[發明欲解決之課題] [0014] 然而，為了獲得專利文獻1、2中記載之鋼材，於鋼材表層部暫時冷卻後，必須復熱且於前述復熱中施以加工而控制組織。因此，以實際生產規模之控制並不容易，對壓延、冷卻設備之負荷大。 [0015] 又，如前述之先前技術，均係以板厚50mm左右之鋼板為對象者，應用於板厚70mm左右之厚壁材時，是否可獲得必要特性尚不清楚。尤其，關於船體構造所必要之板厚方向之龜裂擴展特性亦不清楚。 [0016] 本發明係有利於解決上述問題者，目的在於提供即使板厚超過50mm時亦具有優異之脆性龜裂擴展停止特性，且可以工業上極簡易之製程製造之高強度厚鋼板。又，本發明之目的係以工業上簡易之製程，可安定地製造前述高強度厚鋼板的高強度厚鋼板之製造方法。 [用以解決課題之手段] [0017] 本發明人等為解決上述課題，針對具有優異脆性龜裂擴展停止特性之高強度鋼板及可安定地獲得該鋼板之製造方法重複積極研究之結果，獲得以下見解。 [0018] （1）於奧氏體區域完成壓延時，壓延時之溫度越為低溫越能獲得高的韌性值與集合組織。然而，如板厚超過50mm之厚鋼板中，若壓延溫度降低至變態點附近，則如圖1所示之鋼板表面與板厚中央部之溫度差變大，故表層部變態為鐵素體組織，該鐵素體經壓延而使表層部之韌性劣化。 [0019] （2）為了抑制表層部之鐵素體生成而有必要提高壓延溫度，但提高壓延溫度時，無法使板厚中心之壓延溫度充分降低。 [0020] （3）板厚中心部之壓延溫度未充分降低時，板厚中心部之結晶粒徑變粗大而有韌性變不充分之情況，或有利於龜裂擴展停止特性之集合組織之積集度不充分之情況。 [0021] 為了解決上述問題而進而重複檢討之結果，想到於壓延中途藉由對鋼板表背面加熱而可減低如圖2所示之板厚方向之溫度差，可於迄今以上之低溫安定地壓延。藉此，於迄今相同程度之條件下進行熱軋時，可獲得更高的脆性龜裂擴展停止特性。又，為了獲得相同程度之脆性龜裂擴展停止特性之必要壓延條件與迄今相比可緩和。 [0022] 因此，發現使用上述製程，控制板厚1/2位置及鋼板表面之{113}＜110＞方位強度，可獲得具有優異母材韌性並且獲得極優異之脆性龜裂擴展停止特性。 [0023] 基於以上之見解進行檢討，因而完成本發明。亦即，本發明之要旨構成如下。 [0024] 1. 一種高強度厚鋼板，其以質量%計，含有 C：0.03~0.20%， Si：0.03~0.5%， Mn：0.5~2.2%， P：0.02%以下， S：0.01%以下， Ti：0.005~0.03%， Al：0.005~0.080%，及 N：0.0050%以下， 其餘部分由Fe及不可避免雜質所成， 且具有以下述（1）式定義之Ceq滿足下述（2）式之條件之成分組成， 具有板厚1/2位置之{113}＜110＞方位強度為4.0以上，鋼板表面之{113}＜110＞方位強度為1.7以上之集合組織，其中，上述（1）式中之括弧表示前述高強度厚鋼板之該括弧內之元素的含量（質量%），未含有該元素時表示為0。 [0025] 2. 如上述1之高強度厚鋼板，其板厚為50~ 100mm， Kca（-10℃）為7000N/mm3/2
以上， 板厚1/4位置之vE（-40℃）為250J以上，且 板厚1/4位置之拉伸強度TS為570MPa以上。 [0026] 3. 如上述1或2之高強度厚鋼板，其中板厚1/2位置之組織所佔之貝氏體（bainite）之面積分率為85%以上。 [0027] 4. 如上述1~3中任一項之高強度厚鋼板，其中前述成分組成進而含有以質量%計，選自下述所成之群中之1或2者以上： Nb：0.005~0.05%， Cu：0.01~0.5%， Ni：0.01~1.5%，及 Cr：0.01~0.5%。 [0028] 5. 如上述1~4中任一項之高強度厚鋼板，其中前述成分組成進而含有以質量%計，選自下述所成之群中之1或2者以上： Mo：0.01~0.5%， V：0.001~0.10%， B：0.0030%以下， Ca：0.0050%以下，及 REM：0.0100%以下。 [0029] 6. 如上述1~4中任一項之高強度厚鋼板，其中距鋼板表面5mm位置與板厚1/2位置之vE（-40℃）均為250J以上。 [0030] 7. 一種高強度厚鋼板之製造方法，其係如上述1~6中任一項之高強度厚鋼板之製造方法，且具有下述步驟： 使具有如上述1、4及5中任一項之成分組成之鋼在1000~1200℃之加熱溫度加熱的加熱步驟；及 使經加熱之前述鋼進行熱軋成為熱軋鋼板之熱軋步驟， 前述熱軋步驟包含： 在板厚1/2位置為奧氏體（austenite）再結晶溫度區域之熱軋，與 在板厚1/2位置為奧氏體（austenite）未再結晶溫度區域之熱軋， 於前述熱軋步驟之間，自表背兩面加熱前述鋼。 [0031] 8. 如上述7之高強度厚鋼板之製造方法，其中進而具有以3℃/s以上之冷卻速度，將前述熱軋鋼板冷卻至500℃以下之冷卻停止溫度之冷卻步驟。 [0032] 9. 如上述8之高強度厚鋼板之製造方法，其中進而具有使於前述冷卻步驟冷卻之熱軋鋼板於Ac1
點以下之回火溫度回火的回火步驟。 [0033] 10. 如上述7~9中任一項之高強度厚鋼板之製造方法，其中於自前述表背兩面之加熱結束的時點之前述鋼的表面與板厚1/2位置之溫度差為30℃以下。 [0034] 11. 如上述7~10中任一項之高強度厚鋼板之製造方法，其中自前述表背兩面之加熱係在比前述板厚1/2位置為奧氏體未再結晶溫度區域之熱軋開始更早進行。 [發明效果] [0035] 依據本發明，由於適當控制板厚1/2位置與鋼板表面兩者之集合組織，故即使於板厚超過50mm之情況下，亦可獲得脆性龜裂擴展停止特性優異之高強度厚鋼板。本發明之高強度厚鋼板藉由應用於例如造船領域中之集裝箱船、散裝船等之強力甲板部構造中之與艙口邊緣圍板接合之甲板構件，而有助於船舶之安全性提高，於產業上極為有用。[Problems to be Solved by the Invention] [0014] However, in order to obtain the steel materials described in Patent Documents 1 and 2, after the surface layer portion of the steel material is temporarily cooled, it is necessary to reheat and process the reheating to control the structure. Therefore, the actual production scale control is not easy, and the load on the rolling and cooling equipment is large. [0015] In addition, as in the aforementioned prior art, it is unclear whether the necessary characteristics can be obtained when a steel plate having a thickness of about 50 mm is applied to a thick wall material having a thickness of about 70 mm. In particular, the crack propagation characteristics in the plate thickness direction necessary for the hull structure are unclear. [0016] The present invention is conducive to solving the above problems, and an object thereof is to provide a high-strength thick steel plate that has excellent brittle crack propagation stop characteristics even when the plate thickness exceeds 50 mm, and can be manufactured by an industrially simple process. Furthermore, the object of the present invention is a method for manufacturing a high-strength thick steel plate that can stably manufacture the aforementioned high-strength thick steel plate by an industrially simple process. [Means to Solve the Problem] [0017] In order to solve the above-mentioned problems, the present inventors repeated the results of active research on a high-strength steel plate having excellent brittle crack propagation stop characteristics and a manufacturing method capable of obtaining the steel plate stably. The following insights. [0018] (1) The pressure delay time is completed in the austenite region. The lower the temperature of the pressure delay time, the higher the toughness value and the aggregate structure can be obtained. However, in a thick steel plate with a plate thickness exceeding 50 mm, if the rolling temperature is lowered to the vicinity of the transformation point, the temperature difference between the surface of the steel plate and the center of the plate thickness shown in FIG. 1 becomes large, so the surface layer portion is transformed into a ferrite structure. The ferrite is rolled to deteriorate the toughness of the surface layer portion. [0019] (2) In order to suppress the formation of ferrite in the surface layer portion, it is necessary to increase the rolling temperature. However, when the rolling temperature is increased, the rolling temperature in the center of the plate thickness cannot be sufficiently reduced. [3] (3) When the rolling temperature at the center of the plate thickness is not sufficiently reduced, the crystal grain size at the center of the plate thickness becomes coarse and the toughness becomes insufficient, or the product of the aggregate structure that is beneficial to the crack propagation stop characteristics. Insufficient concentration. [0021] In order to solve the above problems and further review the results, it is thought that the temperature difference in the thickness direction of the plate as shown in FIG. 2 can be reduced by heating the surface and the back of the steel