JP2500944B2 - High carbon steel / low carbon low alloy steel joint rail manufacturing method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a high-carbon / low-carbon joint (or multi-layer) rail made by laminating steel materials having different components and characteristics.

[0002]

Joining rails used in industrial machine railways are made of steel materials having different characteristics by welding method, cast-in-fill casting method, thermal spray deposition method, explosive deposition method, laminated dispersion casting method, multiple layers. Bonded steel slabs are manufactured by laminating by various methods such as continuous casting, followed by heating to a high temperature and hot rolling to manufacture various shapes and dimensions such as shaped steel and steel plates.

In the case of producing a joined steel piece by such a method, there is a problem that a steel material to be joined must be selected because of a problem that peel crack occurs at the joining interface. For example, when manufacturing a multi-layer rail having other properties such as high toughness and fatigue damage resistance while ensuring the wear resistance of the properties that the rail should originally have, it is recommended to use high carbon steel with high eutectoid carbon content. Multi-layering of low carbon, low alloy steel is required.

Carbon is diffused from the high-carbon steel side to the low-carbon steel side at high temperature during the production of the multi-layer material, the pressing of the rail of the multi-layer steel material, and the heat treatment. At this time, the low carbon steel side, which diffused and increased carbon, increased the hardenability and generated high carbon martensite, which caused cracks at the multi-layer interface and caused fatigue damage due to the generation of tensile residual stress locations. There was also a problem.

In order to prevent such harmful effects due to the diffusion of carbon, a technique of interposing an insert material between two members to be joined is used, for example, as disclosed in Japanese Patent Publication No. 64-11397. However, when such an insert material is used for a multi-layer rail, carbon diffusion can be prevented, but since the structure is such that foreign materials are mixed between both members , breakage during train passage is prevented, so in a short period of time. take
It was necessary to replace it, and there was a problem in economic efficiency .

[0006]

SUMMARY OF THE INVENTION In the present invention, when a rail is manufactured by joining (or multi-layering) a high carbon steel and a low carbon steel, a joint interface crack or a joint interface crack caused by carbon diffused between the joints is produced. It is an object of the present invention to provide a method for manufacturing a joint rail that prevents deterioration in fatigue damage resistance.

[0007]

The gist of the present invention is carbon:
High carbon steel containing 0.6-1.0% and carbon: 0.5%
When joining low-carbon low-alloy steel containing the following, the average amount of carbon on the high-carbon steel side and low-carbon low-alloy steel side, the content of components other than carbon on the low-carbon low-alloy steel side , high carbon steel or low carbon low alloy steel bonding rate combined with steel that satisfies the following equation
It is a manufacturing method of le .

[Equation 2]

The present invention will be described in detail below. High-carbon steel and low-carbon low-alloy steel with different steel components to be joined are two layers of molten steel produced by a normal melting furnace such as a converter or electric furnace, or a vacuum degassing furnace When producing a slab or a cast slab, or by combining with another method such as a post-hot working method or a bombardment method after forming a slab into a steel piece by a continuous casting method or an agglomerating and slumping method.

[0009] The high-carbon steel for use in the present invention, high strength required for the rail, a material that possesses high strength characteristics such as high hardness, its properties are provided by the carbon content. Carbon is a component necessary for obtaining high-strength steel, and it tends to be softened in a small content of less than 0.6% and hardened and embrittled in an excessive content of more than 1.0%. Further, steel containing carbon in this range exhibits a metal structure mainly composed of pearlite to improve wear resistance, and is optimal for a rail member.

Further, by suppressing the carbon content in the steel of the low carbon low alloy steel joined to the high carbon steel to 0.5% or less, a structure mainly composed of ferrite -pearlite or bainite is exhibited and the steel has strength. While retaining toughness, proper wear under rolling contact such as rails prevents accumulation of surface fatigue, improves surface damage resistance, and improves service life.

At this time, the metal structure is changed to ferrite-parler.
And bainite
In order to retain the alloy, if the carbon content is less than 0.5%, the alloy
Need to be added. The head of the rail should be on the high carbon steel side.
Whether it is on the low carbon low alloy steel side or not depends on the above characteristics.
It may be appropriately selected.

