AT521405A1 - Track part made of hypereutectoid steel - Google Patents

Abstract

In the case of a track part, in particular a rail for rail vehicles, made of hypereutectoid steel with a rail foot, a web and a head area, steel is used with the following directional analysis: 0.98-1.17% by weight c 0.90-1.35 % By weight Mn 0.70-1.10% by weight Si 0.15-0.70% by weight Cr and the steel has a pearlitic structure, essentially free of secondary cementite networks, at least in the head region of the rail.

Description

Austrian Patent Office (IO) AT 521405 A1 2020-01 -15 dp) Austrian patent application

(21) Application number: A 201/2018 (51) Int. Cl .: C22C 38/02 (2006.01 (22) filing: 07/10/2018 C22C 38/04 (2006.01 (43) Published on: 01/15/2020 C21D 9/04 (2006.01 C21D8 / 00 (2006.01 0220 38/06 (2006.01 0220 38/24 (2006.01 0220 38/26 (2006.01 0220 38/28 (2006.01

AT 521405 A1 2020-01-15

(56) Citations: (71) Patent applicants: US 2004187981 A1 Voestalpine Schienen GmbH JP 2002256393 A US 5762723 A (72) 8700 Leoben (AT) JP 2004162106 A Inventor: Goriupp Jürgen Dipl.lng. Dr. 8770 St. Michael (AT) kiss Mario Dipl.lng. Dr. 8700 Leoben (AT) (74) representative: Haffner and Keschmann Patentanwälte GmbH 1010 Vienna (AT)

(54) Track part made of hypereutectoid steel (57) In the case of a track part, in particular rail for rail vehicles, made of hypereutectoid steel with a rail foot, a web and a head area, steel is used with the following directional analysis:

0.98 - 1.17 wt% c

0.90 - 1.35 wt% Mn

0.70-1.10 wt% Si

0.15-0.70% by weight of Cr and the steel has a pearlitic structure essentially free of secondary cementite networks, at least in the head region of the rail.

With a track part, especially rail for

Rail vehicles, made of a hypereutectoid steel with a rail foot, a web and a head area

Steel used with the following directional analysis:

Summary:

0.98 - 1.17 Wt. o, “o c 0.90 - 1.35 Wt. O O Mn 0.70 - 1.10 Wt. o ~ o Si 0.15 - 0.70 Wt. ö 0 Cr

and the steel, at least in the head region of the rail, has a pearlitic structure essentially free of secondary cementite networks.

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The invention relates to a track part, in particular a rail for rail vehicles, made of hypereutectoid steel with a rail foot, a web and a head region.

The invention further relates to a method for producing such a track part.

In recent times, the weight of the transported loads in rail traffic and the driving speed have been continuously increased in order to increase the efficiency of rail transport. Railway tracks are therefore subject to difficult operating conditions and must be of higher quality and strength in order to withstand the higher loads. Concrete problems can be seen in a sharp increase in wear, particularly in the rails mounted in arches, and by the occurrence of material fatigue damage, which develops primarily at the driving edge, which is the main point of contact of the rail with the wheels in the arch. This leads to rolling contact fatigue damage (RCF rolling-contact-fatigue). Examples of RCF surface damage are e.g. Head checks (fatigue), spalling (flaking), squats (plastic

Surface deformation), slip waves and corrugations. This damage to the surface leads to a shortened rail service life, increased noise emissions and operational disabilities. The increased occurrence of errors is also accelerated by the steadily increasing traffic loads. The immediate consequence of this development is an increased need for maintenance of the rails. However, the increasing need for maintenance contradicts the increasingly smaller maintenance windows. Higher train densities increasingly reduce the periods in which rails can be exchanged or processed.

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The RCF damage mentioned can be removed by grinding at an early stage, but the splint must be replaced if it is severely damaged. There has been no shortage of attempts in the past to improve both wear resistance and resistance to RCF damage in order to increase the life cycle of the rails.

With regard to pearlitic rail steels, it has been shown that increasing strength has an extremely favorable effect on wear behavior and RCF resistance, which has led to the development of hypereutectoid rail steels in the past.

