Quenching and high temperature tempering：: namely the comprehensive heat treatment process of quenching and tempering at high temperature.
Tempering parts mostly work under relatively large dynamic load, they bear the role of stretching, compression, bending, torsion, or shear, some surfaces also have friction, require certain wear resistance, and so on. In short, the parts work under a variety of composite stresses. These parts are mainly structural parts of various machines and mechanisms, such as shafts, connecting rods, studs, gears, etc. They are widely used in the manufacturing industry of machine tools, automobiles, tractors, etc. Especially for large parts in heavy machinery, tempering is used more. Therefore, tempering treatment plays a very important role in heat treatment.
Tempering parts in mechanical products, due to their different stress conditions, the required performance is not exactly the same. Generally speaking, all kinds of tempering parts should have excellent comprehensive mechanical properties, that is, the appropriate combination of high strength and high toughness, in order to ensure that the parts work smoothly for a long time.
Quenching and tempering usually refer to quenching + high temperature tempering to obtain the heat treatment process of tempering Soxhlet. The method is quenching, quenching temperature: Ac3+30~50℃; The hypereutectoid steel was Ac1+30~50℃. Alloy steel is slightly superior to carbon steel. After quenching, it can be tempered at 500~650℃.
Is it difficult to temper?
The simplest is actually the hardest.
Sometimes this is the case, both to conform to the rules, but also to be flexible, the “degree” is difficult to grasp.
Here’s how the masters of the heat treatment forum say:
I: Take me in the professional heat treatment plant as an example to say the difficulty of tempering:
1. The materials provided by many customers are not accurate. Until now, there are delivery notes stating “carbon steel”, “cold-rolled plate” and “spring steel”, which is really embarrassing.
2. Some parts are of complex shape and critical size, and each heat treatment plant is equipped with limitations. If you do not choose a good quenching temperature and quenching agent, cracking or deformation will occur; The high quenching temperature is easy to crack. The unreasonable holding time will increase the deformation, and the quenching temperature will below. In order to maintain the hardness, the tempering temperature will be reduced. Although the hardness is qualified, the microstructure and performance indexes cannot meet the requirements of the drawing.
3, quenched and tempered treatment is important, but is just a process of the product manufacturing process, improve the quality at the same time, also must look the former, pay attention to the forging process with and without problems and subsequent machining facilities, otherwise people will come to you the quality, forging said you conditioning technology is bad, machining quality of said you can’t, difficult processing…
4. Some tempering products used in wind power or extreme environments require impact toughness of minus 30 or 40 degrees. To be honest, tempering temperature, time, cooling and tempering must reach the most ideal state., did in recent 10 years in the professional heat treatment processing factory, to summarize, tempering, quenching, the other as long as the intention to drill, heat treatment quality in meeting the requirements of the drawings is not difficult, really difficult is to make sure you do every batch of products, each piece of samples from the beginning to the end of the last batch of parts, are the same quality status is the real difficulty, it is key of poor heat treatment quality level in our country and abroad.
2: I think as long as the equipment can meet, such as the furnace size, furnace temperature uniformity, temperature control precision, quenching delay time, the furnace temperature, heating rate, furnace cooling speed, the cooling speed of quenching liquid (including aging degree, impurities, etc., cycle), the cleaning quality no problem, the best automation control, raw materials have a warranty and into the factory inspection report, workers to strictly carry out the process. Tempering is easy,
Of course, the accumulation of experience is in the ordinary, it is certainly easy to do.
Difficult tempering process: heating temperature, holding time, cooling medium, shape, and size of workpiece, existing equipment, technical requirements, process execution
4. Theoretically speaking, tempering is the process of quenching and tempering at high temperatures to obtain tempering Soxhlet. If one of the steps does not meet the requirements, the conditioning will not be very good, so the difficulty is indeed great. Strictly speaking, not only hardness requirements but also metallographic structure requirements should be met. If only hardness requirement is considered and microstructure performance is not considered, it will not be too difficult, but it will often result in poor tempering structure.
5. Tempering is indeed an important process, but to achieve the desired goal of tempering, we must strictly control the tempering process of each link! Includes heating temperature, holding time, cooling medium, tempering temperature, and so on! From my personal summary, I think the real quality is stable, in the process of production, we must reduce the impact of the human factor! If you want to ensure high-quality tempering parts, you should upgrade the quality production line! Completely rely on equipment, rely on technology to ensure the quality of equipment!!
6. Tempering as a pre-heat treatment, the first consideration of deformation and oxidation room is relatively large, but the quality of tempering is difficult to control! I think the difficulty lies in:
First: the instability of the material! The problem often occurs when this batch of material is qualified and that batch of material is not
Second, the influence of the external environment is the same in summer and the same in winter (this is similar to normalizing, mainly due to the influence of the cooling medium).
The influence of the third equipment, generally as a kind of pre-heat treatment, dry is mostly blank, so no matter loading and unloading or operation, including the design of the furnace are relatively rough, the equipment is not precise and artificial not rigor often have a great impact on the quality of products!
7. Take the crankshaft as an example for the difficulty of tempering, due to the complex shape of parts, quenching temperature and quenching agent choice becomes the key: high quenching temperature choice, there will be cracks; The quenching temperature is low, and the tempering temperature is reduced. Although the hardness is qualified, the microstructure and property indexes cannot meet the requirements of the drawings. If you choose the material in the middle, the situation will be more complicated.
Tempering is not easy, tempering knowledge is very big, do more records to accumulate experience.