RU2232202C1 - Rail steel - Google Patents

Abstract

FIELD: ferrous metallurgy.

SUBSTANCE: invention relates to manufacturing steel for rail runway. Invention claims steel comprising components taken in the following ratio, wt.-%: carbon, 0.3-0.5; silicon, 0.8-1.5; manganese, 1.3-1.7; chrome, 0.6-1.5; vanadium, 0.08-0.15; aluminum, 0.05-0.015; nitrogen, 0.010-0.020; calcium, 0.001-0.020; molybdenum, 0.05-0.4; nickel, 0.001-0.30; iron, the balance. Invention provides enhancing complex of mechanical properties and hardness of steel for elevating exploitation stability of runways.

EFFECT: improved and valuable properties of rail steel and runways.

2 cl, 2 tbl

Description

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

Known rail perlite steel [1], containing 0.71-0.82%; 0.75-1.05% Mn; 0.25-0.45% Si; 0.05-0.15% V; not more than 0.025% P; no more than 0,030% S; no more than 0,020% Al. At the same time, the hardness level of pearlitic steels is insufficient. To increase the wear resistance, it is necessary to increase the hardness of pearlite steels more than HB 400. However, an increase in the hardness of pearlite steel and, accordingly, its wear resistance by increasing its cooling rate is due to a decrease in the temperature of the onset of pearlite transformation and the formation of fine plate perlite. The lower the pearlite transformation temperature, the finer the pearlite, the higher its hardness and wear resistance. The maximum dispersion of perlite is achieved at a cooling rate of rail steel of 640 ° C / min. The temperature of pearlite transformation is relatively high and amounts to 550 ° C. On the other hand, an increase in the hardness of pearlite steel due to an increase in its carbon content causes the appearance of bainitic and martensitic components in its microstructure. Historically, bainite and martensite were not allowed on the rails, because high-carbon (0.8% C) bainite is too soft and does not have such resistance as fine-plate perlite. Such bainitic steels even with HB 500 hardness have lower wear resistance than the best pearlitic steels with lower hardness. As for high-carbon martensite, it has a large plate shape and is very fragile, and therefore prone to the formation of microcracks. However, at a lower carbon content (about 0.6% C), rack martensite is formed, which is not prone to microcracking and is less fragile than plate martensite.

Known selected as a prototype rail steel containing carbon, silicon, manganese, chromium, vanadium, aluminum, nitrogen and optionally containing one or more elements selected from the group comprising rare earth metals zirconium, calcium and barium in the following ratio of components: wt.% : 0.32-0.42 C, 0.17-0.37 Si, 0.25-0.55 Mn, 1.8-2.4 Cr, 0.09-0.15 V, 0.02- 0.06 Al, 0.02-0.04 N, one or more elements selected from the group consisting of rare earth metals 0.0005-0.1%; zirconium 0.005-0.1%; calcium 0.005-0.05%; barium 0.005-0.2%; iron - the rest [2].

Significant disadvantages of steel are low mechanical properties and hardness of steel.

The inventive chemical composition is selected based on the following conditions.

The production of high-strength steel with a bainitic structure is associated with a decrease in carbon content. To obtain this structure, it is necessary to shift the beginning of the transformation to the right and lower the transformation temperature below 400 ° C. This is achieved through alloying, which ensures the grinding of perlite, dispersed hardening and the formation of a solid solution.

The required structure of bainite is rack (needle) ferrite with carbides inside the rails.

The carbon ratio of 0.3-0.5% was chosen based on the fact that at a given carbon concentration, rack martensite is formed, which is less brittle than brittle plate martensite, which forms at a concentration of ~ 0.8% C.

Manganese, chromium and molybdenum increase the hardenability of steel, providing lower bainite having a fine-needle structure, with high strength and toughness. The content of these elements reduces the temperature of transformation (lower bainite) and provides a finer structure and, consequently, an increase in strength, while they exclude transformation in the pearlite region. The selected ratio of manganese and chromium provides subcooling of austenite to a temperature below 400 ° C with the formation of bainite and tempered rack martensite.

The concentration of chromium and molybdenum contributes to an increase in hardness, yield strength and tensile strength, to obtain a finely dispersed structure.

