JP3183324B2 - Manufacturing method of shaped steel by high frequency resistance welding - 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 producing a T-shaped steel or an H-shaped steel by high frequency resistance welding.
More specifically, when welding the web material and the flange material, it is possible to secure the toughness of the welded portion by preheating the flange material to an appropriate temperature, and to prevent a weld line crack due to breakage and impact near the welded portion. The present invention relates to a method for manufacturing a shaped steel.

[0002]

2. Description of the Related Art As is well known, a high-frequency resistance welding method is a method in which a high-frequency current is passed from a high-frequency oscillator directly into the vicinity of a joint of a steel material to be joined, and pressure welding is performed using the resistance heat as a welding heat source. When manufacturing a section steel such as a T-section steel or an H-section steel by applying this high-frequency resistance welding method, the flange material and the web material are subjected to high-frequency resistance welding in a T-shape. Unlike high-resistance welded steel, high-frequency resistance welding of steel has a large area on the flange material side, so that cooling proceeds rapidly and the flange HAZ hardness, which is deeply related to the toughness of the welded portion, increases. The flange HAZ hardness is closely related to the weld quality,
Since the absorbed energy sharply decreases in the vicinity of Hv, the impact strength is low, and the welding line is cracked by the impact of cutting of the blade or the like, and the welded portion is easily broken. Further, in order to stably withstand shocks such as cutting and drilling, 300 Hv
It is also known that the following is required:

[0003] The flange HAZ hardness is mainly determined by welding heat input and Ce.
It is known that the higher the heat input, the lower the hardness, the lower the Ceq, the lower the hardness, and the lower the flange thickness / web thickness ratio, the lower the hardness. ing. However, Ceq, flange thickness /
The web thickness ratio cannot be changed because it is determined by strength and product dimensions. Also, the welding heat input cannot be changed from the appearance of the bead. Therefore, the flange H
It was difficult to reduce the AZ hardness to 300 Hv or less.

On the other hand, Japanese Patent Publication No. 45-40774 discloses that when a flange material and a web material are subjected to high-frequency resistance welding in a T-shape, 1/3 to 1 of the end face on the joining side at the center of the flange material.
A high-frequency resistance welding method that preheats the range of / 2 to 250 to 1050 ° C with a separate power source to prevent buckling of the web material during pressure welding and to improve the welding quality by increasing the effective welding width is described. Have been.

In Japanese Patent Publication No. 45-15859, when a flange material and a web material are pressed by high frequency,
A method is described in which a groove is formed after heating a central portion of a flange material, and a web material is inserted into the grooved portion and pressed against the groove, thereby preventing generation of burrs.

[0006]

However, the above-mentioned conventional high-frequency resistance welding technique has the following problems. 250 to 1050 ° C with a separate power supply at the center of the flange material
The method of heating in advance (Japanese Patent Publication No. 45-40774)
When the heating temperature is high, HAZ softening of the weld (caused by the formation of a ferrite layer) occurs and the toughness is high but the strength is insufficient. If the temperature is too high, the shape (bending and warping) becomes unstable. It is difficult to squeeze out the defects, defects tend to remain, and there is no preheating temperature control for the material, so depending on the material, softening occurs at the HAZ hardness part, and conversely, there is a possibility that the weld may be broken. There is. Also, a method of applying high-frequency pressure welding between the flange material and the web material by forming a groove in the center of the flange material (Japanese Patent Publication No. Sho 4
No. 5-15859) is characterized in that a groove is formed at the center of the flange material as a means for suppressing the generation of undesired burrs as a product shape, but there is no regulation on the heating temperature of the flange material. Heating temperature and HAZ
There is no description about the relationship with the hardness, and no preheating temperature control is performed on the material, so that there is a problem that welding quality, particularly high toughness and high strength, cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of such a conventional problem. In a method of heating the surface of a flange material in advance and performing high-frequency resistance welding, the Ceq change can be prevented by appropriately controlling the preheating temperature of the flange material. An object of the present invention is to propose a method of manufacturing a shaped steel by high-frequency resistance welding that can ensure high toughness and high strength of a welded portion.

