RU2449045C1 - Rail steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to ferrous metallurgy, and namely to making of steel used for manufacture of railway rails. Steel contains carbon, manganese, silica, vanadium, aluminium, chrome, nickel, nitrogen, iron and impurities at the following component ratio, wt %: carbon 0.77 - 0.84, manganese 0.90 - 0.95, silica 0.20 -0.35, vanadium 0.06 - 0.10, aluminium of not more than 0.004, nitrogen 0.010 - 0.018, chrome of not more than 0.15, nickel of not more than 0.15, iron and impurities are the rest. Steel contains the following components as impurities, wt %: sulphur of not more than 0.015, phosphorus of not more than 0.020, copper of not more than 0.20 and oxygen of not more than 0.0018.

EFFECT: improving strength properties of steel, ductility and cold resistance due to formation of disperse structure of hardening sorbite and steel purity increase as to nonmetallic inclusions.

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Description

The invention relates to ferrous metallurgy, in particular to the production of steel for the production of railway rails.

Known rail pearlitic steel [1], containing 0.71-0.82%; 0.75-1.05% Mn; 0.25-0.60% Si; 0.05-0.15% V; not more than 0.025% P; no more than 0,030% S; not more than 0.02% A1.

The creation of high-strength rails with a temporary resistance of more than 1300 N / mm ² and a relative elongation of at least 12.0%, with increased operational reliability and high resistance to defect formation, presupposes a uniform pearlite structure, which can be ensured by volume quenching in oil at a specified wide range of chemical concentrations elements are difficult.

Known steels having the following chemical composition (wt.%):

- 0.65-0.8 C; 0.18-0.40 Si; 0.6-1.2 Mn; 0.001-0.01 Zr; 0.005-0.04 A1; 0.004-0.011 N is one element from the group consisting of Ca and Mg 0.0005-0.015; 0.004-0.040 Nb; 0.05-0.3; Fe - oct. [2].

-0.69-0.82 C; 0.45-0.65 Si; 0.6-0.9 Mn; 0.004-0.011 N; 0.005-0.009 Ti; 0.005-0.009 Al; 0.02-0.10 V; 0.0005-0.004 Ca; 0.0005-0.005 Mg; 0.15-0.4 Cr; Fe - rest [3].

Significant disadvantages of these steels are low toughness and cold resistance, reduced reliability and operational stability.

In steel [2], this is determined by the absence of vanadium and a low nitrogen content. It has a relatively large austenite grain (grades 7-8). The high aluminum content in it leads to contamination with coarse line inclusions of alumina, which significantly reduces the contact fatigue strength of rails.

The indicated drawbacks of steel [3] are associated with the presence of titanium in it and a low content of vanadium and nitrogen. Titanium carbonitrides formed in liquid steel during its cooling sharply reduce the toughness and resistance to brittle fracture of rails.

The relatively low content of vanadium and nitrogen does not provide the formation of the required amount of aluminum nitrides and vanadium carbonitrides necessary for grinding austenitic grain and at the same time increase the strength properties and cold resistance of steel. The austenitic grain in this steel is relatively large and is 7-8 points.

Known steel [4], containing 0.65-0.89%; 0.18-0.65% Si; 0.6-1.2% Mn; 0.004-0.030% N; 0.005-0.02% A1; 0.0004-0.005% Ca; 0.01-0.10% V; 0.001-0.03% Ti; 0.05-0.4% Cr; 0.003-0.1% Mo; vanadium carbonitrides 0.005-0.08%; while Ca and A1 are in a ratio of 1: (4-13); e - the rest.

Significant disadvantages of steel are low toughness, increased tendency to brittle fracture and reduced service life, due to the presence of titanium in steel, low vanadium content, and high aluminum concentration. The resulting titanium carbonitrides sharply reduce the toughness and resistance to brittle fracture.

The low concentration of vanadium does not provide the formation of the required amount of vanadium carbonitrides, necessary for additional grinding of grain and increase the strength properties and cold resistance of steel.

The use of a large amount of aluminum for deoxidation of steel together with calcium leads to its contamination with accumulations of calcium aluminates, rich in alumina, which reduce contact fatigue strength.

The presence of sulfur and phosphorus in large quantities in steel leads to an increase in the red and cold brittleness of steel, respectively.

Known selected as a prototype steel [5], containing (wt.%): 0.78-0.88; 0.75-1.05 Mn; 0.25-0.45 Si; 0.03-0.15 V; not more than 0.02 Al; no more than 0,020 P; no more than 0.015 S.

Rails made of steel E83F are subjected to volume hardening in oil at low temperature and subsequent tempering.

Significant disadvantages of steel are an increased tendency to brittle fracture.

The high aluminum content in the steel leads to contamination by its lower-level inclusions of alumina, which sharply reduce the contact-fatigue strength and operational resistance of rails.

The desired technical result of the invention is the formation of a dispersed structure of quenching sorbitol, an increase in strength properties, ductility, cold resistance, and steel purity from non-metallic inclusions.

