公开(公告)号：US09234268B2

公开(公告)日：2016-01-12

申请号：US14234826

申请日：2012-07-27

申请人： Hiroyuki Kawata ,  Naoki Maruyama ,  Akinobu Murasato ,  Akinobu Minami ,  Takeshi Yasui ,  Takuya Kuwayama ,  Shigeru Yonemura

发明人： Hiroyuki Kawata ,  Naoki Maruyama ,  Akinobu Murasato ,  Akinobu Minami ,  Takeshi Yasui ,  Takuya Kuwayama ,  Shigeru Yonemura

IPC分类号： B32B15/00 ,  C23C2/02 ,  C23C2/28 ,  B32B15/01 ,  C22C38/00 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C21D8/04 ,  C21D9/48 ,  C21D8/02 ,  C23C2/06 ,  C23C2/26 ,  C22C38/12 ,  C22C38/14 ,  C22C38/16 ,  C22C38/34 ,  C22C38/38 ,  C22C18/00

CPC分类号： C23C2/02 ,  B32B15/013 ,  C21D8/0263 ,  C21D8/041 ,  C21D8/0436 ,  C21D8/0473 ,  C21D9/48 ,  C21D2211/001 ,  C21D2211/002 ,  C21D2211/005 ,  C21D2211/008 ,  C22C18/00 ,  C22C38/001 ,  C22C38/002 ,  C22C38/005 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/12 ,  C22C38/14 ,  C22C38/16 ,  C22C38/34 ,  C22C38/38 ,  C23C2/06 ,  C23C2/26 ,  C23C2/28 ,  Y10T428/12611 ,  Y10T428/12799

摘要： The present invention provides a high-strength galvanized steel sheet with maximum tensile strength of 900 MPa or more. The high-strength galvanized steel sheet has an alloyed galvanized layer formed on a surface of a base steel sheet containing predetermined amounts of C, Si, Mn, P, S, Al, N, O with a balance being constituted of iron and inevitable impurities, in which in a structure of the base steel sheet, retained austenite is limited to 8% or less in volume fraction, kurtosis K* of the hardness distribution between 2% hardness and 98% hardness is −0.30 or less, a ratio between Vickers hardness of surface layer of the base steel sheet and Vickers hardness of ¼ thickness of the base steel sheet is 0.35 to 0.70, and a content of iron in the alloyed galvanized layer is 8 to 12% in mass %.

摘要翻译： 本发明提供一种抗拉强度为900MPa以上的高强度镀锌钢板。 高强度镀锌钢板具有在含有规定量的C，Si，Mn，P，S，Al，N，O的基础钢板的表面上形成的合金镀锌层，余量由铁和不可避免的杂质构成 其中，在基体钢板的结构中，残留奥氏体的体积分数限制在8％以下，2％硬度与98％硬度之间的硬度分布的峰度K *为-0.30以下，维氏 基体钢板的表面层的硬度和基体钢板的1/4厚度的维氏硬度为0.35〜0.70，合金化镀锌层的铁含量为8〜12质量％。

公开(公告)号：US20140212684A1

公开(公告)日：2014-07-31

申请号：US14234826

申请日：2012-07-27

申请人： Hiroyuki Kawata ,  Naoki Maruyama ,  Akinobu Murasato ,  Akinobu Minami ,  Takeshi Yasui ,  Takuya Kuwayama ,  Shigeru Yonemura

发明人： Hiroyuki Kawata ,  Naoki Maruyama ,  Akinobu Murasato ,  Akinobu Minami ,  Takeshi Yasui ,  Takuya Kuwayama ,  Shigeru Yonemura

IPC分类号： C23C2/02 ,  C21D8/02

CPC分类号： C23C2/02 ,  B32B15/013 ,  C21D8/0263 ,  C21D8/041 ,  C21D8/0436 ,  C21D8/0473 ,  C21D9/48 ,  C21D2211/001 ,  C21D2211/002 ,  C21D2211/005 ,  C21D2211/008 ,  C22C18/00 ,  C22C38/001 ,  C22C38/002 ,  C22C38/005 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/12 ,  C22C38/14 ,  C22C38/16 ,  C22C38/34 ,  C22C38/38 ,  C23C2/06 ,  C23C2/26 ,  C23C2/28 ,  Y10T428/12611 ,  Y10T428/12799

