JP4982438B2 - Method for preventing mass outflow of defects in steel - Google Patents

Description

  The present invention relates to a method for preventing mass outflow of defects in steel materials.

  A steel material made of special steel is obtained by rolling a steel piece. Usually, multi-stage rolling is performed by a rough row rolling mill, a middle row rolling mill, and a finishing row rolling mill arranged in tandem. By this rolling, the steel slab is gradually reduced in diameter and lengthened to obtain a steel material. Depending on the user's request, the steel material obtained by rolling is further subjected to heat treatment, peeling processing, etc. to obtain a product.

  The steel material manufactured in this way may have surface flaws. There may be a surface flaw caused by a flaw of a steel slab, or it may be a surface flaw generated in rolling or a later process, but depending on the shape and size of the surface flaw, the quality of the steel material is impaired. Therefore, it is necessary to inspect the final product according to the use of the steel material and to ship only high-quality steel material.

  An example of the product inspection flow is to detect the presence and depth of flaws in a steel bar rolled steel bar with a magnetic flux flaw detector, then clarify the position of the flaws by wet magnetic particle flaw detection, and the operator uses a grinder etc.研 削 Work to grind one by one.

  When the wrinkles detected by an inspection device such as a leakage magnetic flux flaw detector are confirmed by magnetic particle flaw detection and repaired, the risk of overlooking the flaw by the magnetic particle flaw detection increases as the wrinkle is crimped. If such flaws occur during casting, the continuous casting method spans a large number of steel numbers (charge number, hereinafter also referred to as C #), so the danger target range increases drastically.

  In particular, when mold powder bites due to peeling of the continuous casting mold in the continuous casting process, defective outflows across a large number of C # s may occur.

  Even if such a wrinkle is not enough to stop the process due to a large wobbling load, the wringing operation becomes higher than a normal level. Wrinkle defects are also higher than normal. It is necessary to have a mechanism for issuing a warning as a danger object when this state extends over many steel numbers.

As a conventional system for detecting flaws, for example, the flaw detection material information acquisition means acquires flaw detection material information on the type and material of the flaw detection material, and the pass / fail criterion information acquisition means for each flaw detection material. After acquiring the information on the pass / fail criteria for the internal flaws defined in advance, the ultrasonic flaw detection means flaws the presence / absence of the internal flaw of the material to be detected, and the pass / fail judgment means is based on each information obtained by these means. There is a system that can easily and accurately carry out pass / fail determination for each flaw detection material by determining the pass / fail for each flaw detection material (for example, see Patent Document 1).
JP 2007-2713750

  Conventionally, as a specific acceptance / rejection determination standard, the manufacturing process is stopped when the defect rate (defect weight / inspection weight) is 50 to 100%. However, even for products that were not recognized as defective at the inspection stage, there were many claims in this standard, so it was necessary to further tighten the standard. It is also necessary to set a standard that matches the product specifications.

  The present invention has been made to solve such a conventional problem, and provides a method capable of effectively preventing the outflow of defective products by making warning conditions more strict. It is.

  The method for preventing large-scale leakage of defects in steel materials according to the present invention is a method of performing a product inspection on each of a plurality of steel materials manufactured from the same steel number to detect the depth of the defects, and a total of a plurality of steel materials subjected to product inspection. The weight is the inspection weight, the number of multiple steel products to be inspected is the number of inspections, the total weight of multiple steel materials whose depth exceeds the allowable depth is taken as the defect weight, and the depth of the defect is predetermined. The number of steel materials that exceed the allowable depth of steel, but is within the depth that can be cut, is the number of cuts, the value obtained by dividing the weight of the bad by the inspection weight is the defect rate, and the number of scraps is divided by the number of inspections. If the inspection value is equal to or greater than a predetermined weight, the defect rate is equal to or greater than a predetermined value, and the yield rate is equal to or greater than a predetermined value. Recognize steel numbers as dangerous steel numbers and re-use steel materials manufactured from dangerous steel numbers.査又 is characterized by performing peeling.

  According to the method for preventing large-scale outflow of defects in steel materials according to the present invention, it is possible to detect steel materials that may cause defects that have been missed in the past, and it is possible to prevent large-scale outflow of defects in defects. .

  Hereinafter, a method for preventing mass outflow of defects in steel material that is an embodiment of the present invention will be described in detail.

  First, the manufacturing process of special steel will be briefly described. First, scraps are melted in an electric furnace, and the whole amount is transferred to a ladle. This division of the ladle unit is called a charge, and a number (C #) is added to each. Subsequently, it is cut into a plurality of steel pieces by continuous casting through a ladle refining step and an RH degassing step. After that, a steel slab rolling process, a steel slab inspection process, and a steel bar rolling process are performed to produce a plurality of steel materials, and a product inspection process to which the mass defect prevention method for defects in this embodiment is applied is performed. The steel materials that have passed are shipped.

  Next, a description will be given of a product inspection process to which the method for preventing a large amount of wrinkle leakage according to this embodiment is applied.

  In the product inspection process, the presence and depth of the flaw are detected by a leakage magnetic flux flaw detector for each of a plurality of steel materials manufactured from the same C #. Next, the position of the wrinkles is specified by wet magnetic particle inspection.

  Here, as a result of the leakage magnetic flux flaw detection and the wet magnetic particle flaw detection, the scissors that exceed the scooping depth cannot be scooped and are collected in a subsequent process.

  In addition, when the depth of the ridge is within the product specifications (allowable heel depth), the product is shipped as an acceptable product. The wrinkle allowable depth is a value that is appropriately set according to product specifications.

