RU2512695C1 - Method for producing elastic terminal for rail attachment, and elastic terminal - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: hot-rolled rod with diameter of 13-17 mm is made from steel containing the following, wt %: carbon 0.50-0.65, silicon 0.05-0.20, manganese 0.07-0.15, aluminium 0.02-0.09, nitrogen 0.004-0.016, titanium 0.025-0.10, niobium 0.010-0.035, chrome 0.05-0.10, nickel 0.05-0.10, copper 0.15-0.20, iron and inevitable impurities are the rest; a B-shaped terminal is made from the rod, heated up to 850-920°C, then cooled with a fast water flow during 6-8 seconds and annealing is performed at 180°C during 2 hours so that annealing martensite structures are provided in the surface layer of the terminal, and troostosorbite is provided in the core.

EFFECT: providing stability of mechanical properties of elastic terminals, relaxation stability and cyclic durability.

2 cl, 1 tbl, 1 ex

Description

The invention relates to the field of engineering and metallurgy, in particular to the manufacture of a spring product in the form of an elastic terminal of the upper structure of the track, subject to high loads in operation.

A known method of manufacturing an elastic terminal made of steel for rail fastening, including the shaping of the terminal from the bar and heat treatment (see RU 2227812 C2, C21D 9/02, 04/27/2004) [1].

Known elastic rail fastening terminal made of a steel bar containing a loop-shaped middle part, two intermediate sections located on both sides of it, two loops resting on the upper part of the rail sole (RU 2189417 C2, ЕВВ 9/48, 09/20/2002) [ 2].

Known elastic rail fastening terminal made of steel bar with the formation of a B-shaped in the plane of the terminal (RU 2252287 C2, EB 9/00, 05/20/2005) [3].

During operation, the elastic terminals of the track’s upper structure are subjected to prolonged loads in the form of bending moment, torque and their combination under the influence of atmospheric precipitation of various climatic zones and the aggressive effect of transported goods. The materials used for the manufacture of terminals have specific requirements, namely: resistance to small plastic deformations and high relaxation resistance.

The stability of the elastic characteristics at the operational content of the elastic terminals provides a high holding ability of the rails against theft, a stable gauge and high fatigue strength of the terminals under cyclic loading.

Steel 60С2А according to GOST 14959-79 with through hardenability with ensuring uniform hardness over the cross section - 45-49 HRC found the widest application for the manufacture of terminals.

Known terminal with a gradient of hardness in the cross section of steel according to GOST 1050-88 - steel 58 (55PP).

Steel 58 (55PP) contains, wt.%: Carbon 0.55-0.63; silicon 0.10-0.30; manganese <0.20; chrome <0.15; nickel <0.25; copper <0.25; iron is the basis.

A disadvantage of the known steel-made terminals is the lack of stability of the mechanical properties obtained by the heat treatment, microstructure and hardness over the cross section of rods with diameters of 13-17 mm, and, accordingly, the stability of the relaxation resistance and cyclic durability of the terminals. The lack of stability of these characteristics during the heat treatment of terminals made of steel 58 (55PP) from rods with a diameter of 13-17 mm does not allow to achieve optimal properties for elastic terminals with stable characteristics in terms of holding capacity against rail theft, track width and cyclic durability. The technical result is to ensure the stability of the mechanical properties of the elastic terminals, relaxation resistance and cyclic durability.

To achieve a technical result, the invention on a method for manufacturing an elastic terminal for rail fastening includes steelmaking in the following ratio of components, wt.%:

carbon 0.50-0.65 silicon 0.05-0.20 manganese 0.07-0.15 aluminum 0.02-0.09 nitrogen 0.004-0.016 titanium 0.025-0.10 niobium 0.010-0.035 chromium 0.05-0.10 nickel 0.05-0.10 copper 0.15-0.20 copper 0.15-0.20 iron and inevitable impurities rest,

production of hot-rolled bars with a diameter of 13-17 mm, shaping from a bar of a B-shaped terminal in the plane of the terminal, heating to 850-920 ° C, cooling with a fast-moving stream of water for 6-8 s and tempering at 180 ° C for 2 hours providing in the surface layer of the terminal the structure of the martensite of tempering, and in the core - troost-sorbitol structure.

To achieve the technical invention claimed elastic terminal for rail fastening, made in the form of a hot-rolled steel rod with a diameter of 13-17 mm, containing, wt.%:

carbon 0.50-0.65 silicon 0.05-0.20 manganese 0.07-0.15 aluminum 0.02-0.09 nitrogen 0.004-0.016 titanium 0.025-0.10 niobium 0.010-0.035 chromium 0.05-0.10 nickel 0.05-0.10 copper 0.15-0.20 iron and inevitable impurities rest,

subjected to quenching by a fast moving water flow and low-temperature tempering, having a tempering martensite structure in the surface layer, and troostor sorbitol in the core. The proposed combination of alloying elements and a limitation on the content of impurity elements makes it possible to obtain an initial homogeneous, fine-grained steel structure with an austenitic grain score of 10-12 and reduced hardenability, which ensures, after quenching, by a fast-moving water flow and tempering, obtaining mechanical properties optimal for the terminals, in particular, strength and limit yield strength and elastic limit.

