RU2615425C1 - Steel and all-rolled wheel made of it - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: steel contains the following components, wt %: carbon 0.73-0.77, silicon 0.30-0.50, chromium not more than 0.25, vanadium from more than 0.1 to 0.15, sulfur 0.005-0.015, molybdenum not more than 0.08, phosphorus less than 0.020, copper less than 0.35, nitrogen 0.005-0.020, nickel 0.21-0.35, titanium not more than 0.03, niobium not more than 0.01, manganese, the amount of which is determined by the condition (carbon + 1/4 Mn) = 0.92-0.95, aluminium, the amount of which is determined by the relation of aluminium/nitrogen = 1.5-2.0, the rest is iron and inevitable impurities, including not more than 0.0002 hydrogen.

EFFECT: stable level of physical and mechanical properties of the wheels, increased rim strength characteristics, and around the wheel section, a pearlite structure with ferrite portions is provided.

2 cl, 4 dwg, 13 tbl

Description

The invention relates to the field of metallurgy, in particular to the composition of steel for the manufacture of high-strength wheels for rail, mainly railway, transport, to wheels made from it, in particular to wheels of classes C, D according to AAR standard M-107 / M-208 of various sizes .

Known steel for the production of seamless wheels of wheelsets of freight cars and track machines of main railways, which contains carbon, silicon, manganese, vanadium, niobium, phosphorus, sulfur, nickel, chromium, copper, titanium, molybdenum and iron in the following ratio of components, wt .%: carbon 0.60-0.72, manganese 0.50-1.80, silicon 0.22-0.65, vanadium not more than 0.15, niobium to 0.01, phosphorus not more than 0.035, sulfur 0.005 -0.030, nickel no more than 0.30, chromium no more than 0.50, copper no more than 0.30, titanium up to 0.03, molybdenum no more than 0.08, iron - the rest (patent RU No. 2369658, IPC С22С 38 / 50, publ. 10.10.2009 g.).

Wheels made of steel of the claimed composition have a hardness at a depth of 30 mm from the rim surface of the rim of at least 320 HB, impact strength KCU of the disc metal at a temperature of 20 ° C of at least 18-28 J / cm ² , impact strength KCU of the rim metal at a temperature 20 ° С not less than 16-30 J / cm ² , temporary rim resistance not less than 1020 MPa with elongation not less than 9%, relative narrowing not less than 16% and fracture toughness not less than 50 MPa 50 ^1/2 . This steel under the T brand is introduced in GOST 10791-2011 “Solid-rolled wheels. Technical conditions. "

However, wheels made of steel according to this patent cannot provide rim hardness of more than 360 HB due to insufficient carbon content (not more than 0.72%). When the chromium content in the steel is up to 0.50% with intermittent quenching, a martensite-bainitic structure will certainly form in the rim instead of the pearlitic one that is optimal from the point of view of resistance to operation. This steel cannot be used for the manufacture of class D wheels according to AAR M-107 / M-208 standard, the hardness of the rim surface of which should be 341-415 HB (Clause 10.1 of the standard), and the rim microstructure should not contain martensite.

The closest in technical essence and purpose to the claimed steel is steel for the manufacture of high-strength wheels for rail vehicles according to patent RU No. 2546270, IPC C22C 38/38, publ. 04/10/2015. Steel contains carbon, silicon, manganese, chromium, vanadium, sulfur, molybdenum, if necessary, iron and impurities - phosphorus, copper, nickel in the following ratio of components in wt.%: Carbon 0.65-0.84; silicon 0.02-1.00; Manganese 0.50-1.90; chrome 0.02-0.50; vanadium 0.02-0.20; sulfur 0.04% or less, molybdenum, if necessary, 0-0.2; iron and impurities - the rest. As impurities, steel contains: phosphorus 0.05 or less; copper 0.20 or less and nickel 0.20 or less. For steel components, the following relations should be satisfied: Fn1 = 34≤2.7 + 29.5 × C + 2.9 × Si + 6.9 × Mn + 10.8 × Cr + 30.3 × Mo + 44.3 × V <43 and Fn2 = exp (0.76) × exp (0.05 × C) × exp (1.35 × Si) × exp (0.38 × Mn) × exp (0.77 × Cr) × exp (3.0 × Mo) × exp (4.6 × V) ≤25.