sheet during the rolling, and it can be rolled at a low temperature so far and stable. . Thereby, when hot rolling is performed under the same conditions as before, higher brittle crack growth stop characteristics can be obtained. In addition, the rolling conditions necessary to obtain the brittle crack propagation stop characteristics to the same degree can be relaxed compared with the conventional ones. [0022] Therefore, it was found that by using the above process, controlling the 1/2 position of the plate thickness and the {113} <110> azimuth strength of the steel plate surface, it is possible to obtain excellent base metal toughness and obtain extremely excellent brittle crack propagation stop characteristics. [0023] Based on the above findings, the present invention has been completed. That is, the gist of the present invention is structured as follows. [0024] 1. A high-strength thick steel plate containing C: 0.03 to 0.20%, Si: 0.03 to 0.5%, Mn: 0.5 to 2.2%, P: 0.02% or less, S: 0.01% or less , Ti: 0.005 ~ 0.03%, Al: 0.005 ~ 0.080%, and N: 0.0050% or less, the rest is made of Fe and unavoidable impurities, and has a Ceq defined by the following formula (1) to satisfy the following (2) The component composition of the conditions of the formula has a combined structure of {113} <110> azimuth strength of the plate thickness 1/2 position of 4.0 or more, and {113} <110> azimuth strength of the steel plate surface of 1.7 or more, The parentheses in the above formula (1) represent the content (% by mass) of the elements in the parentheses of the aforementioned high-strength thick steel plate, and are 0 when the elements are not contained. [0025] 2. The high-strength thick steel plate as described above 1 has a plate thickness of 50 to 100 mm, a Kca (-10 ° C) of 7000N / mm 3/2 or more, and a vE (-40 ° C) of the plate thickness 1/4 position. It is 250J or more, and the tensile strength TS of 1/4 position of plate thickness is 570MPa or more. [0026] 3. The high-strength thick steel plate as described in 1 or 2 above, wherein the area fraction of bainite occupied by the structure at the position of 1/2 of the plate thickness is 85% or more. [0027] 4. The high-strength thick steel sheet according to any one of the above 1 to 3, wherein the aforementioned component composition further contains 1 or 2 or more selected from the group consisting of the following in terms of mass%: Nb: 0.005 ~ 0.05%, Cu: 0.01 ~ 0.5%, Ni: 0.01 ~ 1.5%, and Cr: 0.01 ~ 0.5%. [0028] 5. The high-strength thick steel plate according to any one of 1 to 4 above, wherein the aforementioned component composition further contains 1 or 2 or more selected from the group consisting of the following in terms of mass%: Mo: 0.01 ~ 0.5%, V: 0.001 ~ 0.10%, B: 0.0030% or less, Ca: 0.0050% or less, and REM: 0.0100% or less. [0029] 6. The high-strength thick steel plate according to any one of 1 to 4 above, wherein vE (-40 ° C) at a position 5 mm from the surface of the steel plate and at a position 1/2 of the plate thickness are both 250 J or more. [0030] 7. A method for manufacturing a high-strength thick steel plate, which is the method for manufacturing a high-strength thick steel plate according to any one of the above 1 to 6, and has the following steps: A heating step of heating steel having a composition of any one at a heating temperature of 1000 to 1200 ° C; and a hot rolling step of hot-rolling the heated steel into a hot-rolled steel sheet, the hot-rolling step includes: The hot rolling at the / 2 position is the austenite recrystallization temperature region, and the hot rolling at the 1/2 thickness position is the austenite non-recrystallization temperature region. Between the aforementioned hot rolling steps, The aforementioned steel is heated from both sides of the case back. [0031] 8. The method for manufacturing a high-strength thick steel sheet according to the above 7, further comprising a cooling step of cooling the hot-rolled steel sheet to a cooling stop temperature below 500 ° C at a cooling rate of 3 ° C / s or more. [0032] 9. The method for manufacturing a high-strength thick steel sheet as described in 8 above, further comprising a tempering step of tempering the hot-rolled steel sheet cooled in the aforementioned cooling step at a tempering temperature below Ac 1 point. [0033] 10. The method for manufacturing a high-strength thick steel plate according to any one of 7 to 9 above, wherein the temperature difference between the surface of the steel and the plate thickness 1/2 position at the time when the heating from both surfaces of the front and back ends is completed. It is 30 ° C or lower. [0034] 11. The method for manufacturing a high-strength thick steel plate according to any one of 7 to 10 above, wherein the heating from both surfaces of the front and back surfaces is at an austenite non-recrystallization temperature region at a position 1/2 of the thickness of the aforementioned plate. Hot rolling started earlier. [Inventive Effect] [0035] According to the present invention, since the aggregate structure of both the plate thickness 1/2 position and the surface of the steel plate is appropriately controlled, even when the plate thickness exceeds 50 mm, excellent brittle crack propagation stop characteristics can be obtained. High-strength thick steel plate. The high-strength thick steel plate of the present invention contributes to the improvement of the safety of a ship by being applied to a deck member that is joined to a hatch edge coaming plate in a strong deck part structure such as a container ship and a bulk ship in the shipbuilding field. It is extremely useful in industry.
