Sintered alloy having wear resistance for valve seat and method for manufacturing the same

Abstract

A sintered alloy having an improved wear resistance and a workability for a valve seat. The alloy contains iron as a main component, carbon, silicon, chromium, molybdenum, cobalt, maganese, lead, vanadium, advantageously boron nitride, and tungsten. The strength, wear resistance, and material properties are improved by a sub-zero treatment. Sintered alloy with wear resistance used for a valve seat comprises Fe as a main component, C of 1.2 to 1.7 wt %, Cr of 3.5 to 5.0 wt %, Mo of 2.0 to 4.0 wt %, V of 3.0 to 5.0 wt %, W of 7.0 to 10.0 wt %, Co of 2.0 to 3.5 wt %, boron nitride of 0.1 to 1.0 wt %, S of 0.2 to 0.4 wt %, Mn of 0.2 to 0.5 wt %, advantageously 0.2 to 0.6% Si, and Pb of 10.0 to 15.0 wt %. Sintered alloy for an valve seat is manufactured by a sub-zero treatment so that the amount of metallic particles separated from a base matrix decreases and a size of the separated metallic particle becomes small.

What is claimed is:  
     
         1 . An impregnated sintered alloy for use to manufacture a valve seat, the impregnated sintered alloy comprising: Fe as a main component, C of from 1.2 to 1.7 wt %, Cr of 3.5 to 5.0 wt %, Mo of 2.0 to 4.0 wt %, V of 3.0 to 5.0 wt %, W of 7.0 to 10.0 wt %, Co of 2.0 to 3.5 wt %, boron nitride of 0.1 to 1.0 wt %, S of 0.2 to 0.4 wt %, Mn of 0.2 to 0.5 wt %, and Pb of 10.0 to 15.0 wt %.  
     
     
         2 . The impregnated sintered alloy of  claim 1  wherein the impregnated sintered alloy consists essentially of Fe, C, Cr, Mo, V, W, Co, boron nitride, S, Mn, and Pb.  
     
     
         3 . The impregnated sintered alloy of  claim 1  further comprising Si of from 0.2 to 0.6 wt %.  
     
     
         4 . The impregnated sintered alloy of  claim 3  wherein the impregnated sintered alloy consists essentially of Fe, C, Cr, Mo, V, W, Co, boron nitride, S, Mn, Si, and Pb.  
     
     
         5 . A method for manufacturing a sintered alloy with excellent wear resistance for a valve comprising: 
 mixing Fe as a main component, C of from 1.2 to 1.7 wt %, Cr of 3.5 to 5.0 wt %, Mo of 2.0 to 4.0 wt %, V of 3.0 to 5.0 wt %, W of 7.0 to 10.0 wt %, Co of 2.0 to 3.5 wt %, boron nitride of 0.1 to 1.0 wt %, S of 0.2 to 0.4 wt %, Mn of 0.2 to 0.5 wt %, and applying a surface pressure of 5 to 8 ton/cm 3  to obtain a compressed mixed metal powder;    sintering the compressed mixed metal powder at a temperature from 1,140° C. to 1,180° C. to form a sintered alloy and then cooling by air;    performing a sub-zero treatment on the sintered metal powder at a temperature from −200 to −160° C.;    impregnating the sub-zero-treated sintered metal powder with Pb at a temperature from 450 to 550° C. to form an impregnated sintered alloy comprising from 10.0 to 15.0 wt % of Pb; and    performing a barrel process for the sintered metal powder impregnated with the Pb at a temperature from 450 to 550° C.    
     
     
         6 . A valve seat for an automobile engine, the valve seat comprising an impregnated sintered alloy comprising: 
 A) between about 85 parts by weight and a 90 parts by weight, based on 100 parts of impregnated sintered alloy, of a sintered powder alloy comprising: 
 Fe as a main component,  
 1.2 to 1.7 wt % of C,  
 3.5to5.0 wt % of Cr,  
 2.0 to4.0 wt % of Mo,  
 3.0 to 5.0 wt % of V,  
 7.0 to 10.0 wt % of W,  
 2.0 to 3.5 wt % of Co,  
 0.1 to 1.0 wt % of boron nitride,  
 0.2 to 0.4 wt % of S, and  
 0.2 to 0.5 wt % of Mn, wherein the sintered powder alloy comprises porosity; and  
   B) between about 10 to 15 parts by weight of a impregnated metal that has penetrating and lubricating properties, wherein the impregnated metal resides in the porosity.    
     
     
         7 . The impregnated sintered alloy of  claim 6  wherein the impregnated sintered alloy consists essentially of Fe, C, Cr, Mo, V, W, Co, boron nitride, S, and Mn, and wherein the impregnated metal comprises Pb.  
     