The grain size in steel significantly affects its properties. So coarse grain reduces strength, ductility and cold brittleness threshold, and also increases the tendency to brittle fracture of steel and increases hardenability.

The stated carbon content range provides the necessary strength and hardenability. With a content of less than 0.50 wt.%, The required level of strength is not provided and the terminal has increased plasticity, and with a content of more than 0.65 wt.%, Graphitization centers are formed, as a result of which relaxation resistance and durability are reduced.

Silicon not only deoxidizes the steel, but also strengthens it and increases the elastic limit, which increases the relaxation resistance. When the silicon content is less than 0.05 wt.%, The strength and elasticity of the steel become lower than the acceptable level and the required level of deoxidation is not achieved, and when the content is above 0.20 wt.%, Ductility decreases and the steel becomes brittle.

Manganese not only deoxidizes steel, but also increases its strength, elasticity, wear resistance and durability. When the manganese content is more than 0.15 wt.%, Hardenability increases, which for terminals made of bars of the proposed steel with a diameter of 13-17 mm leads to an increase in the depth of the hardened layer, a decrease in the level of compressive stresses in the hardened layer, and, as a consequence, to a decrease in durability terminals and increase their sensitivity to surface voltage concentrators.

The introduction of aluminum in steel in an amount of 0.02-0.09 wt.% Allows not only to deoxidize, but also to modify the steel, in particular, due to the fact that it binds oxygen and nitrogen to oxides and nitrides, which are effective barriers to growth austenitic grain. In addition, the excessive introduction of aluminum of more than 0.09 wt.% Into the steel will lead to its graphitization, which will sharply reduce the operational resistance of the terminals made of this steel.

Nitrogen strengthens the steel due to the formation of aluminum nitrides, which contribute to obtaining a fine-grained structure. To bind aluminum to produce aluminum nitride, the nitrogen content must be at least 0.004 wt.%. When the nitrogen content exceeds 0.016 wt.%, Excess nitrogen appears in the form of bubbles on the surface of the obtained ingot, which reduces the mechanical properties and complicates its further processing.

The content of phosphorus and sulfur is regulated by their ratio for structural steels.

Titanium and niobium in steel in the above ranges contribute to the production of hereditary fine-grained steel.

Microalloying copper is based on the fact that it crystallizes last, concentrating along the grain boundaries, reducing the likelihood of burnout. Therefore, the ductility of steel increases. In addition, copper increases the corrosion resistance of steel, but its effect on corrosion resistance is not noticeable when the content is less than 0.15 wt.%. When the copper content exceeds 0.20 wt.%, Brittle phases of copper will lead to cracking along the grain boundaries during deformation.

Microalloying of chromium is based on the fact that it participates in solid-solution hardening, however, at a content of less than 0.05 wt.%, The strength and hardness of steel become less than the allowable limit for a given class of steels, and at a content of more than 0.10 wt.% The hardenability of steel increases above allowable value.

Nickel microalloying is based on solid solution hardening and increasing corrosion resistance, however, nickel has practically no effect on these characteristics at a content of less than 0.05 wt.%, And an increase in content over 0.10 wt.% Is impractical due to an increase in hardenability.

The structure of tempering martensite and trostano-sorbitol, which is stably obtained during quenching by a fast-moving water flow, provides the required hardness of the surface zone of terminal 55-60 HRC (martensite) and core 30 - 40 HRC (trostano-sorbitol), high terminal strength, operational reliability and durability. The structure of troost-sorbitol in the core of the terminal is more favorable than the troostite structure observed in most standard silicon spring-spring steels, since it has greater strength, ductility and toughness, which increases the durability of the terminals. It should be noted that with the structure of martensite in the surface layer and trostrostorbit in the core, a favorable diagram of internal residual stresses is induced along the terminal bar cross section: compressive stresses in the surface hardened layer and tensile stresses in the core, which best corresponds to the terminal loading during operation.

Example

Experimental swimming trunks were carried out in induction furnaces. Before casting, steel was deoxidized and modified by the introduction of aluminum, titanium, and niobium to provide a hereditarily fine-grained structure. The composition of the smelted steel is given below in table 1. The austenitic grain score was 10-12, which indicates the receipt of a hereditarily fine-grained structure.

Table 1 No. FROM Si Mn A1 N Ti Nb Cr Ni Cu Fe one 0.60 0,07 0.10 0.02 0.01 0,025 0.010 0,07 0.10 0.15 the basis 2 0.62 0.10 0.15 0.08 0.01 0.1 0,035 0.10 0.10 0.16 the basis

A batch of 20 samples was made of hot-rolled bars with a diameter of 13 and 17 mm, which were subjected to heat treatment: quenching by a fast-moving stream of water from a heating temperature of 900 ° C and tempering at 180 ° C for 2 hours.