[0037] 以下具體說明本發明。本發明一實施形態之高強度厚鋼板中，成分組成及集合組織規定如上述。 [0038] [成分組成] 首先，說明將本發明之鋼成分組成限定為如上述之理由。又，成分組成中有關之「%」表示，只要未特別限定，則意指「質量%」。 [0039] C：0.03~0.20% C係提高鋼強度之元素，本發明中，為確保期望強度有必要含有0.03%以上。然而，C含量超過0.20%時，不僅是熔接性劣化，對韌性亦有不良影響。因此，C含量設為0.03~0.20%。又，C含量較好為0.05~0.15%。 [0040] Si：0.03~0.5% Si係作為脫氧元素，且作為鋼的強化元素而有效，但未達0.03%之含量時並無該效果。另一方面，Si含量超過0.5%時，不僅損及鋼的表面性狀，亦使韌性極端劣化。因此，Si含量設為0.03~0.5%。Si含量較好為0.04~0.40%。 [0041] Mn：0.5~2.2% Mn係作為強化元素而含有。Mn含量少於0.5%時，其效果不充分。另一方面，Mn含量超過2.2%時，除了熔接性劣化以外，鋼材成本亦上升。因此，Mn含量設為0.5~2.2%。 [0042] P：0.02%以下 P係鋼中不可避免之雜質，含量多時韌性劣化。因此，為了於如板厚超過50mm之厚鋼板亦保有良好韌性，P含量設為0.02%以下。P含量較好設為0.01%以下，更好0.006%以下。另一方面，下限並未限定，雖亦可為0%，但工業上而言係超過0%。 [0043] S：0.01%以下 S係鋼中不可避免之雜質，含量多時韌性劣化。因此，為了於如板厚超過50mm之厚鋼板亦保有良好韌性，S含量設為0.01%以下。S含量較好設為0.005%以下，更好0.003%以下。另一方面，下限並未限定，雖亦可為0%，但工業上而言係超過0%。 [0044] Ti：0.005~0.03% Ti藉由微量含有，而形成氮化物、碳化物或碳氮化物，具有使結晶粒微細化並提高母材韌性之效果。前述效果若於Ti含量為0.005%以上即可獲得。另一方面，Ti含量超過0.03%時，母材及熔接熱影響部中之韌性降低。因此，Ti含量設為0.005~0.03%。Ti含量較好為0.006~ 0.028%。 [0045] Al：0.005~0.080% Al係作為脫氧材而添加之元素，為了獲得其效果必須添加0.005%以上。另一方面，Al含量超過0.080%時，韌性降低並且熔接時熔接金屬部之韌性降低。因此，Al含量設為0.005~0.080%。又，Al含量較好為0.020~0.040%。 [0046] N：0.0050%以下 N係與鋼中之Al結合，調整壓延加工時之結晶粒徑，強化鋼的元素。然而，N含量超過0.0050%時，韌性劣化，故N含量設為0.0050%以下。另一方面，N含量之下限並未特別限定，但較好為0.0010%以上，更好為0.0015%以上。 [0047] 本發明一實施形態之高強度鋼板之成分組成係由上述元素、其餘部分之Fe及不可避免雜質所成。 [0048] 又，本發明其他實施形態中，為了進而提高特性，上述成分組成可進而任意含有選自Nb、Cu、Ni及Cr所成之群之1或2者以上。 [0049] Nb：0.005~0.05%， Nb係於鐵素體變態時或再加熱時以NbC析出，有助於高強度化。又，Nb具有於奧氏體區域之壓延中擴大未再結晶區域之效果，有助於鐵素體之細粒化，故對於韌性之改善亦有效。其效果藉由含有0.005%以上而得以發揮，但含有超過0.05%時，因析出粗大NbC，反而導致韌性降低。因此，含有Nb時，Nb含量設為0.005~0.05%。 [0050] Cu：0.01~0.5% Cu係提高銅之淬透性的元素，除了提高壓延後之強度以外，亦有助於韌性、高溫強度、耐候性等之功能。該等效果藉由含有0.01%以上而得以發揮，但過度含有時韌性或熔接性反而劣化。因此，Cu含量設為0.01~0.5%。 [0051] Ni：0.01~1.5% Ni係提高鋼的淬透性之元素，除了提高壓延後之強度以外，亦有助於韌性、高溫強度、耐候性等之功能。該等效果藉由含有0.01%以上而得以發揮。另一方面，過度含有時韌性或熔接性反而劣化，此外亦導致合金之成本增加。因此，Ni含量設為0.01~1.5%。 [0052] Cr：0.01~0.5% Cr與Cu同樣係提高鋼的淬透性之元素，除了提高壓延後之強度以外，亦有助於韌性、高溫強度、耐候性等之功能。該等效果藉由含有0.01%以上而得以發揮，但過度含有時韌性或熔接性反而劣化。因此，Cr含量設為0.01~0.5%。 [0053] 又，本發明其他實施形態中，為了進而提高特性，上述成分組成可進而任意含有選自Mo、V、B、Ca及REM所成之群之1或2者以上。 [0054] Mo：0.01~0.5% Mo與Cu及Cr同樣係提高鋼的淬透性之元素，除了提高壓延後之強度以外，亦有助於韌性、高溫強度、耐候性等之功能。該等效果藉由含有0.01%以上而得以發揮，但過度含有時韌性或熔接性反而劣化。因此，Mo含量設為0.01~0.5%。 [0055] V：0.001~0.10% V係藉由作為V（CN）析出之析出強化，而提高鋼強度之元素。該效果藉由含有0.001%以上之V而得以發揮。另一方面，V含有超過0.10%時，反而使韌性降低。因此，含有V時，V含量設為0.001~0.10%。 [0056] B：0.0030%以下 B係微量即具有提高鋼的淬透性效果之元素，可任意含有。然而，B含量超過0.0030%時，熔接部之韌性降低。因此，B含量設為0.0030%以下。又，B含量下限並未特別限定，含有B時，基於獲得良好淬透性之觀點，B含量較好設為0.0006%以上。 [0057] Ca：0.0050%以下 Ca係具有使熔接熱影響部之組織微細化並提高韌性之效果的元素，若適量含有則不會損及本發明效果。因此，可根據需要含有Ca。然而，過度含有Ca時，形成粗大之介隔物並使母材之韌性劣化。因此，含有Ca時，Ca含量設為0.0050%以下。另一方面，Ca含量之下限值並未特別限定，但添加Ca時，為了充分獲得添加效果，較好Ca含量設為0.0001%以上。 [0058] REM：0.0100%以下 REM（稀土類金屬）與Ca同樣，係具有使熔接熱影響部之組織微細化並提高韌性之效果的元素，若適量含有則不會損及本發明效果。因此，可任意含有REM。然而，過度含有REM時，形成粗大之介隔物並使母材之韌性劣化。因此，含有REM時，REM含量設為0.0100%以下。另一方面，REM含量之下限並未特別限定，但添加REM時，為了充分獲得添加效果，較好REM含量設為0.0005%以上。 [0059] [Ceq] 再者，上述成分組成係以下述（1）式定義之碳當量Ceq滿足下述（2）式之條件者。其中，上述（1）式中之括弧表示高強度厚鋼板之該括弧內之元素的含量（質量%），未含有該元素時表示為0。 [0060] 藉由將Ceq設為0.40以上，即使為板厚超過50mm之厚鋼板，亦可確保強度及集合組織強度。另一方面，Ceq之上限並未特別限定，但較好為0.55以下，更好為0.53以下，又更好為0.50以下。 [0061] [集合組織] 本發明中，為了提高對於壓延方向或壓延直角方向等之與板面平行方向擴展之龜裂的龜裂擴展停止特性，而規定板厚1/2位置及鋼板表面之{113}＜110＞方位強度。板厚1/2位置及鋼板表面中，若{113} ＜110＞方位發達，則在龜裂進展之前，發生微觀的龜裂而成為龜裂進展之阻力。又，此處所謂「板厚1/2位置」意指板厚方向之中央位置，所謂「鋼板表面」意指去除垢後之距鋼板表面0.5mm之深度位置。 [0062] 具體而言，成為板厚1/2位置之{113}＜110＞方位強度為4.0以上，鋼板表面之{113}＜110＞方位強度為1.7以上之集合組織。藉由以滿足前述條件之方式控制集合組織，即使為最近於集裝箱船或散裝船等船體外板所用般之板厚超過50mm之厚鋼板，除了確保構造安全性以外，亦可獲得成為目標之Kca（-10℃）≧7000N/mm3/2
之脆性龜裂擴展停止特性。其中，Kca（-10℃）係-10℃下之脆性龜裂擴展停止韌性。又，於要求更優異之龜裂擴展停止特性時，較好板厚1/2位置之{113} ＜110＞方位強度為4.1以上，鋼板表面之{113}＜110＞方位強度為1.9以上。另一方面，板厚1/2位置之{113}＜110＞方位強度之上限並未特別限定，越高越佳，但一般宜為7.0以下。又鋼板表面之{113}＜110＞方位強度之上限亦未特別限定，越高越佳，但一般宜為5.0以下。 [0063] 又，板厚1/2位置之{113}＜110＞方位強度與鋼板表面之{113} ＜110＞方位強度可分別藉由X射線極點圖法，以隨機強度比求得，具體而言，可藉由實施例記載之方法測定。又，前述測定中，容許數%之位置誤差。 [0064] [鋼板內部之組織] 板厚1/2位置之貝氏體之面積分率較好為85%以上。藉由如此控制組織，可提高有利於脆性龜裂擴展停止特性之{113}＜110＞方位。又，前述貝氏體之面積分率更好為90%以上。另一方面，前述貝氏體之面積分率上限並未特別限定，可為100%。又，貝氏體以外之其餘部分並未特別限定，可為任意組織。該等其餘部分組織之面積分率合計較好為15%以下。前述面積分率可藉實施例中記載之方法測定。 [0065] [母材韌性] 藉由如上述控制成分組成與集合組織，可獲得具有優異母材韌性之高強度厚鋼板。具有優異之母材韌性於抑制龜裂進展上具重要性。具體而言，板厚1/4位置之-40℃下之夏比（charpy）吸收能：vE（-40℃）較好為250J以上，更好為280J以上，又更好為300J以上。另一方面，前述vE（-40℃）之上限並未特別限定，但一般可為420J以下，亦可為400J以下。 [0066] 再者，距高強度厚鋼板表面5mm位置（深度）之vE（-40℃）較好為250J以上，更好為280J以上，又更好為300J以上。另一方面，前述vE（-40℃）之上限並未特別限定，但一般可為420J以下，亦可為400J以下。 [0067] 本發明中，如後述，藉由於熱軋步驟之間自表背兩面加熱鋼，可使距鋼板表面5mm位置與板厚1/2位置之vE（-40℃）兩者均為250J以上。 [0068] 又，板厚1/4位置之夏比斷口轉變溫度較好為 -40℃以下。前述夏比斷口轉變溫度之下限並未特別限定，但一般宜為-130℃以上。 [0069] [脆性龜裂擴展停止韌性] 如上述，本發明之高強度厚鋼板中藉由控制集合組織而可實現Kca（-10℃）為7000N/mm3/2
以上之優異脆性龜裂擴展停止特性。Kca（-10℃）較好為7500N/mm3/2
以上，更好為8000N/mm3/2
以上，又更好為9000N/mm3/2
以上。另一方面，由於Kca（-10℃）之值越高越好，故其上限並未特別限定，但一般宜為13000N/mm3/2
以下。又，前述Kca（-10℃）之值可藉由溫度梯度型ESSO試驗測定，具體而言可藉由實施例記載之方法獲得。 [0070] [拉伸強度] 本發明之高強度厚鋼板之拉伸強度（TS）並未特別限定，較好板厚1/4位置之拉伸強度TS為570MPa以上，更好為580MPa以上，又更好為590MPa以上。另一方面，關於TS上限亦未特別限定，但一般板厚1/4位置之拉伸強度TS宜為700MPa以下。 [0071] [板厚] 本發明之高強度厚鋼板之板厚並未特別限定，可為任意值。然而，由於板厚越厚本發明效果越顯著，故板厚較好為50mm以上，更好超過50mm，又更好為60mm以上，再更好為70mm以上。另一方面，板厚上限亦未特別限定，但一般宜為100mm以下。 [0072] [製造方法] 其次，說明本發明一實施形態之高強度厚鋼板之製造方法。 [0073] 本發明之高強度厚鋼板可藉由將具有上述成分組成之鋼在特定條件下熱軋而製造。具體而言，依序進行如下（1）及（2）。 （1）使鋼在1000~1200℃之加熱溫度加熱的加熱步驟。 （2）使經加熱之前述鋼進行熱軋成為熱軋鋼板之熱軋步驟。 而且，前述（2）熱軋步驟中，依序進行如下之（2-1）及（2-2）之步驟。 （2-1）在板厚1/2位置為奧氏體再結晶溫度區域之熱軋（再結晶區域壓延）。 （2-2）在板厚1/2位置為奧氏體未再結晶溫度區域之熱軋（未再結晶區域壓延）。 [0074] 又，前述（2）熱軋步驟之後，亦可任意進行如下之（3）之步驟。 （3）以3℃/s以上之冷卻速度，將前述熱軋鋼板冷卻至500℃以下之冷卻停止溫度之冷卻步驟。 [0075] 再者，前述（3）冷卻步驟之後，亦可任意進行如下之（4）之步驟。 （4）使於前述冷卻步驟冷卻之熱軋鋼板於Ac1
點以下之回火溫度回火的回火步驟。 [0076] 以下針對上述各步驟之條件的限定理由加以說明。 [0077] [加熱步驟] 加熱溫度：1000~1200℃ 於熱軋之前，加熱具有上述成分組成之鋼。此時，加熱溫度未達1000℃時，無法充分確保奧氏體再結晶溫度區域之壓延時間。另一方面，加熱溫度超過1200℃時，奧氏體粒粗大化，反而導致韌性降低，或氧化損失變顯著而使良率降低。因此，加熱溫度設為1000~1200℃。又，基於鋼板之韌性提高之觀點，前述加熱溫度較好為1000~1170℃，更好為1050~1170℃。 [0078] 又，供於前述加熱步驟之鋼並未特別限定，可藉任意方法製造。例如，可使用將具有上述成分組成之熔鋼以轉爐等進行熔製，藉由連續鑄造而得之鋼片（鋼坯）。 [0079] [熱軋] 其次，進行熱軋。熱軋步驟中，首先，進行（2-1）在板厚1/2位置為奧氏體再結晶溫度區域之熱軋（再結晶區域壓延），其次進行（2-2）在板厚1/2位置為奧氏體未再結晶溫度區域之熱軋（未再結晶區域壓延）。前述熱軋步驟中之壓延結束溫度並未特別限定，但較好為Ar3
點以上。 [0080] 上述熱軋之累積壓下率並未特別限定，但（2-1）在板厚1/2位置為奧氏體再結晶溫度區域之熱軋之累積壓下率（再結晶溫度區域累積壓下率）較好為12%以上。前述再結晶溫度區域累積壓下率之上限並未特別限定，但基於壓延負荷之觀點，較好為60%以下。又，（2-2）在板厚1/2位置為奧氏體未再結晶溫度區域之熱軋之累積壓下率（未再結晶溫度區域累積壓下率）較好為45%以上。前述未再結晶溫度區域累積壓下率之上限並未特別限定，但基於壓延負荷之觀點，較好為90%以下。基於集合組織控制之觀點，較好如此控制累積壓下率。 [0081] 本發明中，於前述（2）熱軋步驟期間，自表背兩面加熱前述鋼。藉由前述加熱，可控制板厚方向之溫度分佈，可減小鋼板表面與內部之溫度差，其結果，可獲得上述之板厚中央部與鋼板表面之集合組織。又，藉由進行自前述兩面之加熱，可使距鋼板表面5mm位置與板厚1/2位置之vE（-40℃）均為250J以上。 [0082] 自前述表背兩面之加熱較好以於該加熱結束的時點之前述鋼的表面與板厚1/2位置之溫度差為30℃以下之方式進行。藉此，可使板厚中央於更低溫度下壓延並且可抑制表面生成鐵素體。前述溫度差更好為20℃以下，又更好為10℃以下。另一方面，前述溫度差越小越好，故下限並未特別限定，宜為0℃以上。 [0083] 又，進行上述加熱之時點並未特別限定，只要於熱軋步驟之期間即可。然而，基於集合組織控制之觀點，較好在以加熱結束時更後進行之熱軋的累積壓下率為45%以上之時點進行該加熱，更好在未再結晶區域壓延開始前進行，又更好在再結晶區域壓延結束厚且未再結晶區域壓延開始前進行。於未再結晶區域壓延開始前進行加熱時，基於溫度控制之觀點，較好於該加熱結束後30秒以內開始未再結晶區域壓延。 [0084] 前述熱軋步驟中之加熱並未特別限定，可以感應加熱或爐加熱等之任意方法進行。 [0085] 於未再結晶區域壓延之期間鋼板表面與板厚1/2位置間之溫度差較大時，亦可進而於未再結晶區域壓延之期間，僅對表面加熱。 [0086] [冷卻步驟] 冷卻速度：3℃/s以上 冷卻停止溫度：500℃以下 壓延結束之鋼板，基於保持壓延時發達之集合組織之觀點，較好以3℃/s以上之冷卻速度，冷卻至500℃以下之冷卻停止溫度。冷卻速度之上限並未特別限定，但較好為10℃/s以下。又，冷卻停止溫度之下限並未特別限定，但較好為0℃以上。又，前述冷卻步驟中之冷卻開始溫度較好為Ar3