Steel may contain aluminum 0.20 wt.% Or less.

It is claimed that steel has high wear resistance, fatigue resistance in the rolling contact zone and resistance to chipping, which ensures a long wheel life. It is emphasized that for a wheel in which the wheel steel according to this invention is used as the material, the degree of wear is reduced by 10 to 35% and the fatigue life in the rolling contact zone is increased by 1.4 to 3.2 times compared to A class M wheel according to AAR M-107 / M-208 standard for rail vehicles, and spalling is less likely to occur. Therefore, the steel in accordance with this invention is extremely suitable as a material for a wheel of a rail vehicle used in very harsh environmental conditions with increased transportation distances and increased carrying capacity.

In world practice, steel for the manufacture of seamless-rolled wheels is made according to the scheme: smelting of an intermediate product (in an electric furnace, converter, or other steel-smelting unit) - out-of-furnace treatment at a ladle furnace - evacuation - casting (through an intermediate ladle on a multi-strand continuous casting machine of round billets or a siphon in ingot molds). At the same time, it became possible to obtain steel melts in a narrow range of element content.

Based on this, the disadvantage of steel according to the patent RU No. 2546270 is a wide range of element contents, which does not allow continuous casting by series of smelting - during serial casting at the beginning of casting, the steel of each heat is mixed with the remainder of the steel in the intermediate ladle from the previous smelting. Thus, the chemical composition of a certain part of the melting blanks of the beginning of casting and the end of casting is formed by mixing the steel of the melting itself with the steel of the previous and subsequent melts. With a certain difference in the content of elements in swimming trunks during continuous continuous casting along the length of the obtained continuously cast billets, it is possible to obtain a significant variation in the content of elements, which, when the wheels of each melting are heat treated in a single mode, will result in rejection by their mismatch with the required level of properties. In any case, within the framework of the content of elements defined by this patent, it is necessary to clarify their content by narrowing the range of their content, taking into account the feasibility of thermal hardening of wheels made from mass cast castings, according to a single thermal hardening mode.

The objective of the present invention is to develop a composition of wheeled steel that provides physico-mechanical characteristics of the wheel rim at a level and above the requirements for class D wheels according to AAR standard M-107 / M-208, and stabilization of their values according to the test results of all heats. The objective of the invention is also to simplify the manufacturing technology of steel and wheels from it, namely the ability to carry out continuous casting of steel by a series of melts and heat treatment of wheels made from them, according to the same parameters of heat hardening.

When using the present invention, the following technical result is achieved:

- ensuring the level of mechanical properties of the wheels is not lower than the requirements of the AAR M-107 / M-208 standard for class D wheels, while increasing the strength characteristics of the wheel rim of the inventive steel: hardness in the range 341 to 415 HB, temporary rupture resistance of the rim of at least 1200 MPa , yield strength of at least 820 MPa, achievement of rim fracture toughness of at least 55 MPa√m;

- providing the entire cross-section of the wheel ferrite-pearlite structure;

- reducing the scatter and stabilizing the values of the mechanical properties of the wheels;

- simplification and cheapening of wheel manufacturing technology.

To solve this problem and achieve a technical result, it is claimed that steel for making a railway wheel containing carbon, silicon, manganese, chromium, vanadium, sulfur, molybdenum, phosphorus, copper, nickel, titanium, niobium, nitrogen, aluminum and iron, which according to the invention contains components in the following ratio, wt.%:

carbon 0.73-0.77 silicon 0.30-0.50 chromium no more than 0.25 vanadium from more than 0.1-0.15 sulfur 0.005-0.015 molybdenum no more than 0.08 phosphorus no more than 0,020 copper no more than 0,35 nickel 0.21-0.35 titanium no more than 0,03 niobium no more than 0,01 nitrogen 0.005-0.020 iron and inevitable impurities, including hydrogen no more than 0,0002, rest,

марганца)=0,92-0,95, а содержание алюминия определяется в зависимости от содержания азота из условия Al/N=1,5-2,0.the manganese content in the steel is determined depending on the carbon content from the condition (carbon +

manganese) = 0.92-0.95, and the aluminum content is determined depending on the nitrogen content from the condition Al / N = 1.5-2.0.

