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20 common misunderstandings of heat treatment

Heat treatment as one of the most important processes in the forging industry. many of our heat treatment counterparts will encounter a variety of product problems. This article is an example of some heat treatment misconceptions experienced by an old heat treatment plant manager working for many years. All are real problems encountered in the work. Share out for your reference.

1. This product is your heat treatment. I have problems in use. you heat treatment responsible?

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An enterprise in the use of mold process occurred in the mold fracture injured the operator. the enterprise immediately informed the heat treatment manufacturers: in your home heat treatment of the mold in use injured. you have to compensate how much how much! Asked the reason. the answer is. this product is your heat treatment processing. an accident. so you are required to compensate. Look how justified the reason!
Product failure should be analyzed from the design. material selection. material defects. process defects (including heat treatment). assembly and use. etc.. to find the real cause. In order to shirk responsibility arbitrarily determined that the cause of heat treatment failure is not justified. Why must the doctor see the patient personally. I think and we have to do a comprehensive analysis of the product failure of the design. material selection. material defects. process defects (including heat treatment). assembly and use of the process is a reason. can not be directly identified is which link has the same problem!
This matter was later identified by the most authoritative institutions. the quality of heat treatment is completely normal. not the cause of that accident. The real reason is the use of the problem is overload.

The lack of knowledge of an industry is understandable. but dealing with the problem is not the adoption of a scientific attitude is ignorant. I am happy to work in heat treatment. why? You see heat treatment has been able to “cure all diseases”. everything is looking for heat treatment ah!

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2. I entrusted you with heat treatment. my products are good. you heat treatment messed up. you heat treatment is responsible for compensation?

This statement in the treatment of heat treatment quality problems. will often encounter. after hearing this statement. heat treatment people are really crying and laughing. If you encounter such customers. the problem must be in the customer. not heat treatment problems! Because the customer does not understand the manufacturing quality process control before heat treatment at all. did not consider creating a good pre-treatment state for heat treatment.

3. My product heat treatment hardness HRC can only be 60HRC. 59 or 61HRC I can not accept?

Often encounter commissioned heat treatment products hardness value can only be on a certain determined value. can not have deviation! For example. the requirement of heat treatment hardness to 60HRC. you heat treatment after reaching 59HRC. or 61HRC is considered unqualified products. If you explain to him the reason for heat treatment. he will put on a face of God: Do you want to do my heat treatment products? The market competition! Heat treatment manufacturers had to undertake hard. as for heat treatment manufacturers how to get better? The peers can certainly guess out!
Really “how bold people are. the ground has much production”.

4. Quenching out of the workpiece is not cold to room temperature. can not be tempered?

Some people think that after quenching out. not yet cooled to room temperature. can not enter the tempering process. In fact. many steel grades. especially low and medium carbon steel. the martensite transformation end point is mostly higher than the room temperature. cold to room temperature. but easy to crack. quenched out as soon as possible after the tempering process.

5. Quenching out of the workpiece must be tempered with temperature?

This practice is not desirable. according to the steel martensite transformation point to determine the tempering temperature after quenching before the furnace! In order to prevent quenching and cracking. you can not presume to use a generalized approach to tempering with temperature!

6. My products after annealing. to be placed after a week. you can heat treatment quenching?

Individual bosses claim to have the secret to improve the service life of the mold! What is his secret? To find out what it is. it is surprising that the heat treaters are required to do the annealing treatment after the quenching and tempering treatment can not be carried out immediately. The mold must be left at room temperature for a week between annealing and quenching! Say: release annealing stress! This reasoning does not know which experts can give answers?
The world is really big!

7. The size of the product processing has been fully completed. the heat treatment to ensure that no deformation?

Some people in order to save product processing costs. before the heat treatment. all the dimensions of the end of processing. and then go to the heat treatment quenching and tempering. Heat treaters are required to ensure that no deformation in the heat treatment process. or only allow the amount of deformation in the last cold working tolerance band value! The process of heat treatment is essentially a stage of tissue deformation. the accumulation of deformation on a microscopic level. who dares to guarantee that it does not manifest itself in the macroscopic level as dimensional deformation?
In order to save his own costs. the problem is transferred to the heat treatment. these people “smart”. right?

