Bearings are important parts of many lathe machinery, and their quality requirements are very high in use, so it is necessary to start from the smelting of raw materials to ensure their quality. Briefly introduce to you what matters need to be noticed and what requirements are met when smelting bearing steel by induction melting furnace?
1. Strict chemical composition requirements
The general bearing steel is mainly high-carbon chromium bearing steel, that is, a carbon content of about 1%, added about 1.5% of chromium, and contains a small amount of manganese, silicon hypereutectoid steel. Chromium can improve heat treatment performance, hardenability, microstructure uniformity, tempering stability, and can also improve the rust prevention and grinding performance of steel. However, when the chromium content exceeds 1.65%, the residual austenite in the steel will increase after quenching, reduce the hardness and dimensional stability, increase the unevenness of carbides, and reduce the impact toughness and fatigue strength of the steel. For this reason, the chromium content in high-carbon chromium bearing steel is generally controlled below 1.65%. Only by strictly controlling the chemical composition in the bearing steel can the structure and hardness satisfying the performance of the bearing be obtained through the heat treatment process
2.High-precision size requirements
The rolling bearing steel requires high dimensional accuracy of the steel, because most bearing parts are subjected to pressure forming. In order to save material and improve labor productivity, most of the bearing rings are forged. Steel balls are cold-formed or hot-rolled. Small-sized rollers are also cold-formed. If the dimensional accuracy of the steel is not high, the size and weight of the blanking cannot be accurately calculated, the product quality of the bearing parts cannot be guaranteed, and equipment and molds are easily damaged.
3. Particularly strict purity requirements
The purity of steel refers to the amount of non-metallic inclusions in the steel. The higher the purity, the less non-metallic inclusions in the steel. The harmful inclusions such as oxides and silicates in bearing steel are the main reasons that cause early fatigue spalling of bearings and significantly reduce bearing life. In particular, brittle inclusions are the most harmful, because they are easy to peel off from the metal substrate during processing, which seriously affects the surface quality of the bearing parts after finishing. Therefore, in order to improve the service life and reliability of the bearing, the content of inclusions in the bearing steel must be reduced.
4.Strict requirements for low magnification and microscopic (high magnification) organization
The low magnification structure of bearing steel refers to the general looseness, central looseness and flattening. The microscopic (high magnification) structure includes the annealed structure of steel, carbide network, band shape and liquid precipitation. The carbide solution is hard and brittle, and its harm is the same as that of brittle inclusions. Reticulated carbides reduce the impact toughness of steel and make its structure non-uniform, and easily deform and crack during quenching. Banded carbides affect the annealed and quenched and tempered structures and contact fatigue strength. The pros and cons of low and high magnification organizations have a great impact on the performance and service life of rolling bearings, so there are strict requirements for low and high magnification organizations in bearing material standards.
As part of the requirements for bearing steel smelting at the above four points, in addition to paying attention to the smelting process, we must also pay attention to the purchase of high-quality induction melting furnace equipment. Good equipment is a very important aid.
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