Distinctive features of the claimed invention in comparison with the prototype is the introduction of titanium, niobium and nitrogen into the composition of the steel, an increase in the copper content of not more than 0.35 wt.%, Nickel to 0.21-0.35%, the limitation of hydrogen content is not more than 0.0002 wt.% and a new ratio of components, as well as the mandatory fulfillment of conditions on the ratios of the amount of carbon and manganese, aluminum and nitrogen.

When establishing the necessary ratio of components, we proceeded from the following premises.

Improving the mechanical properties and hardness of wheel steel can be achieved in two main ways: by increasing the carbon content or adding a large amount of alloying elements. However, for wheels that are massive, at the same time highly responsible products, the use of any one method is impractical. So, alloying significantly increases the cost of wheels and reduces their competitiveness, and an increased carbon content leads to a decrease in toughness, steel reliability with respect to brittle fracture and machinability, which is important from the point of view of maintenance during operation.

Thus, it was necessary to find an alternative solution that provides an increase in the level of mechanical properties of wheel steel and avoids the disadvantages of these steels.

The optimal solution for increasing the strength properties and hardness of wheel rims while maintaining ductility and viscosity is a comprehensive approach, including a moderate increase in carbon content and microalloying. The main mechanisms for increasing the hardness of steel are solid solution hardening, precipitation hardening and grinding of grain. The latter also leads to an increase in ductility and toughness of steel. The main elements that strengthen the solid solution are carbon, as well as silicon and chromium. In FIG. 1 shows the dependence of the hardness of ferrite-pearlite wheel steel on the carbon content in it.

Carbon and chromium are the main carbide forming elements. When increasing hardness to the required level while maintaining the necessary plastic and viscous characteristics of the rim metal compared to the prototype, the maximum carbon content should be limited to 0.77%, and chromium compared to the prototype should be reduced to 0.25% to provide a pearlite structure over the entire cross section with patches of ferrite.

The high sulfur content of more than 0.030% contributes to the embrittlement of steel and an increase in the number of non-metallic inclusions. To increase the purity of steel, the maximum sulfur content was set to not more than 0.015%. An excessively low content is also unfavorable, since, due to a decrease in the number of sulfide inclusions inhibiting the movement of free hydrogen atoms, flocsensitivity increases. In this regard, the minimum permissible sulfur content is limited to 0.005%. Limiting the hydrogen content in steel to no more than 0.0002% gives the wheels made of it immunity to the formation of flocs. In steel, the nickel content is increased to 0.21-0.35% as an element that increases strength, resistance to brittle fracture and toughness. When the nickel content is less than 0.21%, the effect of its positive effect decreases below the required level, while increasing more than 0.35%, the cost increases significantly. For dispersion hardening and grinding of grain by lowering the temperature of pearlite transformation and preventing recrystallization processes, increasing viscous characteristics, microadditives of carbonitride-forming elements, such as vanadium (from more than 0.1 to 0.15%), nitrogen (up to 0.005-0.020%), are required. and the additional introduction of niobium (up to 0.01%), titanium (up to 0.03%), while in order to obtain the maximum effect, the ratio of aluminum to nitrogen contents in the range of 1.5-2.0 must be maintained. The content in the steel of silicon, molybdenum, copper corresponds to their content in steel of class C according to the AAR M-107 / M-208 standard, and phosphorus as a harmful impurity is limited to at least 0.020%.

