JPH01291149A - Detecting method for defect of material to be inspected - Google Patents

Abstract

PURPOSE:To detect a defect of a material to be inspected by on-line with high accuracy by detecting a surface temperature of the material to be inspected before the material to be inspected which has been brought to quenching is recuperated and the surface temperature is equalized. CONSTITUTION:In order to detect a surface defect of a wire rod 16, a surface temperature of the wire rod 16 which has been brought to quenching in a water cooling zone is detected by a temperature detector 24, while tracking, and recorded in a recorder 28. In this state, in case when a temperature fall exceeding a prescribed threshold has been generated against an average value of the surface temperature, it is decided that a defect exists, and by allowing the tracking length and a temperature fall position to correspond to each other, a position of a defect part is specified. Also, in case when a surface defect exists in the wire rod 16, and the surface defect is a local flaw, a temperature falls within a short range, and in case of a continuous flaw, a temperature falls within a long range. Accordingly, whether the flaw is a local flaw or a continuous flaw can be known from the width of the temperature fall. In such a way, a defect of a material to be inspected can be detected with high accuracy by on-line.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for detecting defects in materials to be inspected, and in particular detects surface defects such as bald eaves and internal defects caused by entrainment of non-metallic inclusions in hot-rolled wire rods, steel bars, and shaped steel. The present invention relates to a method for detecting defects in materials to be inspected, which is suitable for use in many cases.

[Conventional technology]

If rolled materials such as wire rods, steel bars, or shaped steel manufactured on a hot rolling line have flaws on the surface of the product,
The defect must be corrected in a subsequent line, and if the eaves cannot be corrected, the finished product must be removed from the line. Therefore, the surface flaws on the product must be detected accurately after rolling. As a technique for detecting surface flaws in metal materials such as wire rods and steel bars as described above, there is a surface flaw detection method using a hot eddy current flaw detection device as disclosed in Japanese Patent Application Laid-Open No. 53-13977. That is, in this method, first, the surface layer is heated by passing an induced current through an induction heating coil (flaw detection coil) to a depth corresponding to the depth of a flaw in the metal material. Then, the flaw detection coil or the metal material is moved relatively to sequentially inductively heat the surface of the metal material. In this case, in the part of the metal material where the surface flaw exists, the induced current concentrates in a narrow area and the temperature becomes higher than that of the normal part of the metal material. The system is designed to detect flaws. Therefore, if a hot eddy current flaw detection device is used, surface flaws in a rolled material can be detected online.

[Problem to be solved by the invention]

However, there are various problems in flaw detection of rolled materials etc. using the hot eddy current flaw detection apparatus as described above, as described below. In other words, in order to maintain flaw detection accuracy, the distance between the flaw detection coil and the test material must be kept constant and extremely short (for example, about 1 to 3 cm).
As a result of this, scratches, chips, etc. may occur in rolled products. Furthermore, each time the dimensions of the material to be inspected are changed, it is necessary to replace the flaw detection coil with one of a different diameter in order to maintain accuracy, but this replacement work is time-consuming and imposes a large workload. Furthermore, when a rolled product that has been rolled at high speed is used as a material to be inspected, the accuracy in detecting continuous flaws is reduced. In addition, hot eddy current flaw detection equipment has a problem in that its equipment costs, spare parts, etc. are high and expensive. By the way, defects that exist in rolled materials include, in addition to the above-mentioned surface defects, internal defects that occur during the manufacturing process and the like. Conventionally, there was no technology that could detect such internal defects online in a rolling line. In addition, inspection for internal defects is not carried out at the finished product stage after rolling because the length of the product is long and the number of countries required. was occurring. Therefore, there has been a need for a technology that can continuously detect internal defects in test materials online.

[Purpose of the invention]

The present invention has been made in order to solve the above-mentioned conventional problems, and is capable of accurately detecting defects in a test material online without using an eddy current flaw detector or in combination with an eddy current flaw detector. The purpose is to provide a method for detecting defects in inspection materials.

