TWI523957B - High-strength high-strength thick steel sheet for high-heat input welding for excellent brittle crack propagation characteristics and manufacturing method thereof - Google Patents

Description

脆性龜裂傳播停止特性優異的高熱能輸入焊接用高強度厚鋼板及其製造方法 High-strength thick steel plate for high heat energy input welding excellent in brittle crack propagation stop characteristics and manufacturing method thereof

本發明關於脆性龜裂傳播停止特性(brittle crack arrestability)優異的高熱能輸入焊接(high heat input welding)用高強度厚鋼板(high-strength thick steel plate)及其製造方法，尤其是關於很適用於船舶的板厚為50mm以上的鋼板。 The present invention relates to a high-strength thick steel plate for high heat input welding and a method for producing the same, which are excellent for brittle crack arrestability, and particularly relates to a method suitable for A steel plate with a plate thickness of 50 mm or more.

在船舶之類的大型構造物中，因脆性破壞(brittle fracture)而導致的事故對於經濟方面和環境方面的影響很大。因此，一直都在要求必須提昇安全性，對於所使用的鋼材，則是特別針對於使用溫度時的韌性(toughness)和脆性龜裂傳播停止特性加以要求。 In large structures such as ships, accidents caused by brittle fracture have a great economic and environmental impact. Therefore, it has been demanded that safety must be improved, and the steel to be used is particularly required for toughness and brittle crack propagation stop characteristics at the time of use temperature.

貨櫃船或散裝貨輪之類的船舶，在其構造上，船體外板(outer plate of ship's hull)是使用高強度的厚鋼材。近年來隨著船體的大型化，高強度厚鋼板化更為進展，一般而言，鋼板的脆性龜裂傳播停止特性，是愈隨著鋼板的高強度化或厚鋼材化而愈有變差的傾向，因此 對於脆性龜裂傳播停止特性的要求也更為高度化。 For ships such as container ships or bulk carriers, the outer plate of ship's hull is made of high-strength thick steel. In recent years, with the increase in the size of the hull, the high-strength thick steel plate has progressed. In general, the brittle crack propagation characteristics of the steel plate are more deteriorated as the steel plate is strengthened or thickened. Tendency The requirements for the brittle crack propagation stop characteristics are also more advanced.

作為用來提昇鋼材的脆性龜裂傳播停止特性的技術方案，以往所知的方法，是使Ni含量增加的方法，在液化天然氣(LNG：Liquefied Natural Gas)的儲存槽中，是以商業規模使用了Ni含量9%的鋼。 As a technical solution for improving the brittle crack propagation stop characteristic of steel, a conventionally known method is a method of increasing the Ni content, which is used in a commercial tank of a liquefied natural gas (LNG: Liquefied Natural Gas) storage tank. A steel with a Ni content of 9%.

然而，含Ni量的增加將無可避免地導致成本的大幅上昇，因此很難適用到LNG儲存槽以外的用途。 However, an increase in the amount of Ni will inevitably lead to a substantial increase in cost, and thus it is difficult to apply to applications other than LNG storage tanks.

另一方面，針對於尚未達到LNG的這種程度的極低溫(ultra low temperature)之船舶或管線所使用的板厚未達50mm之較薄的鋼材，則是藉由TMCP法(Thermo-Mechanical Control Process；熱機構控制法)來謀求細粒化，係可利用提昇低溫韌性的作法，來帶給鋼材優異的脆性龜裂傳播停止特性。 On the other hand, for thinner steels with a thickness of less than 50 mm used for ships or pipelines that have not yet reached the level of LNG, the TMCP method (Thermo-Mechanical Control) is used. Process; thermal mechanism control method) In order to achieve fine granulation, it is possible to improve the low-temperature toughness of the steel to impart excellent brittle crack propagation characteristics to the steel.

此外，專利文獻1所提議的技術方案的鋼材，是為了達到：無需增加合金成本即可提昇脆性龜裂傳播停止特性，因此將表層部的組織予以超細微化(ultra fine grained steel)。 Further, the steel material of the technical solution proposed in Patent Document 1 is intended to improve the brittle crack propagation stop characteristic without increasing the alloy cost, and thus the microstructure of the surface layer portion is ultra fine grained steel.

專利文獻1所揭示的鋼材的，是著眼於：脆性龜裂在進行傳播時，發生於鋼材表層部的剪力唇(塑性變形領域；shear-lips)是有提昇脆性龜裂傳播停止特性的效果，乃將剪力唇部分的結晶粒予以細微化，使其吸收具有傳播脆性龜裂的傳播能量作為其特徵之脆性龜裂傳播停止特性優異的鋼材。 The steel material disclosed in Patent Document 1 focuses on the shearing lip (shear-lips) which occurs in the surface layer portion of the steel material when the brittle crack propagates, and has the effect of improving the brittle crack propagation stop characteristic. The crystal grain of the shear lip portion is made fine to absorb the propagation energy having the propagation of the brittle crack as a characteristic steel material having excellent brittle crack propagation stop characteristics.

又，專利文獻1所揭示的，是藉由熱軋後的 控制冷卻來將表層部分予以冷卻到A_r3變態點(transformation point)以下，然後，停止控制冷卻(controlled cooling)，將表層部分予以復熱(recuperate)到達變態點以上的這種工序，反覆地進行一次以上，並在這個期間中，對於鋼材施加輥軋，使其反覆地變態或者形成加工再結晶，因而在表層部分生成超細微的肥粒鐵組織(ferrite structure)或者變韌鐵組織(bainite structure)。 Further, as disclosed in Patent Document 1, the surface layer portion is cooled to below the _Ar3 transformation point by controlled cooling after hot rolling, and then the controlled cooling is stopped to restore the surface portion. The process of recoiler reaching above the metamorphic point is repeated one or more times, and during this period, the steel material is subjected to rolling, which is repeatedly deformed or formed into a process recrystallization, thereby generating ultrafine particles in the surface layer portion. Ferrite structure or bainite structure.

此外，專利文獻2是揭示：為了在以肥粒鐵-波來鐵(pearlite)為主體的細微組織的鋼材中，提昇脆性龜裂傳播停止特性，將鋼材的兩個表面部，以具有50%以上的肥粒鐵組織的層來構成，而且該肥粒鐵組織是具有：相當於圓之粒徑(circle-equivalent average grain size)為5μm以下，長寬比(aspect ratio of the grains)為2以上的肥粒鐵粒，並且抑制肥粒鐵粒徑的大小差異是很重要的。用來抑制大小差異的方法，藉由將最終精製輥軋中的每一次輥軋的最大輥軋率(maximum rolling reduction)設定在12%以下，以資抑制局部性的再結晶現象。 Further, Patent Document 2 discloses that in order to enhance the brittle crack propagation stop characteristic in a steel material having a fine structure mainly composed of ferrite iron-pearlite, the two surface portions of the steel material have 50%. The above-described layer of the ferrite-grained iron structure has a circle-equivalent average grain size of 5 μm or less and an aspect ratio of the grains of 2 It is important that the above ferrite iron particles and the size difference of the ferrite iron particle size are suppressed. The method for suppressing the difference in size is to suppress the local recrystallization phenomenon by setting the maximum rolling rate (maximum rolling reduction) of each rolling in the final refining rolling to 12% or less.

然而，專利文獻1、2所揭示之脆性龜裂傳播停止特性優異的鋼材，是只有將鋼材表層部先暫時予以冷卻之後，再予以復熱，並且藉由在復熱過程中實施加工，以資獲得特定的組織，因此如果是在實際的生產規模的話，則不容易進行控制。尤其是板厚超過50mm的厚鋼材 的情況下，是對於輥軋、冷卻設備的負荷很大的製程。 However, in the steel materials excellent in the brittle crack propagation stop characteristics disclosed in Patent Documents 1 and 2, only the surface layer portion of the steel material is temporarily cooled, and then reheated, and processed by reheating. Obtaining a specific organization, so if it is in the actual production scale, it is not easy to control. Especially thick steel with a thickness of more than 50mm In the case of the rolling, the load on the cooling equipment is very large.

另一方面，專利文獻3揭示的技術，不僅是著眼於肥粒鐵結晶粒的細微化，也著眼於形成在肥粒鐵結晶粒內的次粒子(subgrain)，係屬於用來提昇脆性龜裂傳播停止特性的TMCP法所延伸出來的技術。 On the other hand, the technique disclosed in Patent Document 3 focuses not only on the miniaturization of the ferrite grains, but also on the subgrains formed in the ferrite grains, which are used to enhance brittle cracks. A technique extended by the TMCP method of propagation stop characteristics.

具體而言，針對於板厚為30~40mm的鋼板，不必實施鋼板表層的冷卻與復熱之類的複雜的溫度控制，而是藉由(a)確保細微的肥粒鐵結晶粒的輥軋條件、(b)在鋼材板厚的5%以上的部分，生成細微肥粒鐵組織的輥軋條件、(c)促使集合組織(texture)在細微肥粒鐵發達起來，並且將因加工(輥軋)而導入的轉位(dislocation)利用熱能予以再配置，使其形成次粒子之輥軋條件、(d)可抑制所形成的細微的肥粒鐵結晶粒與細微的次粒子的粒徑的粗大化之冷卻條件，來提昇脆性龜裂傳播停止特性。 Specifically, for a steel plate having a thickness of 30 to 40 mm, it is not necessary to perform complicated temperature control such as cooling and reheating of the surface layer of the steel sheet, but (A) ensuring rolling of fine ferrite iron crystal grains. (b) Rolling conditions for producing a fine ferrite iron structure in a portion of 5% or more of the steel sheet thickness, and (c) promoting the development of fine texture iron in the fine grain iron, and processing (roller) The dislocation introduced by rolling is reconfigured by thermal energy to form a rolling condition of the secondary particles, and (d) the particle size of the fine ferrite particles and the fine subparticles can be suppressed. The coarsened cooling conditions are used to enhance the brittle crack propagation stop characteristics.

此外，也知道有一種在控制輥軋過程中，對於已經變態後的肥粒鐵實施輥軋而令其集合組織發達起來，藉此，以提昇脆性龜裂傳播停止特性的方法。這種方法是在鋼材的破壞面上，促使分離部分(separation)生成於與板面呈平行的方向上，使其緩和脆性龜裂前端的應力，藉此，來提昇對於脆性破壞的阻力。 Further, it is also known that there is a method of improving the brittle crack propagation stop characteristics by rolling the ferrite iron after the deformation has been carried out in the process of controlling the rolling. In this method, the separation surface of the steel is caused to cause the separation to be generated in a direction parallel to the surface of the plate to relax the stress at the front end of the brittle fracture, thereby improving the resistance to brittle fracture.

例如：專利文獻4所揭示的技術，是利用控制輥軋將(110)面X射線強度比(X-ray plane intensity ratio in the(110)plane showing a texture developing degree)設定為2以上，並且將相當於圓之直徑(diameter equivalent to a circle in the crystal grains)為20μm以上的粗大粒子變成10%以下，藉此，以資提昇耐脆性破壞特性。 For example, the technique disclosed in Patent Document 4 uses X-ray plane intensity ratio in the (110) plane showing a texture developing by controlling rolling. The degree is set to 2 or more, and the coarse particles having a diameter equivalent to a circle in the crystal grains of 20 μm or more are made 10% or less, thereby improving the brittle fracture resistance.