點以上。 [0087] [回火步驟] 回火溫度：Ac1
點以下 於前述冷卻步驟之後進行回火處理時，較好於Ac1
點以下之回火溫度進行回火。其理由為回火溫度高於Ac1
點時，有失去壓延時發達之集合組織之情況。回火溫度之下限並未特別限定，但較好為400℃以上。 [0088] 又，以上說明中，板厚1/2位置之溫度係藉由自以輻射溫度計測定之鋼板表面溫度之傳熱計算，或基於事先測定之中心溫度計算而求得。又，壓延後之冷卻條件中之溫度係板厚1/2位置之溫度。 [0089] （實施例） 以下針對本發明實施例加以說明。 將具有表1所示各成分組成之熔鋼以轉爐熔製，藉由連續鑄造法作成鋼坯。其次，加熱前述鋼坯厚，以成為板厚：50~100mm之方式進行熱軋。前述加熱與熱軋之條件如表2所示。隨後，以表2所示之條件進行冷卻，隨後，放冷獲得高強度厚鋼板。針對一部分鋼板，於冷卻後以表2所示之溫度進行回火。 [0090] 前述熱軋期間，除一部分比較例以外，自表背兩面加熱鋼。前述加熱係於再結晶區域壓延結束後、未再結晶區域壓延開始前進行。又，此時，未再結晶區域壓延於結束加熱後於30秒以內開始。前述加熱可藉由使用環境爐之爐加熱及高頻之感應加熱而實施。 [0091][0092][0093] 針對所得高強度厚鋼板之各者，藉由以下方法，評價韌性、拉伸強度、集合組織、組織及脆性龜裂擴展停止特性。評價結果示於表3。 [0094] [韌性] 為了評價所得高強度厚鋼板之韌性，進行夏比衝擊試驗，測定各鋼板之（1）距鋼板表面5mm之位置、（2）板厚1/4位置及（3）板厚1/2位置之3部位之-40℃下之夏比吸收能vE（-40℃）。前述夏比衝擊試驗係使用JIS（日本工業規格）規定之4號衝擊試驗片（長55mm，寬10mm，厚10mm），以使該試驗片之長度方向平行於鋼板之壓延方向之方式採取前述試驗片。又，用以測定距前述鋼板表面5mm之位置之vE（-40℃）之試驗片，係去除鋼板表面所形成之垢（黑皮）後，自該鋼板表面採取。試驗片厚度為10mm，故前述試驗片之測定位置為該試驗片厚度方向之中心位置，亦即距鋼板表面於板厚方向5mm之位置。 [0095] [拉伸強度] 自所得高強度厚鋼板之板厚1/4位置，以試驗片之長度方向與壓延方向垂直之方式，採取JIS 4號試驗片。使用前述試驗片，依據JIS Z 2241之規定進行拉伸試驗，求出板厚1/4位置之拉伸強度（TS）。 [0096] [集合組織] 為了評價所得高強度厚鋼板之集合組織，藉以下方法測定（1）板厚1/2位置及（2）鋼板表面之{113}＜110＞方位強度。首先，去除形成於前述鋼板表面之垢後，以使（1）板厚1/2位置及（2）距鋼板表面0.5mm深之位置成為測定位置之方式，採取板厚厚度1mm之樣品。其次，藉由機械研磨‧電解研磨所採取之樣品與板面平行之面，而準備X射線繞射用之試驗片。又，針對板厚表面之樣品，研磨接近鋼板表面之側的面。針對所得試驗片之各者，使用利用Mo線源之X射線繞射裝置實施X射線繞射測定，求出（200）、（110）及（211）正極點圖。自所得正極點圖求出三次元結晶方位密度函數，藉此算出{113}＜110＞方位強度相對於隨機強度之比。 [0097] [組織] 以與壓延方向平行之面作為觀察面之方式，自板厚1/2位置採取試料。鏡面研磨前述試料表面後，拍攝藉由蝕刻而露出之金屬組織之光學顯微鏡照片，藉由圖像解析評價貝氏體之面積分率。 [0098] [脆性龜裂擴展停止特性] 為了評價脆性龜裂擴展停止特性，進行溫度梯度型ESSO試驗，求出前述高強度厚鋼板之-10℃之Kca值（以下亦記為Kca（-10℃））。於前述溫度梯度型ESSO試驗中使用全厚試驗片。 [0099] 如由表3所示結果所了解，滿足本發明條件之高強度厚鋼板，距鋼板表面5mm位置、板厚1/2位置及板厚1/4位置之vE（-40℃）均為250J以上，Kca（-10℃）為7000N/mm3/2
以上，具備優異之脆性龜裂擴展停止特性。另一方面，未滿足本發明條件之比較例之高強度厚鋼板，板厚1/4位置之vE（-40℃）、Kca（-10℃）之至少一者劣化。 [0100] [0037] The present invention will be specifically described below. In the high-strength thick steel plate according to an embodiment of the present invention, the composition and the aggregate structure are specified as described above. [Component Composition] First, the reason for limiting the steel component composition of the present invention to the above is explained. In addition, the expression "%" in the component composition means "mass%" as long as it is not particularly limited. [0039] C: 0.03 to 0.20% C is an element that increases the strength of steel. In the present invention, it is necessary to contain 0.03% or more in order to ensure the desired strength. However, when the C content exceeds 0.20%, not only the weldability deteriorates, but the toughness is also adversely affected. Therefore, the C content is set to 0.03 to 0.20%. The C content is preferably 0.05 to 0.15%. [0040] Si: 0.03 to 0.5% Si is effective as a deoxidizing element and as a reinforcing element of steel, but the effect is not achieved when the content is less than 0.03%. On the other hand, when the Si content exceeds 0.5%, not only the surface properties of the steel are impaired, but the toughness is extremely deteriorated. Therefore, the Si content is set to 0.03 to 0.5%. The Si content is preferably 0.04 to 0.40%. [0041] Mn: 0.5 to 2.2% Mn is contained as a reinforcing element. When the Mn content is less than 0.5%, the effect is insufficient. On the other hand, when the Mn content exceeds 2.2%, in addition to the deterioration of weldability, the cost of the steel also increases. Therefore, the Mn content is set to 0.5 to 2.2%. [0042] P: 0.02% or less An unavoidable impurity in the P-based steel. When the content is large, toughness is deteriorated. Therefore, in order to maintain good toughness even in thick steel plates having a plate thickness exceeding 50 mm, the P content is set to 0.02% or less. The P content is preferably set to 0.01% or less, and more preferably 0.006% or less. On the other hand, the lower limit is not limited, and although it may be 0%, it is more than 0% industrially. [0043] S: 0.01% or less An unavoidable impurity in S-based steel. When the content is large, toughness is deteriorated. Therefore, in order to maintain good toughness even in a thick steel plate having a plate thickness exceeding 50 mm, the S content is set to 0.01% or less. The S content is preferably set to 0.005% or less, and more preferably 0.003% or less. On the other hand, the lower limit is not limited, and although it may be 0%, it is more than 0% industrially. [0044] Ti: 0.005 to 0.03% Ti contains nitrides, carbides, or carbonitrides in a trace amount, and has the effect of miniaturizing crystal grains and improving the toughness of the base material. The aforementioned effect can be obtained if the Ti content is 0.005% or more. On the other hand, when the Ti content exceeds 0.03%, the toughness in the base material and the heat-affected zone is reduced. Therefore, the Ti content is set to 0.005 to 0.03%. The Ti content is preferably 0.006 to 0.028%. [0045] Al: 0.005 to 0.080% Al is an element added as a deoxidizing material, and in order to obtain its effect, 0.005% or more must be added. On the other hand, when the Al content exceeds 0.080%, the toughness decreases and the toughness of the welded metal portion decreases during welding. Therefore, the Al content is set to 0.005 to 0.080%. The Al content is preferably 0.020 to 0.040%. [0046] N: 0.0050% or less N is an element that combines with Al in steel, adjusts the crystal grain size during rolling, and strengthens the steel. However, if the N content exceeds 0.0050%, the toughness deteriorates, so the N content is set to 0.0050% or less. On the other hand, the lower limit of the N content is not particularly limited, but is preferably 0.0010% or more, and more preferably 0.0015% or more. [0047] The composition of the high-strength steel sheet according to an embodiment of the present invention is made of the above-mentioned elements, the rest of Fe, and unavoidable impurities. [0048] In another embodiment of the present invention, in order to further improve the characteristics, the component composition may further include any one or two or more selected from the group consisting of Nb, Cu, Ni, and Cr. [0049] Nb: 0.005 to 0.05%. Nb is precipitated as NbC during ferrite transformation or reheating, which contributes to high strength. In addition, Nb has the effect of expanding the