Hypereutectoid steels for the production of rails are known for example from EP 2388352 A1. With a carbon content (C content) of 0.77% by weight of carbon and 723 ° C, the iron-carbon diagram shows a eutectoid, at which point a solid direct phase transition from the austenite phase to the pearlite phase takes place upon cooling. Perlite is preferred for rails in terms of wear resistance and elongation at break compared to other steel modifications, since this is best due to the lamellar structure against wear.

By definition, the pearlitic structure comprises a ferrite phase, the ferrite fraction in the pearlite phase being a tough and ductile phase and a fixed size due to the C content of the rail steel used, which varies within very small limits, and one

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Cementite phase, which are lamellar to each other.

Carbon contents higher than 0.77% by weight are preferred for greater hardness and therefore for wear resistance, since a higher carbon content in the steel leads to a minimization of the cementite lamella spacing and a strengthening of the thickness of the cementite lamella in the pearlite phase. However, excessive carbon contents should also be avoided in the pearlite phase, since the cementite can occur not only in the pearlite lamellae, but also as a separate phase in the structure.

These structural components, known as secondary cementite deposits, are significantly influenced by a combination of alloy and heat treatment technology.

Knowledge of the precipitation temperature of the secondary cementite is of crucial importance and this should not be undercut before the subsequent heat treatment. In addition, the cooling rate during the heat treatment process should be as high as possible in order to suppress the precipitation of secondary cementite. Excessive proportions of secondary cementite can have a negative impact on the fracture properties of steels, since the fracture behavior becomes increasingly intergranular.

A high level of wear resistance is therefore essential for the quality of a rail, for which the hardness (for example given as Brinell hardness) of the rail is essentially characteristic. However, the hardness that is desirable on the one hand inevitably leads to a reduction in toughness

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accompanied by what is especially in the heavy load area, where the rail is particularly high when being run over by a rail vehicle

Bending stresses is exposed to the durability of the

Track part is detrimental.

The invention therefore aims to improve a track part, in particular a rail, which, for reasons of cost and ease of welding, should consist of a low-alloy steel in such a way that, due to the great hardness of the material, the wear resistance even with increased wheel loads in the rail head is increased to such an extent that a lying period of more than 30 years can be ensured. Finally, the track part should be easy to weld and similar other material properties such as Steels that have been tried and tested in rail construction have a similar electrical conductivity and a similar coefficient of thermal expansion.

Furthermore, the invention aims to provide a simple manufacturing process for a track part according to the invention, which is characterized by a short process duration (avoidance of glow phases), high reproducibility and high economic efficiency. The process is intended for the production of long rails of e.g. over 100 m in length, whereby material properties that meet specifications are to be ensured over the entire length of the rail.

To achieve this object, the invention provides according to a first aspect a track part, in particular a rail of the type mentioned, which is characterized according to the invention in that steel with the following

24.5

Directional analysis is used:

0, 98 - 1.17 Wt. o. o c 0.90 - 1.35 Wt. o, o Mn 0.70 - 1.10 Wt. o o Si 0.15 - 0.70 Wt. o O Cr

and the steel has a pearlitic structure essentially free of secondary cementite networks, at least in the head region of the rail.

In the development of the rail according to the invention, this steel composition has proven to be extremely suitable, since a hardness in the range of 460 HB and higher could be achieved and the rail according to the invention at the same time has a sufficient elongation at break for the heavy-duty area. In the context of the present invention, the feature means that, at least in the head region of the rail, a pearlitic structure essentially free of secondary cementite networks, that at most 5% of the existing secondary cementite precipitates are in the form of secondary cementite networks.

Secondary cementite deposits reduce the carbon supply for the formation of pearlitic cementite flakes, which are required for wear resistance. For these reasons, the suppression of secondary cementite in hypereutectoid rail steels can be regarded as advantageous.

The concentration of manganese in the present steel is selected such that, due to its austenite-stabilizing effect, it shifts the formation of embrittling secondary cementite to lower temperatures, which results in grain-refining

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Rolling at low rolling temperatures of hypereutectoids

Rail steels while suppressing the

Secondary cementite excretion is made possible.