摘要： The present invention provides a high-strength galvanized steel sheet with maximum tensile strength of 900 MPa or more. The high-strength galvanized steel sheet has an alloyed galvanized layer formed on a surface of a base steel sheet containing predetermined amounts of C, Si, Mn, P, S, Al, N, O with a balance being constituted of iron and inevitable impurities, in which in a structure of the base steel sheet, retained austenite is limited to 8% or less in volume fraction, kurtosis K* of the hardness distribution between 2% hardness and 98% hardness is −0.30 or less, a ratio between Vickers hardness of surface layer of the base steel sheet and Vickers hardness of ¼ thickness of the base steel sheet is 0.35 to 0.70, and a content of iron in the alloyed galvanized layer is 8 to 12% in mass %.

摘要翻译： 本发明提供一种抗拉强度为900MPa以上的高强度镀锌钢板。 高强度镀锌钢板具有在含有规定量的C，Si，Mn，P，S，Al，N，O的基础钢板的表面上形成的合金镀锌层，余量由铁和不可避免的杂质构成 其中，在基体钢板的结构中，残留奥氏体的体积分数限制在8％以下，2％硬度与98％硬度之间的硬度分布的峰度K *为-0.30以下，维氏 基体钢板的表面层的硬度和基体钢板的1/4厚度的维氏硬度为0.35〜0.70，合金化镀锌层的铁含量为8〜12质量％。

公开(公告)号：US20140170440A1

公开(公告)日：2014-06-19

申请号：US14235681

申请日：2012-07-27

申请人： Hiroyuki Kawata ,  Naoki Maruyama ,  Akinobu Murasato ,  Akinobu Minami ,  Masafumi Azuma ,  Takuya Kuwayama ,  Shigeru Yonemura

发明人： Hiroyuki Kawata ,  Naoki Maruyama ,  Akinobu Murasato ,  Akinobu Minami ,  Masafumi Azuma ,  Takuya Kuwayama ,  Shigeru Yonemura

IPC分类号： B32B15/01 ,  C22C38/58 ,  C22C38/54 ,  C22C38/50 ,  C22C38/48 ,  C22C38/44 ,  C22C38/42 ,  C22C38/16 ,  C22C38/14 ,  C22C38/12 ,  C22C38/08 ,  C22C38/06 ,  C22C38/04 ,  C22C38/02 ,  C22C38/34 ,  C22C38/00 ,  C21D8/02

CPC分类号： B32B15/013 ,  C21D1/19 ,  C21D8/0205 ,  C21D8/0247 ,  C21D8/0263 ,  C21D9/46 ,  C21D2211/002 ,  C21D2211/004 ,  C21D2211/005 ,  C21D2211/008 ,  C22C38/001 ,  C22C38/002 ,  C22C38/005 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/08 ,  C22C38/12 ,  C22C38/14 ,  C22C38/16 ,  C22C38/34 ,  C22C38/42 ,  C22C38/44 ,  C22C38/48 ,  C22C38/50 ,  C22C38/54 ,  C22C38/58 ,  C23C2/02 ,  C23C2/06 ,  C23C2/28 ,  C25D5/36 ,  Y10T428/12799

摘要： High strength steel sheet which secures tensile maximum strength 900 MPa or more high strength while having excellent shapeability, which high strength steel sheet which is excellent in shapeability characterized by having a predetermined composition of ingredients, by the steel sheet structure including a ferrite phase and martensite phase, by the ratio of Cu particles incoherent with the bcc iron being 15% or more with respect to the Cu particles as a whole, by a density of Cu particles in the ferrite phase being 1.0×1018/m3 or more, and by an average particle size of Cu particles in the ferrite phase being 2.0 nm or more.