The manganese ratio was chosen on the basis that the latter, pearlite transformation, contributes to the overcooling of austenite to a temperature below 400 ° C. An increase in its content to 2% reduces the negative effect of carbon on the cold brittleness threshold and modifies the release of cementite, excluding its release along grain boundaries. The use of manganese can reduce the temperature of the formation of ferrite and contributes to some grinding of grain. The upper limit of the manganese content is selected based on the fact that when the manganese concentration is up to 1.7%, the tensile strength, toughness and resistance to brittle fracture increase. The lower limit is chosen on the basis that manganese, with other advantages, increases the solubility of nitrogen in steel.

Silicon up to 1.5% increases the yield strength and strength, increases the hardenability of steel. With a decrease in silicon concentration of less than 0.8%, these characteristics significantly decrease.

The desired technical results of the invention are to increase the complex of mechanical properties and hardness of steel, increasing the operational stability of rails. For this, steel containing carbon, silicon, manganese, chromium, vanadium, aluminum, nitrogen and calcium additionally contains molybdenum and nickel in the following ratio, wt.%:

Carbon 0.3-0.5

Silicon 0.8-1.5

Manganese 1.3-1.7

Chrome 0.6-1.5

Vanadium 0.08-0.15

Aluminum 0.005-0.015

Nitrogen 0.010-0.020

Calcium 0.001-0.020

Molybdenum 0.05-0.4

Nickel 0.001-0.30

Iron Else

In addition, in its composition, the amount of impurities in the following ratio can be further limited, wt.%:

Sulfur no more than 0,020

Phosphorus no more than 0,020

Copper no more than 0,020

Chrome up to 1.5% increases the tensile strength, increases the hardenability of steel, provides a dispersed structure and, as a result, provides high wear resistance. A decrease in chromium content of less than 0.6% reduces the hardenability of steel.

Molybdenum in the selected range increases hardenability, solubility of nitrogen in iron, and tempering resistance. An increase in its concentration of more than 0.4% reduces the ultimate cooling rate.

Vanadium like chromium, molybdenum and manganese increases the solubility of nitrogen. Vanadium binds nitrogen into strong chemical compounds (nitrides, carbonitrides), which grind austenite grain, which provides increased strength (hardening by dispersed particles). However, without the use of nitrogen, vanadium reduces the viscosity and increases the cold resistance of bainitic steel. Additives of vanadium, aluminum, nitrogen provide high resistance to brittle fracture, increase the cold resistance of steel due to grinding of grain with the resulting nitrides and carbonitrides. Based on this, the optimal values for vanadium are its content of more than 0.08%. The upper limit of the concentration of vanadium is selected on the basis of economic considerations. A nitrogen concentration of less than 0.010% does not provide the required carbonitride hardening. With an increase in nitrogen of more than 0.020%, there may be cases of spotted segregation and “nitrogen boiling” (bubbles in steel).

Nickel has a positive effect on increasing ductility and resistance to brittle fracture, and increases the hardenability of steel.

Calcium within the claimed limits is introduced to modify non-metallic inclusions: it excludes the formation of “dangerous” alumina inclusions, increases the purity of steel by oxide and sulfide inclusions, ensures the formation of globular inclusions and eliminates the formation of line-like inclusions of aluminates.

The limitation of the content of copper, sulfur and phosphorus is selected based on the surface quality of the finished rails after rolling and the mechanical properties of the steel.

A series of experimental melts was smelted in electric arc furnaces DSP-100I7. The chemical composition of the experimental melts is shown in table 1. After casting the steel at the continuous casting machine, railway rails of the P65 type were rolled. The results of mechanical properties tests (table 2) show that the claimed chemical composition of rail steel provides an increase in the set of mechanical properties and hardness of steel (especially on the head rolling surface), which in turn increases the wear resistance and operational stability of railway rails.

Sources of information

1. GOST 51685 “Railroad rails. General specifications. ”

2. A.S. No. 603689, IPC ⁵ C 22 C 38/24.

Claims (2)

1. Steel containing carbon, silicon, manganese, chromium, vanadium, aluminum, nitrogen and calcium, characterized in that it additionally contains molybdenum and nickel in the following ratio of components, wt.%: Carbon 0.3-0.5 Silicon 0.8-1.5 Manganese 1.3-1.7 Chrome 0.6-1.5 Vanadium 0.08-0.15 Aluminum 0.005-0.015 Nitrogen 0.010-0.020 Calcium 0.001-0.020 Molybdenum 0.05-0.4 Nickel 0.001-0.30 Iron Else 2. Steel according to claim 1, characterized in that its composition is additionally limited by the amount of impurities in the following ratio, wt.%: Sulfur Not more than 0,020 Phosphorus Not more than 0,020 Copper Not more than 0.20

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