Nitrocarburized microalloyed steel member

Abstract

A nitrocarburized microalloyed steel member consists of a microalloyed steel that includes a nitrocarburized layer on a surface, a cross-sectional structure of which steel except for the nitrocarburized layer includes a ferrite and pearlite structure. The microalloyed steel mainly consists of Fe and has a composition: C having a content of 0.30 mass % or more and 0.50 mass % or less; Si having a content of 0.05 mass % or more and 0.30 mass % or less; Mn having a content of 0.50 mass % or more and 1.00 mass % or less; S having a content of 0.03 mass % or more and 0.20 mass % or less; Cu having a content of 0.05 mass % or more and 0.60 mass % or less; Ni having a content of 0.02 mass % or more and 1.00 mass % or less; and Cr having a content of 0.05 mass % or more and 0.30 mass % or less. If the contents of the Cu, the Ni, and the Cr are represented by WCu, WNi, and WCr mass %, respectively, and composition parameters F 1 and F 2 are 185WCr+50WCu and 8+4WNi+1.5WCu−44WCr, respectively, then the composition parameters F 1 and F 2 satisfy F 1> 20 and F 2> 0.

1 . A nitrocarburized microalloyed steel member consisting of a microalloyed steel that includes a nitrocarburized layer on a surface, a cross-sectional structure of the steel except for the nitrocarburized layer including a ferrite and pearlite structure, wherein 
 the microalloyed steel mainly consists of Fe and has a composition:    C having a content equal to or more than 0.30 mass % and equal to or less than 0.50 mass %;    Si having a content equal to or more than 0.05 mass % and equal to or less than 0.30 mass %;    Mn having a content equal to or more than 0.50 mass % and equal to or less than 1.00 mass %;    S having a content equal to or more than 0.03 mass % and equal to or less than 0.20 mass %;    Cu having a content equal to or more than 0.05 mass % and equal to or less than 0.60 mass %;    Ni having a content equal to or more than 0.02 mass % and equal to or less than 1.00 mass %; and    Cr having a content equal to or more than 0.05 mass % and equal to or less than 0.30 mass %, and wherein    if the contents of the Cu, the Ni, and the Cr are represented by WCu, WNi, and WCr mass %, respectively, and composition parameters F 1  and F 2  are 185WCr+50WCu and 8+4WNi+1.5WCu−44WCr, respectively, then the composition parameters F 1  and F 2  satisfy:      F1>20  (1)  and  F2>0  (2).    
     
     
         2 . The nitrocarburized microalloyed steel member according to  claim 1 , wherein 
 the microalloyed steel further contains:    Ti having a content equal to or more than 0.0020 mass % and equal to or less than 0.0120 mass %;    N having a content equal to or more than 0.0050 mass % and equal to or less than 0.0250 mass %; and    O having a content equal to or more than 0.0005 mass % and equal to or less than 0.008 mass %.    
     
     
         3 . The nitrocarburized microalloyed steel member according to  claim 2 , wherein 
 if the contents of the O, the N, and the Ti are represented by WO, WN, and WTi mass %, respectively, the WO, the WN, and the WTi satisfy:      0.12WTi<WO<2.5WTi  (3)  and  0.04WN<WO<0.7WN  (4).    
     
     
         4 . The nitrocarburized microalloyed steel member according to  claim 1 , wherein 
 the microalloyed steel further contains Ca having a content equal to or more than 0.0005 mass % and equal to or less than 0.0050 mass %.    
     
     
         5 . The nitrocarburized microalloyed steel member according to  claim 1 , wherein 
 a Vickers hardness at a position 0.05 millimeters away from an uppermost surface of the nitrocarburized layer is equal to or higher than 280 Hv and equal to or lower than 380 Hv.    
     
     
         6 . The nitrocarburized microalloyed steel member according to  claim 1 , wherein 
 a ferrite area percentage in an area of the ferrite and pearlite structure is equal to or more than 20 percent and equal to or less than 60 percent.    
     
     
         7 . The nitrocarburized microalloyed steel member according to  claim 2 , wherein 
 the microalloyed steel further contains Ca having a content equal to or more than 0.0005 mass % and equal to or less than 0.0050 mass %.    
     
