In industrial production,
heat treatment is one of the important processes to improve material properties. However, there are many misunderstandings about heat treatment, which not only affect production efficiency, but also may lead to product quality problems. This article will explore some common heat treatment misunderstandings, aiming to help relevant practitioners deeply understand the
heat treatment process and avoid unnecessary losses caused by bias and misperception.
An enterprise broke and injured the operator in the process of using the mold, and immediately notified the heat treatment manufacturer to ask for compensation, because the mold was heat treated by them. Product failure needs to be comprehensively analyzed from the aspects of design, material selection, material defects, process defects (including heat treatment), assembly and use, and can not simply shift the responsibility to heat treatment. Just as a doctor must personally observe a patient, a
forging part failure should be comprehensively analyzed and not arbitrarily attributed to a single link.
Some people think that after quenching the workpiece is not cooled to room temperature can not be tempered. In fact, many steel grades, especially low and medium carbon steels, have martensitic transition ending points that are usually higher than room temperature. Tempering before cooling to room temperature can avoid cracking.
A common misconception is that tempering must be performed after quenching, but this practice does not apply to all steel grades. The tempering temperature after quenching should be adjusted according to the martensite transition point to prevent quenching cracking, and should not be generalized.
Individual companies claim that the annealed mold must be left at room temperature for a week before it can be quenched. This statement lacks scientific basis, and the annealed mold should be subjected to subsequent heat treatment as soon as possible to release the internal stress.
Some enterprises have completed all dimensional processing before heat treatment, and require no deformation during heat treatment. However, the heat treatment process is essentially a process of tissue deformation, and it cannot be guaranteed that there will be no macroscopic size deformation.
Many companies in the acceptance of heat treatment after the product, the hardness test is found to be unqualified, the problem is not removed on the decarbonization layer. The correct practice is to ensure that the decarbonized layer is removed before processing to ensure the accuracy of the test results.
Although iron-carbon equilibrium phase diagrams are considered important knowledge in heat treatment, their application is not applicable to all steel grades. The equilibrium phase diagram is only applicable to iron-carbon alloys, and the heat treatment process in actual production is often non-equilibrium. Therefore, heat treatment workers need to understand the iron-carbon equilibrium phase diagram as a basic knowledge, rather than relying on it to solve actual process problems.
In the annealing process of low carbon steel, the expectation of obtaining equiaxed grains is not always realized. Especially after annealing of the cold extruded deformed parts, the grain may still show obvious deformed structure.
A common misconception is that the lower the hardness, the easier the extrusion deformation. In fact, pearlite spheroidized microstructure has the highest deformation capacity, but its hardness is usually higher. Therefore, the original structure of the extruded parts should be required to be pearlite spheroidized, rather than the pursuit of minimum hardness.
In the use of hot forging dies, many users mistakenly think that high hardness is a necessary condition for forging dies, and even require 52-55HRC. That is wrong. The service life of forging die is not only related to hardness, but also combined with red hardness and heat treatment process. Suitable hardness and good red hardness can ensure the long life of the forging die.
The heat treatment industry is often considered to be a high-technology but low-processing value industry, partly because of the bias in people's understanding of heat treatment. Many people simplify the process of "burning red and putting it in water" when they need heat treatment, ignoring the complexity and professionalism of heat treatment. The importance of heat treatment cannot be ignored, but biases and misunderstandings in the industry still exist.
It is hoped that this paper will trigger attention to heat treatment knowledge in the industry and encourage practitioners to continue to learn and improve to ensure the effectiveness and reliability of heat treatment in production. Only heat treatment based on science can truly create value for enterprises and achieve higher production benefits.
