[發明所欲解決之課題] [0008] 此外，就船舶用的鋼材而言，已知有開發作為貨油艙用或壓載艙用之鋼材。然而，煤船及煤・礦石兼用船的船艙的使用環境係如上述，在因腐蝕環境（溫度・濕度・腐蝕性物質等）及內容物而有無引起機械損傷等方面係與貨油艙或壓載艙的使用環境完全不同。因此，煤船及煤・礦石兼用船船艙用的鋼材需要獨特的材料設計或特性評定。 [0009] 就此，專利文獻1所示之鋼材係以改善船舶外板或壓載艙、貨油艙、礦石船貨艙等在共同的使用環境下的耐蝕性為目標，就鋼材的耐蝕性之評定，係考量貨油艙及壓載艙的使用環境。惟，專利文獻1中並未顯示考量到煤船及煤・礦石兼用船的船艙使用環境，亦即乾濕反覆循環且因煤的硫成分所引起之低pH環境的腐蝕試驗結果。 [0010] 又，專利文獻2及3中，亦評定模擬礦石搬運船的船艙的使用環境之鋼材在腐蝕環境下的耐蝕性，惟其仍未顯示考量到煤船及煤・礦石兼用船的船艙使用環境的腐蝕試驗結果。 [0011] 再者，船艙通常焊接底板與漏斗給料板、上甲板背板與縱樑等而構成，於其焊接連接部，會沿板厚方向承受拉伸應力。而且，於此種焊接連接部，近來已闡明有發生層狀撕裂的危險性。於此，所稱層狀撕裂，係指在十字形連接部、T形連接部、方形連接部等沿板厚方向承受拉伸應力的焊接連接部，因拉伸應力而沿與鋼板表面平行的方向，於鋼材內部加深龜裂而產生破裂的現象。 因此，煤船及煤・礦石兼用船的船艙用鋼材，除上述煤船及煤・礦石兼用船的船艙在使用環境下的耐蝕性外，亦要求耐層狀撕裂性優良。 [0012] 然而，專利文獻1～3均完全未考量到在焊接連接部發生層狀撕裂的風險，且未考量到任何關於耐層狀撕裂性者。 [0013] 本發明係有鑑於上述現況而開發者，茲以提供一種煤船及煤・礦石兼用船的船艙在使用環境下的耐蝕性優異，且耐層狀撕裂性亦優良的煤船及煤・礦石兼用船船艙用鋼材為目的。 又，本發明係以提供一種使用上述之煤船及煤・礦石兼用船船艙用鋼材而成的船舶為目的。 [解決課題之手段] [0014] 從而，本案發明人等為解決上述課題而致力反覆研究，獲得以下見解： （1）要提升煤船及煤・礦石兼用船的船艙在使用環境，亦即乾濕反覆循環且因煤的硫成分所引起之低pH環境下的耐蝕性，與Sn共同複合添加選自Cu、Ni、Sb、W、Mo及Nb當中的1種或2種以上係屬有效。 （2）另一方面，基於耐層狀撕裂性觀點，減少鋼中的S量並同時減少Sn係屬有效。 [0015] 如此，基於提升煤船及煤・礦石兼用船的船艙在使用環境下的耐蝕性的觀點，添加Sn係屬有效，但基於耐層狀撕裂性的觀點，減少Sn則屬有效。因此，本案發明人等以上述見解為基礎，為了兼具耐蝕性與耐層狀撕裂性而進一步反覆研究。 [0016] 其結果，獲得以下見解： （3）只要抑制Sn的中心偏析，使Sn朝鋼材全體極力擴散，即使含有既定量的Sn也能獲得優良的耐層狀撕裂性；亦即，只要適當地調整Sn量，同時抑制Sn的中心偏析，使Sn朝鋼材全體擴散，則可兼具煤船及煤・礦石兼用船的船艙在使用環境下的耐蝕性與耐層狀撕裂性。 又，獲得以下見解： （4）依據S量嚴謹地控制Sn量，可進一步提升耐層狀撕裂性。 本發明係基於上述見解，進一步反覆研究而完成者。 [0017] 亦即，本發明之要旨構成如下。 1.一種煤船及煤・礦石兼用船船艙用鋼材，其係具有：含有以質量%計為 C：0.03～0.18%、 Si：0.01～1.50%、 Mn：0.10～2.00%、 P：0.030%以下、 S：0.0070%以下、 Al：0.005～0.100%、 Sn：0.01～0.20%及 N：0.0080%以下 ，同時含有選自 Cu：0.01～0.50%、 Ni：0.01～0.50%、 Sb：0.01～0.30%、 W：0.01～0.50%、 Mo：0.01～0.50%及 Nb：0.0010～0.10% 當中的1種或2種以上，且其餘由Fe及無可避免之雜質所構成的成分組成，而且 Sn偏析度未達18； 於此，Sn偏析度係依下式(1)定義： [Sn偏析度]=[中心偏析部的Sn濃度]/[平均Sn濃度]--- (1)。 [0018] 2.如前述1之煤船及煤・礦石兼用船船艙用鋼材，其中前述成分組成中的S含量與Sn含量係滿足下式(2)之關係： 10000×[%S]×[%Sn]2
≦ 1.40 --- (2) 於此，[%S]及[%Sn]分別為成分組成中S及Sn的含量（質量%）。 [0019] 3.如前述1或2之煤船及煤・礦石兼用船船艙用鋼材，其中前述成分組成進一步含有選自以質量%計為 Cr：0.01～0.50%及 Co：0.01～0.50% 當中的1種或2種。 [0020] 4.如前述1～3中任一項之煤船及煤・礦石兼用船船艙用鋼材，其中前述成分組成進一步含有選自以質量%計為 Ti：0.001～0.100%、 Zr：0.001～0.100%及 V：0.001～0.100% 當中的1種或2種以上。 [0021] 5.如前述1～4中任一項之煤船及煤・礦石兼用船船艙用鋼材，其中前述成分組成進一步含有選自以質量%計為 Ca：0.0001～0.0100%、 Mg：0.0001～0.0200%及 REM：0.0002～0.2000% 當中的1種或2種以上。 [0022] 6.如前述1～5中任一項之煤船及煤・礦石兼用船船艙用鋼材，其中前述成分組成進一步含有以質量%計為 B：0.0001～0.0300%者。 [0023] 7.一種船舶，其係使用如前述1～6中任一項之煤船及煤・礦石兼用船船艙用鋼材而成。 [發明之效果] [0024] 根據本發明，可獲得一種煤船及煤・礦石兼用船的船艙在使用環境下的耐蝕性優異，且耐層狀撕裂性亦優良的煤船及煤・礦石兼用船船艙用鋼材。 而且，藉由將本發明之煤船及煤・礦石兼用船船艙用鋼材應用於船舶的船艙，可確保高安全性，同時可降低船艙的檢查或塗裝所需的費用。[Problems to be Solved by the Invention] [0008] In addition, steel materials for ships are known to be developed as steel materials for cargo tanks or ballast tanks. However, the use environment of the cabins of coal ships and coal and ore dual-use ships is as described above, and it is related to the cargo tanks or pressure tanks due to the mechanical damage caused by the corrosive environment (temperature, humidity, corrosive substances, etc.) and the contents. Cargo tanks are used in completely different environments. Therefore, the steel used in the cabins of coal ships and coal / ore ships requires unique material design or property evaluation. [0009] In this regard, the steel materials shown in Patent Document 1 are aimed at improving the corrosion resistance of ship outer plates or ballast tanks, cargo oil tanks, ore ship cargo tanks, etc. under a common use environment, and the corrosion resistance of steel is evaluated. , Considering the use of cargo oil tanks and ballast tanks. However, Patent Document 1 does not show the results of a corrosion test in a low pH environment that takes into account the environment in which a coal ship and a coal / ore combined ship are used, that is, the wet and dry cycles, and the sulfur content of the coal. [0010] In addition, in Patent Documents 2 and 3, the corrosion resistance of steel used to simulate the use environment of the cabin of an ore carrier is also evaluated in a corrosive environment, but it has not been shown that the use of the cabin of a coal ship and a coal / ore combined ship Environmental corrosion test results. [0011] Furthermore, the cabin is usually constructed by welding a bottom plate and a hopper feed plate, an upper deck back plate, a side member, and the like, and a welded connection portion thereof receives tensile stress in the thickness direction of the plate. In addition, recently, it has been clarified that there is a risk that lamellar tearing may occur in such a welded joint. Here, the so-called lamellar tear refers to a welded connection that undergoes tensile stress in the thickness direction of the plate, such as a cross-shaped connection, a T-shaped connection, a square connection, etc., and is parallel to the surface of the steel plate due to the tensile stress. Direction, deepening cracks inside the steel and cracking. Therefore, in addition to the corrosion resistance of the cabins of coal ships and coal and ore ships, the lamellar tear resistance is required in addition to the corrosion resistance of the cabins of the coal ships and coal and ore ships in the use environment. [0012] However, all of Patent Documents 1 to 3 do not consider the risk of lamellar tearing at the welded connection at all, and do not take into account anything about the lamellar tear resistance. [0013] The present invention has been developed in view of the above-mentioned circumstances, and therefore provides a coal ship and a coal and ore dual-purpose ship cabin