A method for revealing grain boundaries of high-carbon chromium bearing steel

Abstract

The present invention relates to the technical field of grain boundary detection of bearing steel, and particularly relates to a method for revealing grain boundaries of high-carbon chromium bearing steel. The method includes first performing tempering treatment on the high-carbon chromium bearing steel to obtain a tempered specimen; subsequently, subjecting the tempered specimen to a first post-treatment to obtain a tempered sample; first using an etchant to etch the tempered sample to obtain an etched specimen; and then taking out the etched specimen and performing a second post-treatment to obtain a test sample. The present invention can solve the problem that the difficulty of austenite grain size etching increases due to the low content of impurity elements (i.e., high cleanliness) in high-carbon chromium bearing steel.

Description

Technical Field

[0001] The present invention relates to the technical field of grain boundary detection of bearing steel, and particularly relates to a method for revealing grain boundaries of high-carbon chromium bearing steel. Background Art

[0002] As the "heart" of a roadheader, a bearing plays the role of withstanding high impact, large thrust, large eccentric load and large torque during the tunneling process, and has extremely high reliability requirements. High-carbon chromium bearing steel, as the most commonly used bearing steel, is often used as the raw material for the main bearing of a shield machine. Usually, the raw materials purchased from a forging factory are annealed steel, and it is necessary to inspect the properties of the purchased steel. The austenite grain size is an essential inspection item. Because coarse austenite grains have a certain genetic effect, it will cause the subsequent heat treatment structure to be coarse, seriously affecting the mechanical properties and fatigue life of the main bearing of the shield machine.

[0003] When detecting the austenite grain size of the purchased steel, a grain size etchant needs to be used. Since impurity elements in the steel, such as non-metallic elements such as S, P, B, Si, and C, are likely to accumulate at grain boundaries, resulting in differences in chemical composition between grain boundaries and within grains. When contacting with the grain size etchant, grains and grain boundaries exhibit different electrochemical characteristics, so the grain boundaries can be revealed. The performance level of the steel can be judged according to the grain size and the display of dendritic crystals.

[0004] However, with the continuous development of steelmaking technology, the content of impurity elements in high-carbon chromium bearing steel decreases, that is, the cleanliness is getting higher and higher, and the difficulty of austenite grain size corrosion also increases accordingly. Ordinary grain size etchants on the market are difficult to show grain boundaries for high-carbon chromium bearing steel.

[0005] In summary, a method for revealing grain boundaries of high-carbon chromium bearing steel is needed to solve the problem that the decrease in the content of impurity elements in high-carbon chromium bearing steel (i.e., high cleanliness) leads to an increase in the difficulty of austenite grain size corrosion. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for revealing grain boundaries of high-carbon chromium bearing steel, and the specific technical solutions are as follows:

[0007] In the first aspect, the present invention provides an etchant for revealing grain boundaries of high-carbon chromium bearing steel, which comprises the following raw material components in parts by weight: 8-10 parts of sodium metabisulfite, 2-4 parts of dishwashing liquid, 8-10 parts of surfactant, 5-8 parts of acid solution, and 95-105 parts of water.

[0008] Optionally, the acid solution includes nitric acid; the mass fraction of the nitric acid is 60%-80%.

[0009] Optionally, the surfactant includes sodium dodecylbenzenesulfonate.

[0010] In a second aspect, the present invention provides a method for grain boundary display of high-carbon chromium bearing steel, comprising:

[0011] Step S1, preparing a tempered sample;

[0012] First, perform tempering treatment on the high-carbon chromium bearing steel to obtain a tempered specimen; subsequently, subject the tempered specimen to a first post-treatment to obtain a tempered sample;

[0013] Step S2, obtaining a test sample;

[0014] First, use the corrosion agent to perform corrosion treatment on the tempered sample to obtain a corroded specimen; subsequently, take out the corroded specimen and then perform a second post-treatment to obtain a test sample;

[0015] The corrosion temperature for the corrosion treatment is 40 - 50 °C, and the corrosion time is 5 - 10 min or 2 - 5 min.

[0016] Optionally, the tempering temperature for the tempering treatment is 600 - 650 °C, the tempering holding time is 2 - 2.5 h; the heating rate for the tempering treatment is 10 - 15 °C / min.

[0017] Optionally, the first post-treatment includes grinding treatment and polishing treatment performed in sequence;

[0018] The grinding treatment includes successively using grinding tools with increasing mesh numbers to grind the tempered specimen to a target size;

[0019] The polishing treatment successively uses a combination of polishing agents and lubricants with decreasing particle sizes to polish and eliminate the scratches on the surface of the tempered specimen.

[0020] Optionally, the grinding tools include silicon carbide sandpaper; the mesh number range of the silicon carbide sandpaper is 80 - 1000 meshes.

