Method for displaying grain boundary of high-carbon chromium bearing steel

Abstract

The invention relates to the technical field of bearing steel grain boundary detection, in particular to a high-carbon-chromium bearing steel grain boundary display method. The method comprises the following steps: tempering the high-carbon chromium bearing steel to obtain a tempered sample; then, the tempered sample is subjected to first-time post-treatment, and a tempered sample is obtained; the tempered sample is subjected to corrosion treatment through a corrosive agent, and a corrosion sample is obtained; and then taking out the corrosion sample, and carrying out secondary post-treatment to obtain a detection sample. The problem that the austenite grain size corrosion difficulty is increased due to the fact that the content of impurity elements in the high-carbon-chromium bearing steel is low (namely, the cleanliness is high) can be solved.

Description

Technical Field

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

[0002] As the "heart" of the tunnel boring machine, the bearing bears high impact, large thrust, large offset 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 bearings of the shield machine. Usually, the raw materials purchased from the forging factory are annealed steel. The performance of the purchased steel needs to be tested, and the austenite grain size is an essential test item. Because the austenite grains are coarse and have a certain genetic effect, the subsequent heat treatment structure will be coarse, which will seriously affect the mechanical properties and fatigue life of the main bearings of the shield machine.

[0003] When testing the austenite grain size of purchased steel, a grain size corrosive is required. Impurity elements in steel, such as non-metallic elements such as S, P, B, Si and C, are easily enriched at the grain boundaries, resulting in differences in the chemical composition between the grain boundaries and the grains. When in contact with the grain size corrosive, the grains and grain boundaries exhibit different electrochemical properties, so the grain boundaries can be displayed. The performance level of the steel can be judged based on the grain size and the display of dendrites.

[0004] However, with the continuous development of steelmaking technology, the content of impurity elements in high carbon chromium bearing steel has decreased, that is, the cleanliness has become higher and higher, and the difficulty of austenite grain corrosion has also increased. The corrosion effect of ordinary grain etchants on high carbon chromium bearing steel on the market is difficult to show grain boundaries.

[0005] In summary, it is necessary to provide a method for displaying grain boundaries of high carbon chromium bearing steel to solve the problem that the corrosion difficulty of austenite grain size increases due to the low content of impurity elements in high carbon chromium bearing steel (i.e., high cleanliness). Summary of the invention

[0006] The object of the present invention is to provide a method for displaying grain boundaries of high carbon chromium bearing steel. The specific technical scheme is as follows: In a first aspect, the present invention provides a high carbon chromium bearing steel grain boundary display corrosive agent, comprising the following raw material components in parts by weight: 8-10 parts of sodium metabisulfite, 2-4 parts of detergent, 8-10 parts of surfactant, 5-8 parts of acid solution and 95-105 parts of water.

[0007] Optionally, the acid solution includes nitric acid; the mass fraction of the nitric acid is 60%-80%.

[0008] Optionally, the surfactant includes sodium dodecylbenzene sulfonate.

[0009] In a second aspect, the present invention provides a method for displaying grain boundaries of high carbon chromium bearing steel, comprising: Step S1, preparing a tempered sample; Firstly, the high carbon chromium bearing steel is tempered to obtain a tempered sample; then, the tempered sample is subjected to a first post-treatment to obtain a tempered sample; Step S2, obtaining a test sample; Firstly, the tempered sample is corroded by the corrosive agent to obtain a corrosion sample; then the corrosion sample is taken out and subjected to a second post-processing to obtain a test sample; The corrosion treatment adopts a corrosion temperature of 40-50° C. and a corrosion time of 5-10 min or 2-5 min.

[0010] Optionally, the tempering temperature used in the tempering treatment is 600-650°C, and the tempering holding time is 2-2.5h; the heating rate used in the tempering treatment is 10-15°C / min.

[0011] Optionally, the first post-processing includes a grinding process and a polishing process performed sequentially; The polishing process includes successively polishing the tempered sample to a target size using polishing equipment with increasing mesh sizes; The polishing treatment uses a polishing agent with decreasing particle sizes in combination with a lubricant to polish and eliminate scratches on the surface of the tempered sample.