8. Heat treatment of products without hardness?

Many entrusted products out of the processing of enterprises. a few years ago learned to require incoming inspection. since the leadership of this request. then the guys are treated seriously. also go to buy a Rockwell hardness tester back. put in the factory. began to heat treatment of the product began incoming inspection. These would have been unquestionable. but they always failed the heat treatment product inspection! This can be busy heat treatment company. how can it? How can it be? It is clear that the products are inspected and qualified. how can they fail in the hands of users? The company is unable to understand.
The heat treatment company took it seriously and sent staff to deal with the matter urgently! Really do not know. a look at a shock! It turns out that they do not remove the decarburization layer of the heat-treated products (processing margin is sufficient to ensure that after processing. no residual decarburization layer). and directly on the surface of the workpiece hit the HRC hardness! How can this be high hardness.

9. Heat treatment engineering good iron-carbon equilibrium phase diagram can be?

In many materials. it is explained that the iron-carbon equilibrium phase diagram in heat treatment is very important knowledge. is the basis for the development of the heating process of steel materials. and pointed out that: especially heat treatment workers must be skilled in iron-carbon equilibrium phase diagram.
The iron-carbon phase diagram is the composition of the iron-carbon alloy in equilibrium. but not to obtain non-equilibrium martensite. bainite and other organizational transformation diagram. The critical temperature parameters of the Fe-Carbon phase diagram are limited to carbon steel and cast iron only. and non-alloyed steel and alloyed cast iron. The equilibrium state diagrams of alloyed steel and alloyed cast iron are still very different from the Fe-Carbon equilibrium state diagrams due to the addition of other alloying elements.
Iron and carbon equilibrium phase diagram is the heating and cooling process is the result of its slow speed. and is limited to iron-carbon alloy steel. this theoretical state. is not possible in the actual production of a large number of applications. the actual quenching and other heat treatment heating and cooling process tissue transformation are in a certain heating rate and cooling rate. not completely reach equilibrium state. Therefore. the iron-carbon equilibrium phase diagram is only the study of heat treatment. learning the necessary basic knowledge and starting point for heat treatment. but not directly in the heat treatment process using the phase diagram.
Heat treatment workers skilled in the knowledge of iron-carbon equilibrium phase diagram is only the beginning of heat treatment learning. can not reach the use of iron-carbon equilibrium phase diagram to deal with the realm of practical problems in the process.
Heat treaters have a good iron-carbon phase diagram is only one of the introductory knowledge of heat treatment.

10. Can annealed workpieces form equiaxed grains?

In the low carbon steel annealing process. many people think they can get equiaxed grains. In fact. it is easy to obtain equiaxed grain size in boiling steels. It is very difficult to achieve equiaxial grain size in Al-Al ballast steels. Especially after cold extrusion of deformed parts annealed. the grains are clearly in the form of deformed extruded tissue! Even at annealing temperatures above 950°C. it is difficult to achieve equiaxial grain size.
Believe it or not!

11. The lower the hardness extrusion deformation is better. the easier?

People’s direct thinking is: the lower the hardness. the easier extrusion deformation. In the extrusion process of steel. pearlite spheroidized tissue state deformation ability is the highest. but this tissue state is generally higher than the hardness of lamellar pearlite. so the original tissue of extruded parts is required to be the technical requirement of pearlite spheroidized tissue. and the lowest hardness of lamellar pearlite tissue cannot be used.

12. Is it correct to require high hardness for forging die?

Among the users of hot forging die. many people like to ask for high hardness. even 52-55 HRC. this concept is wrong.
The reason for this phenomenon is that some unregulated heat treatment enterprises or some “masters” do not really quench the forging dies according to their service conditions. but lower the quenching temperature and shorten the holding time. just to meet the hardness requirements of users. This hardness value seems to meet the standard (or specification) hardness range of forging die. due to no consideration of red hardness. in use. the forging die’s poor tempering resistance. hardness will soon be reduced. the user of this used forging die re-test. found that the forging die heat treatment hardness is not high. The “boss” of the forging die had a brainstorm: the next heat treatment to improve the hardness requirements. and found that the hardness of the forging die than the last hardness value selected in accordance with the standards and norms of the forging die life increased. so he was very happy: the original hardness can be improved to solve the problem. How could he know that the incompetent heat treatment level of the heat treatment manufacturer or “master” caused the mystery of long life beyond the standard hardness? As a result. this problem has been misrepresented. resulting in the technical requirements of hot forging die hardness values getting higher every day!

