JP2023167628A - Method for manufacturing steel material joint body - Google Patents

Abstract

To provide a method for manufacturing a steel material joint body, which can easily and effectively increase the joining strength of steel materials.SOLUTION: This steel material joint body manufacturing method for joining a plurality of steel materials comprises: an arrangement step of arranging a carbonaceous material on the joined surface of at least one of steel materials to be joined; a stacking step of stacking the steel materials by self-weight or applying a pressing load only by pressing the joined surfaces of the steel materials to be joined to each other via the carbonaceous material; a heating step of heating the steel materials at a reached highest temperature generated by a liquid phase of the carbonaceous material by the self-weight or applying the pressing load only by pressing the steel materials the joined surfaces of which have been stacked; and a cooling step of cooling the heated steel materials.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method of manufacturing a steel joined body.

Previously, the challenge was to develop a technology that could easily and efficiently join hot-worked steel materials in an actual factory, and that could also obtain high enough joint strength that it would not interfere with the subsequent rolling process. A hot joining method for steel materials is disclosed in which a carbonaceous material is applied or dispersed, the hot steel materials are overlapped or abutted, and the hot steel materials are heated and pressure-welded in a reducing atmosphere (see Patent Document 1).

Japanese Patent Application Publication No. 6-7970

However, the steel joined body obtained by the technique described in Patent Document 1 could not be said to have effectively improved the bonding strength between the steel materials. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for manufacturing a steel joined body that can simply and effectively improve the bonding strength between steel materials.

The method for manufacturing a joined steel material according to the present invention is a method for manufacturing a joined steel material in which a plurality of steel materials are joined together, and the method includes arranging a carbonaceous substance on at least one joint surface of the steel materials to be joined. a superimposition step in which the joint surfaces of the steel materials to be joined are pressed against each other via the carbonaceous substance, either by their own weight or while applying a pressing load; and a superposition step in which the steel materials with the joint surfaces overlapped are pressed The method includes a heating step of heating the carbonaceous material to a maximum temperature at which a liquid phase is produced by applying a pressing load or by applying a pressing load, and a cooling step of cooling the heated steel material.

According to the present invention, it is possible to provide a method for manufacturing a steel joined body that can simply and effectively improve the bonding strength between steel materials.

FIG. 2 is a process flow diagram for explaining a method for manufacturing a steel joined body according to an embodiment of the present invention. FIG. 1 is a conceptual diagram for explaining a method for manufacturing a steel joined body according to a first specific embodiment of the present invention. FIG. 7 is a conceptual diagram for explaining a method for manufacturing a steel joined body according to a second specific embodiment of the present invention. 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 effects of the present invention. 1 is a photograph of the appearance of a steel joined body obtained in Example 1. It is a figure explaining the observation position and the calculation method of a joining rate when confirming a joining rate. 1 is a diagram illustrating a location where the metallographic structure of the steel joined bodies obtained in Example 1 and Example 2 is confirmed, and a photograph of the metallographic structure of this location. FIG. 2 is a diagram illustrating a location where the metallographic structure of the steel joined bodies obtained in Example 3 to Example 5 is confirmed, and a photograph of the metallographic structure of this location. FIG.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a process flow diagram for explaining a method for manufacturing a steel joined body according to an embodiment of the present invention.
As shown in FIG. 1, the method for manufacturing a joined steel material according to the present embodiment is a method for manufacturing a joined steel material in which a plurality of steel materials are joined together, and includes at least one joint surface of the joined steel materials. A placement step (step S100 shown in FIG. 1) in which a carbonaceous material is placed on the carbonaceous material, and the above-mentioned joining surfaces of the steel materials to be joined are pressed against each other through this carbonaceous material, and the stacking process is performed by using their own weight or while applying a pressing load. The overlapping step (step S110 shown in FIG. 1) and the maximum temperature at which the liquid phase of the carbonaceous material is generated by simply pressing the joined surfaces of the steel materials together under their own weight or while applying a pressing load. and a cooling step (step S130 shown in FIG. 1) to cool the heated steel material.
The method for manufacturing a steel joined body according to the present invention includes the process flow described above, thereby making it possible to simply and effectively improve the bonding strength between steel materials.
Each of these steps will be explained in detail below.

