Composite structure type high tensile strength steel plate, plated plate of composite structure type high tensile strength steel and method for their production

Abstract

The invention proposes a high-strength dual-phase cold rolled steel sheet having an excellent deep drawability, wherein the steel sheet has a composition comprising C: 0.01-0.08 mass %, Si: not more than 2.0 mass %, Mn: not more than 3.0 mass %, P: not more than 0.10 mass %, S: not more than 0.02 mass %, A1: 0.005-0.20 mass %, N: not more than 0.02 mass % and V: 0.01-0.5 mass %, provided that V and C satisfy a relationship of 0.5×C/12≦V/51≦3×C/12, and the remainder being Fe and inevitable impurities, and has a microstructure consisting of a ferrite phase as a primary phase and a secondary phase including martensite phase at an area ratio of not less than 1% to a whole of the microstructure and a high-strength dual-phase galvanized steel sheet comprising a galvanized coating on the above steel sheet as well as a method of producing the same.

1 . A high-strength dual-phase cold rolled steel sheet having an excellent deep drawability, characterized in that the steel sheet has a composition comprising C: 0.01-0.08 mass %, Si: not more than 2.0 mass %, Mn: not more than 3.0 mass %, P: not more than 0.10 mass %, S: not more than 0.02 mass %, Al: 0.005-0.20 mass %, N: not more than 0.02 mass % and V: 0.01-0.5 mass %, provided that V and C satisfy a relationship of 0.5×C/12≦V/51≦3×C/12, and the remainder being Fe and inevitable impurities, and has a microstructure consisting of a ferrite phase as a primary phase and a secondary phase including martensite phase at an area ratio of not less than 1% to a whole of the microstructure.  
     
     
         2 . A high-strength dual-phase cold rolled steel sheet having an excellent deep drawability, characterized in that the steel sheet has a composition comprising C: 0.01-0.08 mass %, Si: not more than 2.0 mass %, Mn: not more than 3.0 mass %, P: not more than 0.10 mass %, S: not more than 0.02 mass %, Al: 0.005-0.20 mass %, N: not more than 0.02 mass % and V: 0.01-0.5 mass % and further comprising not more than 0.3 mass % in total of one or two of Nb: more than 0 mass % but not more than 0.3 mass % and Ti: more than 0 mass % but not more than 0.3 mass %, provided that V, Nb, Ti and C satisfy a relationship of 0.5×C/12≦(V/51+2×Nb/93+2×Ti/48)≦3×C/12, and the remainder being Fe and inevitable impurities, and has a microstructure consisting of a ferrite phase as a primary phase and a secondary phase including martensite phase at an area ratio of not less than 1% to a whole of the microstructure.  
     
     
         3 . A high-strength dual-phase cold rolled steel sheet having an excellent deep drawability according to  claim 2 , wherein the steel sheet comprises not more than 0.3 mass % in total of one or two of Nb: 0.001-0.3 mass % and Ti: 0.001-0.3 mass %.  
     
     
         4 . A high-strength dual-phase cold rolled steel sheet having an excellent deep drawability according to  claim 2 , wherein the steel sheet comprises C: 0.03-0.08 mass %, Si: 0.1-2.0 mass %, Mn: 1.0-3.0 mass %, P: not more than 0.05 mass % and S: not more than 0.01 mass %, provided that V, Nb and Ti satisfy a relationship of 1.5≦(2×Nb/93+2×Ti/48)/(V/51)≦15.  
     
     
         5 . A high-strength dual-phase cold rolled steel sheet having an excellent deep drawability according to any one of claims  1 - 4 , wherein the steel sheet further comprises one or two of the following A-group and B-group: 
 A-group: not more than 2.0 mass % in total of one or two of Cr and Mo;    B-group: not more than 2.0 mass % in total of one or two of Cu and Ni.    
     
     
         6 . A method of producing a high-strength dual-phase cold rolled steel sheet having an excellent deep drawability, which comprises hot rolling a steel slab having a composition comprising C: 0.01-0.08 mass %, Si: not more than 2.0 mass %, Mn: not more than 3.0 mass %, P: not more than 0.10 mass %, S: not more than 0.02 mass %, Al: 0.005-0.20 mass %, N: not more than 0.02 mass % and V: 0.01-0.5 mass %, provided that V and C satisfy a relationship of 0.5×C/12≦V/51≦3×C/12, and the remainder being Fe and inevitable impurities, pickling, cold rolling and then subjecting to a continuous annealing at a temperature range from a A C1  transformation point to a A C3  transformation point.  
     
     
         7 . A method of producing a high-strength dual-phase cold rolled steel sheet having an excellent deep drawability, which comprises hot rolling a steel slab having a composition comprising C: 0.01-0.08 mass %, Si: not more than 2.0 mass %, Mn: not more than 3.0 mass %, P: not more than 0.10 mass %, S: not more than 0.02 mass %, Al: 0.005-0.20 mass %, N: not more than 0.02 mass % and V: 0.01-0.5 mass % and further comprising not more than 0.3 mass % in total of one or two of Nb: more than 0 mass % but not more than 0.3 mass % and Ti: more than 0 mass % but not more than 0.3 mass %, provided that V, Nb, Ti and C satisfy a relationship of 0.5×C/12≦(V/51+2×Nb/93+2×Ti/48)≦3×C/12, and the remainder being Fe and inevitable impurities, pickling, cold rolling and then subjecting to a continuous annealing at a temperature range from a A C1  transformation point to a A C3  transformation point.  
     