with excellent corrosion resistance under the use environment and a coal ship with excellent laminar tear resistance. The purpose is to use steel for cabins of coal and ore vessels. Moreover, this invention aims at providing the ship which used the steel material for the cabin of the coal ship and the coal and ore ship. [Means for Solving the Problem] [0014] Therefore, the inventors of this case have made repeated researches to solve the above-mentioned problems and obtained the following insights: (1) To improve the operating environment of the cabins of coal ships and coal and ore dual-use ships, that is, dry Corrosion resistance under low pH environment caused by wet repeated cycles and due to sulfur content of coal is effective in combination with Sn by adding one or two or more kinds selected from Cu, Ni, Sb, W, Mo and Nb. (2) On the other hand, from the viewpoint of laminar tear resistance, it is effective to reduce the amount of S in steel and reduce Sn at the same time. [0015] In this way, from the viewpoint of improving the corrosion resistance of the cabin of the coal ship and the coal / ore combined ship in the use environment, the addition of Sn is effective, but from the viewpoint of laminar tear resistance, reducing Sn is effective. Therefore, based on the above-mentioned findings, the inventors of the present case have conducted further studies in order to have both corrosion resistance and lamellar tear resistance. [0016] As a result, the following insights were obtained: (3) As long as the central segregation of Sn is suppressed and Sn is diffused as much as possible to the entire steel, even if it contains a predetermined amount of Sn, excellent lamellar tear resistance can be obtained; that is, as long as Properly adjusting the amount of Sn while suppressing the central segregation of Sn, so that Sn diffuses to the entire steel, can have both the corrosion resistance and lamellar tear resistance of the cabins of coal ships and coal and ore combined ships in the use environment. In addition, the following insights were obtained: (4) Strictly controlling the amount of Sn based on the amount of S can further improve the resistance to lamellar tearing. The present invention was completed based on the above findings and further research. [0017] That is, the gist of the present invention is structured as follows. 1. A steel material for cabins of coal ships and coal / ore ships, comprising: C: 0.03 to 0.18% by mass; Si: 0.01 to 1.50%; Mn: 0.10 to 2.00%; P: 0.030% Below, S: 0.0070% or less, Al: 0.005 to 0.100%, Sn: 0.01 to 0.20%, and N: 0.0080% or less, and selected from Cu: 0.01 to 0.50%, Ni: 0.01 to 0.50%, and Sb: 0.01 to 0.30%, W: 0.01 to 0.50%, Mo: 0.01 to 0.50%, and Nb: 0.0010 to 0.10%, one or more of them, and the rest are composed of Fe and unavoidable impurities, and Sn The degree of segregation is less than 18; Here, the degree of Sn segregation is defined by the following formula (1): [Sn segregation degree] = [Sn concentration in the central segregation part] / [average Sn concentration] --- (1). [0018] 2. The steel for cabins of coal ships and coal and ore ships as described in 1 above, wherein the S content and the Sn content in the aforementioned component composition satisfy the relationship of the following formula (2): 10000 × [% S] × [ % Sn] 2 ≦ 1.40 --- (2) Here, [% S] and [% Sn] are the contents (mass%) of S and Sn in the component composition, respectively. [0019] 3. The steel materials for cabins of coal ships and coal and ore dual-use ships as described in 1 or 2 above, wherein the aforementioned component composition further contains a material selected from the group consisting of Cr: 0.01 to 0.50% and Co: 0.01 to 0.50% by mass%. 1 or 2 species. [0020] 4. The steel material for the cabin of a coal ship and a coal / ore ship as described in any one of the above 1 to 3, wherein the aforementioned component composition further contains a material selected from the group consisting of Ti: 0.001 to 0.100% and Zr: 0.001 in terms of mass%. ~ 0.100% and V: One or more of 0.001 ~ 0.100%. [0021] 5. The steel material for the cabin of a coal ship and a coal and ore combined ship according to any one of 1 to 4 above, wherein the aforementioned composition further contains a material selected from the group consisting of Ca: 0.0001 to 0.0100% by mass, and Mg: 0.0001. ~ 0.0200% and REM: One or more of 0.0002 to 0.2000%. [0022] 6. The steel materials for cabins of coal ships and coal / ore ships as described in any one of 1 to 5 above, wherein the aforementioned component composition further contains B: 0.0001 to 0.0300% by mass%. [0023] 7. A ship formed by using a steel material for a cabin of a coal ship and a coal / ore dual-purpose ship according to any one of 1 to 6 above. [Effects of the Invention] [0024] According to the present invention, a coal ship and a coal and ore combined ship can obtain a coal ship and a coal and ore that are excellent in corrosion resistance under the use environment and have excellent laminar tear resistance. Steel for cabins of dual-purpose vessels. Furthermore, by applying the steel materials for the cabin of the coal ship and the coal and ore dual-purpose ship according to the present invention to the cabin of the ship, it is possible to ensure high safety, and at the same time, it is possible to reduce costs required for inspection or painting of the cabin.