  In addition, when the depth of the ridge exceeds the allowable depth of the ridge but is within the depth that can be removed, the grinder confirms the ridge confirmed by the wet magnetic particle inspection for each steel material. Shipped after removing the wrinkle to be removed and correcting the wrinkle depth to within the product specifications.

  Here, the total weight of the number of steel materials whose depth of iron exceeds the depth that can be trimmed is regarded as the defective weight, and the defective weight is divided by the inspection weight, which is the total weight of the inspected steel materials. Is defined as “defect rate (%)”.

  In addition, when the depth of the ridge exceeds the allowable depth of the ridge but is within the depth that can be trimmed, the number of trimmed by the operator is taken as the number of trimmed, and this number of scraped is the number of inspections. The value obtained by dividing is defined as “recovery rate (%)”.

The above relationship is expressed in the following formula: 疵 Defect rate (%) = 疵 Defect weight / inspection weight 疵 Decision rate (%) ＝ Number of defects acquired / Number of inspections

(Setting of product inspection amount)
Here, in the method for preventing a large amount of wrinkle leakage of the present embodiment, it is preferable that the inspection weight for the same C # is 20% or more of the weight per charge. For example, when the weight per charge is 150 t, it is preferably 30 t or more. This is because when 100% of the weight per charge is set, most of the products are shipped and there is no remaining steel piece, so feedback cannot be made.

(Setting defect rate)
Further, in the method for preventing a large amount of defects of defects in this embodiment, it is preferable that a steel material having a defect ratio of 1.0% or more is recognized as a risk target C #. This is because the defect rate in the case of complaints in actual products was about 1.4%, and the standard was further tightened to 1.0% as a prevention of powder bites. The defect rate is not limited to this, and may be determined based on the defect rate when a complaint occurs in an actual product.

(Setting of take-off rate)
Moreover, in the method for preventing large-scale leakage of defects in the present embodiment, it is preferable that a steel material having a scraping rate of 10.0% or more is recognized as a risk target C #. Even if the defect rate is less than 1.0%, if the yield rate is 10.0% or more, it means that the load of the operator's scraping work is increasing. This is because defective products may be missed due to human error.

  And, in the method for preventing large-scale spillage of defects in this embodiment, when the inspection weight is 30 t or more, the steel that satisfies the conditions that the defect rate is 1.0% or more and / or the scraping rate is 10.0% or more. The number is recognized as dangerous C #, and the steel material manufactured from dangerous C # is re-inspected or peeled off.

(Response after inspection, shipment, receipt, in-process material, pre-allocation billet)
When the risk C # is recognized by the method for preventing large defects from defects in the present embodiment, the same C # products that have already been shipped are repurchased and re-inspected. Is subjected to re-inspection, and in-process materials are inspected with stricter inspection standards. Re-inspection is performed on pre-alloyed steel slabs, or peeling is performed on round steel slabs.

  Examples of the present invention will be described below. However, the present invention is not limited to the following examples.

  Tables 1 and 2 are diagrams showing the results of calculating the defect rate and the defect rate for C # 1 to C # 70. In the table, the numerical values are enclosed in squares for portions where the defect rate is 1.0% or more and where the defect rate is 10.0% or more.

  As shown in Table 1, there are six C # s 49, 50, 51, 59, 67, and 70 having a scraping rate of 10.0% or more even in C # where the defect rate does not exceed 1.0%. Thus, it can be seen that the steel material that may cause a defect that has been missed in the past can also be detected by the method for preventing a large amount of wrinkle leakage of the present embodiment.

  In addition, the defect rate has been around 0.3%, which is worse than the C # 48 series, and the inspected steel material of C # 54 certified as dangerous C # is carefully re-examined by magnetic particle inspection. Upon inspection, the presence of sputum was observed. This may be a factor of oversight due to an increase in workload exceeding 10% of the collection rate. When the cross-sectional microscopicity of the remaining wrinkles was investigated, it was found that the wrinkle width was very narrow due to the entrainment of mold powder during continuous casting. In the magnetic particle inspection, it is estimated that such close wrinkles were missed because the fluorescent magnetic powder hardly aggregates and the indication becomes thin. According to the method for preventing a large amount of wrinkle defects of this embodiment, all C # with a scraping rate of 10% or more are re-inspected or peeled, so that oversight of wrinkle defects due to powder biting as described above occurs. The possibility of doing is very low. Therefore, the validity of the present invention was proved.

Claims (4)

Product inspection is performed on each of a plurality of steel products manufactured from the same steel number to detect the depth of the flaw,
The total weight of the plurality of steel materials for performing the product inspection is set as an inspection weight, the number of the plurality of steel materials for performing the product inspection is set as the number of inspections, and the depth of the wrinkles exceeds the depth that can be cut off. The total weight of the steel material is the defect weight, and the depth of the defect exceeds a predetermined allowable defect depth, but the number of the steel materials that are within the depth that can be removed is the defect number, and the defect defect weight When the value divided by the inspection weight is the defect rate, and the value obtained by dividing the number of scraps by the number of inspections is the scrap rate,
In the case where the inspection weight is a predetermined weight or more,
The steel number that meets at least one of the conditions in which the defect rate is greater than or equal to a predetermined value and the scraping rate is greater than or equal to a predetermined value is recognized as a dangerous steel number,
A method for preventing large-scale outflow of flaws in steel materials, wherein reinspection or peeling is performed on steel materials manufactured from the dangerous steel numbers.   The method of claim 1, wherein the inspection weight is 20% or more of the total weight of the plurality of steel materials.   The method for preventing a large amount of defects in a steel material according to claim 1 or 2, wherein the defect rate is 1.0% or more. The method according to claim 1, wherein the scraping rate is 10% or more.