[0021] Optionally, the polishing agent includes diamond polishing agent; the particle size range of the diamond polishing agent is 1 - 3.5 μm;

[0022] The lubricant includes water.

[0023] Optionally, the second post-treatment includes first rinsing the corroded specimen with clear water, then rinsing the corroded specimen with alcohol, and finally drying it.

[0024] Optionally, the high-carbon chromium bearing steel includes GCr15SiMn round steel.

[0025] Applying the technical solution of the present invention has at least the following beneficial effects:

[0026] (1)A method for revealing grain boundaries of high-carbon chromium bearing steel provided by the present invention can solve the problem that the difficulty of austenite grain size corrosion increases due to the low content of impurity elements (i.e., high cleanliness) in high-carbon chromium bearing steel. Specifically, the present invention performs tempering treatment on the high-carbon chromium bearing steel in step S1, causing the second type of temper brittleness in the tempered sample, thereby resulting in the segregation of impurity elements and alloying elements at the grain boundaries; further, the present invention uses the corrosion agent to perform corrosion treatment on the tempered sample in step S2. Under the conditions of controlling the corrosion time at 5-10 minutes and the corrosion temperature at 40-50 °C, the requirement of corroding the grain size to reveal the grain boundaries can be achieved, and thus the performance level of the steel can be judged according to the grain size; under the conditions of controlling the corrosion time at 2-5 minutes and the corrosion temperature at 40-50 °C, the dendritic structure in the high-carbon chromium bearing steel can be corroded, and then the dendrites can be revealed. Based on the dendritic structure, the level of the steel slab can be judged.

[0027] (2)The corrosion agent used in the present invention has excellent electrochemical properties and can preferentially corrode the grain boundaries of the tempered sample that has undergone the second type of temper brittleness to reveal the grain boundaries; among them, the tempered sample with the second type of temper brittleness is obtained by the tempering treatment in step S1. Specifically, the corrosion agent uses a specific electrolyte, sodium metabisulfite, and an acid solution in combination. Under the conditions of controlling the corrosion time and the corrosion temperature, it can accelerate the corrosion of impurity elements in the high-carbon chromium bearing steel, and then reveal the grain boundaries; among them, sodium metabisulfite can undergo redox reactions with impurity elements such as S and P at the grain boundaries, so that the corrosion rate of the metal matrix is slower than that of the grain boundaries, and then the grain boundaries are revealed; the surfactant plays a corrosion inhibition role in the crystal grains to ensure that the crystal grains are not easily corroded; in addition, a combination of dishwashing liquid and surfactant is used to reduce the surface tension of the corrosion agent, producing effects such as wetting, emulsification, defoaming, and solubilization, improving the corrosion efficiency at the grain boundaries, and helping to form a uniform corrosion surface.

[0028] In addition to the purposes, features, and advantages described above, the present invention has other purposes, features, and advantages. The following will refer to the drawings for a further detailed description of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0030] Figure 1 is the metallographic diagram of the test sample in Example 1;

[0031] Figure 2 is the metallographic diagram of the test sample in Example 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention belong to the scope of protection of the present invention. Embodiment 1:

[0033] An etchant for grain boundary display of high-carbon chromium bearing steel, comprising the following raw material components in parts by weight: 9 parts of sodium metabisulfite, 3 parts of dishwashing liquid, 9 parts of a surfactant (specifically sodium dodecylbenzenesulfonate), 6 parts of an acid solution (specifically nitric acid with a mass fraction of 70%), and 100 parts of water.

[0034] A method for grain boundary display of high-carbon chromium bearing steel, comprising:

[0035] Step S1, preparing a tempered sample;

[0036] First, high-carbon chromium bearing steel (specifically, a GCr15SiMn round steel with a diameter of Φ100mm, the chemical composition and corresponding mass percentages thereof are as follows: C: 0.95 - 1.05%; Si: 0.45 - 0.75%; Mn: 0.95 - 1.25%; Cr: 1.40 - 1.65%; Mo: ≤0.10%; S: ≤0.025%; P: ≤0.025%; Ni: ≤0.30%; Cu: ≤0.25%; specifically, the chemical composition and corresponding mass percentages of the GCr15SiMn round steel are as follows: C: 0.95 - 1.05%; Si: 0.45 - 0.75%; Mn: 0.95 - 1.25%; Cr: 1.40 - 1.65%; Mo: ≤0.10%; S: ≤0.025%; P: ≤0.025%; Ni: ≤0.30%; Cu: ≤0.25%) is tempered to obtain a tempered specimen, and then the tempered specimen is subjected to a first post-treatment to obtain a tempered sample;

[0037] Step S2, obtaining a test sample;

[0038] First, the tempered sample is etched with the etchant to obtain an etched specimen; then the etched specimen is taken out and subjected to a second post-treatment to obtain a test sample;

[0039] The etching temperature for the etching treatment is 40 - 50°C (specifically 45°C), and the etching time is 5 - 10 min (specifically 8 min).

