JPS6314814A - Heat treatment of rail - Google Patents

Abstract

PURPOSE:To stably produce a rail having fine pearlite structure with decreased fatigue damages at a low cost by passing the rail through an air-liquid mixed spraying zone of a high temp. where pressurized hot water of a specific temp. is sprayed thereby subjecting the rail top to force cooling under adequate conditions. CONSTITUTION:The rail consisting of a steel which does not contain a large amt. of costly alloy elements is passed through the high-temp. air-liquid mixed spraying zone obtd. by spraying the pressurized hot water of 100-170 deg.C from series-disposed nozzles. The above-mentioned rail top is subjected to the force cooling in said zone at 1-30 deg.C/sec cooling rate from the austenite region down to 750-500 deg.C. The rail top is thereby converted to fine pearlite structure. The rail top is thereafter preferably force-cooled by blast cooling from 500 deg.C down to the force cooling stop temp. to prevent the softening of the fine pearlite. The rail which decreases the wear of the rail top in the curved part under a heavy axial load and the fatigue damages such as flaws at the rail top during high-speed running is obtd. by the above-mentioned force cooling.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention The present invention relates to a method for heat treatment of rails, and in particular to prevent fatigue such as wear of the rail head at curved sections and shearing flaws in the rail head during high speed operation. The aim is to produce the necessary fine pearlite structure stably and at low cost in order to manufacture rails with less damage.

Industrial applications: A method for heat treatment of rails that responds to the increasing load and speed of rail transportation.

Conventional technology In recent years, railway transportation has become more heavy-duty and faster.
The usage conditions for rails are becoming stricter, and in response to these demands, a fine pearlite structure as the metallurgical structure of the rail head has shown the best characteristics in terms of wear resistance and damage resistance required for rails. Are known.

However, the following two manufacturing methods are generally known as methods for obtaining such a metallurgical structure.

The first method is to add Si, (:r,
This is a method (hereinafter referred to as the alloy steel rail method) in which the fine pearlite structure is obtained under natural cooling conditions after rolling by adding large amounts of alloying elements such as MO and V, singly or in combination.

The second method is to obtain the fine pearlite structure by accelerating a carbon steel rail, which can stably obtain pearlite, after rolling or after heating, at a predetermined cooling rate from the temperature in the austenite region (hereinafter referred to as the heat-treated rail method). ).

However, this heat treatment rail method is further divided into the following methods (1) and (2).

- Sen/Method: A method in which the material is cooled after rolling, reheated off-line to the austenite region using gas flame heating or high-frequency induction heating, and then heat treated.

■Method: After hot rolling, the austenite region is subsequently accelerated and heat treated at a predetermined cooling rate online.

The following three methods are known as forced cooling methods for the heat treatment.

■ Cooling by blast.

■ Cooling by water spray and water mist.

○ Immersion cooling in a molten salt bath, etc.

Problems to be Solved by the Invention However, each of the above conventional methods has its own problems.

That is, even if the first alloy steel rail method can be manufactured as rolled, it requires a large amount of expensive alloying elements, resulting in high manufacturing costs. Furthermore, when welding long rails, the cooling rate after welding is around 2°C/sec, which is faster than the cooling rate after rolling, so a martensitic structure is generated in the welded joint. Therefore, after welding the joint, post-heat treatment is required, which inevitably reduces the efficiency of joint welding.

Method (2) in the second heat treatment rail method is unavoidably disadvantageous because it increases the time and cost of reheating the material once it has been cooled.

Although method (1) of this heat treatment rail method does not have the disadvantages mentioned above in method (2), methods (2) to (3) adopted for forced cooling have the following disadvantages.

Cooling by blast (2) has a small cooling capacity, and it is difficult to secure the required cooling rate determined by the components. In the case of off-line heat treatment, the required cooling capacity is reduced by making the temperature gradient steeper from the surface of the rail head to the inside, thereby utilizing heat removal into the rail. Furthermore, since the cooling capacity depends on the speed of collision with the material to be cooled, possible ways to improve the cooling performance include reducing the distance between the blast nozzle and the material to be cooled, and increasing the discharge pressure. In the former case, it is necessary to control the blast nozzle to follow the bending of the rail during the forced cooling process, and as the heat treatment speed increases, the equipment mechanism becomes complicated. In the latter case, the flow rate of the blast increases, leading to an increase in the size of the supply device, which is disadvantageous in terms of equipment costs and running costs. In addition, Cr! ,t.

