JP2023039174A - Steel material joint body - Google Patents

Abstract

To provide a steel material joint body that is capable of effectively improving the bonding strength between steel materials, and capable of improving also wear resistance of an outer peripheral surface in the vicinity of a joint part.SOLUTION: In a steel material joint body 1, a plurality of steel materials 10, 20 are joined to each other, and a carbon concentration of a joint interface 30 between the steel materials 10, 20 is 0.20 mass% to 2.10 mass%. Further, the steel material joint body 1 includes concentration gradients in which the carbon concentration decreases when alienating from the joint interface 30.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a steel joined body.

In the past, the challenge was to develop a technology that would enable the joining of hot steel materials to be performed easily and efficiently in an actual factory, and yet to obtain a high joining strength that would not hinder the subsequent rolling process. A method for hot joining steel materials is disclosed in which hot steel materials are coated or sprayed with a carbonaceous substance, superimposed or butted together, heated in a reducing atmosphere, and pressure-welded (see Patent Document 1).

JP-A-6-7970

However, it cannot be said that the steel material joined body obtained by the technique described in Patent Document 1 has an effectively improved joint strength between the steel materials. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a joined steel product that can effectively improve the joint strength between steel members and also improve the wear resistance of the outer peripheral surface near the joint.

A steel joined body according to the present invention is a steel joined body in which a plurality of steel materials are joined together, wherein a carbon concentration at a joint interface between the steel materials is 0.20 mass% or more and 2.10 mass% or less, and the joining It is characterized by having a concentration gradient layer in which the carbon concentration decreases as the distance from the interface increases.

Further, a steel joined body according to the present invention is a joined steel body in which a plurality of medium carbon steel steel materials are joined together, and the carbon concentration at the joint interface between the steel materials is 0.50 mass% or more and 2.10 mass%. % or less, and has a concentration gradient layer in which the carbon concentration decreases with increasing distance from the bonding interface.

Advantageous Effects of Invention According to the present invention, it is possible to provide a steel joined body that can effectively improve the joint strength between steel materials and also improve the wear resistance of the outer peripheral surface in the vicinity of the joint.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a conceptual diagram for explaining a steel joined body according to an embodiment of the present invention; 1 is a phase diagram of an iron-cementite system for explaining the effects of the present invention. FIG. It is a conceptual diagram for explaining the effect of the present invention. FIG. 2 is a conceptual diagram for explaining a portion of a steel joined body at which metal structure is to be checked; 5 shows metallographic images at points A, B, and C on the cross section L shown in FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a conceptual diagram for explaining a steel joined body according to this embodiment.
As shown in FIG. 1, a steel material joined body 1 according to this embodiment includes a plurality of steel materials 10 and 20 joined together. In addition, the carbon concentration (carbon concentration A shown in FIG. 1) at the joint interface 30 (the hatched portion in FIG. 1) where the plurality of steel materials 10 and 20 (hereinafter also referred to as “materials”) are joined together is 0.20 mass% or more. 2. It is 10 mass% or less. Furthermore, it has concentration gradient layers 15 and 25 in which the carbon concentration decreases as the distance from the junction interface 30 increases.

In the steel material joined body 1 according to the present embodiment, the carbon concentration at the joint interface 30 is 0.20 mass% or more and 2.10 mass% or less, so that the joint strength between the steel materials 10 and 20 can be effectively improved. It is also possible to improve the wear resistance of the outer peripheral surface near the portion 31 (within the range where the concentration gradient layers 15 and 25 are formed).
Specifically, since the carbon concentration at the joint interface 30 is 2.10 mass % or less, crystallization of the solidified structure at the joint interface 30 is suppressed. Therefore, since crystallization of a hard and brittle solidified structure can be suppressed at the joint interface 30, the joint strength between the steel materials 10 and 20 can be effectively improved. Moreover, since the carbon concentration of the bonding interface 30 is 0.20 mass % or more, the hardness of the bonding interface 30 can be increased. Therefore, the wear resistance of the outer peripheral surface in the vicinity of the joint portion 31 can also be improved.