摘要翻译： 通过具有铁素体相和马氏体的钢板结构，能够确保拉伸最大强度900MPa以上，同时具有优异的成形性的高强度钢板，其特征在于具有规定的成分组成的成形性优异的高强度钢板 相中，相对于Cu颗粒整体来说，与bcc铁不相干的Cu粒子的比例为15％以上，铁素体相中的Cu粒子的密度为1.0×1018 / m3以上， 铁素体相中的Cu粒子的平均粒径为2.0nm以上。

公开(公告)号：US09694561B2

公开(公告)日：2017-07-04

申请号：US14235681

申请日：2012-07-27

申请人： Hiroyuki Kawata ,  Naoki Maruyama ,  Akinobu Murasato ,  Akinobu Minami ,  Masafumi Azuma ,  Takuya Kuwayama ,  Shigeru Yonemura

发明人： Hiroyuki Kawata ,  Naoki Maruyama ,  Akinobu Murasato ,  Akinobu Minami ,  Masafumi Azuma ,  Takuya Kuwayama ,  Shigeru Yonemura

IPC分类号： B32B15/01 ,  C23C2/02 ,  C23C2/06 ,  C23C2/28 ,  C25D5/36 ,  C21D8/02 ,  C21D9/46 ,  C21D1/19 ,  C22C38/00 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/08 ,  C22C38/12 ,  C22C38/14 ,  C22C38/16 ,  C22C38/34 ,  C22C38/42 ,  C22C38/44 ,  C22C38/48 ,  C22C38/50 ,  C22C38/54 ,  C22C38/58

CPC分类号： B32B15/013 ,  C21D1/19 ,  C21D8/0205 ,  C21D8/0247 ,  C21D8/0263 ,  C21D9/46 ,  C21D2211/002 ,  C21D2211/004 ,  C21D2211/005 ,  C21D2211/008 ,  C22C38/001 ,  C22C38/002 ,  C22C38/005 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/08 ,  C22C38/12 ,  C22C38/14 ,  C22C38/16 ,  C22C38/34 ,  C22C38/42 ,  C22C38/44 ,  C22C38/48 ,  C22C38/50 ,  C22C38/54 ,  C22C38/58 ,  C23C2/02 ,  C23C2/06 ,  C23C2/28 ,  C25D5/36 ,  Y10T428/12799

摘要： High strength steel sheet which secures tensile maximum strength 900 MPa or more high strength while having excellent shapeability, which high strength steel sheet which is excellent in shapeability characterized by having a predetermined composition of ingredients, by the steel sheet structure including a ferrite phase and martensite phase, by the ratio of Cu particles incoherent with the bcc iron being 15% or more with respect to the Cu particles as a whole, by a density of Cu particles in the ferrite phase being 1.0×1018/m3 or more, and by an average particle size of Cu particles in the ferrite phase being 2.0 nm or more.

公开(公告)号：US09988700B2

公开(公告)日：2018-06-05

申请号：US14234938

申请日：2012-07-27

申请人： Akinobu Minami ,  Hiroyuki Kawata ,  Akinobu Murasato ,  Yuji Yamaguchi ,  Natsuko Sugiura ,  Takuya Kuwayama ,  Naoki Maruyama ,  Takamasa Suzuki

发明人： Akinobu Minami ,  Hiroyuki Kawata ,  Akinobu Murasato ,  Yuji Yamaguchi ,  Natsuko Sugiura ,  Takuya Kuwayama ,  Naoki Maruyama ,  Takamasa Suzuki

IPC分类号： C23C2/02 ,  C22C38/38 ,  C22C38/34 ,  C22C38/26 ,  C22C38/16 ,  C22C38/00 ,  C22C38/12 ,  C22C38/08 ,  C22C38/06 ,  C22C38/04 ,  C22C38/02 ,  C22C38/14 ,  C21D8/02 ,  C23C2/06 ,  C23C2/28 ,  C21D9/46 ,  C21D1/19 ,  C25D5/36 ,  C25D7/06 ,  C25D3/22

CPC分类号： C23C2/02 ,  C21D1/19 ,  C21D8/0205 ,  C21D8/0247 ,  C21D8/0263 ,  C21D9/46 ,  C21D2211/001 ,  C21D2211/002 ,  C21D2211/005 ,  C22C38/001 ,  C22C38/002 ,  C22C38/005 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/08 ,  C22C38/12 ,  C22C38/14 ,  C22C38/16 ,  C22C38/26 ,  C22C38/34 ,  C22C38/38 ,  C23C2/06 ,  C23C2/28 ,  C25D3/22 ,  C25D5/36 ,  C25D7/0614 ,  Y10T428/12799