To achieve this, steel containing carbon, manganese, silicon, vanadium, aluminum, additionally contains chromium, nickel, nitrogen in the following ratio of components (wt.%):

carbon 0.77-0.84 manganese 0.90-0.95 silicon 0.20-0.35 vanadium 0.06-0.10 aluminum no more than 0,004 nitrogen 0.010-0.018 chromium no more than 0,15 nickel no more than 0,15

In addition, its composition is additionally limited by the amount of impurities in the following ratio (wt.%):

sulfur no more than 0.015 phosphorus no more than 0,020 copper no more than 0.20 oxygen no more than 0,0018

The inventive chemical composition is selected based on the following conditions. The selected carbon content ensures a uniform quenching sorbitol structure with volume hardening with a temporary tensile strength of more than 1300 N / mm ² , elongation of more than 0.12% and narrowing of more than 35%.

When the carbon content is less than 0.77%, the required level of mechanical properties is not provided.

Rails made of steel containing more than 0.84% C have a reduced impact strength at minus 60 ° C (0.15 MJ / m ² ). The introduction of Mn, V, Cr is also associated with the need to increase the viscosity and wear resistance of steel during the working contact of the wheel-rail.

The increase in silicon content is associated with the need to increase the deoxidation of steel with a decrease in the aluminum content in it, providing an increase in the purity of steel by inclusions of plastic silicates, which reduce the toughness.

The selected ratio of Mn, Si, Ni, Cr in steel containing 0.77-0.84% C provides a decrease in the austenite transformation temperature and a more dispersed quenching sorbitol structure is obtained.

The decrease in manganese compared to the prototype is due to the introduction of sufficient amounts of chromium into the steel to increase hardenability and resistance to wear. Moreover, the claimed concentrations of Ni and Cr exclude the formation of upper bainite in the microstructure, which is not allowed in the working part of the rail head. However, with a carbon content of 0.77-0.84% and a high concentration of manganese (> 0.95%), sections of upper bainite are observed in the structure of heat-strengthened rails.

As a result, the claimed contents of Mn, Si, Cr, Ni provide the required decrease in the austenite transformation temperature and the formation of a structure of dispersed quenching sorbitol, which has higher mechanical properties, hardness, and wear resistance.

The positive effect of small additions of chromium is that it, forming carbides, increases wear resistance. In the presence of chromium, the ability of Mn and V to restrain the growth of austenite grain increases.

The introduction of Nickel in the claimed range provides, along with aluminum and vanadium, obtaining a guaranteed toughness of steel at positive and negative temperatures. Its content up to 0.15% has a positive effect on toughness, and at a concentration of more than 0.15% it is possible to obtain an unacceptable structure of unacceptable upper bainite in rails.

A decrease in the aluminum content to 0.004% and oxygen less than 0.0018% provides an increase in the purity of the metal by inclusions of aluminates, leading to a decrease in their size and quantity. An aluminum content of more than 0.004% and oxygen of more than 0.0018% leads to steel contamination with lines of non-metallic inclusions of large sizes.

The use of vanadium in steel is due to the fact that it, like Cr and Mn, increases the solubility of nitrogen in the metal, binding it to strong chemical compounds (nitrides, vanadium carbonitrides), which grind austenite grain and reduce its tendency to grow when heated.

The introduction of V, N within the claimed limits into steel leads to grinding of austenite grains to points 9-12 and a decrease in its tendency to grow when heated due to the formation of dispersed particles of vanadium carbonitrides, to increase strength and viscosity properties and resistance to brittle fracture (cold resistance). However, without the use of nitrogen, vanadium at high concentrations (> 0.1%) reduces the toughness and increases the cold brittleness of steel. Vanadium increases the endurance limit, improves weldability.

In steel containing at least 0.010% N, the optimal concentration of vanadium is 0.06-0.10%. The lower limit of the vanadium content in steel was chosen because it begins to grind grain at a concentration of more than 0.06%. The upper limit of the vanadium content is established based on the fact that with an increase in its concentration above 0.10%, the relative nitrogen fraction in the vanadium carbonitride decreases, a carbonitride is formed, which is similar in composition to vanadium carbide, which reduces the toughness.

A nitrogen concentration of less than 0.010% in steel containing less than 0.06% vanadium does not provide the required level of strength properties, impact strength at minus 60 ° C and grinding of austenite grain. With an increase in the content of vanadium and nitrogen in steel to the declared limits, the amount of carbonitrides in it increases, providing an increase in strength properties and cold resistance. However, with an increase in nitrogen of more than 0.018%, cases of spotted segregation and "nitrogen boiling" (bubbles in steel) are possible.

The limitation of the content of copper, sulfur, and phosphorus was chosen in order to improve the quality of the surface and increase the ductility and toughness of steel. In addition, the concentration of sulfur determines the red brittleness, phosphorus - cold brittle steel.