The carbon concentration is preferably 0.20 mass% or more and 0.90 mass% or less. By setting the carbon concentration at the joint interface 30 to 0.20 mass % or more and 0.90 mass % or less, the joint strength between the steel materials 10 and 20 can be improved more effectively.
Specifically, by setting the carbon concentration at the joint interface 30 to 0.90 mass % or less, precipitation of cementite at the austenite grain boundaries is suppressed. Therefore, since precipitation of cementite at hard and brittle austenite grain boundaries can be suppressed at the joint interface 30, the joint strength between the steel materials 10 and 20 can be improved more effectively.

The carbon concentration at the joint interface 30 in the steel joined body 1 according to the present embodiment is measured by cutting the steel joined body 1 along the joint interface 30, polishing the cross section, and using an electron probe microanalyzer (EPMA) or an energy dispersion type. It can be measured using an elemental distribution analyzer such as X-ray analysis (EDX). In the present invention, the numerical value of the carbon concentration of the bonding interface 30 is calculated by measuring five arbitrary points on the polished cross section and calculating the average value thereof.

Further, the steel material joined body 1 according to the present embodiment has the concentration gradient layers 15 and 25 in which the carbon concentration decreases as the distance from the joining interface 30 increases. Therefore, since the carbon concentration is high at the joint interface 30 (see carbon concentration A shown in FIG. 1), the joint strength between the steel materials 10 and 20 can be effectively improved. In addition, since the carbon concentration (carbon concentration B in FIG. 1) on the side opposite to the bonding interface 30 in the concentration gradient layers 15 and 25 (on the side of the steel materials (materials 10 and 20) before bonding) is lower than the bonding interface 30, The material 10, 20 side can express "elongation". Therefore, the steel material joined body 1 according to the present embodiment can be suitably used for applications requiring "elongation" on the material 10, 20 side.

As shown in FIG. 1, the concentration gradient layers 15 and 25 preferably have a carbon concentration that decreases continuously as the distance from the junction interface 30 increases.
The term "continuously decreasing" as used in the present invention means that the numerical value of the carbon concentration decreases proportionally from the joint interface 30 toward the plurality of steel materials (materials) 10 and 20, as shown in FIG. .
Since the concentration graded layers 15 and 25 have such decreasing tendencies, the ductility and toughness at the bonding interface 30 are improved in addition to the effects described above.

The carbon concentrations of the concentration gradient layers 15 and 25 in the steel joined body 1 according to the present embodiment are measured by cutting the steel joined body 1 along the joint interface 30, and then separating from the cut joint interface 30 surface (material 10 , 20 side direction), then polish the cross section cut in the separating direction, and use an element distribution measuring device such as an electron probe microanalyzer (EPMA) or an energy dispersive X-ray analysis (EDX). can be measured.
In the present invention, the decreasing tendency of the concentration gradient layers 15 and 25 is measured by measuring the carbon concentration at the bonding interface 30 from the carbon concentration at the bonding interface 30 in each direction from the bonding interface 30 to the materials 10 and 20 side of the polished cross section in the separating direction. Measure the carbon concentration at any five locations (10 locations in total) on the straight line until the carbon concentration reaches 10 and 20 using the above-described element distribution measuring device, and measure the distance from the joint interface 30 horizontally. It can be confirmed by creating a graph as shown in FIG.

In addition, although the steel material joined body 1 according to the present embodiment does not depend on the structural form of the joining interface 30, it is preferable that the joining interface 30 is made of pearlite. This pearlite can be obtained by air-cooling or slow-cooling the steel material joined body 1 in the austenitic state. Since the joint interface 30 is made of pearlite, the tensile strength and the bending strength are increased, so that the joint strength of the joint interface 30 can be improved more effectively. The structural form of the joint interface 30 is confirmed by cutting the steel joined body 1 along the joint interface 30, polishing the cut cross section, and applying nital corrosion to the polished cross section with an optical microscope. be able to.