摘要： The present invention provides a high-strength steel sheet excellent in shape fixability. The high-strength steel sheet contains C, Si, Mn, P, S, Al, N, and O with predetermined contents, in which a retained austenite phase of 5 to 20% in volume fraction is contained, an amount of solid-solution C contained in the retained austenite phase is 0.80 to 1.00% in mass %, WSiγ is 1.10 times or more WSi*, WMnγ is 1.10 times or more WMn*, and when a frequency distribution is measured with respect to a sum of a ratio between WSi and WSi* and a ratio between WAl and WAl*, a mode value of the frequency distribution is 1.95 to 2.05, and a kurtosis is 2.00 or more.

公开(公告)号：US20140242414A1

公开(公告)日：2014-08-28

申请号：US14234938

申请日：2012-07-27

申请人： Akinobu Minami ,  Hiroyuki Kawata ,  Akinobu Murasato ,  Yuji Yamaguchi ,  Natsuko Sugiura ,  Takuya Kuwayama ,  Naoki Maruyama ,  Takamasa Suzuki

发明人： Akinobu Minami ,  Hiroyuki Kawata ,  Akinobu Murasato ,  Yuji Yamaguchi ,  Natsuko Sugiura ,  Takuya Kuwayama ,  Naoki Maruyama ,  Takamasa Suzuki

IPC分类号： C23C2/02 ,  C22C38/38 ,  C22C38/34 ,  C22C38/26 ,  C22C38/16 ,  C22C38/00 ,  C22C38/12 ,  C22C38/08 ,  C22C38/06 ,  C22C38/04 ,  C22C38/02 ,  C21D8/02 ,  C22C38/14

CPC分类号： C23C2/02 ,  C21D1/19 ,  C21D8/0205 ,  C21D8/0247 ,  C21D8/0263 ,  C21D9/46 ,  C21D2211/001 ,  C21D2211/002 ,  C21D2211/005 ,  C22C38/001 ,  C22C38/002 ,  C22C38/005 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/08 ,  C22C38/12 ,  C22C38/14 ,  C22C38/16 ,  C22C38/26 ,  C22C38/34 ,  C22C38/38 ,  C23C2/06 ,  C23C2/28 ,  C25D3/22 ,  C25D5/36 ,  C25D7/0614 ,  Y10T428/12799

摘要： The present invention provides a high-strength steel sheet excellent in shape fixability. The high-strength steel sheet contains C, Si, Mn, P, S, Al, N, and O with predetermined contents, in which a retained austenite phase of 5 to 20% in volume fraction is contained, an amount of solid-solution C contained in the retained austenite phase is 0.80 to 1.00% in mass %, WSiγ is 1.10 times or more WSi*, WMnγ is 1.10 times or more WMn*, and when a frequency distribution is measured with respect to a sum of a ratio between WSi and WSi* and a ratio between WAl and WAl*, a mode value of the frequency distribution is 1.95 to 2.05, and a kurtosis is 2.00 or more.

摘要翻译： 本发明提供一种形状定型性优异的高强度钢板。 高强度钢板含有预定含量的C，Si，Mn，P，S，Al，N和O，其中含有5〜20体积％的残留奥氏体相，固溶量 残存奥氏体相中含有的C为0.80〜1.00质量％，WSiγ为1.10倍以上WSi *，WMnγ为1.10倍以上WMn *，当测定频率分布相对于 WSi和WSi *以及WA1和WA1 *之间的比率，频率分布的模式值为1.95〜2.05，峰度为2.00以上。

公开(公告)号：US09896751B2

公开(公告)日：2018-02-20

申请号：US14235550

申请日：2012-07-27

申请人： Hiroyuki Kawata ,  Naoki Maruyama ,  Akinobu Murasato ,  Akinobu Minami ,  Takeshi Yasui ,  Yuji Yamaguchi ,  Natsuko Sugiura