     
         8 . The impregnated sintered alloy of  claim 6  further comprising from 0.2 to0.6wt % of Si.  
     
     
         9 . The impregnated sintered alloy of  claim 8  wherein the impregnated sintered alloy consists essentially of Fe, C, Cr, Mo, V, W, Co, boron nitride, Si, S, and Mn, and wherein the impregnated metal comprises Pb.  
     
     
         10 . The impregnated sintered alloy of  claim 8  wherein the impregnated sintered alloy comprises at least about 63.9% of Fe and wherein the impregnated metal consists essentially of Pb.  
     
     
         11 . The impregnated sintered alloy of  claim 8  wherein the impregnated sintered alloy comprises at least about 63.9% of Fe.  
     
     
         12 . The impregnated sintered alloy of  claim 6  wherein the sintered alloy comprises at least about 63.9% of Fe, and wherein the sintered alloy was sintered at a temperature between about 1,140 to about 1,180° C., and then cooled to a temperature of from about −200° C. to about −160° C. for a time sufficient to reduce the residual austenite in the sintered alloy.  
     
     
         13 . The impregnated sintered alloy of  claim 9  wherein the sintered alloy comprises at least about 63.9% of Fe, and wherein the sintered alloy was sintered at a temperature between about 1,140 to about 1,180° C., and then cooled to a temperature of from about −200° C. to about −160° C. for a time sufficient to reduce the residual austenite in the sintered alloy.  
     
     
         14 . The impregnated sintered alloy of  claim 13  wherein the sintered alloy was held at a temperature of from about −200° C. to about −160° C. for about 5 to about 20 minutes.  
     
     
         15 . The impregnated sintered alloy of  claim 6  wherein 
 at least about 63.9% of Fe;  
 about 1.4% of C is present in the sintered metal;  
 about 4% of Cr is present in the sintered metal;  
 about 3% of Mo is present in the sintered metal;  
 about 3.5% to about 4% of V is present in the sintered metal;  
 about 8.5% to about 9% of W is present in the sintered metal;  
 about 2.5% to about 3% of Co is present in the sintered metal;  
 about 0.4% to about 0.6% of boron nitride is present in the sintered metal;  
 0.2 to 0.4 wt % of S is present in the sintered metal;  
 about 0.3% of Mn is present in the sintered metal; and  
 wherein the impregnated metal consists essentially of lead.  
 
     
     
         16 . The impregnated sintered alloy of  claim 15  wherein the sintered alloy comprises about 0.4% of Si, and wherein the sintered alloy was sintered at a temperature between about 1,140 to about 1,180° C., and then cooled to a temperature of from about −200° C. to about −160° C. for a time sufficient to reduce the residual austenite in the sintered alloy.  
     
     
         17 . A method for manufacturing an engine valve comprising: 
 providing a sinterable alloy powder, wherein the sinterable alloy powder consists essentially of Fe as the main component; 1.2 to 1.7 wt % of C; 3.5 to 5.0 wt % of Cr; 2 to 4 wt % of Mo; 3 to 5 wt % of V; 7 to 10 wt % of W; 2 to 3.5 wt % of Co; 0.1 to 1.0 wt % of boron nitride; 0.2 to 0.4 wt % of S; and 0.2 to 0.5 wt % of Mn, wherein the sinterable alloy powder is in a mold;    applying a surface pressure of 5 to 8 ton/cm 3  on the powder to obtain a compressed alloy powder having porosity;    sintering the compressed alloy powder at a temperature from 1,140° C. to 1,180° C. to form a sintered alloy;    cooling the sintered alloy to a temperature of from −200 to −160° C. for at least about 5 minutes, thereby forming a treated sintered alloy;    heating the treated sintered alloy to a temperature from about 450 to about 550° C. and impregnating the treated sintered alloy with a penetrating metal comprising Pb; thereby forming an impregnated treated sintered alloy wherein the penetrating metal is present in the porosity in an amount between 10 to 15 wt % of penetrating metal; and    performing a barrel process on the impregnated treated sintered alloy.    
     
     
         18 . The method of  claim 17  wherein the sintered alloy further comprises 0.2 to 0.6% of Si.  
     
     
         19 . The method of  claim 17  wherein a least a portion of the sinterable alloy powder grains comprise Fe as the main component; C; Cr; Mo; V; W; Co; boron nitride; and Mn.  
     
     
         20 . The method of  claim 18  wherein substantially all of the sinterable alloy powder grains comprise Fe as the main component; C; Cr; Mo; V; W; Co; boron nitride; and Mn.