KR20140119153A - Steel for producing parts for railway, railway crossings and switches and method for producing said parts - Google Patents

Abstract

The invention relates to a mild steel having the following composition (% by weight) for producing parts for rails, rail crossings or rail switches, said mild steel comprising 0.01 to 0.15% carbon; Up to 0.5% silicone; 10 - 15% manganese; At least 0.6 to 3.95% molybdenum; Alternatively, i. 0.05 to 0.2% nickel and / or ii. 0.05 to 0.2% cobalt and / or iii. 0.02 to 0.30% Cr and / or iv. 0.05 to 0.2% copper; V. Up to 5 ppm H; Vi. Up to 0.20% V; Ⅶ. Up to 0.10% Nb; Ⅷ. Up to 0.20% Ti and / or Zr; Ⅸ. Up to 50 ppm B; X. Up to 250 ppm N; xi. Up to 0.2% Al; xii. Up to 0.08% S; xiii. Up to 0.08% P; xiv. Up to 1.5% W; , The balance iron and unavoidable impurities, and the present invention also relates to a process for producing said mild steel and its use.

Description

TECHNICAL FIELD [0001] The present invention relates to a steel for manufacturing parts for rails, rail crossings, and switches, and a method for manufacturing these parts. BACKGROUND OF THE INVENTION < RTI ID =

The present invention relates to a wrought steel for manufacturing parts for rail crossing and switches and a method of manufacturing these parts.

Switches and crossings (S & C) are components of rail systems that are subject to considerable loads when used on rail tracks.

Several techniques have been used to fabricate these S & C. At present, S & C parts are manufactured in a significant proportion of cast austenitic-manganese steel (AMS). AMS has traditionally been used because of its high work hardening capacity for impact, excellent solubility in subsequent solution processing and water quenching, and very good wear resistance in work-hardened conditions. Nominal chemical analysis of AMS is 1.2% C, 13% Mn and 0.5% Si, and this AMS produces bulk hardness in the range of 200-250 HB. After a certain amount of traffic, the hardness of the S & C can reach levels of 500 to 550 HB.

In addition, AMS has a number of drawbacks such as low 0.2% proof stress. Railway points and crossings are used during use to produce work hardening and plastic deformation that increases the material strength to a level with a higher resistance to additional plastic flow, Is often experienced. However, it is not desirable to change an inevitable related dimension in the original uncured state. In the track, differential loading will lead to uneven hardening and local plastic deformation, resulting in a bad ride and ultimately it will be necessary to rebuild the deformed profile with a weld deposit. As a result, in heavy axle load applications, AMS requires frequent grinding to remove lipping and requires weld repair to restore strain height loss.

AMS is a material that is difficult to cast or machine into complex shapes required for S & C. In addition, any change to the footprint of the rail crossing requires a new mold to manufacture a very expensive new crossing profile. The narrow freezing range of AMS results in a number of cavity-type defects that can be the origin of the cracks encountered during use. Generally, the pores in the AMS crossing occur at a depth of about 10 to 15 mm at the new surface, and once the depth approaches, the weld restoration to rebuild the crossing due to the risk of cracking starting from any residual pores There is no practicality. For AMS components, it is normally considered a normal life of about 10 years, beyond which the degree of defects is so severe that it is uneconomical to continue repairing the orthodontic weld and the components must be replaced. Another problem associated with AMS is thermal instability of the austenitic microstructure, which makes the material difficult to weld. This difficulty of welding is a problem not only when welding components in situ, but also during component manufacturing, since the rails must be welded to the components before they are installed on the rail track.

As a result of this problem, several alternatives have been developed for the conventional AMS crossing type. Some S & C are made of materials that are in the form of composite metal sandwiches made of hard, wear-resistant plate steel of different composition, microstructure and characteristics, with the wheels touching the passing train. The bottoms of these materials are made from base steel compositions. While this solution typically provides an inexpensive alternative with better weld repair capabilities, the nature of the crossing nose depends on the precise level of steel composition that makes up the crossing nose. In many cases, such compositions do not meet the wear resistance, especially the rolling contact fatigue resistance provided by the AMS crossing. Moreover, these solutions are more difficult to produce as a result of composite sandwiches of different steels.

Another alternative to AMS is to provide a high manganese component having a work hardened layer prior to installing these components on the rail track. Surface pre-hardening techniques may include shot blasting, rolling or explosive hardening. Explosion hardening among these techniques is a generally preferred choice because it provides a cured layer of sufficient thickness to satisfy the S & C usage requirements. However, it is difficult to control the thickness of the cured layer by such a surface hardening technique. Moreover, surface hardening does not address welding repair problems and casting defects associated with high manganese cast parts.