There is a method of increasing hardenability and reducing the required cooling rate by adding alloys such as, but adding alloys increases manufacturing costs.

Compared to blast cooling, cooling using water spray and water mist is advantageous in that the cost of the cooling medium is lower, the cooling capacity is greater, and the cooling capacity can be adjusted by changing the flow rate density. As a cooling property, the cooling capacity increases as the surface temperature of the material to be cooled decreases, and a water wetting phenomenon occurs that reaches its maximum at the point where the material moves from the membrane to the core. In the case of water mist, the same phenomenon occurs although it differs slightly depending on the air-water ratio, and this phenomenon largely depends on the surface temperature and surface properties of the material to be cooled. Such cooling characteristics of water make cooling control difficult, causing uneven quality due to variations in cooling capacity conditions, and the generation of bainite and martensite structures that are harmful to rail properties due to local supercooling due to water wetting. Become.

In immersion cooling in a molten salt bath, etc., the rail position is restricted to the immersion position, and it is difficult to adjust the cooling capacity for each part or over time. Therefore, this is disadvantageous in terms of equipment design and selection of heat treatment conditions.

"Structure of the Invention" Means for Solving the Problems Cooling rate from the austenite region to 750 to 500°C is 1 to b.In making the rail head a fine pearlite structure, the cooling rate is 100 to 170°C from nozzles arranged in series. A rail heat treatment method characterized by forcing the rail head to cool by passing it through a high-temperature gas-liquid mixed spray zone obtained by injecting pressurized hot water.

The droplets of hot water ejected from the working nozzle provide stable cooling with little change in cooling capacity.

The cooling capacity can be adjusted in response to changes in hardenability due to rail components, and droplets that collide with the material to be cooled are instantaneously vaporized, resulting in appropriate drainage.

EXAMPLE To further explain the present invention as described above, in the present invention, repeated studies have been made to solve the problems of the conventional ones described above, and the rail head is made of a fine pearlite structure with excellent wear resistance and damage resistance. In order to achieve this, the rail head is cooled at an accelerated rate below the austenite range temperature, without producing bainite or martensitic structures that are harmful to the rail properties, and without causing hardness softening due to self-annealing after heat treatment.
We succeeded in obtaining a cooling or cooling control method for heat treatment at low cost and with high efficiency.

That is, the present invention generally relates to tJt% (hereinafter simply referred to as %).
So, C: 0.50-0.85%, Si: 0.10-1
．． 00%, Mn: 0.50-1.50%, P: 0
．． 035% or less, S20. 035% or less, Aβ: 0.
05% or less, and the balance is Fe and unavoidable impurities as a basic composition, and if necessary Cr: 0.05 to 150%
.

MO+0.05~0.20%, V:0.03~0.10
%.

Ni: 0.10-1.00%, Nb: 0.005-0,
A rail having a chemical composition in which one or more of 0.050% and 0.050% is added is heat-treated to a fine pearlite structure at a cooling rate of 1 to b at a head temperature of 700 to 500°C from the austenite range. In this process, pressurized hot water of 120 to 170°C is injected through a nozzle to cover the entire temperature range of the forced cooling, creating a high-temperature gas-liquid mixed spray (hereinafter referred to as hot water spray), that is, using such a hot water spray header. The rails are passed through the arranged rows to forcibly cool the rail heads. In addition, this forced cooling is performed from the start of forced cooling to 500°C using the hot water spray cooling head, and from 500°C to the forced cooling stop temperature, the head is forced to pass through the above rail through the row of blast cooling headers. It provides cooling.

In the present invention, the temperature of the rail head is accelerated from the austenite region to the temperature of the austenite region, and hot water spray or a combination of hot water spray and blast is used as the cooling medium when heat treating the rail head to a fine pearlite structure. This is due to the following reasons.

