JP2008068297A - Method of manufacturing large diameter wire rod for cold forging - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a large diameter wire rod which is high in the yield and excellent in cold forging property by effectively suppressing occurrence of scabs on the large diameter wire rod when manufacturing the large diameter wire rod having the diameter of ≥20 mm by hot-rolling a square billet. <P>SOLUTION: Hot rolling is performed after removing not only flaws detected by a magnetic particle inspection but bruises and scratches ('bruises or the like' is a general term for these) which are not detected by the magnetic particle inspection. When removing the bruises or the like, it is preferable to chamfer the whole of the corner parts of the square billet, where the bruises or the like are apt to occur, along the longitudinal direction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a large-diameter wire having a diameter of 20 mm or more by hot-rolling a square steel slab, and specifically relates to a technique for suppressing the occurrence of lashes in such a large-diameter wire.

  Conventionally, square steel slabs are processed into wire rods by hot rolling after removing the wrinkles detected by magnetic particle flaw detection with a grinder, etc., and further finished by cold forging, such as valve springs and suspension springs. It was processed into.

  And with recent advances in cold forging technology, there is a need to increase the diameter of the wire for the purpose of reducing the manufacturing cost in the wire manufacturing stage and increasing the strength of the final product (that is, a large diameter wire having a diameter of 20 mm or more) Demand) is increasing.

  However, with the increase in diameter of such wire rods, the appearance rate of lashes in the wire rods has increased, and the yield and quality (especially cold forgeability) of the wire rods have deteriorated. Yes.

  The reason is assumed as follows. In other words, magnetic particle inspection of a square steel slab is performed by sprinkling fluorescent magnetic powder on a magnetized square steel slab and visually observing the magnetic powder pattern in a dark room. However, comparatively shallow and shallow wrinkles such as hammering and rubbing wrinkles are difficult to detect because the magnetic powder pattern is not clear. However, the conventional thin wire rod has a large area reduction ratio (rolling rate) from the square steel slab, so it is healed in the hot rolling process without removing comparatively shallow wrinkles that are not detected by magnetic particle flaw detection. It seems that it was not a problem. On the other hand, in the large-diameter wire having a diameter of 20 mm or more, the reduction in area from the square steel piece is lower than that in the conventional thin-diameter wire. It is thought that even if it is a shallow ridge, even if it goes through a hot rolling process, it will not heal completely and will remain as a beard ridge.

  However, it is still unclear as to how much of the wrinkles present in the square steel slabs will become bulges in the large-diameter wire, and the present situation is that a coping method has not been established.

Here, for the method of care of the steel slab, for example, in Patent Document 1, there is disclosed a relationship between the removal trace of the steel slab by the injection of the water jet containing abrasive grains and the bald ridge after rolling, There is no description whatsoever about the type, form, location, etc. of the steel slab to be removed.
Japanese Patent No. 2825769

  In the present invention, when a square steel slab is hot-rolled to produce a large-diameter wire having a diameter of 20 mm or more, the large-diameter wire is effectively restrained from being bald and thereby cooled at a high yield. It aims at providing the manufacturing method of the large diameter wire rod excellent in the forgeability.

  In order to verify the assumed mechanism of the increase in the amount of lashes associated with the increase in the diameter of the wire, the present inventors generate defects in square steel pieces that are not detected by magnetic particle flaw detection and in the large-diameter wire after hot rolling. We investigated the relationship with Hege-an.

  That is, first, with respect to a square steel piece (billet) having a length of 195 mm × 1000 mm, during the removal of the wrinkles discovered (detected) by the magnetic particle flaw detection, the newly found visual hits and rubbing wrinkles (hereinafter, Marking was applied to the “spots etc.”), and these newly found slashes were hot-rolled without being removed and processed into a large-diameter wire having a diameter of 46 mm. Then, by visually observing a portion corresponding to the marking portion of the surface of the large-diameter wire after the hot rolling and observing a cross section with a microscope, the newly found hammering or the like is obtained after the hot rolling. Was also investigated. As a result, scratches and the like were found in six places at the stage of the square steel slab, and as shown in FIG. 3, three pieces of them had a depth of about 0.03 to 0.4 mm even after hot rolling. Was found to remain.