FIG. 2 is a conceptual diagram for explaining a method for manufacturing a steel joined body according to a first specific embodiment of the present invention. FIG. 3 is a conceptual diagram for explaining a method for manufacturing a steel joined body according to a second specific embodiment of the present invention. The first embodiment shown in FIG. 2 and the second embodiment shown in FIG. 3 differ only in the form of the carbonaceous material disposed on the joint surface of the steel material.

<About the placement process (step S100)>
In the manufacturing method of the steel joined body 1 according to the first and second embodiments, in the arrangement step (step S100), as shown in FIGS. 2(a) and 3(a), the steel materials (10, 20 ) A carbonaceous material (30 or 40) is placed on at least one of the bonding surfaces (10a and/or 20a: one bonding surface in FIGS. 2(a) and 3(a)).
At this time, the carbonaceous material is heated in such a way that a liquid phase L (see FIG. 4; described later) is generated on the joint surfaces (10a and 20a) at the highest temperature reached during heating in the heating step (step S120), which will be described later. It is preferable to arrange. By arranging them in this way, the bonding strength between steel materials can be more effectively improved.

Here, the material of the steel materials (10, 20) to be joined is not particularly limited as long as it is any steel material that can be integrated with each other. For example, low carbon steel, medium carbon steel, high carbon steel, etc. can be used.
Note that the term "medium carbon steel" as used 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. Incidentally, 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%. Further, when using low carbon steel, medium carbon steel, and high carbon steel, the alloying element other than carbon is not particularly limited, but for example, Si: 1.5 mass as specified in JIS G 4051. % or less, Mn: 1.0 mass% or less, and the balance may be composed of Fe and unavoidable impurities.

The shape of the steel materials (10, 20) has bonding surfaces (10a, 20a), respectively, and if it is possible to overlap these bonding surfaces (10a and 20a) and integrate them, especially Not limited. For example, a cylindrical shape, a prismatic shape, a threaded shape, an uneven shape, etc. can be used.

Further, the carbonaceous material (30, 40) can be placed on at least one joint surface (10a and/or 20a) of the steel materials (10, 20) to be joined, and the joint surfaces (10a and 20a) are The material and shape are not particularly limited as long as they can be integrated. For example, a powdery carbonaceous material (30) shown in FIG. 2 or a sheet-like carbonaceous material (40) shown in FIG. 3 can be used. Here, when using a powdery carbonaceous material (30), it can be placed by applying it to the joint surface (10a and/or 20a). When using a sheet-like carbonaceous material (40), it can be placed directly on the joint surface (10a and/or 20a).

<About the overlapping process (step S110)>
In the manufacturing method of the steel joined body 1 according to the first and second embodiments, in the overlapping step (step S110), as shown in FIG. 2(b) and FIG. )'' The joining surfaces (10a and 20a) of the above-mentioned steel materials (10, 20) to be joined are overlapped by simply pressing against each other via the carbonaceous material (30 or 40) arranged in the structure.
In this overlapping step (step S110), when overlapping the joining surfaces (10a and 20a) of the steel materials (10, 20) by simply pressing them together, it is preferable to fix the joining surfaces together by their own weight. In the stacking process of the present embodiment, the bonding force between the steel materials (10 and 20) can be increased by fixing the joint surfaces (10a and 20a) of the steel materials (10, 20) with their own weight in this way. It is possible.

In addition, in this overlapping step (step S110), when overlapping the joint surfaces (10a and 20a) of the steel materials (10, 20) by simply pressing them together, a load (pressing load) is applied to fix the joint surfaces together. ) is preferable. In the stacking process of this embodiment, the bonding force between the steel materials (10 and 20) is increased by applying a load to fix the joint surfaces (10a and 20a) of the steel materials (10, 20). It is possible to increase In addition, when applying such a pressing load, the overlapping of the joining surfaces (10a and 20a) of the steel materials (10, 20) is not done in the vertical direction as shown in FIGS. 2 and 3, but in the horizontal direction. (not shown) is also possible, which is preferable.