Steel compositions were recognized as particularly preferred in the context of the invention, which are characterized in that C in amounts of 1.05 to 1.17% by weight, preferably 1.06 to 1.15% by weight, and particularly preferably 1 , 08 wt .-%, is used. These carbon contents ensure the best possible balance between wear resistance and elongation at break.

In order to further increase the elongation at break, according to a preferred embodiment of the present invention, the directional analysis of the rail steel can be designed in such a way that Al (aluminum) is additionally used in amounts of 0.01 0.06% by weight. This leads to a minimization of the pearlite grain size, which is conducive to elongation at break.

From the same point of view as the addition of Al, V (vanadium) can additionally be used in amounts of 0.10-0.20% by weight, which corresponds to a preferred embodiment of the present invention.

Likewise, according to a preferred embodiment of the present invention, Nb (niobium) can also be used in amounts of 0.010-0.030 wt

To minimize pearlite grain size and thereby positively influence the elongation at break of the splint according to the invention.

From the same point of view as the addition of Al, Ti (titanium) can additionally be used in amounts of 0.015-0.05% by weight.

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It has proven to be particularly preferred that V is additionally used in amounts of 0.10-0.2% by weight together with Nb in amounts of 0.010-0.030% by weight. This simultaneous use of V and Nb led to a particularly high elongation at break, as can be seen from the exemplary embodiments of the present invention set out below.

From the same point of view, it has proven to be particularly preferred that Al is additionally used in amounts of 0.01-0.06% by weight together with Nb in amounts of 0.01-0.03% by weight.

Furthermore, the grain-refining effect can be increased by adding the above-mentioned alloying elements (Al, Ti, V, Nb) through a nitrogen content set in the steel in the range of 40120 ppm, which corresponds to a preferred embodiment of the present invention.

In particular, a steel quality is achieved with the composition according to the present invention, which enables the production of a track part in which the steel has a tensile strength of more than 1500 MPa, an elongation at break of more than 8% and a Brinell hardness (according to EN ISO 6506-1) of greater than 460 HB, which corresponds to a preferred embodiment of the present invention.

The method according to the invention for producing a track part according to the invention is characterized in that rail steel with a composition just described is distinguished at a temperature of 1000-1300 ° C.

8/24 is removed from an oven, then rolled at temperatures of 850 - 950 ° C final rolling temperature and then subjected to forced cooling to a temperature of 450 ° C to 600 ° C. The furnace is preferably a walking beam furnace. The steel with the composition according to the invention is removed from the furnace and rolled into the track part, in particular the rail of the desired shape. Here, in order to avoid secondary cementite precipitates during the non-eutectoid transition from the austenite phase to the pearlite phase, a finish rolling temperature, i.e. the temperature of the steel at the end of the rolling mill should not fall below 850 ° C, since secondary cementite precipitations at the pearlite grain boundaries can lead to unacceptable embrittlement of the rail, particularly when secondary cementite networks are formed. The conditions in the rolling mill are selected with the help of the accumulated degree of deformation within continuous rolling passes on the finishing mill so that, taking into account the forming speed of the pass, the temperature and the alloy composition, a recrystallization-controlled rolling process is achieved that is achieved by means of deformation-induced precipitates and precipitates in solution , at least in the head area of the rail, a small former austenite grain size of 8 μm to 35 μm. to realize. This is followed, according to the invention, by rapid cooling to below 600 ° C., in which temperature range no more secondary cementite is precipitated, resulting in an extremely wear-resistant fine pearlitic structure with sufficient elongation at break for the heavy load range.

The forced cooling takes place according to a preferred one

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Embodiment of the present invention at least in

Head area of the rail, at least there the pearlitic

Ensure structure.

The cooling rate is chosen so high that secondary cementite deposits are largely suppressed, but no undesirable secondary phases such as wear-promoting bainite or martensite are formed.

In order to excrete as little secondary cementite as possible in the pearlite structure, the method according to the invention is preferably developed in such a way that the forced cooling takes place in a bath with a non-aqueous cooling medium. With non-aqueous cooling media, evaporation effects on the surface of the rail to be cooled can be avoided, which on the one hand leads to improved heat transfer from hot steel to the cooling medium and, in the interest of avoiding secondary cement deposits, leads to faster cooling, and on the other hand the development of soft spots on the surface the rail stops.

