JPH057991A - Manufacture of joined steel stock for high carbon steel and low carbon-low alloy steel - Google Patents

Abstract

PURPOSE:To prevent crack in a joined interface by combining a high carbon steel and a low carbon.low alloy steel with steel stock satisfying the specific expression with respect to the average carbon content of carbon in the high carbon steel side and carbon in the low carbon.low alloy steel side and the component contents except carbon in the low carbon.low alloy steel side at the time of joining the high carbon steel and the low carbon.low alloy steel. CONSTITUTION:The high carbon steel containing 0.6-1.0% carbon and the low carbon.low alloy steel containing <=0.5% carbon, are joined. At this time, the joining steel stock of high carbon steel and low carbon.low alloy steel is made to the steel stock satisfying the expression 1 with respect to the average carbon content of carbon in the high carbon steel side and carbon in the low carbon.low alloy steel side and the component contents except the carbon in the low carbon.low alloy steel side. By this method, the crack in the joined interface and lowering of fatigue damaging resistance caused by the carbon diffused at the joined part between the high carbon steel and the low carbon.low alloy steel can be prevented.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Joined steel materials used as many materials such as steel for industrial machine structures and steel for rails are steel materials having different characteristics by welding method, cast-in-fill casting method, thermal spray overlaying method, explosive welding method, lamination method. We manufacture bonded steel slabs by laminating by various methods such as dispersion casting method and multi-layer continuous casting method, then heating to high temperature and hot rolling to produce various shapes and dimensions such as shaped steel and steel sheets. ..
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 the problem that peel cracks occur at the joining interface. For example, when manufacturing a rail with a multi-layer structure 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 necessary to use high carbon steel with a 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 the 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 hardenability to generate high carbon martensite, which causes cracks at the multi-layer interface and fatigue damage due to the generation of tensile residual stress locations. There was also a problem.

In order to prevent such a harmful effect due to the diffusion of carbon, for example, a technique of interposing an insert material between two members to be joined is used, as in Japanese Patent Publication No. 64-11397. However, when such an insert material is used for a multi-layer rail, although carbon diffusion can be prevented, there is a problem that it breaks in a short time while the train is passing due to the structure in which foreign matter is mixed between both members. ..

[0004]

SUMMARY OF THE INVENTION According to the present invention, when high-carbon steel and low-carbon steel are joined (or multi-layered) to manufacture rails and other products of various shapes, the cause of carbon diffused between the joints It is an object of the present invention to provide a method for manufacturing a joined steel material, which prevents the joint interface cracking and the decrease in fatigue damage resistance that occur in 1.

[0005]

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 , Of

[Equation 2] It is a method of manufacturing high-carbon steel / low-carbon low-alloy steel joined steel materials that combine steel materials that satisfy the requirements.

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 manufacturing a slab or a cast slab, or by combining it with other methods such as a post-hot-working method or an explosion-bonding method after forming a slab into a steel piece by a continuous casting method or an ingot-agglomeration method.

The high carbon steel used in the present invention is a material possessing high strength characteristics such as high strength and high hardness required for rails and other exterior members of industrial machines, and its properties depend on the carbon content. To be done. 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. In addition, the carbon content of the low carbon low alloy steel joined to the high carbon steel is 0.5%.
By suppressing the following, the structure mainly composed of ferrite or bainite is exhibited to retain the strength and toughness of the steel, and proper wear under rolling contact such as rail prevents the accumulation of surface fatigue, Improves surface damage and lifespan.

Further, in the present invention, when the molten steel melted in different component compositions is cast, or when the steel pieces produced through the subsequent steps are superposed and bonded by four-round welding or vacuum drawing. , 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 are

[Equation 3] It is necessary to join so as to satisfy. This formula uses the characteristics that each component enhances the hardenability of steel and the effects are independent and reciprocal, and tests the degree of influence of the individual components on the hardenability. Is expressed in the form of a multiple of the component amount.

In this equation, the value on the left side of the equation is changed by combining various components under a cooling rate of maximum 5 ° C./s,
The relationship with the formation of martensite structure was sought. However, when the multiple value of this equation exceeds 13, there is a problem that a martensitic structure is generated to enhance cold cracking susceptibility and a tensile residual stress field is generated to reduce fatigue damage resistance.

This equation also shows that when the joining material is heated to a high temperature, even if the C component diffuses to the low carbon low alloy steel side from the high carbon 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 obtained. Therefore, the steel pieces bonded and joined in consideration of the regulation of the content of each component as described above are heated to a high temperature and hot-rolled into various product shapes to obtain high carbon steel / low carbon low alloy steel. It is possible to manufacture joined steel materials.

The joining steel material of the high carbon steel / low carbon low alloy steel produced by the method of the present invention as described above is cold cracking or fatigue resistant due to an abnormal (martensite) structure that is easily formed at the joining 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.

[0012]

[Examples] Table 1 shows cold cracks when various high-carbon steels and low-carbon low-alloy steels are bonded together by various methods to manufacture bonded steel pieces, which are then heated to a high temperature and hot-rolled into each product. The results of evaluation of sensitivity and fatigue damage resistance based on the presence or absence of martensite structure generated at the joint interface are shown. As is clear from the experimental results, in the method of the present invention in which the value (the hardenability of the interface: D) obtained by the above-mentioned equation of the present invention is 13 or less, the joining interface exhibits properties such as toughness and fatigue damage resistance. An improved bainite structure and a pearlite structure are formed, but a martensite structure that deteriorates various properties is formed at the bonded interface in the comparative method exceeding 13.

[0013]

[Table 1]

[0014]

INDUSTRIAL APPLICABILITY The present invention can prevent joint interface cracking and reduction in fatigue damage resistance caused by carbon diffused during joining of high carbon steel and low carbon low alloy steel.

Front Page Continuation (72) Inventor Toshikatsu Miyata 1-1 Tobahata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Co., Ltd. Yawata Works

Claims (1)

Claims: 1. When joining high carbon steel containing carbon: 0.6 to 1.0% and low carbon low alloy steel containing carbon: 0.5% or less, The average amount of carbon on the 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 are expressed by the following formula. High carbon steel characterized by combining steel materials that satisfy
Low carbon low alloy steel Joined steel manufacturing method.