35CrMo (after forging quenching and tempering treatment) non-metallic inclusions

Nonmetallic Impurities of 35CrMo After Forging and Heat Treatment

35CrMo is a Chinese alloy steel commonly used in the manufacture of aerospace, ships, hydraulic pipes and valves, but also for motor vehicles, ships, high temperature and pressure valves, etc. Nonmetallic impurities are always present in metal, which are only harmful to the entire metal forming process but also have a great impact on the performance of the finished material. Therefore, reducing nonmetallic impurities of 35CrMo is a prerequisite for improving quality.

The nonmetallic impurities of 35CrMo steel are mainly carbon-containing compounds, oxides, sulfides, graphite, silicates and ferro-silicates, and the content is generally measured by melt-gas analysis. In order to reduce the contain of nonmetallic inclusions in 35CrMo, degassing, deslagging and chemical purification before the melting process should be done. During the smelting process, the Si and Mn content in the steel should be reduced and the Al content increased; the furnace should be kept clean and sufficient slag coverage should be maintained.

When the smelting reaches the temperature and purity required for steel, it is forged and tempered to obtain the required characteristics. During forging and other processes of 35CrMo, nonmetallic impurities are further refined and enriched. Hot rolling and high temperature and pressure treatment are also important steps in the improvement of nonmetallic impurity. The grain size of the material should be properly controlled, and the deformation speed should be properly adjusted. The rolling should generally be from small to large, and the temperature of the rolling should not be too high. In addition, the cooling rate and cooling medium should also be selected reasonably.

In recent years, the composite refining method has been widely adopted for the purification of 35CrMo. The composite refining method can reduce and distribute the oxide and sulfide inclusion in the steel effectively and improve the gas content in the steel. The main component of the inclusions of composite refining is Mg-Si-C-O-N multi-element composite, which is more effective against harmful inclusions.

In summary, the nonmetallic inclusions of 35CrMo after forging and heat treatment can be effectively reduced by proper selection of melting process, smelting furnace, forging speed and temperature, cooling rate and cooling medium, as well as through the use of the composite refining method. This could help to improve the quality of the finished material.

35CrMo steel is a medium carbon alloy steel which is widely used in the manufacture of tools, dies, engines and components subjected to very high stresses. It is a modification of 34CrMo4 steel, with improved hardenability and creep strength. A variety of non-metallic elements, such as carbon, oxygen, nitrogen and sulfur, can be found in the 35CrMo steel.

The 35CrMo steel is extensively quenched from 930°C to obtain martensite and to reduce its hardness. It is subjected to tempering at temperatures of 200-300°C depending on the application. Usually, the tempering temperature is higher to obtain better toughness and increased ductility.

The 35CrMo steel is then worked to its design dimensions. The design dimensions are limited by the amount of strain that can be tolerated before cracking occurs. The strain tolerance is given by the elastic limit. For example, in the case of hot-forging and hot-rolling, the elastic limit is lowered to reduce strain imposed on the metal during operation.

The chemical composition of 35CrMo steel is of importance as it determines the mechanical properties. Chromium, for example, increases strength and hardenability, and molybdenum increases strength, creep strength, and resistance to tempering. The chemical composition of 35CrMo steel is as follows: 0.32-0.40% Carbon, 0.90-1.20% Manganese, 0.15-0.30% Silicon, 0.80-1.10% Chromium, 0.15-0.30% Molybdenum, 0.035 Max Sulfur, 0.035 Max Phosphorus, and 0.30-0.50% Copper.

The presence of non-metallic impurities in 35CrMo steel, such as sulfur, oxygen, carbon and nitrogen, can influence its mechanical and chemical properties. However, these elements are absent in steel produced not just with industrial means, but also with labor costs and short production times, such as induction-melted steel.

The combination of medium carbon content and alloying elements makes 35CrMo steel suitable for a wide range of die making and engine application. Its medium carbon content makes it relatively easy to machine and the alloying elements enhance the strength, creep strength and temperability.