     
         8 . A method of producing a high-strength dual-phase cold rolled steel sheet having an excellent deep drawability according to  claim 7 , wherein the steel slab comprises not more than 0.3 mass % in total of one or two of Nb: 0.001-0.3 mass % and Ti: 0.001-0.3 mass %.  
     
     
         9 . A method of producing a high-strength dual-phase cold rolled steel sheet having an excellent deep drawability according to  claim 7 , wherein the steel slab comprises C: 0.03-0.08 mass %, Si: 0.1-2.0 mass %, Mn: 1.0-3.0 mass %, P: not more than 0.05 mass % and S: not more than 0.01 mass %, provided that V, Nb and Ti satisfy a relationship of 1.5≦(2×Nb/93+2×Ti/48)/(V/51)≦15.  
     
     
         10 . A method of producing a high-strength dual-phase cold rolled steel sheet having an excellent deep drawability according to any one of claims  6 - 9 , wherein the steel slab further comprises one or two of the following A-group and B-group: A-group: not more than 2.0 mass % in total of one or two of Cr and Mo; B-group: not more than 2.0 mass % in total of one or two of Cu and Ni.  
     
     
         11 . A high-strength dual-phase galvanized steel sheet having an excellent deep drawability comprising a galvanized coating on the steel sheet as claimed in  claim 1 .  
     
     
         12 . A high-strength dual-phase galvanized steel sheet having an excellent deep drawability comprising a galvanized coating on the steel sheet as claimed in  claim 2 .  
     
     
         13 . A high-strength dual-phase galvanized steel sheet having an excellent deep drawability comprising a galvanized coating on the steel sheet as claimed in  claim 3 .  
     
     
         14 . A high-strength dual-phase galvanized steel sheet having an excellent deep drawability comprising a galvanized coating on the steel sheet as claimed in  claim 4 .  
     
     
         15 . A high-strength dual-phase galvanized steel sheet having an excellent deep drawability comprising a galvanized coating on the steel sheet as claimed in  claim 5 .  
     
     
         16 . A method of producing a high-strength dual-phase galvanized steel sheet having an excellent deep drawability, characterized by subjecting to a galvanization after the continuous annealing at a temperature range from a A C1  transformation point to a A C3  transformation point in the method claimed in  claim 6 .  
     
     
         17 . A method of producing a high-strength dual-phase galvanized steel sheet having an excellent deep drawability according to  claim 16 , characterized by further comprising a continuous annealing step between the cold rolling step and the continuous annealing step at a temperature range from a A C1  transformation point to a A C3  transformation point.  
     
     
         18 . A method of producing a high-strength dual-phase galvanized steel sheet having an excellent deep drawability, characterized by subjecting to a galvanization after the continuous annealing at a temperature range from a A C1  transformation point to a A C3  transformation point in the method claimed in  claim 7 .  
     
     
         19 . A method of producing a high-strength dual-phase galvanized steel sheet having an excellent deep drawability according to  claim 18 , characterized by further comprising a continuous annealing step between the cold rolling step and the continuous annealing step at a temperature range from a A C1  transformation point to a A C3  transformation point.  
     
     
         20 . A method of producing a high-strength dual-phase galvanized steel sheet having an excellent deep drawability, characterized by subjecting to a galvanization after the continuous annealing at a temperature range from a A C1  transformation point to a A C3  transformation point in the method claimed in  claim 8 .  
     
     
         21 . A method of producing a high-strength dual-phase galvanized steel sheet having an excellent deep drawability according to  claim 20 , characterized by further comprising a continuous annealing step between the cold rolling step and the continuous annealing step at a temperature range from a A C1  transformation point to a A C3  transformation point.  
     
     
         22 . A method of producing a high-strength dual-phase galvanized steel sheet having an excellent deep drawability, characterized by subjecting to a galvanization after the continuous annealing at a temperature range from a A C1  transformation point to a A C3  transformation point in the method claimed in  claim 9 .  
     
     
         23 . A method of producing a high-strength dual-phase galvanized steel sheet having an excellent deep drawability according to  claim 22 , characterized by further comprising a continuous annealing step between the cold rolling step and the continuous annealing step at a temperature range from a A C1  transformation point to a A C3  transformation point.  
     
     
         24 . A method of producing a high-strength dual-phase galvanized steel sheet having an excellent deep drawability according to any one of claims  16 - 23 , wherein the steel slab further comprises one or two of the following A-group and B-group: 
 A-group: not more than 2.0 mass % in total of one or two of Cr and Mo;    B-group: not more than 2.0 mass % in total of one or two of Cu and Ni.