Bond interface 30 is preferably free of cementite at the austenite grain boundaries. The presence of intergranular cementite may serve as a starting point for cracking in tension and bending.
It should be noted that the above-mentioned "not provided" does not mean that the grain boundary cementite is not provided at all, but means that the existence ratio of the grain boundary cementite at the bonding interface 30 is less than 10%. Here, confirmation of the existence ratio of grain boundary cementite at the joint interface 30 is performed by applying nital corrosion to the cross section and then using the point counting method based on JIS G0555 for the cross section.

Incidentally, in the steel material joined body 1 according to the present embodiment, the materials of the steel materials (materials) 10 and 20 to be joined are arbitrary steel materials, and are not particularly limited as long as they are metals that can be integrated with each other. In addition, the alloying elements other than carbon in the bonding interface 30 and the plurality of steel materials (raw materials) 10 and 20 before bonding are not particularly limited, and are generally Si:1 as specified in JIS G 4051, for example. 0.50 mass % or less, Mn: 1.00 mass % or less, and the balance being Fe and unavoidable impurities. The shape of the plurality of steel materials (materials) 10 and 20 before joining is not particularly limited as long as they each have a joining surface and can be integrated with each other by overlapping the joining surfaces. For the steel materials (raw materials) 10 and 20, for example, a cylindrical shape, prismatic shape, screw shape, uneven shape, or the like can be adopted.

Another steel material joined body 1A according to this embodiment, as shown in FIG. In addition, the carbon concentration (carbon concentration A shown in FIG. 1) at the joint interface 30 (hatched portion in FIG. 1) where the plurality of steel materials 10 and 20 of medium carbon steel are joined together is 0.50 mass% or more and 2.10 mass%. % or less. Furthermore, it has concentration gradient layers 15 and 25 in which the carbon concentration decreases as the distance from the junction interface 30 increases.
That is, the steel joined body 1A has a different carbon concentration range than the steel joined body 1 .

Thus, when medium carbon steel is used as a plurality of steel materials (materials) before joining, setting the carbon concentration to 0.50 mass% or more and 2.10 mass% or less is advantageous in achieving the object of the present invention. becomes. Specifically, since the carbon concentration at the joint interface 30 is 2.10 mass % or less, crystallization of the solidified structure at the joint interface 30 is suppressed. Therefore, since crystallization of a hard and brittle solidified structure can be suppressed at the joint interface 30, the joint strength between the steel materials 10 and 20 can be effectively improved.
Moreover, since the carbon concentration of the bonding interface 30 is 0.50 mass % or more, the hardness of the bonding interface 30 can be increased. Therefore, the wear resistance of the peripheral surface 31 near the joint can be improved.

Further, the carbon concentration in the other steel joined body 1A according to the present embodiment is preferably 0.50 mass% or more and 0.90 mass% or less. By setting the carbon concentration at the joint interface 30 to 0.50 mass % or more and 0.90 mass % or less, the joint strength between the steel materials 10 and 20 can be improved more effectively.
Specifically, by setting the carbon concentration at the joint interface 30 to 0.90 mass % or less, precipitation of cementite at the austenite grain boundaries is suppressed. Therefore, since precipitation of cementite at hard and brittle austenite grain boundaries can be suppressed at the joint interface 30, the joint strength between the steel materials 10 and 20 can be improved more effectively.

Further, another steel joined body 1A according to this embodiment has concentration gradient layers 15 and 25 in which the carbon concentration decreases as the distance from the joining interface 30 increases. Therefore, since the carbon concentration is high at the joint interface 30 (see carbon concentration A shown in FIG. 1), the joint strength between the steel materials 10 and 20 can be effectively improved. In addition, since the carbon concentration (carbon concentration B in FIG. The 10th and 20th sides can express "elongation". Therefore, the steel joined body 1A according to the present embodiment and the materials 10 and 20 can be suitably used for applications requiring "elongation".

