JPH0238041B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a hot extrusion method that can make the microstructure uniform after hot extrusion. [Prior Art] Steel pipes and the like are manufactured by hot extrusion. In this hot extrusion process, a billet-shaped extruded material is heated in an induction heating furnace, etc., and then the extruded material is heated in a hot extrusion press machine. The product is obtained by extrusion. In a hot extrusion press,
The extruded material is first pushed into the container together with the dummy block, and then it is continuously subjected to retrograde deformation through the concentric hole formed by the die and mandrel by the pressurized advancement of the stem, and extruded. It becomes a coarse tube. A steel pipe product is obtained by cutting this rough pipe. [Problems to be Solved by the Invention] However, in the conventional method, it takes 30 seconds to several minutes to transport the extruded material from the heating step to the extrusion step, and the extruded material is cooled during that time. By cooling the extruded material, the temperature at both ends of the extruded material is significantly reduced, particularly due to the end face cooling effect. Furthermore, in the extrusion process, the rear end of the material is in direct contact with the low-temperature dummy block, so the temperature of this part is further reduced. Since the temperature of the extruded material varies significantly in the longitudinal direction, the austenite grain size after extrusion varies greatly in the longitudinal direction, as shown in FIG. Figure 3 plots the change in grain size from the top to the bottom of the material after hot extruding SUS304 steel. according to this,
The austenite grain size of SUS304 steel is approximately 10 to
It varies extremely by 30μm. As the particle size changes, the material also changes, so the top and bottom portions usually have to be removed, resulting in a problem of low yield. [Means for Solving the Problems] The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a hot extrusion processing method that can make the microstructure of a material uniform in the longitudinal direction. purpose. In the hot extrusion method according to the present invention, the extruded material is heated by 15 mm in the longitudinal direction from the front end and the rear end of the extruded material, respectively.
Heat the area between 100 mm and 100 mm to a temperature 10 to 200°C higher than the center of the material, and create a thermal conductivity of 0.08 cal/cm between the extruded material and the dummy block.
It is characterized by extruding the extruded material through the interposition of an auxiliary member made of a material of sec/deg or less and having a thickness of 1 mm or more. As a result of repeated studies on various factors that affect the crystal structure of extruded materials, the inventors of the present application have found that the heating temperature, extrusion temperature, extrusion ratio, extrusion speed, etc. of extruded materials affect the microstructure and material quality of extruded materials. However, it has been found that when the extrusion ratio and extrusion speed are held constant, the extrusion temperature has a greater influence on the microstructure than the heating temperature. In addition, the non-uniform extrusion temperature of hot extruded materials is caused by the fact that the extruded materials are cooled from the heating process to the extrusion process, and due to the end face cooling effect, the temperature at both ends of the extruded materials is lower than other parts. This is caused by the fact that the rear end of the extruded material comes into direct contact with a low-temperature dummy block during extrusion, and the temperature of the rear end decreases. Therefore, in order to reduce the non-uniformity of the microstructure of the extruded material, it is sufficient to control the extrusion temperature, which has the greatest effect on the microstructure of the extruded material, to be constant, so that the temperature drop Both end portions may be heated to a higher temperature than other portions so that the temperature is uniform in the longitudinal direction of the material during extrusion processing. In addition, in order to effectively prevent the temperature drop at the rear end of the material that comes into contact with the dummy block, a heat insulator is inserted between the rear end of the extruded material and the dummy block, and the dummy block removes heat from the extruded material. suppress things.
This makes it possible to make the extrusion temperature of the material uniform and to make the microstructure of both ends of the extruded material uniform. This invention will be explained in detail below. In Figure 2, the horizontal axis represents the distance from the top of the extruded material, and the vertical axis represents the heating temperature of the extruded material, the extrusion temperature, and the austenite grain size of the extruded material.
FIG. 2 is a graph diagram showing the relationship between the longitudinal position of an extruded material, heating temperature, extrusion temperature, and austenite grain size. The material of the extruded material is SUS304 steel,
The extruded steel pipe has a steel material thickness of 10mm and a pipe diameter of 100mm.
mm, and the length is 7m. Figure 2 a shows the case of the conventional extrusion method in which the heating temperature of the extruded material is constant, but the temperature decreases at both ends of the material during extrusion, and the austenite grain size at both ends decreases accordingly. It has declined significantly. b is the case where the extruded material is heated from both ends to the center so that each 50 mm long region is 10 to 50°C higher than the center; the actual extrusion temperature is lower than that of the conventional method. The variation in the microstructure at both ends is reduced compared to case a. On the other hand, for c, the heating conditions during extrusion are the same as those for b, and furthermore, during the extrusion process, the thermal conductivity between the extruded material and the dummy block in the container is 0.04 cal/cm・sec・deg, and the thickness is This is a case where a ceramic heat insulating material with a diameter of 5 mm is charged, the extrusion temperature is almost uniform, and the microstructure at both ends of the extruded material is uniform. Next, the reasons for limiting the manufacturing conditions in the present invention will be described. When heating the extruded material, the area to be heated higher than the center of the extruded material is set to 15 to 100 mm in the longitudinal direction from both ends of the extruded material. The length of the area where the temperature drops due to the end face cooling effect at both ends of the heated material is approximately 3√(here, k
=λ/cρ, λ: thermal conductivity of the extruded material, c: specific heat of the material, ρ: density of the material, t: elapsed time from heating to actual extrusion). In this case, in hot extrusion of steel materials, t is 5 to 300
Since it is in seconds, this 3√ is calculated as 15 to 100mm. Therefore, in order to compensate for the temperature in this temperature-lowering region, it is heated to a higher temperature than other regions in the 15 to 100 mm region. When heating the material, both ends are heated 10 to 200°C higher than the center. This means that the degree of end face cooling at both ends of the heated material is approximately 50 h ² ktT ₀ (where h = α/λ, α; surface thermal conductivity of the end face of the material,
T ₀ ; heating temperature at the center of the material), and in the case of hot extrusion of steel materials, T ₀ is 950 to 1250°C
Therefore, calculating this cooling degree of 50h ² ktT ₀ is 2
The temperature ranges from 200℃ to 200℃. Considering the accuracy of heat treatment,
The temperature should be 10 to 200℃. In addition, as a means of heating only both ends of the extruded material to a high temperature, after performing normal uniform heating, heating only both ends locally using a burner etc., the number of turns of the induction heating coil of an induction furnace, There is one that heats only the ends so that there is a temperature gradient between the center and both ends. The thermal conductivity of the insulation material interposed between the rear end of the extruded material and the dummy block is 0.08 cal/cm・sec・
It is less than deg. This means that the thermal conductivity of the insulation material is
This is because if it exceeds 0.08 cal/cm・sec・deg, the thermal conductivity is not much different from that of a commonly used dummy block, and the function as a heat insulating material cannot be obtained sufficiently. The thickness of the heat insulating material is 1 mm or more. this is,
This is because if the thickness is less than 1 mm, the heat insulating effect of the heat insulating material will be reduced and it will not work effectively as a heat insulating material. By processing under the above conditions, a hot extruded material with a uniform microstructure can be obtained. Note that this invention is characterized in that the heating temperature at both ends of the extruded material is set higher than in the center, and that a heat insulating material is interposed between the rear end of the extruded material and the dummy block. Although the use of either method alone is less sufficient than when both methods are used together, it is more effective in making the microstructure uniform than conventional methods. [Examples] Examples of the present invention will be described below. Using SUS304 steel and 42Ni alloy (42Ni-21Cr-3Mo) with the composition shown in Table 1, the heating temperature was 1100.
Hot extrusion was performed at temperatures ranging from 1150°C.