Therefore, in the present invention, when casting molten steel melted with different component compositions, or when laminating steel pieces produced through a further post-process and laminating by four-circle welding or vacuuming It is necessary to join so that the average amount of carbon on the high carbon steel side and the carbon on the low carbon low alloy steel side and the content of components other than carbon on the low carbon low alloy steel side satisfy the following formula.

(Equation 3)

The intermediate term of this formula is to improve the hardenability of the steel by the respective components, and by utilizing the characteristics that the effects are independent and additive, the influence of the individual components on the hardenability is described. The degree is expressed in the form of a multiple of the amount of the component.

In this formula, under the cooling rate of 5 ° C./s, the multiple value of this formula is changed by the combination of various components,
The relationship between the strength of both layers and the formation of martensitic structure at the bonded interface was obtained. As a result, its value is less than 2.2
Addition of alloy on the side of low carbon low alloy steel with carbon content of 0.5% or less
Insufficient amount to satisfy the strength required for rails
In addition, when the multiple value is 13 or more, a martensite structure is generated at the joint interface to enhance cold cracking susceptibility, and a tensile residual stress field is generated to reduce fatigue damage resistance. I understand.

Further, this formula shows that when the joining material is heated to a high temperature, even if the C component diffuses from the high carbon steel side to the low carbon low alloy steel side, the C component at the interface is the high carbon steel side. It has also been confirmed that the average content on the low carbon low alloy steel side is reached. Therefore, it is necessary to heat it to a high temperature with steel pieces that are bonded and joined in consideration of the regulation of the content of each component.
By hot rolling into a rail shape, it becomes possible to manufacture high carbon steel / low carbon low alloy steel joint rails .

The high-carbon steel / low-carbon low-alloy steel joint rail manufactured by the method of the present invention as described above has cold cracking and fatigue resistance due to an abnormal (martensite) structure that is likely to be formed at the joint interface. It is possible to exhibit the respective properties such as the wear resistance of high carbon steel and the surface damage resistance and high toughness of low carbon low alloy steel without causing deterioration of damage.

[0017]

[Examples] Table 1 shows cold cracks when various high carbon steels and low carbon low alloy steels are laminated by various methods to manufacture bonded steel pieces, which are then heated to a high temperature and hot rolled into respective products. The results of evaluation of susceptibility and fatigue damage resistance are shown based on the presence or absence of martensite structure generated at the joint interface. As is clear from the experimental results, when the value (hardenability of interface: D) obtained by the above-mentioned formula of the present invention is 2.2 or more, the strength of both layers of the joined steel materials is high.
In the method of the present invention in which the value is less than 13, while maintaining the degree of strength, a bainite structure and a pearlite structure that improve properties such as toughness and fatigue damage resistance are formed at the joint interface, but a comparison of 13 or more is made. In the method, a martensitic structure that deteriorates various properties is generated at the joint interface.

[0018]

[Table 1]

[0019]

INDUSTRIAL APPLICABILITY The present invention can prevent a decrease in joint interface cracking and fatigue damage resistance caused by carbon diffused between the joints of high carbon steel and low carbon low alloy steel.

Front page continuation (72) Inventor Toshikatsu Miyata 1-1 Tobahata-cho, Tobata-ku, Kitakyushu, Fukuoka Nippon Steel Co., Ltd. Yawata Works (56) Reference JP-A-56-23393 (JP, A) Special Kai-sho 50-67258 (JP, A) JP-B 61-11152 (JP, B2)

Claims (1)

(57) [Claims] 1. When joining a high carbon steel containing carbon: 0.6 to 1.0% and a low carbon low alloy steel containing carbon: 0.5% or less, the carbon on the high carbon steel side is joined. A high carbon steel / low carbon low alloy characterized in that the average amount of carbon on the low carbon low alloy steel side and the content of components other than carbon on the low carbon low alloy steel side are combined in a steel material that satisfies the following formula: Steel joint rail manufacturing method. [Equation 1]