JP4427439B2 - Manufacturing method for hollow forging steel and cylindrical forging - Google Patents

Description

  The present invention relates to a method for producing a hollow forging steel material and a method for producing a cylindrical forged product.

  A cylindrical forged product is obtained by casting molten steel into a mold by vacuum casting or down-casting, then solidifying the mold to obtain a steel ingot, compressing the steel ingot, and then along the compression direction. It is manufactured by forging the center part in the axial direction and then forging. The mold used at this time is generally provided with a feeder part. The feeder part is heated from the outside, and the molten steel in the feeder part is kept warm. Therefore, the molten steel in the feeder part becomes the final solidified part, and defects such as shrinkage and component segregation are concentrated, so the quality is poor. Therefore, in order to ensure the quality of the forged product, it is necessary to cut and remove the feeder part from the steel ingot after solidification. However, since the mass of the feeder part occupies 10% or more with respect to the mass of the entire steel ingot, the yield decreases when the portion corresponding to the feeder part is cut and removed. In addition, the cutting cost is also required to cut the feeder part. For these reasons, there has been a demand for a method for producing a steel for forging using a mold having no feeder.

  As a method for manufacturing a forging ingot using a mold without a feeder part, the technique of Patent Document 1 has been proposed. In this technique, the ingot height / ingot diameter ratio is set to 1.3 or less, and the top surface of the molten metal is covered with a heat insulating material in order to delay the cooling of the molten metal upper surface from the time of casting to solidification of the molten metal. Covering. However, this technique manufactures an ingot in a form suitable for a plate-like product or a hollow product, and has not taken into account defects such as shrinkage nests generated in the ingot and component segregation. Therefore, as a result of investigations by the present inventors, defects and component segregation are generated in the ingot, and in order to produce a cylindrical forged product by removing such a portion, it is necessary to extract most of the central portion of the ingot. Therefore, the yield is significantly reduced.

Moreover, in the said patent document 1, the upper surface of the ingot is covered with the heat insulating material from the time of subcast casting. However, if the upper surface of the ingot is covered with a heat insulating material during the subcast casting, the heat insulating material may be wound around the molten steel and burnt, which causes boiling. As a result, inclusions may be generated in the steel ingot, and carburizing gas may be generated to cause carburization.
Japanese Patent Laid-Open No. 55-22490 (see claims, upper right column on page 2)

  This invention is made | formed in view of such a condition, The objective is drawing the center part of the steel ingot cast using the casting_mold | template without a feeder part, and manufacturing the hollow steel material for forging. At the same time, the yield is improved by reducing the number of parts extracted from the steel ingot, and a method for producing a high-quality hollow forging steel with less defects such as shrinkage and component segregation is provided even if the number of extracted parts is reduced. There is. Another object is to provide a method for producing a high-quality cylindrical forged product by forging a hollow forging steel material obtained by such a production method.

  The inventors of the present invention have earnestly studied to increase the yield and the quality of the hollow forging steel material when manufacturing the hollow forging steel material. As a result, it has been found that the above problem can be solved brilliantly if the conditions for keeping the surface of the molten steel cast in the mold are specified and the shape of the steel ingot obtained by solidification is specified strictly. Was completed.

  That is, the method for producing a hollow forging steel material according to the present invention is a method for producing a hollow forging steel material, in which molten steel is applied to a mold without a feeder part by a vacuum casting method or a down-pour casting method. A casting step, after casting the molten steel, a step of solidifying the molten steel by covering the surface of the molten steel with a heat insulating material, a step of compressing the obtained steel ingot, and a central portion in the axial direction along the compression direction Including the step of removing, the ratio of the height H to the diameter D (H / D ratio) of the shape of the solidified steel ingot is 1.3 to 2, the thickness of the heat insulating material is 50 to 500 mm, When the diameter of the steel ingot after compression is set to Dp, it has a gist in that a cylinder having a diameter of 0.1 × Dp to 0.5 × Dp is extracted as a central part. The shape of the mold is not particularly limited, but a columnar or chrysanthemum shape can be used.

  The manufacturing method of the cylindrical forged product according to the present invention has a gist in that the hollow forging steel material obtained by the manufacturing method of the hollow forging steel material is forged into a cylindrical shape.