non-recrystallized region during the rolling of the austenite region, and contributes to the fine graining of ferrite, so it is effective for improving the toughness. The effect is exhibited by containing 0.005% or more, but if the content exceeds 0.05%, coarse NbC is precipitated and the toughness is reduced. Therefore, when Nb is contained, the Nb content is set to 0.005 to 0.05%. [0050] Cu: 0.01 to 0.5% Cu is an element that improves the hardenability of copper. In addition to improving the strength after rolling, it also contributes to the functions of toughness, high temperature strength, and weather resistance. These effects are exhibited by containing 0.01% or more, but toughness or weldability deteriorates when contained excessively. Therefore, the Cu content is set to 0.01 to 0.5%. [0051] Ni: 0.01 to 1.5% Ni is an element that improves the hardenability of steel. In addition to improving the strength after rolling, it also contributes to the functions of toughness, high temperature strength, and weather resistance. These effects are exhibited by containing 0.01% or more. On the other hand, when it is excessively contained, toughness or weldability deteriorates, and the cost of the alloy increases. Therefore, the Ni content is set to 0.01 to 1.5%. [0052] Cr: 0.01 ~ 0.5% Cr, like Cu, is an element that improves the hardenability of steel. In addition to improving the strength after rolling, it also contributes to the functions of toughness, high temperature strength, and weather resistance. These effects are exhibited by containing 0.01% or more, but toughness or weldability deteriorates when contained excessively. Therefore, the Cr content is set to 0.01 to 0.5%. [0053] In another embodiment of the present invention, in order to further improve the characteristics, the above-mentioned component composition may further optionally contain one or two or more selected from the group consisting of Mo, V, B, Ca, and REM. [0054] Mo: 0.01 ~ 0.5% Mo, like Cu and Cr, is an element that improves the hardenability of steel. In addition to improving the strength after rolling, Mo also contributes to the functions such as toughness, high temperature strength, and weather resistance. These effects are exhibited by containing 0.01% or more, but toughness or weldability deteriorates when contained excessively. Therefore, the Mo content is set to 0.01 to 0.5%. [0055] V: 0.001 to 0.10% V is an element that enhances the strength of steel by precipitation strengthening as a precipitation of V (CN). This effect is exhibited by containing V of 0.001% or more. On the other hand, when the V content exceeds 0.10%, the toughness is reduced. Therefore, when V is contained, the V content is set to 0.001 to 0.10%. [0056] B: 0.0030% or less B is a trace element that has an effect of improving the hardenability of steel and may be arbitrarily contained. However, when the B content exceeds 0.0030%, the toughness of the welded portion decreases. Therefore, the B content is set to 0.0030% or less. The lower limit of the B content is not particularly limited. When B is contained, the B content is preferably 0.0006% or more from the viewpoint of obtaining good hardenability. [0057] Ca: 0.0050% or less Ca is an element that has the effect of miniaturizing the structure of the welded heat-affected zone and improving the toughness. If it is contained in an appropriate amount, the effect of the present invention will not be impaired. Therefore, Ca can be contained as needed. However, if Ca is contained excessively, coarse spacers are formed and the toughness of the base material is deteriorated. Therefore, when Ca is contained, the Ca content is set to 0.0050% or less. On the other hand, the lower limit of the Ca content is not particularly limited, but when Ca is added, it is preferable to set the Ca content to 0.0001% or more in order to fully obtain the effect of addition. [0058] REM: 0.0100% or less REM (rare earth metal), like Ca, is an element that has the effect of miniaturizing the structure of the welded heat-affected zone and improving toughness. If it is contained in an appropriate amount, the effect of the present invention is not impaired. Therefore, REM may be contained arbitrarily. However, when REM is contained excessively, coarse spacers are formed and the toughness of the base material is deteriorated. Therefore, when REM is contained, the REM content is set to 0.0100% or less. On the other hand, the lower limit of the REM content is not particularly limited, but when REM is added, it is preferable to set the REM content to be 0.0005% or more in order to fully obtain the effect of addition. [0059] The above-mentioned component composition is a carbon equivalent Ceq defined by the following formula (1) that satisfies the conditions of the following formula (2). Among them, the parentheses in the above formula (1) represent the content (% by mass) of the elements in the brackets of the high-strength thick steel plate, and are 0 when the elements are not contained. [0060] By setting Ceq to 0.40 or more, even if it is a thick steel plate with a plate thickness exceeding 50 mm, the strength and the aggregate structure strength can be secured. On the other hand, the upper limit of Ceq is not particularly limited, but is preferably 0.55 or less, more preferably 0.53 or less, and still more preferably 0.50 or less. [Assembly Structure] In the present invention, in order to improve the crack propagation stop characteristics of cracks extending in a direction parallel to the plate surface, such as a rolling direction or a right-angle rolling direction, a position where the plate thickness is 1/2 and the surface of the steel plate is defined. {113} <110> Azimuth intensity. If the {113} <110> orientation is developed in the plate thickness 1/2 position and the surface of the steel sheet, microcracks occur before the cracks progress and become resistance to the progress of the cracks. Here, the "plate thickness 1/2 position" means a center position in the plate thickness direction, and the "steel plate surface" means a depth position of 0.5 mm from the surface of the steel plate after descaling. [0062] Specifically, the {113} <110> azimuth strength of the plate thickness 1/2 position is 4.0 or more, and the {113} <110> azimuth strength of the steel plate surface is an aggregate structure of 1.7 or more. By controlling the assembly organization in a way that satisfies the aforementioned conditions, even if it is a thick steel