The manganese content in steel, unlike the prototype, is set depending on the carbon content in it, based on the need to fulfill the condition (C + 1/4 Mn), wt.%, In the range of 0.92-0.95. In practice, in order to ensure a given level of physicomechanical properties of the wheels, the cooling time during quenching, tempering parameters are set depending on the total carbon content of carbon wheels in steel plus 1/4 manganese. Any steel grade according to this indicator, taking into account the range of C and Mn contents, is divided into several groups according to the assigned intermittent hardening and tempering modes. The duration of hardening of wheels with a minimum and maximum content in steel (C + 1/4 Mn), wt.%, Can vary up to two or more times. All this leads to a violation of the rhythm of the work of production shops, based on the need for float processing and acceptance of the wheels to complicate the organization of the float flow in them, the marriage of the wheels when they lag behind the stream. Despite this division of the wheels into groups within each steel grade, it is not possible to achieve the same level of mechanical properties on the wheels of various swimming trunks.

When using the inventive steel composition, it becomes possible to cast steel both in a series of melts on a continuous casting machine and siphon-float into molds, and wheels made of them can be thermo-strengthened using the same parameters for quenching, hardening and tempering. This achieves stability and minimal variation in the values of the physicomechanical properties of the wheels during mass production, which ultimately determine their operational stability. Since the service life of the wheelset is determined by the service life of the wheel with the worst properties, when they are formed by wheels with an equally high level of properties, this resource will increase. In FIG. 2 shows a comparative distribution of the hardness of the wheels of class C steel, heat-strengthened in groups depending on the value of the sum (C + 1/4 Mn), wt.%, And for one mode with the value of the sum in the range of 0.92-0.95% - in the latter case, the spread of hardness values of the rims of the wheels is reduced by at least 2 times.

In FIG. Figure 1 shows the dependence of the hardness of ferrite-pearlite wheel steel on the carbon content in it, which shows the degree of increase in the hardness of the steel from the increase in its carbon content.

In FIG. 2 shows a comparative distribution of hardness of wheels made of steel of class C:

- during heat treatment in groups, depending on the value of the sum (C + 1 / 4Mn) - light columns;

- during heat treatment in one mode with the value of the sum in the range of 0.92-0.95% (according to the claimed invention) - dark columns.

The graphs show that heat treatment of the wheels of the inventive steel according to common parameters reduces the dispersion of the hardness values of the rims by at least 2 times.

In FIG. 3 shows the macrostructure of a J-36 wheel.

In FIG. 4 shows the macrostructure of an H-36 wheel.

In FIG. Figures 3 and 4 show that the metal does not contain martensite and bainite, since there are no bands of increased trauma in the macrostructure of wheel rims.

Concrete example

For the manufacture of seamless-rolled railway wheels with a diameter of 914 mm, class D, experimental melting was performed, the chemical composition of which corresponds to this invention and the requirements of AAR standard M-107 / M-208 for class C steel. The chemical composition of the experimental melting is shown in Table 1. The chemical composition is given for comparison. the composition of the steel corresponding to the prototype.

The value of C + 1/4 Mn for the inventive steel composition was 0.935%, the value of the ratio A1 / N was 1.57. For the steel of the prototype, the value of Fn1 is 35.175, Fn2 is 9.83.

Of the inventive steel, wheels with a diameter of 914 mm were made of two structures (H-36 and J-36), and of the steel of the prototype, wheels of N-36.

Wheel hardening

After heating the wheels to a temperature of 820 ° C for 2 hours, they were subjected to intermittent hardening. The wheels were hardened in vertical hardening devices by three-sided spray cooling of the rims for 160 seconds, while the water pressure in the spray devices was proportionally increased from 0.00-0.01 MPa to 0.18-0.20 MPa for 55 seconds, further cooling was carried out at a pressure of 0.18-0.20 MPa. After hardening, the wheels were subjected to air conditioning and tempering at the optimum temperature.

The obtained physical and mechanical properties are presented below in tables 2-13 and in FIG. 1-4.

The hardness measurement on the lateral surface of the rim from the outside was carried out in accordance with the requirements of paragraph 10.2 of AAR standard M-107 / M-208.

