RU2277135C1 - Steel - Google Patents

Abstract

FIELD: ferrous metallurgy, steels used for manufacture of critical parts working under high contact loads and sliding friction in diesel oil medium; injectors for fuel injection pumps.

SUBSTANCE: proposed steel contains carbon, silicon, manganese, chromium, vanadium, sulfur, zirconium, nitrogen, phosphorus, nickel and iron at the following ratio of components, mass-%: carbon, 1.6-1.8; silicon, 0.7-1.0; manganese, 0.15-0.40; chromium, 12.6-13.5; vanadium, 1.0-1.2; sulfur, 0.01-0.05; zirconium, 0.01-0.15; nitrogen, 0.01-0.05; phosphorus, lesser than 0.03; nickel, lesser than 0.35; the remainder being iron. Provision is made for reduction of tendency to setting at sliding over engageable surface and ensuring hardness higher than 61 HRc after hardening and tempering at temperature higher than 300°C, as well as reduction of tendency to absorption of decomposition products of diesel fuel.

EFFECT: enhanced contact fatigue strength during operation in diesel fuel.

2 tbl

Description

The invention relates to ferrous metallurgy, in particular to alloys of the steel group, and can be applied to critical parts operating simultaneously under conditions of high contact loads and sliding friction in a diesel fuel, in particular for nozzles of nozzles of fuel pump nozzles.

Specific conditions for the production and operation of atomizer needles impose special requirements on the material to ensure high contact fatigue strength, a minimum tendency to coking surfaces and a minimum coefficient of friction to prevent the needle from hanging.

Currently used for the manufacture of atomizer needles, P18 steel (GOST 19265-73), having high hardness and wear resistance, is prone to surface absorption by elements that are part of diesel fuel (coking), and simultaneous microcracking during contact-fatigue loads, setting during sliding with mating steel surface. With an increase in the service life of fuel pumps to 12-14 thousand hours, the needles of the atomizers limit their operability.

The prototype of the proposed invention is steel X12F1 (GOST 5950-73), related to the cheapest grades of steels having a high complex of physical and mechanical properties, with the following chemical composition, wt.%:

Carbon 1.25-1.45 Manganese 0.15-0.40 Chromium 11.0-12.5 Vanadium 0.7-0.9 Silicon 0.15-0.35 Sulfur no more than 0,03 Phosphorus no more than 0,03 Nickel no more than 0,35 Iron rest

After quenching and tempering, this steel shows the following set of physical and mechanical properties:

- contact fatigue strength - 1100 MPa,

- average coefficient of friction - 0.135,

- hardness - 57 HRc,

- the surface of the needle after 5000 hours of operation in an environment of diesel fuel is black, with a network of small cracks.

Such a set of physicomechanical properties of X12F1 steel cannot satisfy the increased requirements for the nozzles of the nozzles of fuel pump nozzles due to the low level of contact fatigue strength and hardness, a large friction coefficient at which the needle may hang.

The invention achieves the technical result, which consists in:

- increase contact fatigue strength when working in diesel fuel,

- a decrease in the tendency to seize when sliding along the mating surface (decrease in the coefficient of friction),

- providing hardness of more than 61 HRc after quenching and tempering (at temperatures above 300 ° C),

- reducing the tendency to absorption by the surface of the decomposition products of diesel fuel.

The specified technical result is achieved in that the steel according to the invention contains carbon, silicon, manganese, chromium, vanadium, sulfur, zirconium, nitrogen, phosphorus, nickel and iron in the following ratio of components, wt.%:

Carbon 1.6-1.8 Silicon 0.7-1.0 Manganese 0.15-0.40 Chromium 12.6-13.5 Vanadium 1.0-1.2 Sulfur 0.01-0.05 Zirconium 0.01-0.15 Nitrogen 0.01-0.05 Phosphorus less than 0.03 Nickel less than 0.35 Iron rest

The carbon content is limited to 1.6-1.8% to obtain the optimal amount of special carbides and cementite phase. When the carbon content is less than 1.6% during tempering, a metastable ξ - carbide phase is formed, the change in the parameters of which contributes to the lattice distortion of the α phase and an increase in the absorption capacity. If the carbon content exceeds 1.8%, then at a given content of carbide-forming elements, twinning martensite may form, when quenched from the optimum temperature, the internal stress of which contributes to the formation of microcracks.

The lower limit for silicon is limited to 0.7%. The silicon content below this limit will not provide the necessary hardening of the solid solution and accelerate the selection of alloying elements from it for the formation of carbide phases during tempering. A silicon content above 1.0% will lead to embrittlement of the steel by reducing the resistance to crack nucleation.

The lower limit for chromium is 12.6%. A chromium content below this level will not provide enough special carbides, which will negatively affect contact fatigue strength. The upper limit for chromium is limited to 13.5%. The chromium content above this limit will cause the formation of an excess of special carbides, which does not give the optimal amount of carbon in the solid solution and the necessary hardening and will lead to increased coking of the surface.