The life of a hot forging die with red-hardness within the standard hardness range is good! It is not true that forging dies require high hardness!

13. Does the surface wrinkles of aluminum alloy parts after treatment mean that the heat treatment is overburned?

After the solution aging treatment of aluminum alloy parts. there are two methods to determine whether the solution is overheated: metallographic method and surface state color method. According to the surface color and state of the workpiece. it is easy to determine whether it is overheated during the solution heat treatment. but it requires rich experience. The metallographic method is accurate. but it is destructive to dissect the object. which is easy to cause waste.
Judgment according to the surface color and state of the workpiece.

  • ① The surface of the workpiece is dark gray.
  • ② Small bubbles on the surface of the workpiece.
  • ③ Cracks appear and the crack fracture is rough.

If there is one of the above situations. there is a possibility of overburning. This is only observed on the workpiece after heat treatment. When the solution-aged parts have been subsequently processed and then observed. and abnormal phenomena are found on the surface of the aluminum alloy workpiece. roughness. deformation. wrinkles. etc.. it cannot be simply considered that the heat treatment is overburned. Since the strength of aluminum alloy is still low compared with ferrous metal. the role and influence of the subsequent process should be analyzed. Especially the subsequent polishing and sandblasting treatment. the influence on the surface cannot be ignored. When a “water ripple” type wrinkle appears in the workpiece. it cannot be judged that the heat treatment is over-burned. but the pressure of sandblasting is too high or the time of sandblasting is too long. and the deformation layer formed on the surface of aluminum alloy is the reason. This “ripple on water” type wrinkle does not have the characteristics of overburned aluminum alloy. but has the characteristics of plastic deformation formed by the impact on the surface. which should be judged as: sandblasting defect! The metallographic method is used to determine and confirm that it is a sandblasting defect.

14. The manual says you can heat treat and quench to reach this hardness. why can’t you do this hardness?

Some people think that he designed the hardness selection is selected in accordance with the range of hardness in the manual. you heat treatment how to say you can not reach this hardness?

For example. the spring outline 60Si2Mn to make large pieces. due to the actual thickness of the workpiece is very large. the thickness is significantly thin. heat treatment has no good way to reach the required hardness standards. The hardness in the manual is 58-60 HRC. but there is no way to achieve it with the actual workpiece. Only the heat treatment requirements can be reduced.
The hardness of the heat treatment is controlled by the following factors: the material grade. the size of the mold. the weight of the workpiece. the shape and structure of the workpiece. the subsequent processing method and other factors. The hardness of the mold after heat treatment is not the same inside and outside. according to the size of the mold to choose the material and design size. not directly according to the technical standards and hardness requirements in the design manual to choose. the hardness standards in the manual is from the heat treatment results of small samples. when applied to the real thing must be the actual situation to determine a reasonable hardness index. Unreasonable hardness index. such as too high hardness. will lose the toughness of the workpiece. resulting in the use of the workpiece cracking.

15. Treat heat treatment of this industry why has been high technology content low processing value?

Many people who understand heat treatment believe that heat treatment is difficult to learn. difficult to do. and the growth of actual talent is not easy. Some people also say: heat treatment is to burn the workpiece red. put it into the water. it is good. Is it that simple? Since it has become a discipline. it is certainly not that simple. If you look at all the problems from the point of view of those who “burn red and put it in water”. there will be nothing difficult in the world. When the plane accelerates. it goes to the sky? When the train is added to the coal does not run up? Spaceship flung into space will not be able to fly? The computer is powered on the computer can not be used? A bridge across the sea with a few steel wire to get up will not do? According to those “low-value” people’s point of view. everything in the world can be used “a ……. on ……” to see The world can be viewed as “one when those people don’t need heat treatment. they always boast about how important heat treatment is and how people pay attention to it.
When he needs to entrust others to do heat treatment processing. said heat treatment “burn red. put it in the water can be”. unwilling to pay a more reasonable heat treatment processing costs.
When there are problems such as cracking. low service life. etc.. they think that “heat treatment is the first of all evils” and that heat treatment is to blame.
When the national heat treatment has certain deficiencies. said a country heat treatment how how advanced. advanced.
Heat treatment industry has been the real reason for the high technology content and low processing value is the problem of the concept and some people’s prejudice against the heat treatment industry.