Therefore, the present inventors have started to devise a solution to the above-mentioned problems.

It is an object of the present invention to provide an alternative to AMS, especially a new mild steel for S & C as an alternative to casting AMS.

It is also an object of the present invention to provide a new mild steel for S & C that can be easily welded for field repair by an upper-of-head weld repair method as an alternative to AMS .

It is also an object of the present invention to provide a new mild steel which is more resistant to nose batter.

It is also an object of the present invention to provide a new mild steel for S & C that can be welded to conventional pearlitic rails.

It is also an object of the present invention to provide a new mild steel for S & C flash-butt weldable to conventional pearlitic rails.

One or more of the objects of the present invention is achieved by providing a mild steel having the following composition (wt%) for producing components for rails, rail crossings or rail switches.

0.01 - 0.15% carbon;

Up to 0.5% silicon;

10 - 15% manganese;

At least 0.6 to 3.95% molybdenum;

Optionally,

    I. 0.05 to 0.2% nickel and / or

    Ii. 0.05 to 0.2% cobalt and / or

    Iii. 0.02 to 0.30% Cr and / or

    Iv. 0.05 to 0.2% copper;

    V. Up to 5 ppm H;

    Vi. Up to 0.20% V;

    Ⅶ. Up to 0.10% Nb;

    Ⅷ. Up to 0.20% Ti and / or Zr;

    Ⅸ. Up to 50 ppm B;

    X. Up to 250 ppm N;

    xi. Up to 0.2% Al;

    xii. Up to 0.08% S;

    xiii. Up to 0.08% P;

    xiv. Up to 1.5% W;

    One or more of,

· Residual iron and unavoidable impurities.

The present invention can produce a single type of feedstock blank that can be subsequently machined with any crossing design necessary to satisfy local conditions. Computer-controlled machining achieves a close tolerance at low cost. Since rails can have cross angles at various angles to meet local needs, various casting molds are needed to manufacture these parts from AMS castings, which is reflected at a relatively high cost. Thus, the present invention provides significant cost savings.

The role of carbon in this steel is to obtain sufficient hardness of the steel, mainly by strengthening the solid solution. On the other hand, the high carbon content increases the amount of retained austenite, leading to a decrease in hardness. Increasing the carbon content significantly increases the risk of grain boundary embrittlement of these steels due to the formation of carbide networks in the as-prepared state and subsequent welding. Thus, in order to maintain a subtle balance between hardness and brittle hazards, the carbon content for these steels (all compositions are given in weight percent unless otherwise stated) is required to be between 0.01 and 0.15%. More preferably, the carbon content is from 0.01 to 0.12%. As a result of their low carbon content, most of these alloys are easy to weld. In order to further improve the weldability, the carbon content is preferably at most 0.10%, more preferably at most 0.08%.

To achieve the desired microstructure, the carbon content is at least 0.01%, preferably at least 0.02%. The appropriate minimum carbon content from the steelmaking point is 0.04%.

Manganese is an austenite promoting element. Manganese stabilizes austenite by increasing the temperature range in which austenite is present.

It has been found that, in the variation of the manganese content in the steel according to the present invention, the maximum hardness is obtained at a manganese content of at least 10%. At very high manganese levels, for example 15% manganese levels, the hardness is reduced to an inadequate level. Hardness has a strong correlation with abrasion resistance, and this wear resistance is a determinant of the life span of most rail components including S & C. A low wear rate means less need to repair parts frequently. Significant differences in abrasion resistance between steel with a manganese content of less than 10% and steel with a manganese content of greater than 10% are due to differences in microstructure. Martensite-based microstructure is obtained at a manganese level of less than 10%, while retained austenite, epsilon-martensite (hexagonal close-packed or HCP martensite) at a level of 10% Indicating the mixed microstructure of the martensite. Preferably, the manganese level is at least 11%. It has been found that the abrasion resistance of a steel having a completely martensitic microstructure is lower than that of a steel having a mixed microstructure having martensite and retained austenite. However, the increase in manganese content also leads to an increase in retained austenite. At a manganese content of 15% or more, the level of retained austenite begins to increase considerably, which means that the increase in the hardness of the martensite phase is further offset by the increase in the proportion of soft austenite, And a decrease in resistance to abrasion. The resistance to crack propagation is high, which is associated with very slow progressive failure. This increases the chance of detecting any fatigue crack formation and increases the chance of repairing defective or defective parts during use or repairing before complete failure occurs. Based on the above reasoning, the manganese content is preferably at least 11% to at most 15%. Also, since manganese is an expensive alloying element, the optimum maximum manganese content is 14%, even 13%. The appropriate minimum manganese content was 11.5%. The maximum values of hardness and abrasion resistance were achieved when the manganese content was between 12 and 13% Mn. At these levels, on the one hand the amount of residual austenite + epsilon-martensite and on the other hand the amount of hard martensite is about 50: 50, thereby providing a satisfactory combination of impact toughness and hardness.

