JP2005059069A - Method for hot-piercing billet for hot-extrusion pipe-making - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a lateral broken flaw developed on the outer surface of a billet when the billet for pipe-making is hot-pierced by a hot-extrusion. <P>SOLUTION: In a method for hot-piercing the billet for hot-extrusion pipe-making by charging the hollow billet being supplied for the pipe-making by the hot-extrusion into a container and using a plug having i (mm) diameter, the inner surface of the container has a tapered surface opened upward and the above hollow billet is constituted of the billet body part and the billet bottom part containing the lower end part of the hollow billet and close to the inner surface of the container. When the diameter of the billet body part is expressed as D (mm), the diameter of the lower end part at the bottom part of the billet as d (mm) and the length at the bottom part of the billet as L (mm), the outer surface shape of the hollow billet is set to satisfy expression (1): d≤D-6 mm and expression (2): L≥(D-i)/2. It is desirable to adopt the method to the above hollow billet formed of a material to be difficult to work. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a hot drilling method for a hot-extrusion pipe billet supplied to Eugene Sejurune pipe, and more specifically, when a billet for pipe manufacturing is inserted into a container and hot drilled, The present invention relates to a hot drilling method optimal for processing difficult-to-process materials, which can prevent cross-cuts generated on the outer surface.

  The Eugene Sejurune pipe manufacturing method, which uses glass as a lubricant for hot extrusion, can add a relatively high degree of workability to the billet and is excellent in pipe forming ability. It is often used in the manufacture of seamless pipes. The billet for pipe making supplied to the hot extrusion is processed into a hollow shape by cutting a guide hole in advance by machining so that a mandrel of an extrusion press can be inserted.

  However, when a billet is extruded by using a large-diameter mandrel, it is necessary to prepare a billet hole corresponding to the billet, and the mechanical efficiency required for the hole preparation is remarkably lowered and the yield loss is also increased. For this reason, normally, in this hot pipe making method, hot drilling is performed as a preliminary process on the billet for pipe making supplied to the extrusion press.

  FIG. 1 is a view for explaining a processing step of a hot drilling method performed as a preliminary processing of a billet for pipe making. FIG. 1 (a) shows a situation where a hollow billet is inserted into a container, FIG. 1 (b) shows a process of drilling the hollow billet, and FIG. 1 (c) shows a situation of the hollow billet after drilling.

  As shown in FIG. 1 (a), after heating the hollow billet 1 having a 20-30 mm guide hole 1a machined in advance to about 1100-1200 ° C., the billet bottom is in contact with the inner surface of the container. Insert. Thereafter, a glass lubricant is applied to the upper surface of the hollow billet 1 or the inner surface of the guide hole 1a.

  Next, as shown in FIGS. 1B and 1C, an expansion plug 3 having a predetermined diameter is attached to the mandrel 4, and the hollow billet 1 is perforated while expanding the inner diameter. Thereafter, the perforated billet 1 is pushed up by an ejector from below, extracted from the container 2, reheated, and then supplied to the Eugene Sejurune tube.

  Usually, the container 2 is provided with a taper on its inner surface in consideration of workability during billet charging and extraction. And taper angle (theta) provided in the container inner surface is the range of 0.02 degree-0.10 degree. The billet outer diameter after hot drilling is defined by the container inner diameter and falls within the range of the taper angle θ.

  In the hot drilling shown in FIG. 1, in a difficult-to-work material such as a high alloy composed of a high Cr-high Ni composition and containing many alloy elements, or an alloy steel containing Ti, B in FIG. It becomes easy to generate cross-cuts on the outer surface of the bottom of the billet 1 indicated by the part. Transverse wrinkles occur as tear-like defects in a direction perpendicular to the billet axis, and are considered to occur due to the quality of the billet material.

  If cross-cuts are generated on the inner surface of the billet by hot drilling, they remain in the seamless pipe after hot extrusion, causing a product defect. Therefore, in the case of hot extrusion of difficult-to-process materials that are prone to external defects such as cross-cut defects, the billet after hot drilling is cooled, the external defects are removed by machining, and then heated again. Extrusion is performed. For this reason, the work efficiency is reduced, the amount of heat used is increased, and the yield is further deteriorated, which causes an increase in manufacturing cost.

  2. Description of the Related Art Conventionally, a manufacturing method for preventing external flaws generated in a hollow billet or extruded tube as a workpiece in hot drilling and hot extrusion has been proposed. For example, Patent Document 1 is an invention relating to a manufacturing method of a billet for pipe making used for hot extrusion, but prevents external burr by preventing the influence of burrs generated in hot drilling from affecting hot extrusion. Furthermore, a manufacturing method that can improve the uneven thickness ratio in hot drilling has been proposed.