[0012] Optionally, the polishing equipment includes silicon carbide sandpaper; the mesh size of the silicon carbide sandpaper ranges from 80 to 1000.

[0013] Optionally, the polishing agent includes a diamond polishing agent; the particle size of the diamond polishing agent ranges from 1 to 3.5 μm; The lubricant includes water.

[0014] Optionally, the second post-processing includes first rinsing the corrosion sample with water, then rinsing the corrosion sample with alcohol, and finally blowing it dry.

[0015] Optionally, the high carbon chromium bearing steel includes GCr15SiMn round steel.

[0016] The application of the technical solution of the present invention has at least the following beneficial effects: (1) The method for displaying grain boundaries of high carbon chromium bearing steel provided by the present invention can solve the problem that the high carbon chromium bearing steel has a low content of impurity elements (i.e., high cleanliness) which leads to an increased difficulty in corroding austenite grain size. Specifically, the present invention uses step S1 to perform a tempering treatment on the high carbon chromium bearing steel, so that the tempered sample produces a second type of temper brittleness, thereby causing the impurity elements and alloy elements to segregate at the grain boundaries; further, the present invention uses the corrosive agent to perform a corrosion treatment on the tempered sample with the aid of step S2, and under the conditions of controlling the corrosion time to 5-10min and the corrosion temperature to 40-50°C, the requirement of corroding the grain size to display the grain boundaries can be achieved, and then the performance level of the steel can be judged according to the grain size; under the conditions of controlling the corrosion time to 2-5min and the corrosion temperature to 40-50°C, the dendrite structure in the high carbon chromium bearing steel can be corroded, and then the dendrites can be displayed, and the level of the steel ingot can be judged according to the dendrite structure.

[0017] (2) The corrosive agent used in the present invention has excellent electrochemical properties and can preferentially corrode the grain boundaries of the tempered samples that have undergone the second type of temper brittleness to display the grain boundaries; wherein the tempered samples of the second type of temper brittleness are obtained by tempering treatment in step S1. Specifically, the corrosive agent uses a specific electrolyte sodium metabisulfite and an acid solution in combination, and under the condition of controlling the corrosion time and corrosion temperature, it can accelerate the corrosion of impurity elements in high carbon chromium bearing steel, thereby displaying the grain boundaries; wherein sodium metabisulfite can undergo an oxidation-reduction reaction with impurity elements such as S and P at the grain boundaries, thereby causing the metal matrix to be corroded more slowly than the grain boundaries, thereby displaying the grain boundaries; the surfactant has a corrosion-inhibiting effect on the grains, ensuring that the grains are not easily corroded; in addition, the combination of detergent and surfactant can reduce the surface tension of the corrosive agent, produce wetting, emulsification, defoaming and solubilization effects, improve the corrosion efficiency at the grain boundaries, and help form a uniform corrosion surface.

[0018] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary 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: Figure 1 is a metallographic image of the sample tested in Example 1; Figure 2 This is the metallographic image of the sample tested in Example 2. DETAILED DESCRIPTION

[0020] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention. Embodiment 1:

[0021] A corrosive agent for grain boundary display of high carbon chromium bearing steel comprises the following raw material components in parts by weight: 9 parts of sodium metabisulfite, 3 parts of detergent, 9 parts of surfactant (specifically sodium dodecylbenzene sulfonate), 6 parts of acid solution (specifically nitric acid, with a mass fraction of nitric acid of 70%) and 100 parts of water.

[0022] A method for displaying grain boundaries of high carbon chromium bearing steel, comprising: Step S1, preparing a tempered sample; First, high carbon chromium bearing steel (specifically Φ100mm GCr15SiMn round steel, the chemical composition and corresponding mass percentage of which 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, G The chemical composition and corresponding mass percentage of Cr15SiMn 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%), and the tempered sample is obtained by the first post-treatment to obtain the tempered sample; Step S2, obtaining a test sample; Firstly, the tempered sample is corroded by the corrosive agent to obtain a corrosion sample; then the corrosion sample is taken out and subjected to a second post-processing to obtain a test sample; The corrosion treatment adopts a corrosion temperature of 40-50° C. (specifically 45° C.) and a corrosion time of 5-10 min (specifically 8 min).