Furthermore, in the overlapping step of the present embodiment, it is preferable to adjust the inclination of the joint surfaces of the steel materials to be joined during the pressing. By adjusting the inclination of the joint surfaces in this manner, the joint strength between steel materials can be more effectively improved.

<About the heating process (step S120)>
In the manufacturing method of the steel joined body 1 according to the first and second embodiments, in the heating step (step S120), as shown in FIG. 2(c) and FIG. )", the steel materials (10, 20) with their joined surfaces (10a and 20a) overlapped are simply pressed against each other, and the joined surfaces are fixed together by their own weight and heated. Here, the maximum temperature at which the steel materials (10, 20) are heated is set within a range where the liquid phase L is generated at the joint surface 50 (see FIG. 4, described later).
In addition, the heating may be performed while applying a load (pressing load) in order to fix the joint surfaces by simply pressing the steel materials (10, 20) that overlap the joint surfaces (10a and 20a). preferable.
In this way, by heating while applying a load to fix the steel materials (10, 20) with their joining surfaces (10a and 20a) superimposed on each other, it is possible to increase the joining strength between the steel materials (10 and 20). It is possible. In addition, when applying such a pressing load, the heating of the joining surfaces (10a and 20a) of the steel materials (10, 20) is not done in the vertical direction as shown in FIGS. 2 and 3, but in the horizontal direction ( (not shown) is also possible, which is preferable.

As described above, in the arrangement step (step S100), the carbonaceous material is heated such that the liquid phase L is generated on the bonding surface 50 at the highest temperature reached during heating in the heating step (step S120). The mass of the material is adjusted and arranged.
Therefore, since such a carbonaceous material is disposed on the bonding surface, the carbon concentration of the bonding surface 50 becomes high. Therefore, the tensile strength and bending strength of the joint surface 50 are increased, so that the joint strength of the joint surface 50, that is, the joint strength between the steel materials can be effectively increased.

In addition, in order to adjust the mass of the carbonaceous material and arrange it so that the liquid phase L (see FIG. 4) is generated on the bonding surface 50 at the highest temperature reached during heating of the carbonaceous material, for example, Using steel materials (10, 20) that have the same shape and carbon concentration as the steel material joined body that will become the product, the mass of the carbonaceous material placed on the joint surface 50 is changed, and each material is heated and joined at the same maximum temperature. By conducting a test and evaluating the bonding rate, which will be described later, it is possible to determine an appropriate mass of the carbonaceous material for which the liquid phase L is generated.

Preferably, the carbonaceous material is arranged so that a liquid phase is generated over the entire joint surface at the maximum temperature.
By arranging the carbonaceous material so that a liquid phase is generated over the entire surface of the bonding surface, bonding can be achieved over the entire surface of the bonding surface. Therefore, the bonding strength between steel materials can be further effectively improved.

The heating means in the heating step (step S120) is not particularly limited as long as it does not impair the effects of the present invention, and may include high-frequency induction heating (100) using a conventionally known heating coil 60, a heating furnace other than high-frequency induction heating, and a laser. Various heating methods using heating etc. can be employed.
Further, the atmosphere during heating in the heating step (step S120) is not particularly limited.
The atmosphere includes, for example, an oxidizing atmosphere (oxygen, air, etc.) and a non-oxidizing atmosphere (nitrogen, argon, etc.).

The heating step (step S120) of the present invention is preferably performed by high frequency induction heating (100). Since the high-frequency induction heating (100) can accurately and rapidly heat up to a desired temperature, the above-mentioned steel joined body (1) can be manufactured.

Then, in the heating step (step S120) of the present invention, the steel materials (10 and 20) are joined together at the stage when the liquid phase L generated at the joint surface 50 of the steel materials (10, 20) disappears ( 2(d) and 3(d)).

<About the cooling process (step S130)>
The cooling step (step S130) after heating in the heating step (step S120) of the present invention is not particularly limited, and conventionally known cooling, gas cooling, injection cooling with a quenching coolant such as a polymer, etc. are employed. can do.