  Next, when a lot of square steel slabs were examined for the occurrence of newly found bruises by the same method as described above, there were few bruises on the flat part of the square steel slabs and concentrated on the corners. It was found that the generation rate at the corners reached about 80 to 90% of the whole.

  Then, the present inventors have further studied based on the above findings and have completed the following invention.

  According to the first aspect of the present invention, when a square steel slab is hot-rolled to produce a large-diameter wire having a diameter of 20 mm or more, from the square steel slab, a flaw that is detected by magnetic particle flaw detection, and a hammer that is not detected by magnetic particle flaw detection, The present invention is a method for producing a large-diameter wire for cold forging having a high deterrent effect on the generation of lashes, wherein hot rolling is performed after removing wrinkles and rubbing wrinkles.

  The invention according to claim 2 removes wrinkles detected by magnetic particle flaw detection from the square steel piece when hot-rolling the square steel piece to produce a large-diameter wire having a diameter of 20 mm or more. This is a method for producing a large-diameter wire for cold forging, which has a high deterrent effect on the occurrence of lashing, characterized by chamfering the entire portion along its longitudinal direction and then hot rolling.

  Invention of Claim 3 is a manufacturing method of the large diameter wire for cold forging of Claim 1 or 2 which makes the burr height after removing the wrinkles of the said square steel piece 1 mm or less.

  According to the present invention, a large-diameter wire having a diameter of 20 mm or more is manufactured by hot rolling after removing not only wrinkles detected by magnetic particle flaw detection but also striking not detected by magnetic particle flaw detection from square steel pieces. Even so, it has become possible to effectively suppress the occurrence of lashes in the wire, and a large-diameter wire having excellent cold forgeability can be produced at a high yield.

Embodiment 1
FIG. 1 is a flowchart showing a process for producing a large-diameter wire from a square steel piece according to an embodiment of the present invention. Hereinafter, each process is demonstrated in detail along the flow.

(1) Magnetic particle flaw detection First, after magnetizing a square steel piece, fluorescent magnetic powder is sprinkled on the surface, the magnetic powder pattern is visually observed in a dark room, and marking is applied to the detected wrinkles.

(2) Detection of visual hits, etc. Next, in the scraping work place, the hits that were not detected by the magnetic particle flaw detection were detected visually, and the newly detected hits were also marked. Keep it.

(3) Removal of wrinkles Then, the operation for removing the wrinkles detected in the steps (1) and (2) is performed. For example, the wrinkles can be removed by grinding and removing with a grinder, as in the conventional case, but can also be hot-scraped with hot scarfing.

  Here, as described above, most of the hammers and the like detected in the step (2) are concentrated on the corners of the square steel pieces. For example, the corners in the corner can be removed by chamfering the corner along the longitudinal direction with a grinder, for example. However, when chamfering a corner with a grinder, as shown in the examples below, if the grinder is chamfered at once by grinding once, the burr height resulting from the chamfer exceeds 1 mm. It is recommended that the chamfering angle be gradually changed by a plurality of times of grinding so that the height of the burr becomes 1 mm or less because it causes scabs.

(4) Hot rolling After cutting off, the square steel slab is heated to a predetermined temperature in a heating furnace, and then gradually reduced in a plurality of stages of rolling mills to reduce the surface, thereby obtaining a large-diameter wire having a predetermined diameter. To process.

  The large-diameter wire produced in this way has been removed in advance from the square slab prior to hot rolling, which can cause lashes, which can effectively prevent the occurrence of lashes. A large-diameter wire having excellent cold forgeability at a high yield can be produced.

[Embodiment 2]
In Embodiment 1 described above, in the step (2), an example of visually detecting a hammer or the like was shown. However, since most of the hammer or the like is concentrated on the corner of the square steel piece, The step (2), that is, the detection operation such as visual hitting may be omitted, and the corners may be uniformly chamfered along the longitudinal direction. Compared to the first embodiment, although the possibility of occurrence of lashes due to the rivets existing in the flat portion of the square steel piece remains, since the probability of occurrence is low, the occurrence of lashes is greatly reduced compared to the conventional case. It will be possible. In addition, compared to the first embodiment, although the problem of yield reduction due to chamfering even corners without striking occurs, instead of the detection work such as visual striking can be omitted, The effect of greatly reducing the work load can be obtained.