Similarly, in the other steel material joined body 1A according to the present embodiment, the concentration gradient layers 15 and 25 similarly have a carbon concentration that decreases continuously as the distance from the joining interface 30 increases, as shown in FIG. is preferred.
Since the concentration graded layers 15 and 25 have such decreasing tendencies, the ductility and toughness at the bonding interface 30 are improved in addition to the effects described above.
Incidentally, the same conditions and methods as those of the steel material joined body 1 according to the present embodiment described above can be used for measuring the carbon concentration of the joint interface 30 and the concentration gradient layers 15 and 25 .

In addition, the medium carbon steel referred to in the present invention refers to a steel material having a carbon concentration of 0.30 mass% or more and 0.50 mass% or less. For reference, low-carbon steel refers to steel with a carbon concentration of less than 0.30 mass%, and high-carbon steel refers to steel with a carbon concentration of more than 0.50 mass%. Also, since the metal structure of the joint interface 30 of the other steel joined body 1A according to the present embodiment is the same as that of the steel joined body 1 according to the above-described present embodiment, description thereof will be omitted here.

The mechanism by which the joining force between the steel materials is enhanced in the steel joined bodies 1 and 1A according to the present embodiment will be described below with reference to the drawings.
FIG. 2 is a phase diagram of an iron-cementite system for explaining the effects of the present invention. FIG. 3 is a conceptual diagram for explaining the effect of the present invention, and more specifically, a conceptual diagram showing reactions that occur at the bonding interface. As a method for manufacturing the steel material joined bodies 1 and 1A according to the present embodiment, carbon powder (carbonaceous substance) is placed on at least one of the joining surfaces of the steel materials to be joined, and joining is performed via this carbonaceous substance. The steel material in which the joint surfaces of the steel material are overlapped is heated under a predetermined atmosphere (for example, in an air atmosphere) at a maximum temperature of 1150 ° C. or higher and 1500 ° C. or lower (preferably 1150 ° C. or higher and 1300 ° C. or lower) (Fig. 3 ( a)).

When the temperature of the joint surface between the steel materials reaches, for example, 1250° C., a liquid phase L with a carbon concentration of 3.5 mass % is generated at the interface between the steel material and the carbonaceous substance (see the portion indicated by □ in FIG. 2). This liquid phase L increases until the carbonaceous substance disappears (see FIG. 3(b)).

In addition, the carbon concentration at the interface between the "austenite phase γ" region and the "austenite phase γ + liquid phase L" region (see the part indicated by ○ in FIG. 2) at 1250 ° C. is 1.6 mass% (see FIG. 2 reference). Diffusion of carbon at 1250° C. is extremely rapid, and when this temperature is maintained, carbon diffuses at a high rate from the joining surface of the steel material into the austenite phase γ inside. As a result, at the interface between the liquid phase L and the austenite γ, the austenite phase γ side takes away carbon from the liquid phase L side in an attempt to keep the carbon concentration at 1.6 mass%. On the other hand, since the liquid phase L tries to keep the carbon concentration at 3.5 mass%, the liquid phase L decreases (see FIG. 3(c)). Finally, the liquid phase L disappears and the joining of the steel materials is completed (see FIG. 3(d)).

Immediately after the liquid phase L disappears, the carbon concentration of this joint surface may be high. Further, in order to suppress the precipitation of intergranular cementite as described above, in the steel joined body 1, it is necessary to reduce the carbon concentration at the joining interface to 0.20 mass% or more and 0.90 mass% or less. Further, in the steel joined body 1A, it is necessary to reduce the carbon concentration to 0.50 mass% or more and 0.90 mass% or less. This decrease in carbon concentration at the bonding interface can be controlled by lengthening the heating and maintaining time at the highest temperature.

