The first step in identifying any physical evidence is usually a macroscopic examination.

The same applies to metal particles.

It is necessary to use the naked eye, a magnifying glass, or a stereomicroscope to confirm the shape, color, size, and processing marks of the metal particles.

This step is relatively simple.

The researchers had already done this when they first discovered these metal particles.

Shen Ting confirmed there were no problems and proceeded directly to the second step.

Metallographic analysis!

This is the core content of metal identification.

The internal microstructure of a metal is usually referred to as its metallographic structure.

Different elemental compositions, different heat treatments and processing techniques will result in different metallographic structures.

Metallographic structure can be considered equivalent to the fingerprint of metal.

The steps involved in metallographic analysis are much more complex.

First, tiny samples are obtained, and then the samples are fixed with resin.

Next, the sample surface is polished to make it as smooth as possible, like a mirror.

Then, specific chemical reagents are used to corrode the surface of the metal particles.

This allows the grain boundaries and phase microstructure of the metal to be revealed.

Finally, of course, comes observation.

Use a specialized metallurgical microscope or scanning electron microscope to observe and photograph the processed samples.

The whole process seemed quite easy.

Almost all the appraisers around Shen Ting could understand it at a glance.

With a few practice sessions, they can easily master the skill on their own.

The most difficult part is actually the last step: "observation"!

This step requires neither complex nor precise operations.

What's needed is a vast amount of knowledge about metals.

Because by observing the metallographic structure, it is necessary to trace the processes that the metal has undergone.

Has it undergone quenching?

Has it undergone tempering?

And casting and forging?

Have you ever done carburizing or nitriding?

Has the surface been electroplated? Hot-dip galvanized? Or vapor-deposited?

These details require a keen eye.

And the eye for metal came from my knowledge of metals.

Therefore!

Previously, I thought the forensic experts seemed relaxed when they processed the samples.

At this moment, watching Shen Ting write down professional terms such as copper alloy base and spraying process in the appraisal book after a long period of observation, they all showed a bewildered expression.

They can easily learn how to process metal samples.

But how can we observe the sample to draw accurate conclusions about the precise metallographic structure?

This is not something they can learn just by wanting to.

It took Shen Ting a while to complete the second step: metallographic analysis.

The third step is component analysis.

This step typically involves using a scanning electron microscope/energy dispersive spectroscopy (EDS) to perform qualitative and quantitative elemental analysis on the metal particles.

This determines the specific chemical element composition and content.

The fourth and fifth steps are fracture analysis and mechanical property testing, respectively.

It is mainly used to determine the cross-sectional shape of metal.

And by determining properties such as hardness and strength, it helps to identify the type and state of metals.

These two steps are not necessary for all metals.

Shen Ting quickly skipped over it.

He then selected several more metal particles and repeated the identification.

This is also the standard procedure.

The conclusions drawn from identifying only a single particle are not convincing.

As the number of particles identified increased, a hint of surprise appeared on Shen Ting's face.

From dawn until the sun is high in the sky, then it begins to set in the west.

Around 3 p.m., Shen Ting wrote and drew on the appraisal report and signed it at the end.

After piecing together the reports, Shen Ting looked at Director Ma beside him:

"We have the results."

"So fast?"

What was the result?

Will it help with the case investigation?

Director Ma quickly replied.

The other appraisers around also looked at Shen Ting with curiosity.

From the moment they started observing the metallographic structure, all they could really understand was how Shen Ting operated the instruments.

What he was observing, and the conclusions he drew from those characteristics, remained completely unknown to everyone.

Shen Ting glanced at Guan Guandu and Zheng Yuanqiao, who were also anxiously waiting outside the appraisal room, and smiled:

"Let's talk outside!"

...