The limits for manganese are selected in the range of 0.15-0.4%. A manganese content below 0.15 will not provide sufficient deoxidation of the metal, above 0.4% - will lead to the facilitation of the formation of a metastable carbide phase, enhancing the absorbent capacity of steel.

The vanadium limits are limited to 1.0-1.2%. A vanadium content below 1.0% will not ensure complete carbon binding and the release of special carbides and carbonitrides during high tempering, which will negatively affect contact strength. A content of vanadium above 1.2% leads to an increase in residual austenite after quenching, a decrease in hardness during tempering due to its decomposition at elevated temperatures, and a decrease in the dispersion of the carbide phase and, as a consequence, a decrease in contact fatigue strength.

The lower limit for zirconium is defined as 0.01%. The content of zirconium below this limit will not provide the necessary refinement of grain boundaries and their optimal size of 6-8 points.

The upper limit for zirconium is limited to 0.15%. The zirconium content above this limit does not change the grain size, but leads to the formation of complex carbides of chromium and zirconium, which, located at the grain boundaries, contribute to increased absorption of fuel decomposition products.

The sulfur content is limited to 0.01-0.05%, thereby eliminating the possibility of setting metal during translational motion, as a result of which the coefficient of friction is reduced. A sulfur content above 0.05% will lead to excessive contamination of the steel with non-metallic inclusions and a decrease in contact strength.

The lower limit for nitrogen is determined to be 0.01%. A nitrogen content below this limit will not provide dispersion precipitation of a sufficient amount of chromium carbonitrides during tempering, resulting in a decrease in hardness.

The upper limit on nitrogen is 0.05%. A nitrogen content above this limit will lead to the formation of large chromium carbonitrides, high carbide heterogeneity, and an increase in the coefficient of friction.

The maximum limitation of phosphorus and nickel is determined by the capabilities of the electric steelmaking unit.

Joint additional alloying of the proposed alloy with zirconium, nitrogen, silicon, as well as an increased content of carbon, vanadium and chromium in the indicated ranges made it possible to obtain the necessary complex of its operational characteristics.

Steel chemical composition according to the invention is manufactured in electric steelmaking units. There are no special features in loading the charge, conducting smelting, and casting. Ferrovanadium (TU 14-5-98-78), nitrogenous ferrochrome (GOST 4757-59), ferrosilicacirconium (TU 14-5-83-77), silicocalcium (GOST 4762-71) are added to the charge.

Table 1 shows the chemical composition of the steels (in% by weight) smelted during the implementation of the invention (see melting No. 1-3), as well as the chemical composition of steels that fall outside the ranges specified in the proposed invention (see melting No. 4- 10).

Table 2 shows the characteristics of the physicomechanical properties of steels according to table 1, which are of primary importance for the working conditions of atomizer needles.

Steels (smelting No. 1-3) have greater contact fatigue strength and a reduced coefficient of friction with respect to steels (smelting No. 4-9) and significantly exceed the known steel X12F1 (smelting No. 10) in terms of performance.

Thus, after quenching 1150 ° C and tempering 520 ° C, the proposed steel has the following set of physico-mechanical properties:

- hardness - 65-68 HRc,

- coefficient of friction - 0,080-0,086,

- contact fatigue strength - 1600-1750 MPa,

- the surface of the spray needles after 5000 hours of operation in a diesel fuel environment is clean, light brown, without cracks.

The expected economic effect is due to a decrease in the cost of the material used and an increase in the service life of the fuel pump nozzles and will amount to about 25 million rubles.

Table 1 No. of swimming trunks Carbon Silicon Manganese Chromium Vanadium Sulfur Zirconium Nitrogen Iron one 1.65 0.7 0.15 12.6 1,2 0,025 0.01 0.01 rest 2 1,6 0.95 0.28 12.8 1,0 0,026 0.09 0.017 rest 3 1.8 1,0 0.40 13.5 1,1 0,020 0.15 0,025 rest four 1.45 0.7 0.25 12.5 0.8 0,022 0.24 0.015 rest 5 1,5 1.20 0.26 12.7 0.8 0,042 0.09 0.015 rest 6 1.4 0.9 0.22 13.1 0.8 0.05 0.08 0.009 rest 7 1.7 0.6 0.21 13,2 1.15 0,022 0.26 0,026 rest 8 1,6 0.5 0.30 12.8 1.25 0,025 0.05 0.016 rest 9 1.85 1.4 0.35 12.5 0.8 0,020 0.06 0.017 rest 10 (prototype) 1.25-1.45 0.15-0.35 0.15-0.40 11.0-12.5 0.7-0.9 0,030 - - rest

Claims (1)

Steel containing carbon, silicon, manganese, chromium, vanadium, sulfur, zirconium, nitrogen, phosphorus, nickel and iron in the following ratio, wt.%: Carbon 1.6-1.8 Silicon 0.7-1.0 Manganese  0.15-0.40 Chromium 12.6-13.5 Vanadium 1.0-1.2 Sulfur 0.01-0.05 Zirconium 0.01-0.15 Nitrogen 0.01-0.05 Phosphorus Less than 0.03 Nickel Less than 0.35 Iron Rest