Chapter five hundred and fiftieth chapters answer like a flow
Ding Huaizhong has already told Liu Lang the identities of these eleven professors. Professor Phils is very famous and is a senior domestic expert in material smelting.
"Professor Phils, I am very honored by your request!"
Liu Lang answered with a smile.
I am a metallurgist, so please explain heat treatment to me!
Phils asked.
This question is a basic subject in the metallurgical industry. In order to make pig iron into steel, it must be heat treated, so Liu Lang came up with it.
The overall heat treatment is a metal heat treatment process that heats the workpiece as a whole and then cools it at an appropriate speed to change its overall mechanical properties. The overall heat treatment of steel generally has four basic processes: annealing, normalizing, quenching and tempering. Annealing, normalizing,
Quenching and tempering are the "four fires" in overall heat treatment. Among them, quenching and tempering are closely related and are often used together. One is indispensable...
Liu Lang explained annealing, normalizing, quenching and tempering in detail, and it only took five minutes in total.
"Well, not bad, I've finished asking my questions!"
Phils nodded.
This question is really simple, because it is basically a noun explanation question! But it is indeed a question within the scope of undergraduate courses and will not cause any doubts.
However, Claire, who was sitting not far away, curled his lips. Apparently he felt that asking such a question in an exam of this level was really out of standard.
"Liu Lang, my name is David Dulin, I am also majoring in metallurgy. Professor Phils asked a very good question just now, but I want to ask another question, that is, what is the difference between tempering and annealing?"
Liu Lang nodded and answered directly without thinking.
“The difference between annealing and tempering is that annealing does not require hardness, while tempering retains a certain hardness.
The structure obtained by high temperature tempering is tempered troostite. 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 and high temperature tempering according to the different tempering temperatures. Tempered martensite, troostite and troostite are obtained respectively. The heat treatment that combines high temperature tempering after quenching is called quenching and tempering treatment
, its purpose is to obtain comprehensive mechanical properties with good strength, hardness, plasticity and toughness.
Pearlite transformation occurs during the annealing process. The main purpose of annealing is to make the internal structure of the metal reach or approach an equilibrium state to prepare for subsequent processing and final heat treatment.
Stress relief annealing is an annealing process performed to eliminate residual stress in castings caused by plastic deformation, welding, etc. There are internal stresses inside the workpiece after forging, casting, welding and cutting. If not eliminated in time,
This will cause the workpiece to deform during processing and use, affecting the accuracy of the workpiece."
"Well, well, yes, yes, heat treatment is the essence of smelting. It will give the steel a soul. It's pretty good that you can master it to this extent."
The other party nodded repeatedly.
In fact, this question is also simple. It is basically found in textbooks, but it is not as concise as Liu Lang's answer. Liu Lang has done experiments in the heat treatment workshop with Professor Xiong Huaizhi and other experienced experts, and knows every step well.
"That's a good answer, let me ask next!"
The third brother is an expert in mold design.
"There is a batch of Cr12MoV steel used to make more complex molds. The molds all have Φ60mm round holes. After the heat treatment of the molds, some of the mold round holes appear elliptical, causing the molds to be scrapped. Generally speaking, Cr12MoV steel is a micro-deformed steel and should not have larger
Deformation. We conducted metallographic analysis on severely deformed molds and found that the mold steel contains a large amount of eutectic carbides, which are distributed in strips and blocks. Let me ask you, what may be the cause of mold deformation? How to prevent it?
"
The difficulty of this question suddenly increased because it is a subjective question that will not appear in books and requires candidates to have strong practical and analytical abilities.
"This old Joseph always asks these difficult questions that he has encountered!"
Phils glared at the other party fiercely, because he felt that this question was beyond the scope of what ordinary undergraduates could answer.
Liu Lang thought for a moment and said.
"The cause of mold deformation is the existence of uneven carbides distributed in a certain direction in the mold steel. The expansion coefficient of carbides is about 30% smaller than the matrix structure of the steel. It prevents the inner pores of the mold from expanding when heated, and prevents the inner pores of the mold from expanding when cooled.
It prevents the inner hole of the mold from shrinking and causes uneven deformation of the inner hole of the mold, causing the round hole of the mold to appear elliptical.”
The answer was very concise, and the other party nodded slightly. It was obvious that Liu Lang was very accurate.
“The preventive measure is to choose mold steel with less carbide segregation when manufacturing precision and complex molds.
For mold steels with severe segregation of carbides, reasonable forging must be carried out to break the carbide crystal blocks, reduce the level of uneven distribution of carbides, and eliminate anisotropy in performance.
The forged mold steel must be quenched and tempered to obtain a uniformly distributed, fine and dispersed sorbite structure, thereby reducing the deformation of precision and complex molds after heat treatment.
For molds that are large in size or cannot be forged, solid solution double refinement treatment can be used to refine the carbide, distribute it evenly, and round the edges and corners, which can achieve the purpose of reducing the heat treatment deformation of the mold."
Liu Lang continued.
"Well said, you are right. I never thought you could answer this question so concisely. Molds are the foundation of all processing and manufacturing. Without molds, nothing can be made. Liu Lang, you may consider coming to my place!"
"Old Joseph, what is a mold that is the basis of manufacturing? How can you make a mold without good materials?"
Phils was a little unhappy, but it was not because the other party emphasized the importance of the mold, but because he was poaching his own "corner" in front of him.
"Fiers, the future of the manufacturing industry is precision instruments and CNC machine tools. Without molds, what can you make?"
Professor Joseph retorted on the spot.
"Huh, CNC machine tools also need to be made of alloy materials. If you don't have materials, just use scrap iron to make molds!"
The other party retorted.
Liu Lang chuckled to himself. These two people were over a hundred years old in total, but they were still noisy like children. In fact, Liu Lang liked people like this. Experts like them had "simple" thoughts and there was nothing messy about them.
The idea is that such talents will not be affected by external factors and can devote themselves to their work.
Professor Xiong Huaizhi is also such a person. He raises issues when he sees something wrong. However, during the chaos of those ten years, such people were sent to the bullpen. In the United States, only such pure people can achieve success.
"Stop making noise!"
The host reminded the two of them.
"Professor Phils, it is Professor Joseph who is asking the question now, no one else can interrupt him!"
"Okay, let him ask!"
Phils spread his hands.
"I have finished asking, and classmate Liu Lang answered very well!"
Professor Phils said.
"Okay, let's ask the next professor!"
"Liu Lang, please tell me the types of grinding wheel clogging!"
Next a professor asked.
“The types of grinding wheel clogging include embedded type, adhesive type and mixed type.
Embedded clogging is a clogging state in which the grinding debris is embedded in the gaps on the working surface of the grinding wheel; adhesive clogging is a clogging state in which the wear debris is fused to the abrasive grains and binders; mixed clogging is a clogging state in which there are both embedded clogging and adhesive clogging.
Blocked…!”
Liu Lang answered immediately, and the result was that the other party nodded repeatedly.
After three questions, everyone already thought that there would be no problem for Liu Lang to become a graduate student, and they felt that Liu Lang was able to master so much knowledge despite China's current backward education level, and that his talent in mechanics was outstanding.