Each process included in the present invention has been described above, and next, a specific example of a mechanism for increasing the bonding strength of steel materials by performing each of these processes will be described using the drawings.
FIG. 4 is a phase diagram of the iron-cementite system for explaining the effects of the present invention. FIG. 5 is a conceptual diagram for explaining the effects of the present invention, and more specifically, it is a conceptual diagram showing reactions that occur at the bonding interface. The method for manufacturing the steel joined body 1 according to the present embodiment includes the carbon whose mass is adjusted so that a liquid phase L is generated at the highest temperature during heating on at least one joint surface of the steel materials to be joined. Powder (carbonaceous material) is placed, and the joint surfaces of the steel materials that are joined via this carbonaceous material are overlapped and heated to a predetermined maximum temperature in a predetermined atmosphere (e.g., atmospheric atmosphere). (See Figure 3(a)).

From FIG. 4, the temperature at which the liquid phase L is generated at the bonding interface between the steel material and the carbonaceous material is 1150° C. or higher and 1500° C. or lower.
Specifically, when the maximum temperature near the joint surface between 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 material (Figure 4 (See the part marked with a □). This liquid phase L increases until the carbonaceous material disappears (see FIG. 5(b)).

The carbon concentration at the interface between the "austenite phase γ" region and the "austenite phase γ+liquid phase L" region (see the part marked with a circle in FIG. 4) at 1250° C. is 1.6 mass%. Therefore, at 1250°C, most of the steel material becomes an austenite phase γ single phase. Incidentally, when the carbon content exceeds 1.6 mass%, two phases, an austenite phase γ and a liquid phase L, coexist. Carbon diffusion at 1250° C. is extremely fast, and when maintained at this temperature, carbon diffuses from the joint surface of the steel material into the internal austenite phase γ at a high rate. As a result, at the interface between the liquid phase L and the austenite phase γ, the austenite phase γ side takes carbon from the liquid phase L side in an attempt to maintain the carbon concentration at 1.6 mass%, and the liquid phase L maintains the carbon concentration at 3.6 mass%. The liquid phase L decreases because it tries to maintain it at 5 mass% (see FIG. 5(c)). The liquid phase L eventually disappears and the joining of the steel materials is completed (see FIG. 5(d)).

The effect of the present invention in the heating step (step S120) of the present invention was explained using the maximum temperature of 1250°C, but the effect of the present invention described above can be seen from the phase diagram of the iron-cementite system in FIG. 4 and the examples described later. It is thought that this is obtained in a temperature range (the maximum temperature reached is 1150° C. or higher and 1500° C. or lower) in which the “austenite phase γ” region and the “austenite phase γ+liquid phase L” region are formed.
As described above, the mass of the carbonaceous material is adjusted and the carbonaceous material is arranged so that the liquid phase L is generated on the joint surface, and the steel material with the joint surfaces overlapped is heated at a temperature of 1150°C or higher and 1500°C or lower. The above bonding can be performed by heating at the highest temperature reached.
Therefore, it is preferable that the maximum temperature reached is 1150°C or more and 1500°C or less.
Thereby, the bonding strength between steel materials can be improved more effectively.

It is more preferable that the maximum temperature reached is 1150°C or more and 1300°C or less. By setting the maximum temperature to 1300°C or less, it is possible to efficiently cool the heating member (coil, etc.) for heating the steel material, and it is also possible to suppress deformation of the steel material assembly itself due to heat. can. The maximum temperature in the heating step (S120) can be measured with a platinum-rhodium thermocouple welded to the outer peripheral surface of the steel material (material) within 2 mm from the joint surface 50 of the steel materials to be joined.

Next, the present invention will be explained in more detail through Examples and Comparative Examples. Note that the present invention is not limited to these examples in any way.

