CN105352966A - A method for inspecting the internal quality of high carbon steel continuous casting slabs - Google Patents

Abstract

The invention relates to a method for inspecting the internal quality of a high-carbon steel continuous casting billet, belonging to the technical field of inspection of the internal quality of the continuous casting billet. The technical scheme is as follows: firstly, processing a continuous casting blank into a strip shape or a block shape, then carrying out quenching and tempering heat treatment on a processed sample, carrying out milling, grinding and polishing treatment on the heat-treated sample, carrying out deep corrosion on a polished surface by using a nitric acid alcohol corrosive liquid with the concentration of 4%, then carrying out metallographic detection by using inspection equipment such as an optical lens/electron microscope and taking a photo, and using an inspection image by using a computer Adobe? Photoshop software performs image processing. The invention can more clearly and comprehensively display solidification structures such as a casting blank chilling layer, columnar crystals, mixed crystals, equiaxial crystals and the like, and accurately obtain casting blank structure information such as primary dendrite spacing, secondary dendrite spacing, equiaxial crystal size and the like; the control condition of the casting blank segregation is displayed more clearly, the metallographic picture image is processed by software, qualitative and quantitative analysis of defects such as a casting blank segregation zone, the number of carbides, the size and the like is realized, objective evaluation is carried out on the internal quality of the casting blank, and the improvement and optimization of the continuous casting process are guided.

Description

A method for inspecting the internal quality of high carbon steel continuous casting slabs

technical field

The invention relates to a method for inspecting the internal quality of high-carbon steel continuous casting slabs, and belongs to the technical field of internal quality inspection of continuous casting slabs.

Background technique

At present, the methods used for internal quality inspection of continuous casting slabs are mainly low-magnification structure inspection and microstructure inspection. Commonly used low-magnification inspection methods include hot acid corrosion method, dendrite corrosion, etc., and commonly used microstructure inspection methods include metallographic inspection method, electronic probe, etc. Hot acid corrosion method, such as "A hot acid electrolytic corrosion method for low-magnification inspection of metal samples" in patent application number 200810233915.1, can clearly show various defects inside the slab, such as white spots, cracks, shrinkage cavities, looseness, etc. , can quantitatively evaluate the segregation of the center, but the evaluation is more macroscopic, the solidification structure of the hot acid corrosion cast slab is poor, and the hot acid has a greater impact on workers and the environment; dendrite corrosion technology such as patent application number 201110004123.9 "Continuous casting slab solidification structure and defect dendritic corrosion low-magnification inspection reagent and preparation method" and patent application number 201010274298.7 "Dendrite corrosion low-magnification inspection integrated method" can better display the casting slab solidification structure and various defects The continuous casting process can also be evaluated by quantitatively measuring the distance between dendrites, etc., but the requirements for the corrosion solution and the surface roughness of the sample are relatively high; the metallographic inspection method can clearly display the microstructure of the slab, and can achieve quantitative evaluation, but It is impossible to clearly display the solidification structure of the slab, and it is difficult to distinguish the difference between different position controls inside the slab; the electronic probe can realize the composition analysis of the small composition area of the slab sample, and can perform qualitative and quantitative analysis of the constituent elements. However, the evaluation is relatively microscopic, and the solidification structure of the slab cannot be displayed, and the inspection cost is relatively high.

The above inspection methods for evaluating the internal quality of continuous casting slabs have a wide range of applications and can cover all steel types with carbon content. However, due to the differences between steel types, the internal quality and defect evaluation of some steel types are poor. Patents specifically aimed at the quality inspection of high-carbon steel slabs, such as the application number 200810099408.3 "Reagent for Quickly Displaying Internal Structure Defects of Steel—Cold Decoration Solution", describe corrosive liquids, and focus on displaying structural defects, making it difficult to quantitatively describe the solidification structure of slabs; Patent Application No. 201110096202.7 "Method for Evaluating High Carbon Steel Continuous Casting Billet Longitudinal Section Low-magnification Microstructure Quality" and 201110096212.0 "High Carbon Steel Continuous Casting Billet Longitudinal Section Low-magnification Defect Exposure Method" focuses on evaluating casting billet longitudinal section defects, The method adopted is essentially carbon deviation analysis and acid corrosion, and the solidification structure and internal defects of the slab are poorly displayed and difficult to quantitatively evaluate.

Contents of the invention

The purpose of the present invention is to provide an inspection method for the internal quality of high-carbon steel continuous casting slabs, which uses the corrosion resistance of dendrites and interdendritic tempered structures after quenching and tempering treatment of high-carbon steel (C≥0.77%) casting slabs Significantly different characteristics, the internal quality of the high-carbon steel continuous casting slab is inspected, and the above-mentioned problems existing in the background technology are solved.