发明人： Hiroyuki Kawata ,  Naoki Maruyama ,  Akinobu Murasato ,  Akinobu Minami ,  Takeshi Yasui ,  Yuji Yamaguchi ,  Natsuko Sugiura

IPC分类号： C22C38/38 ,  C23C2/06 ,  C23C2/28 ,  B32B15/01 ,  C21D8/02 ,  C21D9/46 ,  C22C38/00 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/08 ,  C22C38/12 ,  C22C38/14 ,  C22C38/16 ,  C22C38/22 ,  C22C38/26 ,  C22C38/28 ,  C22C38/32 ,  C22C38/34 ,  C23C2/02

CPC分类号： C22C38/38 ,  B32B15/013 ,  C21D8/0205 ,  C21D8/0236 ,  C21D8/0263 ,  C21D9/46 ,  C21D2211/001 ,  C21D2211/002 ,  C21D2211/008 ,  C22C38/001 ,  C22C38/002 ,  C22C38/005 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/08 ,  C22C38/12 ,  C22C38/14 ,  C22C38/16 ,  C22C38/22 ,  C22C38/26 ,  C22C38/28 ,  C22C38/32 ,  C22C38/34 ,  C23C2/02 ,  C23C2/06 ,  C23C2/28 ,  Y10T428/12799

摘要： High strength steel sheet and high strength galvanized steel sheet which are excellent in shapeability which secure a tensile maximum strength 900 MPa or more high strength while obtaining excellent ductility and stretch flangeability, which sheets have predetermined compositions of ingredients, have steel sheet structures which contain volume fraction 1 to 20% of residual austenite phases, and which have martensite transformation points of the residual austenite phases of −60° C. or less.

公开(公告)号：US09551057B2

公开(公告)日：2017-01-24

申请号：US14235155

申请日：2012-07-27

申请人： Hiroyuki Kawata ,  Naoki Maruyama ,  Akinobu Murasato ,  Akinobu Minami ,  Takeshi Yasui

发明人： Hiroyuki Kawata ,  Naoki Maruyama ,  Akinobu Murasato ,  Akinobu Minami ,  Takeshi Yasui

IPC分类号： B32B15/00 ,  C23C2/28 ,  C23C2/06 ,  B32B15/01 ,  C22C18/00 ,  C22C38/00 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C21D8/04

CPC分类号： C23C2/28 ,  B32B15/013 ,  C21D8/041 ,  C21D8/0473 ,  C21D8/0484 ,  C21D2211/001 ,  C21D2211/002 ,  C21D2211/005 ,  C21D2211/008 ,  C22C18/00 ,  C22C38/001 ,  C22C38/002 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C23C2/06 ,  Y10T428/12611 ,  Y10T428/12618 ,  Y10T428/12799

摘要： Provided are: a galvannealed steel sheet, improved in the adhesiveness of a plated layer with a base steel sheet, as a galvannealed steel sheet, prepared by using a high-strength steel sheet as a base material; and a method for producing the galvannealed steel sheet. A galvannealed layer is formed on the base steel sheet including a high-strength steel having a predetermined composition. The average amount of Fe in the galvannealed layer is 8.0 to 12.0%. The absolute value of a difference (ΔFe) between the amount of Fe in the vicinity of an interface with the base steel sheet and the amount of Fe in the vicinity of the external surface of the plated layer in the plated layer is 0.0 to 3.0%.

摘要翻译： 提供：通过使用高强度钢板作为基材而制备的，将镀层与基材钢板的粘合性提高为合金化热浸镀锌钢板的合金化热浸镀锌钢板; 以及合金化热浸镀锌钢板的制造方法。 在包括具有预定组成的高强度钢的基础钢板上形成合金化热浸镀层。 合金化热浸镀层中Fe的平均含量为8.0〜12.0％。 与基体钢板的界面附近的Fe量与镀层的镀层外表面附近的Fe的量之差（ΔFe）的绝对值为0.0〜3.0％ 。

公开(公告)号：US20140162088A1

公开(公告)日：2014-06-12

申请号：US14235550

申请日：2012-07-27

申请人： Hiroyuki Kawata ,  Naoki Maruyama ,  Akinobu Murasato ,  Akinobu Minami ,  Takeshi Yasui ,  Yuji Yamaguchi ,  Natsuko Sugiura