plate with a plate thickness of more than 50mm, which has been recently used for hull plates such as container ships or bulk ships, in addition to ensuring structural safety, the target Kca can be obtained. (-10 ℃) ≥7000N / mm 3/2 brittle crack propagation stop characteristics. Among them, Kca (-10 ° C) is a brittle crack propagation stop toughness at -10 ° C. When more excellent crack propagation stop characteristics are required, it is preferable that the {113} <110> azimuth strength of the plate thickness 1/2 position is 4.1 or more, and the {113} <110> azimuth strength of the steel plate surface is 1.9 or more. On the other hand, the upper limit of the {113} <110> azimuth strength at the position of 1/2 of the plate thickness is not particularly limited, the higher the better, but generally it is 7.0 or less. Also, the upper limit of the {113} <110> azimuth strength of the steel plate surface is not particularly limited, the higher the better, but generally it is preferably 5.0 or less. [0063] In addition, the {113} <110> azimuth intensity of the plate thickness 1/2 position and the {113} <110> azimuth intensity of the steel plate surface can be obtained by the random intensity ratio by the X-ray pole map method, specifically, In other words, it can be measured by the method described in the examples. In the above measurement, a positional error of several% is allowed. [Organization inside the steel sheet] The area fraction of the bainite at the 1/2 thickness position is preferably 85% or more. By controlling the structure in this way, it is possible to increase the {113} <110> orientation which is favorable for the brittle crack propagation stop characteristics. The area fraction of the bainite is more preferably 90% or more. On the other hand, the upper limit of the area fraction of the bainite is not particularly limited, but may be 100%. In addition, the remainder other than bainite is not particularly limited, and may be any structure. The total area fraction of these remaining tissues is preferably 15% or less. The aforementioned area fraction can be measured by the method described in the examples. [Base material toughness] By controlling the component composition and aggregate structure as described above, a high-strength thick steel plate having excellent base material toughness can be obtained. Having excellent toughness of the base metal is important in suppressing the progress of cracking. Specifically, the Charpy absorption energy at -40 ° C at 1/4 position of the plate thickness: vE (-40 ° C) is preferably 250J or more, more preferably 280J or more, and even more preferably 300J or more. On the other hand, the upper limit of the aforementioned vE (-40 ° C) is not particularly limited, but may generally be 420J or lower and 400J or lower. [0066] Furthermore, the vE (-40 ° C) at a position (depth) of 5 mm from the surface of the high-strength thick steel plate is preferably 250 J or more, more preferably 280 J or more, and even more preferably 300 J or more. On the other hand, the upper limit of the aforementioned vE (-40 ° C) is not particularly limited, but may generally be 420J or lower and 400J or lower. [0067] In the present invention, as will be described later, by heating the steel from the front and back surfaces between the hot rolling steps, vE (-40 ° C) at a position 5 mm from the surface of the steel plate and at a position 1/2 of the plate thickness can be both 250J. the above. [0068] The Charpy fracture transition temperature at the position of 1/4 of the plate thickness is preferably -40 ° C or lower. The lower limit of the Charpy fracture transition temperature is not particularly limited, but is generally preferably -130 ° C or higher. [Brittleness crack propagation stop toughness] As described above, in the high-strength thick steel plate of the present invention, by controlling the aggregate structure, excellent brittle crack growth with a Kca (-10 ° C) of 7000 N / mm 3/2 or more can be achieved. Stop characteristics. Kca (-10 ℃) preferably 7500N / mm 3/2 or more, more preferably 8000N / mm 3/2 or more, and more preferably 9000N / mm 3/2 or more. On the other hand, the higher the value of Kca (-10 ° C), the better, so the upper limit is not particularly limited, but it is generally preferred to be 13000 N / mm 3/2 or less. The value of Kca (-10 ° C) can be measured by a temperature gradient ESSO test, and specifically, can be obtained by the method described in the examples. [Tensile strength] The tensile strength (TS) of the high-strength thick steel plate of the present invention is not particularly limited, and the tensile strength TS at the 1/4 position of the plate thickness is preferably 570 MPa or more, more preferably 580 MPa or more, It is more preferably 590 MPa or more. On the other hand, the upper limit of TS is not particularly limited, but the tensile strength TS at a position of 1/4 of the plate thickness is generally 700 MPa or less. [Sheet Thickness] The plate thickness of the high-strength thick steel sheet of the present invention is not particularly limited, and may be any value. However, since the effect of the present invention is more significant as the plate thickness is thicker, the plate thickness is preferably 50 mm or more, more preferably more than 50 mm, more preferably 60 mm or more, and even more preferably 70 mm or more. On the other hand, the upper limit of the plate thickness is not particularly limited, but is generally preferably 100 mm or less. [Manufacturing Method] Next, a method for manufacturing a high-strength thick steel plate according to an embodiment of the present invention will be described. [0073] The high-strength thick steel sheet of the present invention can be produced by hot-rolling a steel having the above-mentioned component composition under specific conditions. Specifically, the following steps (1) and (2) are performed in order. (1) A heating step of heating the steel at a heating temperature of 1000 to 1200 ° C. (2) A step of hot rolling the heated steel into a hot rolled steel sheet. In the aforementioned (2) hot rolling step, the following steps (2-1) and (2-2) are sequentially performed. (2-1) Hot rolling in the austenite recrystallization temperature region at a position where the plate thickness is 1/2 (rolling in the recrystallization region). (2-2) Hot rolling in the austenite non-recrystallization temperature region at the position where the plate thickness is 1/2 (rolling in the non-recrystallization