  According to the present invention, the conditions for maintaining the surface of the molten steel cast into the mold are specified, and the shape of the steel ingot to be cast into the mold is strictly specified, thereby producing a hollow forging steel material. The yield can be increased, and the quality of the hollow forging steel can also be improved. If the hollow steel for forging obtained by such a manufacturing method is used, a high-quality cylindrical forged product can be manufactured.

The method for producing the hollow forging steel according to the present invention is as follows:
(A) a step of casting molten steel into a mold without a feeder part by a vacuum casting method or a bottom casting method,
(B) After casting the molten steel, a step of solidifying the molten steel by covering the surface of the molten steel with a heat insulating material;
(C) the step of compressing the obtained steel ingot, and (d) the step of removing the central portion in the axial direction along the compression direction. When the ratio of H to diameter D (H / D ratio) is 1.3 to 2, the thickness of the heat insulating material is 50 to 500 mm, and in the extracting step, the diameter of the steel ingot after compression is Dp It is important to pull out a cylinder having a diameter of 0.1 × Dp to 0.5 × Dp as a central portion.

  First, the shape of a steel ingot obtained by solidifying molten steel will be described. The shape of the steel ingot obtained by solidifying the molten steel is a cylindrical shape having an H / D ratio of 1.3 to 2 where the height is H and the diameter is D. By adopting such a shape, it is possible to increase the cooling rate in the radial direction when the molten steel solidifies and to solidify quickly. For this reason, defects such as shrinkage and component segregation occurring in the steel ingot are concentrated in the vicinity of the central axis of the steel ingot. As a result, even if the central portion where defects or component segregation occurs is extracted, the radial size of the extracted portion can be reduced, so that the yield can be increased. A preferred H / D ratio is greater than 1.3, more preferably 1.4 or greater. However, if the H / D ratio exceeds 2, a defect occurs over a wide range of the upper part of the steel ingot, and the part including the defect cannot be completely removed. The preferred H / D ratio is 1.9 or less, more preferably 1.8 or less.

  Here, the diameter of the steel ingot is a value calculated from the inner diameter of the mold. When the mold is cylindrical, the diameter of the mold is used. When the mold is not cylindrical (for example, chrysanthemum), the inscribed circle of the mold is used. Refers to equivalent diameter. Hereinafter, the same meaning is applied to the present invention regardless of before and after compression. Further, the height of the steel ingot can be controlled by adjusting the amount of molten steel cast into the mold.

  In Patent Document 1, the height / diameter ratio of the steel ingot is set to 1.3 or less in order to manufacture an ingot (steel ingot) having a form suitable for a plate-like product or a hollow product. When the height / diameter ratio of the steel ingot is 1.3 or less, the steel ingot is large in the radial direction and small in the height direction. In this case, since solidification of the molten steel proceeds from the surface toward the inside, the cooling rate in the radial direction of the steel ingot is reduced. As a result, defects and component segregation are generated over a wide range in the center of the steel ingot. Therefore, in order to completely remove the portion where such defects and component segregation are generated, the central portion of the steel ingot must be largely removed in the radial direction, resulting in poor yield.

  Next, the manufacturing method of the hollow forging steel material according to the present invention will be described in order.

(A) Step of casting molten steel in a mold without a feeder part by vacuum casting method or bottom casting method In the present invention, by casting a molten steel using a mold without a feeder part, obtaining a steel ingot, There is no need to cut and remove the feeder from the steel ingot. For this reason, the yield is improved and the processing cost for cutting the feeder is not required.

  The shape of the mold is not particularly limited. For example, a mold such as a columnar or chrysanthemum shape or a polygonal mold (polygon means five or more corners) can be used. Further, the size of the mold is not particularly limited as long as the shape of the steel ingot obtained by casting with the mold satisfies the above requirements. Generally, the size of the mold bottom is about 700 to 2800 mm in diameter.

  Molten steel is cast into the mold by vacuum casting or bottom casting. In the vacuum casting method, since casting is performed through an intermediate pan (tundish), it is possible to cast a very large hydrogen ingot with extremely low hydrogen. In addition, if the downcasting method is employed, defects such as baldness caused by molten steel adhering to the mold wall surface can be prevented. By the way, in the top pouring method, the molten steel that bounces off the bottom of the mold may adhere to the mold wall surface and cause defects such as lashes.

