vacuum heat treatment problems summary

---

11. After annealing of my product, you can heat treat and quench it after a week?

Some owners claim to have the secret to improve the service life of the mould! What’s his secret? After all, the heat treater is required to finish the annealing treatment, and can not immediately carry out the quenching and tempering treatment. The mould must be kept at room temperature for a week between annealing and quenching! Say yes: release annealing stress! I don’t know if that expert can answer this question?

12. The product dimension processing has been completed completely, and the heat treatment is required to ensure no deformation?

Some people in order to save the cost of product processing, before heat treatment, all dimensions of the processing end, and then go to heat treatment quenching and tempering. The heat treater is required to ensure no deformation during heat treatment, or only the deformation is allowed within the tolerance zone value of the last cold working! The process of heat treatment is essentially a stage of structural deformation. Who can guarantee that the deformation accumulation on the micro level will not show up as dimensional deformation on the macro level?

13. Does the heat-treated product have hardness?

Many enterprises entrusted with external processing of products have learned to require incoming inspection for a long time. Since the leaders put forward this requirement, the guys treat it seriously. They also go to buy a Rockwell hardness tester and put it in the factory to start incoming inspection for the products after heat treatment. These are beyond reproach, but they always fail in the inspection of heat treatment products! This can be a busy heat treatment company, how can it? It’s clear that the factory is qualified after inspection. How can it be unqualified in the hands of users?

The heat treatment company takes it seriously. Send someone to deal with it urgently! I don’t know if I don’t see it. I’m scared at first sight! In fact, they did not remove the decarburization layer of the heat-treated products (the machining allowance was enough to ensure that the decarburization layer would not remain after processing), so they directly punched HRC hardness on the surface of the workpiece! How can it have high hardness?

14. It’s OK for heat treatment workers to learn the iron carbon equilibrium phase diagram?

In many materials, it is explained that the iron carbon equilibrium phase diagram is a very important knowledge in heat treatment, which is the basis for making heating process of iron and steel materials.

The phase diagram of iron carbon is the structure composition diagram of iron carbon alloy in equilibrium state, not the transformation diagram of non-equilibrium martensite and bainite. The critical temperature parameters of Fe-C phase diagram are only limited to carbon steel and cast iron, non alloy steel and alloy cast iron. The equilibrium state diagram of alloy steel and alloy cast iron is quite different from that of iron carbon due to the addition of other alloy elements.

The equilibrium phase diagram of iron and carbon is the result of the slow heating and cooling process, and it is also limited to the iron carbon alloy steel. This theoretical state can not be widely used in the actual production. In the actual heating and cooling process of heat treatment such as quenching, the structural transformation is carried out at a certain heating speed and cooling speed, not completely reaching the equilibrium state. Therefore, the equilibrium phase diagram of iron and carbon is only the necessary basic knowledge and starting point to study heat treatment, rather than the phase diagram directly used in the heat treatment process.

It is only the beginning of heat treatment study that heat treatment workers master the knowledge of iron carbon equilibrium phase diagram, which can not reach the state of using iron carbon equilibrium phase diagram to deal with practical process problems.

A good understanding of iron carbon phase diagram is only one of the basic knowledge of heat treatment.

15. Can the annealed workpiece form equiaxed grains?

In the annealing process of low carbon steel, many people think that equiaxed grains can be obtained. In fact, the equiaxed grain size can be easily obtained in boiling steel. It is difficult to achieve equiaxed grain structure in Al Al killed steel. Especially after the cold extrusion of the deformed parts annealing, the grain is very obvious deformation extrusion structure! Even the annealing temperature above 950 ℃ is difficult to reach the equiaxed grain.

16. The lower the hardness, the better the extrusion deformation, the easier?

People’s direct thinking is: the lower the hardness, the easier the extrusion deformation. In the extrusion process of steel, the deformation ability of pearlite spheroidized structure is the highest, but the hardness of this structure is generally higher than that of lamellar pearlite. Therefore, the original structure of the extrusion part is required to be the technical requirement of pearlite spheroidized structure, instead of the lamellar pearlite structure with the lowest hardness.

17. Is it correct to require high hardness for forging dies?
In the use of hot forging die users, many people like to put forward high hardness requirements, and even require 52-55HRC. This idea is wrong.

The emergence of this phenomenon, investigate its reason, it should be some non-standard forging die for heat treatment, heat treatment companies doing not really according to the service condition of the forging die quenching, but reduce the quenching temperature and shorten the time of heat preservation, only satisfy the requirement of the user red hardness, the hardness value seems to accord with a standard (or specification) of forging die hardness range, without considering rigid, when use, forging die of tempering resistance is poor, hardness will soon be reduced, the user when used to this kind of forging die test again, found that the hardness of heat treatment of die is not high. The “boss” of forging die thinks: next time when heat treatment raises hardness requirement, the result discovers the forging die that raises hardness is compared with the forging die of the hardness value that chooses last time according to standard, specification life is increased, so he is very happy: raise hardness originally can solve this problem. How could he know that it was the inept heat treatment level of the heat treatment manufacturer that caused the hardness beyond the standard but the secret of the long life? As a result, this problem is misreported, resulting in the technical requirements of hot forging die hardness value higher and higher day by day!

Hot forging dies with red hardness in the standard hardness range have a good life! It is not correct to require high hardness for forging die!

18. Are the surface wrinkles of aluminum alloy after treatment after heat treatment?
There are two methods to determine whether the aluminum alloy is overburned after the solution aging treatment: metallographic method and surface state color method. According to the color and state of the surface of the workpiece, it is convenient to judge whether the solution is overheated in the heat treatment in time, but rich experience is needed. Metallography is accurate, but to dissect the object, is a destructive detection, easy to cause waste.
Judge according to the color and state of the workpiece surface:
The surface of the workpiece is dark gray,
The surface of the workpiece has vesicles,
Crack appears, crack fracture rough

In one of these cases, there is a possibility of overburning. This is only observed on the workpiece after heat treatment. When the solution aging parts have been further processed and observed, the surface of the aluminum alloy workpiece is found to have abnormal phenomena — roughness, deformation, wrinkles, etc., which cannot simply be considered as heat treatment over burning.
Because the strength of aluminum alloy is still lower than that of ferrous metal, it is necessary to analyze the role and influence of subsequent processes. Especially the subsequent polishing, sandblasting treatment, the impact on the surface can not be ignored.
When the part of the workpiece appears “water surface ripple” type wrinkles, can not be determined as heat treatment over burning, but sandblasting pressure is too high or sandblasting time is too long, the formation of the deformation layer on the surface of aluminum alloy. This “water surface ripple” type furrow does not have the characteristic that aluminium alloy overburns, have the characteristic that the surface suffers impact to form plasticity to deform however, should judge at this time for: blast sand flaw!
The metallographic method was used to determine that it was a sandblasting defect.

Learn more: Vacuum Heat Treatment Furnace