RU2447183C1 - Heat-resistant bearing steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed steel comprises carbon, silicon, manganese, nickel, molybdenum, vanadium, nitrogen, sulfur and iron at the following ratio in wt %: carbon - 0.8 - 1.1, silicon - 0.3 - 0.5, manganese - 0.1 - 0.4, chromium - 4.5 - 5.5, tungsten - 1-1.5, nickel - 0.15 0.4, molybdenum - 3.0 - 3.5, vanadium - 0.5 - 1.0, niobium - 0.1-0.3, tantalum - 0.05-0.15, iron making the rest.

EFFECT: higher fatigue strength, flexural strength, impact number and structural uniformity.

2 tbl, 1 ex

Description

The invention relates to the field of metallurgy, in particular to the creation of heat-resistant steels for bearings operating at temperatures up to 500 ° C and used, for example, for aircraft gas turbine engines (GTE) and helicopter gearboxes.

Known heat-resistant bearing steel grade 8X4M4V2F1Sh of the following chemical composition, wt.%:

carbon 0.75-0.85 manganese ≤0.40 silicon ≤0.40 chromium 3.9-4.4 tungsten 1.5-2.0 vanadium 0.9-1.2 molybdenum 3.9-4.4 nickel no more than 0,35 iron rest

A.G. Spector, B.M. Zelbet, S.A. Kiseleva. The structure and properties of bearing steels. M .: Metallurgy, 1980, p.16.

A disadvantage of the known steel is the increased decarburization at hot deformation, annealing and hardening temperatures and increased sensitivity to oxidation, as well as the instability of the impact strength.

Also known heat-resistant bearing steel grade M50 of the following chemical composition, wt.%:

carbon 0.77-0.85 manganese ≤0.35 silicon ≤0.25 chromium 3.75-4.25 vanadium 0.9-1.10 molybdenum 4.0-4.50 iron rest

A.G. Spector, B.M. Zelbet, S.A. Kiseleva. The structure and properties of bearing steels. M .: Metallurgy, 1980, p.16.

The disadvantage of steel is low heat resistance during prolonged heating up to 500 ° C. Steel is prone to grain growth, has insufficient toughness and is sensitive to decarburization and oxidation.

Known low-carbon masonry steel for large bearings of the following chemical composition, wt.%:

carbon 0.1-0.3 manganese 0.2-1.0 silicon 0.2-0.6 chromium no more than 1,2 vanadium 0.25-0.85 molybdenum 4-6 nickel 2.5-3.5 iron the rest (US Patent No. 4004952)

An increase in the molybdenum content in known steel up to 6% contributes to the formation of a saturated carbide zone on the surface, which prevents the diffusion of carbon deeper into the layer and reduces its static bending strength and fatigue strength.

The closest analogue taken as a prototype is heat-resistant bearing steel of the following chemical composition, wt.%:

carbon 0.7-0.8 manganese 0.05-0.4 silicon 0.05-0.4 chromium 4.0-4.6 tungsten 8.5-9.5 vanadium 1.40-1.70 cerium 0.005-0.10 calcium 0.005-0.10 yttrium 0.005-0.10 iron the rest (RF Patent No. 2185458)

Microalloying of steel is not optimal due to the presence of an increased amount of tungsten, which contributes to an increase in the amount of M ₆ C carbide, which coagulates strongly during slow cooling, and as a result, large carbides with an angular or square shape are formed. Such carbides, unlike ordinary smaller and rounded ones, inhibit grain growth less when heated for hardening, and the hardened steel turns out to be coarser-grained, which leads to a decrease in static bending strength, fatigue strength, impact strength and an increase in the level of carbide inhomogeneity according to GOST 19265 Carbide heterogeneity contributes to the chipping of the working surface of the bearings.

The technical task of the invention is the creation of heat-resistant bearing steel, operating up to 500 ° C, with improved characteristics of fatigue strength, static bending strength, high uniformity of the structure with fine grain and significantly finer carbides, providing high values of impact strength.

