High strength medium manganese steel with high hydrogen embrittlement resistance and its manufacturing method

Abstract

Disclosed herein is a high-strength medium-manganese steel with excellent hydrogen embrittlement resistance, which contains 3 to 5 wt manganese (Mn), 0.1 to 0.3 wt carbon (C), 0.2 to 0.7 wt silicon (Si), 0.01 to 0.07 wt sulfur(S), and 0.005 to 0.06 wt titanium (Ti), with the remainder being iron (Fe) and inevitable impurities.

What is claimed is: 
     
         1 . A high-strength medium-manganese steel with excellent hydrogen embrittlement resistance, which contains 3 to 5 wt % manganese (Mn), 0.1 to 0.3 wt % carbon (C), 0.2 to 0.7 wt % silicon (Si), 0.01 to 0.07 wt % sulfur(S), and 0.005 to 0.06 wt % titanium (Ti), with the remainder being iron (Fe) and inevitable impurities. 
     
     
         2 . The high-strength medium-manganese steel of  claim 1 , which consists of martensite and 3 to 5 vol % retained austenite at room temperature. 
     
     
         3 . The high-strength medium-manganese steel of  claim 1 , which has MnS inclusions and TiN—MnS complex inclusions, or has MnS inclusions and Ti(C,N)—MnS complex inclusions. 
     
     
         4 . The high-strength medium-manganese steel of  claim 3 , wherein a density of the inclusions is 90 to 4,000 ea/mm 2 . 
     
     
         5 . The high-strength medium-manganese steel of  claim 3 , wherein each of the inclusions has an aspect ratio of 1 to 35. 
     
     
         6 . The high-strength medium-manganese steel of  claim 5 , wherein each of the inclusions has a width of 0.3 to 3.0 μm and a length of 0.5 to 31.0 μm. 
     
     
         7 . A method of producing a high-strength medium-manganese steel with excellent hydrogen embrittlement resistance, the method comprising steps of:
 (S1) melting an alloy containing 3 to 5 wt % manganese (Mn), 0.1 to 0.3 wt % carbon (C), 0.2 to 0.7 wt % silicon (Si), 0.01 to 0.07 wt % sulfur(S), and 0.005 to 0.06 wt % titanium (Ti), with the remainder being iron (Fe) and inevitable impurities, and making the molten alloy into a steel;   (S2) homogenizing the steel;   (S3) hot-rolling the homogenized steel, followed by cooling;   (S4) cold-rolling the hot-rolled steel;   (S5) annealing and cooling the cold-rolled steel; and   (S6) austenitizing the annealed steel, and forming the austenitized steel into a predetermined shape, followed by cooling.   
     
     
         8 . The method of  claim 7 , wherein the homogenizing in step (S2) is performed at 1,200 to 1,300° C. 
     
     
         9 . The method of  claim 7 , wherein the hot rolling in step (S3) is performed at 900 to 1,100° C. 
     
     
         10 . The method of  claim 7 , wherein the cold rolling in step (S4) is performed at a reduction ratio of 45 to 55% at room temperature. 
     
     
         11 . The method of  claim 7 , wherein the annealing in step (S5) is performed at 750° C. 
     
     
         12 . The method of  claim 7 , wherein the austenitizing in step (S6) is performed at an austenite single phase region A 3  temperature or higher. 
     
     
         13 . The method of  claim 12 , wherein the austenitizing in step (S6) is performed at 750° C. to lower than 850° C. 
     
     
         14 . The method of  claim 13 , wherein the austenitizing in step (S6) is performed at 750° C. 
     
     
         15 . The method of  claim 12 , wherein the austenitizing in step (S6) is performed at 850 to 1,000° C. 
     
     
         16 . The method of  claim 7 , wherein the produced medium-manganese steel consists of martensite and 3 to 5 vol % retained austenite at room temperature. 
     
     
         17 . The method of  claim 7 , wherein the produced medium-manganese steel has MnS inclusions and TiN—MnS complex inclusions, or has MnS inclusions and Ti(C,N)—MnS complex inclusions. 
     
     
         18 . The method of  claim 17 , wherein a density of the inclusions is 90 to 4,000 ea/mm 2 . 
     
     
         19 . The method of  claim 17 , wherein each of the inclusions has an aspect ratio of 1 to 35. 
     
     
         20 . The method of  claim 19 , wherein each of the inclusions has a width of 0.3 to 3.0 μm and a length of 0.5 to 31.0 μm.