Spray forming, also known as spray casting or spray deposition, was the first academic thought proposed by Professor Singer of Swansea University in 1969 and was developed by Osprey Metals Ltd. in the UK for many years. , a new technology for the preparation of rapid solidification materials that gradually matured in the late 1980s, so it is also called Osprey technology.
Osprey technology is a near-final forming technology developed on the basis of powder metallurgy inert gas atomization powder making. It makes full use of the refined liquid metal and uses high-pressure inert gas to atomize the alloy liquid flow into fine molten droplets. , the molten droplets fly under the action of high-speed airflow and are cooled by the atomized gas. Before these molten droplets are completely solidified, they are deposited on the receiver with a certain shape. By controlling the movement of the receiver, a certain shape can be obtained. The blank is deposited. Materials manufactured using Osprey technology have the following technical characteristics:
(1) No macro segregation;
(2) Isotropic and evenly dispersed;
(3) The initial crystal grains are dispersed and precipitated;
(4) low oxygen content;
(5) Thermal processing performance is improved.
Because of the above-mentioned characteristics of Osprey technology, the use of Osprey technology to manufacture high-speed steel rolls has attracted people’s attention. Domestic Zhou Candong and others have studied the structure and performance of spray-formed high-speed steel rolls. The main components (mass fraction %) of high-speed steel roll materials are: 0.9-1.1C, 0.35-0.45Si, 0.70-0.80Mn, 7.90-8.20Cr , 1.45-1.55Mo, 1.5-1.7V, 0.45-0.55W.
The important parameters during the spray forming operation are Φ5 mm catheter, 2.5 MPa atomized nitrogen pressure, 350 mm spray distance, and 10 t/min substrate rotation speed. No obvious carbide was observed in the optical microstructure of the spray-formed high-speed steel roll, but there was a certain amount of retained austenite in the structure. Discontinuously distributed carbide particles were observed on the grain boundaries under a scanning electron microscope. In addition, the grains of the spray-formed samples were significantly refined. X-ray diffraction analysis shows that the matrix structure of spray-formed samples is composed of retained austenite and martensite.
In the microstructure of as-cast high-speed steel rolls, due to the slow cooling rate, there are more or less typical carbides such as MC, M6C, and M2C distributed in a continuous network, and the matrix is composed of martensite and retained austenite. The microstructure of spray-formed high-speed steel is characterized by an equiaxed cell-like organization, which is basically martensite and retained austenite. The structure is relatively uniform and has less segregation. The microstructure of the spray-formed sample is obviously finer and more uniform than that of the master alloy as-cast sample. The carbides are mainly MC and M2C, and there is no fishbone carbide M6C. Moreover, the M2C carbides in the spray-formed samples are also significantly different from those in the as-cast samples of the master alloy. The M2C carbides in the spray-formed samples are in the shape of round rods, while the M2C carbides in the master alloy as-cast samples are in complex and regular shapes.
Due to the rapid solidification, for the spray-formed sample, there is no diffusion of alloy elements in the austenite during the solidification process, so there is a higher content of solute, which reduces the Ms point of the high-speed steel, and the result is that there is more retained austenite is manifested in the lower microhardness of the spray-formed specimens than that of the master alloy as-cast specimens.
In addition, the high-temperature tensile test shows that the injection-formed specimen has a higher tensile elongation in the temperature range of 780-810°C, indicating that large-deformation thermal processing can be used to densify the specimen in this temperature range to further improve the high-speed Properties of steel rolls.