The carbonaceous substance referred to here is not particularly limited in material and shape as long as it is disposed on at least one of the joint surfaces of the steel materials to be joined and the joint surfaces can be integrated with each other. As the carbonaceous substance, for example, a powder of graphite particles (carbon powder) having an average particle size of 1 μm can be used.

In Example 1, a steel material (low carbon steel) having a cylindrical shape (length X: 150 mm, diameter φ: 15 mm (diameter of joint surface)) as shown in FIG. 1 and having a carbon concentration of 0.045 mass% were prepared. Then, as a test piece, these two steel materials were joined together to produce a steel joined body as indicated by reference numeral 1 in FIG. At this time, carbon powder (carbonaceous substance) was placed on the joint surface of each of the two steel materials, and the joint surfaces of the steel materials to be joined via the carbonaceous substance were overlapped. Next, high-frequency induction heating was performed at a maximum temperature of 1250° C. in an air atmosphere, followed by slow cooling. Here, the mass of the carbon powder placed on the joint surface of each of the two steel materials was adjusted so that the reaction at the joint interface as shown in FIGS. 2 and 3 could occur. In addition, the carbon concentration at the bonding interface after high-frequency induction heating was adjusted to 0.20 mass% by controlling the heating maintenance time at the highest temperature.

In Example 1, the following "confirmation of bonding strength and wear resistance" was performed on the prepared specimen (steel material joined body).
(Presence or absence of concentration gradient layer, confirmation of main structure of bonding interface, bonding strength and wear resistance)
Presence or absence of a concentration gradient layer (a concentration gradient layer in which the carbon concentration decreases as the distance from the bonding interface increases), the main structural structure of the bonding interface, and bonding strength (○ high, △ low ) and wear resistance (○ high, △ low) were confirmed. The presence or absence of the concentration gradient layer was determined by creating a graph such as that shown in FIG. 1, in which the carbon concentration is plotted against the distance described above, and by determining whether or not there is a tendency for the carbon concentration to decrease. To confirm the main structural structure (metallic structure) of the joint interface, a predetermined portion of the joint interface of the manufactured steel joined body was observed with an optical microscope in a state of nital corrosion. FIG. 4 shows a diagram for explaining locations where the metal structure is to be confirmed. The steel joined body shown in FIG. 4(b) is obtained by cutting the steel joined body along the L cross section as shown in FIG. 4(a). The presence or absence of the metal structure (perlite, etc.) in each image was confirmed by image processing the metal structure image in . Bonding strength was measured and evaluated as tensile strength. This tensile strength was tested using JIS No. 9A (GL100 mm). In addition, wear resistance was evaluated by using a wear tester to adjust the speed and final load in a dry environment, using a grindstone made of cubic silicon nitride with a grain size number of 400 as the mating material, and measuring the outer peripheral surface of the joint. was evaluated by the specific wear amount. Table 1 below shows the results of confirmation of the above confirmation items.

In Example 2, a steel material (medium carbon steel) having a cylindrical shape (length X: 150 mm, diameter φ: 15 mm (diameter of joint surface)) as shown in FIG. 1 and having a carbon concentration of 0.450 mass% were prepared. The carbon concentration at the bonding interface after high-frequency induction heating was adjusted to 0.50 mass % by controlling the heating maintenance time at the highest temperature. A test body (steel joined body) was produced under the same conditions and method as in Example 1 except for this.

In Example 2, in the same manner as in Example 1, "presence or absence of a concentration gradient layer, main structure of the joint interface, confirmation of joint strength and wear resistance" were performed. Here, the same conditions and method as in Example 1 were adopted when performing the final confirmation. Therefore, descriptions of these conditions and methods are omitted. Table 1 below shows the confirmation results of Example 2 together with the confirmation results of Example 1.

