Ding Huaizhong has already told Liu Lang the identities of these eleven professors, this Professor Fils is very famous, and he is a senior expert in material smelting in China.

"Professor Firth, I am very honored by your request!"

Liu Lang replied with a smile.

I'm an expert in metallurgy, so you can explain heat treatment to me!

Fils asked.

This problem is the basic discipline of the metallurgical industry, and if pig iron wants to be made into steel, it must be heat treated, so Liu Lang opened his mouth to come.

Integral heat treatment is a metal heat treatment process in which the workpiece is heated as a whole and then cooled at an appropriate rate to change its overall mechanical properties. There are four basic processes for the overall heat treatment of steel: annealing, normalizing, quenching and tempering. Annealing, normalizing, quenching and tempering are the "four fires" in the overall heat treatment, in which quenching and tempering are closely related, often used together, and all of them .........are indispensable.

Liu Lang explained the annealing, normalizing, quenching and tempering in detail, and it took only five minutes to share.

"Well, yes, I'm done with my question!"

Fils nodded.

It's a simple question, because it's just a noun explanation question, but it's also a question that doesn't raise any questions about the scope of an undergraduate course.

However, Claire, who was sitting not far away, pouted, obviously feeling that it was a big mistake to ask such a question in an exam of this level.

"Liu Lang, my name is David Dulin, I also majored in metallurgy, Professor Fils asked a good question just now, but I want to ask a question, that is, what is the difference between tempering and annealing?"

Liu Lang nodded and replied directly without thinking.

"The difference between annealing and tempering is that annealing is not hardness, and tempering still retains a certain hardness.

The structure obtained by high temperature tempering is tempered sostenite. Tempering is generally not used alone, the main purpose is to eliminate quenching stress and obtain the required structure.

Tempering is divided into low temperature, medium temperature and high temperature tempering according to the different tempering temperatures. Tempered martensite, drossite, and soxenite were obtained, respectively. Among them, the heat treatment combined with high temperature tempering after quenching is called quenching and tempering treatment, and its purpose is to obtain comprehensive mechanical properties with good strength, hardness, plasticity and toughness.

The main purpose of annealing is to bring the internal structure of the metal to or near equilibrium in preparation for subsequent processing and final heat treatment.

Stress relief annealing is an annealing process that eliminates residual stresses caused by plastic deformation processing, welding, etc., as well as within castings. There is internal stress in the workpiece after forging, casting, welding and cutting, if it is not eliminated in time, the workpiece will be deformed in the process of processing and use, and the accuracy of the workpiece will be affected. ”

"Well, well, yes, yes, heat treatment is the essence of smelting, it gives the soul of steel, and it's good that you've mastered it to such an extent. ”

The other party nodded again and again.

In fact, this question is also very simple, basically in the textbook, but not as concise as Liu Lang's answer, Liu Lang and Professor Xiong Huaizhi and their old experts have done experiments in the heat treatment workshop, and they know every step well.

"That's a good answer, I'll ask!"

The third brother is an expert in mold design.

"There is a batch of Cr12MoV steel, manufacturing more complex molds, the molds are with Φ60mm round holes, after the mold heat treatment, part of the mold round holes appear elliptical, resulting in the mold scrapped. Generally speaking, Cr12MoV steel is a slightly deformed steel and should not exhibit large deformation. We have carried out metallographic analysis on the mold with serious deformation and found that the mold steel contains a large amount of eutectic carbide, and it is distributed in strips and blocks.

The difficulty of this question comes up all of a sudden, because it is a subjective question that will not appear in books, and requires candidates to have strong practical and analytical skills.

"This old Joseph always asks these questions about the problems he has encountered!"

Fils glared at the other fiercely, because he felt that the question was beyond the scope of the average undergraduate's answer.

Liu Lang thought for a moment and said.

"The reason for the mold deformation is because of the existence of uneven carbides distributed in a certain direction in the mold steel, the expansion coefficient of carbide is about 30% smaller than the matrix structure of steel, it prevents the expansion of the mold hole when heating, and prevents the mold hole from shrinking when cooling, so that the mold hole is unevenly deformed, so that the round hole of the mold is elliptical. ”

The answer was very concise, and the other party nodded slightly, obviously Liu Lang said very accurately.

"The precautionary measure is to choose a die steel with less carbide segregation when manufacturing delicate and complex molds.

For die steels with serious carbide segregation, reasonable forging should be carried out to break the carbide crystals, reduce the grade of uneven distribution of carbide, and eliminate the anisotropy of performance.

The forged die steel should be quenched and tempered to obtain a homogeneous, fine and diffuse sostenite structure with uniform carbide distribution, so as to reduce the deformation of the precision and complex die after heat treatment.

For molds with large size or cannot be forged, solid solution double refinement treatment can be used to refine and distribute carbides, and round edges and corners, which can achieve the purpose of reducing the heat treatment deformation of molds. ”

Liu Lang continued.

"Well said, that's right, I really can't imagine that you can answer this question so succinctly, mold is the foundation of all processing and manufacturing, without mold, nothing can be made, Liu Lang, you can consider coming to me!"

"Old Joseph, what is the basis of molding, and what do you use to make molds without good materials?"

Fils was a little unhappy, but he was not because the other party highlighted the importance of the mold, but dug his "corner" in front of him.

"Fils, the future of the manufacturing industry is precision instruments and CNC machine tools, what do you use to build without molds?"

Professor Joseph went back on the spot.

"Hmph, CNC machine tools also need to be made of alloy materials, if there is no material, you can use scrap iron to make molds!"

The other side retorted.

Liu Lang laughed secretly on the side, these two people are more than 100 years old together, but they are still noisy like children, in fact, Liu Lang likes this kind of person, experts like them are very "simple", there is no nonsense of ideas, such talents will not be affected by external factors, and can devote themselves to work.

Professor Xiong Huaizhi is also such a person, he sees something wrong and brings it up, but in the chaos of the decade, such people were sent to the cowshed, and in the United States, such a pure person will succeed.

"Don't make any noise!"

The host reminded the two.

"Professor Firth, it's Professor Joseph asking the question now, and no one else can interrupt him!"

"Okay, he asked!"

Phils spread his hands.

"I've finished asking, and Liu Lang answered very well!"

Professor Fils said.

"Okay, then the next professor asks a question!"

"Liu Lang, tell me about the several types of grinding wheel blockage!"

The next professor asked.

"There are types of grinding wheel jams: flushed, bonded and mixed.

Embedded plugging is the plugging state of abrasive chips impounding in the void of the working surface of the grinding wheel, adhesive plugging is the plugging state of abrasive chips fused on abrasive particles and binders, and mixed plugging is the ......... of both embedded and adhesive plugging!"

Liu Lang replied immediately, and the result was that the other party nodded again and again.

After the three questions, everyone already thought that Liu Lang had no problem becoming a graduate student, and they felt that Liu Lang could master so much knowledge under China's current backward education level, and his talent in mechanics was outstanding.