Don't be misled by these heat treatment problems when treating steel pipes -A!

1. Does vacuum heating cause quenching and carbonization?
When analyzing the carbonization phenomenon of vacuum heat treatment workpieces, there are two misunderstandings: one is that the workpiece is carbonized in the quenching oil; and the other is that the graphite parts in the heating chamber are carbonized. In fact, in many cases, it is not these two reasons, but the cleanliness of the heating chamber is not high. A large amount of quenching oil is brought into the hot chamber when the workpiece enters and exits the furnace, the material basket is polluted, and the feeding trolley enters and exits. It remains on the cold wall of the hot chamber, forming a volatile reducing atmosphere during heating, which increases the carbonization of the workpiece.
Except for directly entering the oil at a temperature above 1050℃. When the heated workpiece is oil quenched below 1050℃, a slight pre-cooling before entering the oil will not form an obvious carbonization phenomenon. The carbonization phenomenon of vacuum heating quenching is more serious because of the pollution of the furnace by the quenching oil, not the so-called quenching in oil or graphite parts!

2. Is the deformation of vacuum heat treatment (quenching) small?
There are two concepts in heat treatment deformation: organizational deformation and shape and structure deformation. The result of the study is: that vacuum heat treatment has the smallest deformation when the same structure and hardness are obtained as other furnace-type heat treatments. That is: the deformation of the structure is the smallest. For shape and structure deformation, vacuum heat treatment is often not as small as other furnace-type heat treatments. Other furnace-type heat treatments, such as quenching, can easily use grading, isothermal, and out-of-furnace straightening methods to control the amount of deformation. Vacuum quenching sometimes increases the deformation due to the imperfection of these functions. The confusion of these two concepts gives people the impression that vacuum heat treatment has small deformation, which is a wrong or incomplete understanding!

3. Is tempering color related to temperature?
After tempering, the surface of the steel presents a color of an oxide film, which is called tempering color. In many cases, the tempering temperature needs to be determined based on the tempering color. The tempering color changes with temperature, so the tempering temperature can be roughly determined based on the tempering color. However, the tempering color is also related to the tempering time, which is usually based on 5 minutes.

The tempering color of carbon steel at different temperatures, based on 5 minutes, the surface color is as follows:
Light yellow: 200℃; straw yellow: 220℃; brown: 240℃; purple: 260℃; blue-purple: 280℃; dark blue: 290℃; blue: 300℃; light blue: 320℃; blue-gray: 350℃; gray: 400℃.
The tempering color of stainless steel at different temperatures:
Light wheat yellow: 290℃; wheat yellow: 340℃; light reddish brown: 390℃; light red: 450℃; light blue: 530℃; dark blue: 600℃.
Tempering color of low alloy steel at different temperatures:
Light wheat yellow: 225℃; wheat yellow: 235℃; light reddish brown: 265℃; light red: 280℃; light blue: 290℃; dark blue: 315℃.
However, in many materials, only the relationship between color and temperature is mentioned, ignoring the key premise of time. At the same temperature, as the insulation time increases, the final color will tend to be a higher temperature color. Often it will cause a misjudgment of the actual temperature.

4 The forging size of the steel pipe is qualified, and the heat treatment quality problem has nothing to do with the forging of the steel pipe.
The forging process is to eliminate material defects, improve the organizational morphology, and improve material performance. Save mechanical cutting processing and improve material utilization. However, today's forgers have completely forgotten "eliminating material defects and improving organizational morphology", and only "working hard" on ensuring the forging size, completely ignoring the requirements for improving material performance. What is even more amazing is that some materials have not improved the material performance through the forging process, but have damaged the material performance. The forger indiscriminately used the forging residual heat annealing method, resulting in the formation of a severe network carbide structure in the material.
Since the heating temperature of the material forging is mostly much higher than the heating temperature of the heat treatment quenching, the "serious network carbide structure" has tissue inheritance, which has serious consequences for product quality.

6. The heat treatment hardness of the steel pipe is qualified, and the early failure of the steel pipe has nothing to do with the heat treatment.
Heat treatment should not only ensure the qualified hardness value but also pay attention to process selection and process control. Overheated quenching and tempering can achieve the required hardness; similarly, underheated quenching can also make do with the required hardness range by adjusting the tempering temperature. This practice is common. Some underheat quenching to save electricity; some underheat quenching due to the extreme temperature limit of the heating furnace. How can the early failure of such heat-treated products have nothing to do with heat treatment?

7. When the buyer entrusts the heat treatment, the steel pipe is good, and you mess up the heat treatment. Is the heat treatment of the steel pipe responsible for compensation?
This statement is often encountered when dealing with heat treatment quality issues. After hearing this statement, heat treatment people don't know whether to laugh or cry. If you encounter such a customer, the problem must be with the customer, not the heat treatment! Because the customer has no understanding of the manufacturing quality process control before heat treatment and has not considered creating a good pretreatment state for heat treatment.

8. You can achieve this hardness by heat treatment quenching, why can't you achieve this hardness?
Some people think that the hardness selection during design is selected according to the hardness range in the manual. How can the heat treatment of steel pipes not reach this hardness?
For example: using spring steel 60Si2Mn to make large parts, due to the large thickness of the actual workpiece, the thickness is significant, and there is no good way to achieve the required hardness standard by heat treatment. The hardness in the manual can reach: 58-60HRC. There is no way to achieve it in combination with the actual workpiece. The heat treatment requirements can only be reduced. The hardness of heat treatment is controlled by the following factors: material brand, mold size, workpiece weight, shape structure, subsequent processing method, and other factors. After heat treatment, the hardness of the mold inside and outside is not the same. The material and design size should be selected according to the size of the mold. It cannot be selected directly according to the technical standards and hardness requirements in the design manual. The hardness standard in the manual is from the heat treatment results of small samples. When applied to the actual object, it is necessary to determine the reasonable hardness index according to the actual situation. Unreasonable hardness index, such as too high hardness, will lose the toughness of the workpiece and cause the workpiece to crack during use.

9. This steel pipe is heat-treated. If there is a problem during use, is the heat treatment responsible?
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 reason. It is unreasonable to arbitrarily determine that the failure is caused by heat treatment to shirk responsibility. Why doctors must see the patient in person when seeing a doctor? I think it is the same as we need to conduct a comprehensive analysis of the design, material selection, material defects, process defects (including heat treatment), assembly and use process of the waste product for product failure. It is not possible to directly determine which link has a problem!

This matter was later identified by the most authoritative organization. The quality of heat treatment is completely normal and is not the cause of the accident. The real reason is the use problem-----overload!