Particularly effective cooling succeeds in the interest of avoiding secondary cementite precipitates if the forced cooling takes place in a polymer bath at a temperature of 10-70 ° C., as is provided in accordance with a preferred embodiment of the present invention. The method is particularly preferably carried out in such a way that, in order to avoid secondary cementite deposits, forced cooling at a rate of at least 4 ° C / sec., Preferably at least 8 ° C / sec., Particularly preferably at least 12 ° C / sec. he follows. That way

10/24 quickly crossed the area of formation of secondary cementite precipitates in the iron-carbon diagram so that the embrittlement of the rail steel can be effectively avoided.

The invention is explained in more detail below on the basis of exemplary embodiments according to the invention.

Example 1:

? · · · ♦ · · • · ♦ ♦ · · ♦ · ··· ··

A rail for rail vehicles was produced from a hypereutectoid steel with the following directional analysis using the method according to the invention:

1.13 wt% C

1.28 wt% Mn

0.87 wt% Si

0.39 wt% gr

0.15 wt% V

0.03 wt% Nb

Accompanying and trace elements, rest Fe.

A splint with a tensile strength of 1580 MPa / mm ² , an elongation at break (As) of 8.5% and a hardness (RS) of 475 HB (Brinell hardness) was obtained.

Example 2:

A rail for rail vehicles was produced from a hypereutectoid steel with the following directional analysis using the method according to the invention:

1.12% by weight of C

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• .. •• .. • 1.1 ·· .. · ... ·:

1.10% by weight Μη

0.85 wt% Si

0.45% by weight Or

0.15 wt% V

0.015 wt% Nb

Accompanying and trace elements, rest Fe.

There was a rail with a tensile strength of 1550

MPa / mm ² , an elongation at break (A5) of 9.2% and a hardness (RS) of 470 HB (Brinell hardness).

Example 3:

A rail for rail vehicles was produced from a hypereutectoid steel with the following directional analysis using the method according to the invention:

0, 98 Wt. Q. ~ O c 1.15 Wt. Ok Mn 0.95 Wt. G. 0 Si 0.55 Wt. G 0 Gr

Accompanying and trace elements, rest Fe.

It became a rail with a tensile strength of 1515

MPa / mm ² , an elongation at break (A ₅ ) of 9.7% and a hardness (RS) of 463 HB (Brinell hardness).

Example 4:

A rail for rail vehicles was produced from a hypereutectoid steel with the following directional analysis using the method according to the invention:

1.01 wt% C

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1.2

0.90% by weight Μη

0.90 wt% Si

0.53 wt% Cr

Accompanying and trace elements, rest Fe.

It became a splint with a tensile strength of 1500

MPa / mm ² , an elongation at break (Ä ₅ ) of 9.6% and a hardness (RS) of 460 HB (Brinell hardness).

Example 5:

A rail for rail vehicles was produced from a hypereutectoid steel with the following directional analysis using the method according to the invention:

1.06 wt% C

1.20 wt% Mn

0.95 wt% Si

0.56 wt% Cr

0.15 wt% V

0.015 wt% Nb

Accompanying and trace elements, rest Fe.

It became a rail with a tensile strength of 1570

MPa / mm ² , an elongation at break (Ä ₅ ) of 9.2% and a hardness (RS) of 478 HB (Brinell hardness).

In the context of the present invention, the upper limit values for the accompanying and trace elements are listed as follows:

0.017% by weight

0.017% by weight

0.10% by weight

Ni

13/24 • ♦ · · ·· · * · * :::

.. .. * w .. · ... ·:

0.15 Wt ^-.% Cu 0.05 Wt ^-.% Ti 0.02 Wt. "% Mo 0.03 Wt. "% sn 0,003 Wt .-% 0 1.4 ppm H 0,012 Wt.% ace 0.01 Wt .-% pb 0.01 Wt .-% Co 0.01 Wt ^-.% sb 0,012 Wt.% N Rest: Fe

The rails produced according to Examples 1 to 5 have a purely pearlitic structure, essentially free of secondary cementite networks according to FIG. 1.

