Steel Sheet for Formed Member Having Enhanced Ductility, Formed Member, and Method for Manufacturing the Formed Member

Abstract

Provided is a steel sheet for a formed member having enhanced ductility, a formed member, and a method for manufacturing the formed member, and more particularly, to a steel sheet for making a formed member having high strength and ductility such as an automotive structural member and a reinforcing member, a formed member, and a method for manufacturing the formed member. The steel sheet for a formed member has enhanced ductility, and includes, by weight %, C: 0.1% to 1.0%, Si+Al: 0.4% to 3.0%, Mn: 0.1% to 5.0%, P: 0.0001% to 0.1%, S: 0.0001% to 0.03%, N: 0.03% or less (but not 0%), and the balance of Fe and inevitable impurities. The formed member having high strength and ductility that can be used for forming an automotive structural member, a reinforcing member, etc. In addition, the formed member can be used for a heat-treatable impact resistant member.

1 . A steel sheet for a formed member having enhanced ductility, the steel sheet comprising, by weight%, C: 0.1% to 1.0%, Si+Al: 0.4% to 3.0%, Mn: 0.1% to 5.0%, P: 0.0001% to 0.1%, S: 0.0001% to 0.03%, N: 0.03% or less but not 0%, and the balance of Fe and inevitable impurities. 
     
     
         2 . The steel sheet of  claim 1 , further comprising at least one selected from the group consisting of (a), (b), (c), (d), and (e), wherein:
 (a) at least one selected from the group consisting of Cr: 0.01% to 2.0%, Mo: 0.01% to 2.0%, and W: 0.01% to 2.0%;   (b) at least one selected from the group consisting of Ti: 0.001% to 0.4%, Nb: 0.001% to 0.4%, Zr: 0.001% to 0.4%, and V: 0.001% to 0.4%;   (c) at least one of Cu: 0.005% to 2.0% and Ni: 0.005% to 2.0%;   (d) B: 0.0001% to 0.01%; and   (e) Sb: 0.001% to 0.1%.   
     
     
         3 . The steel sheet of  claim 1 , wherein the steel sheet is one of a hot-rolled steel sheet, a cold-rolled steel sheet, and a plated steel sheet. 
     
     
         4 . The steel sheet of  claim 3 , wherein the plated steel sheet is a hot-rolled or cold-rolled steel sheet on which a metal or resin coating layer is formed. 
     
     
         5 . The steel sheet of  claim 4 , wherein the metal coating layer is formed by one of aluminum plating, zinc plating, alloyed zinc plating, and zinc electroplating. 
     
     
         6 . The steel sheet of  claim 4 , wherein the resin coating layer is formed of at least one of solgel and aluminum powder. 
     
     
         7 . The steel sheet of  claim 1 , wherein after a heat treatment, the steel sheet has a microstructure comprising by area fraction: 5% to 40% of retained austenite, 60% to 95% of martensite, and 10% or less (including 0%) of ferrite. 
     
     
         8 . A formed member having enhanced ductility, the formed member comprising, by weight%, C: 0.1% to 1.0%, Si+Al: 0.4% to 3.0%, Mn: 0.1% to 5.0%, P: 0.0001% to 0.1%, S: 0.0001% to 0.03%, N: 0.03% or-less but not 0%, and the balance of Fe and inevitable impurities,
 wherein the formed member has a microstructure comprising by area fraction: 5% to 40% of retained austenite, 60% to 95% of martensite, and 10% or less (including 0%) of ferrite.   
     
     
         9 . The formed member of  claim 8 , further comprising at least one selected from the group consisting of (a), (b), (c), (d), and (e), wherein:
 (a) at least one selected from the group consisting of Cr: 0.01% to 2.0%, Mo: 0.01% to 2.0%, and W: 0.01% to 2.0%;   (b) at least one selected from the group consisting of Ti: 0.001% to 0.4%, Nb: 0.001% to 0.4%, Zr: 0.001% to 0.4%, and V: 0.001% to 0.4%;   (c) at least one of Cu: 0.005% to 2.0% and Ni: 0.005% to 2.0%;   (d) B: 0.0001% to 0.01%; and   (e) Sb: 0.001% to 0.1%.   
     
     
         10 . The formed member of  claim 8 , wherein the formed member has a tensile strength of 1000 Mpa or greater and an elongation of 10% or greater. 
     
     
         11 . A method for manufacturing a formed member, the method comprising:
 performing a pressing process on a steel sheet comprising, by weight%, C: 0.1% to 1.0%, Si+Al: 0.4% to 3.0%, Mn: 0.1% to 5.0%, P: 0.0001% to 0.1%, S: 0.0001% to 0.03%, N: 0.03% or less but not 0%, and the balance of Fe and inevitable impurities;   quenching the steel sheet to an Ms-Mf temperature range; and   heating the quenched steel sheet to a temperature range equal to or lower than Ac1 and maintaining the steel sheet within the temperature range.   
     
     
         12 . The method of 11, wherein the formed member further comprises at least one selected from the group consisting of (a), (b), (c), (d), and (e), wherein:
 (a) at least one selected from the group consisting of Cr: 0.01% to 2.0%, Mo: 0.01% to 2.0%, and W: 0.01% to 2.0%;   (b) at least one selected from the group consisting of Ti: 0.001% to 0.4%, Nb: 0.001% to 0.4%, Zr: 0.001% to 0.4%, and V: 0.001% to 0.4%;   (c) at least one of Cu: 0.005% to 2.0% and Ni: 0.005% to 2.0%;   (d) B: 0.0001% to 0.01%; and   (e) Sb: 0.001% to 0.1%.   
     
     
         13 . The method of  claim 11 , wherein before performing the pressing process, the method further comprises heating the steel sheet to an austenite temperature range equal to or higher than Ac3. 
     
     
         14 . The method of  claim 11 , wherein after performing the pressing process, the method further comprises heating the steel sheet to an austenite temperature range equal to or higher than Ac3. 
     
     
         15 . The method of  claim 11 , wherein the quenching is performed at a rate of 10 ° C./s to 500° C./s. 
     
     
         16 . The method of  claim 11 , wherein the maintaining of the steel sheet within the temperature range continues for 1 second to 10000 seconds. 
     
     
         17 . The steel sheet of  claim 2 , wherein after a heat treatment, the steel sheet has a microstructure comprising by area fraction: 5% to 40% of retained austenite, 60% to 95% of martensite, and 10% or less (including 0%) of ferrite. 
     
     
         18 . The steel sheet of  claim 3 , wherein after a heat treatment, the steel sheet has a microstructure comprising by area fraction: 5% to 40% of retained austenite, 60% to 95% of martensite, and 10% or less (including 0%) of ferrite. 
     
     
         19 . The steel sheet of  claim 4 , wherein after a heat treatment, the steel sheet has a microstructure comprising by area fraction: 5% to 40% of retained austenite, 60% to 95% of martensite, and 10% or less (including 0%) of ferrite. 
     
     
         20 . The steel sheet of  claim 5 , wherein after a heat treatment, the steel sheet has a microstructure comprising by area fraction: 5% to 40% of retained austenite, 60% to 95% of martensite, and 10% or less (including 0%) of ferrite.