RU2365667C1 - Rail steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to ferrous metallurgy, namely to making of rail steel. Steel contains carbon, silicon, manganese, chromium, vanadium, aluminium, nitrogen, molybdenum, nickel, boron, one of the elements selected from the group including niobium and titanium, one or several elements selected from the group including rare-earth metals, zirconium, strontium, calcium and barium, iron and impurities with the following ratio of the components, wt %: carbon 0.25 - 0.37, silicon from 0.90 to 1.0 maximum, manganese from 1.29 minimum to 1.50 maximum, chromium 1.00 - 1.40, vanadium 0.08 - 0.15, aluminium 0.005 maximum, nitrogen 0.012 - 0.020, molybdenum from 0.10 to 0.20 maximum, nickel 0.01 - 0.30, boron 0.0003 - 0.002, one or several elements, selected from the group including rare-earth metals, zirconium, strontium, calcium and barium in the amount of 0.0005 - 0.005 each, one of the elements, selected from the group including niobium and titanium: niobium 0.003 - 0.05, titanium 0.001 - 0.02, the rest is iron and additives. The additives in steel are sulphur 0.015 maximum, phosphorus 0.020 maximum and copper 0.020 maximum.

EFFECT: well-balanced complex of mechanical properties of steel and improved service durability of the rails.

2 tbl

Description

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

Known rail pearlitic steels [1] containing 0.71-0.82% C; 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% AI.

A significant drawback of pearlitic rail steels is their limited ability to achieve hardness on rails of more than 400 HB when quenching in the temperature range of pearlite transformation.

Also known rail steel, selected as a prototype, containing carbon, silicon, manganese, chromium, vanadium, aluminum, nitrogen and additionally containing one or more elements selected from the group comprising REM, zirconium, calcium and barium in the following ratio of components, weight .%: 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% AI, 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 the uneven hardness of the metal over the rail section, as well as an insufficient level of ductility and toughness.

The desired technical result of the invention is to achieve a balanced set of mechanical properties of steel and increase the operational stability of rails.

To achieve this, steel containing carbon, silicon, manganese, chromium, vanadium, aluminum, nitrogen, molybdenum, nickel, iron and one or more elements selected from the group consisting of rare-earth metals, zirconium, strontium, calcium, barium, additionally contains boron and one of the elements selected from the group comprising niobium and titanium, in the following ratio of components, wt.%:

carbon 0.25-0.37 silicon from 0.90 to less than 1.00 manganese from more than 1.29 to less than 1.50 chromium 1.00-1.40 vanadium 0.08-0.15 aluminum no more than 0,005 nitrogen 0.012-0.020 molybdenum from 0.10 to less than 0.20 nickel 0.01-0.30 boron 0.0003-0.002

One or more elements selected from the group comprising REM, zirconium, strontium, calcium, barium:

REM 0.0005-0.005 zirconium 0.0005-0.005 strontium 0.0005-0.005 calcium 0.0005-0.005 barium 0.0005-0.005

One of the elements selected from the group comprising niobium, titanium:

niobium 0.003-0.05 titanium 0.001-0.02 iron and impurities rest,

however, as impurities, steel contains sulfur not more than 0.015, phosphorus not more than 0, 020, copper not more than 0.20.

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

The carbon ratio of 0.25-0.37% is selected based on the receipt of needle bainite over the entire cross section of the rail. When the content is less than 0.25%, the likelihood of formation of upper bainite increases, which is characterized by low hardness, ductility and impact strength. When the carbon content is more than 0.37%, the likelihood of martensite formation in the sole of the rails, which is characterized by high hardness and brittleness, increases.

Manganese, chromium and molybdenum in selected ratios increase the stability of supercooled austenite, providing lower bainite having high strength and viscosity.

When the content of manganese is less than 1.29%, chromium less than 1.00% and molybdenum less than 0.10%, the degree of stability of supercooled austenite required to obtain a finely dispersed structure of bainite is not provided. With a manganese content of more than 1.50%, chromium of more than 1.40% and molybdenum of more than 0.20%, the likelihood of the formation of a martensitic structure increases, which imparts increased hardness and fragility to the rail.

At the selected concentration limits of carbon, manganese, chromium, molybdenum, the silicon content in the range of 0.90-1.00% is the most optimal, it increases the yield strength and strength, increases the hardenability of steel. With a decrease in silicon concentration of less than 0.90%, these characteristics are significantly reduced. With a silicon content of more than 1.00%, the likelihood of the formation of a solid and brittle structural component, martensite, also increases.

