Microscopic measurement method for thinning rate of thin steel plate tensile sample

Abstract

The invention discloses a microcosmic measurement method for the thinning rate of a thin steel plate tensile sample, which comprises the following steps: drawing a straight line on the sample as a mark, shearing a fracture of a steel plate along the marked straight line on a plate shearing machine, and placing two separated parts adjacent to each other after the fracture; adjusting the plane of the fracture after the tensile test to be perpendicular to the direction of the sample table, enabling the fracture direction to be upward, setting SEM parameters, observing the shape of the rectangular fracture by using the SEM, obtaining an electronic image, and shooting a low-multiple and full-fracture macroscopic shape picture of the tension rectangular fracture; measuring numerical values in the thickness direction of the sample on the fractured sample for multiple times, and after the position of the minimum thickness is determined, measuring to obtain the minimum thickness value; and the thinning rate is calculated according to a national standard formula. The technology reduces the measurement error of the thinning rate of the tensile sample in the production process of cold and hot rolled sheets, reduces the cost, and is more visual and accurate.

Description

Technical Field

[0001] The invention relates to a microscopic measurement method for the thinning rate of a thin steel plate tensile specimen, and belongs to the field of material analysis and testing. Background Art

[0002] In the field of tensile testing of metal materials, rectangular tensile specimens are used for tensile testing. The thickness change of the specimens at a specified engineering strain level or after tensile fracture is measured, and the relevant parameters of the thinning rate are calculated. The thinning rate of the specimens after cold and hot rolled thin plate tensile testing is one of the important quality evaluation indicators in the material forming process. The thinning rate detection method is based on the national standard "GB / T33965-2017 Metal Material Tensile Test Rectangular Tensile Specimens Determination of Thinning Rate". The thickness of the necking part of the specimen after fracture is measured, and the thinning rate is calculated as the percentage of the change in the specimen thickness direction to the original thickness. The measurement of the thinning rate of the tensile specimen after fracture is an important technical link in the entire test work. Whether the measurement process is convenient will affect the detection efficiency of large quantities of specimens.

[0003] The thinning rate refers to the percentage of the ratio of the change in the thickness direction of the specimen to the original thickness. When measuring the thickness, measure the thickness values at the center and both ends of the gauge length respectively, and take the arithmetic mean as the original thickness. After visiting, investigating and searching the literature, at present, in order to complete the measurement of the thinning rate of rectangular tensile specimens of metal materials after fracture, the broken parts of the specimens need to be carefully matched together so that the axes are in the same straight line. Generally, two operators are required to cooperate with each other. One operator is responsible for adjusting the position of the specimen and fixing the specimen, and the other operator holds a pointed micrometer to measure the minimum thickness of the necked part of the specimen. This working mode not only reduces work efficiency, but also makes it difficult to ensure the accuracy and consistency of the measurement, especially for thin steel plates. Therefore, GB / T33965-2017 has a large error in measuring the thinning rate of tensile specimens of thin steel plates (≤3mm).

[0004] The present invention provides a technical method for measuring the thinning rate of a steel plate tensile specimen with an original thickness of 3 mm or less by using a scanning electron microscope (SEM), thereby reducing the measurement error of the thinning rate of the tensile specimen in the industrial production process of cold-rolled and hot-rolled thin plates and lowering production costs. Summary of the Invention

[0005] This invention provides a microscopic measurement method for thinning reduction of steel plate tensile specimens with an original thickness of 3 mm or less using a scanning electron microscope. Leveraging the scanning electron microscope's large depth of field and high, adjustable magnification, it addresses the challenges of manual measurement, including low efficiency and the inability to guarantee accuracy and consistency. This method is more accurate, scientific, convenient, and intuitive to operate, filling a gap in this field.

[0006] A microscopic measurement method for thinning rate of a thin steel plate tensile specimen, comprising the following steps:

[0007] (1) Sample preparation: Draw a straight line on the sample as a mark, and cut the steel plate along the marked line on the shearing machine. Place the two parts after the fracture next to each other to ensure that the sample can be placed stably on the sample table. If the sample shakes, fix the sample first.

[0008] Preferably, the mark should be parallel to the fracture surface of the tensile rectangular fracture of the steel plate.

[0009] Preferably, due to the depth of field limitation of the scanning electron microscope, the fracture specimen height should be ≤5 cm.

[0010] (2) Scanning electron microscope photography: After the tensile test, the fracture plane should be adjusted to be perpendicular to the sample stage, with the fracture direction facing upward. Subsequently, appropriate scanning electron microscope parameters are selected, and the rectangular fracture morphology of the steel plate under tension is observed using a scanning electron microscope (SEM). Secondary electron images of the measured fracture morphology are obtained, and low-magnification and full-fracture macroscopic morphology images of the rectangular fracture of the steel plate under tension are taken.

[0011] Preferably, the parameters of the scanning electron microscope are an operating voltage of 15 to 20 kV and a working distance of 10 to 15 mm.