專利文獻5所揭示的技術，是作為接頭部之脆性龜裂傳播停止性能優異的焊接構造用鋼，是以板厚內部的輥軋面中的(100)面的X射線面強度比是1.5以上為其特徵的鋼板，是利用因為該集合組織的發達所產生之應力負荷方向與龜裂傳播方向的角度的錯開，而可獲得優異的脆性龜裂傳播停止特性。 The technique disclosed in Patent Document 5 is a steel for welded structure excellent in brittle crack propagation stop performance of the joint portion, and the X-ray surface intensity ratio of the (100) plane in the rolled surface inside the thickness is 1.5 or more. The steel sheet characterized by the use is an offset of the angle between the stress load direction and the crack propagation direction due to the development of the aggregate structure, and excellent brittle crack propagation stop characteristics can be obtained.

[先前技術文獻] [Previous Technical Literature] [專利文獻] [Patent Literature]

專利文獻1：日本特公平7-100814號公報 Patent Document 1: Japanese Patent Publication No. 7-201814

專利文獻2：日本特開2002-256375號公報 Patent Document 2: Japanese Laid-Open Patent Publication No. 2002-256375

專利文獻3：日本特許第3467767號公報 Patent Document 3: Japanese Patent No. 3467767

專利文獻4：日本特許第3548349號公報 Patent Document 4: Japanese Patent No. 3548349

專利文獻5：日本特許第2659661號公報 Patent Document 5: Japanese Patent No. 2659661

專利文獻6：日本特許第3546308號公報 Patent Document 6: Japanese Patent No. 3546308

[非專利文獻] [Non-patent literature]

非專利文獻1：由“井上”等人所發表之「高厚度造船用鋼中的長大脆性龜裂傳播舉動」，日本船舶海洋工學會演講會論文集第3號，2006年，p359~362。 Non-Patent Document 1: "Long and Brittle Crack Propagation in High-Thickness Shipbuilding Steel" published by "Inoue", etc., Proceedings of the Nippon Marine Engineering Society Lecture No. 3, 2006, p359~362.

非專利文獻2：「脆性龜裂傳播停止特性設計指 南」，2009年9月；財團法人日本海事協會。 Non-Patent Document 2: "Design of Brittle Crack Propagation Stop Characteristics" South, September 2009; Japan Maritime Association.

然而，最近之超過6，000TEU(二十呎貨櫃換算單元；Twenty-foot Equivalent Unit)的大型貨櫃船，是使用了板厚超過50mm的厚鋼板。在非專利文獻1，是針對板厚為65mm的鋼板的脆性龜裂傳播停止性能加以評比，根據母材之大型脆性龜裂傳播停止試驗，來報告出脆性龜裂未停止的結果。 However, the recent large container ships with more than 6,000 TEU (Twenty-foot Equivalent Unit) use thick steel plates with a thickness of more than 50 mm. In Non-Patent Document 1, the brittle crack propagation stop performance of a steel sheet having a thickness of 65 mm was evaluated, and the result of the brittle cracking was not stopped based on the large brittle crack propagation stop test of the base material.

又，在供試材的標準ESSO試驗(ESSO test compliant with WES 3003)中，顯示出：使用溫度為-10℃時的Kca值(以下，有時候也稱為Kca(-10℃))係未達到3000N/mm^3/2的結果，這個結果暗示出：在應用了板厚超過50mm的鋼板之船體構造的情況下，安全性的確保將成為其課題。 In addition, in the standard ESSO test (ESSO test compliant with WES 3003) of the test material, it is shown that the Kca value at the use temperature of -10 ° C (hereinafter, sometimes referred to as Kca (-10 ° C)) is not As a result of reaching 3000 N/mm ^3/2 , this result implies that safety is ensured in the case where a hull structure of a steel sheet having a thickness of more than 50 mm is applied.

上述專利文獻1~5所揭示的脆性龜裂傳播停止特性優異的鋼板，由其製造條件和揭示的實驗數據來研判，其是以板厚度最大為50mm程度的鋼板作為主要的對象。如果將專利文獻1~5所揭示的技術應用到厚度超過50mm的厚鋼材的情況下，是否能夠獲得預定的特性尚不明確，針對於船體構造所需之對於板厚方向的龜裂傳播特性，也完全未做驗證。 The steel sheets having excellent brittle crack propagation stop characteristics disclosed in the above Patent Documents 1 to 5 are judged from the production conditions and the experimental data disclosed, and are mainly steel sheets having a thickness of about 50 mm. When the techniques disclosed in Patent Documents 1 to 5 are applied to a thick steel material having a thickness of more than 50 mm, it is not clear whether or not a predetermined characteristic can be obtained, and the crack propagation characteristics for the thickness direction of the hull structure are required. , also did not verify at all.

另一方面，隨著鋼板的增大厚度化，在焊接 施工中應用了例如：潛弧焊接(submerged are welding)、氣電焊接(electrogas arc welding)、電渣焊接(electroslag welding)之類的高效能(high efficiency)的高熱能輸入焊接。一般而言，如果焊接輸入熱量變大的話，焊接熱影響部(Heat Affected Zone；HAZ)的組織會變得粗大，因此，焊接熱影響部的韌性會下降，這是周知的事情。為了解決這種因為高熱能輸入焊接所導致的韌性降低的問題，已經有人開發出高熱能輸入焊接用鋼材，而且已經達到實用化的階段。例如：專利文獻6所揭示的技術，是藉由控制在鋼中晶析出來的TiN，來防止焊接熱影響部組織的粗大化現象(coarsening)，並且藉由分散肥粒鐵生成核來促進晶粒內的肥粒鐵的變態，藉此可使焊接熱影響部高韌性化。然而，高熱能輸入焊接部的焊接熱影響部的韌性雖然優異，但其並未考慮到脆性龜裂傳播停止特性，因此無法得到能夠同時符合兩種特性的鋼材。 On the other hand, as the steel plate increases in thickness, it is welded. High efficiency high heat input welding such as submerged are welding, electrogas arc welding, electroslag welding, etc. is applied during construction. In general, if the welding input heat is increased, the structure of the Heat Affected Zone (HAZ) becomes coarse, and therefore the toughness of the welded heat affected zone is lowered, which is well known. In order to solve the problem of reduced toughness due to high heat input welding, a steel material for high heat input welding has been developed and has reached a practical stage. For example, the technique disclosed in Patent Document 6 prevents the coarsening of the microstructure of the welded heat-affected zone by controlling the TiN crystallized in the steel, and promotes the crystal by dispersing the ferrite iron to form a core. The metamorphosis of the ferrite iron in the grain can thereby make the weld heat affected zone highly tough. However, although the weld heat affected zone of the high heat energy input welded portion has excellent toughness, it does not take into consideration the brittle crack propagation stop characteristic, and thus it is not possible to obtain a steel material which can simultaneously satisfy both characteristics.

因此，本發明之目的是要提供：將鋼成分以及輥軋條件予以最佳化，只要利用可控制板厚方向上的集合組織之在工業上極為簡單的製程，就能夠穩定地製造出來的脆性龜裂傳播停止特性優異的高熱能輸入焊接用高強度厚鋼板及其製造方法。 Accordingly, it is an object of the present invention to provide for the optimization of the steel composition and the rolling conditions, as long as the brittleness which can be stably produced can be stably produced by an industrially extremely simple process which can control the aggregate structure in the thickness direction. A high-strength thick steel plate for high heat energy input welding excellent in crack propagation stop characteristics and a method for producing the same.

本發明人等，為了達成上述技術課題而不斷努力地研究，終於針對於：雖然屬於大厚度鋼板，還是具 有優異的脆性龜裂傳播停止特性之高強度厚鋼板，獲得下列的創見。 The inventors of the present invention have been working hard to achieve the above-mentioned technical problems, and finally aim at: A high-strength thick steel plate having excellent brittle crack propagation characteristics, and the following original findings were obtained.

1.針對於板厚超過50mm的厚鋼板，進行了標準ESSO試驗。第1圖(a)(b)是以示意圖的方式顯示出：從標準ESSO試驗片1的凹溝2穿入的龜裂3在母材5中，藉由前端形狀4來停止了龜裂傳播的例子。在看到如第1圖(a)所顯示的這種短龜裂的分叉3a的情況下，係被確認出可獲得較高的脆性龜裂傳播停止特性。其原因是被推測為：是因為龜裂的分叉3a而使得應力被緩和的結果。 1. For the thick steel plate with a thickness of more than 50 mm, a standard ESSO test was carried out. Fig. 1 (a) and (b) are schematic views showing that the crack 3 penetrating from the groove 2 of the standard ESSO test piece 1 is stopped in the base material 5 by the front end shape 4 to prevent crack propagation. example of. When the split 3a of such a short crack as shown in Fig. 1(a) is seen, it is confirmed that a high brittle crack propagation stop characteristic can be obtained. The reason for this is that it is presumed that the stress is alleviated due to the bifurcation 3a of the crack.

2.想要獲得上述的破斷面形態，必須形成可使龜裂分叉的組織形態。此處，與以肥粒鐵為主體的鋼組織相較，是以在內部具有封包(packet)等存在的變韌鐵為主體的鋼組織比較有利，此外，將裂開面(100)面集中於對龜裂的進展方向也就是輥軋方向或板寬度方向呈傾斜的方向的作法是有效的。 2. In order to obtain the above-described fractured cross-sectional shape, it is necessary to form a structure in which the crack can be bifurcated. Here, compared with the steel structure mainly composed of the ferrite-grained iron, it is advantageous to have a steel structure mainly composed of a toughened iron existing inside a package, and the surface of the split surface (100) is concentrated. It is effective to perform the direction in which the crack progresses, that is, the direction in which the rolling direction or the sheet width direction is inclined.

3.另一方面，如果過度地提高(100)面的密集度的話，將會從極短的龜裂的分叉產生大的龜裂的分叉。如顯示出船體構造的脆性龜裂傳播停止特性設計指南之非專利文獻2所記載，在標準ESSO試驗中，必須要抑制脆性龜裂的分叉，因此為了要防止龜裂的明顯的分叉，必須要規定面密集度的上限。 3. On the other hand, if the density of the (100) plane is excessively increased, a large crack bifurcation will be generated from the extremely short splitting of the crack. In the standard ESSO test, it is necessary to suppress the bifurcation of the brittle crack, as described in Non-Patent Document 2, which is a design guide for the brittle crack propagation stop characteristic of the hull structure. Therefore, in order to prevent the obvious bifurcation of the crack, The upper limit of the surface density must be specified.

4.將標準ESSO試驗的破斷面予以詳細觀察和解析的結果可以得知，控制會成為龜裂的前端部之板厚中央部 的材質的作法，對於改善脆性龜裂傳播停止特性是有效的，尤其將與板厚中央部的韌性以及集合組織相關的指標，予以符合下列數式(2)的作法是有效的：vTrs_(1/2t)-12×I_{RD//(110)[1/2t]}≦-70．．．數式(2) 4. As a result of detailed observation and analysis of the broken section of the standard ESSO test, it is known that the control becomes the material of the center portion of the thickness of the tip end portion of the crack, and is effective for improving the brittle crack propagation stop characteristic. In particular, it is effective to comply with the following equation (2) with respect to the toughness of the central portion of the plate thickness and the index of the aggregate structure: vTrs _(1/2t) -12×I _{RD//(110)[1/ 2t]} ≦-70. . . Number (2)

在上述數式(2)中，vTrs_(1/2t)：板厚中央部(=1/2t)夏丕衝擊試驗韌脆轉換溫度(℃)；I_{RD//(110)[1/2t]}：板厚中央部(=1/2t)的RD//(110)面的密集度；t是板厚(mm)。 In the above formula (2), vTrs _(1/2t) : central portion of the plate thickness (= 1/2 t), summer impact test, ductile-brittle transition temperature (°C); I _{RD//(110) [1/2t]} : the density of the RD//(110) plane at the center of the plate thickness (=1/2t); t is the plate thickness (mm).

