What are the reasons why the hardness of Hydraulic Cylinder Rod induction hardened parts cannot meet the technical requirements？
There are many reasons why the hardness of Hydraulic Cylinder Rod induction hardened parts cannot meet the technical requirements.
(1) The quenching temperature of Hydraulic Cylinder Rod is not enough
That is, the heating is insufficient, and the austenitizing temperature requirement is not reached. For medium carbon structural steels, there is undissolved ferrite in the austenite, and there is undissolved ferrite in the quenched structure except for the martensite, and the quenched surface of the workpiece is often blue. It can also be seen from the appearance of the induction hardened parts that the normally quenched surface is beige and the overheated surface is white.
(2) Insufficient cooling of Hydraulic Cylinder Rod
That is, the cooling rate is lower than the critical cooling rate. In addition to some Martensite in the quenched structure, there is troostite. The larger the troostite, the lower the hardness. It often occurs when the quenching medium concentration, temperature, pressure fluctuate, and the spray hole is blocked.
(3) The self-tempering temperature of Hydraulic Cylinder Rod is too high
The problem of excessively high self-tempering temperature occurs in shaft scanning quenching, which generally occurs during horizontal shaft quenching or stepped shaft vertical quenching. When the width of the sprayer is short, the heating surface quickly passes through the sprayer without cooling the quenched section enough, and the water flow is blocked by the steps (large diameter section is on the top and small diameter section is on the bottom), which is generated when the quenched section cannot be cooled. Therefore, the quenched surface can often be observed and detected obvious self-tempering temperature is too high.
(4) Soft spots or spiral black belt
The soft spots and blocks on the quenched surface are often black, and the typical spiral black band is a common defect phenomenon in scanning quenched parts. This black band is also the soft band, which is often the troostite structure. The solution is to spray the liquid evenly. Increasing the rotation speed of the workpiece can also reduce the pitch of the black belt, but the most basic is that the structure of the liquid sprayer should make the heating surface cool evenly. Clogging of the spray hole is often one of the causes of soft spots.
(5) Influence of material chemical composition
The reduction of material composition, especially carbon content, is one of the factors that reduce hardness. If necessary, select carbon content can be used for important parts to narrow the upper and lower limits of w(C) to less than 0.05%.
(6) Preliminary heat treatment
Changes in the quenching and tempering process and the black skin of the rolled material remaining on the quenched surface are also the reasons why the hardness of the induction hardened parts cannot meet the technical requirements.
(7) Surface decarbonization, carbon-poor
It often occurs on the surface of cold drawn materials. Therefore, after quenching, the hardness of these bars can be ground to remove the outer layer by 0.5mm and then the hardness. If the surface hardness is low, the hardness of the inner layer is higher than the surface, indicating that there is a carbon-poor or decarburized layer. (Exceptions for special geometric shapes such as cam peach and gear top).
(8) Banded primitive organization
The band-like structure in the original structure of the quenched part will cause insufficient hardness after quenching. There is undissolved ferrite in the band structure, which cannot be dissolved during the austenitization process, and the hardness after quenching is bound to be insufficient. Even if the heating temperature is increased, the band structure is difficult to eliminate.