  Further, in Patent Document 2, in order to prevent external flaws due to poor lubrication during extrusion processing, an end surface that is widened by hot drilling, that is, an outer peripheral portion of an end surface on the side that becomes an extrusion tip by an extrusion press is specified. We have proposed a pipe making method to process into a curved shape. By configuring the extrusion tip with a smooth curved surface, a stable lubrication state is secured and the outer surface flaws are eliminated.

  However, the manufacturing method of the billet for pipe making and the pipe manufacturing method of hot extrusion proposed in Patent Documents 1 and 2 are all aimed at suppressing outer surface flaws during hot extrusion, and the outer surface generated by hot drilling. It is not intended to prevent wrinkles that are caused by the quality of billet material.

JP 62-54538 A

JP-A-1-91910

  As described above, the occurrence of cross-cuts on the outer surface of the pipe making billet by hot drilling also affects the product quality after hot extrusion. Thus, after hot drilling of a billet that is prone to generate cross-cut wrinkles, it is possible to employ measures to cool the billet and remove the cross-cut wrinkles by machining, but this increases the manufacturing cost.

  Furthermore, in order to prevent the occurrence of cross-cut wrinkles, the drilling speed can be lowered so that the strain rate in the drilling process is reduced. However, if the drilling speed is reduced, the productivity in hot drilling is significantly reduced, and the processing cost of the billet for pipe making is increased, so it cannot be an effective measure.

  The present invention has been made in view of the problem of cross-cut flaws generated by such hot drilling, and in the hot drilling of the billet for pipe making, the outer surface shape of the hollow billet is appropriately managed to perform drilling. An object of the present invention is to provide a hot drilling method for a hot-extrusion pipe billet that can prevent cross-cuts generated on the outer surface of the billet later.

  In order to solve the above-mentioned problems, the present inventor has studied a drilling method capable of preventing transverse flaws generated on the outer surface of the billet during hot drilling while varying various billet materials, billet shapes, surface properties, and the like. went. As a result, we focused on the fact that the temperature variation of the billet outer surface that occurs during hot drilling affects the hot workability.

  When the billet is inserted from above the container during hot drilling, the outer periphery of the end of the billet bottom comes into contact with the tapered inner surface of the container. For this reason, the billet heated to about 1100-1200 degreeC receives heat removal effect from a container. For this reason, at the bottom of the billet, although it depends on the waiting time until drilling, the temperature drops by about 100 ° C. Accordingly, hot workability is remarkably deteriorated at the outer surface portion of the billet bottom.

  Therefore, if hot drilling is performed in this state, the longitudinal tensile force concentrates on the billet bottom in accordance with the deterioration of hot workability at the billet bottom. Further progress will be made.

  In order to reduce the heat removal effect from the container, preheating the container to about 500 ° C. and inserting the billet can reduce the heat removal effect immediately after preheating, but the number of perforations increases. At the same time, the temperature of the container gradually decreases. As a result, as the drilling process continues, a temperature drop at the bottom of the billet occurs and a cross-cut flaw occurs on the outer surface of the billet, which is not an effective measure.

  In order to reduce the effect of removing heat from the container, it is necessary to prevent any part of the hollow billet from coming into contact with the inner surface of the container. In particular, at the billet bottom where the tensile force in the longitudinal direction tends to concentrate, contact with the container must be avoided. That is, the diameter of the billet bottom is made smaller than the diameter of the billet main body in order to eliminate the state in which the billet bottom contacts the inner surface of the container as shown in FIG. Thereby, the temperature fall of a billet bottom part can be prevented and the cross-cut flaw which generate | occur | produces on the outer surface can be prevented.

  Patent Documents 1 and 2 mentioned above also show that the end of the billet bottom is processed during hot drilling. Specifically, FIG. 1 of Patent Document 1 discloses that R processing (3A ′) is performed on the outer periphery of the corresponding end portion. Further, in Patent Document 2, it is shown in FIG. 2 that a curved surface shape having a radius of curvature of 5 to 80 mm is processed at the end of the billet bottom, and in FIG. 6, a tapered portion is similarly provided at the end. It is shown.

  However, the R processing and the taper processing shown in Patent Documents 1 and 2 are not sufficient to reduce the heat removal action from the container, and in particular, when hot drilling of difficult-to-process materials, the occurrence of cross-cut flaws is prevented. I can't. Therefore, in order to remove heat from the container and prevent a temperature drop at the bottom of the billet, it is necessary not only to avoid contact with the container at the bottom of the billet, but also to appropriately manage the outer shape of the billet. I found out.

