below the Ar3 metamorphic point is determined as the hall, and the finishing rolling temperature is determined as the β (four) metamorphic point -3rCMAr3 metamorphic point. The above hot slap. 97136408 46