JPS5817352A - Inclusion detection method for hot-rolled sheets and hot-rolled pickled sheets - Google Patents

Abstract

PURPOSE:To inspect debris in a hot rolled plate or a deoxidized hot rolled plate by magnetic flaw detection thereof after surface defects are removed from the top surface and the bottom surface thereof during the casting. CONSTITUTION:A sample is made in size of about 300mm. in length x overall out of a hot rolled strip about 2.5mm. thick obtained from a hot rolling of a cast piece produced by a curved continuous casting method by cutting it off at the tail end of the rolling. Then, the surface of the sample corresponding to the top surface during the hot rolling is ground away by 200mum while the opposite surface thereof is ground off away by 30mum and then, a visual inspection is conducted to make use that there is surface flaw left. After that, the surface thereof corresponding to the top surface thereof during the hot rolling undergoes a magnetic powder detection to inspect debris therein.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting inclusions in a hot-rolled sheet or a hot-rolled pickled sheet, and particularly for those with a thin thickness, for example,
It is intended for those with a thickness of 3.

Examples of steel plates that have extremely strict inclusion cleanliness requirements include tinplate for DI cans, tin-free steel, and cold-rolled steel for the inside of automobile outer panels. That's a problem.

Conventionally, inclusion inspection has been carried out using magnetic flaw detection at the final product stage of tinplate, etc.1, but this method limits where the product can be transferred in the event of a failure, and it takes a long time to produce the product again. There was a problem that it was necessary.

However, when hot-rolled steel strip or hot-rolled pickled steel strip is sold as a material for tinplate etc., inspection for inclusions is not currently carried out for various reasons. If it is possible to detect inclusions in a certain hot-rolled sheet or hot-rolled pickled sheet, it will be of great industrial value, and the effects of improving yield and reducing costs can be expected.

Now, it is now well known that it is advantageous to manufacture steel materials with strict requirements for inclusion cleanliness by continuous casting.
In particular, it is common to cast by a curved continuous casting method. Regarding the inclusion distribution of slabs cast by the curved continuous casting method, the distribution of inclusions is from 0 to 30% in the slab thickness direction from the top surface (hereinafter referred to as the "down surface") side at the time of casting (ratio to slab thickness). It is known that it is distributed in Therefore, from 5% to 3% of the surface layer of the surface corresponding to the slab surface of the hot-rolled plate or hot-rolled pickled plate
A method of inspecting inclusions by magnetic flaw detection after removing a portion equivalent to 5% was separately developed and previously filed.

By the way, this method can be applied to plate thickness 1. C1+w to 4.0 proverbial heat □When applied to rolled sheets or hot-rolled pickled sheets, it is possible to detect surface defects on the opposite surface to the above-mentioned surface, that is, the back surface (hereinafter referred to as 2nd surface), in addition to inclusions. Newly discovered. tsut, 9t
It has been found that magnetic flaw detection using only surface polishing has the problem of detecting more defects than the number of inclusions actually present in the steel sheet.

An object of the present invention is to provide a method for performing magnetic flaw detection after removing surface defects not only on the L-plane but also on the F-plane, in order to solve the drawbacks of the previous methods as described above. .

The method of the present invention will be explained in detail below.

Generally, on the front and back surfaces of hot rolled steel strip or hot rolled pickled steel strip,
There are surface defects that do not hinder operations such as cold rolling.

Among these surface defects are hot rolling roll indentations,
There are flaws with smooth irregularities, such as roll marks printed on the steel material during rolling, but there are also flaws with sharp edges, such as scratches and percussion flaws, which are caused by contact with the rolling line table, etc. It will be done. In magnetic flaw detection of hot rolled sheets, it is the latter sharp defects that are detected as surface defects on the back side of the flaw detection surface.

In particular, when a section is cut out from a hot-rolled steel strip or hot-rolled pickled steel strip and subjected to magnetic flaw detection in a sampling inspection, the most economical method is to collect samples for flaw detection from both ends of the copper strip. However, both ends of the copper strip have many surface defects such as scratches and scratches that pose problems in magnetic testing.

