Advantages: The billet needs to be side-skinned, the heating temperature is generally 1100t109C, and the furnace tail preheating temperature cluster is 800°C. When heating, it is necessary to prevent sulfur from infiltrating into the billet, because nickel and sulfur easily form low melting point sulfides, causing "hot brittleness" . "Kovar" alloy tube has high plasticity in the range of 1100-1250°C, so there is no difficulty in perforating. However, if the temperature exceeds 1270°C, overburning will occur and the plasticity will decrease significantly. Therefore, the furnace temperature must be strictly controlled. The reason for the blue brittleness is that most of the fine-rolled steel pipes for micro-motor housings with ferrite-pearlite structure, with the increase of temperature, the toughness decreases at about 300℃. It occurs in the temperature range where there is a blue oxide film on the surface of the finish-rolled steel pipe for the micromotor shell, so it is called blue brittle. Blue brittleness occurs in annealed or normalized micro-motor shell finish-rolled steel pipes with very low alloying elements.
Blue brittleness was observed in the following three cases.
1. Measure the strength and toughness of the fine-rolled steel pipe for micro-motor housing in the temperature range of 150～350℃;
2. Carry out warm processing in the temperature range of 150～350℃, and then measure the strength and toughness of the fine-rolled steel pipe for micro-motor housing at room temperature;
3. After being cold-worked at room temperature, it is heated in the temperature range of 150-350°C, and the strength and toughness of the fine-rolled steel pipe for micro-motor housing are measured at room temperature. Blue brittleness was observed in the following three cases.
1. Measure the strength and toughness of the fine-rolled steel pipe for micro-motor housing in the temperature range of 150～350℃;
2. Carry out warm processing in the temperature range of 150～350℃, and then measure the strength and toughness of the fine-rolled steel pipe for micro-motor housing at room temperature;
3. After being cold-worked at room temperature, it is heated in the temperature range of 150-350°C, and the strength and toughness of the fine-rolled steel pipe for micro-motor housing are measured at room temperature.
a. Deformation aging of finish-rolled steel pipes and nitrogen interstitial atoms for aluminum die-casting motor housings. When deformed in the temperature range of 150-350°C, the activated dislocations are quickly anchored by the diffusible carbon and nitrogen atoms, forming a Korotel air mass (Korotkoff air mass). In order to continue the deformation, new dislocations must be initiated. As a result, the density of dislocations increases under a given strain in the finish-rolled steel pipe for micro-motor housings, resulting in increased strength and decreased toughness. In order to eliminate the blue brittleness of the finished rolled steel pipe for aluminum die-cast motor housing, a certain amount of strong carbide and nitride forming elements such as titanium, niobium, and vanadium are added to the finished rolled steel pipe for aluminum die-cast motor housing to form Tic and TiN in the steel. , NbC, NbN, vC, vN, fix carbon and nitrogen atoms. In addition, adding a small amount of aluminum can form AlN with nitrogen in addition to deoxidation, which can also reduce the tendency of blue brittleness.