Molybdenum in the selected range increases hardenability, solubility of nitrogen in iron, and tempering resistance. An increase in its concentration of more than 0.20% reduces the ultimate cooling rate.

Vanadium binds nitrogen into strong chemical compounds (nitrides, carbonitrides) that 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 brittleness 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 0.012% 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).

The limitation of the aluminum content to 0.005% ensures the absence of line-wise inclusions of alumina, which leads to an increase in the fatigue limit and contact fatigue strength of the rails.

Nickel in the range of 0.01-0.30% positively affects the increase in ductility and resistance to brittle fracture, increases the hardenability of steel. With a lower nickel content, the effectiveness of its effect on increasing ductility decreases markedly, with a content of more than 0.30%, the stability of austenite increases and the conversion curve shifts to the right, which can lead to the formation of a martensite structure.

Strontium, zirconium, rare-earth metals, calcium and barium are introduced within the claimed limits to modify non-metallic inclusions: the formation of “dangerous” alumina inclusions is excluded, the purity of steel by oxide and sulfide inclusions is increased, the formation of globular inclusions is ensured, and the formation of line inclusions of aluminates is eliminated. This helps to improve the ductility and toughness of steel. With a lower content of these elements is not fully provided for the purification of steel from non-metallic inclusions. Additives of these elements in excess of predetermined limits lead to metal contamination by complex multiphase inclusions, which, when the rails are operated, lead to the emergence of contact fatigue defects.

The limitation of the content of copper, sulfur and phosphorus is selected based on the need to obtain a satisfactory surface quality of the finished rails after rolling and the mechanical properties of the steel. The presence in the steel of sulfur and phosphorus in excess of the specified limits leads to an increase in the red and cold brittleness of the steel.

The introduction of boron into steel within the stated limits prevents the formation of structurally free ferrite in steel, which favorably affects the hardness and strength characteristics of rails. With a higher boron content, the likelihood of the formation of a boride eutectic increases, which adversely affects the properties of steel. When the boron content is less than 0.0003%, the effectiveness of its influence on structure formation decreases.

The selected content of niobium and titanium contributes to the grinding of steel grain due to the formation of stable carbonitrides and nitrides, thereby contributing to an increase in the strength and viscosity properties of steel. With a lower content of these elements, grain grinding is not achieved. When the niobium content is more than 0.05%, and titanium more than 0.02%, the proportion of nitrogen in the carbonitride phase decreases, and the carbon increases. This leads to increased strength and lower toughness of steel.

A series of experimental melts was smelted in electric arc furnaces DSP-100I7. The chemical composition of the experimental heats is given in table 1. After casting steel at the continuous casting machine, rolling of railway rails of the P65 type was carried out. The results of mechanical properties tests (Table 2) show that the claimed chemical composition of rail steel provides a balanced set of mechanical properties and hardness of steel, which, in turn, increases the operational stability of railway rails.

Information sources

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

2. A.S. No. 603689, IPC ⁵ C22C 38/24.

Claims (1)

Rail steel containing carbon, silicon, manganese, chromium, vanadium, aluminum, nitrogen, molybdenum, nickel, one or more elements selected from the group consisting of rare-earth metals, zirconium, strontium, calcium and barium, iron and impurities, characterized in that it additionally contains boron and one of the elements selected from the group comprising niobium and titanium in the following ratio of components, wt.%:
carbon 0.25-0.37 silicon from 0.90 to less than 1.0 manganese from more than 1.29 to less than 1.50 chromium 1.00-1.40 vanadium 0.08-0.15 aluminum no more than 0,005 nitrogen 0.012-0.020 molybdenum from 0.10 to less than 0.20 nickel 0.01-0.30 boron 0.0003-0.002
one or more elements selected from the group comprising REM, zirconium, strontium, calcium, barium:
REM 0.0005-0.005 zirconium 0.0005-0.005 strontium 0.0005-0.005 calcium 0.0005-0.005 barium 0.0005-0.005
one of the elements selected from the group comprising niobium and titanium:
niobium 0.003-0.05 titanium 0.001-0.02 iron and impurities rest,
while as impurities, the steel contains sulfur not more than 0.015, phosphorus not more than 0.020, copper not more than 0.20.