[實施發明之形態] [0025] 以下，具體地說明本發明。首先，針對在本發明中將鋼的成分組成限定於前述範圍的理由加以說明。此外，鋼的成分組成中元素的含量的單位皆為「質量%」，以下，除非特別合先敘明，否則僅以「%」表示。 [0026] C：0.03～0.18% C為用來提高鋼的強度之元素。為確保所要的強度（490～620MPa），C量係取0.03%以上。惟，C量若超過0.18%，則焊接性及焊接熱影響部的韌性會劣化。從而，C量係取0.03～0.18%的範圍。較佳為0.05%以上、0.16%以下。 [0027] Si：0.01～1.50% Si為添加作為脫氧劑之元素。又，Si亦為對提高鋼的強度屬有效的元素，為確保所要之強度，Si量係取0.01%以上。惟，Si量若超過1.50%，則會使鋼的韌性劣化。從而，Si量係取0.01～1.50%的範圍。較佳為0.03%以上、1.00%以下。更佳為0.04%以上、0.50%以下。 [0028] Mn：0.10～2.00% Mn為用來提高鋼的強度之元素。為確保上述之所要的強度，Mn量係取0.10%以上。惟，Mn量若超過2.00%，則鋼的韌性及焊接性會劣化。又，因Mn的中心偏析，使耐層狀撕裂性亦劣化。從而，Mn量係取0.10～2.00%的範圍。較佳為0.60%以上、1.80%以下。更佳為0.80%以上、1.60%以下。 [0029] P：0.030%以下 P會使韌性及焊接性劣化。因此，P量係取0.030%以下。較佳為0.025%以下。更佳為0.015%以下。此外，就其下限不特別限定，較佳取0.003%。 [0030] S：0.0070%以下 S為參與耐層狀撕裂性的重要元素。亦即，S為會形成大體積的MnS，其為非金屬夾雜物，此MnS會成為層狀撕裂的起點。尤其是，S量超過0.0070%的話，會導致耐層狀撕裂性大幅劣化。從而，S量係取0.0070%以下。較佳為0.0060%以下。更佳為0.0050%以下。此外，就其下限不特別限定，較佳取0.0003%。 [0031] Al：0.005～0.100% Al為添加作為脫氧劑之元素，Al量係取0.005%以上。惟，Al量若超過0.100%，則鋼的韌性會劣化。因此，Al量係取0.005～0.100%的範圍。 [0032] Sn：0.01～0.20% Sn係為了提升煤船及煤・礦石兼用船的船艙在使用環境下的耐蝕性所需的元素，同時為參與耐層狀撕裂性的重要元素。具體而言，Sn為可提升耐蝕性，但另一面會使耐層狀撕裂性劣化的元素。 亦即，Sn在煤船及煤・礦石兼用船的船艙之反覆發生乾濕且低pH的腐蝕環境下，於鋼材表面形成難溶性被膜。與此同時，Sn會摻入於鋼材表面的鐵鏽中，而抑制會促進腐蝕的SO4 2-
等陰離子物種之擴散。藉此，可提升耐蝕性。此等效果可藉由將Sn量取0.01%以上而顯現。較佳為0.02%以上。 另一方面，由於Sn易偏析於鋼材中心部，且於此種偏析部，硬度會顯著增大，以致耐層狀撕裂性劣化。尤其是Sn量超過0.20%的話，耐層狀撕裂性會大幅劣化。從而，基於確保耐層狀撕裂性的觀點，Sn量係取0.20%以下。較佳為0.15%以下。更佳為0.10%以下。 [0033] N：0.0080%以下 N為會使韌性劣化的有害元素，故以極力減少為佳。尤其是N量超過0.0080%的話，韌性會大幅劣化。從而，N量係取0.0080%以下。較佳為0.0070%。此外，就其下限不特別限定，較佳取0.0005%。 [0034] 選自Cu：0.01～0.50%、Ni：0.01～0.50%、Sb：0.01～0.30%、W：0.01～0.50%、Mo：0.01～0.50%及Nb：0.0010～0.10%當中的1種或2種以上 Cu、Ni、Sb、W、Mo及Nb為透過與Sn共同複合添加，而能夠提升煤船及煤・礦石兼用船的船艙在使用環境下的耐蝕性之元素。 諸如上述，Sn雖為可有效提升耐蝕性的元素，但基於耐層狀撕裂性觀點卻無法使其大量含有。因此，要兼具煤船及煤・礦石兼用船的船艙在使用環境下的耐蝕性與耐層狀撕裂性，則需使其含有選自Cu：0.01～0.50%、Ni：0.01～0.50%、Sb：0.01～0.30%、W：0.01～0.50%、Mo：0.01～0.50%及Nb：0.0010～0.10%當中的1種或2種以上。 於此，Cu、Ni、Sb及Nb各自會隨著腐蝕的進行，自鋼材表面以Cu2 ＋
、Ni2 ＋
、Sb5 ＋
及Nb4 ＋
游離，使腐蝕生成物緻密化，而抑制SO4 2 －
等腐蝕性陰離子向鋼界面（鐵鏽層與基底鐵之界面）的穿透。又，W及Mo會各自以WO4 2-
及MoO4 2-
游離，摻入至鐵鏽中，對鐵鏽賦予陽離子選擇穿透性，而電性抑制SO4 2-
等腐蝕性陰離子向鋼界面的穿透。 此等效果，在上述Sn之防蝕作用共存時更為顯著，Cu、Ni、Sb、W及Mo量分別為0.01%以上、Nb量為0.0010%以上則可顯現。惟，使任一種元素均大量含有時，則會使焊接性或韌性劣化，基於成本觀點亦屬不利。 從而，Cu量係取0.01～0.50%的範圍，Ni量係取0.01～0.50%的範圍，Sb量係取0.01～0.30%的範圍，W量係取0.01～0.50%的範圍，Mo量係取0.01～0.50%的範圍，Nb量係取0.0010～0.10%的範圍。 較佳的是，Cu量為0.02%以上、0.40%以下，Ni量為0.02%以上、0.40%以下，Sb量為0.02%以上、0.25%以下，W量為0.02%以上、0.40%以下，Mo量為0.02%以上、0.40%以下，Nb量為0.0020%以上、0.08%以下。 [0035] 又，諸如上述，Sn所引起之耐層狀撕裂性的劣化機構係有別於S所引起之耐層狀撕裂性的劣化機構。惟，S與Sn所引起之耐層狀撕裂性的劣化彼此會相乘性地作用。因此，基於進一步提升耐層狀撕裂性的觀點，就S及Sn的含量，宜使其滿足下式(2)之關係： 10000×[%S]×[%Sn]2
≦ 1.40 --- (2) 於此，[%S]及[%Sn]分別為成分組成中S及Sn的含量（質量%）。 [0036] 上述(2)式係意指Sn量對耐層狀撕裂性的影響遠大於S量對其之影響。亦即，其意指在確保耐層狀撕裂性上，特別重要的是嚴謹地控管Sn。 於此，10000×[%S]×[%Sn]2
更佳定為1.20以下。就10000×[%S]×[%Sn]2
的下限而言不特別限定，較佳定為0.001。 此外，欲抑制層狀撕裂時，理當應以將S量與Sn量均限定於上述範圍為前提。 [0037] 以上，已針對基本成分加以說明，惟在本發明之煤船及煤・礦石兼用船船艙用鋼材中，可適宜使其含有以下所述元素。 選自Cr：0.01～0.50%及Co：0.01～0.50%當中的1種或2種 Cr及Co會隨著腐蝕的進行而轉移至鐵鏽層中，藉由阻斷SO4 2 －
等腐蝕性陰離子向鐵鏽層的侵入，可抑制SO4 2 －
等腐蝕性陰離子在鐵鏽層與基底鐵之界面的濃縮，由此有助於耐蝕性的進一步提升。 此種效果在Cr量或Co量未達0.01%時無法充分地獲得。另一方面，Cr量或Co量若超過0.50%，則會使焊接部的韌性劣化。又，就Cr而言為發生水解反應的元素，而會使腐蝕部的pH降低。亦即，過量添加Cr，則有使整體的耐蝕性劣化之虞。 從而，使其含有Cr及Co時，其量均取0.01～0.50%的範圍。較佳為0.02%以上、0.30%以下。更佳為0.03%以上、0.20%以下。 [0038] 選自Ti：0.001～0.100%、Zr：0.001～0.100%及V：0.001～0.100%當中的1種或2種以上 Ti、Zr及V，基於確保所要之強度的觀點，可單獨或複合性地添加。惟，使任一種元素均過量地含有時，則會使韌性及焊接性劣化。因此，使其含有Ti、Zr及V時，其量均取0.001～0.100%的範圍。較佳為0.005%以上、0.050%以下。 [0039] 選自Ca：0.0001～0.0100%、Mg：0.0001～0.0200%及REM：0.0002～0.2000%當中的1種或2種以上 Ca、Mg及REM，基於提升焊接部的韌性的觀點，可單獨或複合性地添加。惟，使任一種元素均過量地含有時，反而會導致焊接部的韌性劣化。又，也會增加成本。從而，使其含有Ca、Mg及REM時，Ca量係取0.0001～0.0100%、Mg量係取0.0001～0.0200%、REM量係取0.0002～0.2000%的範圍。 [0040] B：0.0001～0.0300% B為使鋼材的淬透性提升的元素。又，基於確保所要之強度的觀點，可使其含有B。由此種觀點而言，將B量取0.0001%以上係屬有效。惟，使B過量含有，尤其是B量超過0.0300%的話，則會導致韌性大幅劣化。從而，使其含有B時，其量係取0.0001～0.0300%的範圍。 [0041] 上述以外的成分為Fe及無可避免之雜質。 [0042] 以上，已針對本發明之煤船及煤・礦石兼用船船艙用鋼材的成分組成加以說明，惟就本發明之煤船及煤・礦石兼用船船艙用鋼材，如下控制Sn偏析度係極為重要。 Sn偏析度：未達18 由於Sn的中心偏析，偏析部的硬度會大幅增加。而且，此種偏析部會成為層狀撕裂發生的起點。亦即，要確保含有Sn的成分組成中優良的耐層狀撕裂特性，重要的是抑制Sn的中心偏析而抑制偏析部的硬度增加。由此種觀點而言，Sn偏析度係定為未達18。較佳為未達16。更佳為15以下。就其下限不特別限定，較佳定為2。 [0043] 此外，此處所稱Sn偏析度，係指在與鋼材的軋製方向平行地切割出來的剖面（與鋼材表面垂直的剖面）上，藉由電子束微分析器（以下表示為EPMA）的線分析所得之中心偏析部的Sn濃度對平均Sn濃度的比。 具體而言，設鋼材的厚度為t（mm）、寬度（與鋼材的軋製方向及厚度方向垂直的方向）為W（mm）時，首先，在與鋼材的軋製方向平行地切割出來的剖面（與鋼材表面垂直的剖面）之鋼材的厚度方向：(0.5±0.1)×t、軋製方向：15mm的面區域（即包含鋼材的厚度方向之中心位置的面區域），以束徑：20μm、間距：20μm的條件實施Sn的EPMA面分析。此外，Sn的EPMA面分析係於1/4×W、1/2×W及3/4×W之位置此3個剖面視野實施。 接著，由上述EPMA面分析選出在各剖面視野中Sn濃度最高的位置，在該位置分別沿鋼材的厚度方向以束徑：5μm、間距：5μm的條件實施Sn的EPMA線分析。此外，在實施EPMA線分析之際，係由鋼材的表背面分別排除25μm前的區域。 然後，按每條測定線求出Sn濃度（質量濃度）的最大值，以此等的平均值作為中心偏析部的Sn濃度（質量濃度），並以此中心偏析部的Sn濃度除以測定線之全部測定值的算術平均值，即平均Sn濃度（質量濃度）所得的值作為Sn偏析度。 亦即， [Sn偏析度]＝[中心偏析部的Sn濃度]/[平均Sn濃度]。 [0044] 諸如上述，本發明之煤船及煤・礦石兼用船船艙用鋼材，基於確保優良的耐層狀撕裂特性的觀點，極為重要的是抑制Sn的中心偏析，也就是將表示Sn的中心偏析之程度的Sn偏析度控制成既定值以下。於此，即使成分組成相同，Sn偏析度仍會隨製造條件大幅變化。因此，要抑制Sn的中心偏析，極為重要的是適切地控制鋼材的製造方法。 以下，就本發明之煤船及煤・礦石兼用船船艙用鋼材的較佳製造方法加以說明。 [0045] 亦即，本發明之鋼材可藉由將調整成上述之成分組成的鋼，使用轉爐或電爐、真空除氣等周知之精煉程序進行熔製，並以連續鑄造法或者造塊-分塊壓延法作成鋼素材（鋼胚, slab），接著將此鋼素材視需求再加熱後進行熱軋，作成鋼板或型鋼等來製造。此外，鋼材的厚度不特別限定，較佳為2～100mm。更佳為3～80mm。再更佳為4～60mm。 於此，採連續鑄造時，鑄造速度（拉取速度）較佳取0.3～2.8m/min。鑄造速度未達0.3m/min，作業效率會變差。另一方面，鑄造速度若超過2.8m/min，則會發生表面溫度不均，而且無法充分地向扁胚內部供給熔鋼，而促進Sn的中心偏析。基於抑制Sn的中心偏析的觀點，更佳為0.4m/min以上、2.6m/min以下。再更佳為1.5m/min以下。 此外，較佳進行輕輥軋法，其係將具有未凝固層的凝固末期之扁胚，一邊以相當於凝固收縮量與熱收縮量的和之程度的輥軋總量及輥軋速度，藉由輾壓輥群緩緩地進行輥軋一邊進行鑄造。 [0046] 其次，將上述之鋼素材熱軋成所要尺寸形狀之際，較佳加熱至900℃～1350℃的溫度。加熱溫度未達900℃，變形阻力較大，不易進行熱軋。另一方面，加熱溫度若超過1350℃，則會產生表面痕、或使氧化皮損耗或燃料原單位增加。 又，尤其是加熱溫度愈高則愈可促進中心偏析部之Sn的擴散，因此由確保耐層狀撕裂性觀點而言係屬有利。由此種觀點而言，加熱溫度更佳取1030℃以上。 再者，上述加熱溫度下的保持時間較佳取60min以上。藉此，可充分促進中心偏析部之Sn的擴散。更佳為150min以上。此外，就其上限不特別限定，較佳取1000min。 [0047] 此外，當鋼素材的溫度原本即為1030～1350℃的範圍時，且經保持於此溫度範圍60min以上時，可無需加熱而直接供予熱軋。又，亦可對熱軋後所得的熱軋板實施再加熱處理、酸性、冷軋，而製成既定板厚的冷軋板。 