Method for manufacturing a structural member of a vehicle

Abstract

A method of manufacturing a structural member of a vehicle includes the steps of preparing a steel essentially including Fe, 0.20-0.25 weight % of C, not more than 0.3 weight % of Si, 1.0-1.2 weight % of Mn, not more than 0.02 weight % of P, and not more than 0.005 weight % of S. The method includes forming a structural member by pressing the steel and heat treating a portion of the structural member where a supplementary reinforcement is required for enhancing the strength of the structural member. The heat treating is performed by means of direct-heating, whereby a traditional reinforcing process can be eliminated and the weight of the structural member can be reduced.

What is claimed is:  
     
         1 . A manufacturing method for a structural member of a vehicle, the method comprising: 
 preparing a steel essentially consisting mainly of Fe, 0.20-0.25 weight % of C, not more than 0.3 weight % of Si, 1.0-1.2 weight % of Mn, not more than 0.02 weight % of P, and not more than 0.005 weight % of S;    forming a structural member by pressing the steel; and    heat treating a portion of the structural member where a supplementary reinforcement is required for enhancing the strength of the structural member by means of direct-heating.    
     
     
         2 . A manufacturing method for a structural member of a vehicle according to  claim 1 , wherein the heat treating process by means of direct-heating is conducted under conditions of: a frequency of about 15-25 kHz, a power of about 40-60 kW, a heating duration of about 20-40 sec, a cooling duration of about 15-25 sec, a flow rate of coolant of about 1000-1500 L/min, and a temperature of direct-heating of about 900° C. or higher.  
     
     
         3 . A manufacturing method for forming a structural member of a vehicle, the method comprising: 
 preparing a steel comprising predominately Fe, about 0.20-0.25 weight % of C, not more than about 0.3 weight % of Si, about 1.0-1.2 weight % of Mn, not more than about 0.02 weight % of P, and not more than about 0.005 weight % of S;    forming a structural member with said steel by a pressing method; and    heat treating a portion of said structural member, by direct-heating, at a position where a supplementary reinforcement is required such that the strength of the structural member is enhanced at that position.    
     
     
         4 . The manufacturing method of  claim 3 , wherein said heat treating is by direct-heating under the conditions of: a frequency of about 15-25 kHz, a power of about 40-60 kW, a heating duration of about 20-40 sec, a cooling duration of about 15-25 sec, a flow rate of coolant of about 1000-1500 L/min, and a temperature of direct-heating of at least about 900° C.