JP2003294708A - Method of preventing outflow of material unadaptable to quenching crack flaw standard of hardening/ tempering material by leakage magnetic flux flaw detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of eliminating an accidental outflow to a subsequent process of a material unadaptable to the flaw standard as an unadaptable material in the determination of a quenching crack flaw of a hardening/ tempering steel material by a leakage magnetic flux flaw detector. <P>SOLUTION: A method for preventing the outflow of a material incompatible with the flaw standard comprises: first detecting leakage magnetic fluxes 4 by a leakage magnetic flux flaw detector to determine quenching crack flaws 2 of hardened/tempered steel materials such as a steel bar 1 according to a determination standard stricter than the customer standard to distinguish compatible materials from incompatible materials; and then determining steel materials once determined as the incompatible materials according to the customer standard of flaw depth after further polish of the quenching crack flaw 2 site to distinguish determination-pass materials from materials incompatible with flaw standard. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nondestructive inspection of surface flaws of steel materials, and more particularly to a method for preventing outflow of quenching crack flaw standard non-compliant material of a quenched and tempered material using a leakage flux flaw detector.

[0002]

2. Description of the Related Art In the manufacture of steel materials, nondestructive inspection is often carried out in order to ensure that the materials satisfy the customer's requirements. Typical examples thereof include the flaw detection method and the eddy current flaw detection method.

Among them, the leakage magnetic flux flaw detection method is a method of magnetizing a material to be inspected and detecting the magnetic flux leaking from the flaw portion by a sensor such as a coil or a magnetic sensitive element. The electrical signal (defect signal) from the sensor has the property of increasing in proportion to the depth of the defect, so if sensitivity calibration is performed using a material with a defect of known depth beforehand, The flaw depth can be estimated from the magnitude of the flaw signal detected from the inspected material.

In the actual flaw inspection, a sensor is made to scan along the surface of the material to be inspected, and the flaw depth and site are detected by the flaw signal obtained. If the result of the flaw depth for each of the steel materials thus obtained is larger than the normal standard value, it is classified as a material that does not conform to the defect standard from the acceptable material, and the nonstandard material is prevented from flowing into the process as the conforming material.

[0005]

SUMMARY OF THE INVENTION However, it occurs in a material that has been hardened and tempered, and particularly in a material having good hardenability, such as a mechanical structural alloy steel containing C: 0.26% or more by mass%. Some of the crevice cracks have a flaw depth as deep as several mm, but a flaw signal of a size corresponding to that is not detected. In this case, if the flaw depth detected shallower than the actual depth is smaller than the standard, it will be a passing material, so in reality, a flaw standard non-compliant material with a flaw deeper than the standard, that is, a non-standard material will There is a risk of leaking into the process. The problem to be solved by the present invention is to provide a method for solving a problem that a flaw standard nonconforming material flows out to a subsequent process as a conforming material in the determination of a quench cracking flaw of a quenched and tempered material by a leakage flux flaw detector. is there.

[0006]

As means for solving the problems of the present invention, first, the judgment standard of the leakage flux flaw detector, which conventionally used the standard value of the customer, was detected shallower than the actual depth. Even if it is a cracked cracked flaw material, it will be strict as far as it can be separated from the accepted material as a material that does not conform to the flaw judgment. Next, for the material once classified as a material that does not conform to the defect judgment, the defective part of the material is polished by a grinder etc., and the judgment is made according to the customer's standard of the defect depth, and it is classified into the acceptable material and the material not conforming to the defect standard. . By doing so, it becomes possible to prevent a flaw standard non-compliant material having a quench crack flaw deeper than the standard from flowing out to a subsequent process.

The details will be described below. When the quenching and tempering steel bar 1 was inspected for a quench crack 2 which was detected as a flaw shallower than the actual flaw depth by a leakage flux flaw detector, a scale 3 was formed inside the flaw as shown in Fig. 1 (b).
Was observed. As shown in FIG. 1A, this is considered to be the scale 3 generated inside the quenching crack 2 during tempering after the quenching crack 2 was generated by the rapid cooling of the quenching treatment. In this way, the scale 3 is placed inside the fire crack 2
When the material is clogged, when the material to be inspected is magnetized, a magnetic flux that should originally leak from the flaw portion partially passes through the scale 3 and does not leak. That is, as shown in FIG. 1A, a large amount of the leakage magnetic flux 4 should be leaked, but as the magnetic flux passes through the scale 3, the actually leaked magnetic flux is reduced, and as shown in FIG. The leakage magnetic flux 4 is small. As a result, it is considered that only the flaw signal corresponding to the flaw significantly shallower than the flaw signal corresponding to the depth of the true quenching crack flaw 2 is detected.

In view of this, in the present invention, first, in the case where a flaw inspection is performed on a material that may have a quench crack 2 filled with scale inside with a leakage flux flaw detector, it is detected shallower than the actual depth. Even for the fire cracked flawed material, the judgment criteria will be strict to a level at which it can be discriminated from the accepted material as a material not conforming to the flaw determination, and the outflow of the material not conforming to the flaw standard in the leakage flux flaw detector. As a result of the investigation, it was found that the criterion for judgment by this leakage magnetic flux flaw detector is that a passing signal should be a flaw signal with a flaw depth of 0.2 mm or less.