[Example 1]
In Example 1, two S45C steel materials (medium carbon steel) were prepared as round bars with a joint surface diameter of 14.7 mm and an axial length L of 47 mm. Then, the bonding surfaces of these S45C steel materials were overlapped and heat bonded via a carbonaceous material (PGS graphite sheet manufactured by Panasonic Corporation) having a size of 20 mm long x 20 mm wide x 16 μm thick. The mass (grams) of this graphite sheet is adjusted so that the carbon concentration is such that a liquid phase L is generated on the joint surface of the steel materials at the maximum temperature (1250° C.) described below.
Further, the following maximum temperature was measured by welding a platinum-rhodium thermocouple to the outer peripheral surface of the S45C steel material within 2 mm from the position where the joint surface would be.

In other words, as shown in the process flow of FIG. 1, a placement process (step S100), an overlapping process (step S110), a heating process (step S120), and a cooling process (step S130) were performed in this order. In this overlapping process, the joining surfaces of the steel materials to be joined were simply pressed against each other via a carbonaceous material, and the steel materials were overlaid under a pressure of 7.0 MPa, that is, while applying a pressing load.
In this heating step, these S45C steel materials were heated to a maximum temperature of 1250° C. in 20 seconds by high-frequency induction heating at a frequency of 10 kHz in the air, held at this temperature for 20 seconds, and then air cooled to room temperature. Heating in this atmospheric atmosphere was performed by simply pressing the joint surfaces of S45C steel materials together via a carbonaceous material, at a pressure of 7.2 MPa (load for fixing the joint interface), that is, while applying a pressing load. Heat bonding was performed. In the cooling step, at least the joint surface of the heated steel material was cooled by air cooling.
In Example 1, the steel joined body obtained through these steps was used as a test specimen.

The appearance of the steel joined body obtained in Example 1 was observed with a camera. FIG. 6 shows a photograph of the appearance of the steel joined body obtained in Example 1. Further, in Example 1, the joining rate of the obtained steel joined body was confirmed. Here, the bonding rate was confirmed by observing the bonding interface of the obtained steel material bonded body under an optical microscope in a non-etched state. FIG. 7 shows a diagram illustrating the observation position and the method for calculating the bonding rate when checking the bonding rate.
As shown in FIG. 7(a), the observation position for checking the joining rate is when the steel joint is cut at an L cross section parallel to the central axis α, as shown in FIG. 7(a). As shown in Fig. 7(b), the bonding rate is calculated as "(d-ΣLv)/d×100" using these values, where d is the diameter of the steel joint and Lv is the length of the void. ” was calculated as the value. Table 1 below shows the results of checking the bonding rate together with other results.

Furthermore, in Example 1, the metal structure at the joint interface portion of the obtained steel joined body was confirmed. Here, the metallographic structure was confirmed by observing with a camera a predetermined location at the joint interface on the surface of the heat-bonded steel joint body cut in an L cross section as shown in FIG. 7(a) in a non-etched state. FIG. 8 shows a diagram illustrating a location where the metallographic structure is to be confirmed and a photograph of the metallographic structure of this location. The steel joint shown in FIG. 8(a) is obtained by cutting the steel joint at the joint interface as shown in FIG. 7(a), and A, B, and C on the cross section of this joint interface are respectively The metallographic structure was confirmed at the location. FIG. 8(b) shows photos of the metal structure of each of these locations A, B, and C together with other metal structure photos.

[Example 2]
In Example 2, the "joining rate" and "metal structure at the joint interface part" of the obtained steel joined body were confirmed in the same manner as in Example 1. Here, when performing these checks, the same method as in Example 1 was adopted. Therefore, explanation regarding these methods will be omitted.

In Example 2, as in Example 1, as shown in the process flow of FIG. 1, the arrangement process (step S100), the overlapping process (step S110), and the heating process (step S120) were performed in this order. The conditions in Example 2 differ from those in Example 1 in that the heating in this heating step was performed in a nitrogen gas atmosphere. In this heating in a nitrogen gas atmosphere, the flow rate of nitrogen gas was set to 100 L/min, and the joint surfaces of the S45C steel materials through the carbonaceous material were pressurized with a pressure of 7.2 MPa (load for fixing the joint interface). Heat bonding was performed while

Table 1 below shows the results of checking the bonding rate together with the results of Example 1. FIG. 8 shows a diagram illustrating the location where the metallographic structure is to be confirmed and a photo of the metallographic structure of this location together with the photo of the metallographic structure of Example 1.