To solve this problem, we propose a heat-resistant bearing steel containing carbon, manganese, silicon, chromium, tungsten, vanadium, iron, which additionally contains molybdenum, nickel, niobium and tantalum in the following ratio of components, wt.%:

carbon 0.8-1.1 manganese 0.1-0.4 silicon 0.3-0.5 chromium 4,5-5,5 tungsten 1-1.5 vanadium 0.5-1.0 molybdenum 3-3.5 nickel 0.15-0.4 niobium 0.1-0.3 tantalum 0.05-0.15 iron rest

Alloying steel with molybdenum at the stated tungsten content made it possible to obtain significantly lower carbide heterogeneity and higher values of fatigue strength, static bending strength, and impact strength. Additional alloying with nickel made it possible to increase the viscosity of the α matrix, which also contributed to an increase in impact strength.

The introduction of niobium and tantalum made it possible to obtain very stable carbides (NbC, Tac), which are practically insoluble in austenite, delaying grain growth upon heating under quenching. Grinding grain improves toughness and hardening.

Thus, reducing the amount of tungsten, alloying with molybdenum, nickel, as well as microalloying with niobium and tantalum with the declared content and ratio of components increase the mechanical properties of heat-resistant bearing steel.

Examples of implementation

In experimental laboratory conditions, the proposed steel was tested (examples 1-3), smelted in a vacuum induction furnace using electroslag remelting. The chemical composition and mechanical properties of the proposed steel and steel prototype (example 4) are shown in tables 1, 2.

The ingots of the proposed steel were subjected to hot plastic deformation (forging) to produce bars of various sections. After annealing, samples were made from rods to determine the mechanical properties. On the samples after quenching and tempering of the precipitation hardening, a hardness of 60-65 HRC was provided. The steel prototype after heat treatment had a hardness of 59-63 HRC.

As can be seen from table 2, the proposed steel surpasses the prototype steel in static bending strength ~ 15%, impact strength ~ 2.5-3 times, fatigue strength ~ 15%.

The carbide heterogeneity of the proposed steel is 1 point instead of 4 according to the prototype, and the carbide size is 10 μm instead of 20 μm.

The proposed steel is technologically advanced in production. The ability to manufacture bearings by rolling from a tube billet instead of forging reduces labor intensity by 25-30%.

The use of heat-resistant bearing steel will improve the reliability and service life of gas turbine engines.

Table number 1 Steel number The content of elements (wt.%) C Mn Si Cr W V Mo Ni Nb Ta Ce Sa Y Fe one 0.8 od 0.3 4,5 1,0 0.5 3.0 0.15 0.1 0.05 - - - rest 2 0.9 0.3 0.4 5,0 1.3 0.8 3.2 0.3 0.2 0.10 - - - - // - 3 1,1 0.4 0.5 5.5 1,5 1,0 3,5 0.4 0.3 0.15 - - - - // - prototype 0.7 0.2 0.2 4.3 9.0 1,5 - - - - 0.1 0.1 0.1 - // -

Table number 2 No. p / p Mechanical properties Carbide heterogeneity score The size of carbides, microns Grain size, point Static bending strength σ _in ^mfd, MPa Impact strength KS, J / cm ² Fatigue strength σ _-1 based on 2 × 10 ⁷ cycles, MPa prototype 2100 2 700 four twenty 5 one 2400 5 800 one 10 9 2 2500 5 820 one 10 10 3 2600 6 850 one 10 10

Claims (1)

Heat-resistant bearing steel containing carbon, manganese, silicon, chromium, tungsten, vanadium and iron, characterized in that it additionally contains molybdenum, nickel, niobium and tantalum in the following ratio, wt.%:
carbon 0.8-1.1 manganese 0.1-0.4 silicon 0.3-0.5 chromium 4,5-5,5 tungsten 1.0-1.5 vanadium 0.5-1.0 molybdenum 3.0-3.5 nickel 0.15-0.4 niobium 0.1-0.3 tantalum 0.05-0.15 iron rest