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In this study, after heat treatment of six different products of the case company, the data of four physical characteristics: hardness, length, inner diameter, outer diameter, were collected. 25 samples of each product were collected to determine whether there were significant differences in these four physical properties before and after heat treatment by statistical methods of T-test and Variation Analysis (ANOVA). By t-test and ANOVA, there were significant differences in the four physical properties of the six different products before and after heat treatment. The results are as follows:
(I) Hardness.
1. S45C: The physical holding difference becomes large after heat treatment. The hardness shows a large difference. Heat treatment should be done by a relatively large company to make the hardness more stable. Medium carbon steel is currently the largest amount of all steel, heat treatment, high-frequency, commonly used in various mechanical processing or accessories processing, is also one of the most commonly used by customers.
2. SKD11: After heat treatment, the product’s physical properties became vary greatly, it has excellent hardness and is not easy to change. At the meantime it can also bring out its characteristics. If there is no vacuum heat treatment, it is generally used as medium carbon steel, and the price difference is very large, and it will be usually used in the processing of rotating dies or special places.
3. Rod iron: The physical characteristics of rod iron are vary greatly after carburization heat treatment, because the quality of the material has no carbon. It needs carburization heat treatment in order to be processed, but the quality is not stable, and the secondary processing is not easy to process. It is generally rarely used for heat treatment, its cost is gradually close to the medium carbon, and its advantages are gradually losing competition.
(II) Length.
1. S45C: After heat treatment, its length becomes longer. The quality of medium carbon steel varies from manufacturer to manufacturer and from brand to brand because the carbon composition is different, so it is not easy to control the temperature and length. Because the price of heat treatment is not expensive, so the customer is also commonly used due to the cost.
2. SKD11: After the vacuum heat treatment, the length and size of the treated products are smaller than before the treatment, showing little difference. However, the hardness difference is large, so the deformation rate is small and "extremely stable". Although the cost is a bit high, it is very popular because of the good reputation of customers.
3. Rod iron: Its physical characteristics length is less than before heat treatment after carburizing heat treatment. This material is less used for heat treatment, so low cost is more favored by customers. However, its wear-resistant is poor and not easy to process. With high processing costs and the increase of the price of rod iron, it is almost replaced by medium carbon. The cost of manual processing is high, so it is slowly used less for heat treatment.
(C) internal diameter.
1. S45C: The size of medium carbon steel after treatment is smaller than before treatment after heat treatment, and there is a significant difference. It is not difficult to process the secondary processing by reserving the inner hole for reworking. High deformation rate is currently the most difficult for customers to accept, so to precision size must be ground or secondary processing, but its material cost is relatively low and generally high acceptance.
2. SKD11: After vacuum heat treatment, the inner hole is smaller than before treatment, and the inner hole must be precision machined or ground in order to be used precisely.
3. Rod iron: The results of the carburizing treatment on the rod iron show that the "inner diameter" is significantly smaller after the heat treatment than before the treatment, so they must be refined before use.
(iv) Outside diameter.
1. S45C: The "outer diameter" of medium carbon steel after heat treatment is significantly larger than before treatment, so it must generally be reserved for processing. Medium carbon steel is different in each brand, due to the poor equipment of heat treatment manufacturers, so the finished product varies greatly and the true roundness is even worse. Thus, the processing size must be reserved to meet the requirements of customers.
2. SKD11: After vacuum heat treatment, the "outside diameter" is significantly smaller than before heat treatment. SKD11 material has high thermal stability and is often used for more important structural parts, which is very popular among customers.
3. Rod iron: After the carburizing heat treatment, the outer diameter is significantly smaller than before the treatment, and the true roundness of the outer diameter is easily deformed. Since the secondary processing cost is not cheap, it is not easy to reserve and process, so it is not generally accepted.
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