阅读说明：本技术 一种金相化学抛光液及在奥氏体不锈钢金相检测领域的应用 (Metallographic chemical polishing solution and application thereof in field of austenitic stainless steel metallographic detection ) 是由 张鸿武 杨东旭 冯楠楠 岳增武 邵明星 马永泉 高明德 李晓宇 邓化凌 张广成 于 2020-07-10 设计创作，主要内容包括：本发明具体涉及一种金相化学抛光液及在奥氏体不锈钢金相检测领域的应用。传统化学抛光液应用于奥氏体不锈钢表面检测难以达到理想的抛光效果,本发明提供了一种适用于18Cr-8Ni型奥氏体不锈钢金相检测的化学抛光液,所述化学抛光液中各成分及比例如下：盐酸120ml/L～160ml/L、磷酸120ml/L～160ml/L、硝酸钠50g/L～70g/L、30％过氧化氢300ml/L、乙醇100ml/L、硫脲5g/L、盐酸抑雾剂1g/L,余量为水。该化学抛光液应用于奥氏体不锈钢能够有效抑制抛光过程中产生的酸雾、配制方法简便安全性高,能够得到清晰的金相组织表面。(The invention particularly relates to a metallographic chemical polishing solution and application thereof in the field of metallographic detection of austenitic stainless steel. The invention provides a chemical polishing solution suitable for 18Cr-8Ni type austenitic stainless steel metallographic detection, which is applied to austenitic stainless steel surface detection and is difficult to achieve an ideal polishing effect, and comprises the following components in parts by weight: 120 ml/L-160 ml/L of hydrochloric acid, 120 ml/L-160 ml/L of phosphoric acid, 50 g/L-70 g/L of sodium nitrate, 300ml/L of 30% hydrogen peroxide, 100ml/L of ethanol, 5g/L of thiourea, 1g/L of hydrochloric acid fog inhibitor and the balance of water. The chemical polishing solution applied to austenitic stainless steel can effectively inhibit acid mist generated in the polishing process, the preparation method is simple and convenient, the safety is high, and a clear metallographic structure surface can be obtained.)

1. The metallographic chemical polishing solution is characterized by comprising the following components: hydrochloric acid, phosphoric acid, sodium nitrate, hydrogen peroxide, ethanol, thiourea, a hydrochloric acid fog inhibitor and the balance of water.

2. The metallographic chemical polishing solution according to claim 1, wherein the hydrochloric acid concentration is 1.4 to 1.92 mol/L.

Or the concentration of the phosphoric acid is 1.8 mol/L-2.4 mol/L;

or the content of the sodium nitrate is 50 g/L-70 g/L.

3. The metallographic chemical polishing solution according to claim 1, wherein the hydrogen peroxide concentration is 80 to 100 ml/L;

or the concentration of the ethanol is 80-120 ml/L;

or the content of the thiourea is 4-6 g/L;

or the content of the hydrochloric acid fog inhibitor is 0.8-1.2 g/L.

4. The metallographic chemical polishing solution according to claim 2 or 3, wherein each liter of the chemical polishing solution comprises the following components in percentage by weight: 140ml of commercial analytical pure concentrated hydrochloric acid, 140ml of commercial analytical pure concentrated phosphoric acid, 60g of sodium nitrate, 300ml of 30% hydrogen peroxide, 100ml of absolute ethyl alcohol, 5g of thiourea, 1g of hydrochloric acid fog inhibitor and the balance of distilled water;

or the chemical polishing solution per liter comprises the following components in proportion: 130ml of commercial analytical pure concentrated hydrochloric acid, 160ml of commercial analytical pure concentrated phosphoric acid, 50g of sodium nitrate, 280ml of 30% hydrogen peroxide, 110ml of absolute ethyl alcohol, 6g of thiourea, 0.8g of hydrochloric acid antifogging agent and the balance of distilled water;

or the chemical polishing solution per liter comprises the following components in proportion: 150ml of commercial analytically pure concentrated hydrochloric acid, 120ml of commercial analytically pure concentrated phosphoric acid, 70g of sodium nitrate, 310ml of 30% hydrogen peroxide, 80ml of absolute ethyl alcohol, 4g of thiourea, 1.2g of hydrochloric acid antifogging agent and the balance of distilled water.

