Surface heat treatment refers to a metal thermal processing process in which the chemical composition and structure of the material surface are changed by means of heating, heat preservation and cooling in a solid state to obtain the required properties. The following are six surface heat treatment methods.
surface hardening
The workpiece is rapidly heated by different heat sources, and when the surface temperature of the part reaches above the critical point (at this time, the temperature of the workpiece core is below the critical point), it is rapidly cooled, so that the surface of the workpiece obtains a hardened structure while the core remains the original organization. The most widely used in industry are induction heating and flame heating surface quenching.
chemical heat treatment
The workpiece is heated and kept warm in a medium containing active elements, so that the active atoms in the medium penetrate into the surface of the workpiece or form a covering layer of a certain compound to change the structure and chemical composition of the surface layer, so that the surface of the part has a special mechanical or physicochemical properties. For example, nitriding treatment, nitriding treatment refers to a chemical heat treatment process in which nitrogen atoms penetrate into the surface of the workpiece in a certain medium at a certain temperature. Nitrided products have excellent wear resistance, fatigue resistance, corrosion resistance and high temperature resistance.
Contact resistance heating and quenching
A voltage of less than 5 volts is applied to the workpiece through the electrode, and a large current flows through the contact between the electrode and the workpiece, and a large amount of resistance heat is generated, so that the surface of the workpiece is heated to the quenching temperature, and then the electrode is removed, and the heat is transferred. It enters the workpiece and the surface cools rapidly, that is, to achieve the purpose of quenching.
Electrolytic heating and quenching
The workpiece is placed in the electrolyte of 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, oxygen is released on the anode, and hydrogen is released on the workpiece. Hydrogen forms a gas film around the workpiece and becomes a resistor body to generate heat, rapidly heating the workpiece surface to the quenching temperature, and then power off, the gas film disappears immediately, and the electrolyte becomes a quenching medium, which rapidly cools and hardens the workpiece surface.
Laser heat treatment
The application research 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 (10W/cm) laser irradiates the metal surface, the metal surface rises to the quenching temperature within a few hundredths of a second or even a few thousandths of a second.
Electron beam heat treatment
The electron beam surface quenching has the same characteristics as the laser except that it should be carried out in a vacuum. When the electron beam bombards the metal surface, the bombardment spot is rapidly heated. The depth to which the electron beam penetrates the material depends on the accelerating voltage and the material density.