The inventive chemical composition of rail steel provides high-strength, wear- and cold-resistant reed rails of increased contact fatigue resistance with volume quenching in oil, followed by tempering.

The steel of the claimed composition (table 1) was smelted in a 100-ton electric arc furnace DSP-100 I7 and cast in a continuous casting machine. The obtained billets were heated and rolled according to the usual technology onto P65 rails, which were quenched in oil from a temperature of 800-820 ° C and tempered at 460 ° C. The data presented in table 2 show that the mechanical properties, the hardness of the space-hardened rails of the inventive steel is significantly higher than the rails of steel E83F [4]. The inventive chemical composition of rail steel also provides a high level of plasticity and high resistance to brittle fracture (KCU-60 ° C≥0.2 MJ / m ² ). Increasing the hardness, strength, plastic and viscosity properties of rails increases their wear and cold resistance, contact fatigue strength and operational reliability.

List of sources taken into account during the examination

1. GOST R 51685-2000 "Railroad rails. General specifications."

2. A.S. USSR No. 1435650, M. cl. C22C 38/16, 1987

3. A.S. USSR No. 1239164, M. cl. C22C 38/16, 1984

4. RF patent No. 1633008, M. cl. C22C 38/16, 1989

5. TU 0921-125-01124328-2001 "Railway rails with increased wear resistance and contact endurance."

Table 1 The chemical composition of steel Structure Mass fraction of elements,% FROM Mn Si V A1 Cr Ni Cu S R N ₂ O ₂ one 0.77 0.90 0.31 0.06 0.004 0.05 0.05 0.05 0.006 0.007 0.012 0.0014 2 0.87 0.95 0.39 0.09 0.002 0.08 0.10 0.10 0.009 0.012 0.014 0.0014 3 0.83 0.95 0.30 0.10 0.004 0.15 0.12 0.12 0.006 0.017 0.017 0.0018 four 0.84 0.90 0.20 0.08 0.004 0.25 0.15 0.15 0.012 0.013 0.015 0.0014 5 0.81 0.95 0.30 0,07 0.002 0.11 0.15 0.15 0.006 0.010 0,020 0.0014 6 0.85 0.90 0.35 0.10 0.003 0.05 0.10 0.10 0.008 0.014 0.018 0.0013 7 0.78 0.91 0.31 0.08 0.003 0.06 0.05 0.05 0.013 0.010 0.013 0.0016 8 0.79 0.95 0.25 0,07 0.003 0.10 0.12 0.12 0.006 0.009 0.015 0.0013 9 0.80 0.93 0.21 0.06 0.002 0.10 0.10 0.10 0.010 0.011 0.018 0.0012 10 0.84 0.94 0.20 0,07 0.004 0.12 0.11 0.11 0.012 0.013 0,020 0.0014 Prototype
TU-0921-01124328-2001
Steel E83F 0.78-0.88 0.75-1.05 0.25-0.45 0.03-0.15 no more than 0,02 ≤0.15 ≤0.15 ≤0.20 ≤0.025 ≤0.25 - -

table 2 The mechanical properties of rails Option σ σB δ5 ψ Hardness KCU, J / cm ²
at temperature, ° С N / mm ² % HB10 HB22 Nvsh НВпод HBPC +20 -60 one 900 1313 13 40 388 378 352 378 390 49; 47 25; 26 2 930 1300 12 39 388 373 363 363 388 47; 43 24; 28 3 980 1333 12 43 385 363 352 352 388 45; 45 25; 25 four 980 1320 13 42 388 375 363 363 389 44; 42 29; 24 5 950 1312 fourteen 43 388 363 375 363 388 45; 40 27; 28 6 890 1312 13 40 388 375 375 363 390 44; 41 27; 26 7 920 1323 12 39 383 372 363 370 395 41; 42 26; 27 8 980 1343 12 33 385 373 363 352 390 37; 38 25; 27 9 990 1340 12 39 388 375 375 363 390 36; 35 24; 25 10 1000 1350 12 43 388 375 375 363 401 36; 35 23; 22 prototype 880 1274 7 26 ≥352 ≥341 ≤401 ≤401 ≥363 0.2 0.15 Note: NVPCG - hardness on the rolling surface of the rail head; HB10, HB22 - hardness at a distance of 10 and 22 mm, respectively; НВш - neck hardness; HBp - hardness in the sole.

Claims (1)

Rail steel containing carbon, manganese, silicon, vanadium, aluminum and iron, characterized in that it additionally contains chromium, nickel, nitrogen in the following ratio, wt.%:
carbon 0.77-0.84 manganese 0.90-0.95 silicon 0.20-0.35 vanadium 0.06-0.10 aluminum no more than 0,004 nitrogen 0.010-0.018 chromium no more than 0,15 nickel no more than 0,15 iron rest
while it additionally limits the amount of impurities at
the following ratio, wt.%:
sulfur no more than 0.015 phosphorus no more than 0,020 copper no more than 0.20 oxygen no more than 0,0018