[0023] The tempering temperature used in the tempering treatment is 600°C, and the tempering holding time is 2h; the heating rate used in the tempering treatment is 10°C / min.

[0024] The first post-processing includes a grinding process and a polishing process performed in sequence; The polishing process includes successively polishing the tempered sample to a target size (specifically 10 mm×10 mm×10 mm) using polishing equipment with increasing mesh sizes; The polishing treatment uses a polishing agent with decreasing particle sizes in combination with a lubricant to polish and eliminate scratches on the surface of the tempered sample.

[0025] The polishing equipment is silicon carbide sandpaper; the mesh numbers of the silicon carbide sandpaper are 80 mesh, 240 mesh, 400 mesh, 600 mesh, 800 mesh and 1000 mesh respectively.

[0026] The polishing agent is a diamond polishing agent; the particle size of the diamond polishing agent is 3.5 μm and 1 μm; The lubricant is water.

[0027] The second post-treatment includes first rinsing the corrosion sample with water, then rinsing the corrosion sample with alcohol, and finally drying it.

[0028] The sample obtained in Example 1 was observed under a metallographic microscope to clearly show the grain size of the high carbon chromium bearing steel. Figure 1 This shows that by combining steps S1-S2 in Example 1 and controlling the etching time to 5-10 min and the etching temperature to 40-50° C., the requirement of etching the grain size to display the grain boundary can be achieved. Embodiment 2:

[0029] Different from Example 1, the high carbon chromium bearing steel is specifically Φ50mm GCr15SiMn round steel; the tempering temperature used in the tempering treatment is 650°C; the target size is polished to 10mm×10mm×25mm); the corrosion time is 2-5min (specifically 4min).

[0030] The dendrite structure of high carbon chromium bearing steel can be clearly seen by observing the test sample obtained in Example 2 with a metallographic microscope. For specific results, see Figure 2 This shows that by combining steps S1-S2 in Example 2 and controlling the corrosion time to 2-5 min and the corrosion temperature to 40-50° C., the dendrite structure in the high carbon chromium bearing steel can be corroded, thereby showing the dendrite grain boundaries.

[0031] The above description is only a preferred embodiment of the present invention and is 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 in the protection scope of the present invention.

Claims

1. A method for displaying grain boundaries of high carbon chromium bearing steel, characterized in that: include: Step S1, preparing a tempered sample; Firstly, the high carbon chromium bearing steel is tempered to obtain a tempered sample; Subsequently, the tempered specimens were subjected to a first post-treatment to obtain tempered samples; Step S2, obtaining a test sample; Firstly, the tempered sample is corroded by using a corrosive agent to obtain a corrosion sample; The corrosion samples were then taken out and subjected to a second post-processing to obtain the test samples; The corrosive agent comprises the following raw material components in parts by weight: 8-10 parts of sodium metabisulfite, 2-4 parts of detergent, 8-10 parts of surfactant, 5-8 parts of acid solution and 95-105 parts of water; The corrosion treatment adopts a corrosion temperature of 40-50° C. and a corrosion time of 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, characterized in that The surfactant includes sodium dodecylbenzene sulfonate.

4. The method according to claim 1, characterized in that The tempering temperature used in the tempering treatment is 600-650°C, and the tempering holding time is 2-2.5h; the heating rate used in the tempering treatment is 10-15°C / min.

5. The method according to claim 1, characterized in that The first post-processing includes a grinding process and a polishing process performed in sequence; The polishing process includes successively polishing the tempered sample to a target size using polishing equipment with increasing mesh sizes; The polishing treatment uses a polishing agent with decreasing particle sizes in combination with a lubricant to polish and eliminate scratches on the surface of the tempered sample.

6. The method according to claim 5, characterized in that The polishing equipment includes silicon carbide sandpaper; the mesh number of the silicon carbide sandpaper ranges from 80 to 1000 meshes.

7. The method according to claim 5, characterized in that The polishing agent includes diamond polishing agent; the particle size of the diamond polishing agent ranges from 1 to 3.5 μm.

8. The method according to claim 5, characterized in that The lubricant includes water.

9. The method according to claim 1, characterized in that: The second post-treatment includes first rinsing the corrosion sample with water, then rinsing the corrosion sample with alcohol, and finally drying it.

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

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