Continuous press hardening process and apparatus therefor

Abstract

The present invention relates to a method of continuous hardening press and an apparatus thereof. The process of continuous press hardening, includes: slab casting that makes a slab by continuous-casting molten steel refined by an electric furnace or a blast furnace, and then reheats and hot-rolls the slab into a hot-rolled steel sheet; blanking that conveys the hot-rolled steel sheet to a blank through a sealed oven and blanks the hot-rolled steel sheet, after the slab casting; and press hardening that conveys the hot-rolled steel sheet to a press die and presses the hot-rolled steel sheet, after the blanking. According to the embodiments of the present invention, since a high-temperature steel sheet formed by hot rolling is directly put into press hardening, reheating is not required such that the entire process is simplified and reduction of manufacturing cost can be expected.

1 . A process of continuous press hardening, comprising:
 slab casting step that comprises making a slab by continuously casting molten steel, and then reheating and hot-rolling the slab into a hot-rolled steel sheet;   blanking step that comprises, after the slab casting step, conveying the hot-rolled steel sheet to a blanking device through a sealed oven and blanking the hot-rolled steel sheet; and   press hardening step that comprises, after the blanking step, conveying the hot-rolled steel sheet to a press die and pressing the hot-rolled steel sheet.   
     
     
         2 . A process of continuous press hardening, comprising:
 thin slab casting or strip casting step that comprises making a hot-rolled steel sheet by continuous-casting molten steel;   blanking step that comprises, after the thin slab casting or strip casting step, conveying the hot-rolled steel sheet to a blanking device through a sealed oven and blanking the hot-rolled steel sheet; and   press hardening step that comprises, after the blanking step, conveying the hot-rolled steel sheet to a press die disposed at an outlet of the sealed oven and pressing the hot-rolled steel sheet.   
     
     
         3 . The process of continuous press hardening according to  claim 1 , wherein the blanking of a hot-rolled steel sheet is performed in the sealed oven that is supplied with hot air from a blast furnace or an electric furnace. 
     
     
         4 . The process of continuous press hardening according to  claim 3 , wherein the internal temperature of the sealed oven is maintained between 1000° C. and 1200° C. such that the temperature of the hot-rolled steel sheet is maintained within an austenite region. 
     
     
         5 . The process of continuous press hardening according to  claim 4 , wherein the steel sheet pressed in the press hardening is cooled such that the structure becomes to a martensite structure. 
     
     
         6 . The process of continuous press hardening according to  claim 1 , comprising a path changing process that changes a conveying path of the hot-rolled steel sheet, when a problem occurs in the press die. 
     
     
         7 . The process of continuous press hardening according to  claim 6 , wherein the path changing process includes:
 sensing, by a sensor, a problem in the press die and outputting a signal;   determining, by a controller, whether a problem has occurred in the press die in response to the signal from the sensor, and changing a conveying path of the hot-rolled steel sheet by driving an emergency cutter and leading roller, when a problem has occurred; and   winding the hot-rolled steel sheet transferred through the changed conveying path.   
     
     
         8 . The process of continuous press hardening according to  claim 1 , wherein when a problem has occurred in the press die, a plurality of press dies is operated to continuously press the blanked hot-rolled steel sheet, wherein a conveying direction of the blanked hot-rolled steel sheet is determined by the controller receiving the signal from a sensor that has sensed the problem, and the blanked hot-rolled steel sheet is supplied to a corresponding press die through a high-speed conveyer disposed between the outlet of the sealed oven and the press dies. 
     
     
         9 . An apparatus for press hardening, comprising:
 a slab casting device that manufactures a hot-rolled steel sheet;   a blanking device that is disposed at an outlet of a rolling machine in the slab casting device and blanks the hot-rolled steel sheet in a predetermined size;   a press die that comprises into upper and lower die portions located at an outlet side of the blanking device and presses the blanked steel sheet at a high temperature; and   a sealed oven that is disposed between the outlet of the rolling machine and the press die such that the blanking device is positioned therein, and connected with an air channel of a blast furnace or an electric furnace to maintain the temperature of the hot-rolled steel sheet passing through the sealed oven within an austenite region.   
     
     
         10 . The apparatus for press hardening according to  claim 9 , wherein the sealed oven has an inlet and an outlet and is provided with a conveying line extending from the inlet toward the outlet therein such that the hot-rolled steel sheet is conveyed. 
     
     
         11 . The apparatus for press hardening according to  claim 10 , further comprising leading rollers that guides the hot-rolled steel sheet toward a position lower than the outlet of the rolling machine when a problem occurs in the press die and a winder that winds the hot-rolled steel sheet guided by the leading rollers disposed between the outlet of the rolling machine and the sealed oven. 
     
     
         12 . The apparatus for press hardening according to  claim 10 , wherein a plurality of the press dies are provided, and a high-speed conveyer that conveys the hot-rolled steel sheet discharged from the outlet of the sealed oven to the press dies and is disposed between the outlet of the sealed oven and the press die. 
     
     
         13 . The process of continuous press hardening according to  claim 1 , wherein the temperature of the hot-rolled steel sheet is maintained in an austenite region between hot-rolling and the press hardening step. 
     
     
         14 . The process of continuous press hardening according to  claim 2 , wherein the blanking of a hot-rolled steel sheet is performed in the sealed oven that is supplied with hot air from a blast furnace or an electric furnace. 
     
     
         15 . The process of continuous press hardening according to  claim 14 , wherein the internal temperature of the sealed oven is maintained between 1000° C. and 1200° C. such that the temperature of the hot-rolled steel sheet is maintained within an austenite region. 
     
     
         16 . The process of continuous press hardening according to  claim 15 , wherein the steel sheet pressed in the press hardening is cooled such that the structure becomes to a martensite structure. 
     
     
         17 . The process of continuous press hardening according to  claim 2 , comprising a path changing process that changes a conveying path of the hot-rolled steel sheet, when a problem occurs in the press die. 
     
     
         18 . The process of continuous press hardening according to  claim 17 , wherein the path changing process includes:
 sensing, by a sensor, a problem in the press die and outputting a signal;   determining, by a controller, whether a problem has occurred in the press die in response to the signal from the sensor, and changing a conveying path of the hot-rolled steel sheet by driving an emergency cutter and leading roller, when a problem has occurred; and   winding the hot-rolled steel sheet transferred through the changed conveying path.   
     
     
         19 . The process of continuous press hardening according to  claim 2 , wherein when a problem has occurred in the press die, a plurality of press dies is operated to continuously press the blanked hot-rolled steel sheet, wherein a conveying direction of the blanked hot-rolled steel sheet is determined by the controller receiving the signal from a sensor that has sensed the problem, and the blanked hot-rolled steel sheet is supplied to a corresponding press die through a high-speed conveyer disposed between the outlet of the sealed oven and the press dies. 
     
     
         20 . The process of continuous press hardening according to  claim 2 , wherein the temperature of the hot-rolled steel sheet is maintained in an austenite region between hot-rolling and the press hardening step.