Abstract: An austenitic wear-resistant steel plate according to an aspect of the present invention has a predetermined chemical composition, amounts of C and Mn by mass % satisfy ?13.75×C+16.5?Mn??20×C+30, the volume fraction of austenite in a metallographic structure is 40% or more and less than 95%, and the average grain size of the austenite is 40 to 300 ?m.

Abstract: An austenitic wear-resistant steel plate according to an aspect of the present invention has a predetermined chemical composition, amounts of C and Mn by mass % satisfy ?13.75×C+16.5?Mn??20×C+30, the volume fraction of austenite in a metallographic structure is 40% or more and less than 95%, and the average grain size of the austenite is 40 to 300 ?m.

Abstract: A high-tensile steel plate of low acoustic anisotropy and high weldability having yield stress of 450 MPa or greater and tensile strength of 570 MPa or greater and a process for producing the steel plate are provided. The steel has an Si content of 0.10% or less, thereby achieving a volume ratio of island martensite of 3% or less, contains Nb?0.025% and Ti?0.005% so as to satisfy 0.045%?[Nb]+2×[Ti]?0.105%, contains Nb, Ti, C and N in ranges such that the value of A=([Nb]+2×[Ti])×([C]+[N]×12/14) is 0.0022 to 0.0055, and has a steel structure wherein bainite volume ratio is 30% or more and pearlite volume ratio is less than 5%.

Abstract: The present invention provides high strength thick-gauge steel plate superior in weldability and having a tensile strength of 780 MPa or more and provides a method of production of the high strength thick-gauge steel plate by omitting tempering heat treatment in the production. The high strength thick-gauge steel plate of the present invention is high strength thick-gauge steel plate containing, by mass %, C: 0.030 to 0.055%, Mn: 2.4 to 3.5%, P: 0.01% or less, S: 0.0010% or less, Al: 0.06 to 0.10%, B: 0.0005 to 0.0020%, and N: 0.0015 to 0.0060%, having a weld cracking susceptibility parameter Pcm of 0.18% to 0.24%, and comprised mainly of martensite. The method of production of high strength thick-gauge steel plate of the present invention comprises heating a steel slab or cast slab having a predetermined composition of ingredients to 950 to 1100° C., rolling it at 820° C. or more, then starting accelerated cooling from 700° C. or more by a cooling rate of 8 to 80° C.

Abstract: In a method of manufacturing a high tensile strength thick steel plate, a steel slab contains 0.03-0.055% of C, 3.0-3.5% of Mn, and 0.002-0.10% of Al, the amount of Mo is limited to 0.03% or less, the amount of Si is limited to 0.09% or less, the amount of V is limited to 0.01% or less, the amount of Ti is limited to 0.003% or less, the amount of B is limited to 0.0003% or less, and of which Pcm value representing a weld cracking parameter is fallen within the range of 0.20-0.24% and DI value representing a hardenability index is fallen within the range of 1.00-2.60, is heated to 950-1100° C. The steel slab is subjected to a rolling process with a cumulative draft of 70-90% when a temperature is in a range of 850° C. or more, and then, the steel slab is subjected to a rolling process at 780° C. or higher with a cumulative draft of 10-40% when a temperature is in a range of 780-830° C., and subsequently, accelerated cooling at a cooling rate of 8-80° C./sec is started from 700° C.

Abstract: The present invention provides high strength thick-gauge steel plate superior in weldability and having a tensile strength of 780 MPa or more and provides a method of production of the high strength thick-gauge steel plate by omitting tempering heat treatment in the production. The high strength thick-gauge steel plate of the present invention is high strength thick-gauge steel plate containing, by mass %, C: 0.030 to 0.055%, Mn: 2.4 to 3.5%, P: 0.01% or less, S: 0.0010% or less, Al: 0.06 to 0.10%, B: 0.0005 to 0.0020%, and N: 0.0015 to 0.0060%, having a weld cracking susceptibility parameter Pcm of 0.18% to 0.24%, and comprised mainly of martensite. The method of production of high strength thick-gauge steel plate of the present invention comprises heating a steel slab or cast slab having a predetermined composition of ingredients to 950 to 1100° C., rolling it at 820° C. or more, then starting accelerated cooling from 700° C. or more by a cooling rate of 8 to 80° C.