The technical scheme of the invention is:

An inspection method for the internal quality of high-carbon steel continuous casting slabs, which uses the characteristics of significant differences in corrosion resistance between dendrites and interdendritic tempered structures after high-carbon steel slabs with C≥0.77% are quenched and tempered. The internal quality of high-carbon steel continuous casting slabs is inspected; firstly, the continuous casting slabs are processed into strips or blocks, and then the processed samples are subjected to quenching + tempering heat treatment, and the heat-treated samples are processed by milling, grinding, and polishing. The concentration of 4% nitric acid alcohol corrosion solution deeply etches the polished surface, and then conducts metallographic inspection with light microscope/electron microscope and other inspection equipment and takes pictures, and uses the computer Adobe Photoshop software for image processing on the inspection image.

More specific process steps are as follows:

Slab Analysis Sample Machining

According to the inspection requirements, the continuous casting slab is processed on a sawing machine, and processed into a strip or block analysis sample with a length ≥ 10mm, a width of 10-20mm, and a height of about 10mm, which is convenient for subsequent heat treatment, machining, metallographic inspection and testing. Image analysis and processing;

Sample quenching + tempering heat treatment

The analysis sample is subjected to quenching + tempering heat treatment; after quenching, the sample is quenched martensite structure, and martensite is a supersaturated solid solution of carbon in α-Fe, which is a metastable phase, and supersaturated carbon atoms have The trend of spontaneous precipitation in the medium, tempering can continuously precipitate ε-carbides coherent with martensite from the martensite; the ε-carbides precipitated by tempering are extremely thin layers, which can be seen under an ordinary metallographic microscope. The results of its precipitation greatly reduce the corrosion resistance of martensite, so after the sample is corroded, the color becomes dark under the microscope, and the solidification structure of the slab can be clearly displayed by using the difference in color of the sample after corroding and internal defects;

Quenching process: temperature 820-840°C, time 20-30min, coolant: oil;

Tempering process: temperature 150°C-300°C, time 60-120min.

Milling, grinding and polishing of heat treatment samples

Place the heat-treated sample on a milling machine for processing, milling off 1-2mm to fully eliminate the influence of the decarburization layer of the sample; analyze and polish the test surface of the sample on the grinding machine, the roughness requirement should reach Ra≤0.8um, and then Polishing treatment, the surface roughness reaches Ra≤0.1um;

Specimen corrosion

Use 4% nitric acid alcohol solution to deeply corrode the surface of the analysis sample to clearly show the solidification structure of the billet, display internal defects such as segregation, shrinkage cavity, cracks, and microstructure morphology such as segregated carbide particles;

Sample metallographic inspection, photographing

The surface of the corrosion sample is subjected to metallographic inspection on light microscope/electron microscope inspection equipment, and photographs are taken to facilitate the analysis and processing of the photos of the internal structure of the slab.

Image Processing

The photographed metallographic images are processed with Adobe Photoshop software to clearly display the dendrite structure, carbide and segregation control of the slab, and quantitatively evaluate the internal quality defects of the continuous casting slab.

The technical key points of the present invention are: quenching+tempering heat treatment is carried out on the high-carbon steel billet processing sample to obtain a tempered structure with a large difference in corrosion resistance; milling, grinding, and polishing the sample of the tempered structure, The 4% concentration of nitric acid alcohol corrosion solution deeply corrodes, clearly showing the solidification structure and internal defects of the cast slab.

The positive effect of the present invention: the corrosion degree of the high carbon steel continuous casting slab compared with hot acid corrosion, dendrite corrosion and other methods in the present invention is lighter, and it can more clearly and comprehensively display the chilled layer of the slab, columnar crystals, mixed crystals, Solidification structures such as equiaxed crystals can accurately obtain information on the slab structure such as primary dendrite spacing, secondary dendrite spacing, and equiaxed crystal size; compared with normal tissue corrosion, the corrosion of defective parts such as segregation zones in the slab is The color difference is obvious, and the segregation control of the slab can be displayed more clearly, especially the display of defects such as eutectic carbides, solidification porosity, and shrinkage cavities in more serious parts; Qualitative and quantitative analysis of slab segregation zone, carbide quantity, size and other defects, objectively evaluate the internal quality of slab, and guide the improvement and optimization of continuous casting process.

