Engine piston and method of manufacturing the same

Abstract

A method of manufacturing an engine piston may include performing upper-body formation for forming an upper body as an upper portion of a piston body by pressing a powder-type sintered material, performing lower-body formation for forming a lower body as a lower portion of the piston body by pressing a powder-type sintered material, performing bonding for forming the piston body by providing a brazing material between the upper body and the lower body and brazing the upper body and the lower body to each other while sintering a sintered material, performing machining for removing pores from the surface of the piston body by machining the surface, and performing heat treatment for forming a passive film by performing at least one of nitriding heat treatment or oxidation heat treatment on the surface of the piston body.

1 - 11 . (canceled) 
     
     
         12 . An engine piston comprising:
 a piston body formed by sintering an upper body and a lower body, formed through compression molding of a powder, brazing the upper body and the lower body to each other simultaneously with the sintering, and machining a surface of the piston body to remove pores from the surface of the piston body; and   a passive film formed on the surface of the piston body, the passive film including at least one of oxide or nitride.   
     
     
         13 . The engine piston according to  claim 12 , wherein the piston body has a density of 6.9 to 7.3 g/cm 3 . 
     
     
         14 . The engine piston according to  claim 12 , wherein the piston body has an internal porosity of 7.5 to 12%. 
     
     
         15 . The engine piston according to  claim 12 , wherein the passive film comprises a first oxide layer comprising Fe 3 O 4 , the first oxide layer being formed to have a thickness of 2 to 8 μm on the surface of the piston body. 
     
     
         16 . The engine piston according to  claim 12 , wherein the passive film comprises a nitride layer comprising iron nitride, the nitride layer being formed to have a thickness of 4 to 20 μm on the surface of the piston body. 
     
     
         17 . The engine piston according to  claim 12 , wherein the passive film comprises:
 a nitride layer including iron nitride, the nitride layer being formed to have a thickness of 4 to 20 μm on the surface of the piston body; and   a second oxide layer including Fe 3 O 4 , the second oxide layer being formed to have a thickness of 1 to 3 μm on an upper surface of the nitride layer.   
     
     
         18 . The engine piston according to  claim 12 , wherein the powder forming the piston body comprises 0.45 to 0.6 wt % of C, 1.3 to 1.7 wt % of Cr, 0.15 to 0.35 wt % of Mo, 0.25 to 0.40 wt % of Mn, 0.1 to 0.2 wt % of S, and a remainder of Fe and inevitable impurities. 
     
     
         19 . The engine piston according to  claim 12 , wherein the powder forming the piston body comprises 0.5 to 0.8 wt % of C, 0.8 to 0.9 wt % of Mo, 0.25 to 0.40 wt % of Mn, 0.1 to 0.2 wt % of S, and a remainder of Fe and inevitable impurities.