Rapid Nitriding Through Nitriding Potential Control

Abstract

A disclosure is directed to a method for rapidly nitriding steel, the method including: placing the steel in a furnace having an atmosphere comprising partially dissociated ammonia gas; heating the steel to a highest temperature in a range of 400 to 600° C. while holding a nitriding potential below 15 atm−1/2 during heat-up from 400° C. up to the highest temperature; and holding the steel at the highest temperature while continuing to maintain the nitriding potential below 15 atm−1/2, where a total time taken for the heating and holding the steel in the range of 400 to 600° C. during the nitriding is 15 hours or less, and where a composition of the steel comprises at least one of the group consisting of Al, Cr, Mo, V, and Ti.

1 - 13 . (canceled) 
     
     
         14 . A nitrided steel having an alloy composition comprising by weight:
 C: from 0.1 to 2.2%;   Mn: from 0 to 1.2%;   Al: from 0 to 1.5%;   Cr: from 0 to 5.5%;   Mo: from 0.15 to 1.8%;   Si: from 0 to 1.8%;   V: from 0 to 1.2%; and   Iron and acceptable trace elements: remaining balance;   wherein the steel is rapid nitrided in response to:
 being placed in a furnace having an atmosphere comprising partially dissociated ammonia gas; 
 being heated to a highest temperature in a range of 400° C. to 600° C. while holding a nitriding potential below 15 atm −1/2  during heat-up from 400° C. up to the highest temperature; and 
 being held at the highest temperature while continuing to maintain the nitriding potential below 15 atm −1/2 ; 
   wherein a total time taken for heating and holding the steel in the range of 400° C. to 600° C. during the nitriding is 15 hours or less.   
     
     
         15 . The nitrided steel according  claim 14 , wherein the alloy composition further comprises:
 C: from 0.1 to 0.43%;   Mn: from 0.75 to 1.2%;   Al: from 0.08 to 0.13%;   Cr: from 0.8 to 1.2%;   Mo: from 0.15 to 0.25%;   Si: from 0.15 to 0.35%;   V: from 0.05 to 0.1%; and   Iron and acceptable trace elements: remaining balance.   
     
     
         16 . The nitrided steel according to  claim 14 , wherein the nitrided steel maintains a hardness value of 57 HRC or higher in a region from a surface to a thickness of 75 or more of the steel. 
     
     
         17 . The nitrided steel according to  claim 14 , wherein the nitrided steel maintains a hardness value that is 35 HRC or higher in a region from a surface to a thickness of 250 or more for steels with core hardness of 32 HRC or lower. 
     
     
         18 . The nitrided steel according to  claim 14 , wherein a white layer on a surface of the nitrided steel has a thickness of 2 or less. 
     
     
         19 . The nitrided steel according to  claim 14 , wherein a white layer on a surface of the nitrided steel has a thickness of 1 or less. 
     
     
         20 . The nitrided steel according to  claim 14 , wherein a TGP (thin phase) layer on a surface of the nitrided steel has a thickness of 5 or less.