於熱軋中，精軋結束溫度較佳取650℃以上。精軋結束溫度未達650℃，會因變形阻力增大而使軋製負載增加，而不易實施軋製。 [0048] 熱軋後的冷卻可採氣冷、加速冷卻任一種方法，而欲獲得更高的強度時，係以進行加速冷卻為佳。 於此，進行加速冷卻時，較佳將冷卻速度設為2～100℃/s、冷卻停止溫度設為700～400℃。亦即，冷卻速度未達2℃/s、及/或冷卻停止溫度超過700℃時，加速冷卻的效果較小，而無法達到充分的高強度化。另一方面，冷卻速度超過100℃/s、及/或冷卻停止溫度未達400℃時，鋼材的韌性會劣化、或鋼材的形狀會產生變形。惟，於後續步驟中實施熱處理時則不在此限。 [實施例] [0049] 將成分組成為表1所示者的鋼（其餘為Fe及無可避免之雜質）以真空熔解爐或轉爐進行熔製，藉由表2所示條件的連續鑄造作成鋼胚。將此等鋼胚再度加熱至1150℃後，以表2所示條件保持，再實施精軋結束溫度：930℃的熱軋，而得到板厚：30mm的鋼板。此外，熱軋後的冷卻係採用冷卻速度：10℃/s、冷卻停止溫度：550℃的水冷卻（加速冷卻）。 然後，根據上述方法，求取所得鋼板中的Sn偏析度。將結果併記於表2。 [0050] 再者，針對如上述方式所得的鋼板，依以下要領進行模擬煤船及煤・礦石兼用船的船艙之使用環境的腐蝕試驗，並進行煤船及煤・礦石兼用船的船艙在使用環境下的耐蝕性的評定。 （1）耐蝕性的評定 由如上述方式所得之No.1～60之鋼板分別採取5mmt×50mmW×75mmL的試片，對其表面進行噴砂，來去除表面的鏽皮或油分。以此面為試驗面，評定塗膜剝離後之鋼材的耐蝕性。以矽系密封劑塗敷背面與端面後，嵌入於丙烯酸製之治具，於其上鋪滿5g的煤，並藉由恆溫恆濕器賦予環境A（溫度：60℃，相對濕度：95%，20小時)⇔環境B（溫度：30℃，相對濕度：95%，3小時)、各過渡時間：0.5小時的溫度濕度循環84天。於此，記號「 ⇔ 」係以重複之意義使用。此外，煤係使用秤量5g，在常溫下浸漬於100ml的蒸餾水2小時後，進行過濾並稀釋成200ml之煤滲出液的pH經調成3.0者。於此，係藉由在上述之條件下進行試驗，來模擬煤船及煤・礦石兼用船的船艙內底板的腐蝕環境。 試驗後，使用鐵鏽剝離液剝離各試片的鐵鏽並測定各試片在腐蝕試驗前後的質量減少量，以其為腐蝕量。又，使用深度計，測定各試片的最大孔蝕深度。然後，以未添加Sn或Cu、Ni、Sb、W、Mo及Nb的No.53為基底鋼，根據相對於此基底鋼的質量減少量及最大孔蝕深度的比率，按以下基準評定耐蝕性。 ○（合格）：相對於基底鋼的質量減少量及最大孔蝕深度的比率皆未達70% △（不合格）：相對於基底鋼的質量減少量及最大孔蝕深度的比率當中，任一者為70%以上且未達80%，而且另一者未達80% ×（不合格）：相對於基底鋼的質量減少量及最大孔蝕深度的比率當中，至少一者為80%以上 [0051] 進而，依以下要領，進行耐層狀撕裂性的評定。 （2）耐層狀撕裂性的評定 依據ClassNK 鋼船規則・同檢查要領（K篇第2章），對如上述方式所得之No.1～60之鋼板實施鋼板之板厚方向（Z方向）的拉伸試驗，並算出縮面率（RA, Reduction of Area）。然後，基於算出之縮面率（RA），按以下基準評定耐層狀撕裂性。 ◎（合格，特優）：70以上 ○（合格）：35以上且未達70 △（不合格）：25以上且未達35 ×（不合格）：未達25 [0052] 將（1）及（2）之評定結果併記於表2。此外，表2中的綜合評定係將上述（1）及（2）之評定全為「○」或「◎」時評為「合格」，將（1）及（2）之評定中任1個有「△」或「×」時評為「不合格」。 [0053] [0054][0055] 如表2所示，發明例皆兼備優良的耐蝕性與耐層狀撕裂性。 相對於此，就比較例，就耐蝕性及耐層狀撕裂性之至少一者，未能獲得充分之特性。 [0056] 亦即，比較例No.50及52由於S量超過上限，且未含有既定量的Cu、Ni、Sb、W、Mo及Nb，就耐蝕性及耐層狀撕裂性，未能獲得充分之特性。 比較例No.51、55及58由於Sn量超過上限，就耐層狀撕裂性，未能獲得充分之特性。 比較例No.54由於S量及Sn量超過上限，就耐層狀撕裂性，未能獲得充分之特性。 比較例No.56及60由於S量超過上限，就耐層狀撕裂性，未能獲得充分之特性。 比較例No.57由於未含有既定量的Cu、Ni、Sb、W、Mo及Nb，就耐蝕性，未能獲得充分之特性。 比較例No.59由於S量超過上限，且Sn量低於下限，就耐蝕性及耐層狀撕裂性，未能獲得充分之特性。 比較例No.61～64由於Sn偏析度超過上限，就耐層狀撕裂性，未能獲得充分之特性。[Mode for Carrying Out the Invention] [0025] Hereinafter, the present invention will be specifically described. First, the reason why the component composition of steel is limited to the aforementioned range in the present invention will be described. In addition, the unit of the content of the elements in the composition of the steel is "mass%". Hereinafter, unless otherwise specified, it is only expressed in "%". [0026] C: 0.03 to 0.18% C is an element for improving the strength of steel. In order to ensure the required strength (490 to 620 MPa), the amount of C is taken as 0.03% or more. However, if the amount of C exceeds 0.18%, the weldability and the toughness of the heat-affected zone are deteriorated. Therefore, the amount of C is in the range of 0.03 to 0.18%. It is preferably at least 0.05% and at most 0.16%. [0027] Si: 0.01 to 1.50% Si is an element added as a deoxidizer. In addition, Si is also an element effective for increasing the strength of steel. To ensure the required strength, the amount of Si is set to 0.01% or more. However, if the amount of Si exceeds 1.50%, the toughness of the steel is deteriorated. Therefore, the amount of Si is in the range of 0.01 to 1.50%. It is preferably 0.03% or more and 1.00% or less. More preferably, it is 0.04% or more and 0.50% or less. [0028] Mn: 0.10 to 2.00% Mn is an element for improving the strength of steel. To ensure the above-mentioned desired strength, the amount of Mn is taken to be 0.10% or more. However, when the Mn content exceeds 2.00%, the toughness and weldability of the steel are deteriorated. In addition, due to the segregation of the center of Mn, laminar tear resistance is also deteriorated. Therefore, the Mn content is in the range of 0.10 to 2.00%. It is preferably 0.60% or more and 1.80% or less. More preferably, it is 0.80% or more and 1.60% or less. [0029] P: 0.030% or less P deteriorates toughness and weldability. Therefore, the amount of P is taken as 0.030% or less. It is preferably 0.025% or less. It is more preferably 0.015% or less. In addition, the lower limit is not particularly limited, but 0.003% is preferable. [0030] S: 0.0070% or less S is an important element involved in lamellar tear resistance. That is, S is a MnS that will form a large volume, which is a non-metallic inclusion, and this MnS will become the starting point of lamellar tearing. In particular, when the amount of S exceeds 0.0070%, the lamellar tear resistance is significantly deteriorated. Therefore, the amount of S is taken as 0.0070% or less. It is preferably 0.0060% or less. It is more preferably 0.0050% or less. In addition, the lower limit is not particularly limited, but 0.0003% is preferable. [0031] Al: 0.005 to 0.100% Al is an element added as a deoxidizer, and the amount of Al is taken to be 0.005% or more. However, when the Al content exceeds 0.100%, the toughness of the steel is deteriorated. Therefore, the amount of Al is in the range of 0.005 to 0.100%. [0032] Sn: 0.01 to 0.20% Sn is an element required to improve the corrosion resistance of the cabin of a coal ship and a coal / ore dual-purpose ship under the use environment, and it is also an important element that participates in resistance to lamellar tearing. Specifically, Sn is an element that improves corrosion resistance, but on the other side, degrades lamellar tear resistance. That is, Sn forms a poorly soluble coating on the surface of steel materials under the corrosive environment of dry and wet and low pH repeatedly in the cabins