region). [0074] After the hot rolling step (2), the following step (3) may be arbitrarily performed. (3) A cooling step of cooling the aforementioned hot-rolled steel sheet to a cooling stop temperature below 500 ° C at a cooling rate of 3 ° C / s or more. [0075] Furthermore, after the aforementioned (3) cooling step, the following step (4) may be arbitrarily performed. (4) A tempering step of tempering the hot-rolled steel sheet cooled in the aforementioned cooling step at a tempering temperature below Ac 1 point. [0076] The reasons for limiting the conditions of the above steps will be described below. [Heating step] Heating temperature: 1000 to 1200 ° C Before hot rolling, the steel having the above-mentioned component composition is heated. At this time, if the heating temperature is less than 1000 ° C, the rolling time in the austenite recrystallization temperature region cannot be sufficiently ensured. On the other hand, when the heating temperature exceeds 1200 ° C, the austenite grains coarsen, which in turn leads to a decrease in toughness, or a significant loss in oxidation, thereby reducing the yield. Therefore, the heating temperature is set to 1000 to 1200 ° C. From the viewpoint of improving the toughness of the steel sheet, the heating temperature is preferably 1000 to 1170 ° C, and more preferably 1050 to 1170 ° C. [0078] The steel used in the heating step is not particularly limited, and can be produced by any method. For example, a steel sheet (slab) obtained by melting a molten steel having the above-mentioned composition in a converter or the like and continuously casting it can be used. [Hot Rolling] Next, hot rolling is performed. In the hot rolling step, first, (2-1) hot rolling at a position where the plate thickness 1/2 is in the austenite recrystallization temperature range (recrystallization region rolling), and then (2-2) at a plate thickness 1 / The 2 position is hot rolling in the austenite non-recrystallization temperature region (rolling in the non-recrystallization region). In the hot rolling step of rolling end temperature is not particularly limited, but is preferably Ar 3 point or more. [0080] The cumulative reduction ratio of the above-mentioned hot rolling is not particularly limited, but (2-1) the cumulative reduction ratio of the hot rolling (recrystallization temperature region in the austenite recrystallization temperature region at the position where the plate thickness is 1/2) The cumulative reduction ratio is preferably 12% or more. The upper limit of the cumulative reduction ratio in the recrystallization temperature region is not particularly limited, but from the viewpoint of the rolling load, it is preferably 60% or less. (2-2) The cumulative reduction ratio of the hot rolling in the austenite non-recrystallization temperature region at the position where the plate thickness is 1/2 is preferably 45% or more. The upper limit of the cumulative reduction ratio in the non-recrystallization temperature range is not particularly limited, but is preferably 90% or less from the viewpoint of the rolling load. From the viewpoint of collective organization control, it is better to control the cumulative reduction rate in this way. [0081] In the present invention, during the aforementioned (2) hot rolling step, the aforementioned steel is heated from both sides of the front and back surfaces. By the aforementioned heating, the temperature distribution in the thickness direction of the plate can be controlled, and the temperature difference between the surface of the steel plate and the interior can be reduced. As a result, the above-mentioned aggregate structure of the central portion of the plate thickness and the surface of the steel plate can be obtained. In addition, by heating from both sides, vE (-40 ° C) at a position 5 mm from the surface of the steel plate and at a position 1/2 of the thickness of the steel plate can be 250 J or more. [0082] The heating from both the front and back surfaces is preferably performed such that the temperature difference between the surface of the steel and the plate thickness 1/2 position at the time when the heating ends is 30 ° C or less. Thereby, the center of the plate thickness can be rolled at a lower temperature, and the formation of ferrite on the surface can be suppressed. The temperature difference is more preferably 20 ° C or lower, and even more preferably 10 ° C or lower. On the other hand, the smaller the temperature difference, the better, so the lower limit is not particularly limited, but it is preferably 0 ° C or higher. [0083] The timing for performing the heating is not particularly limited as long as it is during the hot rolling step. However, from the viewpoint of the control of the aggregate structure, it is preferable to perform the heating at a point when the cumulative reduction ratio of hot rolling performed at the end of heating is 45% or more, and it is more preferable to perform the rolling before rolling in the non-recrystallized area. More preferably, the rolling is completed before the rolling in the recrystallized region is completed and the rolling in the non-recrystallized region is started. When heating is performed before rolling in the non-recrystallized region, from the viewpoint of temperature control, it is preferable to start rolling in the non-recrystallized region within 30 seconds after completion of the heating. [0084] The heating in the hot rolling step is not particularly limited, and may be performed by any method such as induction heating or furnace heating. [0085] When the temperature difference between the surface of the steel sheet and the thickness 1/2 position is large during the rolling in the non-recrystallized region, only the surface may be heated during the rolling in the non-recrystallized region. [Cooling step] Cooling rate: 3 ° C / s or more. Cooling stop temperature: 500 ° C or less. From the standpoint of maintaining an aggregate structure where the rolling delay is developed, it is preferable to use a cooling rate of 3 ° C / s or more. Cool to a cooling stop temperature below 500 ° C. The upper limit of the cooling rate is not particularly limited, but is preferably 10 ° C / s or less. The lower limit of the cooling stop temperature is not particularly limited, but is preferably 0 ° C or higher. The cooling start temperature in the cooling step is preferably Ar 3 or higher. [Tempering step] Tempering temperature: When tempering treatment is performed