The results of Brinell hardness measurements from the outer side surface of the wheel rim of structures H-36 and J-36 at three points are presented in table 2.

The assessment of tensile circumferential stresses was determined in accordance with the requirements of clause 3.1.3 of Appendix C to AAR standard M-107 / M-208. Two marks at a distance of 100 mm were applied to the middle of the rim thickness from the outside of the wheel. A radial cut of the wheel rim was carried out with its continuation into parts of the disk to a depth of a little more than 1 inch (25.4 cm) from the edge of the inner diameter of the wheel towards the hub. After cutting, the distance between the marked marks was measured. The convergence of the wheel rims is shown in table 3.

The tensile test was carried out in accordance with the requirements of paragraph 3.1.1 of Appendix C to AAR standard M-107 / M-208.

The results of the tensile test are presented in tables 4, 5.

The hardness of the wheel rim cross section was measured in accordance with the requirements of clause 11.5 of the AAR standard M-107 / M-208 and clause 3.1.4 of Appendix C to this standard. The results of measuring the hardness in the cross section of the wheel rims according to Brinell are presented in table 6.

The results of measuring the hardness in the cross section of the rims of the wheels according to Rockwell are presented in table 7.

The results of measuring Brinell hardness over the cross section of the wheel disc are presented in table 8.

The test to determine the fracture toughness index was determined in accordance with the requirements of clause 3.1.5 of Appendix C of AAR standard M-107 / M-208, the results are presented in table 9.

The wear and chipping test was carried out in accordance with the requirements of paragraph 3.1.6 of Appendix C to AAR standard M-107 / M-208, the test results are presented in tables 10, 11.

The microstructure was evaluated in accordance with the requirements of clause 3.1.2 of Appendix C of AAR standard M-107 / M-208, the evaluation results are presented in tables 12, 13. An analysis of the results shows that an equilibrium pearlite metal structure is ensured over the entire cross-section of the wheel rims with areas of ferrite without martensite and bainite.

The macrostructure was evaluated by hot etching in a 50% aqueous hydrochloric acid solution. The control results are presented in FIG. 3 and 4. The absence of fringe bands in the macrostructure of the wheel rims also indicates that the metal does not contain martensite and bainite.

The test results show that the inventive steel compared with the prototype allows to obtain higher strength characteristics of the wheels, their greater resistance to abrasion and chipping, to obtain wheels with a level of properties significantly higher than the requirements of the standard AAR M-107 / M-208 for class D wheels with providing a fully pearlitic metal structure with ferrite sites. The introduction of the value of the condition С + 1/4 Mn within narrow predetermined limits allows continuous casting of steel by series of melting for melting, heat strengthening of the wheels of all melts in a single mode, which simplifies the technology of their production, increases productivity and reduces cost. At the same time, the level of wheel properties is stabilized, which allows to reduce the difference in their operational properties in the wheelset. Thus, the inventive steel and wheels made of it, ensure the achievement of the technical result of the invention.

Claims (16)

1. Steel for a seamless-rolled railway wheel containing carbon, silicon, manganese, chromium, vanadium, sulfur, molybdenum, phosphorus, copper, nickel, titanium, niobium, nitrogen, aluminum and iron, characterized in that it contains components in the following ratio , wt.%: carbon 0.73-0.77 silicon 0.30-0.50 chrome no more than 0.25 vanadium from more than 0.1 to 0.15 sulfur 0.005-0.015 molybdenum not more than 0.08 phosphorus no more than 0,020 copper no more than 0.35 nickel 0.21-0.35 titanium not more than 0.03 niobium not more than 0.01 nitrogen 0.005-0.020 iron and inevitable impurities, including hydrogen not more than 0.0002, - the rest, the manganese content in the steel is determined depending on the carbon content from the condition (carbon +

manganese) = 0.92-0.95, and the aluminum content is determined depending on the nitrogen content from the condition Al / N = 1.5-2.0. 2. Solid-rolled railway wheel, characterized in that it is made of steel according to claim 1.

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