of coal ships and coal and ore combined ships. At the same time, Sn will be incorporated into the rust on the surface of the steel, and inhibit the diffusion of anion species such as SO 4 2- which will promote corrosion. This improves corrosion resistance. These effects can be exhibited by taking the amount of Sn to 0.01% or more. It is preferably at least 0.02%. On the other hand, since Sn tends to segregate in the center portion of the steel, and in such a segregated portion, the hardness is remarkably increased, so that the lamellar tear resistance is deteriorated. In particular, when the amount of Sn exceeds 0.20%, the lamellar tear resistance is significantly deteriorated. Therefore, from the viewpoint of ensuring laminar tear resistance, the amount of Sn is 0.20% or less. It is preferably 0.15% or less. It is more preferably 0.10% or less. [0033] N: 0.0080% or less Since N is a harmful element that deteriorates toughness, it is preferably reduced as much as possible. In particular, when the amount of N exceeds 0.0080%, toughness is significantly deteriorated. Therefore, the amount of N is taken to be 0.0080% or less. It is preferably 0.0070%. In addition, the lower limit is not particularly limited, but it is preferably 0.0005%. [0034] One selected from Cu: 0.01 to 0.50%, Ni: 0.01 to 0.50%, Sb: 0.01 to 0.30%, W: 0.01 to 0.50%, Mo: 0.01 to 0.50%, and Nb: 0.0010 to 0.10% Or two or more kinds of Cu, Ni, Sb, W, Mo, and Nb are elements that can be added in combination with Sn to improve the corrosion resistance of the cabin of coal ships and coal / ore ships in the environment of use. As described above, although Sn is an element that can effectively improve the corrosion resistance, it cannot be contained in large amounts from the viewpoint of laminar tear resistance. Therefore, in order to have the corrosion resistance and lamellar tear resistance of the cabin of a coal ship and a combined coal and ore ship in the use environment, it is necessary to make it selected from the group consisting of Cu: 0.01 to 0.50%, Ni: 0.01 to 0.50% , One or more of Sb: 0.01 to 0.30%, W: 0.01 to 0.50%, Mo: 0.01 to 0.50%, and Nb: 0.0010 to 0.10%. Here, Cu, Ni, Sb, and Nb each progress with the corrosion, and Cu 2 + , Ni 2 + , Sb 5 +, and Nb 4 + are released from the surface of the steel to densify the corrosion products and suppress SO 4 2 - Penetration of isocorrosive anions into the steel interface (the interface between the rust layer and the base iron). In addition, W and Mo are freely incorporated into rust as WO 4 2- and MoO 4 2- , respectively, and impart cation selective penetration to the rust, and electrically suppress the corrosion of anions such as SO 4 2- to the steel interface. penetrate. These effects are more significant when the above-mentioned anticorrosive effects of Sn coexist, and the amounts of Cu, Ni, Sb, W, and Mo are respectively 0.01% or more and the amount of Nb is 0.0010% or more. However, if any of these elements is contained in a large amount, weldability and toughness are deteriorated, which is disadvantageous from the viewpoint of cost. Therefore, the amount of Cu is in the range of 0.01 to 0.50%, the amount of Ni is in the range of 0.01 to 0.50%, the amount of Sb is in the range of 0.01 to 0.30%, the amount of W is in the range of 0.01 to 0.50%, and the amount of Mo is in the range of 0.01 to 0.50%. In the range of 0.01 to 0.50%, the amount of Nb is in the range of 0.0010 to 0.10%. Preferably, the Cu content is 0.02% or more and 0.40% or less, the Ni content is 0.02% or more and 0.40% or less, the Sb content is 0.02% or more and 0.25% or less, the W content is 0.02% or more and 0.40% or less, Mo The amount is 0.02% or more and 0.40% or less, and the Nb amount is 0.0020% or more and 0.08% or less. [0035] In addition, as described above, the lamellar tear resistance deterioration mechanism caused by Sn is different from the lamellar tear resistance deterioration mechanism caused by S. However, the lamellar tear resistance deterioration caused by S and Sn acts synergistically with each other. Therefore, from the viewpoint of further improving the laminar tear resistance, it is appropriate to satisfy the relationship of the following formula (2) with respect to the contents of S and Sn: 10000 × [% S] × [% Sn] 2 ≦ 1.40 --- (2) Here, [% S] and [% Sn] are the contents (mass%) of S and Sn in the component composition, respectively. [0036] The above formula (2) means that the effect of the amount of Sn on laminar tear resistance is much greater than the effect of the amount of S on it. That is, it means that it is particularly important to strictly control Sn in ensuring laminar tear resistance. Here, 10000 × [% S] × [% Sn] 2 is more preferably 1.20 or less. The lower limit of 10000 × [% S] × [% Sn] 2 is not particularly limited, but is preferably 0.001. In addition, when suppressing lamellar tearing, it should be assumed that both the S amount and the Sn amount are limited to the above range. [0037] The basic components have been described above. However, the steel materials for the cabins of the coal ship and the coal / ore ship of the present invention may suitably contain the following elements. One or two types of Cr and Co selected from Cr: 0.01 to 0.50% and Co: 0.01 to 0.50% will be transferred to the rust layer as the corrosion progresses, and by blocking SO 4 2 - and other corrosive anions The intrusion into the rust layer can suppress the concentration of corrosive anions such