Furthermore, after cutting the sample for flaw detection from the copper strip, there is a high possibility that there will be handling flaws until it is subjected to magnetic flaw detection, and surface defects on the back side of the flaw detection surface become a serious problem when detecting inclusions.

The influence of surface defects on the back surface of the surface to be detected in inclusion inspection using magnetic flaw detection of hot rolled steel sheets was confirmed as follows.

That is, from a slab cast by the curved continuous casting method, the plate thickness is 2.
A hot-rolled plate with a length of 300m+ was cut out from the rolling tail side end of a 5mm hot-rolled copper strip, and the surface corresponded to the L surface (this was the top surface during hot rolling). From 200
After removing μm by polishing, the magnetic powder (BY
Flaws were detected using a 9000° magnetic powder solution with a concentration of 0.4% (volume ratio).

After that, the F side (lower surface during hot rolling) is 20 μm each,
After polishing to 50 μm and 80 μm, magnetic flaw detection was carried out under the flaw detection conditions as described above and P1.

Figure 1 shows the relationship between the F-surface polishing depth and the detected magnetic particle lines.

Figure 1 is a graph in which the horizontal axis shows the polishing depth (μm) from the F plane, and the vertical axis shows the number of magnetic particle lines/samples (pieces) detected from the L plane, and the numbers in the graph indicate the number of particles. .

At the same time, the surface defects (presumed to be scratches based on the morphology) on the second side were visually counted and the results are shown in FIG.

In Figure 2, the horizontal axis shows the F surface polishing depth (μm), and the vertical axis shows the F surface polishing depth (μm).
Visually visible surface flaws/sample taken.

When the C cross section (the surface perpendicular to the rolling direction) of the magnetic powder wire portion remaining after polishing 80 μm on the F side was examined using a microscope with a magnification of 500 times, inclusions were found in all of the parts. In other words, it can be seen that F-face grinding is a very accurate flaw detection method.

Generally, the depth of surface defects on hot-rolled sheets or hot-rolled pickled sheets is 20 μm to 50 μm, and from this test result, 20 μm
It was confirmed that accurate flaw detection can be expected by polishing the entire surface to about 50 μm and then polishing until there are no visible surface defects.

Examples are shown below.

Example: A sample having a length of 3QQ11111 After removing 200 μm from the surface side and polishing 30 μm from the F side, it was visually confirmed that no surface flaws remained, and magnetic particle flaws were detected from the L side.

The hot-rolled copper strip from which this sample was cut is 0.211111.
After cold rolling and finishing into tinplate products, magnetic flaw detection was performed.

As a result, the number of inclusions detected by magnetic flaw detection in hot rolled sheets according to the present invention/number of inclusions detected by magnetic flaw detection in samples and tinplate products/
rr? As shown in Fig. 3, a good correspondence can be seen.

Figure 3 shows the number of magnetic powder wire sides/sample of the hot-rolled sheet on the horizontal axis.
The vertical axis represents the number of magnetic particle lines/m' on the tin plate, and this also confirms the effectiveness of the flaw detection method of the present invention.

[Brief explanation of drawings]

Figure 1 is a graph showing the comparison between the F-side polishing depth and the number of magnetic particle lines detected from the L-side/sample, and Figure 2 is a graph showing the comparison between the IdF-side polishing depth and the number of visible surface flaws on the F-side. The graph shown in FIG. 3 is a graph showing a comparison between the number of magnetic particle wire sides/sample obtained by magnetic flaw detection of a hot-rolled sheet and the number of magnetic powder wire sides/m' measured by magnetic flaw detection of a tinplate plate. Rod 1 time Rod 2 figure F tP et al. 75 Ji Tang liveliness

Claims (1)

[Claims] To detect inclusions in a hot-rolled plate or a hot-rolled pickled plate manufactured from a slab cast by the curved continuous casting method from the surface corresponding to the top surface during casting using the leakage magnetic flux detection method. A method for detecting inclusions in a hot-rolled sheet and a hot-rolled pickled sheet, which comprises performing magnetic flaw detection after removing surface defects on the surface to be tested and the opposite surface.