5. The metallographic chemical polishing solution according to claim 1, wherein the chemical gold image polishing solution is prepared by the following method: weighing distilled water, absolute ethyl alcohol and hydrogen peroxide, uniformly mixing, then adding hydrochloric acid and phosphoric acid, uniformly stirring, and then sequentially adding sodium nitrate, thiourea and a hydrochloric acid antifogging agent.

6. Use of the metallographic chemical polishing solution according to any one of claims 1 to 5 in the field of metallographic examination of austenitic stainless steel.

7. The application of the metallographic chemical polishing solution in the field of metallographic detection of austenitic stainless steel according to claim 6, wherein the austenitic stainless steel contains about 18% of Cr and 8-10% of Ni, namely 18Cr-8Ni type austenitic stainless steel.

8. The application of the metallographic chemical polishing solution in the field of metallographic detection of austenitic stainless steel as defined in claim 6, wherein the polishing method of the metallographic chemical polishing solution comprises the following steps: dipping a water-absorbing material in the metallographic chemical polishing solution to wipe the metallographic surface, and cleaning and drying the metallographic surface after scratches disappear by observing the surface scratch condition;

preferably, the cleaning step is performed by using absolute ethyl alcohol;

or, the polishing method of the metallographic chemical polishing solution comprises the following steps: adding a workpiece to be polished into the metallographic chemical polishing solution for soaking, and wiping the metallographic surface by adopting a water absorbing material;

preferably, the water absorbing material includes, but is not limited to, absorbent cotton, non-woven fabric, wool, or velvet.

9. An austenitic stainless steel metallographic examination kit, characterized in that the examination kit comprises a metallographic chemical polishing solution according to any one of claims 1 to 5.

10. The kit for metallographic examination of austenitic stainless steel according to claim 9, wherein in the kit for metallographic examination of austenitic stainless steel, the raw materials of the chemical polishing solution for metallographic phase, hydrochloric acid, phosphoric acid, sodium nitrate, hydrogen peroxide, ethanol, thiourea, antifogging agent for hydrochloric acid and water are packaged separately and mixed well in a container before use;

or in the austenitic stainless steel metallographic detection kit, the metallographic chemical polishing solution is a reagent prepared by premixing all raw materials according to a ratio;

or, the austenitic stainless steel metallographic detection kit further comprises other polishing tools, and the other polishing tools include, but are not limited to, bamboo clips, tweezers, absorbent cotton, polishing cloth or absolute ethyl alcohol.

Technical Field

The invention belongs to the technical field of metallographic detection and polishing, and particularly relates to a metallographic chemical polishing solution, a preparation method of the polishing solution and application of the metallographic chemical polishing solution in the field of 18Cr-8Ni austenitic stainless steel metallographic detection.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

In recent years, with the rapid development of power station boilers in the directions of high parameter, large capacity and high efficiency, higher requirements are put forward on the service performance and the processing performance of heated part materials. The 18Cr-8Ni type austenitic stainless steel is widely applied to heating surface tubes of supercritical power station boilers due to good structure stability, higher creep strength, excellent oxidation resistance and high-temperature corrosion resistance. The heated surface pipe is usually operated under extremely severe working conditions (particularly on a unit with larger installed capacity, the temperature of flue gas on the outer surface of the pipe exceeds 1000 ℃, the temperature of high-pressure steam flowing in the pipe is over 540 ℃, and the pressure reaches over 16 MPa), and along with the accumulation of operating time, the defects of tissue aging, corrosion, intergranular cracks and the like are inevitable, and the generation of the defects seriously influences the safe operation of the unit, so that the metallographic detection of austenitic stainless steel is an important part in a metal supervision project of a power station boiler, and the on-site metallographic preparation is required in the actual metal supervision process on the premise of not damaging parts. Due to the complexity of the field working conditions and the limitation of the environmental conditions, the difficulty of the field metallographic preparation is far greater than that of the laboratory preparation. One of the main difficulties restricting the on-site metallographic preparation process is metallographic polishing.

In the field metallographic detection process, the steps of polishing, eroding, observing and the like are mainly adopted. The quality of the polishing quality directly affects the definition of a metallographic structure, and if the polishing quality is not good, some tiny defects (such as precipitation of carbides, intergranular cracks and the like) are not easy to be found, so that the detection leakage is formed. Therefore, the most common polishing mode in the field at present is mechanical polishing, which is performed by using a portable handheld electric polishing machine and matching diamond polishing solution, but the method is limited by the shape and the environment position of a workpiece, the polishing process is difficult to control, the required polishing time is long, scratches are not easy to be removed, the phenomenon of local overheating is easy to occur, and the polishing effect is not ideal.

The chemical polishing is a polishing process commonly used for stainless steel metallographic detection, can polish parts with complex shapes, and has high detection efficiency. In terms of functionality, chemical polishing can remove a mechanical damage layer and a stress layer after grinding on the surface of a stainless steel metallographic measuring point to obtain a surface with mechanical cleanliness besides the surface with physical and chemical cleanliness. However, the application of the conventional chemical polishing method to austenitic stainless steel has some disadvantages: because the content of alloy elements such as Cr, Ni and the like in austenitic stainless steel is high (the sum of the mass fractions is close to 30 percent in general), the traditional metallographic chemical polishing solution cannot carry out chemical polishing on the austenitic stainless steel due to the factors such as insufficient acidity and the like.

Disclosure of Invention

In view of the above background, the present invention provides a simplified metallographic detection and polishing method, which can improve the efficiency of on-site detection. In order to realize the technical purpose, the invention provides a chemical polishing solution for metallographic detection of stainless steel, which is applied to surface chemical polishing of 18Cr-8Ni type austenitic steel metallographic point, and the obtained metallographic structure is clear and convenient to observe, and the polishing efficiency is high and the speed is convenient to control.

Based on the technical effects, the invention provides the following technical scheme:

in a first aspect of the present invention, a metallographic chemical polishing solution is provided, which comprises the following components: hydrochloric acid, phosphoric acid, sodium nitrate, hydrogen peroxide, ethanol, thiourea, a hydrochloric acid fog inhibitor and the balance of water.

Hydrochloric acid is an inorganic strong acid without oxidability, is a strong corrosive agent and mainly plays a role in dissolving metals. But the hydrochloric acid alone does not have the effect of dissolving the stainless steel product, and only has certain dissolving capacity by combining with nitric acid and other auxiliary agents, and is used for removing an oxide layer on the surface of the stainless steel.

Phosphoric acid is a medium-strength ternary inorganic acid, can increase the viscosity of the polishing solution, reduce the acidity of the polishing solution and effectively inhibit the excessive dissolution of stainless steel. The method plays a role in dissolving the metal surface in the chemical polishing process, and can generate a layer of insoluble phosphate passivation film on the surface, and the formation and dissolution of the passivation film can flatten the surface of a metallographic measuring point and has the polishing effect.

Sodium nitrate is a strong oxidant, and is matched with hydrochloric acid to play a role in dissolution, so that an oxide layer is effectively removed, and a passivation film can be formed at a metallographic measuring point. Compared with the traditional polishing solution in which nitric acid is used as a raw material, the polishing solution provided by the invention adopts sodium nitrate as a substitute, so that the same good polishing effect can be obtained, yellow smoke generated in the polishing process can be effectively avoided, and the preparation safety of the polishing solution is improved.

Hydrogen peroxide can eliminate corrosion residue and dissolved carbon and carbide, improve the surface smoothness of stainless steel, and eliminate bumping of NOx. The addition of the absolute ethyl alcohol can improve the stability of hydrogen peroxide in a chemical polishing solution system and assist in improving the surface smoothness of the stainless steel.

In the chemical polishing process, the main path of generating acid mist is that a part of the surface metal is accompanied by hydrogen generated under the corrosion action of the polishing solution, and the other part is generated by thermal volatilization of the acid solution. The hydrochloric acid mist inhibitor contains a surfactant, can generate certain foams to cover the surface of the polishing solution, inhibits the volatilization of acid, greatly reduces hydrogen released by corrosion of acid liquor and the exposed metal surface, reduces the temperature of the acid liquor to be below an acid dew point, reduces the brought acid liquor, and reduces the loss of the acid. Reduce pollution and harm to the bodies of test and detection personnel. Can also remove various oil stains, slow down or inhibit the corrosion of hydrochloric acid to metal, has good synergistic effect with hydrochloric acid, and is suitable for hydrochloric acid at various temperatures.

In a second aspect of the invention, the application of the metallographic chemical polishing solution of the first aspect in the field of metallographic detection of austenitic stainless steel is provided.

In a third aspect of the invention, an austenitic stainless steel metallographic detection kit is provided, and the detection kit comprises the metallographic chemical polishing solution of the first aspect.

The beneficial effects of one or more technical schemes are as follows:

1. compared with the existing chemical polishing solution, the metallographic chemical polishing solution provided by the invention simplifies the components, is simpler to prepare, and further improves the safety of the preparation process and reduces the pollution risk by adding the fog inhibitor.

2. The prepared chemical metallographic polishing solution is convenient to store and carry, can be contained by using a common plastic reagent bottle, is suitable for laboratory detection, and can also be carried to a production site for metallographic detection. And the components are stable in property and not easy to deteriorate after being mixed, and can be used for a long time.

3. The chemical polishing solution provided by the invention is simple to operate when being applied to metallographic surface detection, high in field adaptability, free of mechanical equipment, good in polishing effect, easy to control in polishing speed due to the addition of thiourea serving as a corrosion inhibitor, and clear and real in obtained metallographic structure.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.

FIG. 1 is a photograph of the surface of the metallographic structure of the 18Cr-8Ni austenitic stainless steel in example 5 after chemical polishing;

wherein, FIG. 1a shows the metallographic structure surface after only chemical polishing; FIG. 1b is a metallographic structure surface after chemical polishing only and etching; fig. 1c shows the metallographic structure surface after mechanical polishing alone and etching.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

As described in the background art, the chemical polishing solution applied to austenitic stainless steel in the prior art is difficult to achieve the ideal effect, and may have the problems of gray film, no light, incapability of removing grinding scratches and the like. In order to solve the technical problems, the invention provides a metallographic chemical polishing solution which is applied to stainless steel surface treatment, and particularly can obtain a clear metallographic structure by austenitic stainless steel surface treatment.

In a first aspect of the present invention, a metallographic chemical polishing solution is provided, which comprises the following components: hydrochloric acid, phosphoric acid, sodium nitrate, hydrogen peroxide, ethanol, thiourea, a hydrochloric acid fog inhibitor and the balance of water.

Preferably, the concentration of hydrochloric acid in the chemical polishing solution is 1.4-1.92 mol/L.

More preferably, the present invention provides a method for preparing the above hydrochloric acid, wherein the chemical polishing solution is prepared from commercially available concentrated hydrochloric acid, and contains 120ml to 160ml of commercially available analytically pure hydrochloric acid in 1L of the chemical polishing solution, and the same is true for the chemical polishing solutions having other hydrochloric acid concentrations.

Furthermore, the 1L of chemical polishing solution contains 130-150 ml of commercially available analytically pure hydrochloric acid.

In some embodiments with better results, the concentrated hydrochloric acid content is 140ml per L, i.e. 1.68 mol/L.

In order to take polishing effect and economic cost into consideration, the hydrochloric acid is analytically pure commercial concentrated hydrochloric acid, usually a concentrated hydrochloric acid product with the mass fraction of 36-38%, and the concentration deviation does not influence the configuration and polishing effect of the chemical polishing solution disclosed by the invention.

According to the research of the invention, when the hydrochloric acid is lower than 1.4mol/L, the polishing solution has small chemical dissolution effect, slow dissolution speed, incomplete removal of an oxide layer and unsatisfactory polishing effect; when the concentration of hydrochloric acid exceeds 1.92mol/L, the dissolution corrosion process is aggravated, over corrosion is generated on the surface of stainless steel, the polishing performance of the polishing solution is reduced, and acid mist is easily formed due to serious volatilization, so that the sight is influenced. Test results show that when the concentration of the hydrochloric acid is 1.68mol/L, the polishing speed and the polishing quality can be both considered, and the effect is optimal.

Preferably, the concentration of the phosphoric acid is 1.8mol/L to 2.4 mol/L.

The research of the invention shows that the concentration of phosphoric acid has a great influence on the polishing quality, when the concentration of phosphoric acid is lower than 1.8mol/L, the phosphate conversion film on the surface of the metallographic measuring point is discontinuous, over-corrosion of the metallographic measuring point under the action of hydrochloric acid and nitric acid cannot be inhibited, and the polishing solution only has a corrosion effect on the metallographic measuring point; when the phosphoric acid concentration exceeds 2.4mol/L, the thickness and formation rate of the phosphate conversion film on the stainless steel surface are increased, the progress of the dissolution reaction is suppressed, and the polishing effect cannot be achieved. When the concentration of the phosphoric acid is 1.8mol/L, the polishing quality is optimal, the dissolution effect is realized, and an insoluble phosphate conversion film can be formed on the surface of the stainless steel, so that the over-dissolution of the metal is effectively inhibited.

The invention also provides a preparation method of the phosphoric acid, which adopts commercially available concentrated phosphoric acid (analytically pure, mass fraction is more than or equal to 85%) as a raw material to prepare the phosphoric acid, wherein the concentration of the phosphoric acid is 1.8-2.4 mol/L, namely, 120-160 ml of commercially available concentrated phosphoric acid product is added into 1L of chemical polishing solution. The concentration of the commercially available analytically pure concentrated phosphoric acid product is usually more than or equal to 85% by mass, and the concentration deviation does not influence the preparation and polishing effect of the chemical polishing solution.

Preferably, the content of the sodium nitrate is 50g/L to 70 g/L.

When the concentration of sodium nitrate in the solution is lower than 50g/L, an oxide layer on the surface of the metallographic measuring point is difficult to remove, and corrosion pits and pockmarks appear on the surface; when the concentration of sodium nitrate exceeds 70g/L, passivation is exerted on the surface of stainless steel, and the dissolution rate is reduced. The test result shows that when the concentration of the sodium nitrate is 60g/L, the polishing quality is optimal.

Preferably, the sodium nitrate is an analytically pure product, and the mass fraction is more than or equal to 99%.

Preferably, the concentration of the hydrogen peroxide is 80-100 ml/L. The hydrogen peroxide is viscous liquid, and the concentration of the hydrogen peroxide in the chemical polishing solution provided by the invention is 80-100 ml of pure hydrogen peroxide in each L of polishing solution. Because the hydrogen peroxide commercially available in the field is usually an analytically pure hydrogen peroxide (30% by mass), when the chemical polishing solution is prepared by using the commercially available product, 280-320 ml of 30% hydrogen peroxide product is required to be added into each L of the chemical polishing solution.

Preferably, the concentration of the absolute ethyl alcohol is 80-120 ml/L.

Preferably, the content of the thiourea is 4-6 g/L.

Preferably, the content of the hydrochloric acid fog inhibitor is 0.8-1.2 g/L.

In some specific embodiments of the above preferred technical solution, the chemical polishing solution per liter has the following component ratios: 140ml of commercial analytical pure concentrated hydrochloric acid, 140ml of commercial analytical pure concentrated phosphoric acid, 60g of sodium nitrate, 300ml of 30% hydrogen peroxide, 100ml of absolute ethyl alcohol, 5g of thiourea, 1g of antifogging agent hydrochloride and the balance of distilled water.

In some embodiments of the above preferred embodiment, the chemical polishing solution per liter has the following composition ratios: 130ml of commercial analytical pure concentrated hydrochloric acid, 160ml of commercial analytical pure concentrated phosphoric acid, 50g of sodium nitrate, 280ml of 30% hydrogen peroxide, 110ml of absolute ethyl alcohol, 6g of thiourea, 0.8g of hydrochloric acid antifogging agent and the balance of distilled water.

In some embodiments of the above preferred embodiment, the chemical polishing solution per liter has the following composition ratios: 150ml of commercial analytically pure concentrated hydrochloric acid, 120ml of commercial analytically pure concentrated phosphoric acid, 70g of sodium nitrate, 310ml of 30% hydrogen peroxide, 80ml of absolute ethyl alcohol, 4g of thiourea, 1.2g of hydrochloric acid antifogging agent and the balance of distilled water.

Preferably, the chemical gold image polishing solution is prepared by the following method: weighing distilled water, absolute ethyl alcohol and hydrogen peroxide, uniformly mixing, then adding hydrochloric acid and phosphoric acid, uniformly stirring, and then sequentially adding sodium nitrate, thiourea and a hydrochloric acid antifogging agent.

In a second aspect of the invention, the application of the metallographic chemical polishing solution of the first aspect in the field of metallographic detection of austenitic stainless steel is provided.

Preferably, the austenitic stainless steel contains about 18% of Cr and 8% -10% of Ni, namely 18Cr-8Ni type austenitic stainless steel.

Preferably, the polishing method of the metallographic chemical polishing solution comprises the following steps: adopt water absorbing material to dip in get metallography chemical polishing liquid cleans the metallography surface, through observing the surperficial mar condition, treats that the mar disappears, washs the metallography surface is dry.

Further preferably, the washing step uses absolute ethyl alcohol for washing.

Preferably, the polishing method of the metallographic chemical polishing solution comprises the following steps: and adding a workpiece to be polished into the metallographic chemical polishing solution for soaking, and wiping the metallographic surface by adopting a water absorbing material.

Further preferably, the water-absorbing material includes, but is not limited to, absorbent cotton, non-woven fabric, woolen cloth or velvet.

In a third aspect of the invention, an austenitic stainless steel metallographic detection kit is provided, and the detection kit comprises the metallographic chemical polishing solution of the first aspect.

Preferably, in the kit for metallographic examination of austenitic stainless steel, the raw materials of the metallographic chemical polishing solution, hydrochloric acid, phosphoric acid, sodium nitrate, hydrogen peroxide, ethanol, thiourea, a hydrochloric acid mist inhibitor and water are independently packaged and mixed uniformly in a container before use.

Preferably, in the austenitic stainless steel metallographic detection kit, the metallographic chemical polishing solution is a reagent prepared by premixing raw materials according to a ratio.

Preferably, the austenitic stainless steel metallographic detection kit further comprises other polishing tools, and the other polishing tools include, but are not limited to, bamboo clips, tweezers, absorbent cotton, polishing cloth, absolute ethyl alcohol and the like.

In order to make the technical solution of the present invention more clearly understood by those skilled in the art, the technical solution of the present invention will be described in detail with reference to specific examples, and the components of the following examples are all commercially available products unless otherwise specified.