5.此外，藉由處在沃斯田鐵再結晶溫度域的狀態下進行累積輥軋率設為20%以上的輥軋，以謀求組織的細粒化，然後，處在沃斯田鐵未再結晶溫度域的狀態下，進行累積輥軋率設為40~70%，而且最初一道輥軋的輥軋溫度與最後一道輥軋的輥軋溫度的差值在40℃以內的輥軋，藉此，可以控制板厚中央部的集合組織，而可獲得上述的組織。 5. In addition, the rolling mill having a cumulative rolling ratio of 20% or more is placed in the recrystallization temperature range of the Worthite iron to achieve fine granulation of the structure, and then, at Worthite Iron In the state of the recrystallization temperature range, the cumulative rolling ratio is set to 40 to 70%, and the difference between the rolling temperature of the first rolling and the rolling temperature of the last rolling is within 40 ° C. Thereby, the collective organization of the central portion of the thickness can be controlled, and the above-described organization can be obtained.

6.作為用來提昇高熱能輸入焊接部的韌性的手法，促使TiN、CaS與MnS的複合硫化物細微地***，抑制被暴露在焊接的高溫時的晶粒成長，並且在其後的冷卻過程中促進粒內變態，來將室溫下的熱影響部的組織予以細微化的作法是有效的。 6. As a method for improving the toughness of the high heat input welding portion, the composite sulfide of TiN, CaS and MnS is finely split, and the grain growth which is exposed to the high temperature of welding is suppressed, and the subsequent cooling process It is effective to promote intragranular metamorphism to fine-tune the tissue of the heat-affected zone at room temperature.

本發明是依據上述所獲得的創見，進一步地加以檢討之後，開發完成的。亦即，本申請案是包含下列 的五個發明： The present invention has been developed based on the above-mentioned findings and further reviewed. That is, the present application contains the following Five inventions:

1.一種脆性龜裂傳播停止特性優異的高熱能輸入焊接用高強度厚鋼板，其特徵為：其鋼組成分以質量%計，是含有C：0.03~0.15%、Si：0.01~0.5%、Mn：1.40~2.50%、Al：0.005~0.08%、P：0.03%以下、S：0.0005~0.0030%、N：0.0036~0.0070%、Ti：0.004~0.030%、Ca：0.0005~0.0030%，並且Ca、O、S的各含量是符合下列數式(1)的關係，其餘部分是Fe及不可避免的雜質，金屬組織是以變韌鐵為主體，且具有在板厚中央部的RD//(110)面的密集度為1.5~4.0的集合組織，並且在表層部以及板厚中央部的夏丕衝擊試驗韌脆轉換溫度vTrs為-40℃以下，0.30≦(Ca-(0.18+130×Ca)×O)/1.25/S≦0.80．．．數式(1)在數式(1)中，Ca、O、S都是以含量(質量%)來計算。 A high-strength thick steel plate for high thermal energy input welding excellent in brittle crack propagation stop characteristics, characterized in that the steel composition is C% 0.03 to 0.15% and Si: 0.01 to 0.5% in terms of mass%. Mn: 1.40 to 2.50%, Al: 0.005 to 0.08%, P: 0.03% or less, S: 0.0005 to 0.0030%, N: 0.0036 to 0.0070%, Ti: 0.004 to 0.030%, Ca: 0.0005 to 0.0030%, and Ca The contents of O, S are in accordance with the following formula (1), the rest are Fe and inevitable impurities, and the metal structure is mainly composed of toughened iron and has RD// in the central portion of the plate thickness. 110) The density of the surface is 1.5~4.0, and the ductile-brittle transition temperature vTrs in the surface layer and the central portion of the plate thickness is below -40 °C, 0.30 ≦ (Ca-(0.18+130×Ca) ) × O) / 1.25 / S ≦ 0.80. . . Equation (1) in Equation (1), Ca, O, S are based on the content (mass%) is calculated.

2.如第1項所述的脆性龜裂傳播停止特性優異的高熱能輸入焊接用高強度厚鋼板，其中，鋼組成分以質量%計，又含有從Nb：0.05%以下、Cu：1.0%以下、Ni：1.0%以下、Cr：0.5%以下、Mo：0.5%以下、V：0.2%以下、B：0.003%以下、REM(稀土金屬)：0.01%以下，之中所選出的1種或2種以上。 2. The high-strength thick steel plate for high heat energy input welding which is excellent in the brittle crack propagation stop characteristic according to the first aspect, wherein the steel composition component contains Nb: 0.05% or less and Cu: 1.0% by mass%. Hereinafter, one selected from Ni: 1.0% or less, Cr: 0.5% or less, Mo: 0.5% or less, V: 0.2% or less, B: 0.003% or less, and REM (rare earth metal): 0.01% or less. 2 or more types.

3.如第1項或第2項所述的脆性龜裂傳播停止特性 優異的高熱能輸入焊接用高強度厚鋼板，其中，在板厚中央部的夏丕衝擊試驗韌脆轉換溫度以及RD//(110)面的密集度是符合下列數式(2)的關係：vTrs_(1/2t)-12×I_{RD//(110)[1/2t]}≦-70．．．數式(2)在數式(2)中，vTrs_(1/2t)：板厚中央部(1/2t)的夏丕衝擊試驗韌脆轉換溫度(℃)；I_{RD//(110)[1/2t]}為板厚中央部(1/2t)的RD//(110)面的密集度；t為板厚(mm)。 3. The high-strength thick steel plate for high heat energy input welding which is excellent in the brittle crack propagation stop characteristic according to the first or the second item, wherein the ductile-brittle transition temperature and the RD/ in the center portion of the plate thickness are tested. The density of the /(110) plane is in accordance with the following equation (2): vTrs _(1/2t) -12×I _{RD//(110)[1/2t]} ≦-70. . . Equation (2) in Equation _{(2), vTrs (1 /} 2t): center of the thickness (1 / 2t) summer Pi impact tests ductile to brittle transition temperature _{(℃); I RD // (} 110) [ _1/2t] is the density of the RD//(110) plane at the center of the plate thickness (1/2t); t is the plate thickness (mm).

4.一種脆性龜裂傳播停止特性優異的高熱能輸入焊接用高強度厚鋼板的製造方法，其特徵為：將具有如第1項或第2項所述的組成分的鋼素材，加熱到1000~1200℃的溫度，實施將在沃斯田鐵再結晶溫度域與沃斯田鐵未再結晶溫度域時的累積輥軋率的合計值設定在65%以上的輥軋，這個時候，在板厚中央部處於沃斯田鐵再結晶溫度域的狀態下，實施累積輥軋率為20%以上的輥軋，接下來，在板厚中央部處於沃斯田鐵未再結晶溫度域的狀態下，實施累積輥軋率為40~70%的輥軋，而且在前述板厚中央部處於沃斯田鐵未再結晶溫度域的狀態下所實施的輥軋之中，最初一道輥軋的輥軋溫度與最後一道輥軋的輥軋溫度的差值在40℃以內，然後，再以4.0℃/s以上的冷卻速度，進行冷卻直到450℃以下。 4. A method for producing a high-strength thick steel sheet for high heat energy input welding which is excellent in brittle crack propagation stop characteristics, characterized in that a steel material having a composition as described in the first or second item is heated to 1000 At a temperature of 1200 ° C, the total value of the cumulative rolling ratio at the time of the recrystallization temperature of the Worthite iron and the non-recrystallization temperature of the Worthite iron is set to be 65% or more, at this time, in the plate. In the state in which the center portion of the thick portion is in the recrystallization temperature range of the Worthite iron, the rolling having a cumulative rolling ratio of 20% or more is performed, and then, in the state where the center portion of the sheet thickness is in the unrecrystallized temperature range of the Worthite iron Rolling in which the cumulative rolling ratio is 40 to 70%, and the rolling of the first rolling is performed in the rolling performed in the state where the center portion of the sheet thickness is in the unrecrystallized temperature range of the Worthite iron. The difference between the temperature and the rolling temperature of the last rolling is within 40 ° C, and then cooling is carried out at a cooling rate of 4.0 ° C / s or more until 450 ° C or less.

5.如第4項所述的脆性龜裂傳播停止特性優異的高熱能輸入焊接用高強度厚鋼板的製造方法，其中，加速冷卻到達450℃以下之後，又具有：回火到達A_C1點以下的溫度的回火工序。 5. The method for producing a high-strength thick steel plate for high heat energy input welding which is excellent in the brittle crack propagation stop characteristic according to the item 4, wherein after the accelerated cooling reaches 450 ° C or lower, the tempering reaches the point below the A _C1 point. The tempering process of the temperature.

根據本發明，係在板厚方向上，適度地控制集合組織，而可獲得脆性龜裂傳播停止特性優異的高熱能輸入焊接用高強度厚鋼板及其製造方法。將本發明應用在板厚為50mm以上，較佳為板厚超過50mm，更佳為板厚55mm以上，更優為板厚60mm以上的鋼板的作法，是對於習知技術的鋼，可以發揮更顯著的優越性，因此是很有效的。並且，例如在造船領域中，藉由將本發明應用在大型的貨櫃船、散裝貨輪上的強力甲板部構造中的艙口圍板或甲板構件的話，可對於提昇船舶的安全性具有貢獻，在產業上極有用處。 According to the present invention, the aggregate structure is appropriately controlled in the thickness direction, and a high-strength thick steel sheet for high heat energy input welding excellent in brittle crack propagation stop characteristics and a method for producing the same can be obtained. The present invention is applied to a steel sheet having a thickness of 50 mm or more, preferably a thickness of more than 50 mm, more preferably a thickness of 55 mm or more, and more preferably a thickness of 60 mm or more, which is a steel of the prior art and can be used more. Significant superiority, so it is very effective. Moreover, for example, in the field of shipbuilding, by applying the present invention to a hatch coaming or deck member in a strong deck structure on a large container ship or a bulk carrier, it is possible to contribute to the safety of the ship. The industry is extremely useful.

1‧‧‧標準ESSO試驗片 1‧‧‧Standard ESSO test piece

2‧‧‧凹溝 2‧‧‧ groove

3‧‧‧龜裂 3‧‧‧ cracking

3a‧‧‧分叉 3a‧‧‧ fork

4‧‧‧前端形狀 4‧‧‧ front end shape

5‧‧‧母材 5‧‧‧Material

第1圖是以示意圖方式來顯示出：板厚超過50mm的厚鋼板之標準ESSO試驗的破斷面形態，第1圖(a)是將試驗片由平面側來進行觀察時的圖；第1圖(b)是顯示試驗片的破斷面的圖。 Fig. 1 is a schematic cross-sectional view showing a standard ESSO test of a thick steel plate having a thickness of more than 50 mm, and Fig. 1 (a) is a view showing the test piece from the plane side; Figure (b) is a view showing a broken section of the test piece.