Abstract: In a method of manufacturing a high tensile strength thick steel plate, a steel slab contains 0.03-0.055% of C, 3.0-3.5% of Mn, and 0.002-0.10% of Al, the amount of Mo is limited to 0.03% or less, the amount of Si is limited to 0.09% or less, the amount of V is limited to 0.01% or less, the amount of Ti is limited to 0.003% or less, the amount of B is limited to 0.0003% or less, and of which Pcm value representing a weld cracking parameter is fallen within the range of 0.20-0.24% and DI value representing a hardenability index is fallen within the range of 1.00-2.60, is heated to 950-1100° C. The steel slab is subjected to a rolling process with a cumulative draft of 70-90% when a temperature is in a range of 850° C. or more, and then, the steel slab is subjected to a rolling process at 780° C. or higher with a cumulative draft of 10-40% when a temperature is in a range of 780-830° C., and subsequently, accelerated cooling at a cooling rate of 8-80° C./sec is started from 700° C.

Abstract: A high-tensile steel plate of low acoustic anisotropy and high weldability having yield stress of 450 MPa or greater and tensile strength of 570 MPa or greater and a process for producing the steel plate are provided. The steel has an Si content of 0.10% or less, thereby achieving a volume ratio of island martensite of 3% or less, contains Nb?0.025% and Ti?0.005% so as to satisfy 0.045%?[Nb]+2×[Ti]?0.105%, contains Nb, Ti, C and N in ranges such that the value of A=([Nb]+2×[Ti])×([C]+[N]×12/14) is 0.0022 to 0.0055, and has a steel structure wherein bainite volume ratio is 30% or more and pearlite volume ratio is less than 5%.

Abstract: The present invention provides a high tension steel plate of a tensile strength of 570 MPa or more with a small acoustic anisotropy and with excellent weldability tensile strength and a method of production of steel plate predicated on the high productivity accelerated cooling stop process, which steel sheet is a high tension steel plate with a value of 0.045%?Nb+2Ti?0.105%, A=(Nb+2Ti)×(C+N×12/14) satisfying 0.0025 to 0.0055 and with a steel composition containing bainite in an amount of 30 vol % or more and pearlite+martensite-austenite constituent (MA) in an amount of less than 5 vol %. The steel is heated to 1200° C. or more, rough rolled at 1020° C. or more, then rolled at a cumulative reduction rate from over 920° C. to less than 1020° C. of 15% or less and a cumulative reduction rate from 860 to 920° C. of 20 to 50%, then starting accelerated cooling giving a cooling rate of 2 to 30° C./sec at 800° C. or more, stopping the accelerated cooling at 600 to 700° C., then cooling by 0.4° C./sec or less.

Abstract: A steel plate having a high toughness, low yield ratio and high fatigue strength is provided by preserving the fine metallographical microstructure of martensite or bainite while austenitizing extremely fine portions of the microstructure, and during cooling, dispersing the portions as martensite, retained austenite, cementite or mixture thereof in a tempered martensite or tempered bainite phase.

Abstract: A steel containing predetermined components is rolled in a recrystallization temperature region or a non-recrystallization temperature region of an austenite and is subsequently subjected to repeated hot bending. Alternatively, a surface layer portion is cooled during rolling of the steel described above to an .alpha. single phase or a .gamma./.alpha. dual phase temperature region, rolling is then effected and is finished at the point of time when the surface temperature of the plate rises above an Ac.sub.3 point due to recuperative heat, and repeated bending is carried out. Still alternatively, the steel described above is rolled to a cumulative reduction ratio of at least 20% in the non-recrystallization temperature region and is then subjected to repeated bending. Further alternatively, the surface layer portion is cooled during hot rolling of the steel described above to an .alpha. single or .gamma./.alpha.

Abstract: A method of estimating the properties of a steel product, comprising completing a computation for determining metallurgical phenomena based on information concerning steel ingredients and production conditions in steps from casting to heat treatment to successively determine the state of a metallic structure and estimating the properties of a steel product from the final state of the metallic structure.