On the other hand, by using this strict judgment standard, it is necessary to prevent even a material having only a truly shallow quenching crack defect within the standard from becoming a material not conforming to the defect standard. Therefore, for materials that have been once classified as non-conforming material for flaw determination, the flawed portion is ground with a grinder etc., and the flaw depth of the polished flawed portion is judged according to the customer's standard. By classifying into the above, it is possible to prevent only the material which does not conform to the defect standard, which has the quenching crack which is deeper than the specification, from being erroneously discharged to the process as the acceptable material.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present embodiment, a bloom produced by melting in an electric furnace and continuously cast is rolled into a steel slab, and the steel slab is further rolled into a predetermined size, followed by quenching and tempering treatment. The AISI 4150 equivalent material was used as the material to be inspected. Table 1 shows the main chemical composition of the material to be inspected, Table 2 shows the dimensions of the material to be inspected, the true flaw depth obtained from the microstructure observation result of the flaw cross section, the flaw depth estimated from the flaw signal and the inside of the flaw. Shows the fullness of the scale of. No. of material to be inspected 1-4
Up to the above, it is a material that does not conform to the flaw standard, and although there is a quench crack that greatly exceeds the standard value: flaw depth of 0.5 mm or less, only a flaw signal corresponding to a shallow flaw is detected. In addition, these are filled with scale inside the flaw. Inspected material N
o. 5, No. Although 6 is a passing material, it is a material that does not conform to the defect determination once. The scale inside the flaw is scattered. The inspected material 7 is an acceptable material even if the criteria for determination by the leakage flux flaw detector is strict up to a flaw depth of 0.2 mm, and in this case, there is almost no scale inside the flaw.

[0011]

[Table 1]

[0012]

[Table 2]

[0013]

EXAMPLES Examples of materials in the above-described embodiment will be described. The graph of FIG. 2 shows the results of flaw inspection of these materials to be inspected by the leakage flux flaw detector. From this, when judged by the customer standard value, the inspected material No. Regarding Nos. 1 to 4, although the actual flaw depth is a material that does not conform to the flaw standard, which is much higher than the standard value, it will flow out because only the flaw signal corresponding to the shallow flaw is detected. In the example, 0.2mm is used as the criterion for determining the flaw depth with a leakage flux flaw detector.
The leakage was prevented by these magnetic flux flaw detectors, and it was once classified as a material that does not conform to the flaw determination. As for the inspected material 7, since the flaw depth is very shallow,
The material has passed the strict criteria. The material to be inspected No. 5, No. In No. 6, the actual flaw depth itself is shallower than the standard, but due to strict criteria, it became a material that did not meet the flaw criteria. After this, these inspected material Nos. Which were once classified as non-compliant with flaw standards were used. For 1 to 6,
Furthermore, the actual flaw depth was checked by grinding, etc., and the No. 5, No. It was confirmed that the actual flaw depth was shallower than the standard, and therefore, No. 6 passed, and the remaining inspection material No. 6 was obtained. With respect to 1 to 4, it was confirmed that there was a quenching crack flaw deeper than the standard, and the outflow of these flaw standard non-compliant materials was prevented.

[0014]

As described above, according to the method of the present invention, it is possible to prevent erroneous outflow of the flaw standard nonconforming material having a flaw deeper than the standard.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a comparison of a leakage magnetic flux in the case where there is no scale inside the flaw and in a case where the flaw is full.

FIG. 2 is a diagram showing a relationship between a flaw signal of a material to be inspected, a true flaw depth, and a judgment criterion.

[Explanation of symbols]

1 steel bar 2 Burn cracks 3 scale 4 Leakage magnetic flux

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tomohide Uno             No. 3007 Nakajima-Character Nakashima, Himeji City, Hyogo Prefecture               Sanyo Special Steel Co., Ltd. (72) Inventor Masaki Miyamoto             No. 3007 Nakajima-Character Nakashima, Himeji City, Hyogo Prefecture               Sanyo Special Steel Co., Ltd. F term (reference) 2G053 AA11 AB22 BA02 BA13 BB10

Claims (2)

[Claims] Claim: What is claimed is: 1. What is claimed is:
First, the leakage magnetic flux flaw detector is used to make a judgment based on a stricter judgment standard than the customer's standard to classify it into a material that passed the judgment and a material that does not meet the judgment. A method for preventing the outflow of flaw standard non-conforming material, characterized in that the flaw depth is judged according to the customer's standard by confirmation by polishing, and it is classified into a material that has passed the judgment and a material that does not conform to the flaw standard. 2. The flaw standard according to claim 1, wherein the criteria for judging by the leakage flux flaw detector is that a flaw signal with a flaw depth of 0.2 mm or less, which is stricter than the customer's standard, is passed. How to prevent outflow of incompatible materials.