[Means to solve the problem]

The present invention is a method for detecting defects in a test material, in which the test material is rapidly cooled, and the surface temperature of the test material is detected before the rapidly cooled test material recovers heat and its surface temperature becomes uniform. However, the above object is achieved by detecting defects in the material to be inspected based on the detected surface temperature. Further, the defects of the test material to be detected may be either surface defects or internal defects, and regarding surface defects,
The detected surface temperature is detected based on the presence of a portion where the detected surface temperature is lower than other portions, and an internal defect is detected based on the presence of a portion where the detected surface temperature is higher than other portions. be able to.

[Operation and effects of the invention]

Hereinafter, the present invention will be applied to a case where defects are detected in a rolled material 11 finish-rolled by a finishing mill 10 as shown in FIG. This will be explained using an example. Now, suppose that after a rolled material is hot-rolled, it is rapidly cooled in a short time (hereinafter referred to as quenching) by supplying cooling water. At this time, if there are surface defects such as scratches on the surface of the rolled material, the thermal conductivity locally increases depending on the form of the defect, so the area where the defect exists (hereinafter referred to as defective area) , the area is cooled more strongly than the area where no defects exist (hereinafter referred to as the normal area). The difference in cooling results between the normal part and the defective part will be explained next. An example of the result of detecting the temperature of the rolled material 11 (in this case, steel material) that is rolled in the finishing rolling 810, air-cooled, and then cooled in the water-cooling zone 12, and recording this detected temperature with the recorder 28 described later. is shown in Figure 2. In this case, the steel material after finish rolling has a normal section with a cross-sectional shape as shown in FIG. 3(A) and a defective section with a cross-sectional shape as shown in FIG. 3(B). In addition, the steel material has a temperature of 900 to 1100°C on the 12-person side of the water cooling zone, and is conveyed on the line at a speed of 10 to 100 m and 7 seconds.
Enter water cooling zone 12. The water cooling zone 12 has a length of 7.5 to 22 m, and has a cooling capacity capable of rapid cooling with a heat transfer coefficient a = 2000 to 12000 Kcal/rh''C. , a radiation thermometer 14 for detecting temperature from heat radiation is provided, and the detection result of this thermometer 14 is recorded by the recorder 28. In addition, in FIG. 2, the solid line A indicates the surface temperature of the normal area. , and the dashed-dotted line B is the surface TfJ temperature of the defective part.The broken line A1 in FIG. 2 is the average temperature of the normal part, and the dashed-two dotted line B1 is the average temperature of the defective part. As shown in Fig. 2, during water cooling, the surface temperature of the defective part is significantly lower than that of the normal part, causing local temperature unevenness. ,
This is because the test material changes from a film boiling state in which it is always covered with a vapor film of cooling water to a nucleate boiling state in which steam bubbles are generated independently at defective parts, and the cooling rate becomes faster. Therefore,
Detects surface defects on the test material from the presence of parts where the surface temperature after water cooling is lower than the surface temperature of the normal part, such as flaws that have caused a change in the cross-sectional area or surface area of the test material. be able to. However, once the material to be tested has ripened and the surface temperature has become uniform, it is no longer possible to identify the defective part, so it is necessary to detect the surface temperature before reheating. For example, in FIG. 2, it is desirable to detect the temperature at the time indicated by C. The present invention was made based on such knowledge,
According to the present invention, surface defects can be detected online with high precision, and the quality of the material to be inspected can be enhanced. Furthermore, the temperature detection device is less expensive than the eddy current detection device, so it is more economical. Furthermore, unlike an eddy current detection device, there is no need to replace the detection coil depending on the size of the material to be inspected, so defects can be detected in a simple procedure. Furthermore, as will be described later, it is possible to detect defects even in cases of continuous defects that could not be detected by the eddy current detection device. In addition, when detecting the surface defects, by using the method of the present invention in combination with a hot eddy current flaw detector, it is possible to prevent overlooking of surface defects and further improve the accuracy of defect detection. According to their measurements, when the defect detection rate of the hot eddy current flaw detector is 96% and the detection rate of defects detected using the present invention is 92%, it is possible to increase the defect detection rate by using both together. I can't increase it to 98%. On the other hand, if there are internal defects such as non-metallic inclusions rather than surface defects in the specimen material such as steel as described above, a difference in thermal conductivity occurs due to the influence of the internal defects, and the specimen material is cooled. Even if the surface is rapidly cooled with water or the like, the surface of the portion where the internal defect exists is cooled more slowly than the surface of the normal portion, resulting in a high temperature. Therefore, the presence of internal defects in the material to be inspected can be determined from this difference in surface temperature. As mentioned above, in order to find out that the surface temperature drop during cooling of the portion of the test material where internal defects are present is small, the inventors conducted a simulation to find out when a plurality of test materials with predetermined internal defects were rapidly cooled. The temperature change was measured. Figure 4 shows the measurement results. In this case, as shown in Figure 4, the test material had an outer diameter of 5.5 qm and an internal defect diameter d of 0.1.2 u. After heating it to 1,050°C, it was fed at a conveying speed of 9,011/sec to a thermal conductivity of α = 11,000 cal/h°C.
Cooling water was supplied for rapid cooling. From FIG. 4, it is understood that the temperature drop due to cooling is smaller when an internal defect exists (d=1.2 am) than when there is no internal defect (d=0).For example, In the results shown in the figure, the temperature of each test material 0.5 seconds after cooling is 853°C when there is no internal defect, and 964°C when there is an internal defect (d==1.2+am).
℃, 997℃. Therefore, by detecting the surface temperature of the test material after quenching, internal defects can be detected from the presence of a portion with a higher surface temperature than the pond portion. Therefore, it is possible to accurately detect internal defects in steel materials, etc. during the rolling process, which could not be detected in the past, online, and there will be no processing defects due to defects in the secondary processing process.
It is possible to strengthen the quality assurance of steel bars, shaped steel, and other materials to be inspected. In the above explanation, high-temperature steel was used as an example of the material to be tested, and cooling water was supplied to it, but the material to be tested is not limited to such materials. As long as the material to be tested can be rapidly cooled in relation to the coolant supplied to it, it can be used with any material to be tested (e.g. hot-formed material) and with any coolant. , with which the present invention can be implemented.

