JPS62161917A - Manufacture of head end-heattreated rail excellent in resistance to damage and wear - Google Patents

Abstract

PURPOSE:To obtain a rail free from softened part and excellent in resistance to damage and wear at a low cost, by subjecting the railhead end composed of a steel with a specific composition to forced cooling from the temp. of austenitic range after the conclusion of hot rolling. CONSTITUTION:The railhead end consisting of 0.55-0.85% C, 0.20-1.20% Si, 0.50-1.65% Mn, and the balance Fe is subjected to forced cooling from the temp. of austenitic range after the conclusion of hot rolling between 800 deg.C and 450 deg.C at 1-4 deg.C/sec cooling rate. In this way, the above is completely free from formation of softened part and, moreover, deterioration in hardness in the boundary between the heat-treated and non-heat-treated parts can be retarded to a greater extent than heretofore. Further, vibration and impact at the end during the passage of trains can be minimized. In addition, retained heat of the rail after not rolling can be intactly utilized, so that this material contributes to energy saving, and besides, a handling stage for reheat treatment can be simplified.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention aims to prevent peeling defects at the end of the rail that occur at the joints of railway rails. This invention relates to a method for manufacturing rails with heat-treated end heads that have excellent wear resistance and damage resistance by forced cooling.

(Prior Art) The most common type of damage to railway rails is what is called a broken end at a rail joint. This is because the joint part is subjected to vibrations accompanied by a large impact force when a train passes by, and there are three types of end damage called broken ends.

(1) Fatigue failure from bolt holes for joint plates (2) Loss of the end head called end chipping (3) Horizontal cracks at the ends caused by fretting fatigue under the jaws of the joint plate and rail head These causes One example is the increase in impact force due to the joints at the ends. Conventionally, as a method to prevent this, fine pearlite heat treatment has been applied to the end head of the rail. However, the conventional method is as follows:
Similar to the heat treatment method for the entire length of the rail introduced in Japanese Patent Publication No. 60,84610, etc., the rail that had been left to cool after hot rolling was reheated to the austenite region and then forcedly cooled using compressed air. .

(Problems to be Solved by the Invention) In the conventional method, there is a part with gradually decreasing hardness called a "decreasing part" between the high-strength part having a fine pearlite structure at the end and the base material, and the hardness is continuous. Oriented towards change. However, it is unavoidable that a softened part is inevitably generated between the base material part and the "depleted part" due to reheating. The problem was that this softened part became abrasive due to the passing of the train, causing considerable impact to the end.

Therefore, the present invention has been made to solve these difficulties.

(Means and effects for solving the problem) The present invention is O:0
．． 55-0.85%, 8i: 0.20-1.20
%.

Mn: 0.50 to 1.65%, the balance being iron and unavoidable impurities, the end head of the rail is cooled from the temperature of the austenite region after hot rolling to 800 to 450°C at a cooling rate of 1 to 4°C/ This is a method for manufacturing an end heat-treated rail with excellent wear resistance and damage resistance, which performs accelerated cooling in seconds.

In other words, the present invention not only does not generate any softened parts by forced cooling from the austenite region after hot rolling, but also makes it possible to smooth the decrease in hardness at the boundary between the heat-treated part and the non-heat-treated part more than ever before. Moreover, it minimizes vibrations and shocks at the ends when trains pass, and utilizes the heat retained in the rail after hot rolling, which not only contributes to energy savings but also simplifies the handling process for reheating. The present invention provides a heat treatment method for rails that can be

The present invention will be explained in detail below.

First, we will explain the reason why the composition of the rail was determined as above.OC is an essential element for increasing strength and forming a pearlite structure, and is also an element that has a unique effect on wear resistance. If it is less than 0.55%, a large amount of pro-eutectoid ferrite, which is unfavorable for wear resistance, will be formed at the austenite grain boundaries, and the
．． If it exceeds 85%, harmful pro-eutectoid cementite will be generated at the austenite grain boundaries, or martensite will be generated in the micro-segregation areas of the heat-treated layer, causing embrittlement, so 0.55~
It was limited to 0.8596.

Si is an element that increases strength and improves wear resistance by solidly dissolving in ferrite in pearlite structure, but it also needs to be added as a deoxidizing element in an amount of 0.20% or more, and 1.20% If it exceeds 0, embrittlement will occur.
．． It was limited to 20-1.20%.

Like C, Mn is an element that contributes to high strength by lowering the pearlite transformation temperature and increasing hardenability.

However, if it is less than 0.50%, its contribution is small, and 1
If it exceeds 50%, martensite is likely to be generated in the segregated portion, so it is limited to 0.50 to 1.50%.

The rails with the above-mentioned composition are made by melting molten steel in commonly used melting furnaces such as converters and electric furnaces, using the ingot blooming method, continuous casting method, or hot rolling. Manufactured. After hot rolling, the rail is cooled at an accelerated rate from the temperature in the austenite region.

In this case, the cooling start temperature is set to the austenite region temperature in order to generate a uniform and fine pearlite structure and obtain an end portion with excellent wear resistance and damage resistance. The cooling control temperature range is 800 to 450°C (preferably 500°C), and includes the complete austenite temperature range to the end temperature of pearlite transformation. The cooling rate during this period is 1 to b. This cooling rate is the shore hardness I (
S) Within the cooling rate range necessary to satisfy 48±3, a slow cooling rate of 1°C or less cannot fulfill the role of rail end heat treatment. On the other hand, at high speeds exceeding 4°C and 8 ec, only the joints, which have better wear resistance than the base metal, will not wear out and will impede normal train operation, or the edges will have martensite or This causes the formation of brittle structures such as bainite, which may actually cause edge chipping.

Therefore, the cooling rate range is limited to 1 to 4°C and 8eC.

(Example) An example of the present invention will be described below. Table 1 shows the chemical composition of the invention steel, comparative steel, and conventional steel at 800 to 450℃.
This figure shows the cooling rate between

FIG. 1 shows the hardness distribution in the cross section of the end of the heat-treated end head, and FIG. 2 shows the hardness distribution in the longitudinal section. As is clear from these figures, the rolling speed was 2.1°C/sec after hot rolling.

800-450℃ at 2.8℃, 1.6℃/sec
Inventive steels A, B, and O, which were forcedly cooled between
It shows a stable hardness distribution within the range. Furthermore, it can be seen that the hardness of steel F, which was reheated and cooled by the conventional method, rapidly decreased on the base metal side and the formation of softened parts was also observed, whereas the steel of the present invention gradually reached the hardness of the base metal.

(Effects of the Invention) As described above, the present invention provides a stable rail with no softened parts and excellent wear resistance and damage resistance at a low cost by forcibly cooling the end head of the rail after hot rolling. It can be made by

[Brief explanation of drawings]

FIG. 1(a) is a diagram showing the cross-sectional hardness of the heat-treated part, FIG. 1(b) is a diagram showing the measurement direction of FIG. 1(a), and FIG. 2(a)
) is a diagram showing the longitudinal section hardness at a point 1 mm below the surface, and FIG. 2(b) is a diagram showing the measurement direction at a point 1 mm below the surface of FIG. 2(a). 1st (!I C)

Claims (1)

[Claims] C: 0.55 to 0.85% Si: 0.20 to 1.20% Mn: 0.50 to 1.65% The remainder is iron and inevitable impurities. is 80% from the temperature of the austenite region after hot rolling.
A method for manufacturing an end heat-treated rail with excellent wear resistance and damage resistance, characterized by performing accelerated cooling between 0 and 450C at a cooling rate of 1 to 4C/sec.