Molybdenum is effective in increasing impact toughness. Also, by the scavenging effect of molybdenum on the phosphorus, the temper embrittlement phenomenon is prevented. At 0.6% level of Mo, the increase in impact toughness is already noticeable, but an additional increase in impact toughness is obtained at values above 0.6%. The impact toughness level is no longer increased at a value of 1.5%. Therefore, the molybdenum addition in the steels of the present invention is required between 0.6% and 3.95%, preferably the molybdenum content is at most 2.95% and / or at least 1.25%. The molybdenum content of 1.5% was found to be a suitable minimum value for stable impact toughness values. It has been found that a molybdenum content of 1.90% is a suitable maximum value from a cost and technical point of view, and that an addition value of more than 1.90% results in only minor improvements which are not so great.

Silicone has been found to have little impact on impact toughness and abrasion resistance of the steel of the present invention, but it provides an increase in tensile strength and hardness through strengthening of the solution. It also acts as a killing agent during steel production. Based on this, a maximum value of 0.5% Si is recommended. A suitable minimum silicon content was found to be 0.10%, even 0.15%, and / or an appropriate maximum silicon content was found to be 0.40%, even 0.35%.

Nickel (Ni), cobalt (Co) and copper (Cu) have a beneficial effect on manganese as an austenite promoting element. To some extent, these elements may be added instead of or in addition to manganese. Ni, Co, and Cu may be added at a maximum of 1% per element, 3% or less in total. Preferably, the maximum value of Ni, Co and / or Cu is 0.5%.

The alloys according to the invention have proven to be readily machinable. If desired, one or more of sulfur, calcium, tellurium or selenium or other known machinability improving elements may be added to these alloys.

The phosphorus content is generally maintained at 0.08% or less, preferably 0.05% or less, preferably 0.02% or less, in order to minimize the tendency of hot cracking. Phosphorus is a residual element in these steels. If sulfur is not added to improve machinability, the sulfur content is generally kept below the 0.02% impurity level. If sulfur is added, the appropriate maximum sulfur content is 0.08%, preferably 0.05%. If the following elements are added as alloying elements, their preferred ranges are: 0.02 to 0.20% V, 0.02 to 0.10% Nb, 0.02 to 0.20% Ti, 0.02 to 0.20% Zr, 5 to 50 ppm B and 10 To 250 ppm N. A suitable maximum content which contributes to the crystallization of the steel is 0.10% V, 0.075% Nb, 0.10% Zr and / or 0.10% Ti. B, V, Nb, Zr and Ti.

The steel according to the invention is preferably a silicon-killed steel. The steel may also be an aluminum-killed or aluminum-silicon killed steel, provided that the cleanliness of the steel is maintained in accordance with specifications in view of the maximum value of aluminum oxide inclusions. When added as an alloying element, the maximum total aluminum content is 0.2%. Preferably, the total aluminum content (when added as an alloying element) is 0.02 to 0.15%. When aluminum is added, the metal aluminum (i.e., not present as an oxide) content will be lower depending on the oxide content of the molten steel.

The steel according to the present invention has a hydrogen content of not more than 5 ppm, preferably not more than 3.5 ppm, more preferably not more than 2.5 ppm.

In some applications, chromium can be added to levels up to 0.3%, although it is not intentionally added because chromium is preferably kept below 0.15% impurity level. The appropriate maximum chromium content is 0.2%.

It should be noted that the steel composition according to the present invention can also be used to produce castings, but since the low carbon composition is more expensive than conventional AMS Hadfield type steels with high carbon content, It is not economically attractive to use the composition according to the invention for producing cast materials unless it yields better properties.

According to a second aspect of the present invention, there is provided a mild steel manufacturing method for use in a rail track such as rail crossing or rail switches.

