The process by which nickel and nickel alloys are melted, cast, and rolled into sheets or coils. Nickel and nickel alloys have the advantages of high melting point, good thermal stability, corrosion resistance, high strength, and good processing performance. Nickel alloy strips are widely used in precision instruments, electronics, medical equipment, aerospace and other fields.
The thickness of the hot-rolled plate is 5~20mm, the thickness of the cold-rolled plate is 0.5~10mm, and the width is not larger than 1000mm; the thickness of the strip is 0.05~1. 5mm, and the width is not larger than 300mm in one roll.
The basic production process of nickel and nickel alloy laths is as follows:
Molten cast nickel and nickel alloy melts can absorb large amounts of gas and undergo intense oxidation. One stream is smelted in an induction furnace, the surface of the melt is covered with glass, and then deoxidized with charcoal, manganese, silicon, magnesium, titanium, etc., and high-purity nickel and nickel alloys are melted in a vacuum. Alloys such as Monel (NCu28-2.5-1.5) are melted by electroslag. The melting temperature is 1450~1560°C, which varies with the alloy. Usually, flat ingots are cast in pig iron molds (see pig iron ingots) or semi-continuous casting (see semi-continuous ingots). The weight of the ingot is between30~400kg. Defects such as inclusions and insulation on the surface of the steel ingot should be cleaned up.
Hot-rolled nickel and nickel alloys have good high-temperature plasticity and high deformation resistance, and the heating temperature is between 1050°C and 1250°C. If a gas furnace is used, the sulfur content of the gas must be strictly controlled to avoid thermal embrittlement. A nickel ingot weighing 400kg and having a thickness of 200mm is hot rolled to a thickness of 10mm in 11 passes. Sometimes forging is done before hot rolling to improve the internal structure.
Pickling of milled surfaces of nickel and nickel alloys (see milled surfaces of non-ferrous alloy ingots) tends to stick to tools, so pickling is commonly used to remove oxides on the surface of hot-rolled slabs. Pickling is carried out with a mixed acid of sulfuric acid and nitric acid or with nitric acid alone. In order to improve the pickling effect, small reduction cold rolling is performed before pickling to break the oxide layer that extends less than the matrix to facilitate reaction with the acid.
Cold rolling: Hot-rolled billets with a thickness of 5.0~13.5mm need to be repeatedly cold-rolled and annealed many times to reach a finished material thickness. The reduction rate between two different annealings can reach 70%~85%. Four-high mills are commonly used in cold rolling companies. High-strength nickel alloy thin strips are finished using 12-roll or 20-roll mills. Lubrication and cold rolling should be fully utilized during cold rolling to prevent roll sticking and affect the quality of the surface work.
Annealing: Annealing is divided into intermediate annealing and complete annealing. The purpose of intermediate annealing is to eliminate work hardening caused by cold rolling,and the purpose of finished product annealing is to control the properties of the finished product. The temperature for complete annealing of nickel and nickel alloys is between 570 and 850 IC, depending on the composition of the alloy and the thickness of the product. It will stick easily when annealed, so it should be re-rolled before annealing. Since the scale on nickel alloys is difficult to remove, bell jar vacuum furnaces are usually used for annealing. Complex nickel alloys such as nickel-aluminum and nickel-titanium can be hardened by solid solution/aging treatments to increase strength.