In Example 3, a steel material (medium carbon steel) having a cylindrical shape (length X: 150 mm, diameter φ: 15 mm (diameter of joint surface)) as shown in FIG. 1 and having a carbon concentration of 0.450 mass% were prepared. The carbon concentration at the bonding interface after high-frequency induction heating was adjusted to 0.90 mass % by controlling the heating maintenance time at the highest temperature. A test body (steel joined body) was produced under the same conditions and method as in Example 1 except for this.

In Example 3, in the same manner as in Example 1, "presence or absence of a concentration gradient layer, main structure of the joint interface, confirmation of joint strength and wear resistance" were performed. Here, the same conditions and method as in Example 1 were adopted when performing the final confirmation. Therefore, descriptions of these conditions and methods are omitted. Table 1 below shows the confirmation results of Example 3 together with the confirmation results of Example 1.
As a reference, FIG. 5 shows metallographic images at points A, B, and C on the cross section L shown in FIG.

In Example 4, a steel material (medium carbon steel) having a cylindrical shape (length X: 150 mm, diameter φ: 15 mm (diameter of joint surface)) as shown in FIG. 1 and having a carbon concentration of 0.450 mass% were prepared. The carbon concentration at the bonding interface after high-frequency induction heating was adjusted to 1.30 mass % by controlling the heating maintenance time at the highest temperature. A test body (steel joined body) was produced under the same conditions and method as in Example 1 except for this.

In Example 4, in the same manner as in Example 1, "presence or absence of a gradient concentration layer, main structure of the joint interface, confirmation of joint strength and wear resistance" were performed. Here, the same conditions and method as in Example 1 were adopted when performing the final confirmation. Therefore, descriptions of these conditions and methods are omitted. Table 1 below shows the confirmation results of Example 4 together with the confirmation results of Example 1.

In Example 5, a steel material (medium carbon steel) having a cylindrical shape (length X: 150 mm, diameter φ: 15 mm (diameter of joint surface)) as shown in FIG. 1 and having a carbon concentration of 0.450 mass% were prepared. The carbon concentration at the bonding interface after high-frequency induction heating was adjusted to 1.70 mass % by controlling the heating maintenance time at the highest temperature. A test body (steel joined body) was produced under the same conditions and method as in Example 1 except for this.

In Example 5, in the same manner as in Example 1, "presence or absence of a gradient concentration layer, main structure of the joint interface, confirmation of joint strength and wear resistance" were performed. Here, the same conditions and method as in Example 1 were adopted when performing the final confirmation. Therefore, descriptions of these conditions and methods are omitted. Table 1 below shows the confirmation results of Example 5 together with the confirmation results of Example 1.

In Example 6, a steel material (medium carbon steel) having a cylindrical shape (length X: 150 mm, diameter φ: 15 mm (diameter of joint surface)) and a carbon concentration of 0.450 mass% as shown in FIG. were prepared. The carbon concentration at the bonding interface after high-frequency induction heating was adjusted to 2.10 mass % by controlling the heating maintenance time at the highest temperature. A test body (steel joined body) was produced under the same conditions and method as in Example 1 except for this.

In Example 6, in the same manner as in Example 1, "presence or absence of a concentration gradient layer, main structure of the joint interface, confirmation of joint strength and wear resistance" were performed. Here, the same conditions and method as in Example 1 were adopted when performing the final confirmation. Therefore, descriptions of these conditions and methods are omitted. Table 1 below shows the confirmation results of Example 6 together with the confirmation results of Example 1.

Comparative example

[Comparative Example 1]
In Comparative Example 1, a steel material (low carbon steel) having a cylindrical shape (length X: 150 mm, diameter φ: 15 mm (diameter of joint surface)) as shown in FIG. 1 and having a carbon concentration of 0.045 mass% were prepared. The carbon concentration at the bonding interface after high-frequency induction heating was adjusted to 0.10 mass% by controlling the heating maintenance time at the highest temperature. A test body (steel joined body) was produced under the same conditions and method as in Example 1 except for this.