In the above manufacturing method,

Providing a starting material, such as a bloom or ingot, having a composition according to any one of claims 1 to 10;

Providing the starting material to a suitable temperature for hot rolling the plate or rail; From here,

  i. The hot-rolled plate has a sufficient thickness for machining the component from the hot-rolled plate, or

  Ii. The rail

    a. Having a desired rail profile for machining with parts for switches such as rail crossings and switchblades, or

     b. Having a desired rail profile for use as a rail,

Cooling the plate or rail after the final hot deformation to achieve the desired mechanical properties; And

Machining from hot rolled and cooled plates or rails into rail crossing and switch parts.

Mild steel can be used to produce components for crossing by machining parts from hot-rolled and cooled plates. The mild steel may also be provided in the form of a rail having the desired geometric profile, and these hot rolled and cooled rails may be used to weld to the part or to machine the switch blade. Also, the rails can be used like this.

The method according to the present invention can produce blanks of different lengths that can be machine operated with crossings having a wide angle. Further, the hot-rolled plate can be slit into a thin length machined with the subsequent switch blade. However, in order to form the switch blades, it may be desirable to hot-roll the cast bloom to the rails of the desired geometric profile and then machine the rails to fabricate the switch blades.

According to a third aspect of the present invention there is also provided a use in a rail, rail crossing or rail switch of a mild steel part made according to the invention and / or having a composition according to the invention, Is at least partially welded by the welding repair method in the field.

The flash butt weld according to the present invention is a stainless steel insert which acts as a sandwich filler to improve conformity to high integrity welds. The crossing is first welded to the crossing prior to welding to the pearlitic rail .

Figure 1 shows the components for a switch in a common crossing.
Fig. 2 shows the program on the right and the check-rail on the left.
3 is a graph showing the relationship between RCF and HB.
4 is a graph showing the relationship between molybdenum content and Charpy toughness.
5A is a graph showing the relationship between the stress after three cycles of + 1 to -1% and the work hardening rate.
Fig. 5B is a partially enlarged view of Fig. 5A. Fig.
6 is a graph showing the wear rate of the material.

The steel according to the present invention can be used to manufacture components for rail crossing and switches such as frogs in a common crossing as shown in Fig. This shows a single spinning program in a common crossing. This self-guarding frog without guardrail has a raised flange on the frog that is supported on the face of the wheel as it passes through the frog. The mild steel according to the present invention is primarily intended to be applied to components for rail switches such as rails, rail crossings or fog and switch blades, but such mild steels may also be used for other track components such as expansion joints, insulating rail joints or rails .

In addition, Frog forms part of a railway switch and is also used in a level junction (flat crossing). Frog is designed to ensure that the wheel traverses this gap without "falling" into the gap in the rail; The wheel and rail profile ensures that the wheel is always supported by at least one rail. To ensure that the wheel follows a proper flangeway, a check-rail or guard rail is installed inside the rail opposite to the Frog. Fig. 2 shows the program on the right and the check-rail on the left. Frog or double-frog will typically be made of steel according to the present invention.

The invention is further illustrated by the following non-limiting examples.

A series of prepared castings and their chemical compositions are given in Table 1.

The mechanical properties of the steel are excellent as shown in Table 2.

The evaluation of the rolling contact fatigue (RCF) resistance of the steel according to the invention is carried out by a twin disk wear test at room temperature with a rolling contact stress of 900 MPa, a slip level of 5% and a small amount of lubricant applied during the test period.

The rigs used in these tests and tests are described in Fletcher & Bay, "Development of a machine for closely controlled rolling contact fatigue and wear testing ", J Test. Eval. 28 (2000), 267-275. The RCF resistance is defined as the number of cycles for crack initiation. The test data show that the new material doubles the alternative rail steel in the current market. In the case of premium grade heat treated rails, for example, the number of cycles before crack initiation is typically 110,000 cycles. In addition, the new material exhibits RCF resistance comparable to AMS and Maraging Steel (AMS and MS in Fig. 3, respectively), with RCF crack initiation only after 300,000 cycles. From the viewpoint of low cycle fatigue, the steel according to the present invention proved to be superior to AMS in this regard.

Compared with other rail materials, the steel according to the present invention has been found to exhibit better impact toughness values than steels suitable for the purposes of manufacturing rail crossings and switch components. Figure 4 shows the Charpy toughness value (at J at 20 [deg.] C), which justifies the minimum for Mo of 0.6% as a function of molybdenum content. Open circles correspond to microalloyed samples 12JF26 and 27.