The rail material structure, at least in the standardized tensile test position of the rail (10 mm below the driving edge), has a pearlitic structure with 3% nital etching, essentially free of secondary cementite networks in accordance with the standard series in FIG. 3.

The cementite lamella thickness is significantly increased in the rail according to the invention compared to a rail from the prior art (rail R400HT 1t. EN 13674-1), as can be seen in FIG. 2.

The level of secondary cementite itself can be determined with the help of a series of guidelines for the assessment of

Assess secondary cementite deposits on the structure as shown in Fig. 3.

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0 .... free of secondary cementite

1 ..... very few traces of secondary cementite

2 .. .. isolated secondary cementite structures

3 .. .. closed secondary cementite network

The wear resistance of rails, which correspond to the examples, was measured using a test device according to nach 409 766 B (wheel-rail test stand) and compared with that of conventional rail steels according to EN 13674-1 (Figure 4).

The results obtained show that the wear resistance of the invention examples compared to the commercially available railroad tracks could be increased significantly, so that the increased demands on the product properties can be met significantly better with the help of the invention.

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Claims (18)

Claims ί 1, 15 ^ wt .-%, and particularly preferably 1.08 wt .-% is used. 1. Track part, in particular rail for rail vehicles, made of a hypereutectoid steel with a rail foot, a web and a head area, characterized in that / steel is used with the following directional analysis: t 0, 98 - 1.17 '' Wt. o ~~ 0 c 0.90 - 1.35 Wt. _ 0, o Mn 0.70 - 1.10 Wt. O_ 0 Si 0.15 - 0.70 Wt. g, o Cr and the steel has a pearlitic structure essentially free of secondary cementite networks, at least in the head region of the rail. 2. Track part according to claim 1, characterized in that C in amounts of 1.05 - 1.17 wt .-%, preferably 1.06 - 3. Track part according to claim 1 or 2, characterized in that Al is additionally used in amounts of 0.01 0.06% by weight. 4. Track part according to claim 1 or 2, characterized in that V is additionally used in amounts of 0.10-0.20% by weight. 5. Track part according to claim 1 or 2, characterized in that in addition Nb is used in amounts of 0.01 0.03% by weight. 6. Track part according to claim 1 or 2, characterized in that Ti is additionally used in amounts of 0.015 0.05% by weight. 7. Track part according to claim 1 or 2, characterized in that V is additionally used in amounts of 0.10-0.2% by weight together with Nb in amounts of 0.01-0.03% by weight. 8. Track part according to claim 1 or 2, characterized in that Al is additionally used in amounts of 0.01 0.06% by weight together with Nb in amounts of 0.01-0.03% by weight. 9. Track part according to claim 3 or 4, characterized in that in addition N is used in the range between 40 and 120ppm. I 10 _{: a} · * track part according to one of claims 1 to 9, characterized in that the steel has at least in the head region of the rail a tensile strength greater than 1500 MPa, an elongation at break of greater than 8% and a Brinell hardness of greater than 460 HB , 11. A method for producing a track part according to one of claims 1 to 10, characterized in that rail steel with a composition according to one of claims 1 to 9 is removed from an oven at a temperature of 1000-1300 ° C, then at temperatures of 850 - 950 ° C final rolling temperature is rolled and then subjected to forced cooling to a temperature of 450 ° C to 600 ° C. 12. The method according to claim 11, characterized in that the deformation in the temperature range 1000-850 ° C at least in the head region of the rail has an accumulated comparative degree of deformation of 1.4 min. 13. The method according to any one of claims 11 or 12, characterized in that the forced cooling takes place at least in the head region of the rail. 14. The method according to any one of claims 11 to 13, characterized in that the forced cooling takes place in a bath with a non-aqueous cooling medium. 15. The method according to any one of claims 11 to 14, characterized in that the forced cooling takes place in a polymer bath at a temperature of 15-50 ° C. 16. The method according to any one of claims 11 to 15, characterized in that the forced cooling at a rate of at least 4 ° C / sec., Preferably at least 8 ° C / sec., Particularly preferably at least 12 ° C / sec. he follows. Vienna, July 10, 2018 Applicants by: Haffner and Keschmann old GmbH nta 16/24 17/24 18/24 • · · · · ····