[Table] Table 2 shows the hot extrusion conditions. Note that the superheating degree condition is a condition in which both ends of the material are heated to a higher temperature than the center.

[Table] In Table 2, Examples 1 and 2 are within the range defined by the present invention, and Comparative Examples 1 and 2 are outside the range. In Example 1, SUS304
Using a heater, set the heating temperature to 1100℃, and heat the extruded material from 10 to 10 mm from the center in a 50 mm area from each end of the extruded material.
Heated to a temperature 50°C higher. In Example 2, a 42Ni alloy was used, the heating temperature was set at 1150°C, and regions 70 mm from both ends of the extruded material were heated to a temperature 20 to 70°C higher than the center. In addition, the heat insulating material inserted between the extruded material and the dummy block was as described in Example 1.
In Example 2, a ceramic member was used with a thickness of 5 mm, and in Example 2, a ceramic member with a thickness of 10 mm and a thermal conductivity of 0.04 cal/cm·sec·deg. For Comparative Example 1, similar to Example 1, SUS304 steel was used and the heating temperature was set to 1100°C, and for Comparative Example 2, the same as Example 2 was used.
42Ni alloy is used and the heating temperature is set at 1150°C, but in both cases a conventional heating method is used in which the heating temperature of the extruded material is constant. Table 3 shows the austenite grain size of the extruded material when hot extruded under the conditions shown in Table 2.
According to this, in Examples 1 and 2, the austenite grain size of the extruded material is almost the same at both ends and the center, whereas in Comparative Examples 1 and 2, the austenite grain size at both ends, especially at the rear end. You can see that the diameter is getting smaller.

[Table] Note that the present invention is of course applicable to extrusion of not only iron-based alloys but also other metal alloys such as Ni-based alloys. [Effects of the Invention] According to the present invention, the microstructure at both ends of the hot extruded material can be made uniform, and there is no need to cut off both ends of the extruded material, so the yield is significantly improved. This invention is extremely practical.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the longitudinal position of the hot extruded material, heating temperature, extrusion temperature, and austenite grain size, and Figure 2 shows the variation in austenite grain size due to the conventional hot extrusion processing method. FIG.

Claims (1)

[Claims] 1. Heat the extruded material so that the area 15 to 100 mm in the longitudinal direction from the front end and rear end thereof has a temperature 10 to 200°C higher than the center of the material, and between the extruded material and the dummy block, thermal conductivity
Made from materials below 0.08cal/cm・sec・deg,
A hot extrusion processing method characterized by extruding an extruded material with an auxiliary member having a thickness of 1 mm or more interposed.