In Comparative Example 1, in the same manner as in Example 1, "presence or absence of a gradient concentration layer, confirmation of the main structural structure of the bonding interface, bonding strength, and wear resistance" were performed. Here, the same conditions and method as in Example 1 were adopted when performing the final confirmation. Therefore, descriptions of these conditions and methods are omitted. Table 1 shown below shows the confirmation results of Comparative Example 1 together with the confirmation results of Example 1.

[Comparative Example 2]
In Comparative Example 2, a steel material (medium carbon steel) having a cylindrical shape (length X: 150 mm, diameter φ: 15 mm (diameter of joint surface)) and a carbon concentration of 0.450 mass% as shown in FIG. were prepared. The carbon concentration at the bonding interface after high-frequency induction heating was adjusted to 2.30 mass % by controlling the heating maintenance time at the highest temperature. A test body (steel joined body) was produced under the same conditions and method as in Example 1 except for this.

In Comparative Example 2, in the same manner as in Example 1, "presence or absence of a concentration gradient layer, main structure of the joint interface, confirmation of joint strength and wear resistance" were performed. Here, the same conditions and method as in Example 1 were adopted when performing the final confirmation. Therefore, descriptions of these conditions and methods are omitted. In Table 1 shown below, the confirmation results of Comparative Example 2 are shown together with the confirmation results of Example 1.

(Results and discussion)
As can be seen from the results in Table 1, when the carbon concentration at the joint interface of the test piece (steel material joint) is 0.20 mass% or more and 2.10 mass% or less (Examples 1 to 6), the joint strength and It was confirmed that the wear resistance is high. On the other hand, in Comparative Example 1, it was confirmed that the wear resistance decreased because the carbon concentration at the joint interface was low. In addition, in Comparative Example 2, since crystallization of solidified structure was confirmed as the structure of the joint interface, it was confirmed that the joint strength was lowered.

Moreover, in the steel material joined bodies of Examples 4 to 6, in addition to pearlite, cementite (including cementite at austenite grain boundaries) was confirmed as a main structure at the joining interface. On the other hand, in the steel material joined bodies of Examples 1 to 3, pearlite was confirmed as the main structure of the joint interface, and cementite was not confirmed. Therefore, in the steel joined bodies of Examples 1 to 3 in which hard and brittle cementite was not confirmed (when the carbon concentration at the joint interface is 0.20 mass% or more and 0.90 mass% or less), the joint strength and wear resistance likely to be more sexual. Furthermore, from this confirmation result, when medium carbon steel is used as the steel material to be joined, it is more advantageous for achieving the object of the present invention that the carbon concentration at the joining interface is 0.50 mass% or more and 0.90 mass% or less. is considered to be

1, 1A Steel joined body 10 Steel (material)
15 Gradient concentration layer 20 Steel material 25 Gradient concentration layer 30 Joint interface 31 Joint A Carbon concentration (joint interface)
B Carbon concentration (on the side opposite to the bonding interface of the concentration gradient layer)
X length (steel)
φ diameter (steel)
γ Austenite phase L Liquid phase

Claims (5)

A steel joined body in which a plurality of steel materials are joined together,
The carbon concentration at the joint interface between the steel materials is 0.20 mass% or more and 2.10 mass% or less,
A steel joined body having a concentration gradient layer in which the carbon concentration decreases with increasing distance from the joining interface. The steel joined body according to claim 1, wherein the carbon concentration is 0.20 mass% or more and 0.90 mass% or less. A steel joined body in which a plurality of medium carbon steel steel materials are joined together,
The carbon concentration at the joint interface between the steel materials is 0.50 mass% or more and 2.10 mass% or less,
A steel joined body having a concentration gradient layer in which the carbon concentration decreases with increasing distance from the joining interface. The steel joined body according to claim 3, wherein the carbon concentration is 0.50 mass% or more and 0.90 mass% or less. 5. The steel material joined body according to claim 1, wherein said concentration gradient layer has a carbon concentration that decreases continuously as the distance from said joining interface increases.

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