16. My heat treatment hardness qualified. your product early failure and my heat treatment has nothing to do with?

Heat treatment should not only ensure qualified hardness value. but also focus on process selection and process control. Overheated quenching and tempering can achieve the required hardness; likewise. quenching and underheating. by adjusting the tempering temperature. can also be made up to the required hardness range. This practice is widely used. Some are underheated quenching to save electricity; some are underheated quenching due to the limit temperature limitation of the heating furnace. How can such early failure of heat-treated products be unrelated to heat treatment?

17. My forging size qualified. heat treatment quality problems have nothing to do with my forging?

Forging process is to eliminate material defects. improve the organization and morphology. and improve material properties. Save the amount of mechanical cutting and improve material utilization. But today’s forgers to “eliminate material defects. improve the organization of the morphology” forgotten all together. only to ensure that the forging size “work”. regardless of the requirements of improving material properties. More amazing is that some materials through the forging process. not to improve the performance of the material. but the performance of the material is spoiled. Forging indiscriminately using forging afterheat annealing method. the result in the material to form a serious network of carbide organization.
As the heating temperature of the material forging is mostly much higher than the heating temperature of the heat treatment quenching. that “severe reticulated carbide tissue” tissue inheritance. bringing serious consequences to product quality.

18. Vacuum heating with quenching carbon increase?

In the analysis of vacuum heat treatment workpiece carbonization phenomenon. there are two misconceptions: first. that the workpiece in the quenching oil carbonization; second. that the heating of the hot chamber of the graphite parts caused by carbonization. In fact. in many cases is not these two reasons. but the heating of the hot chamber is not high cleanliness. there are a lot of quenching oil in the workpiece into and out of the furnace. the material basket pollution. feeding trolley in and out brought into the hot chamber. residual in the cold wall of the hot chamber. heating the formation of volatile reducing atmosphere. carbonization of the workpiece.
In addition to the high temperature above 1050 ℃ directly into the oil. 1050 ℃ below the heating of the workpiece oil quenching. a little pre-cooling into the oil will not form a significant carbon increase phenomenon.
To the heating chamber of the graphite parts. etc. on the workpiece carbon increase can not be ruled out. but there is absolutely no residual quenching of the atmosphere serious.
Vacuum heating quenching carbon increase phenomenon is more serious from the quenching oil pollution of the furnace chamber. and not what people say quenching in oil or graphite parts!

19. Vacuum heat treatment (quenching) deformation is small?

There are two concepts in heat treatment deformation: tissue deformation and shape structure deformation. The results obtained from the study are: vacuum heat treatment than other furnace type heat treatment to obtain the same organization and hardness. deformation is the smallest. That is. the tissue deformation is minimal.
For shape structure deformation. vacuum heat treatment is often less deformed than other furnace type heat treatment. other furnace type heat treatment. such as quenching. it is easy to use grading. isothermal. outside the furnace straightening and other methods to control the amount of deformation. vacuum quenching due to the imperfection of these features. but sometimes increased.
Confusion between these two concepts. giving people the impression that the vacuum heat treatment deformation is small. which is a wrong or incomplete understanding!

20. Tempering color is related to temperature?

After tempering. the surface of the steel shows a color of oxide film. called tempering color. In many cases. it is necessary to determine the tempering temperature according to the tempering color. Tempering color varies with temperature. so the tempering temperature can be generally determined by 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-violet: 280℃
  • Dark blue:290℃
  • Blue:300℃
  • Light blue:320℃
  • Blue-gray:350℃
  • Gray: 400℃
  • Tempering color of stainless steel forgings at different temperatures.
  • Pale 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.
  • Pale wheat yellow: 225℃
  • Wheat yellow: 235℃
  • Light reddish brown: 265℃
  • Light red: 280℃
  • Light blue: 290℃
  • Dark blue:315℃

However. in many materials. only just mention the relationship between color and temperature. ignoring the key premise of time. the same temperature. with the extension of the holding time. the final color will be biased towards higher temperature color. It often causes misjudgment of the actual temperature.

Source: Network Arrangement – China Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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