     
         8 . The nitrocarburized microalloyed steel member according to  claim 3 , wherein 
 the microalloyed steel further contains Ca having a content equal to or more than 0.0005 mass % and equal to or less than 0.0050 mass %.    
     
     
         9 . The nitrocarburized microalloyed steel member according to  claim 2 , wherein 
 a Vickers hardness at apposition 0.05 millimeters away from an uppermost surface of the nitrocarburized layer is equal to or higher than 280 Hv and equal to or lower than 380 Hv.    
     
     
         10 . The nitrocarburized microalloyed steel member according to  claim 3 , wherein 
 a Vickers hardness at a position 0.05 millimeters away from an uppermost surface of the nitrocarburized layer is equal to or higher than 280 Hv and equal to or lower than 380 Hv.    
     
     
         11 . The nitrocarburized microalloyed steel member according to  claim 4 , wherein 
 a Vickers hardness at a position 0.05 millimeters away from an uppermost surface of the nitrocarburized layer is equal to or higher than 280 Hv and equal to or lower than 380 Hv.    
     
     
         12 . The nitrocarburized microalloyed steel member according to  claim 7 , wherein 
 a Vickers hardness at a position 0.05 millimeters away from an uppermost surface of the nitrocarburized layer is equal to or higher than 280 Hv and equal to or lower than 380 Hv.    
     
     
         13 . The nitrocarburized microalloyed steel member according to  claim 8 , wherein 
 a Vickers hardness at a position 0.05 millimeters away from an uppermost surface of the nitrocarburized layer is equal to or higher than 280 Hv and equal to or lower than 380 Hv.    
     
     
         14 . The nitrocarburized microalloyed steel member according to  claim 2 , wherein 
 a ferrite area percentage in an area of the ferrite and pearlite structure is equal to or more than 20 percent and equal to or less than 60 percent.    
     
     
         15 . The nitrocarburized microalloyed steel member according to  claim 3 , wherein 
 a ferrite area percentage in an area of the ferrite and pearlite structure is equal to or more than 20 percent and equal to or less than 60 percent.    
     
     
         16 . The nitrocarburized microalloyed steel member according to  claim 4 , wherein 
 a ferrite area percentage in an area of the ferrite and pearlite structure is equal to or more than 20 percent and equal to or less than 60 percent.    
     
     
         17 . The nitrocarburized microalloyed steel member according to  claim 7 , wherein 
 a ferrite area percentage in an area of the ferrite and pearlite structure is equal to or more than 20 percent and equal to or less than 60 percent.    
     
     
         18 . The nitrocarburized microalloyed steel member according to  claim 8 , wherein 
 a ferrite area percentage in an area of the ferrite and pearlite structure is equal to or more than 20 percent and equal to or less than 60 percent.    
     
     
         19 . The nitrocarburized microalloyed steel member according to  claim 5 , wherein 
 a ferrite area percentage in an area of the ferrite and pearlite structure is equal to or more than 20 percent and equal to or less than 60 percent.    
     
     
         20 . The nitrocarburized microalloyed steel member according to  claim 9 , wherein 
 a ferrite area percentage in an area of the ferrite and pearlite structure is equal to or more than 20 percent and equal to or less than 60 percent.    
     
     
         21 . The nitrocarburized microalloyed steel member according to  claim 10 , wherein 
 a ferrite area percentage in an area of the ferrite and pearlite structure is equal to or more than 20 percent and equal to or less than 60 percent.    
     
     
         22 . The nitrocarburized microalloyed steel member according to  claim 11 , wherein 
 a ferrite area percentage in an area of the ferrite and pearlite structure is equal to or more than 20 percent and equal to or less than 60 percent.    
     
     
         23 . The nitrocarburized microalloyed steel member according to  claim 12 , wherein 
 a ferrite area percentage in an area of the ferrite and pearlite structure is equal to or more than 20 percent and equal to or less than 60 percent.    
     
     
         24 . The nitrocarburized microalloyed steel member according to  claim 13 , wherein 
 a ferrite area percentage in an area of the ferrite and pearlite structure is equal to or more than 20 percent and equal to or less than 60 percent.