在本發明中，是制定了：1.鋼組成分；2.板厚表層部以及中央部的韌性與集合組織；3.金屬組織；以及4.製造條件。 In the present invention, it is formulated: 1. steel composition; 2. toughness and aggregate structure of the surface layer portion and the central portion; 3. metal structure; and 4. manufacturing conditions.

1.鋼組成分 Steel composition

以下將說明在本發明中的較佳化學成分。在說明中，%是表示質量%。 Preferred chemical compositions in the present invention will be explained below. In the description, % means mass%.

C：0.03~0.15% C: 0.03~0.15%

C是用來提昇鋼的強度之元素，在本發明中，為了確保所期望的強度，必須的含量是0.03%以上。另一方面，若超過0.15%的話，不僅是焊接性會惡化，對於韌性也會有不良影響。因此，將C含量選定在0.03~0.15%的範圍。較好是0.05~0.15%。 C is an element for increasing the strength of the steel. In the present invention, in order to secure the desired strength, the necessary content is 0.03% or more. On the other hand, when it exceeds 0.15%, not only the weldability will deteriorate, but also the toughness will be adversely affected. Therefore, the C content is selected in the range of 0.03 to 0.15%. It is preferably 0.05 to 0.15%.

Si：0.01~0.5% Si: 0.01~0.5%

Si是可以有效地當作脫氧元素以及鋼的強化元素。但是，若含量未達0.01%的話，不具有其效果。另一方面，若超過0.5%的話，不僅會損及鋼的表面性狀，韌性也會極端地惡化。因此將其添加量選定在0.01~0.5%。較好是0.02~0.45%的範圍。 Si is a strengthening element that can be effectively used as a deoxidizing element and steel. However, if the content is less than 0.01%, it does not have an effect. On the other hand, if it exceeds 0.5%, not only the surface properties of steel but also the toughness will be extremely deteriorated. Therefore, the amount of addition is selected to be 0.01 to 0.5%. It is preferably in the range of 0.02 to 0.45%.

Mn：1.40~2.50% Mn: 1.40~2.50%

Mn是添加作為強化元素。如果小於1.40%的話，其 效果不夠充分。另一方面，若超過2.50%的話，會導致焊接性變差，鋼材的成本也會上昇。因此，將Mn含量選定在1.40~2.50%。較好是1.42~2.40%的範圍。 Mn is added as a strengthening element. If it is less than 1.40%, its The effect is not enough. On the other hand, if it exceeds 2.50%, the weldability is deteriorated, and the cost of the steel material also rises. Therefore, the Mn content is selected to be 1.40 to 2.50%. It is preferably in the range of 1.42 to 2.40%.

P：0.03%以下 P: 0.03% or less

P若超過0.03%的話，會導致焊接部的韌性變差。因此，將其上限選定在0.03%。更好是0.02%以下。 If P exceeds 0.03%, the toughness of the welded portion may be deteriorated. Therefore, the upper limit is selected to be 0.03%. More preferably, it is 0.02% or less.

S：0.0005~0.0030% S: 0.0005~0.0030%

為了生成所需的CaS或MnS，S含量必須為0.0005%以上。另一方面，若超過0.0030%的話，將會導致母材的韌性變差。因此，將S含量選定在0.0005~0.0030%。更好是在0.0006~0.0025%的範圍。 In order to produce the desired CaS or MnS, the S content must be 0.0005% or more. On the other hand, if it exceeds 0.0030%, the toughness of the base material will be deteriorated. Therefore, the S content is selected to be 0.0005 to 0.0030%. More preferably, it is in the range of 0.0006 to 0.0025%.

Al：0.005~0.08% Al: 0.005~0.08%

Al是具有脫氧劑的作用，為了達到這種作用，其含量必須是0.005%以上。但是，含量若超過0.08%的話，會使韌性變差，並且在焊接之後，也會使焊接金屬部的韌性變差。因此，將Al含量限定在0.005~0.08%的範圍。較好是0.02~0.06%。 Al has a function as a deoxidizer, and in order to achieve such an effect, the content must be 0.005% or more. However, if the content exceeds 0.08%, the toughness is deteriorated, and the toughness of the welded metal portion is also deteriorated after the welding. Therefore, the Al content is limited to the range of 0.005 to 0.08%. It is preferably 0.02 to 0.06%.

Ti：0.004~0.030% Ti: 0.004~0.030%

藉由微量地添加Ti來形成氮化物、碳化物、或碳氮化物，以資抑制在焊接熱影響部之沃斯田鐵的粗大化現 象，及/或作為肥粒鐵變態核來促進肥粒鐵變態，藉此，可具有將結晶粒予以細微化而提昇母材韌性的效果。該效果是可藉由0.004%以上的添加而獲得。但是，含量超過0.030%的話，則會因為TiN粒子的粗大化，導致母材及焊接熱影響部的韌性變差。因此，將Ti含量選定在0.004~0.030%的範圍。較好是0.006~0.028%的範圍。 By adding a small amount of Ti to form a nitride, a carbide, or a carbonitride, it is possible to suppress the coarsening of the Worthite iron in the heat affected portion of the weld. For example, and/or as a fermented iron iron metamorphic nucleus to promote the ferrite and iron metamorphosis, thereby having the effect of miniaturizing the crystal grains to enhance the toughness of the base material. This effect can be obtained by addition of 0.004% or more. However, when the content is more than 0.030%, the toughness of the base material and the welded heat-affected zone is deteriorated due to the coarsening of the TiN particles. Therefore, the Ti content is selected in the range of 0.004 to 0.030%. It is preferably in the range of 0.006 to 0.028%.

N：0.0036~0.0070% N: 0.0036~0.0070%

N是用來確保必要量的TiN所必要的元素。若含量未達0.0036%的話，無法獲得充分的TiN量，焊接部韌性會變差。若含量超過0.0070%的話，在承受到焊接的熱周期時，TiN將會再固溶，而生成過多的固溶N，將導致韌性明顯變差。因此，將N含量選定在0.0036~0.0070%。較好是在0.0038~0.0065%的範圍。 N is an element necessary to ensure the necessary amount of TiN. If the content is less than 0.0036%, a sufficient amount of TiN cannot be obtained, and the toughness of the welded portion is deteriorated. If the content exceeds 0.0070%, TiN will re-dissolve when subjected to the thermal cycle of welding, and excessive solid solution N will be formed, which will cause the toughness to be significantly deteriorated. Therefore, the N content is selected to be 0.0036 to 0.0070%. It is preferably in the range of 0.0038 to 0.0065%.

Ca：0.0005~0.0030% Ca: 0.0005~0.0030%

Ca元素是藉由將S予以固定下來，而具有改善韌性的效果。想要發揮這種效果，Ca含量必須為0.0005%以上。但是，若含量超過0.0030%的話，該效果會趨於飽和。因此，在本發明中，將Ca含量限定在0.0005~0.0030%的範圍。較好是在0.0007~0.0028%的範圍。 The Ca element has an effect of improving toughness by fixing S. In order to exert this effect, the Ca content must be 0.0005% or more. However, if the content exceeds 0.0030%, the effect tends to be saturated. Therefore, in the present invention, the Ca content is limited to the range of 0.0005 to 0.0030%. It is preferably in the range of 0.0007 to 0.0028%.

在本發明中，必須符合下列數式(1)的關係： 0.30≦(Ca-(0.18+130×Ca)×O)/1.25/S≦0.80．．．數式(1) In the present invention, the relationship of the following formula (1) must be satisfied: 0.30 ≦ (Ca - (0.18 + 130 × Ca) × O) / 1.25 / S ≦ 0.80. . . Number (1)

在數式(1)中，Ca、O、S是以含量(質量%)來計算。Ca及S的含量必須符合數式(1)的關係。這種情況下，會變成在CaS上有MnS晶析出來之複合硫化物的形態。這種複合硫化物是具有作為肥粒鐵變態核的功能，使得焊接熱影響部的組織細微化而可提昇焊接熱影響部的韌性。如果(Ca-(0.18+130×Ca)×O)/1.25/S的數值未達到0.30的話，不會晶析出來CaS，因此S是以MnS單獨的形態晶析出來。這種MnS在鋼板製造時，會因受到輥軋而被伸長，因而導致母材韌性變差，並且在本發明所著眼的焊接熱影響部，MnS會熔融，所以無法達成細微分散。另一方面，若(Ca-(0.18+130×Ca)×O)/1.25/S的數值超過0.80的話，S幾乎都被Ca所固定住，無法在CaS上晶析出具有肥粒體生成核的作用之MnS，因此無法達成充分的提昇韌性的效果。(Ca-(0.18+130×Ca)×O)/1.25/S的數值的較佳範圍是0.32~0.78%。 In the formula (1), Ca, O, and S are calculated in terms of content (% by mass). The content of Ca and S must conform to the relationship of the formula (1). In this case, it becomes a form of a composite sulfide in which MnS is crystallized on CaS. Such a composite sulfide has a function as a ferrite nucleus of the ferrite, and the microstructure of the welded heat-affected zone is made fine to improve the toughness of the welded heat-affected zone. If the value of (Ca-(0.18+130×Ca)×O)/1.25/S does not reach 0.30, CaS does not crystallize, so S is crystallized in the form of MnS alone. When the steel sheet is produced by the rolling, the MnS is elongated by the rolling, and the toughness of the base material is deteriorated. In the welding heat affected portion of the present invention, MnS is melted, so that fine dispersion cannot be achieved. On the other hand, if the value of (Ca-(0.18+130×Ca)×O)/1.25/S exceeds 0.80, S is almost fixed by Ca, and it is impossible to crystallize the nucleus of the granules formed on the CaS. The effect of MnS is not sufficient to achieve the effect of improving toughness. A preferred range of values for (Ca-(0.18 + 130 × Ca) × O) / 1.25 / S is 0.32 to 0.78%.

以上所說明的是在本發明中的較佳的基本組成分。為了更為提昇特性，亦可含有Nb、Cu、Ni、Cr、Mo、V、B、REM(稀土金屬)之中的1種以上。 What has been described above is a preferred basic component in the present invention. In order to further improve the characteristics, one or more of Nb, Cu, Ni, Cr, Mo, V, B, and REM (rare earth metal) may be contained.

Nb：0.05%以下 Nb: 0.05% or less

Nb會形成NbC在肥粒鐵變態時或再加熱時晶析出來而對於高強度化有幫助。此外，也具有：在進行沃斯田鐵 域的輥軋時，擴大未再結晶溫度域的效果，對於變韌鐵的封包的細粒化有幫助，因此對於改善韌性也有效果。該效果是Nb含量為0.005%以上時才會發揮出來，因此要含有Nb的話，其含量是0.005%以上為宜。然而，若添加量超過0.05%的話，粗大的NbC會晶析出來，反而會導致韌性變差，因此想要含有Nb的話，是將其上限設在0.05%為宜。更好是在0.007~0.045%的範圍。 Nb will form NbC which will crystallize out when the ferrite is metamorphosed or reheated, which is helpful for high strength. In addition, it also has: in the implementation of Vostian Iron In the rolling of the domain, the effect of expanding the non-recrystallization temperature range is enhanced, which contributes to the fine graining of the toughened iron package, and therefore has an effect on improving the toughness. This effect is exhibited when the Nb content is 0.005% or more. Therefore, when Nb is contained, the content is preferably 0.005% or more. However, if the amount added exceeds 0.05%, the coarse NbC crystallizes, and the toughness is deteriorated. Therefore, if Nb is contained, the upper limit is preferably set to 0.05%. More preferably, it is in the range of 0.007 to 0.045%.