as SO 4 2 − at the interface between the rust layer and the base iron, thereby contributing to further improvement of corrosion resistance. Such an effect cannot be sufficiently obtained when the amount of Cr or Co is less than 0.01%. On the other hand, when the amount of Cr or Co exceeds 0.50%, the toughness of the welded portion is deteriorated. In addition, Cr is an element that undergoes a hydrolysis reaction, and lowers the pH of the corroded portion. That is, if Cr is excessively added, the overall corrosion resistance may be deteriorated. Therefore, when it is made to contain Cr and Co, the amounts are each in the range of 0.01 to 0.50%. It is preferably at least 0.02% and at most 0.30%. More preferably, it is 0.03% or more and 0.20% or less. [0038] One or two or more Ti, Zr, and V selected from Ti: 0.001 to 0.100%, Zr: 0.001 to 0.100%, and V: 0.001 to 0.100%. From the viewpoint of ensuring a desired strength, they may be used alone or in combination. Added in combination. However, when any of these elements is contained excessively, toughness and weldability are deteriorated. Therefore, when Ti, Zr, and V are contained, the amounts are all in the range of 0.001 to 0.100%. It is preferably 0.005% or more and 0.050% or less. [0039] One or two or more Ca, Mg, and REM selected from Ca: 0.0001 to 0.0100%, Mg: 0.0001 to 0.0200%, and REM: 0.0002 to 0.2000%. From the viewpoint of improving the toughness of the welded part, they can be separated. Or added in combination. However, if any of these elements is contained in an excessive amount, the toughness of the welded portion is deteriorated instead. It also increases costs. Therefore, when Ca, Mg, and REM are contained, the amount of Ca is 0.0001 to 0.0100%, the amount of Mg is 0.0001 to 0.0200%, and the amount of REM is 0.0002 to 0.2000%. [0040] B: 0.0001 to 0.0300% B is an element that improves the hardenability of the steel. From the viewpoint of ensuring the required strength, B may be contained. From this viewpoint, it is effective to set the amount of B to 0.0001% or more. However, if B is contained excessively, especially when the amount of B exceeds 0.0300%, toughness will be significantly deteriorated. Therefore, when B is contained, the amount is in the range of 0.0001 to 0.0300%. [0041] Components other than the above are Fe and unavoidable impurities. [0042] In the above, the composition of the steel materials for the cabins of the coal ship and the combined coal and ore vessel of the present invention has been described. However, regarding the steel materials for the cabins of the coal ship and the combined coal and ore vessel of the present invention, the Sn segregation degree is controlled as follows. Extremely important. Sn segregation degree: less than 18 Due to the central segregation of Sn, the hardness of the segregation portion is greatly increased. In addition, such a segregation portion becomes a starting point for the occurrence of lamellar tearing. That is, in order to ensure excellent lamellar tear resistance in a composition containing Sn, it is important to suppress the center segregation of Sn and increase the hardness of the segregated portion. From this viewpoint, the degree of Sn segregation is determined to be less than 18. It is preferably less than 16. It is more preferably 15 or less. The lower limit is not particularly limited, but is preferably set to 2. [0043] In addition, the term “Sn segregation degree” herein refers to a cross-section (a cross-section perpendicular to the surface of the steel) cut parallel to the rolling direction of the steel, and an electron beam microanalyzer (hereinafter referred to as EPMA) The ratio of the Sn concentration in the central segregation to the average Sn concentration obtained from the line analysis. Specifically, when the thickness of the steel material is t (mm) and the width (the direction perpendicular to the rolling direction and thickness direction of the steel material) is W (mm), first, cut out parallel to the rolling direction of the steel material. The thickness direction of the steel section (section perpendicular to the steel surface): (0.5 ± 0.1) × t, rolling direction: 15mm surface area (that is, the surface area including the center position of the thickness direction of the steel), with the beam diameter: The EPMA surface analysis of Sn was performed under the conditions of 20 μm and a pitch of 20 μm. In addition, Sn's EPMA surface analysis was performed at three cross-sectional fields of view: 1/4 × W, 1/2 × W, and 3/4 × W. Next, the position of the highest Sn concentration in each of the cross-sectional views was selected from the EPMA surface analysis, and the EPMA line analysis of Sn was performed at the positions along the thickness direction of the steel material under the conditions of beam diameter: 5 μm and pitch: 5 μm. In addition, when the EPMA line analysis was performed, the areas before 25 μm were excluded from the front and back surfaces of the steel. Then, the maximum value of the Sn concentration (mass concentration) is obtained for each measurement line, and the average value is used as the Sn concentration (mass concentration) of the central segregation portion, and the Sn concentration of the central segregation portion is divided by the measurement line. The arithmetic mean of all measured values, that is, the value obtained by averaging the Sn concentration (mass concentration) is taken as the degree of Sn segregation. That is, [Sn