The present invention has been completed on the basis of the above findings, and the gist of the present invention is the hot drilling method of the billet for hot extrusion pipe making of the following (1) and (2).
(1) A method of inserting a hollow billet supplied for pipe making by hot extrusion into a container and hot drilling using a plug having a diameter i (mm), the inner surface of the container facing upward An open taper is provided, and the hollow billet is composed of a billet main body and a billet bottom including the lower end of the hollow billet and close to the inner surface of the container, and the diameter of the billet main body is D (mm) When the diameter of the lower end of the billet bottom is d (mm) and the length of the billet bottom is L (mm), the outer shape of the hollow billet is expressed by the following formulas (1) and (2): A hot drilling method for a billet for hot extrusion pipe making, characterized by being satisfied.

d ≤ D-6mm (1)
L ≧ (Di) / 2 (2)
(2) In the hot perforation method of a billet for hot extrusion pipe making of (1) above, it is desirable to employ when the hollow billet is made of a difficult-to-work material.

  According to the hot drilling method of a hot-extrusion pipe making billet of the present invention, the hot drilling of the pipe making billet eliminates the influence of the heat removal action from the container by appropriately managing the outer shape of the hollow billet. At the same time, it is possible to prevent slippage in the vicinity of the lower end of the hollow billet, and to prevent cross-cuts generated on the outer surface of the billet after drilling. Therefore, by adopting this hot drilling method, hot pipe production by Eugene Sejurune pipe can be carried out efficiently with high productivity and good yield.

  In the drilling method of the present invention, it is premised that the container for charging the hollow billet supplied for pipe making is provided with a taper that opens upward on the inner surface thereof. As described above, the taper provided on the inner surface takes into consideration the workability at the time of loading and extracting the hollow billet into the container, and the angle θ is in the range of 0.02 ° to 0.10 °. .

  When the hollow billet is inserted into the container provided with the taper that opens upward, the bottom of the billet comes into contact with the inner surface of the container as shown in FIG. For this reason, since the billet heated to high temperature receives a heat removal action from the container, a temperature drop occurs at the bottom of the billet, and accordingly, the hot workability at the corresponding portion of the billet is remarkably deteriorated.

  According to the study of the present inventor, when the taper angle θ provided on the inner surface of the container and opening upward is assumed to be 0.02 ° to 0.10 °, the effect of heat removal from the container is eliminated. Needs to satisfy the condition of the following formula (1). In the formula (1), the diameter of the billet main body is D (mm) and the diameter of the lower end of the billet is d (mm), which indicates that it is necessary to provide a difference of 6 mm or more in diameter.

d ≤ D-6mm (1)
FIG. 2 is a diagram showing an example of the outer shape of the hollow billet employed in the drilling method of the present invention. As shown in the figure, the billet 1 is previously machined into a hollow shape by cutting a guide hole 1a by machining so that a punch press can be inserted. And this hollow billet 1 is comprised by the billet main-body part and the billet bottom part containing the lower end part of a hollow billet. The length of the billet bottom is indicated by L (mm), and this billet bottom is placed in the state of being close to the inner surface of the container in the process of being inserted into the container and drilled.

  Further, according to the study of the present inventor, the portion where the transverse crease is likely to occur after hot drilling is the vicinity of the lower end of the hollow billet and the position on the outer surface side of the billet thickness after drilling. This part corresponds to the boundary between the region where the work material flows during hot drilling and the region where the work material does not flow (dead metal). In the vicinity of this, slip occurs on the outer surface of the billet. It becomes clear that is likely to occur.

  As a result of further investigation based on the above technical recognition, in order to prevent slippage in the vicinity of the lower end of the hollow billet and prevent cross-cut wrinkles, the following formula (2) is combined with the above formula (1): It can be seen that the following condition must be satisfied.

L ≧ (Di) / 2 (2)
Here, the dimension i is the diameter (mm) of the perforated plug, and indicates the inner diameter (mm) of the hollow billet after hot perforation. Therefore, since the value of {(D−i) / 2} in the equation (2) corresponds to the thickness of the hollow billet after hot drilling, the above equation (2) expresses the length L ( mm) is controlled to be equal to or greater than the thickness of the hollow billet (mm), which indicates that slippage in the vicinity of the lower end of the hollow billet can be prevented.

  FIG. 3 is a diagram showing an example of the shape of the billet bottom of a hollow billet targeted by the present invention, (a) shows a case where the billet bottom is configured in a straight shape, and (b) shows a taper at the billet bottom. The case where it comprises with a shape is shown. In the hollow billet according to the present invention, any shape of the bottom of the billet can similarly prevent slippage in the vicinity of the lower end, and can be adopted as the shape of the bottom. Further, as long as the above expressions (1) and (2) are satisfied, a curved surface shape (including R processing) can be adopted.

  Furthermore, in the hollow billet of the present invention, a plurality of curved shapes can be combined as the shape of the billet bottom, or a plurality of curved shapes and straight shapes can be used so that corners do not occur at the step diameter portion that changes from the billet main body to the billet bottom. You may make it combine with a shape.