Cu、Ni、Cr、Mo Cu, Ni, Cr, Mo

Cu、Ni、Cr、Mo都是可提昇鋼的淬火硬化性的元素。對於提昇輥軋後的強度有直接的幫助，並且可添加用來提昇：韌性、高溫強度、或耐氣候性之類的功能。這些效果，必須要含有0.01%以上時才會發揮作用，因此想要含有的話，設定在0.01%以上為宜。然而，過度地含有的話，韌性和焊接性會變差，因此想要含有的話，係將各自的上限設成Cu：1.0%、Ni：1.0%、Cr：0.5%、Mo：0.5%為宜。更好的是在Cu：0.02~0.95%、Ni：0.02~0.95%、Cr：0.02~0.46%、Mo：0.02~0.46%的範圍。 Cu, Ni, Cr, and Mo are all elements that can improve the quench hardenability of steel. It is directly helpful in improving the strength after rolling, and can be added to enhance functions such as toughness, high temperature strength, or weather resistance. These effects are required to be contained in an amount of 0.01% or more. Therefore, if it is desired to be contained, it is preferably set to 0.01% or more. However, if it is excessively contained, the toughness and the weldability are deteriorated. Therefore, if it is desired to contain it, it is preferable to set the upper limit to Cu: 1.0%, Ni: 1.0%, Cr: 0.5%, and Mo: 0.5%. More preferably, it is in the range of Cu: 0.02 to 0.95%, Ni: 0.02 to 0.95%, Cr: 0.02 to 0.46%, and Mo: 0.02 to 0.46%.

V：0.2%以下 V: 0.2% or less

V是可形成V(C、N)而具有析出強化作用，係可提昇鋼的強度的元素，想要發揮這種效果的話，只要含有0.001%以上即可。但是，若含量超過0.2%的話，將使得韌性變差。因此，想要含有V的話，其含量設定在0.2% 以下為宜，在0.001~0.10%的範圍更好。 V is an element which can form V (C, N) and has a precipitation strengthening effect, and can increase the strength of steel. If it is desired to exhibit such an effect, it may be 0.001% or more. However, if the content exceeds 0.2%, the toughness is deteriorated. Therefore, if you want to contain V, the content is set at 0.2%. The following is suitable, preferably in the range of 0.001 to 0.10%.

B：0.003%以下 B: 0.003% or less

B是只要微量即可提昇鋼的淬火硬化性之元素。想要發揮這種效果，只要含有0.0005%以上即可。但是，含量若超過0.003%的話，會使焊接部的韌性變差，想要含有B的話，將含量設定在0.003%以下為宜。更好是在0.0006~0.0025%的範圍。 B is an element which enhances the quench hardenability of steel as long as it is traced. If you want to exert this effect, you only need to have 0.0005% or more. However, if the content is more than 0.003%, the toughness of the welded portion may be deteriorated. If it is desired to contain B, the content is preferably set to 0.003% or less. More preferably, it is in the range of 0.0006 to 0.0025%.

REM(稀土金屬)：0.01%以下 REM (rare earth metal): 0.01% or less

REM(稀土金屬)具有可將焊接熱影響部的組織細微化，進而提昇韌性的效果，即使添加也無損本發明的效果，因此可配合需求來進行添加。這種效果是只要含有0.0010%以上的話，就可發揮出來，因此想要添加的話，是含有0.0010%以上為宜。但是，過度添加的話，會形成粗大的夾雜物而使得母材的韌性變差，因此想要添加的話，添加量的上限是設在0.01%為宜。 REM (rare earth metal) has an effect of refining the structure of the heat-affected zone and improving the toughness, and even if it is added, the effect of the present invention is not impaired, so that it can be added in accordance with the demand. This effect is exhibited as long as it is contained in an amount of 0.0010% or more. Therefore, if it is desired to be added, it is preferably contained in an amount of 0.0010% or more. However, if it is excessively added, coarse inclusions are formed and the toughness of the base material is deteriorated. Therefore, if it is desired to add, the upper limit of the amount of addition is preferably 0.01%.

此外，O是當作不可避免的雜質的雜質含在鋼中，會使鋼的清淨度降低。因此，在本發明中，儘量減少含O量為宜。尤其是如果O含量超過0.0050%的話，CaO系夾雜物會變得粗大化而使得母材韌性變差。因此，將含量設在0.0050%以下。 Further, O is an impurity which is an unavoidable impurity contained in the steel, and the purity of the steel is lowered. Therefore, in the present invention, it is preferred to minimize the amount of O. In particular, if the O content exceeds 0.0050%, the CaO-based inclusions become coarser and the base material toughness deteriorates. Therefore, the content is set to 0.0050% or less.

在本發明中，係使Ca當作CaS晶析出來，因此必須在添加入Ca之前，預先將與Ca的結合力較強的O 的量予以減少，添加Ca之前的殘留含氧量是控制在0.0050%以下為宜。減少殘留含氧量的方法，可採用：加強脫氣的方法、或者投入脫氧劑的方法等。 In the present invention, since Ca is crystallized as CaS, it is necessary to previously add a strong binding force to Ca before adding Ca. The amount is reduced, and the residual oxygen content before adding Ca is preferably controlled to be 0.0050% or less. The method of reducing the residual oxygen content may be a method of enhancing degassing or a method of introducing a deoxidizing agent.

上述的組成分以外的其餘部分是Fe以及不可避免的雜質。 The remainder other than the above components is Fe and unavoidable impurities.

2.板厚表層部以及中央部的韌性與集合組織 2. Resilience and collective organization of the surface layer and the central part of the plate thickness

在本發明中，為了要針對於朝輥軋方向或輥軋直角方向之類的水平方向(鋼板的面內方向)進展的龜裂，提昇龜裂傳播停止特性，乃配合所期望的龜裂傳播停止特性，適切地規定了在板厚表層部以及中央部的韌性、以及在板厚中央部的RD//(100)面的密集度。 In the present invention, in order to promote cracking progressing in the horizontal direction (in-plane direction of the steel sheet) such as the rolling direction or the direction perpendicular to the rolling direction, the crack propagation stop characteristic is improved to match the desired crack propagation. The stop characteristics appropriately define the toughness in the surface layer portion and the center portion of the sheet thickness and the density of the RD//(100) plane in the center portion of the sheet thickness.

首先，母材的韌性良好的這種條件，是用來抑制龜裂的進展之前提條件。在本發明的鋼板中，作為在板厚表層部以及中央部的韌性，是採用將：在板厚表層部以及板厚中央部的夏丕衝擊試驗韌脆轉換溫度vTrs規定為-40℃以下。此外，將板厚中央部的夏丕衝擊試驗韌脆轉換溫度vTrs規定為-50℃以下更好。 First, the condition that the toughness of the base material is good is used to suppress the progress of the crack before the conditions are raised. In the steel sheet according to the present invention, the toughness at the thickness of the surface layer portion and the center portion is set to be -40 ° C or lower in the summer impact test brittle-brittle transition temperature vTrs at the thickness of the surface portion and the thickness of the center portion. Further, it is more preferable to set the summer 丕 impact test ductile-brittle transition temperature vTrs at the center portion of the sheet thickness to -50 ° C or lower.

此外，藉由使得RD//(100)面的集合組織更發達，來將裂開面相對於龜裂主方向朝斜方向集中，藉由使其產生細微的龜裂分叉而具有緩和脆性龜裂前端的應力之效果，如此一來，即可提昇脆性龜裂傳播停止性能。被使用於最近的貨櫃船和散裝貨輪之類的船體外板之板厚超過50mm的厚鋼材，為了確保其構造安全性，想要獲得被 當成目標之Kca(-10℃)≧6000N/mm^3/2的脆性龜裂傳播停止性能的話，必須將在板厚中央部的RD//(110)面的密集度設定在1.5以上，較好是1.7以上。因此，在本發明中，乃將在板厚中央部的RD//(110)面的密集度設定為1.5以上，較好是1.7以上。 In addition, by making the aggregate structure of the RD//(100) plane more developed, the split surface is concentrated obliquely with respect to the main direction of the crack, and the brittle crack is moderated by causing a fine crack bifurcation. The effect of the stress at the front end, in this way, can improve the brittle crack propagation stop performance. In order to ensure the structural safety, it is used to obtain Kca (-10 ° C) ≧ 6000 N/mm ³ as the target for the hull plate of the nearest container ship and bulk carrier. ^{In the case} of the fragile crack propagation stop performance of ^/2 , the density of the RD//(110) plane at the center portion of the thickness must be set to 1.5 or more, preferably 1.7 or more. Therefore, in the present invention, the density of the RD//(110) plane at the central portion of the thickness is set to 1.5 or more, preferably 1.7 or more.

另一方面，在板厚中央部的RD//(110)面的密集度若超過4.0的話，集合組織過度地發達，因此就不會產生細微的龜裂分叉，脆性龜裂會很顯著地分叉開來，就難以利用緩和脆性龜裂前端應力的效果來發揮脆性龜裂傳播停止性能。因此，將板厚中央部的RD//(110)面的密集度，設定在1.5~4.0的範圍。 On the other hand, if the density of the RD//(110) plane at the center of the thickness is more than 4.0, the aggregate structure is excessively developed, so that fine cracking and bifurcation does not occur, and brittle cracking is remarkable. When it is branched, it is difficult to utilize the effect of mitigating the brittle fracture front end stress to exhibit brittle crack propagation stop performance. Therefore, the density of the RD//(110) plane at the center of the thickness is set in the range of 1.5 to 4.0.

此處所稱的板厚中央部的RD//(110)面的密集度，係根據下列方法計算出來的。首先，從板厚中央部採取出板厚為1mm的樣本，針對於與板面呈平行的面進行機械研磨暨電解研磨，以製備成X射線繞射用的試驗片。使用這個試驗片，利用Mo光源，使用X射線繞射裝置來進行X射線繞射測定，求出(200)、(110)及(211)的正極點圖，再從所得到的正極點圖，根據Bunge法來進行計算以求出3次元結晶方位密度函數。接下來，從所獲得的3次元結晶方位密度函數，在以Bunge的標示方式之=0°~90°之5°間隔之合計19個剖面圖中，將相對於輥軋方向，其(110)面是保持平行的方位的3次元結晶方位密度函數的值進行積分，而求得積分值，再將這個積分值，除以上述積分後的方位的個數之 後，將所獲得的數值稱為RD//(110)面的密集度。 The density of the RD//(110) plane at the central portion of the sheet thickness referred to herein is calculated according to the following method. First, a sample having a thickness of 1 mm was taken from the center portion of the plate thickness, and mechanical polishing and electrolytic polishing were performed on a surface parallel to the plate surface to prepare a test piece for X-ray diffraction. Using this test piece, X-ray diffraction measurement was performed using an X-ray diffraction apparatus using a Mo light source, and positive electrode maps of (200), (110), and (211) were obtained, and the obtained positive electrode dot pattern was obtained. The calculation was performed according to the Bunge method to obtain a 3-dimensional crystal orientation density function. Next, from the obtained 3-dimensional crystal azimuthal density function, in the manner of Bunge In the total of 19 cross-sectional views of the 0° interval of =0° to 90°, the value of the 3-dimensional crystal azimuth density function in which the (110) plane is parallel to the rolling direction is integrated with respect to the rolling direction. After the integral value is divided by the number of the positions after the above integration, the obtained value is referred to as the density of the RD//(110) plane.