[0012] (3) Minimum thickness measurement: Scanning electron microscopy (SEM) is used to analyze the rectangular tensile fracture morphology and determine the minimum thickness of the fracture surface. Local defects (such as iron oxide scale, cracks, etc.) should not be considered. The thickness direction of the fractured specimen needs to be measured multiple times to determine the minimum thickness position, and then the minimum thickness value is obtained by measurement again. To ensure the accuracy of the measurement results, the minimum thickness position is measured three times and the average value is taken.

[0013] (4) Calculation of thinning rate: Calculate the thinning rate value according to the formula in GB / T33965-2017.

[0014] The present invention provides a microscopic measurement method for the thinning rate of a thin steel plate tensile specimen with an original thickness of ≤3 mm using a scanning electron microscope (SEM), thereby reducing the measurement error of the thinning rate of the tensile specimen during the industrial production of cold-rolled and hot-rolled thin plates and lowering production costs. Compared with the prior art, the thickness accuracy of a thin steel plate with a small deformation is very poor when measured with a micrometer. The scanning electron microscope can magnify the fracture, measure multiple positions to determine the minimum position, and then measure the thinning value, otherwise it will be inaccurate. The technology of the present invention solves the problem of low work efficiency and large errors when manually measuring the thinning rate of a thin steel plate (≤3 mm) tensile specimen, and the inability to guarantee the accuracy and consistency of the measurement. This microscopic measurement method is more intuitive and accurate, filling the detection gap in this area. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is the rectangular tensile fracture morphology observed by scanning electron microscopy (SEM). DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of an exemplary embodiment of the experimental device and method is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0017] Specific implementation method: Take the tensile test specimen of 1180MPa cold-rolled plate with original thickness H=1.6mm as an example.

[0018] Step 1: Sample preparation: Draw a straight line 4 cm from the tensile rectangular fracture surface of the cold-rolled plate. Cut the steel plate along the marked line on a shearing machine. Place the two separated parts next to each other to ensure that the sample can be placed stably on the sample table. If the sample shakes, it should be fixed first.

[0019] Step 2: After the tensile test, the fracture plane should be adjusted perpendicular to the sample stage, with the fracture facing upward. Select HV = 20 kV and WD = 15 mm. Observe the tensile rectangular fracture morphology of the steel plate using a scanning electron microscope (SEM). Take low-magnification and full-fracture macroscopic images of the tensile rectangular fracture of the steel plate.

[0020] Step 3: Use scanning electron microscopy (SEM) to analyze the morphology of the rectangular tensile fracture and determine the minimum thickness of the fracture surface. Local defects (such as iron oxide scale, cracks, etc.) should not be considered. Use scanning electron microscopy to shoot low magnification (7 times), measure the value of the thickness direction of the sample multiple times, determine the minimum thickness position, and then measure again to obtain the minimum thickness value. After three measurements, the sample thicknesses are 1# (top) sample: 845.5μm, 1005.0μm, 798.1μm; 2# (bottom) sample: 846.7μm, 1008.0μm, 894.5μm. The minimum thickness is determined to be: 1#: 882.9μm, 2#: 916.4μm, as shown in the figure.

[0021] Step 4: Calculate the thinning rate according to the formula in GB / T33965-2017. The calculated thinning rates are 1#: 44.8% and 2#: 42.7%.

Claims

1. A microscopic measurement method for thinning rate of thin steel plate tensile specimen, characterized in that: Draw a straight line on the specimen as a mark, cut the steel plate fracture along the marked straight line on a shearing machine, and place the two separated parts adjacent to each other after breaking; adjust the fracture plane after the tensile test to a direction perpendicular to the sample stage, with the fracture direction facing upward, set the scanning electron microscope parameters, observe the rectangular fracture morphology of the tensile steel plate using a scanning electron microscope, obtain the secondary electron image of the measured fracture morphology, take low-magnification and full-fracture macroscopic morphology pictures of the tensile rectangular fracture of the steel plate, determine the minimum thickness position, and measure the value in the minimum thickness direction of the specimen; calculate the thinning rate according to the formula in GB / T33965-2017.

2. The microscopic measurement method of thinning rate of thin steel plate tensile specimen according to claim 1, characterized in that: The mark should be parallel to the fracture surface of the tensile rectangular fracture of the steel plate.

3. The microscopic measurement method of thinning rate of thin steel plate tensile specimen according to claim 1, characterized in that: The height of the fracture specimen should be ≤5cm.

4. The microscopic measurement method of thinning rate of thin steel plate tensile specimen according to claim 1, characterized in that: The parameters of the scanning electron microscope include an operating voltage of 15 to 20 kV and a working distance of 10 to 15 mm.

5. The microscopic measurement method of thinning rate of thin steel plate tensile specimen according to claim 1, characterized in that: Measuring the thickness of the fractured specimen requires measuring the value in the thickness direction of the specimen multiple times to determine the minimum thickness position.

6. The microscopic measurement method of thinning rate of thin steel plate tensile specimen according to claim 5, characterized in that: The minimum thickness position is measured three times and the average value is taken.

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