[0040] The tempering temperature for the tempering treatment is 600°C, and the tempering holding time is 2 h; the heating rate for the tempering treatment is 10°C / min.

[0041] The first post-treatment includes a grinding process and a polishing process carried out in sequence;

[0042] The grinding process includes successively using grinding tools with increasing mesh numbers to grind the tempered specimen to a target size (specifically 10mm×10mm×10mm);

[0043] The polishing process successively uses a combination of a polishing agent and a lubricant with decreasing particle sizes to polish and eliminate the scratches on the surface of the tempered specimen.

[0044] The grinding tools are silicon carbide sandpapers; the mesh numbers of the silicon carbide sandpapers are 80 mesh, 240 mesh, 400 mesh, 600 mesh, 800 mesh, and 1000 mesh in sequence.

[0045] The polishing agent is a diamond polishing agent; the particle sizes of the diamond polishing agent are 3.5μm and 1μm;

[0046] The lubricant is water.

[0047] The second post-treatment includes first rinsing the corroded specimen with clean water, then rinsing the corroded specimen with alcohol, and finally drying it.

[0048] When the test sample obtained in Example 1 is observed with a metallographic microscope, the grain size of the high-carbon chromium bearing steel can be clearly seen. For specific results, see Figure 1 . This shows that in Example 1, by combining steps S1 - S2 and controlling the corrosion time at 5 - 10 min and the corrosion temperature at 40 - 50 °C, the requirement of corroding the grain size to reveal the grain boundaries can be met. Example 2:

[0049] Different from Example 1, the high-carbon chromium bearing steel is specifically a GCr15SiMn round steel with a diameter of Φ50mm; the tempering temperature used in the tempering treatment is 650 °C; the grinding is to a target size of 10mm×10mm×25mm); the corrosion time is 2 - 5 min (specifically 4 min is selected).

[0050] When the test sample obtained in Example 2 is observed with a metallographic microscope, the dendritic structure of the high-carbon chromium bearing steel can be clearly seen. For specific results, see Figure 2 . This shows that in Example 2, by combining steps S1 - S2 and controlling the corrosion time at 2 - 5 min and the corrosion temperature at 40 - 50 °C, the corrosion of the dendritic structure in the high-carbon chromium bearing steel can be achieved, thereby revealing the dendritic grain boundaries.

[0051] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for revealing grain boundaries of high-carbon chromium bearing steel, characterized in that, Including: Step S1, preparing a tempered sample; First, perform tempering treatment on high-carbon chromium bearing steel to obtain a tempered specimen; Subsequently, obtain a tempered sample by subjecting the tempered specimen to a first post-treatment; the tempering temperature used in the tempering treatment is 600 - 650 °C, the tempering holding time is 2 - 2.5 h; the heating rate used in the tempering treatment is 10 - 15 °C / min; Step S2, obtaining a test sample; First, corrode the tempered sample with a corrosion agent to obtain a corroded specimen; then take out the corroded specimen and obtain a test sample through a second post-treatment; The corrosion agent includes the following raw material components in parts by weight: 8 - 10 parts of sodium metabisulfite, 2 - 4 parts of dishwashing liquid, 8 - 10 parts of surfactant, 5 - 8 parts of acid solution, and 95 - 105 parts of water; The corrosion temperature used in the corrosion treatment is 40 - 50 °C, and the corrosion time is 5 - 10 min or 2 - 5 min.

2. The method according to claim 1, characterized in that The acid solution includes nitric acid; the mass fraction of the nitric acid is 60% - 80%.

3. The method according to claim 1, wherein The surfactant includes sodium dodecylbenzenesulfonate.

4. The method according to claim 1, characterized in that The first post-treatment includes grinding treatment and polishing treatment carried out in sequence; The grinding treatment includes successively using grinding tools with increasing mesh numbers to grind the tempered specimen to the target size; The polishing treatment successively uses a combination of a polishing agent and a lubricant with decreasing particle sizes to polish and eliminate the scratches on the surface of the tempered specimen.

5. The method according to claim 4, wherein The grinding tools include silicon carbide sandpaper; the mesh number range of the silicon carbide sandpaper is 80 - 1000 meshes.

6. The method according to claim 4, characterized in that The polishing agent includes diamond polishing agent; the particle size range of the diamond polishing agent is 1 - 3.5 μm.

7. The method according to claim 4, characterized in that, The lubricant includes water.

8. The method according to claim 1, wherein The second post-treatment includes first rinsing the corroded specimen with clean water, then rinsing the corroded specimen with alcohol, and finally drying it.

9. The method according to claim 1, characterized in that, The high-carbon chromium bearing steel includes GCr15SiMn round steel.

Images