To determine hardenability after quenching by a fast-moving stream of water, the rods were cut, the structure was examined, and hardness was measured. The thickness of the hardened layer was 2.5-3.0 mm (for ⌀13 mm) and 3.0-3.5 mm (for ⌀17 mm), the surface hardness was 64-65 HRC (for ⌀13 mm) and 65-66 HRC (for ⌀17 mm), core hardness 35-40 HRC (for ⌀13 mm) and 30-35 HRC (for ⌀17 mm), critical cooling rate: 180 ° C / s (for 013 mm) and 200 ° C / s (for ⌀17 mm).

After tempering at 180 ° C for 2 hours, the hardness of the rods decreased to the following values and amounted to 56–59 HRC (for ⌀ 13 mm) and 56–59 HRC (for ⌀17 mm) for a batch of samples with diameters of 13 and 17 mm ), in the core 35-38 HRC (for ⌀13 mm) and 32-35 HRC (for ⌀17 mm).

The structure of the surface layer after quenching by a fast-moving flow of water and tempering in all the samples was tempering martensite, and the core was trost-sorbitol.

Tests for mechanical properties were carried out on cylindrical samples with a diameter of 6 mm and a design length of 30 mm, made of bars of the proposed steel in the delivery state. The mechanical properties of the hardened layer obtained at the terminals after quenching by a fast moving water flow and tempering were simulated by quenching samples of the indicated sizes with preliminary heating in a salt bath to a quenching temperature of 900 ° C and intensive cooling with a fast moving water stream in a special quenching device. To determine the mechanical properties of the core, cylindrical samples of the indicated sizes were made from the core of the bars of the proposed steel after quenching by a fast-moving stream of water and tempering.

The mechanical properties of the investigated samples of the proposed steel in the delivery state are: steel strength σ _in - 800 MPa, yield strength σ _0.2 - 460 MPa, elastic limit σ _0.05 - 300-350 MPa. The values of these properties in the delivery state positively characterize the proposed steel in terms of machinability.

After quenching, which is close in mode to quenching by a fast-moving water flow, and tempering, the mechanical properties of the proposed steel of the test samples corresponding to the properties of the hardened layer of the terminal are: steel strength σ _в - 2300-2500 MPa, yield strength σ _0.2 - 1950-2000 MPa , elastic limit σ _0.05 - 1600-1750 MPa.

The mechanical properties of the core of the pond of the proposed steel of the test samples after quenching by a fast-moving water flow and tempering are: steel strength σ _in - 1100 MPa, yield strength σ _0.2 - 800 MPa, elastic limit σ _0.05 - 750 MPa.

Stable provision of the described level of mechanical properties in the surface and in the core of the terminals is a distinctive feature of the proposed steel. This combination of properties over the cross section of the terminal bar means obtaining greater strength, relaxation resistance and cyclic durability of both the bars of the proposed steel themselves and the terminals made of it.

The relaxation resistance of the bars of the proposed steel of the studied samples after quenching by a fast-moving flow of water and tempering, determined during static tests of the rods for three-point bending with registration of plastic deformation values, is characterized by the following indicators: yield strength σ _0.2 - 2500 MPa, elastic limit σ _0.05 - 1950 MPa, proportionality limit σ _0.01 - 1250 MPa.

The relaxation resistance of the terminals themselves, made of bars of the proposed steel of the studied samples after quenching by a fast-moving stream of water and tempering, estimated by the value of the residual deformation, is 0.5 mm (the difference between the terminal height after the third and second compression).

The cyclic durability, estimated during tests for three-point bending of the bars of the proposed steel, amounted to 5 million loading cycles with an endurance of 1100-1200 MPa. The cyclic durability of the terminals made of the proposed steel and hardened by quenching with a fast-moving flow of water and tempering is 2 million loading cycles with double movement of the terminal mustache in comparison with standard ones.

As a result of the tests, it was found that these characteristics of steel and terminals made of it are stably provided in the entire range of its chemical composition for rod diameters of 13-17 mm.

Thus, the stabilization of the structure is ensured by the method of complex alloying, and the restriction of the content of the components is selected for effective interaction between each other, which results in fine austenite grain (10-12 points) and the resulting structure of tempering martensite and trostan-sorbitol in the surface layer and core, respectively, high performance including relaxation resistance and cyclic durability.

Claims (2)

1. A method of manufacturing an elastic terminal for rail fastening from a hot-rolled steel bar with a diameter of 13-17 mm, containing, in wt.%:
carbon 0.50-0.65 silicon 0.05-0.20 manganese 0.07-0.15 aluminum 0.02-0.09 nitrogen 0.004-0.016 titanium 0.025-0.10 niobium 0.010-0.035 chromium 0.05-0.10 nickel 0.05-0.10 copper 0.15-0.20 iron and inevitable impurities rest,
including forming a B-shaped terminal, heating to 850-920 ° C, cooling with a fast-moving water stream for 6-8 s and tempering at 180 ° C for 2 hours, providing tempering martensite structure in the surface layer of the terminal, and in the core troost-sorbitol. 2. An elastic terminal for rail fastening, characterized in that it has a tempering martensite structure in the surface layer and troostorosorbite in the core and is made by the method according to claim 1.