[0008]

The method of manufacturing a shaped steel by high frequency resistance welding according to the present invention is directed to a method of manufacturing a shaped steel by high frequency resistance welding. The gist of the invention is to control the heating temperature T (° C.) in a temperature range satisfying the condition shown in the following equation (1).

(480 ° C. × Ceq (%)) + 60 ≦ T ≦ (480 ° C. × Ceq (%)) + 380 (1)

Here, the relationship between the preheating temperature of the flange material and the HAZ hardness will be described. The heat-affected zone, which has been rapidly heated and quenched by high-frequency resistance welding, has a quenched structure such as bainite.However, since heat is retained in the flange portion by performing preheating, the quenched structure is reduced by reducing quenching, and A low-strength structure is obtained by recrystallization similar to the principle of heat treatment. Therefore, the higher the preheating temperature, the lower the HAZ hardness tends to be.

Regarding the relationship between the HAZ hardness and the welding quality, by lowering the HAZ hardness of the welded portion, it is possible to avoid breakage due to the notch effect near the weld due to impact such as cutting of a blade. Therefore, the HAZ hardness can be reduced by increasing the preheating temperature. However, if the preheating temperature is too high, the HAZ hardness becomes high.
AZ softening occurs and strength is insufficient. Therefore, a decrease in HAZ hardness up to the base metal hardness range leads to an improvement in welding quality, but a decrease in HAZ hardness less than that results in poor welding quality.

[0012] Furthermore, since the hardenability becomes better as the Ceq increases, the HAZ hardness increases in proportion to the Ceq,
In the case of preheating at the same temperature, a material having a higher Ceq has a higher hardness. Therefore, for a material having a high Ceq, it is necessary to increase the preheating temperature to a hardness capable of securing toughness.

From the above findings, in order to prevent welding line cracking due to fracture and impact near the welding line, HAZ softening is not generated as the preheating temperature of the flange material and Ce
It is necessary to control the temperature at which toughness can be secured for q.
In the present invention, the preheating temperature satisfies the condition (1). The above formula (1) has been obtained by experiments by the present inventors, and by preheating the flange material to a temperature satisfying this condition, the toughness of the welded portion and the strength of the welded portion are secured against the Ceq change. It became possible to do. The heating temperature of the flange material is controlled in consideration of the temperature after heating, the plate thickness, and the welding speed.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view showing an apparatus in which the method of the present invention is applied to the production of an H-section steel, wherein 1 is a web material, 2 is a flange material, 3 is a squeeze roll, Is a high frequency resistance welding machine, 5 is an induction heater for preheating the flange, and 6 is a thermometer.

That is, when the method of the present invention is carried out, an induction heater 5 for inductively heating the upper and lower flange members 2 is provided in front of the high frequency resistance welding machine 4 (about 3 m). The thermometer 6 is installed to control the heating temperature of the flange material by the induction heater 5. The thermometer 6 controls the heating temperature of the flange material in consideration of the sheet thickness and the welding speed in addition to the temperature after the heating by the induction heater 5. It has become.

In the apparatus for manufacturing an H-section steel shown in FIG. 1, a web material 1 and a flange material 2 are heated to a predetermined welding temperature by a high-frequency resistance welding machine 4 and pressurized by a squeeze roll 3 for welding. In the present invention, the upper and lower flange members 2 are heated by the induction heater 5 in advance so as to be in a temperature range satisfying the condition of the above-mentioned formula (1) before being pressed and welded with the squeeze roll 3. The width of heating of the center of the flange material by the induction heater 5 is not particularly limited, but a width of about 30 mm is appropriate in consideration of energy loss, heating misalignment, and the like.

Here, using the H-section steel manufacturing apparatus shown in FIG. 1, the center of flange 30 mm was formed under the conditions of Ceq 0.25%, flange material and web material thickness 4.5 mm, welding speed: 30 m / min (constant). The results obtained by heating the range and confirming the weld hardness and weld strength are described below. The material of the flange material and the web material is C: 0.13
%, Mn: 0.72% is a 40k steel general steel.