【Example】

Embodiments of the present invention will be described in detail below with reference to the drawings. In this embodiment, the surface of a hot-rolled wire rod or bar (hereinafter abbreviated as wire rod) 16 is uniformly cooled in a water cooling zone 12 shown in FIG. The temperature of the entire circumferential surface of the wire rod 1 is measured, and based on this temperature measurement result, as described later,
This device is designed to detect surface defects or internal defects. In FIG. 0, the water cooling zone 12 is provided with a water cooling nozzle 18 having the structure shown in FIG. The signal system after the radiation thermometer 14 is as shown in FIG. 6. As shown in FIG. 0, the radiation thermometer 14 is equipped with a temperature detector 24 and a signal converter 26. The thermometer 14 and the recorder 28 measure the rolling speed of the wire rod 16,
That is, it is capable of high-speed response and has a response frequency that corresponds to the conveyance speed, and for example, one that has a loop response from temperature detection to recording with a response speed of 1 to 2 (INS) or less can be used. The output of this signal converter 26 is input to a recorder 28 and an alarm output device 30. The recorder 28 is for recording the detected temperature on a recording chart. Further, the alarm output device 30 issues an alarm when a temperature higher than a set value is detected, indicating that a defect has occurred, and marks the defective portion. The effects of the embodiment will be explained below. First, in order to detect surface defects in the wire rod 16, the surface temperature of the wire rod 16 after being rapidly cooled in the water cooling zone 12 is recorded on the recorder 28, and the results of flaw detection of the same wire rod with a hot eddy current flaw detector are recorded in the seventh test. In addition, since the time axis of the thermometer and the time axis of the eddy current flaw detector shown in the figure are displayed differently,
In the figure, detected values at corresponding locations on the wire 16 are connected by broken lines. From the figure, it can be seen that the detection results of the eddy current flaw detector and the area where the temperature has decreased are in good agreement, and therefore, 1. It is understood that surface defects can be detected with high accuracy by implementing the present invention and detecting the temperature. Specifically, the surface temperature of the wire 16 is detected while tracking, and if the temperature decreases by more than a certain threshold value with respect to the average value of the surface temperature, it is determined that a defect exists, and the tracking length and temperature decrease are determined. The position of the defective part is identified by matching the positions. In addition, the types of defects corresponding to each part are described in the figure. Moreover, the type of defect can also be known using the temperature record. That is, as shown in FIG. 8, if there is a surface defect on the wire 16, and the surface defect is a local flaw indicated by reference numeral 32 or a continuous flaw indicated by reference numeral 34, as shown in FIG. Temperature recording results will be obtained. In the case of the local flaw 32,
The temperature decreases in a short range as shown by the reference numeral 36 in FIG. 9, whereas in the case of continuous flaws, the temperature decreases in a long range as shown by the reference numeral 38 in the figure. Therefore,
From the width of this temperature drop, it can be determined whether the flaw is a local flaw or a continuous flaw. On the other hand, when flaw detection is performed using an eddy current flaw detector, as shown in Figure 10, flaw signals are output for local flaws and defects can be detected, but continuous flaws cannot be detected. Therefore, when trying to detect surface flaws using the method of the present invention, it is possible to detect even types of flaws (continuous a:) that cannot be detected with an eddy current flaw detector, and the range of defects that can be detected is wide. That is understood. Next, a case will be described in which internal defects in the wire rod 16 are detected using the apparatus of this embodiment. After being rapidly cooled in the water cooling zone 12, using the radiation thermometer 14,
The results of temperature detection from the tip to the tail end of the wire 16 are shown in FIG. 11. As shown by the symbol ThH in FIG.
It was confirmed that there were internal defects due to non-metallic inclusions (for example, powder) in the high-temperature area. Specifically, the surface temperature of the wire 16 is detected from its tip to its tail while tracking, and this detected temperature is compared with the average value of the temperature. If the difference is higher than a predetermined threshold, it is determined that there is a defect. The presence of an internal defect and the position of the internal defect in the wire 16 were detected by determining that the defect existed and identifying the position of the high temperature portion by associating the determination 1 result with the position on the wire 16. The inventors used the above-mentioned device to detect six cases of internal defects caused by non-metallic inclusions in the wire, and prevented them from flowing downstream of the line, thereby preventing processing problems in the downstream. In the above embodiments, rolled materials such as wire rods, steel bars, and shaped steel were exemplified as test materials, but the test materials to which the present invention can be used are not limited to these, and other test materials can also be used. For example, it can be used to detect defects in hot forged materials.