(Results and evaluation)
From FIG. 6, it can be seen that in the steel joined body obtained in Example 1, the round bars are joined together. Further, from Table 1, no significant difference was observed in the joining rate of the steel joined bodies between Example 1 and Example 2. Further, from FIG. 8, it was confirmed that there was no significant difference in the metal structure of the joint interface portion of the steel material joint between Example 1 and Example 2, and a pearlite phase was formed in both cases.

[Example 3 to Example 5]
Heat bonding was performed using the same process and conditions as Example 2, except that the maximum temperature reached was changed to 1150°C (Example 3), 1200°C (Example 4), and 1300°C (Example 5). . The steel joined bodies obtained by these heating weldings were used as test specimens at the respective maximum temperatures. Regarding each of the obtained steel material joints, the "joining rate" and "metallic structure at the joint interface part" were confirmed in the same manner as in Example 1. Here, when performing these checks, the same method as in Example 1 was adopted. Therefore, explanation regarding these methods will be omitted.

Table 2 below also shows the results of Examples 3 to 5 in which the bonding rates were confirmed. FIG. 9 is a diagram illustrating the location where the metallographic structure is to be confirmed, together with photographs of the metallographic structure of this location in Examples 3 to 5.

(Results and evaluation)
From Table 2, no significant difference was observed between Examples 3 and 5 in terms of the joining rate of the steel joined bodies. Furthermore, no significant difference was observed between Examples 3 to 5 and Examples 1 and 2. In addition, from FIG. 9, it can be seen that there is a significant difference in the metallographic structure of the joint interface part of the steel joined body from Example 3 to Example 5, as well as from Example 3 to Example 5, Example 1, and Example 2. It was confirmed that there was no difference and a pearlite phase was formed in both cases.

[Comparative example 1]
In Comparative Example 1, heat bonding was performed using the same process flow and conditions as Example 2, except that the maximum temperature reached was 1100°C. As a result, no bonding as shown in Examples 1 to 5 was observed, and the bonding rate was 0%.

[Comparative example 2]
Heat bonding was performed under the same process flow and conditions as in Example 2, except that the graphite sheet of Example 1 was not used.
As a result, no bonding as shown in Examples 1 to 5 was observed, and the bonding rate was 0%.
From the above results, it can be seen that the method for manufacturing a steel joined body according to the present invention effectively improves the bonding strength between steel materials by preferably setting the maximum temperature to 1150° C. or more and 1300° C. or less.

According to the method for manufacturing a steel joined body according to the present invention, the bonding strength between steel materials can be simply and effectively improved. Therefore, the method for manufacturing a steel joined body according to the present invention can be suitably employed in manufacturing various structures including a steel joined body.

1 Steel joined body 10 Steel material 10a Joint surface 20 Steel material 20a Joint surface 30 Carbonaceous material 40 Carbonaceous material 50 Joint interface 100 High-frequency induction heating γ Austenite phase L Liquid phase S100 Placement step S110 Layering step S120 Heating step S130 Cooling step

Claims (4)

A method for manufacturing a steel joined body in which a plurality of steel materials are joined together,
a placement step of placing a carbonaceous substance on at least one joint surface of the steel materials to be joined;
an overlapping step of overlapping the joining surfaces of the steel materials to be joined together by pressing them together by their own weight or while applying a pressing load through the carbonaceous material;
a heating step of heating the steel material with the joined surfaces stacked together by its own weight or while applying a pressing load to a maximum temperature at which a liquid phase of the carbonaceous material is generated;
a cooling step of cooling the heated steel material,
A method for manufacturing a steel joint. 2. The method for manufacturing a joined steel material assembly according to claim 1, wherein in the overlapping step, the inclination of the joining surfaces of the steel materials to be joined is adjusted during the pressing. 2. The method of manufacturing a steel joined body according to claim 1, wherein the carbonaceous material is arranged so that a liquid phase is generated on the joint surface at the maximum temperature. The method for manufacturing a steel joined body according to any one of claims 1 to 3, wherein the maximum temperature reached is 1150°C or more and 1500°C or less.

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