First, when welding is performed by a general method without heating by the induction heater 5, the weld hardness is as high as Hv 355 as shown in FIG. 2 and is inferior in toughness. Therefore, a method in which the flange material is preheated and welded by the induction heater 5 is adopted, and the flange material is preheated to 180 ° C. (low-temperature heating) and welded.
The weld hardness decreased to Hv300 or less as shown in FIG. Further, when the preheating temperature was raised and the welding was performed by heating to 530 ° C. (high-temperature heating), the weld hardness further decreased to Hv220 as shown in FIG. However, the hardness of the weld line was lower than that of the base metal, and fracture occurred at the weld.

From the above results, it was found that when the preheating temperature of the flange material was raised to a certain value or more, the center of the weld was softened and the strength was reduced. This is presumably because a ferrite layer was formed at the interface of the welding wire, which caused softening and reduced strength.

The relationship between the temperature and the hardness shown in FIGS. 2, 3 and 4 can be summarized as shown in FIG. That is,
There is a preheating temperature for securing the welding strength at a weld hardness of Hv300 or less, and the optimum preheating temperature is in between. That is,
The optimum preheating temperature is a temperature that satisfies the condition of the above equation (1). By controlling the preheating temperature of the flange material within this temperature range, it is possible to increase the toughness of the welded portion and the strength of the welded portion with respect to the Ceq change. It is possible to secure.

[0021]

EXAMPLE The HAZ hardness and the HAZ hardness were changed by changing the flange thickness, Ceq and preheating temperature (the heating range was 30 mm at the center of the flange material) under the condition that the welding speed was constant at 30 m / min by the H-section steel manufacturing apparatus shown in FIG. Table 1 shows the results of the examination of the welding strength. The material to be welded is C: 0.13%, Mn:
It was 0.72% 40k steel general steel. The HAZ hardness in this example is 0.1 mm with a micro Vickers.
The HAZ portion was measured at the pitch, and the maximum hardness was defined as the hardness value.
Further, the weld strength was evaluated by breaking the end portion by expanding the end portion in the same manner as the expansion of the electric resistance welded pipe, and whether the fracture was a web break or a weld break. Test NO. The heating temperatures of Examples 1 to 9 of the present invention are all temperatures satisfying the condition of the above formula (1).

From the results in Table 1, it can be seen that the method of preheating and welding the flange material is effective in increasing the toughness of the welded portion and ensuring the strength of the welded portion. It can be seen that it is necessary to preheat to a temperature that satisfies the condition of equation (1). Needless to say, such an effect is the same in the case of the T-section steel.

[0023]

[Table 1]

[0024]

As described above, according to the method of the present invention, the temperature at which the flange material is preheated can be properly controlled, so that HAZ softening does not occur and Ceq is not generated.
Can be heated at a temperature at which toughness can be ensured, so that breakage near the weld line and cracks in the weld line due to impact can be prevented.
An excellent effect that the welding quality of a section steel such as a section steel or an H section steel can be remarkably improved.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an apparatus according to an embodiment when the method of the present invention is applied to the manufacture of an H-section steel.

FIG. 2 In the production of an H-section steel by high-frequency resistance welding,
It is a figure which shows an example of the weld part hardness at the time of welding by a general method, without heating a flange material beforehand.

FIG. 3 In the production of an H-section steel by high-frequency resistance welding,
It is a figure which shows an example of the welding part hardness at the time of heating (low temperature heating) to 180 degreeC in advance and welding a flange material.

[FIG. 4] In the production of an H-section steel by high-frequency resistance welding,
It is a figure which shows an example of the welding part hardness at the time of heating (high temperature heating) to 530 degreeC in advance and welding a flange material.

FIG. 5 is a diagram in which the data of FIGS. 2, 3 and 4 are combined into one to show the relationship between the weld hardness and the heating temperature.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Web material 2 Flange material 3 Squeeze roll 4 High frequency resistance welding machine 5 Induction heater for preheating flange 6 Thermometer

Claims (1)

(57) [Claims] In a method for producing a section steel by high-frequency resistance welding, when welding a web material and a flange material, a heating temperature T which satisfies the following conditions is satisfied.
A method for producing a shaped steel by high-frequency resistance welding, characterized by preheating to (° C.). (480 ° C × Ceq (%)) + 60 ≦ T ≦ (480 ° C ×
Ceq (%)) + 380