Description of drawings

Fig. 1 is the inner quality corrosion figure of GCr15 continuous casting slab in embodiment 1;

The columnar crystal morphology can be clearly seen in the figure, and the secondary dendrite spacing can be accurately measured;

Fig. 2 is the internal mass corrosion figure of cast slab in GCr15 steel among the embodiment 1;

In the figure, you can clearly see the solidification structure morphology in the central area, clearly display the segregation between dendrites, observe defects such as shrinkage cavities and eutectic carbides, and quantitatively analyze the area of segregation regions, shrinkage cavities, and eutectic carbonization quantity, proportion, etc.;

Fig. 3 is the internal mass corrosion diagram of GCr15-Y steel continuous casting slab in embodiment 2;

The equiaxed crystal morphology can be clearly seen in the figure, the segregation between dendrites and eutectic carbides precipitated during solidification can be observed, and the number and size of equiaxed crystals can be accurately measured;

Fig. 4 is the internal mass corrosion diagram of GCr15-Y steel continuous casting slab in embodiment 2;

The equiaxed crystal morphology can be clearly seen in the figure, and the segregation between dendrites, shrinkage cavities and a small amount of eutectic carbide can be observed, and the number and size of equiaxed crystals can be accurately measured;

Fig. 5 is the internal mass corrosion diagram of SWRH82B steel continuous casting slab in embodiment 3;

In the figure, we can clearly see the structure information of the slab edge: fine equiaxed crystals and columnar crystals in the chilled layer;

Fig. 6 is the internal mass corrosion diagram of SWRH82B steel continuous casting slab in embodiment 3;

In the figure, the morphology of columnar crystals and the segregation between dendrites can be clearly seen, and the secondary dendrite spacing can be accurately measured;

Fig. 7 is the internal mass corrosion diagram of SWRH82B steel continuous casting slab in embodiment 3;

The equiaxed crystal morphology can be clearly seen in the figure, and defects such as segregation, porosity, and shrinkage cavity of the cast slab can be observed.

The figure is an internal quality corrosion diagram of SWRH77B steel continuous casting slab in Example 4;

In the figure, the morphology of columnar crystals and equiaxed crystals can be clearly seen, and slab segregation and loose defects can be observed.

Fig. 9 is the internal mass corrosion diagram of SWRS87B steel continuous casting slab in embodiment 4;

In the figure, the morphology of columnar crystals and the segregation between dendrites can be clearly seen, and the secondary dendrite spacing can be accurately measured;

Fig. 10 is the internal mass corrosion diagram of SWRS87B steel continuous casting slab in embodiment 5;

The equiaxed crystal morphology can be clearly seen in the figure, and the defects of slab segregation, porosity and shrinkage cavity can be observed.

Fig. 11 is the internal mass corrosion diagram of GCr15-G steel continuous casting slab in embodiment 6;

In the figure, you can clearly see the solidification structure morphology in the central area, clearly show the segregation between dendrites, observe defects such as eutectic carbides, and quantitatively analyze the area of segregation regions and the proportion of eutectic carbides;

Fig. 12 is the internal mass corrosion diagram of GCr15-G steel continuous casting slab in embodiment 6;

In the figure, the segregation between dendrites can be clearly displayed, defects such as shrinkage cavities and eutectic carbides can be observed, and the area of segregation area, size of shrinkage cavities, number and proportion of eutectic carbides can be quantitatively analyzed.

detailed description

The present invention will be further described below through embodiment.

An inspection method for the internal quality of high-carbon steel continuous casting slabs, using the characteristics of significant differences in corrosion resistance between dendrites and interdendritic tempered structures after high-carbon steel slabs with C≥0.77% are quenched and tempered, Inspect the internal quality of high carbon steel continuous casting slabs; first process the continuous casting slabs into strips or blocks, then perform quenching + tempering heat treatment on the processed samples, and mill, grind and polish the heat treated samples. Use 4% nitric acid alcohol etching solution to etch the polished surface deeply, then use light microscope/electron microscope and other inspection equipment for metallographic inspection and take photos, and use computer Adobe Photoshop software for image processing on inspection images.

More specific process steps are as follows:

Slab Analysis Sample Machining

According to the inspection requirements, the continuous casting slab is processed on a sawing machine, and processed into a strip or block analysis sample with a length ≥ 10mm, a width of 10-20mm, and a height of about 10mm, which is convenient for subsequent heat treatment, machining, metallographic inspection and testing. Image analysis and processing;

Sample quenching + tempering heat treatment

The analysis sample is subjected to quenching + tempering heat treatment; after quenching, the sample is quenched martensite structure, and martensite is a supersaturated solid solution of carbon in α-Fe, which is a metastable phase, and supersaturated carbon atoms have The trend of spontaneous precipitation in the medium, tempering can continuously precipitate ε-carbides coherent with martensite from the martensite; the ε-carbides precipitated by tempering are extremely thin layers, which can be seen under an ordinary metallographic microscope. The results of its precipitation greatly reduce the corrosion resistance of martensite, so after the sample is corroded, the color becomes dark under the microscope, and the solidification structure of the slab can be clearly displayed by using the difference in color of the sample after corroding and internal defects;

Quenching process: temperature 820-840°C, time 20-30min, coolant: oil;

Tempering process: temperature 150°C-300°C, time 60-120min.