  On the other hand, when the length L of the billet bottom is excessively large, the processing yield of the billet is lowered. For this reason, it is desirable to manage the length L of the bottom of the billet at ½ or less of the hollow billet (before drilling).

  FIG. 4 is a view showing a state in which a hollow billet employed in the drilling method of the present invention is inserted into a container. By managing the shape of the outer surface of the hollow billet 1 so as to satisfy the above formulas (1) and (2), the effect of heat removal from the container 2 is eliminated, and the slip in the vicinity of the lower end of the hollow billet 1 is eliminated. Generation | occurrence | production can be blocked | prevented and the cross-cut flaw which generate | occur | produces on a billet outer surface can be prevented.

  The difficult-to-work material targeted by the present invention is a material having high deformation resistance and poor hot workability, such as high Cr-high Ni alloy steel, high Cr-ferritic stainless steel, high Cr-Ni alloy, Pure Ti, Ti-containing alloys and the like are applicable.

  Examples of the high Cr-high Ni alloy steel include JIS NCF 800H steel, ASTM S31254, and the like, and an alloy steel containing Cr: 15% or more and Ni: 17% or more can be defined.

  Examples of the high Cr-ferritic stainless steel include ASTM A268-TP446, TPXM-8, JIS SUS444 steel, and the like, and a ferritic stainless steel containing Cr: 16% or more can be specified.

  Further, as the high Cr—Ni alloy, Hastelloy C276 alloy and the like are applicable.

  Furthermore, Ti-6Al-4V etc. correspond as Ti alloy, and can be prescribed | regulated as an alloy containing Ti: 80%.

  The effect at the time of carrying out the hot drilling of the billet for hot extrusion pipe making using the hollow billet employed in the present invention will be described. Three types of plugs with a diameter i of 62 mm, 76 mm, and 110 mm were used. In addition, the container used for drilling was provided with a taper angle θ of 0.05 ° on the inner surface.

  The billet to be processed was Ti-6Al-4V (containing about 90% Ti) as a high Ni alloy, and billets of various dimensions were processed by machining. The obtained billet was heated to about 1200 ° C., charged into the container, and a glass lubricant was sprayed on the outer and inner surfaces of the billet as a lubrication treatment. Table 1 shows the diameter D of the main body of the prepared billet, the diameter d of the lower end, and the length L of the billet bottom.

  After hot drilling, the hollow billet processed from the container was taken out, and the processing status by hot drilling was observed. The results are shown in Table 1. In Table 1, (1) equation value indicates (D-6) -d (mm), and (2) equation value indicates L-{(Di) / 2} (mm). Therefore, when any of them shows a negative (−) value, it indicates that the hollow billet defined in the present invention is out of the outer shape.

  From the results shown in Table 1, test No. 1 in which the outer shape of the hollow billet satisfies the conditions defined by the above formulas (1) and (2) defined in the present invention. 5, 9 (high Ni alloy steel), and test no. In 14 and 16 (Ti alloy), it was confirmed that there was no occurrence of transverse flaws after hot drilling.

The hot drilling method for hot-extrusion pipe billets according to the present invention can effectively prevent the occurrence of cross-cut flaws due to the quality of the billet material. Can be applied to pipes with high reliability.

It is a figure explaining the processing process of the hot drilling method performed as preliminary processing of the billet for pipe making. It is a figure which shows an example of the outer surface shape of the hollow billet employ | adopted with the punching method of this invention. It is a figure which shows the example of a shape of the billet bottom part of the hollow billet which this invention makes object, (a) is a figure which shows the case where it comprises with a straight shape, (b) shows the case where it comprises with a taper shape. It is a figure which shows the state which inserted the hollow billet employ | adopted with the drilling method of this invention in the container.

Explanation of symbols

1: billet, hollow billet, 2: container 3: plug, 4: mandrel 1a: guide hole

Claims (2)

A method of inserting a hollow billet supplied for pipe making by hot extrusion into a container and hot drilling using a plug having a diameter i (mm), wherein the inner surface of the container has a taper that opens upward. The hollow billet is composed of a billet main body and a billet bottom including the lower end of the hollow billet and adjacent to the inner surface of the container, and the billet main body has a diameter D (mm), When the diameter of the lower end of the bottom is d (mm) and the length of the billet bottom is L (mm), the outer shape of the hollow billet satisfies the following formulas (1) and (2) A hot drilling method for a billet for hot extrusion pipe making characterized by the above.
d ≤ D-6mm (1)
L ≧ (Di) / 2 (2) The method of hot perforating a billet for hot extrusion pipe making according to claim 1, wherein the hollow billet is made of a difficult-to-process material.

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