除了上述的母材韌性以及集合組織的規定之外，在板厚中央部的夏丕衝擊試驗韌脆轉換溫度以及RD//(110)面的密集度是符合下列數式(2)的關係為宜。藉由符合下列數式(2)的關係，可獲得更優異的脆性龜裂傳播停止性能。 In addition to the above-mentioned base material toughness and the regulation of the aggregate structure, the relationship between the ductile-brittle transition temperature and the density of the RD//(110) plane at the center of the plate thickness is in accordance with the following equation (2). should. By satisfying the relationship of the following formula (2), more excellent brittle crack propagation stop performance can be obtained.

vTrs_(1/2t)-12×I_{RD//(110)[1/2t]}≦-70．．．數式(2) vTrs _(1/2t) -12×I _{RD//(110)[1/2t]} ≦-70. . . Number (2)

在數式(2)中，vTrs_(1/2t)：板厚中央部的夏丕衝擊試驗韌脆轉換溫度(℃)；I_{RD//(110)[1/2t]}：板厚中央部的RD//(110)面的密集度；t是板厚(mm)。 In the formula (2), vTrs _(1/2t) : summer impact test at the center of the plate thickness; ductile-brittle transition temperature (°C); I _{RD//(110) [1/2t]} : at the center of the plate thickness The density of the RD//(110) plane; t is the plate thickness (mm).

3.金屬組織 3. Metal structure

為了獲得上述的韌性以及集合組織，在沃斯田鐵未再結晶溫度域中，實施了控制輥軋之後，使其變態成變韌鐵的作法是有效的。在輥軋之後，從沃斯田鐵變態成肥粒鐵的情況下，雖然可以獲得所期目的之韌性，但是從沃斯田鐵變態為肥粒鐵之際，係存在著充分的變態時間，因此所獲得的集合組織會變得雜亂，而無法達成想要的RD//(110)面的密集度為1.5以上，較好為1.7以上之目標值。相對於此，在沃斯田鐵未再結晶溫度域被實施了輥軋 後的組織，在變態成變韌鐵的情況下，變態時間不夠充分，會優先地形成特定方位的集合組織，亦即被執行所謂的多樣的選擇，而可獲得RD//(110)面的密集度為1.5以上，較好為1.7以上之目標值。因此，在輥軋和冷卻後所獲得的金屬組織是以變韌鐵為主體。在本發明中，金屬組織是以變韌鐵為主體的金屬組織，係指：變韌鐵相的面積百分率佔全體的80%以上。其餘部分，肥粒鐵、麻田散鐵(包含：島狀麻田散鐵)、波來鐵等，合計的面積百分率為20%以下的話，是可以被許容的。 In order to obtain the above-mentioned toughness and aggregate structure, it is effective to carry out the process of controlling the rolling into a toughened iron after controlling the rolling in the non-recrystallization temperature range of the Worth. After the rolling, when the Worthite iron is transformed into the ferrite iron, although the toughness of the intended purpose can be obtained, when the Worth iron is transformed into the ferrite iron, there is a sufficient metamorphic time. Therefore, the obtained aggregate structure becomes messy, and the desired RD//(110) plane density cannot be achieved to be 1.5 or more, preferably 1.7 or more. In contrast, the rolling of the Worthite iron in the recrystallization temperature range was carried out. In the latter case, in the case of metamorphosis into toughened iron, the metamorphic time is insufficient, and the collective organization of a specific orientation is preferentially formed, that is, the so-called diverse selection is performed, and the RD//(110) plane is obtained. The density is 1.5 or more, preferably a target value of 1.7 or more. Therefore, the metal structure obtained after rolling and cooling is mainly composed of toughened iron. In the present invention, the metal structure is a metal structure mainly composed of toughened iron, which means that the area percentage of the toughened iron phase accounts for 80% or more of the total. The rest, fat iron, Ma Tian loose iron (including: island-shaped Ma Tian loose iron), Bora iron, etc., the total area percentage of 20% or less, can be allowed.

4.製造條件 4. Manufacturing conditions

以下將說明本發明的較佳製造條件。 Preferred manufacturing conditions of the present invention will be described below.

關於製造條件，是就鋼素材的加熱溫度、熱軋條件、冷卻條件等加以規定為宜。尤其是針對於熱軋，除了在沃斯田鐵再結晶溫度域以及沃斯田鐵未再結晶溫度域的合計的累積輥軋率之外，也再分別針對於：板厚中央部處於沃斯田鐵再結晶溫度域的情況，以及處於沃斯田鐵未再結晶溫度域的情況，規定各自的累積輥軋率，並且規定了板厚中央部處於沃斯田鐵未再結晶溫度域的狀態下所執行的輥軋的溫度條件為宜。藉由規定了這些條件，可以針對厚鋼板的表層部以及板厚中央部的夏丕衝擊試驗韌脆轉換溫度vTrs、板厚中央部的RD//(110)面的密集度，來獲得所期望的數值。 Regarding the manufacturing conditions, it is preferable to specify the heating temperature, the hot rolling conditions, the cooling conditions, and the like of the steel material. In particular, for hot rolling, in addition to the cumulative rolling rate in the Worstian iron recrystallization temperature range and the Worthite iron non-recrystallization temperature range, it is again targeted at: the central portion of the plate thickness at Voss In the case of the recrystallization temperature range of the field iron, and in the case of the non-recrystallization temperature range of the Worthite iron, the respective cumulative rolling ratios are specified, and the central portion of the plate thickness is in the state of the unrecrystallized temperature range of the Worthite iron. The temperature conditions of the rolling performed below are preferably. By specifying these conditions, it is possible to obtain the desired density of the ductile portion of the thick steel plate and the mid-thickness of the center portion of the steel plate at the center of the plate thickness test, the ductile-brittle transition temperature vTrs, and the density of the RD//(110) plane at the center portion of the plate thickness. The value.

首先，利用轉爐等設備來熔製出具有上述的 組成分的熔鋼，利用連續鑄造等方法，製作成鋼素材(鋼胚)。 First, using a converter or the like to melt out the above The molten steel of the component composition is produced into a steel material (steel embryo) by a method such as continuous casting.

接下來，將鋼素材加熱到1000~1200℃的溫度之後才進行熱軋為宜。加熱溫度未達1000℃的話就無法充分確保在沃斯田鐵再結晶溫度域中進行輥軋的時間。此外，若超過1200℃的話，則不僅會使得沃斯田鐵粒粗大化而導致韌性變差，氧化損失也會趨於顯著，製品良率會降低。因此，將加熱溫度設定在1000~1200℃為宜。基於韌性的觀點考量，更好的加熱溫度的範圍是1000~1150℃。 Next, it is preferable to heat the steel material to a temperature of 1000 to 1200 ° C before hot rolling. When the heating temperature is less than 1000 ° C, the time for rolling in the recrystallization temperature range of the Worthite iron cannot be sufficiently ensured. In addition, if it exceeds 1200 ° C, not only will the Worthfield iron particles be coarsened, but the toughness will be deteriorated, the oxidation loss will become conspicuous, and the product yield will be lowered. Therefore, it is preferable to set the heating temperature at 1000 to 1200 °C. Based on the viewpoint of toughness, a better heating temperature range is 1000 to 1150 °C.

在本發明中，係以下列所述的方式來規定熱間輥軋條件以及其後續的冷卻條件為宜。如此一來，可使得在沃斯田鐵未再結晶溫度域被輥軋後的組織變態成變韌鐵，因為這種情況的變態時間並不夠充分，所以特定方位的集合組織被優先地形成，亦即藉由被執行所謂的多樣的選擇(variant selection)，可將RD//(110)面的密集度設定為1.5以上，更好是1.7以上。 In the present invention, it is preferred to specify the hot rolling conditions and the subsequent cooling conditions in the manner described below. In this way, the microstructure after rolling in the unrecrystallized temperature range of the Vostian iron can be transformed into toughened iron, because the metamorphic time of this case is not sufficient, so the aggregate structure of a specific orientation is preferentially formed. That is, by performing so-called variety selection, the density of the RD//(110) plane can be set to 1.5 or more, and more preferably 1.7 or more.

熱軋條件，首先是在板厚中央部處於沃斯田鐵再結晶溫度域的狀態下，執行：累積輥軋率為20%以上的輥軋為宜。藉由這種將累積輥軋率設定在20%以上的作法，沃斯田鐵會成細粒化，最終所獲得的金屬組織也成細粒化，而可提昇韌性。累積輥軋率未達20%的話，沃斯田鐵的細粒化不夠充分，在最終所獲得的金屬組織中，韌性無法提昇。 In the hot rolling condition, first, in the state in which the center portion of the sheet thickness is in the recrystallization temperature range of the Worstian iron, it is preferable to perform rolling with a cumulative rolling ratio of 20% or more. By setting the cumulative rolling ratio to 20% or more, the Worthite iron is finely granulated, and finally the obtained metal structure is finely granulated, and the toughness can be improved. When the cumulative rolling ratio is less than 20%, the fine graining of the Worthite iron is insufficient, and the toughness cannot be improved in the metal structure finally obtained.

接下來，在板厚中央部的溫度處於沃斯田鐵未再結晶溫度域的狀態下，執行：累積輥軋率為40~70%以上的輥軋為宜。藉由將在這個溫度域的累積輥軋率設定在40%以上的作法，可以讓板厚中央部的集合組織充分地發達起來，而可使得在板厚中央部的RD//(110)面的密集度變成1.5以上，更好是1.7以上。 Next, in a state where the temperature in the central portion of the thickness is in the range of the re-recrystallization temperature of the Worthite iron, it is preferable to perform rolling with a cumulative rolling ratio of 40 to 70% or more. By setting the cumulative rolling ratio in this temperature range to 40% or more, the aggregate structure at the center portion of the sheet thickness can be sufficiently developed, and the RD//(110) plane at the center portion of the sheet thickness can be made. The density becomes 1.5 or more, and more preferably 1.7 or more.

又，若在這個溫度域的累積輥軋率超過70%的話，集合組織將會過度地發達，RD//(110)面的密集度將會超過4.0。因此，將累積輥軋率的範圍選定在40~70%。 Also, if the cumulative rolling rate in this temperature range exceeds 70%, the aggregate structure will be excessively developed, and the density of the RD//(110) plane will exceed 4.0. Therefore, the range of the cumulative rolling ratio is selected to be 40 to 70%.