In other words, in order to form a fine pearlite structure in the rail head, the cooling rate specified by the rail component (for example, 3-b for AREA-based components) should be set between 700°C and 500°C for 5 mm of the rail surface or surface layer below the austenite range temperature. However, in order to prevent the fine pearlite structure of the transformed head from softening, the forced cooling stop temperature must be set at 450 to 270° C. at the rail surface, taking into account heat recovery from the rail abdomen, etc.

The hot water spray of the present invention can be used at high temperature and high pressure (100 to 170°C).
, 0 to 7.0 kgf/cfflG) is injected into the atmosphere from a nozzle, and the droplets generated at this time are used for cooling. A portion of the hot water injected from the nozzle vaporizes and rapidly expands to several hundred times its volume, and the steam shears and accelerates the hot water into fine droplets, forming a gas-liquid mixed spray. As shown in Figure 6, the cooling performance characteristics of hot water spray are that the cooling performance changes little as the surface temperature of the material to be cooled changes from a high temperature range to a low temperature range, which means that cooling control is easy and stable. shows. In the case of water spray, the cooling capacity changes depending on the surface temperature of the material to be cooled, and the cooling capacity rapidly increases due to the water wetting phenomenon. Since this phenomenon depends on the surface temperature and surface properties, it is necessary to take into consideration that in the case of hot rolled goods, water wetting may occur at a surface temperature of 500°C to 550°C. It has also been shown that the cooling ability of hot water spray is equivalent to or higher than that of water mist, and the explosively expanding steam atomizes the hot water, making it possible to obtain stable droplets over a wide range of flow rates with the same nozzle. Therefore, it is extremely advantageous for adjusting the cooling capacity in response to changes in hardenability due to rail components.

With hot water spray, the droplets that collide with the material to be cooled instantly vaporize, so even hot water spray alone has extremely good water removal properties. By providing this, the water can be completely drained and the cooling conditions can be stabilized.

Next, the reason why hot water spray cooling is used as a cooling medium from the start of cooling to 500°C, and blast cooling is used from 500°C until forced cooling is stopped, is as follows.

That is, in order to obtain fine pearlite, the austenitol barlite transformation requires a cooling rate of 1 to 1 b between 700°C and 500°C, so the above-mentioned hot water spray cooling is used as the cooling medium, and forced cooling is performed after the transformation is completed. is a recuperation suppressing cooling to prevent softening of fine pearlite, and the cooling capacity is 1/1 of that during transformation.
2 or less is sufficient. In addition, in order to avoid the water wetting phenomenon that is noticeable when using water spray, etc., using blast cooling as the cooling medium in the latter half has industrial practicality and is effective in terms of quality stability.

That is, by using the hot water spray cooling of the present invention as a cooling medium during the austenitol barlite transformation, the necessary cooling rate can be ensured sufficiently, and the cooling capacity is stable, so that the rail head can be A fine pearlite structure can be stably obtained without producing harmful bainite or martensite. Note that the forced cooling method according to the present invention as described above can be applied to both cases where after hot rolling is completed, heat treatment is performed on-line following the hot rolling, and when heat treatment is performed after reheating off-line.

To explain a specific embodiment of the present invention as shown in the attached drawings, FIG. The mixed spray forms and forcibly cools the head of the rail 1, which is the material to be cooled. The abdomen of the rail 1
Spray shielding means 3 and the like are provided at the bottom to prevent cooling by hot water spray. Fig. 2 also shows the hot water spray nozzle used in conjunction with the hot water spray nozzle shown in Fig. 1 as described above.
An example of the arrangement of a blast cooling header is shown, and the header 4 is a multi-hole or multi-slit header, and is configured to forcibly cool the head of the rail 1 by injecting high-pressure air.

Furthermore, FIG. 3 shows an example of the arrangement of the hot water spray nozzle and the purge nozzle. By installing the purge nozzle 5 in the area, the injected hot water can be drained more completely, which is effective against local unevenness caused by water wetting.

FIG. 4 is an example of a combination of hot water spray cooling and blast cooling, in which the hot water spray cooling area 6 and the blast cooling area 7 are arranged linearly in the rail passing direction, and the rail 1 is forcedly cooled by passing through it.

Next, Table 1 shows the results of the rails manufactured by the present invention by continuing heat treatment after completion of hot rolling.As a comparative material, the rails were reheated off-line using the conventional method. The rail that has been subjected to slack quenching is also shown.