segregation degree] = [Sn concentration in the central segregation part] / [average Sn concentration]. [0044] As described above, from the viewpoint of ensuring excellent laminar tear resistance, it is extremely important to suppress the central segregation of Sn, that is, the The degree of Sn segregation to a degree of central segregation is controlled to a predetermined value or less. Here, even if the composition of the components is the same, the degree of Sn segregation varies greatly depending on the manufacturing conditions. Therefore, in order to suppress the center segregation of Sn, it is extremely important to appropriately control the manufacturing method of the steel. Hereinafter, a preferred method for manufacturing a steel material for a cabin of a coal ship and a coal / ore vessel of the present invention will be described. [0045] That is, the steel of the present invention can be melted by a well-known refining procedure such as a converter or an electric furnace, vacuum degassing, and the steel adjusted to the above-mentioned composition, and the continuous casting method or agglomeration- The block rolling method is used to prepare a steel material (steel blank, slab), and then the steel material is reheated as required, and then hot rolled to produce a steel plate or a shaped steel. The thickness of the steel material is not particularly limited, but is preferably 2 to 100 mm. More preferably, it is 3 to 80 mm. Still more preferably, it is 4 to 60 mm. Here, in continuous casting, the casting speed (pulling speed) is preferably 0.3 to 2.8 m / min. If the casting speed is less than 0.3m / min, the work efficiency will be deteriorated. On the other hand, if the casting speed exceeds 2.8 m / min, uneven surface temperature occurs, and molten steel cannot be sufficiently supplied into the flat billet to promote the center segregation of Sn. From the viewpoint of suppressing center segregation of Sn, it is more preferably 0.4 m / min or more and 2.6 m / min or less. More preferably, it is 1.5 m / min or less. In addition, a light-rolling method is preferably performed, in which a flat embryo with an unsolidified layer at the end of solidification is used, while the total amount of rolling and the rolling speed are equivalent to the sum of the solidification shrinkage and the heat shrinkage. Casting was performed while rolling by the rolling roller group slowly. [0046] Next, when the above-mentioned steel material is hot rolled into a desired size and shape, it is preferably heated to a temperature of 900 ° C to 1350 ° C. The heating temperature is less than 900 ° C, the deformation resistance is large, and hot rolling is not easy. On the other hand, if the heating temperature exceeds 1350 ° C, surface marks may be generated, scale loss, or fuel unit increase. In addition, in particular, the higher the heating temperature, the more the diffusion of Sn in the central segregation portion can be promoted, so it is advantageous from the viewpoint of ensuring laminar tear resistance. From this viewpoint, the heating temperature is more preferably 1030 ° C or higher. The holding time at the heating temperature is preferably 60 minutes or more. This can sufficiently promote the diffusion of Sn in the central segregation portion. More preferably, it is 150 min or more. In addition, the upper limit thereof is not particularly limited, but it is preferably 1000 min. [0047] In addition, when the temperature of the steel material is originally in the range of 1030 to 1350 ° C, and it is maintained at this temperature range for more than 60 minutes, it can be directly supplied to hot rolling without heating. In addition, the hot-rolled sheet obtained after hot rolling may be subjected to reheating treatment, acid, and cold-rolled to form a cold-rolled sheet having a predetermined thickness. In hot rolling, the finishing rolling temperature is preferably 650 ° C or higher. The finishing rolling temperature is less than 650 ° C, which increases the rolling load due to the increase in deformation resistance, and it is difficult to implement rolling. [0048] The cooling after hot rolling may be either gas cooling or accelerated cooling. If higher strength is desired, accelerated cooling is preferred. Here, when performing accelerated cooling, the cooling rate is preferably set to 2 to 100 ° C / s and the cooling stop temperature is set to 700 to 400 ° C. That is, if the cooling rate does not reach 2 ° C / s and / or the cooling stop temperature exceeds 700 ° C, the effect of accelerated cooling is small, and sufficient strength cannot be achieved. On the other hand, when the cooling rate exceeds 100 ° C / s and / or the cooling stop temperature does not reach 400 ° C, the toughness of the steel material is deteriorated or the shape of the steel material is deformed. However, this is not the case when heat treatment is performed in subsequent steps. [Examples] [0049] Steels with the composition shown in Table 1 (the rest are Fe and unavoidable impurities) were melted in a vacuum melting furnace or a converter, and produced by continuous casting under the conditions shown in Table 2. Steel embryo. After heating these steel slabs to 1150 ° C. again, they were maintained under the conditions shown in Table 2 and then hot-rolled at the finish rolling temperature of 930 ° C. to obtain a steel sheet having a thickness of 30 mm. The cooling system after hot rolling uses water cooling (accelerated cooling) at