Milling, grinding and polishing of heat treatment samples

Place the heat-treated sample on a milling machine for processing, milling off 1-2mm to fully eliminate the influence of the decarburization layer of the sample; analyze and polish the test surface of the sample on the grinding machine, the roughness requirement should reach Ra≤0.8um, and then Polishing treatment, the surface roughness reaches Ra≤0.1um;

Specimen corrosion

Use 4% nitric acid alcohol solution to deeply corrode the surface of the analysis sample to clearly show the solidification structure of the billet, display internal defects such as segregation, shrinkage cavity, cracks, and microstructure morphology such as segregated carbide particles;

Sample metallographic inspection, photographing

The surface of the corrosion sample is subjected to metallographic inspection on light microscope/electron microscope inspection equipment, and photographs are taken to facilitate the analysis and processing of the photos of the internal structure of the slab.

Image Processing

The image of the metallographic photo taken by inspection is processed by Adobe Photoshop software on the computer to clearly display the dendrite structure, carbide and segregation control of the slab, and quantitatively evaluate the internal quality defects of the slab.

Example 1

This example is the internal quality inspection method of bearing steel GCr15 (C:0.98%) continuous casting slab:

Process the GCr15 continuous casting slab (280mm×325mm×10mm) on a sawing machine, and saw along the center of the slab into a 10mm×10mm×162mm sample;

The sample is subjected to quenching + tempering heat treatment, the quenching process is 830 ° C × 20 min, and the tempering process is 150 ° C × 100 min;

Heat treatment test milling machine processing, milling off 2mm, then grinding and polishing treatment, the surface roughness after polishing reaches Ra≤0.1um;

Use 4% concentration of nitric acid alcohol etching solution to etch the polished surface deeply;

Carry out the metallographic structure inspection and take pictures under the light microscope, use the computer Adobe Photoshop software to carry out the image with the inspection image, and the image after processing is referred to as shown in accompanying drawing 1,2.

Example 2

This example is the internal quality inspection method of high-quality bearing steel GCr15-Y (C: 1.00%) continuous casting slab:

Process the GCr15-Y continuous casting slab (280mm×325mm×10mm) on a sawing machine, and saw along the center of the slab into a 10mm×10mm×162mm sample;

The sample is subjected to quenching + tempering heat treatment, the quenching process is 830°C × 30min, and the tempering process is 150°C × 120min;

Heat treatment test milling machine processing, milling off 2.5mm, then grinding and polishing processing, the surface roughness after polishing reaches Ra≤0.1um;

Use 4% concentration of nitric acid alcohol etching solution to etch the polished surface deeply;

Carry out the metallographic structure inspection and take pictures under the light microscope, and use the computer Adobe Photoshop software to carry out the image with the inspection image, and the image after processing is referred to as shown in accompanying drawing 3,4.

Example 3

This embodiment is the internal quality inspection method of steel SWRH82B (C: 0.82%) continuous casting slabs for prestressed steel strands:

Process the SWRH82B continuous casting slab (280mm×325mm×10mm) on a sawing machine, and saw along the center of the slab into a 15mm×10mm×140mm sample;

The sample is subjected to quenching + tempering heat treatment, the quenching process is 830°C×30min, and the tempering process is 150°C×100min;

Heat treatment test milling machine processing, milling off 2mm, then grinding and polishing treatment, the surface roughness after polishing reaches Ra≤0.1um;

Use 4% concentration of nitric acid alcohol etching solution to etch the polished surface deeply;

Carry out the metallographic structure inspection and take pictures under the light microscope, use the computer Adobe Photoshop software to carry out the image with the inspection image, and the image after processing is referred to as shown in accompanying drawing 5,6,7.