(B) After casting the molten steel, the step of covering the surface of the molten steel with a heat insulating material and solidifying the molten steel When the molten steel is solidified to produce the ingot of the above shape, the surface of the molten steel is covered with a heat insulating material. It is necessary to solidify while keeping warm. By covering the surface of the molten steel with a heat insulating material, the portion where defects and component segregation occur can be concentrated on the upper part of the steel ingot. That is, since the upper part of the molten steel is kept warm by covering the surface of the molten steel with a heat insulating material, the cooling rate of the molten steel is reduced. As a result, the heated molten steel becomes the final solidified portion, and defects and component segregation are concentrated in the final solidified portion.

  At this time, the timing of covering the surface of the molten steel with the heat insulating material is after casting the molten steel into the mold. This is because if the molten steel is covered with a heat insulating material while the molten steel is being cast into the mold, the molten steel entrains the heat insulating material while being cast and causes defects such as inclusions in the steel ingot.

  It is also important that the heat insulating material covering the surface of the molten steel has a thickness of 50 to 500 mm. If the thickness of the heat insulation material is less than 50 mm, the heat insulation effect is insufficient, the final solidified part of the molten steel becomes the center of the steel ingot, and the generation position of defects and component segregation can be concentrated on the upper part of the steel ingot. Disappear. Preferably, the thickness of the heat insulating material is 100 mm or more. On the other hand, when the molten steel is solidified to form a solidified shell, an air gap is formed between the mold and the solidified shell due to solidification shrinkage. If the heat insulating material is too thick at this time, The solidified shell may be remelted due to excessive heat retention. When the molten steel flows out from the remelted portion, double skin is generated, so the thickness of the heat insulating material is set to 500 mm or less. Preferably it is 400 mm or less.

  The kind of heat insulating material that can be used in the present invention is not particularly limited, and known materials can be used. For example, rice husks and grilled rice husks, exothermic heat insulating materials, and heat insulating heat insulating materials. In addition, although the heat retention effect of molten steel is somewhat different depending on the type of heat insulation material to be used, such an effect is negligible. In the production method of the present invention, it is important to set the thickness of the heat insulation material within the above range.

  The form of the heat insulating material at the time of covering the surface of the molten steel is not particularly limited, and for example, a heat insulating material such as a plate shape, a granulated shape, and a powder shape can be used.

  In addition, as for the shape of the steel ingot obtained by solidifying molten steel, the ratio (H / D ratio) of the height H and the diameter D of an ingot is set to 1.3-2 as mentioned above.

(C) The process of compressing the obtained steel ingot The steel ingot obtained by casting with the said mold is compressed. Shrinkage defects can be reduced by compressing. Although the conditions when compressing a steel ingot are not specifically limited, a compression rate is about 5-30 (%). The compression rate can be calculated by the following formula.
Compression rate (%) = (1-height of steel ingot after compression / height of steel ingot before compression) × 100

(D) Step of axially removing the central portion along the compression direction From the compressed steel ingot, the central portion is extracted along the compression direction in the axial direction. When the diameter of the lump is Dp, the shape of the center part extracted from the steel lump after compression is a cylinder having a diameter of 0.1 × Dp to 0.5 × Dp. That is, as described above, when solidifying molten steel, the molten steel is covered with a heat insulating material having a specific thickness, and by specifying the shape of the steel ingot obtained by solidification, defects and component segregation generation sites can be identified. In the vicinity of the central axis of the steel plate and above the steel ingot. Therefore, even when the radial size of the central portion extracted from the steel ingot after compression is reduced, defects and component segregation can be easily removed from the steel ingot, that is, when the diameter of the steel ingot after compression is Dp, The central region extracted from the lump can be formed into a small cylindrical shape having a diameter of 0.5 × Dp or less. Therefore, the yield can be improved. Preferably, it is 0.4 × Dp or less. Depending on the shape of the product, the forging ratio, etc., a cylinder having a diameter of more than 0.5 × Dp may be extracted as the center, but the yield decreases when the extracted amount increases.

  On the other hand, as will be clarified in the examples described later, the size of the central portion extracted from the steel ingot after compression is a cylinder having a diameter of at least 0.1 × Dp, where Dp is the diameter of the steel ingot after compression. To do. If the size of the portion to be extracted is too small, defects and component segregation generated in the vicinity of the central axis of the steel ingot cannot be completely removed, so that the quality of the forging steel material is deteriorated. Preferably it is 0.2 × Dp or more.

  As described above, a hollow steel material for forging can be obtained from the compressed steel ingot by removing the central portion in the axial direction along the compression direction.