发明人： Hiroyuki Kawata ,  Naoki Maruyama ,  Akinobu Murasato ,  Akinobu Minami ,  Takeshi Yasui ,  Yuji Yamaguchi ,  Natsuko Sugiura

IPC分类号： C22C38/38 ,  C23C2/02 ,  C22C38/34 ,  C22C38/32 ,  C22C38/28 ,  C22C38/26 ,  C22C38/22 ,  C22C38/16 ,  C22C38/14 ,  C22C38/12 ,  C22C38/08 ,  C22C38/06 ,  C22C38/04 ,  C22C38/02 ,  C22C38/00 ,  B32B15/01 ,  C21D8/02

CPC分类号： C22C38/38 ,  B32B15/013 ,  C21D8/0205 ,  C21D8/0236 ,  C21D8/0263 ,  C21D9/46 ,  C21D2211/001 ,  C21D2211/002 ,  C21D2211/008 ,  C22C38/001 ,  C22C38/002 ,  C22C38/005 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/08 ,  C22C38/12 ,  C22C38/14 ,  C22C38/16 ,  C22C38/22 ,  C22C38/26 ,  C22C38/28 ,  C22C38/32 ,  C22C38/34 ,  C23C2/02 ,  C23C2/06 ,  C23C2/28 ,  Y10T428/12799

摘要： High strength steel sheet and high strength galvanized steel sheet which are excellent in shapeability which secure a tensile maximum strength 900 MPa or more high strength while obtaining excellent ductility and stretch flangeability, which sheets have predetermined compositions of ingredients, have steel sheet structures which contain volume fraction 1 to 20% of residual austenite phases, and which have martensite transformation points of the residual austenite phases of −60° C. or less.

摘要翻译： 具有优异的成型性的高强度钢板和高强度镀锌钢板，其具有900MPa以上的拉伸最大强度，同时获得优异的延展性和拉伸凸缘性，这些板具有预定的成分组成，具有包含体积的钢板结构 残余奥氏体相为1〜20％，残留奥氏体相的马氏体相变点为-60℃以下。

公开(公告)号：US10351937B2

公开(公告)日：2019-07-16

申请号：US14235414

申请日：2012-07-27

申请人： Hiroyuki Kawata ,  Naoki Maruyama ,  Akinobu Murasato ,  Akinobu Minami ,  Hajime Hasegawa ,  Chisato Wakabayashi ,  Tsuyoshi Oki

发明人： Hiroyuki Kawata ,  Naoki Maruyama ,  Akinobu Murasato ,  Akinobu Minami ,  Hajime Hasegawa ,  Chisato Wakabayashi ,  Tsuyoshi Oki

IPC分类号： C22C38/38 ,  C22C38/34 ,  C22C38/28 ,  C22C38/22 ,  C22C38/16 ,  C22C38/14 ,  C22C38/12 ,  C22C38/08 ,  C22C38/06 ,  C22C38/04 ,  C22C38/02 ,  C22C38/00 ,  C25D5/48 ,  C23C2/02 ,  C23C2/06 ,  C23C2/28 ,  C21D8/02 ,  C25D5/36 ,  C22C18/00 ,  C22C18/04 ,  B32B15/01 ,  C25D7/06

摘要： The present invention provides a high-strength steel sheet excellent in impact resistance. The high-strength steel sheet contains predetermined contents of C, Si, Mn, P, S, Al, Ti, N, and O, with the balance being iron and inevitable impurities, and has a steel sheet structure in which, in a ⅛ thickness to ⅜ thickness region across ¼ of a sheet thickness, 1 to 8% retained austenite is contained in volume fraction, an average aspect ratio of the retained austenite is 2.0 or less, an amount of solid-solution Mn in the retained austenite is 1.1 times an average amount of Mn or more, and TiN grains having a 0.5 μm average grain diameter or less are contained, and a density of AlN grains with a 1 μm grain diameter or more is 1.0 pieces/mm2 or less, wherein a maximum tensile strength is 900 MPa or more.