Steel composition
The present invention relates to a steel composition carburizable and/or nitritable, comprising, in percentages by weight of the total composition: Carbon: 0.05-0.40, preferably 0.10-0.30; Chromium: 2.50-5.00, preferably 3.00-4.50; Molybdenum: 4.00-6.00; Tungsten: 0.01-1.80, preferably 0.02-1.50; Vanadium: 1.00-3.00, preferably 1.50-2.50; Nickel: 2.00-4.00; Cobalt: 2.00-8.00, preferably 3.00-7.00; Iron: balance as well as the inevitable impurities, optionally further comprising one or more of the following elements: Niobium: ≤2.00; Nitrogen: ≤0.50, preferably ≤0.20; Silicon: ≤0.70, preferably 0.05-0.50; Manganese: ≤0.70, preferably 0.05-0.50; Aluminum: ≤0.15, preferably ≤0.10; the combined niobium+vanadium content being in the range 1.00-3.50; and the carbon+nitrogen content being in the range 0.05-0.50. It further relates to the method of production thereof, the steel blank obtained and a mechanical device comprising the latter.
1. A steel composition carburizable and/or nitritable comprising, in percentages by weight of the total composition:
Carbon: 0.05-0.40;
Chromium: 2.50-5.00;
Molybdenum: 4.00-6.00;
Tungsten: 0.01-1.80;
Vanadium: 1.00-3.00;
Nickel: 2.00-4.00;
Cobalt: 2.00-8.00;
Iron: balance
as well as the inevitable impurities,
optionally further comprising one or more of the following elements:
Niobium: ≤2.00;
Nitrogen: ≤0.50;
Silicon: ≤0.70;
Manganese: ≤0.70;
Aluminum: ≤0;
the combined niobium+vanadium content being in the range 1.00-3.50;
and the carbon+nitrogen content being in the range 0.05-0.50.
2. The steel composition as claimed in claim 1 , wherein it comprises, in percentages by weight of the total composition:
Carbon: 0.10-0.30;
Chromium: 3.00-4.50;
Molybdenum: 4.00-6.00;
Tungsten 0.02-1.50;
Vanadium: 1.50-2.50;
Nickel: 2.00-4.00;
Cobalt: 3.00-7.00;
Silicon: 0.05-0.50;
Manganese: 0.05-0.50;
Iron: balance
as well as the inevitable impurities,
optionally further comprising one or more of the following elements:
Niobium: ≤2.00;
Nitrogen: ≤0.20;
Aluminum: ≤0.10;
the combined niobium+vanadium content being in the range 1.00-3.50;
and the carbon+nitrogen content being in the range 0.05-0.50.
3. The steel composition as claimed in claim 1 , wherein it comprises at most 1 wt % of inevitable impurities relative to the total weight of the composition.
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 , wherein the tungsten content is in the range 0.03-1.40 in percentages by weight of the total composition.
6. The steel composition as claimed in claim 5 , wherein the tungsten content is in the range 0.04-1.30 in percentages by weight of the total composition.
7. The steel composition as claimed in claim 1 , wherein, after thermochemical treatment, followed by heat treatment, it has a surface hardness greater than or equal to 64 HRC.
8. The steel composition as claimed in claim 7 , wherein the heat treatment comprises solution heat treatment at a temperature between 1090° C.-1160° C. followed by quenching optionally with cooling to a temperature below −40° C. and several tempering operations, at a temperature greater than or equal to 475° C.
9. The steel composition as claimed in claim 1 , wherein, after thermochemical treatment, followed by heat treatment, it has a martensitic structure having a residual austenite content below 10% and that is free from ferrite and pearlite.
10. A mechanical device, formed from steel having the composition as claimed in claim 1 .
11. The mechanical device according to claim 10 , which is a bearing or a gear train.
12. A method for producing a steel blank having the composition as claimed in claim 1 , wherein it comprises:
a) a steelmaking step;
b) a step of processing the steel;
c) a thermochemical treatment;
d) and a heat treatment.
13. The production method as claimed in claim 12 , wherein step b) consists of a step of rolling, forging and/or extrusion.
14. The production method as claimed in claim 12 , wherein the steelmaking step a) is carried out by a conventional production process of arc furnace refining and electro slag remelting (ESR), or by a VIM-VAR process, optionally with a step of electro slag remelting (ESR) and/or vacuum arc remelting (VAR), or by powder metallurgy.
15. A steel blank obtainable by a method as claimed in claim 12 .
16. The production method as claimed in claim 12 , wherein step c) consists of a treatment of carburization or nitriding or carbonitriding or carburization and then nitriding.
17. The production method as claimed in claim 16 , wherein step c) consists of a treatment of carburization.
18. The production method as claimed in claim 12 , wherein step d) comprises solution heat treatment at a temperature between 1090° C.-1160° C., followed by holding at this temperature until there is complete austenitization optionally with cooling to a temperature below −40° C., and several tempering operations, at a temperature greater than or equal to 475° C.
19. The production method as claimed in claim 18 , wherein the tempering operations are carried out at a temperature greater than or equal to 500° C.
20. The production method as claimed in claim 18 , wherein the heat treatment is carried out at a temperature between 1100° C.-1150° C.