  Next, when the obtained steel for forging is forged and formed into a cylindrical shape, a cylindrical forged product is obtained. A well-known method can be adopted as a method for forging the steel for forging. For example, a cored bar is inserted into a steel material from which the central part is removed, the cored bar is attached to a support base, and the cored bar is rotated. At this time, using a flat metal plate, forging is performed by applying a load while sandwiching a hollow forging steel material with a cored bar, and gradually expanding the hole to obtain a cylindrical forged product.

  The component composition of steel to be used in the present invention is not particularly limited as long as it is used as a raw material for forged products. For example, C: 0.01 to 0.5% by mass or Si: 0.10 to 0.0. Steel containing 8% by mass or the like.

  Hereinafter, the present invention will be described in more detail with reference to experimental examples, but the following experimental examples are not intended to limit the present invention, and may be implemented with appropriate modifications within a range that can meet the purpose described above and below. These are all possible and are within the scope of the present invention.

Experimental example 1
After casting molten steel containing 0.15% by mass of C: 0.15% by mass in a cylindrical mold without a feeder, the molten steel is solidified in a state where the surface of the molten steel is covered with a heat insulating material. Got. As the heat insulating material, an exothermic heat insulating material and a heat insulating heat insulating material were used in combination. The shape of the heat insulating material was powdery, and the thickness of the heat insulating material was 150 mm. The size of the steel ingot was such that the H / D ratio was changed from 0.2 to 2.5, where H was the height of the steel ingot and D was the diameter.

  The obtained steel ingot was cut in the longitudinal direction so as to pass through the central axis, and the part where the component segregation occurred was observed in the macro-etched one by comparing the cut surface with the macro-etched one and the sulfur-printed one. The position of occurrence of component segregation was examined by analysis.

The position where the component segregation occurs refers to a position where the component that positive segregates such as C and Si is concentrated about 20% or more around the center of the steel ingot Top portion side. When cutting perpendicular to the height direction of the steel ingot so that it passes through the component segregation part that occurs at the bottom of the height direction of the steel ingot at the position where the component segregation has occurred, The height ratio of the portion including component segregation with respect to the height of the lump (that is, the upper portion of the steel ingot) was calculated using the following equation (1). The relationship between the shape of the steel ingot (H / D ratio) and the height ratio of the portion including component segregation is shown in FIG.
Height ratio of the portion including component segregation = height of the portion including component segregation / height of the steel ingot (1)

  The following can be considered from FIG. When the H / D ratio is 1.3 or more, the height ratio of the portion including component segregation with respect to the height of the steel ingot is small, so that segregation is concentrated in the upper part of the steel ingot. On the other hand, when the H / D ratio is less than 1.3, the height ratio of the portion including the component segregation with respect to the height of the steel ingot is increased, so that the component segregation is from the top to the center of the steel ingot. And diffused over the entire area.

Experimental example 2
After casting molten steel containing 0.130% by mass of C in a chrysanthemum mold without a feeder part, the surface of the molten steel is covered with a heat insulating material, and the molten steel is solidified to form a steel ingot. Obtained. As the heat insulating material, an exothermic heat insulating material and a heat insulating heat insulating material were used in combination. The shape of the heat insulating material was a combination of powder and granular materials, and the thickness of the heat insulating material was 200 mm. The size of the steel ingot was such that the H / D ratio was 2.0 when the height of the steel ingot was H and the diameter was D.

  The obtained steel ingot was cut in the longitudinal direction so as to pass through the central axis, and the cut surface was macro-etched and Sulfur-printed, and C: 0.160 mass% component segregation occurred. We measured the position. The position where component segregation occurs is shown in FIG.

  In FIG. 2, the horizontal axis is the measurement position in the radial direction, the central axis position of the steel ingot is 0 (zero), and the numerical value on the horizontal axis is the ratio of the distance between the central axis position and the measurement position to the radius of the steel ingot (center The distance between the shaft position and the measurement position / the radius of the steel ingot). The vertical axis is the measurement position in the height direction, the lowest point of the steel ingot is 0 (zero), the highest point of the steel ingot is 2.0, and the numerical value on the vertical axis is the highest value of the steel ingot relative to the height of the steel ingot. The ratio of the distance from the lower point to the measurement position (distance from the lowest point of the steel ingot to the measurement position / height of the steel ingot) is shown.