after the aforementioned cooling step below Ac 1 point, tempering is preferably performed at a tempering temperature below Ac 1 point. The reason for this is that when the tempering temperature is higher than Ac 1 point, there may be a case where the pressure-delayed and developed collective structure is lost. The lower limit of the tempering temperature is not particularly limited, but is preferably 400 ° C or higher. [0088] In the above description, the temperature at the ½ position of the plate thickness is calculated by heat transfer calculation from the surface temperature of the steel plate measured with a radiation thermometer, or calculated based on a previously measured center temperature. The temperature in the cooling conditions after rolling is the temperature at 1/2 position of the plate thickness. [0089] (Embodiments) Embodiments of the present invention will be described below. The molten steel having each component composition shown in Table 1 was melted in a converter, and a slab was produced by a continuous casting method. Next, the slab thickness is heated, and hot rolling is performed so as to have a plate thickness of 50 to 100 mm. The conditions for the aforementioned heating and hot rolling are shown in Table 2. Subsequently, cooling was performed under the conditions shown in Table 2, and then cooling was performed to obtain a high-strength thick steel plate. Some steel sheets were tempered at the temperatures shown in Table 2 after cooling. [0090] Except for some of the comparative examples, the steel was heated from both sides of the front and back surfaces during the hot rolling. The heating is performed after the rolling in the recrystallized region is completed and before the rolling in the non-recrystallized region is started. At this time, the rolling of the non-recrystallized region was started within 30 seconds after the heating was completed. The aforementioned heating can be performed by furnace heating using an environmental furnace and high-frequency induction heating. [0091] [0092] [0093] For each of the obtained high-strength thick steel plates, toughness, tensile strength, aggregate structure, microstructure, and brittle crack propagation stop characteristics were evaluated by the following methods. The evaluation results are shown in Table 3. [Toughness] In order to evaluate the toughness of the obtained high-strength thick steel plate, a Charpy impact test was performed, and each steel plate was measured at (1) a position 5 mm from the surface of the steel plate, (2) a 1/4 position of the thickness, and (3) a plate. Charpy specific absorption energy vE (-40 ° C) at -40 ° C at 3 locations where the thickness is 1/2. The Charpy impact test is an impact test piece No. 4 (55mm in length, 10mm in width, and 10mm in thickness) specified by JIS (Japanese Industrial Standards). The aforementioned test is performed so that the length direction of the test piece is parallel to the rolling direction of the steel plate. sheet. A test piece for measuring vE (-40 ° C) at a position 5 mm from the surface of the steel plate was removed from the surface of the steel plate after removing scale (black skin) formed on the surface of the steel plate. The thickness of the test piece is 10 mm, so the measurement position of the aforementioned test piece is the center position in the thickness direction of the test piece, that is, a position 5 mm away from the surface of the steel plate in the thickness direction. [Tensile Strength] From the 1/4 position of the thickness of the obtained high-strength thick steel plate, a JIS No. 4 test piece was adopted so that the length direction of the test piece was perpendicular to the rolling direction. Using the aforementioned test piece, a tensile test was performed in accordance with JIS Z 2241 to determine the tensile strength (TS) at a position of 1/4 of the plate thickness. [Assembly Structure] In order to evaluate the aggregate structure of the obtained high-strength thick steel plate, (1) 1/2 position of the plate thickness and (2) {113} <110> azimuth strength of the surface of the steel plate were measured by the following methods. First, the scale formed on the surface of the steel plate was removed, and a sample having a thickness of 1 mm was taken so that (1) a 1/2 thickness of the plate thickness and (2) a depth of 0.5 mm from the surface of the steel plate became the measurement positions. Next, a test piece for X-ray diffraction was prepared by using a surface parallel to the plate surface of the sample taken by mechanical polishing and electrolytic polishing. In addition, for a sample having a thick surface, a surface close to the surface of the steel plate was polished. For each of the obtained test pieces, an X-ray diffraction measurement was performed using an X-ray diffraction device using a Mo-ray source, and (200), (110), and (211) positive electrode point maps were obtained. A three-dimensional crystalline azimuth density function was obtained from the obtained positive point map, thereby calculating the ratio of the {113} <110> azimuth intensity to the random intensity. [Organization] A sample was taken from a position of 1/2 of the plate thickness with a plane parallel to the rolling direction as an observation surface. After mirror-polishing the surface of the sample, an optical microscope photograph of the metal structure exposed by etching was taken, and the area fraction of bainite was evaluated by image analysis. [Brittle crack growth stop characteristics] In order to evaluate the brittle crack growth stop characteristics, a temperature gradient type ESSO test was performed to determine the Kca value of -10 ° C (hereinafter also referred to as Kca (-10 ° C)). A full-thickness test piece was used in the aforementioned temperature gradient type ESSO test. [0099] As can be understood from the results shown in Table 3, the high-strength thick steel plates satisfying the conditions of the present invention have a vE (-40 ° C.) of 5 mm from the surface of the steel plate, 1/2 of the plate thickness, and 1/4 of the plate thickness. It is 250J or more and Kca (-10 ° C) is 7000N / mm 3/2 or more. It has excellent brittle crack propagation stop characteristics. On the other hand, in the high-strength thick steel plate of the comparative example that did not satisfy the conditions of the present invention, at least one of vE (-40 ° C) and Kca (-10 ° C) at a position of 1/4 of the plate thickness deteriorated. [0100]