vacuum heat treatment problems summary

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1. Is there quenching and Carburization in vacuum heating?
There are two misunderstandings in the analysis of carburization phenomenon of vacuum heat treatment workpiece: first, it is believed that the workpiece is carburized in quenching oil; second, it is believed that the graphite parts in the heating chamber cause carburization. In fact, in many cases, it is not these two reasons, but the cleanliness of the heating chamber is not high. There is a large amount of quenching oil in and out of the furnace, in and out of the material basket, in and out of the feeding trolley into the hot chamber, which remains on the cold wall of the hot chamber. When heating, a volatile reduction atmosphere is formed to increase the carbon of the workpiece.
In addition to 1050 ℃ high temperature above the temperature directly into the oil. When the heated workpiece oil below 1050 ℃ is quenched, a little precooling will not cause obvious carburization.
The carburization of the graphite parts in the heating chamber can not be ruled out, but there is no serious residual quenching atmosphere.
The carburization phenomenon of vacuum heating quenching is more serious because the quenching oil pollutes the furnace, not because of the oil quenching or graphite parts!

2. Small deformation of vacuum heat treatment (quenching)?
There are two concepts in heat treatment deformation: structure deformation and shape structure deformation. The results show that the deformation of vacuum heat treatment is the smallest when the same microstructure and hardness are obtained. That is to say, the tissue deformation is the smallest.
For the deformation of shape and structure, the vacuum heat treatment is often less than that of other furnace types. For the heat treatment of other furnace types, such as quenching, it is easy to control the deformation by grading, isothermal, straightening outside the furnace and other methods. Due to the imperfection of these functions, the vacuum quenching will sometimes increase.
The confusion of these two concepts gives people the impression that the deformation of vacuum heat treatment is small, which is a wrong or incomplete understanding!

3. My forging dimension is qualified, and the quality of heat treatment has nothing to do with my forging?
Forging process is to eliminate material defects, improve microstructure and improve material properties. Save machining amount and improve material utilization. However, today’s forgers forget to “eliminate material defects and improve the structure” and only “work hard” to ensure the forging size, regardless of the requirements of improving material properties. What’s more amazing is that some materials, through forging process, not improve the material performance, but damage the material performance. As a result, serious network carbide structure was formed in the material.
Because the heating temperature of material forging is much higher than that of heat treatment and quenching, the “serious network carbide structure” has structure heredity, which brings serious consequences to product quality.

4. My heat treatment hardness is qualified, and your product’s early failure has nothing to do with my heat treatment?
Heat treatment should not only ensure qualified hardness value, but also pay attention to process selection and process control. The required hardness can be achieved by superheated quenching and tempering; similarly, the required hardness can be achieved by adjusting the tempering temperature by quenching and underheating. There are plenty of people doing this. Some in order to save power consumption, under heat quenching; some due to the limit temperature of the furnace, under heat quenching. How does the early failure of such heat treatment products have nothing to do with heat treatment?

5. When I entrust you with heat treatment, my product is good. If your heat treatment is broken, you are responsible for compensation?
This statement is often encountered when dealing with the quality problems of heat treatment. After hearing this statement, the heat treatment personnel are really in tears. If you meet such a customer, the problem must be the customer, not the heat treatment! Because customers do not understand the manufacturing quality process control before heat treatment, they do not consider creating a good pre-treatment state for heat treatment.

6. The manual says that the hardness can be achieved by heat treatment and quenching. Why can’t you make this hardness?
Some people think that the hardness of his design is selected according to the hardness range in the manual. How can you say that the hardness can not be reached by heat treatment?
For example: the spring size 60Si2Mn is used to make large parts. Because the actual thickness of the workpiece is very large and the thickness is significant, there is no good way to achieve the required hardness standard in heat treatment. The hardness in the manual can reach 58-60HRC. There is no way to achieve it in combination with the actual workpiece. Only heat treatment requirements can be reduced.
The hardness of heat treatment is controlled by the following factors: material brand, die size, workpiece weight, shape and structure, and subsequent processing mode. After heat treatment, the internal and external hardness of the mold are not the same. The material and design size should be selected according to the size of the mold, not directly according to the technical standards and hardness requirements in the design manual. The hardness standards in the manual are the results of heat treatment from small samples. When applied to the real object, the reasonable hardness index must be determined according to the actual situation. Unreasonable hardness index, such as too high hardness, will lose the toughness of the workpiece, resulting in cracking of the workpiece.

7. This product is heat treated by you. I have problems in use. Are you responsible for heat treatment?
When an enterprise breaks the mold and injures the operator in the process of using the mold, the enterprise immediately informs the heat treatment manufacturer: how much do you want to compensate for the injury in the use of your heat treatment mold! Ask the reason, get the answer is, this product is your heat treatment processing, have an accident, so ask you to compensate. See what a justifiable reason!
Product failure should be analyzed from the aspects of design, material selection, material defects, process defects (including heat treatment), assembly and use to find out the real reasons. In order to shirk the responsibility, it is unreasonable to assume that the failure is caused by heat treatment. Why do doctors have to see patients in person? I think it’s the same reason that we need to make a comprehensive analysis of the design, material selection, material defects, process defects (including heat treatment), assembly and use process of waste products when we see products. We can’t directly identify which link has problems!

8. The heat treatment hardness HRC of my product can only be 60HRC. 59 or 61 HRC I can’t accept?
It is often encountered that the hardness value of the entrusted heat treatment product can only be on a certain value, and there can be no deviation! For example, if the hardness of heat treatment is required to reach 60HRC, and you reach 59HRC after heat treatment, or 61HRC is regarded as unqualified product. However, the allowable deviation of Rockwell hardness machine is still 1HRC!

9. The quenched workpiece is not cooled to room temperature and cannot be tempered?
Some people think that after quenching, when it has not cooled to room temperature, it can not enter the tempering process. In fact, the end point of martensitic transformation of many kinds of steel, especially low and medium carbon steel, is higher than room temperature. When it is cold to room temperature, it is easy to crack. After quenching, it can be transferred to tempering process as soon as possible.

10. The quenched workpiece must be tempered with temperature?
This method is not desirable, according to the martensitic transformation point of steel to determine the temperature of the furnace before tempering after quenching! In order to prevent quenching and cracking, it is not allowed to speculate. Generally speaking, tempering with temperature is adopted!

Learn More : Vacuum Heat Treatment Furnace