Steel composition

Abstract

It further relates to method of manufacture thereof, the steel blank obtained and a mechanical device or an injection system comprising same.

1 . A steel composition comprising, in percentages by weight of the total composition:
 Carbon: 0.06-0.20;   Chromium: 2.5-5.0;   Molybdenum: 4.0-6.0;   Tungsten: 0.01-3.0;   Vanadium: 1.0-3.0;   Nickel: 2.0-4.0;   Cobalt: 9.0-12.5;   Iron: remainder   as well as the inevitable impurities,   optionally further comprising one or more of the following elements:   Niobium: ≤2.0;   Nitrogen: ≤0.50;   Silicon: ≤0.70;   Manganese: ≤0.70;   Aluminum: ≤0.15;   the combined niobium+vanadium content being in the range 1.0-3.5;   and the carbon  30  nitrogen content being in the range 0.06-0.50.   
     
     
         2 . The steel composition as claimed in  claim 1 , comprising, in percentages by weight of the total composition:
 Carbon: 0.06-0.20;   Chromium: 3.0-4.5;   Molybdenum: 4.0-6.0;   Tungsten 0.01-3.0;   Vanadium: 1.5-2.5;   Nickel: 2.0-4.0;   Cobalt: 9.5-12.5;   Iron: remainder   as well as the inevitable impurities,   optionally further comprising one or more of the following elements:   Niobium: ≤2.0;   Nitrogen: ≤0.20;   Silicon: ≤0.70;   Manganese: ≤0.70;   Aluminum: ≤0.10;   the combined niobium+vanadium content being in the range 1.0-3.5;   and the carbon+nitrogen content being in the range 0.06-0.50.   
     
     
         3 . The steel composition as claimed in  claim 1 , comprising at most 1 wt % of inevitable impurities. 
     
     
         4 . The steel composition as claimed in  claim 1 , wherein the inevitable impurities are selected from titanium, sulfur, phosphorus, copper, tin, lead, oxygen and mixtures thereof. 
     
     
         5 . The steel composition as claimed in  claim 1 , which is carburizable and/or nitridable. 
     
     
         6 . The steel composition as claimed in  claim 1 , which has, after a thermochemical treatment, followed by a heat treatment, a surface hardness above 67 HRC. 
     
     
         7 . The steel composition as claimed in  claim 1 , which has, after a thermochemical treatment, followed by a heat treatment, a martensitic structure having a residual austenite content below 0.5 wt % and free from ferrite and pearlite. 
     
     
         8 . The steel composition as claimed in  claim 6 , wherein the thermal treatment comprises a solution treatment at a temperature between 1090° C.-1160° C. followed by quenching optionally with cooling and several tempering operations at a temperature between 475° C. and 530° C. 
     
     
         9 . A method of making a steel blank having the composition as claimed in  claim 1 , comprising:
 a) a steelmaking step;   b) a step of transformation of the steel;   c) a thermochemical treatment;   d) and a heat treatment.   
     
     
         10 . The method of making as claimed in  claim 9 , wherein step c) consists of a treatment of carburizing or of nitriding or of carbonitriding or of carburizing and then nitriding. 
     
     
         11 . The method of making as claimed in  claim 9 , wherein step c) consists of a carburizing treatment allowing carbon enrichment of the surface leading to a final surface carbon content of at least 1 wt %. 
     
     
         12 . The method of making as claimed in  claim 9 , wherein step d) comprises a solution treatment at a temperature between 1090° C.-1160° C. followed by holding at this temperature until completion of austenitization optionally with cooling to a temperature below −40° C., and several tempering operations at a temperature between 475° C. and 530° C. 
     
     
         13 . The method of making as claimed in  claim 9 , wherein step b) consists of a step of rolling, forging and/or extrusion. 
     
     
         14 . The method of making as claimed in  claim 9 , wherein the steelmaking step a) is carried out by a conventional steelmaking process in an arc furnace and with refining and remelting under conductive slag (ESR, electroslag remelting), or by a VIM or VIM-VAR process, optionally with a step of remelting under conductive slag (ESR, electroslag remelting) and/or under vacuum (VAR), or by powder metallurgy such as gas atomization and compaction by hot isostatic pressing (HIP). 
     
     
         15 . A steel blank obtainable by a method as claimed in  claim 9 . 
     
     
         16 . (canceled) 
     
     
         17 . A mechanical device made of steel having the composition as claimed in  claim 1 . 
     
     
         18 . An injection system made of steel having the composition as claimed in  claim 1 . 
     
     
         19 . A mechanical device as claimed in  claim 17  which is a transmission component. 
     
     
         20 . A mechanical device as claimed in  claim 17  which is a transmission component, a bearing, or a gear train.