JPS6035205B2 - Io free-cutting steel manufacturing method for seamless steel pipes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing seamless steel pipes of free-cutting steel.

Seamless free-cutting steel pipes are in high demand as materials for machine work, especially tubular parts that are manufactured by cutting, such as hydraulic shock absorbers, hydraulic drive wheels, and other cylinders. Conventionally, the Mannesmann method could not generally be applied to the drilling process for this type of steel material, but the present invention makes it possible to apply this method by elucidating the drilling behavior at the end face of the material pellet, and improves the efficiency of the above-mentioned seamless steel pipe. The aim is to realize mass production at low cost. Free-cutting steel contains a large amount of sulfide, so its workability at high temperatures is extremely inferior to that of ordinary steel, and there is a high risk of cracking during rolling. Therefore, when manufacturing this type of seamless steel pipe using the so-called Mannesmann seamless steel pipe method, which involves drilling a hole with an oblique roll drilling machine and elongating it with a subsequent plug mill or mandrel mill, it is necessary to If cracks occur on the end surface of the tube, it is difficult to apply them to subsequent processes. Therefore, this type of seamless steel pipe has been manufactured exclusively by the extrusion method. However, the extrusion method has a problem of low production efficiency and uneven thickness during drilling, so it is desired to develop a pipe manufacturing method using the Mannesmann method, which allows mass production at low cost. In order to meet the above demands, the inventors conducted numerous experiments and studies, and found that
We obtained the following knowledge.

When the Mannesmann method is applied to free-cutting steel, the appearance of cracks during drilling shows a vertical crack appearance in which the wall thickness is separated in the radial direction, regardless of the size of the wall thickness. It occurs most intensely at the perforation start end of the Qin pipe, and gradually decreases toward the rolling rear end.

Furthermore, the occurrence of such cracks varies greatly depending on the drilling conditions of the chain oblique drilling machine, and the occurrence of such cracks can be considerably reduced by drilling under appropriate drilling conditions. However, it is difficult to completely eliminate cracks at the starting end of the hole by improving the drilling conditions as described above, and even if this type of micro-cracking is slight, it can be caused by subsequent elongation. Since cracks may develop during the rolling process, it is desirable to completely eliminate the occurrence of cracks during drilling.

Therefore, the inventors focused on the fact that the smaller the cracks that occur at the starting end of the perforation, the more minor the cracks will be at the rear end, and if the cracking at the starting end of the perforation can be suppressed, We thought that it would be possible to completely eliminate the occurrence of cracks at the beginning of the drilling process, and conducted various studies on means to prevent the occurrence of cracks at the starting end of the hole.

As a result, by joining common steel with good workability to the drilling start end of the material round pillar before drilling with an inclined roll drilling machine, cracking during drilling can be completely prevented, and this method We found that there is no need to limit the drilling conditions, and that the drilling conditions that have been commonly used in the past are sufficient.
This invention is based on the above findings.

In other words, the present invention involves the steps of preparing a round billet made by welding ordinary steel to free-cutting steel as raw materials, in manufacturing a seamless steel pipe made of sulfur free-cutting steel using the Mannesmann seamless pipe manufacturing method, and then this joining process. The conventional Mannesmann drilling method is applied to the ordinary steel as a lead, and the entire round billet is perforated.Then, the pipe is formed by elongation rolling, and the leading part is connected at the joint before or after this pipe-forming stage. This is a method for manufacturing seamless free-cutting steel pipes, which includes the steps of cutting and removing.

In this invention, in order to join the common steel to the tip of the free-cutting steel, it is only necessary that the joint be finished soundly. Furthermore, submerged arc welding can also be used, and in this case, X-joint shapes, K-joints, etc. are advantageous.

In addition, flash butt welding and friction pressure welding can be performed without creating a bevel.
It is also effective to join using a hoe welding method or the like. Note that it is desirable that the length of the welded portion of ordinary steel be equal to or greater than the machining depth of the guide hole prior to drilling. Furthermore, when joining free-cutting steel and common steel, special care must be taken to avoid defects anywhere on the surface or inside of the joint.

This is because if there is a defect in the joint, cracks may occur on the outer or inner surface of the raw pipe after drilling in a direction perpendicular to the pipe axis direction. Next, the present invention will be specifically explained with reference to examples.

Example {1] Method for making round billet material - Dimensions and chemical composition of free-cutting steel billet (weight%
)・Diameter 58 skin x Length 250 ribs・One end machined to 1200・0.01%C, 0.01%Sj, 0.96%Mn, 0
．． 081%P, 0.325%S, - Dimensions and chemical composition (weight %) of common steel tip - Diameter 58 side x length 2 sides - One end machined to 120o - 0.15%C, 0. 25%Si, 0.50%Mn, 0
．． 018%P, 0.009%S, ・Welding method 1 Arc welding ・Welding method: Covered arc welding rod for European steel (KS-76) ・Joint shape: 60oX development with machined ends facing each other (
(See Figure 1) The material round billet obtained by welding ordinary steel to free-cutting steel under the above conditions was inspected on its longitudinal section to ensure that there were no defects on either the surface or the inside. Confirmed.

Next, a guide hole with an inner diameter of 20 mm, a depth of 10 mm, and an apex angle of 90 degrees was machined into the tipping machine of this bonded round billet, and the lower {2}
The holes were drilled using a mirror slanted roll drill under the drilling conditions shown below.

■ Drilling conditions - Roll gap: 52 ribs (draft rate 10.3%) - Plug advance amount 3 & ribs (contact length 57 ribs) - Plug diameter 42
Rib/shoe spacing 61 Fence/roll inclination angle loo The above drilling conditions are a typical example when drilling ordinary steel. No cracks occurred in any part of the steel that had been cut.

Furthermore, no problems were observed when the obtained perforated blank tube was subjected to elongation rolling using a mandrel mill to produce a tube.

By cutting and removing the joint on the drilling start end side of the thus obtained pipe, a seamless free-cutting steel pipe can be obtained.

Note that the joint portion may be cut and removed before elongation rolling is performed using a mandrel mill or the like to form a pipe.

As explained above using sulfur free-cutting steel (SAE1215) containing a relatively large amount of sulfur (0.325%) as a representative example, the present invention is capable of producing a sound material without cracking during Mannesmann drilling. Since a perforated raw tube is obtained, it can naturally be applied to all commonly called free-cutting steels such as JIS SUMII to SUM43.

As described above, according to the present invention, seamless free-cutting steel pipes can be advantageously manufactured by the Mannesmann seamless steel pipe method, which was previously considered impossible, so mass production of free-cutting steel pipes can be achieved at low cost. Moreover, since the Mannesmann method has a wide range of product dimensions, the applications of the above-mentioned seamless free-cutting steel pipes can be expanded to a large extent.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a groove shape in welding free-cutting steel and common steel. Figure 1

Claims (1)

[Claims] 1. In manufacturing seamless free-cutting steel pipes using the Mannesmann seamless steel pipe method, there are two steps: preparing a round billet made by joining ordinary steel to free-cutting steel as the raw material, and then using this joined ordinary steel as a guide. A stage in which the entire round billet is perforated using the usual Mannesmann drilling method, a stage in which a pipe is formed by extension rolling, and a stage in which the leading portion is cut and removed at the joint before or after this pipe-forming stage. A method for manufacturing a seamless free-cutting steel pipe, characterized by comprising the steps of: