How do you check metallography? How to polish corrosion?

Let's go into more detail, what materials, what samples, what needs to be observed.

There are two methods in the preparation of metallographic samples: chemical corrosion and electrolytic corrosion. Chemical corrosion is to corrode the polished surface of the polished sample in a chemical corrosive agent for a certain period of time, so as to show the microstructure and morphology of the sample.

The equipment used for electrolytic corrosion is the same as for electropolishing, but the operating voltage and current are smaller than those used for electropolishing. At this time, a thin film is generally not formed on the grinding surface of the sample, and due to the different potentials between the phases and between the grains and the grain boundaries, the corrosion degree of each phase is different under the action of weak current, so the structure is displayed. It is suitable for materials with strong corrosion resistance and difficult to be corroded by chemical corrosion.

There are many types of erosion agent formulations, all of which are often specific to the material to be attacked. It's best to have a manual handy, but a special metallographic manual can also be a metal materials manual.

Metallographic corrosion is the metallographic sample after several sandpaper smoothing, flannel polishing and then corroding with the corresponding erosive agent to show the microstructure of the metal material. Corrosive agents include nitric acid alcohol (for general alloy steel), ferric chloride solution (for copper alloy), etc.

The younger brother is engaged in welding control, which belongs to automatic control. Never been exposed to the chemical, metal side before.

However, the welded product, according to the research requirements, can be seen metallographic, that is, two pieces of iron, after resistance welding, the middle part melts and joins together, and then cuts horizontally with a cutting knife to observe the difference between the melted part in the middle and the part that is not melted. It is said that after sanding, a certain amount of corrosive liquid should be added for a certain period of time, and then placed under a microscope for observation, but I don't understand this at all. In this case, what kind of corrosive fluid should be added, and how long is it?

The material is ordinary iron sheets, thank you!

I asked this question before, thanks to the help of netizens, I know that there is this answer:

If you need to do metallographic style, you need to grind first, wipe it with 4% nitric acid alcohol for 4-5 times after polishing, then wash it with water, and then rinse it with alcohol and dry it with hot blow-dryer.

Sanding, sandpaper, polishing, washing, alcohol, 4% nitric acid alcohol corrosion, alcohol, washing, blow drying.

The questions you may ask are very naïve and mentally retarded, but you are very helpless, a complete layman, and the last time you studied chemistry was chemistry in the third year of high school.

2.The specific time when the metal corrodes.

3.The tools for the operation of the above processes and so on.

This is the knowledge of physical optics, before corrosion, because the specimen is relatively flat, most of the light is reflected, so what is seen is bright. After corrosion, there are different shades of surface. The degree of reflex is different, and different tissue characteristics are displayed.

Metals are made up of phases that take on different colors when eroded. One of the tasks of metallographic is to obtain characteristics such as color, morphology, etc.

The corrosion resistance of each substructure is different, for example, martensitic is more corrosion-resistant than ferrite, so after erosion, the corrosion depth is different, and the scattered reflected light under the microscope is different.

In fact, it is okay to adjust the brightness darker.

The steel grades are TP304 and TP347, and now the sample has been inlaid completely, but there is a problem in polishing, the plush fabric used for coarse grinding and the diamond grinding penny with large grinding capacity should not be long and the pressure should not be large.

The strength is moderate to ensure the number of polishing pastes.

Before polishing, you need to:1The abrasive paste is applied evenly; 2.Hold the specimen in your hand and slowly attach it to a rotating polishing cloth.

The polishing process is done:1Do not press the specimen too hard; 2.

Pick it up and observe the polished surface quickly, and grind it slowly again; 3.When adding water, try to pour water along the center of the radius of the polishing cloth, and do not drench your hands, otherwise it will reduce the friction between your hands and the sample, and the sample may fly out.

After polishing, scrub the grinding surface in one direction with an alcohol swab, never rotate the rub, and do not rinse with water.

The key is to use light force at the end.

It should be possible to use aqua regia Generally, austenitic stainless steel can be used, and the wiping effect with ferric chloride hydrochloric acid reagent is also good, and the time is better controlled than aqua regia. If you want to explain, the oxalic acid reagent mentioned upstairs is a good choice.

Perchloric acid electrolytic polishing liquid, be careful when using, the temperature is too high (the current is too high, the temperature will be too high), pay attention to the cooling means, generally I will not use this. Electrolytic corrosion can be considered for corrosion.

The name of this steel, Al-6XN, is imported, and the composition is very consistent with the standard composition.

Corrosion can generally be done with nitric acid alcohol