  It can be considered as follows from FIG. In the vicinity of the center axis of the steel ingot, component segregation occurs at the center or downward with respect to the height of the steel ingot, but as the steel ingot moves toward the outside, the component segregation concentrates on the upper part of the steel ingot. Has occurred. Moreover, the region is almost concentrated within 0.1 in the radial direction.

Experimental example 3
In Experimental Example 2, a steel ingot was obtained under the same conditions except that the size of the steel ingot was set to H / D ratio: 1.3, and component segregation of the obtained steel ingot was observed. The position where component segregation occurs is shown in FIG.

  The following can be considered from FIG. Similar to Experimental Example 2 above, in the vicinity of the center axis of the steel ingot, it occurs at the center or below with respect to the height of the steel ingot. It is concentrated in the upper part. Moreover, the region is almost concentrated within 0.1 in the radial direction.

Experimental Example 4
After casting molten steel containing 0.30% by mass of C in a cylindrical mold without a feeder, the molten steel is solidified while covering the surface of the molten steel with a heat insulating material having a different thickness. A lump was obtained. As the heat insulating material, an exothermic heat insulating material, a heat insulating heat insulating material, and grilled rice husk were used in combination. The shape of the heat insulating material was a powder and a plate, and the thickness of the heat insulating material was 0 to 600 mm. The size of the steel ingot was such that the H / D ratio was 1.7 when the height of the steel ingot was H and the diameter was D.

  The obtained steel ingot is cut in the longitudinal direction so as to pass through the central axis, and the cross-cut surface is macro-etched and the sulfa-printed one is compared, and the position where the shrinkage defect is generated is doubled. The area where skin was generated was measured.

When observing the longitudinal cross section of the steel ingot, the height of the steel ingot passes through the shrinkage defect occurring at the lowest position in the height direction of the steel ingot, among the positions where the shrinkage defect occurs. When cutting perpendicularly to the vertical direction, the height ratio of the portion including the shrinkage defect relative to the height of the steel ingot (that is, the upper portion of the steel ingot) is calculated using the following equation (2).
Height of shrinkage defect occurrence position (%) = (height of the portion including the shrinkage defect / height of the steel ingot) × 100 (2)

The area where the double skin occurs is the bottom of the position where the double skin is generated when the longitudinal cross section of the steel ingot is observed. When cut perpendicular to the height direction of the steel ingot so as to pass through the heavy skin, the height ratio of the portion including the double skin to the height of the steel ingot (ie, the upper part of the steel ingot) is as follows: (3) Calculate using the formula.
Double skin generation area (%) = (height of the portion including double skin / height of the steel ingot) × 100 (3)

  FIG. 4 shows the result of calculating the height of the shrinkage defect generation position and the double skin generation area when the thickness of the heat insulating material is changed. In FIG. 4, the result of the position height where the shrinkage defect is generated is indicated by ●, and the result of the double skin occurrence region is indicated by ◆.

  It can be considered as follows from FIG. When the thickness of the heat insulating material is controlled to 50 to 500 mm, the generation position of the shrinkage defect can be concentrated on the upper part of the steel ingot, and the double skin generation region can be reduced. On the other hand, if the thickness of the heat retaining material is less than 50 mm, the heat retaining effect of the molten steel cannot be obtained, and the occurrence position of the shrinkage defect cannot be concentrated on the upper part of the steel ingot. When the thickness of the heat insulating material exceeds 500 mm, excessive heat retention is caused to cause solidified shell cracking, and double skin is generated over a wide range.

Experimental Example 5
After casting molten steel containing 0.18% by mass of C in a cylindrical mold without a feeder, the molten steel is solidified while covering the surface of the molten steel with a heat insulating material to obtain a steel ingot. It was. As the heat insulating material, an exothermic heat insulating material and a heat insulating heat insulating material were used in combination. The shape of the heat insulating material was a combination of granular and powder, and the thickness of the heat insulating material was 200 mm. The size of the steel ingot is 3765 mm in height and 2670 mm in diameter, and the height / diameter ratio is 1.55 (equivalent to 140T).

  The obtained steel ingot is cut in the longitudinal direction so as to pass through the central axis, and the cross-cut surface is macro-etched and the sulfa-printed one is comparatively observed to determine the position where the component segregation and shrinkage defect occur. It was measured. As a result, the component segregation is concentrated in the range of 8% in the radial direction around the central axis of the steel ingot, and the shrinkage defect is in the range of 4% in the radial direction around the central axis of the steel ingot. Concentrated on. In addition, the position where the component segregation occurs refers to a region where the C concentration exceeds 0.20 mass%.

