Treatment method and process for valve seat

Abstract

A method of treating a valve body is disclosed herein. The method includes using a medium carbon steel, and treating the valve body to a carburizing heating step, an intermediate annealing step, a hardening step, and a tempering step. These steps provide a durable valve seat surface for the valve body such that the valve seat can withstand the conditions that involve high friction or otherwise intense operating conditions, such as oil and gas applications.

1 . A method for treating a valve body, the method comprising:
 a first heating step at a first predetermined temperature for a first predetermined period such that a valve seat surface of the valve body has a carbon content of 0.9%-1.4% up to a predetermined depth from an outer surface of the valve body;   a first cooling step performed via quenching;   a second heating step at a second predetermined temperature for a second predetermined period, wherein the second predetermined temperature is less than the first predetermined temperature;   a third heating step at a third predetermined temperature for a third predetermined period, wherein the third predetermined temperature is greater than the second predetermined temperature; and   a fourth heating step at a fourth predetermined temperature for a fourth predetermined period, wherein the fourth predetermined temperature is less than the third predetermined temperature.   
     
     
         2 . The method according to  claim 1 , wherein the predetermined depth is at least 0.3 mm. 
     
     
         3 . The method according to  claim 1 , wherein the valve body is formed from steel having a carbon content of at least 0.28%. 
     
     
         4 . The method according to  claim 1 , wherein carbides are precipitated in the valve body during the second heating step, and a carbon content of 0.65% to 0.90% is formed in an austenitic matrix phase on the outer surface of the valve body during the third heating step. 
     
     
         5 . The method according to  claim 4 , further comprising quenching the valve body after the third heating step. 
     
     
         6 . The method according to  claim 1 , wherein the third heating step occurs directly after the second heating step. 
     
     
         7 . The method according to  claim 1 , further comprising cooling the valve body to room temperature between the second and third heating steps. 
     
     
         8 . The method according to  claim 1 , wherein the valve body comprises:
 0.15%-0.36% carbon;   0.20%-0.60% silicon;   0.60%-1.80% manganese;   0.80%-2.30% chromium;   0-0.50% nickel;   0.20%-0.90% molybdenum;   0-0.6% vanadium;   0.015%-0.050% aluminum;   0-0.010% sulphur;   0-0.025% phosphor;   0-0.003% titanium;   0.005%-0.015% nitrogen;   0-12 ppm oxygen;   0-0.0035% calcium;   0-0.25% copper; and   a remainder of a composition of the valve body is formed from iron.   
     
     
         9 . The method according to  claim 1 , wherein the second predetermined temperature is 600° C.-660° C. 
     
     
         10 . The method according to  claim 1 , wherein the third predetermined temperature is 800° C.-830° C. 
     
     
         11 . The method according to  claim 1 , wherein the first predetermined temperature is 940° C.-980° C. 
     
     
         12 . The method according to  claim 1 , wherein the fourth predetermined temperature is 100° C.-250° C. 
     
     
         13 . The method according to  claim 1 , wherein the first predetermined temperature is 940° C.-980° C., the second predetermined temperature is 600° C.-660° C., and the third predetermined temperature is 800° C.-830° C. 
     
     
         14 - 20 . (canceled)