a cooling rate of 10 ° C / s and a cooling stop temperature: 550 ° C. Then, the degree of Sn segregation in the obtained steel sheet was determined according to the method described above. The results are shown in Table 2. [0050] Furthermore, for the steel plate obtained as described above, the corrosion test for simulating the use environment of the cabin of a coal ship and a coal / ore ship is carried out according to the following methods, and the cabin of a coal ship and a coal / ore ship is in use Evaluation of corrosion resistance in the environment. (1) Evaluation of corrosion resistance From the steel plates Nos. 1 to 60 obtained as described above, 5 mmt × 50 mmW × 75 mmL test pieces were respectively taken, and the surface was blasted to remove rust or oil on the surface. With this surface as a test surface, the corrosion resistance of the steel material after the peeling of the coating film was evaluated. After coating the back surface and the end surface with a silicon-based sealant, it was embedded in an acrylic jig, and 5g of coal was placed on it, and the environment A (temperature: 60 ° C, relative humidity: 95%) was provided by a constant temperature and humidity device. , 20 hours) ⇔ Environment B (temperature: 30 ° C, relative humidity: 95%, 3 hours), each transition time: 0.5 hours temperature and humidity cycle for 84 days. Here, the symbol "⇔" is used in a repetitive sense. In addition, the coal system weighed 5 g and immersed in 100 ml of distilled water at normal temperature for 2 hours, then filtered and diluted to 200 ml of coal exudate to adjust the pH to 3.0. Here, the test is performed under the above conditions to simulate the corrosive environment of the inner floor of the cabin of a coal ship and a coal / ore ship. After the test, the rust of each test piece was peeled off using a rust stripping solution, and the mass reduction of each test piece before and after the corrosion test was measured, and this was taken as the amount of corrosion. The maximum pitting depth of each test piece was measured using a depth meter. Then, No.53 without Sn or Cu, Ni, Sb, W, Mo, and Nb was used as the base steel, and the corrosion resistance was evaluated according to the following standards based on the mass reduction and the ratio of the maximum pitting depth to the base steel. . ○ (Pass): The ratio of the mass reduction amount to the base steel and the maximum pitting depth is less than 70% △ (Failure): Either of the ratio of the mass reduction amount to the base steel and the maximum pitting depth, either It is more than 70% and less than 80%, and the other is less than 80% × (Unqualified): At least one of the ratio of the mass reduction of the base steel and the maximum pitting depth is more than 80% [ 0051] Further, the evaluation of laminar tear resistance was performed in the following manner. (2) The evaluation of laminar tear resistance is in accordance with the ClassNK steel ship rules and the same inspection methods (Chapter K Chapter 2). The steel plate thickness direction (Z direction) is applied to the steel plates No. 1 to 60 obtained in the above manner. ) Tensile test and calculate the reduction ratio (RA). Then, based on the calculated shrinkage ratio (RA), laminar tear resistance was evaluated according to the following criteria. ◎ (Passed, Excellent): 70 or more ○ (Passed): 35 or more and less than 70 △ (Failed): 25 or more and less than 35 × (Failed): Less than 25 [0052] Put (1) and (2) The evaluation results are recorded in Table 2. In addition, the comprehensive evaluation in Table 2 refers to "Pass" when all the evaluations in (1) and (2) above are "○" or "◎", and any of the evaluations in (1) and (2) have "△" or "×" is rated as "Failed". [0053] [0054] [0055] As shown in Table 2, the invention examples all have excellent corrosion resistance and lamellar tear resistance. On the other hand, in the comparative example, sufficient characteristics were not obtained with respect to at least one of corrosion resistance and lamellar tear resistance. [0056] That is, Comparative Examples Nos. 50 and 52 failed in terms of corrosion resistance and lamellar tear resistance because the amount of S exceeded the upper limit and did not contain a predetermined amount of Cu, Ni, Sb, W, Mo, and Nb. Get full characteristics. In Comparative Examples No. 51, 55, and 58, since the amount of Sn exceeded the upper limit, lamellar tear resistance was not obtained, and sufficient characteristics were not obtained. In Comparative Example No. 54, since the amounts of S and Sn exceeded the upper limit, lamellar tear resistance was not obtained, and sufficient characteristics were not obtained. In Comparative Examples Nos. 56 and 60, since the amount of S exceeded the upper limit, lamellar tear resistance was not obtained, and sufficient characteristics were not obtained. Since Comparative Example No. 57 did not contain a predetermined amount of Cu, Ni, Sb, W, Mo, and Nb, corrosion resistance was not achieved and sufficient characteristics were not obtained. In Comparative Example No. 59, since the amount of S exceeded the upper limit and the amount of Sn was lower than the lower limit, sufficient characteristics were not obtained in terms of corrosion resistance and lamellar tear resistance. In Comparative Examples Nos. 61 to 64, since the degree of Sn segregation exceeded the upper limit, lamellar tear resistance was not obtained, and sufficient characteristics were not obtained.