Example 4

This embodiment is the internal quality inspection method of steel SWRH77B (C: 0.77%) continuous casting slabs for prestressed steel strands:

Process the SWRH77B continuous casting slab (160mm×160mm×10mm) on a sawing machine, and saw along the center of the slab into a 15mm×10mm×160mm sample;

The sample is subjected to quenching + tempering heat treatment, the quenching process is 840°C × 25min, and the tempering process is 150°C × 60min;

Heat treatment test milling machine processing, milling off 2mm, then grinding and polishing treatment, the surface roughness after polishing reaches Ra≤0.1um;

Use 4% concentration of nitric acid alcohol etching solution to etch the polished surface deeply;

Carry out the metallographic structure inspection under the light microscope and take pictures, use the computer Adobe Photoshop software to carry out the image with the inspection image, and the processed image is shown in Figure 8 with reference to.

Example 5

This embodiment is the internal quality inspection method of steel SWRS87B (C: 0.87%) continuous casting slabs for prestressed steel strands:

Process the SWRS87B continuous casting slab (280mm×325mm×10mm) on a sawing machine, and saw along the center of the slab into a 15mm×10mm×140mm sample;

The sample is subjected to quenching + tempering heat treatment, the quenching process is 820°C×30min, and the tempering process is 150°C×120min;

Heat treatment test milling machine processing, milling off 2mm, then grinding and polishing treatment, the surface roughness after polishing reaches Ra≤0.1um;

Use 4% concentration of nitric acid alcohol etching solution to deep-etch the polished surface;

Carry out the metallographic structure inspection and take pictures under the light microscope, and use the computer Adobe Photoshop software to carry out the image with the inspection image, and the image after processing is referred to as shown in accompanying drawing 9,10.

Example 6

This embodiment is the internal quality inspection method of steel GCr15-G (C: 1.00%) continuous casting slabs for prestressed steel strands:

Process the GCr15-G continuous casting slab (280mm×325mm×10mm) on a sawing machine, and saw along the center of the slab into a 15mm×10mm×140mm sample;

The sample is subjected to quenching + tempering heat treatment, the quenching process is 840°C × 20min, and the tempering process is 150°C × 60min;

Heat treatment test milling machine processing, milling off 2mm, then grinding and polishing treatment, the surface roughness after polishing reaches Ra≤0.1um;

Use 4% concentration of nitric acid alcohol etching solution to etch the polished surface deeply;

Carry out the metallographic structure inspection and take pictures under the light microscope, and use the computer Adobe Photoshop software to carry out the image with the inspection image, and the image after processing is referred to as shown in accompanying drawing 11,12.

Claims (2)

1. the method for inspection of a strand casted from high carbon steel internal soundness, after it is characterized in that utilizing the Casting Billet of Highcarbon Steel quenching+tempering process of C >=0.77%, the feature of dendrite and interdendritic tempered structure decay resistance significant difference, tests to strand casted from high carbon steel internal soundness; First continuous casting billet is processed into strip or bulk, then quenching+tempering thermal treatment is carried out to processing sample, heat treatment sample is carried out milling, mill, throwing processing process, with the nitric acid alcohol corrosive liquid of concentration 4% to polished surface deep etch, then carry out metallographic detection with inspection machines such as light microscopic/Electronic Speculum and take pictures, carrying out image procossing with checking image computing machine AdobePhotoshop software.

2. the method for inspection of a kind of strand casted from high carbon steel internal soundness according to claim 1, is characterized in that concrete processing step is as follows:

the machine work of strand analytical sample

Continuous casting billet is carried out processing process at sawing machine, is processed as length >=10mm, wide 10-20mm, the strip of high about 10mm or block analytical sample;

the thermal treatment of sample quenching+tempering

Analytical sample is carried out quenching+tempering thermal treatment;

Quenching technical: temperature 820-840 DEG C, time 20-30min, cooling medium: oil;

Tempering process: temperature 150 DEG C-300 DEG C, time 60-120min;

heat treatment sample milling, mill, throwing mechanical process

Heat treatment sample is placed the enterprising row relax of milling machine, mill 1-2mm; To the polishing process of sample analysis inspection face on grinding machine, roughness requirements reaches Ra≤0.8um, and then carry out polishing, surfaceness reaches Ra≤0.1um;

sample corrodes

With 4% nital, deep etch is carried out to analytical sample surface, with clear display casting blank solidification tissue, the inherent vices such as display segregation, shrinkage cavity, crackle, the displaing micro tissue topographies such as segregation carbide particle;

sample metal lographic examination, to take pictures

Metal lographic examination is carried out in corrosion sample surface on light microscopic/Electronic Speculum class inspection machine, and takes pictures, and carries out analyzing and processing to casting blank inner organization photo;

image procossing

The metallograph image checking image computing machine AdobePhotoshop software of shooting is carried out image procossing, controls situation clearly to show strand arborescent structure, carbonide and segregation, and quantitative evaluation Inner Quality of Billet defect.