Table 1 shows the chemical compositions of the test materials and the cooling conditions for heat treatment, where ASB is the material of the present invention and C and D are comparative materials that were heat treated by the conventional method. B, D,
is a rail steel with a low alloy added to the basic composition.

Table 2 below shows the mechanical properties of the central portion of the rail head after heat treatment.

Both of the materials A and B of the present invention have a tensile strength of 130 kgf7mm2 or more, which is equivalent to that of the conventional heat-treated rail.

Table 2 and Figure 5 show the cross-sectional hardness distribution relationship according to depth and distance from the surface at the center of each rail head obtained as described above. Compared to the quenched comparative material C1D, the effective hardening layer depth of the present inventions A and B due to the heat treatment is deep, and high hardness is ensured to the inside.

Further, the microstructure showed good results, with no structures such as bainite or martensite, and it was confirmed that rails of stable quality could be manufactured at low cost by the cooling method of the present invention.

"Effects of the Invention" According to the present invention as explained above, the rail is capable of producing a rail with less fatigue damage such as abrasion of the rail head on curved sections or curling scratches on the rail head during high-speed operation, especially under the load of the center axis. This invention can be produced stably and at low cost, and has great industrial effects.

[Brief explanation of drawings]

The drawings show the technical content of the present invention, and FIG. 1 is an explanatory diagram of the arrangement relationship in the cross-sectional direction of the rail of the hot water spray according to the present invention, and FIG.
Figure 3 is an explanatory diagram of the arrangement relationship in the rail cross-sectional direction similar to the figure, Figure 3 is an explanatory diagram of the arrangement relationship of hot water spray and purge nozzles in the rail length direction, and Figure 4 is the rail length due to the combination of hot water spray and air blast. Fig. 5 is a diagram showing cross-sectional hardness distribution measurement results for production examples according to the present invention and comparative examples thereof; This is a diagram summarizing the cooling capacity. In these drawings, 1 is the rail, 2 is the hot water spray means, 3 is the spray shielding means, 4 is the blast header, and 5 is the purge nozzle 6. 7 shows the hot water spray cooling area, 7 shows the blast cooling area, and in FIG. 5, AlB shows the one according to the present invention, and C and D show the ones according to the comparative example. Akira Yoshiyuki Taka
Yudo 1) Correct
Hirodo Eihashi Shin-same Teramoto
Yutaka Sodo Fuku 1
) Cultivation Kingdom Qi
Yoshibe Fuji (C) J-face e+ 11! m (→ (D) Procedural amendment (0) Showa e'F, s, ' Japan Patent Office Commissioner M1 Yen Akio 1, Indication of the case Showa IT patent application No. /f'' (P 7.7 No. 2 ,
Name of the invention 1-+ν3@Grudge way 3, Relationship with the case of the person making the amendment W Name of the applicant (name) H$ Steel Tube Co., Ltd. 4, Agent Showa year, month, day Contents of the amendment for shipping 1, the present application In the specification, page 2, line 17, the phrase "after both heating" is corrected to r after reheating and j. 2. In the 15th line of page 4, it says ``in case,'' and then add ``r'' and ``j'' when reheating. 3. On page 5, line 9, the word ``kotos'' is r cost.''
I am corrected. 4. In the 20th line of the same page, correct "cooling capacity condition" to r cooling condition 1. 5. In the 7th line of the same 6th line, the phrase ``disadvantageous in selection'' is corrected to ``r disadvantageous in control''. 6. On page 8, line 8, "120-170°C" should be corrected to "100-170°C." 7. In lines 9 and 10 of page 9, the phrase "fine pearlite... from" has been corrected to "from the rail abdomen, etc., in order to prevent the softening of the fine pearlite structure." .

Claims (1)

[Claims] Forced cooling is performed at a cooling rate of 1 to 30 degrees C/sec from the austenite region to 750 to 500 degrees Celsius, and pressurized hot water of 100 to 170 degrees Celsius is supplied from nozzles arranged in series to form a fine pearlite structure in the rail head. A rail heat treatment method characterized by forcing the rail head to cool by passing it through a high-temperature gas-liquid mixed spray zone obtained by spraying the rail.