Analysis of six major surface heat treatment
Surface heat treatment refers to a metal thermal processing process in which the material is changed in the solid state by means of heating, heat preservation and cooling to change the chemical composition and structure of the material surface to obtain the desired properties. The following are six surface heat treatment methods.
Surface hardening
The workpiece is rapidly heated by different heat sources. When the surface temperature of the part reaches above the critical point (when the core temperature of the workpiece is below the critical point), it is rapidly cooled, so that the surface of the workpiece is hardened and the core remains intact. organization. The most widely used in the industry is induction heating and flame heating surface quenching.
Chemical heat treatment
The workpiece is placed in a medium containing active elements to heat and keep warm, so that the active atoms in the medium penetrate into the surface layer of the workpiece or form a covering layer of a compound to change the texture and chemical composition of the surface layer, so that the surface of the part has a special mechanical mechanism. Or physicochemical properties. For example, nitriding treatment, nitriding treatment refers to a chemical heat treatment process in which a nitrogen atom is infiltrated into the surface layer of a workpiece in a certain medium at a certain temperature. The nitrided article has excellent wear resistance, fatigue resistance, corrosion resistance and high temperature resistance.
Contact resistance heating quenching
A voltage of less than 5 volts is applied to the workpiece through the electrode, a large current flows between the electrode and the workpiece, and a large amount of resistance heat is generated to heat the surface of the workpiece to the quenching temperature, and then the electrode is removed, and the heat is transmitted. After entering the inside of the workpiece and the surface is rapidly cooled, the quenching purpose is achieved.
Electrolytic heating quenching
The workpiece is placed in an electrolyte of an acid, alkali or salt aqueous solution, the workpiece is connected to the cathode, and the electrolytic cell is connected to the anode. After the direct current is turned on, the electrolyte is electrolyzed, and oxygen is released on the anode to release hydrogen on the workpiece. Hydrogen forms a gas film around the workpiece, becomes a resistor to generate heat, rapidly heats the surface of the workpiece to the quenching temperature, and then de-energizes, the film immediately disappears, and the electrolyte becomes a quenching medium, so that the surface of the workpiece is rapidly cooled and hardened.
Laser heat treatment
The application of laser in heat treatment began in the early 1970s, and then entered the production application stage from the laboratory research stage. When a focused high energy density (10 W/cm) laser illuminates the metal surface, the metal surface rises to the quenching temperature in a few hundredths of a second or even a few thousandths of a second.
Electron beam heat treatment
The surface quenching of the electron beam is the same as that of the laser except that it should be carried out in a vacuum. When the electron beam bombards the metal surface, the bombardment point is rapidly heated. The depth of the electron beam penetrating material depends on the accelerating voltage and material density.
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