[Brief explanation of the drawing]

FIG. 1 is a layout diagram including a block diagram showing the configuration of an embodiment of the apparatus of the present invention, and FIG. 2 is a diagram showing the surface temperature of a normal part of a rapidly cooled steel material, for explaining the present invention in detail. A diagram showing an example of a change in surface temperature of a surface defect. Figure 3 is a cross-sectional view showing a normal part and a defective part of the wire. Figure 4 shows a temperature change when a specimen with an internal defect is rapidly cooled. 2 and 5 are cross-sectional views showing the detailed structure of the water cooling nozzle provided in the water cooling zone of the apparatus of the embodiment, and FIG. 6 is the electrical structure of the temperature detection system of the apparatus of the embodiment. FIG. 7 is a diagram comparing the temperature detection results of the above-mentioned example device with the flaw detection results of the hot eddy current flaw detector. FIG. 8 is an enlarged view of the main part showing the types of surface flaws on the wire rod 9 shows a line section showing an example of detecting surface defects of a wire from the temperature record results of the wire using the apparatus of the embodiment, and FIG. Diagram showing an example of flaw detection, 1st
FIG. 1 is a diagram showing an example of detecting internal defects from the results of temperature detection by the apparatus of the embodiment. 10... Finishing rolling mill, 11... Rolled material, 12... Water cooling zone, 14... Radiation thermometer, 16... Wire rod, 18... Water cooling nozzle, 20... Cooling water supply Port, 22... Air pressure inlet, 24... Temperature detector, 26... Signal converter, 28... Recorder, 30... Alarm output device.

Claims (3)

[Claims] (1) The test material is rapidly cooled, and the surface temperature of the test material is detected before the rapidly cooled test material recuperates and its surface temperature becomes uniform. Based on the detected surface temperature, the test material is A method for detecting defects in a material to be inspected, characterized by detecting defects in the material to be inspected. (2) In claim 1, the defect to be detected is a surface defect, and the surface defect is detected based on the presence of a portion where the detected surface temperature is lower than other portions. A method for detecting defects in materials to be inspected. (3) In claim 1, the defect to be detected is an internal defect, and the internal defect is detected based on the presence of a portion where the detected surface temperature is higher than other portions. A method for detecting defects in materials to be inspected.