This material has a very high work hardening rate which results in a stress increase of about 400 MPa after three cycles of + 1 to -1% during the low cycle fatigue test in the standard NF 12 specimen (see FIGS. 5A and 5B). In FIG. 5B, which is a partial enlargement of FIG. 5A, the stress increase during the first (1x), second (2x) and third (3x) cycles is clearly shown.

The evaluation of the rolling contact wear resistance of the steel according to the present invention was carried out at room temperature under a rolling contact stress of 750 MPa and a wear rate measured after 2130 cycles (rolling contact wear resistance is plotted as a function of Brinell hardness (HB) (See Fig. 6). Fig. Wear rate of the material according to the present invention (mg / m of slip) (black dots in Fig. 6) is the same grade and AMS and the newly developed HPRail ^® as compared to (6 indicated by a rhombus in) is 0 to 5 mg / m sleep Range. ≪ / RTI >

The weldability of the steels according to the invention is excellent due to the low carbon content and also much better than the weldability of AMS and this new steel is preferred in applications where weldability is a problem as in the manufacture and use of rail crossings and switch components It is an option.

Claims (15)

For making parts for rails, rail crossings or rail switches, mild steel with the following composition (% by weight).
0.01 - 0.15% carbon;
Up to 0.5% silicon;
10 - 15% manganese;
At least 0.6 to 3.95% molybdenum;
Optionally,
I. 0.05 to 0.2% nickel and / or
Ii. 0.05 to 0.2% cobalt and / or
Iii. 0.02 to 0.30% Cr and / or
Iv. 0.05 to 0.2% copper;
V. Up to 5 ppm H;
Vi. Up to 0.20% V;
Ⅶ. Up to 0.10% Nb;
Ⅷ. Up to 0.20% Ti and / or Zr;
Ⅸ. Up to 50 ppm B;
X. Up to 250 ppm N;
xi. Up to 0.2% Al;
xii. Up to 0.08% S;
xiii. Up to 0.08% P;
xiv. Up to 1.5% W;
One or more of,
· Residual iron and unavoidable impurities. The method according to claim 1,
At most 0.12% C and / or at least 11% Mn, and / or at most 2.95% Mo. The method according to claim 1,
Mild steel, containing up to 0.02% S and up to 0.02% P. 4. The method according to any one of claims 1 to 3,
Mild steel, containing up to 0.10% C 5. The method according to any one of claims 1 to 4,
Mild steel, containing up to 14% Mn. 6. The method according to any one of claims 1 to 5,
Mild steel containing at least 0.10% Si. 7. The method according to any one of claims 1 to 6,
Mild steel comprising at least 15% volume of retained austenite and / or at least 15% volume of retained austenite during use as a component for rails, rail crossings or rail switches in hot rolled condition. 8. The method according to any one of claims 1 to 7,
At least 1% Mo, preferably at least 1.25% Mo, and / or
Mild steel containing at least 2.45% Mo, preferably at most 1.90% Mo. 9. The method according to any one of claims 1 to 8,
Mild steel, containing at least 0.02% C 10. The method according to any one of claims 1 to 9,
Wherein the steel comprises 0.05 to 0.1% vanadium and / or 0.025 to 0.075% Nb. A method of manufacturing a mild steel part for a rail, a rail crossing or a rail switch,
Providing a starting material, such as a bloom or ingot, having a composition according to any one of claims 1 to 10;
Providing the starting material to a temperature for hot rolling the plate or rail; From here,
i. The hot-rolled plate has a thickness for machining the component from the hot-rolled plate, or
Ii. The rail
a. Having desired rail profiles for machining with switch parts such as rail crossings and switch blades, or
b. Having a desired rail profile for use as a rail,
Iii. Cooling the plate or rail after the final hot deformation to achieve desired mechanical properties; And
Machining from hot-rolled and cooled plates or rails into rail-crossing or rail-switch components. 12. The method of claim 11,
Further comprising welding one or more rails to the part. 13. The method according to claim 11 or 12,
Mild steel parts for rails, rail crossings or rail switches are frog or double frog or switch blades. Use in a rail, rail crossing or rail switch of a mild steel part having a composition according to any one of claims 11 to 13 and / or having a composition according to any one of claims 1 to 10. 16. The method of claim 15,
The use of mild steel in which the steel component is at least partially welded by a field repair method.

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