此外，板厚中央部的溫度處於沃斯田鐵未再結晶溫度域的狀態下進行輥軋所耗費的時間，如果太長的話，組織會粗大化，而導致韌性變差。因此，前述之板厚中央部的溫度處於沃斯田鐵未再結晶溫度域的狀態下所進行的輥軋之中，最初一道輥軋的輥軋溫度與最後一道輥軋的輥軋溫度的差值，是保持在40℃以內為宜。這裡所稱的輥軋溫度是指：即將進行輥軋之前的鋼材的板厚中央部的溫度。板厚中央部的溫度，是根據板厚、表面溫度以及熱履歷等，經過模擬計算等方式而求得的。例如：使用差分法，藉由計算板厚方向的溫度分布，來求出鋼板的板厚中央部的溫度。 Further, the temperature in the central portion of the thickness of the sheet is in the state in which the rolling is performed in the state where the Vostian iron is not recrystallized, and if it is too long, the structure is coarsened and the toughness is deteriorated. Therefore, the difference between the rolling temperature of the first rolling and the rolling temperature of the last rolling is performed in the rolling in the state where the temperature of the central portion of the sheet thickness is in the state of the re-recrystallization temperature of the Vostian iron. The value is preferably kept within 40 ° C. The rolling temperature referred to herein means the temperature at the center portion of the thickness of the steel material immediately before the rolling. The temperature at the center of the thickness is obtained by analog calculation or the like based on the thickness, surface temperature, and heat history. For example, the temperature of the center portion of the thickness of the steel sheet is obtained by calculating the temperature distribution in the thickness direction by using the difference method.

上述的沃斯田鐵再結晶溫度域以及沃斯田鐵未再結晶溫度域加在一起之合計的累積輥軋率是設定在65%以上為宜。整體的輥軋率太小的話，組織的輥軋不夠 充分，無法達成韌性以及強度之目標值。藉由將整體的累積輥軋率設定在65%以上的作法，可對於組織確保充分的輥軋量，可達成韌性以及密集度的目標值。 It is preferable that the cumulative rolling ratio of the above-mentioned Worstian iron recrystallization temperature range and the Worstian iron non-recrystallization temperature range is set to be 65% or more. If the overall rolling rate is too small, the rolling of the tissue is not enough. Sufficient, the target value of toughness and strength cannot be achieved. By setting the overall cumulative rolling ratio to 65% or more, a sufficient amount of rolling can be secured to the structure, and a target value of toughness and density can be achieved.

沃斯田鐵再結晶溫度域、以及沃斯田鐵未再結晶溫度域，係可針對於具有該組成分的鋼，進行了改變各種條件的熱履歷暨加工履歷的預備性的實驗，來加以掌握。 In the Vostian iron recrystallization temperature range and the Worthite iron recrystallization temperature range, it is possible to carry out preliminary experiments for changing the heat history and processing history of various conditions for the steel having the composition. grasp.

此外，熱軋結束的溫度則並未特別地限定。基於輥軋效能的觀點考量，是在沃斯田鐵未再結晶溫度域中結束熱軋為宜。 Further, the temperature at the end of hot rolling is not particularly limited. Based on the viewpoint of rolling efficiency, it is preferable to finish hot rolling in the non-recrystallization temperature range of the Worthfield iron.

輥軋結束後的鋼板，再以4.0℃/s以上的冷卻速度來進行冷卻到450℃以下為宜。藉由將冷卻速度設在4.0℃/s以上的作法，組織不會變得粗大化，而且藉由抑制肥粒鐵變態，可獲得細粒的變韌鐵組織，而可獲得所期望目標之優異的韌性和密集度。如果冷卻速度未達4.0℃/s的話，在各個板厚位置，組織的粗大化和肥粒鐵變態會進展，所以不僅是無法獲得所期望的組織，鋼板的強度也下降。 The steel sheet after the completion of the rolling is preferably cooled to 450 ° C or lower at a cooling rate of 4.0 ° C / s or more. By setting the cooling rate to 4.0 ° C / s or more, the structure does not become coarse, and by suppressing the deformation of the ferrite, the tough iron structure of the fine particles can be obtained, and the desired target can be obtained excellent. Resilience and intensity. If the cooling rate is less than 4.0 ° C / s, the coarsening of the structure and the deformation of the ferrite and iron progress at the respective plate thickness positions, so that not only the desired structure cannot be obtained, but also the strength of the steel sheet is lowered.

藉由將冷卻停止溫度設定在450℃以下，可使得變韌鐵變態充分的進行，而可獲得所期望的韌性和密集度。如果冷卻停止溫度高於450℃的話，變韌鐵變態無法充分地進行，因而也會生成肥粒鐵或波來鐵之類的組織，無法獲得本發明所期望目的之以變韌鐵為主體的組織。此外，這些冷卻速度或冷卻停止溫度，是採用鋼板的板厚中 央部的溫度。板厚中央部的溫度是依據：板厚、表面溫度以及冷卻條件等，利用模擬計算等的方式求出來的。例如：利用差分法，計算板厚方向上的溫度分布，而可求出鋼板的板厚中央部的溫度。 By setting the cooling stop temperature to 450 ° C or lower, the toughened iron metamorphosis can be sufficiently performed, and desired toughness and density can be obtained. If the cooling stop temperature is higher than 450 ° C, the toughened iron metamorphosis cannot be sufficiently performed, and thus a structure such as ferrite iron or buck iron is generated, and the toughened iron is not mainly obtained for the purpose of the present invention. organization. In addition, these cooling rates or cooling stop temperatures are in the thickness of the steel plate. The temperature of the central office. The temperature at the center of the thickness is obtained by means of simulation calculation or the like based on the thickness, surface temperature, and cooling conditions. For example, the temperature distribution in the thickness direction can be calculated by the difference method, and the temperature at the center portion of the thickness of the steel sheet can be obtained.

針對於冷卻結束後的鋼板，亦可實施回火處理。藉由實施回火處理，可更為提昇鋼板的韌性。回火溫度是以鋼板平均溫度來設定的，藉由以A_C1點以下的溫度來實施回火處理，可以無損於經由輥軋暨冷卻而獲得的所期望的組織。在本發明中，A_C1點(℃)是根據下列數式而求出來的。 The tempering treatment may be performed on the steel sheet after the cooling is completed. By performing tempering treatment, the toughness of the steel sheet can be further improved. The tempering temperature is set by the average temperature of the steel sheet, and by performing the tempering treatment at a temperature equal to or lower than the point A _C1 , the desired structure obtained by rolling and cooling can be prevented. In the present invention, the A _C1 point (°C) is obtained from the following formula.

A_C1點=751-26.6C+17.6Si-11.6Mn-169Al-23Cu-23Ni+24.1Cr+22.5Mo+233Nb-39.7V-5.7Ti-895B A _C1 point=751-26.6C+17.6Si-11.6Mn-169Al-23Cu-23Ni+24.1Cr+22.5Mo+233Nb-39.7V-5.7Ti-895B

在上述數式中，各元素記號是以鋼中含量(質量%)來計算的，如果未含有的話，就當作0來計算。 In the above formula, each element symbol is calculated based on the content (% by mass) in steel, and if it is not contained, it is calculated as 0.

鋼板的平均溫度也是與板厚中央部的溫度同樣地，是根據板厚、表面溫度以及冷卻條件等，經由模擬計算等方式而求得的。 The average temperature of the steel sheet is also obtained by analog calculation or the like based on the thickness, the surface temperature, the cooling conditions, and the like, similarly to the temperature at the center portion of the thickness.

[實施例] [Examples]

利用轉爐熔製出具有如表1所示的各種組成分的熔鋼(鋼記號A~Q)，利用連續鑄造法製成鋼素材(厚度為250mm或300mm的鋼胚)，經過熱軋形成板厚為55~100mm的鋼板之後，再進行冷卻而獲得No.1~27 的供測試鋼。針對於其中一部分，則是在冷卻後又實施了回火處理。將熱軋條件以及冷卻條件標示於表2。 The molten steel (steel marks A to Q) having various compositions as shown in Table 1 was melted by a converter, and a steel material (a steel blank having a thickness of 250 mm or 300 mm) was formed by a continuous casting method, and a plate was formed by hot rolling. After the steel plate having a thickness of 55 to 100 mm is cooled, it is obtained No. 1 to 27 For testing steel. For some of them, tempering is performed after cooling. The hot rolling conditions and cooling conditions are shown in Table 2.

針對於所製得的厚鋼板，從板厚的1/4部來採取 14mm之日本工業規格JIS14A號的試驗片，而且是以讓試驗片的長軸方向係與輥軋方向形成直角的方式來採取試驗片，並且執行拉伸試驗，測定了降伏強度(YS)、抗拉強度(TS)。 For the thick steel plate produced, take it from 1/4 of the thickness of the plate A test piece of Japanese Industrial Standard JIS 14A of 14 mm, and a test piece was taken in such a manner that the longitudinal direction of the test piece was formed at a right angle to the rolling direction, and a tensile test was performed to measure the fall strength (YS) and the resistance. Pull strength (TS).

此外，為了對於韌性值進行評比，乃從板厚表層部以及板厚中央部(以下的說明中，有時候係將板厚中央部標記為1/2t部)採取日本工業規格JIS4號的衝擊試驗片，而且是以讓試驗片的長軸方向係與輥軋方向呈平行的方式來採取試驗片，然後執行夏丕衝擊試驗，分別求出其夏丕衝擊試驗韌脆轉換溫度(vTrs)。此處的表層部的衝擊試驗片，是將最靠近表面的面，選定為距離鋼板表面1mm深度的面。 In addition, in order to evaluate the toughness value, the impact test of the Japanese Industrial Standard JIS No. 4 was adopted from the surface layer portion and the plate thickness center portion (in the following description, sometimes the center portion of the plate thickness was marked as 1/2 t portion). The test piece was taken in such a manner that the longitudinal direction of the test piece was parallel to the rolling direction, and then the summer impact test was performed to determine the ductile-brittle transition temperature (vTrs) of the summer impact test. Here, the impact test piece of the surface layer portion was a surface which was closest to the surface and was selected to have a depth of 1 mm from the surface of the steel sheet.

對於所製得的厚鋼板中之與輥軋長軸方向呈平行的板厚度方向上的斷面進行鏡面研磨之後，利用蝕刻來使金屬組織暴露出來，再利用光學顯微鏡進行觀察。 After the mirror-polished section of the obtained thick steel plate in the thickness direction parallel to the longitudinal direction of the rolling was mirror-polished, the metal structure was exposed by etching and observed by an optical microscope.

其次，為了對於脆性龜裂傳播停止特性進行評比，乃執行標準ESSO試驗(溫度斜率型ESSO試驗)，來求出-10℃時的Kca值(Kca(-10℃))。 Next, in order to evaluate the brittle fracture propagation stop characteristics, a standard ESSO test (temperature slope type ESSO test) was performed to determine the Kca value (Kca (-10 ° C)) at -10 °C.

此外，以下列方式求出在板厚中央部的RD//(110)面的密集度。首先，從板厚中央部，採取板厚為1mm的樣本，針對於與板面呈平行的面進行機械研磨暨電 解研磨而製備成X射線繞射用的試驗片。使用這種試驗片，採用Mo光源以X射線繞射裝置來實施了X射線繞射測定，求出(200)、(110)以及(211)的正極點圖，從所獲得的正極點圖，利用Bunge法進行計算而求出3次元結晶方位密度函數。其次，從所獲得的3次元結晶方位密度函數，在以Bunge標記方式為=0°~90°之5°間隔之合計共19張剖面圖中，將其(110)面係與輥軋方向呈平行的方位的3次元結晶方位密度函數的值進行積分而求出積分值，再將這個積分值除以前述積分的方位的個數，所獲得的值就被當作RD//(110)面的密集度。 Further, the density of the RD//(110) plane at the center portion of the sheet thickness was obtained in the following manner. First, a sample having a thickness of 1 mm was taken from the center of the plate thickness, and a test piece for X-ray diffraction was prepared by mechanical polishing and electrolytic polishing on a surface parallel to the plate surface. Using this test piece, an X-ray diffraction measurement was performed using an X-ray diffraction apparatus using a Mo light source, and positive electrode maps of (200), (110), and (211) were obtained, from the obtained positive dot map, The three-dimensional crystal orientation density function was obtained by calculation using the Bunge method. Secondly, from the obtained 3 dimensional crystal azimuth density function, in the Bunge mark method In a total of 19 cross-sectional views of the 5° interval of =0° to 90°, the value of the 3-dimensional crystal azimuth density function in which the (110) plane is parallel to the rolling direction is integrated to obtain an integral value. Then, by dividing this integral value by the number of orientations of the aforementioned integrals, the obtained value is taken as the density of the RD//(110) plane.