  Next, the steel ingot obtained in the same manner was compressed in the longitudinal direction (compression rate: 35%) to make the diameter 3000 mm, and then the center of the steel ingot was axially pulled out with a punch along the compression direction. . At this time, a jig having a diameter of 300 mm was used as a jig for removing the central portion of the steel ingot. Therefore, since the central part of 300 mm in diameter is extracted from the steel ingot after compression having a diameter of 3000 mm, when the diameter of the steel ingot after compression is Dp, the cylinder of diameter: 0.1 × Dp is extracted as the central part. That's right.

  When the obtained hollow steel for forging was observed, neither component segregation nor shrinkage defects were found. Therefore, the cylindrical forged product formed by forging the forging steel material into a cylindrical shape is free from component segregation and shrinkage defects and is of high quality.

Experimental Example 6
After casting molten steel containing 0.15% by mass of C in a cylindrical mold without a feeder, the molten steel is solidified while covering the surface of the molten steel with a heat insulating material to obtain a steel ingot. It was. As the heat insulating material, an exothermic heat insulating material and a heat insulating heat insulating material were used in combination. The shape of the heat insulating material was granular or powder, and the thickness of the heat insulating material was 150 mm. The steel ingot has a height of 1370 mm and a diameter of 1020 mm, and a height / diameter ratio of 1.34 (equivalent to 20T).

  The obtained steel ingot is cut in the longitudinal direction so as to pass through the central axis, and the cross-cut surface is macro-etched and the sulfa-printed one is comparatively observed to determine the position where the component segregation and shrinkage defect occur. It was measured. As a result, component segregation is concentrated in the range of 10% in the radial direction around the central axis of the steel ingot, and shrinkage defects are in the range of 4% in the radial direction around the central axis of the steel ingot. It was distributed and concentrated. The position where component segregation occurs refers to a region where the C concentration is 0.18% by mass or more.

  Next, the steel ingot obtained in the same manner was compressed in the longitudinal direction (compression rate: 30%) to a diameter of 1200 mm, and then the center of the steel ingot was axially pulled out with a punch along the compression direction. . At this time, a jig having a diameter of 480 mm was used as a jig for removing the central portion of the steel ingot. Therefore, since the central part of 480 mm in diameter is extracted from the steel ingot after compression with a diameter of 1200 mm, when the diameter of the steel ingot after compression is Dp, a cylinder with a diameter of 0.40 × Dp is extracted as the central part. That's right.

  When the obtained hollow steel for forging was observed, neither component segregation nor shrinkage defects were found. Therefore, the cylindrical forged product formed by forging the forging steel material into a cylindrical shape is free from component segregation and shrinkage defects and is of high quality.

It is a graph which shows the relationship between the shape (H / D ratio) of a steel ingot, and the height ratio of the part containing a component segregation. It is a graph which shows the position where component segregation has occurred. It is a graph which shows the position where component segregation has occurred. It is a graph which shows the result of having measured the height of the position where the shrinkage nest defect has occurred, and the region where the double skin has occurred when the thickness of the heat insulating material is changed.

Claims (3)

A method for producing a hollow forging steel material without using a head heating ingot method or a unidirectional solidification casting method,
The process of casting molten steel into a mold without a feeder using vacuum casting or bottom pouring,
A process of solidifying the molten steel in the radial direction while casting the molten steel and concentrating the portion where defects and component segregation occur on the upper part of the steel ingot by covering the surface of the molten steel with a heat insulating material;
Compressing the obtained steel ingot, and extracting the central portion in the axial direction along the compression direction,
The shape of the solidified steel ingot is a ratio of height H to diameter D (H / D ratio) of 1.4 to 2,
The thickness of the heat insulating material is 100 to 500 mm,
In the extracting step, when the diameter of the steel ingot after compression is Dp, a hollow forging steel material is extracted with a cylinder having a diameter of 0.1 × Dp to 0.5 × Dp as a central portion .   The method according to claim 1, wherein a cylindrical or chrysanthemum mold is used as the mold.   A method for producing a cylindrical forged product, comprising forging a hollow forging steel material obtained by the production method according to claim 1 or 2 into a tubular shape.

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