[Embodiment 3]
Further, in the second embodiment, after performing the step (2), that is, the detection work such as visual hitting, the corners may be uniformly chamfered along the longitudinal direction. . In this case, as compared with the second embodiment, although the effect of reducing the work load cannot be obtained, it is possible to remove the striking and the like existing on the flat portion of the square steel piece, so that it is possible to further reduce the occurrence of baldness.

  The relationship between the grinding method when chamfering the corners of the square steel pieces along the longitudinal direction with a grinder and the occurrence of lashes in the large-diameter wire were investigated as follows.

  After chamfering all the chamfers along the longitudinal direction with three types of grinding methods (a) to (c) shown in FIG. The test which rolled and processed into a large diameter wire with a diameter of 46 mm was implemented. Here, in the same figure, (a) is an example in which the chamfering angle is fixed and the chamfering is performed at once, (b) is an example in which the chamfering angle is changed little by little and the chamfering is performed in three times. c) shows an example in which chamfering is carried out five times by changing the chamfering angle little by little.

As a result of the above test, as shown in Table 1 below, in the case of (a), there is a relatively large burr having a height of more than 1 mm after chamfering and a maximum height of about 2 mm. The occurrence of balding caused by this burr was observed. On the other hand, in the case of (b), although small burrs having a height of 1 mm or less exist after chamfering, no generation of lashes was observed in the large-diameter wire after hot rolling. In the case of (c), the presence of conspicuous burrs was not observed after chamfering, and no generation of lashes was observed in the large-diameter wire after hot rolling.

    In order to confirm the effect of the present invention, a test operation for observing the state of change in the ratio of occurrence of baldness in the large-diameter wire before and after the application of the present invention was performed.

(Comparative example [Conventional method])
About a square steel piece of 195 mm square x 1000 mm length, after removing only the wrinkles detected by magnetic particle flaw detection with a grinder, it was hot-worked and processed into a large-diameter wire having a diameter of 46 mm. And the presence or absence of the occurrence of lashes was investigated by eddy current flaw detection on the processed large-diameter wire.

(Invention example)
For the same square steel pieces as in the above comparative example, a method of removing the wrinkles detected by the magnetic particle flaw detection, omitting the detection work such as visual hitting, and uniformly chamfering all corners along the longitudinal direction. Adopted (see Embodiment 2 above). In addition, the grinding method of the corner | angular part used the method of grinding by 3 times of (b) of the said Example 1 (FIG. 2).

〔Test results〕
Examine the eddy current flaw detection for large diameter wire after processing. If even one piece of lashes is found in one coil, it will be considered as “Hager crease generation”. The case where no hege soot was generated was defined as the case where no hege soot was found, and the ratio of the number of coils with “the occurrence of hege soot” to the total number of coils investigated was defined as the ratio of the occurrence of hege soot.

  As a result of the investigation, the ratio of occurrence of whipping every month was 24 to 37% in the period of the comparative example, but was significantly reduced to 0 to 16% in the period of the invention example.

It is a flowchart which shows the process of manufacturing a large diameter wire from a square steel piece based on one Embodiment of this invention. It is radial direction sectional drawing explaining the grinding method of the corner | angular part of a square steel piece. It is a figure which shows the external appearance, such as hammering of a square steel piece surface, and the external appearance and cross section of the large diameter wire rod surface after hot rolling.

Claims (3)

  When producing a large-diameter wire rod having a diameter of 20 mm or more by hot rolling the square steel pieces, after removing the wrinkles detected by magnetic particle flaw detection, and the striking and rubbing flaws not detected by magnetic particle flaw detection from the square steel pieces, A method for producing a large-diameter wire for cold forging, which has a high deterrent effect on the generation of lashes, characterized by hot rolling.   When producing a large-diameter wire having a diameter of 20 mm or more by hot rolling the square steel pieces, the corners of the square steel pieces are completely removed along the longitudinal direction while removing the wrinkles detected by the magnetic particle flaw detection from the square steel pieces. A method for producing a large-diameter wire for cold forging, which has a high deterrent effect on the generation of lashes, characterized by hot rolling after chamfering. The manufacturing method of the large diameter wire for cold forging of Claim 1 or 2 which makes the burr height after removing the wrinkles of the said square steel piece 1 mm or less.

Images