為了對於高熱能輸入焊接特性進行評比，乃對於供測試鋼板實施了刨邊加工(刨邊角度20°)，使用市售的低溫用鋼用氣電弧焊接用焊條，利用高熱能輸入焊接(300~750kJ/cm)的氣電焊接來製作了焊接部。然後，使用在焊接部形成有2mm的V形凹溝的夏丕衝擊試驗片，求出在試驗溫度-20℃時的吸收能量：vE_-20(3支試驗片的平均值)來當作HAZ韌性值以資評比焊接部的韌性。 In order to evaluate the high heat input welding characteristics, the test steel plate was subjected to planing (planing angle of 20°), and a commercially available low-temperature steel gas arc welding electrode was used, and high heat input welding was used (300~). The welding portion was fabricated by gas welding at 750 kJ/cm. Then, using a Xiayan impact test piece in which a V-shaped groove of 2 mm was formed in the welded portion, the absorbed energy at a test temperature of -20 ° C: vE _-20 (average value of three test pieces) was determined as HAZ. The toughness value is evaluated by the toughness of the welded part.

將這些試驗結果標示於表3。在本發明的範圍內的供測試鋼板(製造編號No.1~11)的情況，Kca(-10℃)是6000N/mm^3/2以上，顯示出優異的脆性龜裂傳播停止性能。又，在高熱能輸入焊接的焊接部的吸收能量：vE_-20≧88J，也顯示出優異的數值。又，將表層部以及板厚中央部的夏丕韌性值(夏丕衝擊試驗韌脆轉換溫度)、 以及RD//(110)密集度係符合數式(2)的關係之供測試鋼板(製造編號No.2~11)與不符合數式(2)的關係之供測試鋼板(製造編號No.1)進行比較可知，係可獲得較高的Kca(-10℃)的數值。此外，這些供測試鋼板(製造編號No.1~11)的金屬組織都是以變韌鐵為主體。 These test results are shown in Table 3. In the case of the test steel sheets (manufacturing Nos. 1 to 11) within the scope of the present invention, Kca (-10 ° C) is 6000 N/mm ^3/2 or more, and exhibits excellent brittle crack propagation stop performance. Moreover, the absorbed energy of the welded portion of the high heat energy input welding: vE _-20 ≧ 88J also showed excellent numerical values. In addition, the test steel plate (manufactured by the relationship between the surface layer portion and the center portion of the thickness of the plate, the summer tamping toughness value (summer impact test ductile-brittle transition temperature), and the RD//(110) density system in accordance with the formula (2) Comparing No. 2 to 11) with the test steel sheet (manufacturing No. 1) which does not satisfy the relationship of the formula (2), it can be seen that a high Kca (-10 ° C) value can be obtained. In addition, the metal structures for the test steel sheets (manufacturing No. 1 to 11) are mainly made of toughened iron.

另一方面，鋼板的組成分雖然落在本發明的較佳範圍內，但是鋼板的製造條件之中的加熱條件、輥軋條件落在本發明的較佳範圍之外的鋼板(製造編號No.20~27)之Kca(-10℃)的數值未達6000N/mm^3/2。鋼板的組成分不符合本發明的條件的供測試鋼板(製造編號No.12~19)，它們的高熱能輸入焊接部的吸收能量：vE_-20為22J以下，因此其效果不及本發明例。 On the other hand, although the composition of the steel sheet falls within the preferred range of the present invention, the heating conditions and the rolling conditions among the manufacturing conditions of the steel sheet fall outside the preferred range of the present invention (manufacturing number No. The value of Kca (-10 °C) of 20~27) is less than 6000N/mm ^3/2 . The composition of the steel sheet is a test steel sheet (manufacturing No. 12 to 19) which does not satisfy the conditions of the present invention, and the energy absorbed by the high heat energy input welded portion: vE _-20 is 22 J or less, and thus the effect is inferior to the example of the present invention.

Claims (5)

一種脆性龜裂傳播停止特性優異的高熱能輸入焊接用高強度厚鋼板，其特徵為：其鋼組成分以質量%計，是含有C：0.03~0.15%、Si：0.01~0.5%、Mn：1.40~2.50%、Al：0.005~0.08%、P：0.03%以下、S：0.0005~0.0030%、N：0.0036~0.0070%、Ti：0.004~0.030%、Ca：0.0005~0.0030%，並且Ca、O、S的各含量是符合下列數式(1)的關係，其餘部分是Fe及不可避免的雜質，金屬組織是以變韌鐵為主體，且具有在板厚中央部的RD//(110)面的密集度為1.5~4.0的集合組織，並且在表層部以及板厚中央部的夏丕衝擊試驗韌脆轉換溫度vTrs為-40℃以下，0.30≦(Ca-(0.18+130×Ca)×O)/1.25/S≦0.80．．．數式(1)在數式(1)中，Ca、O、S都是以含量(質量%)來計算。 A high-strength thick steel plate for high-heat energy input welding excellent in brittle crack propagation stop characteristics, characterized in that the steel composition is C% 0.03 to 0.15%, Si: 0.01 to 0.5%, and Mn: 1.40~2.50%, Al: 0.005~0.08%, P: 0.03% or less, S: 0.0005~0.0030%, N: 0.0036~0.0070%, Ti: 0.004~0.030%, Ca: 0.0005~0.0030%, and Ca, O The content of S is in accordance with the relationship of the following formula (1), the rest is Fe and inevitable impurities, the metal structure is mainly composed of toughened iron, and has RD//(110) at the center of the plate thickness. The density of the surface is 1.5~4.0, and the ductile-brittle transition temperature vTrs in the surface layer and the central portion of the plate thickness is below -40 °C, 0.30 ≦ (Ca-(0.18+130×Ca)× O)/1.25/S≦0.80. . . Equation (1) in Equation (1), Ca, O, S are based on the content (mass%) is calculated. 如申請專利範圍第1項所述的脆性龜裂傳播停止特性優異的高熱能輸入焊接用高強度厚鋼板，其中，鋼組成分以質量%計，又含有從Nb：0.05%以下、Cu：1.0%以下、Ni：1.0%以下、Cr：0.5%以下、Mo：0.5%以下、V：0.2%以下、B：0.003%以下、REM(稀土金屬)：0.01%以下，之中所選出的1種或2種以上。 The high-strength thick steel plate for high heat energy input welding which is excellent in the brittle crack propagation stop characteristic as described in the first aspect of the patent application, wherein the steel composition component contains Nb: 0.05% or less and Cu: 1.0 in mass%. % or less, Ni: 1.0% or less, Cr: 0.5% or less, Mo: 0.5% or less, V: 0.2% or less, B: 0.003% or less, and REM (rare earth metal): 0.01% or less. Or two or more. 如申請專利範圍第1項或第2項所述的脆性龜裂傳播停止特性優異的高熱能輸入焊接用高強度厚鋼板，其 中，在板厚中央部的夏丕衝擊試驗韌脆轉換溫度以及RD//(110)面的密集度是符合下列數式(2)的關係：vTrs_(1/2t)-12×I_{RD//(110)[1/2t]}≦-70．．．數式(2)在數式(2)中，vTrs_(1/2t)：板厚中央部(1/2t)的夏丕衝擊試驗韌脆轉換溫度(℃)；I_{RD//(110)[1/2t]}為板厚中央部(1/2t)的RD//(110)面的密集度；t為板厚(mm)。 High-strength thick steel plate for high-heat energy input welding excellent in brittle crack propagation stop characteristics as described in the first or second aspect of the patent application, wherein the summer 丕 impact test ductile-brittle transition temperature and RD at the center of the plate thickness // The density of the (110) plane is in accordance with the following equation (2): vTrs _(1/2t) -12 × I _{RD / / (110) [1/2t]} ≦ -70. . . Equation (2) in Equation _{(2), vTrs (1 /} 2t): center of the thickness (1 / 2t) summer Pi impact tests ductile to brittle transition temperature _{(℃); I RD // (} 110) [ _1/2t] is the density of the RD//(110) plane at the center of the plate thickness (1/2t); t is the plate thickness (mm). 一種脆性龜裂傳播停止特性優異的高熱能輸入焊接用高強度厚鋼板的製造方法，其特徵為：將具有如請求項1或請求項2所述的組成分的鋼素材，加熱到1000~1200℃的溫度，實施將在沃斯田鐵再結晶溫度域與沃斯田鐵未再結晶溫度域時的累積輥軋率的合計值設定在65%以上的輥軋，這個時候，在板厚中央部處於沃斯田鐵再結晶溫度域的狀態下，實施累積輥軋率為20%以上的輥軋，接下來，在板厚中央部處於沃斯田鐵未再結晶溫度域的狀態下，實施累積輥軋率為40~70%的輥軋，而且在前述板厚中央部處於沃斯田鐵未再結晶溫度域的狀態下所實施的輥軋之中，最初一道輥軋的輥軋溫度與最後一道輥軋的輥軋溫度的差值在40℃以內，然後，再以4.0℃/s以上的冷卻速度，進行冷卻直到450℃以下。 A method for producing a high-strength thick steel plate for high heat energy input welding excellent in brittle crack propagation stop characteristics, characterized in that a steel material having a composition as described in claim 1 or claim 2 is heated to 1000 to 1200 At the temperature of °C, the total value of the cumulative rolling ratio at the time of the recrystallization temperature of the Worthite iron and the non-recrystallization temperature of the Worthite iron is set to be 65% or more. At this time, in the center of the plate thickness. In the state in which the part is in the recrystallization temperature range of the Worthite iron, the rolling having a cumulative rolling ratio of 20% or more is performed, and then, in the state where the center portion of the thickness is in the unrecrystallized temperature range of the Worthite iron, the implementation is carried out. The rolling rate is 40 to 70%, and the rolling temperature of the first rolling is performed in the rolling performed in the state where the center portion of the thickness is in the non-recrystallization temperature range of the Worthite iron. The difference in the rolling temperature of the last rolling is within 40 ° C, and then cooling is carried out at a cooling rate of 4.0 ° C / s or more until 450 ° C or less. 如申請專利範圍第4項所述的脆性龜裂傳播停止特性優異的高熱能輸入焊接用高強度厚鋼板的製造方法， 其中，在加速冷卻到達450℃以下之後，又具有：回火到達A_C1點以下的溫度之回火工序。 A method for producing a high-strength thick steel plate for high heat input welding excellent in brittle crack propagation stop characteristics according to the fourth aspect of the invention, wherein after the accelerated cooling reaches 450 ° C or lower, the tempering reaches A _C1 The tempering process of the temperature below the point.