Six surface heat treatment

Surface heat treatment is a kind of metal hot working technology that changes the chemical composition and structure of the material surface and obtains the required properties by means of heating, heat preservation and cooling in the solid state. Here are six surface heat treatment methods.

Surface quenching

The workpiece is heated rapidly by different heat sources. When the surface temperature of the workpiece reaches above the critical point (when the core temperature of the workpiece is below the critical point), the workpiece is cooled rapidly. In this way, the surface of the workpiece is hardened and the core remains the original structure. Induction heating and flame heating surface quenching are widely used in industry.

Chemical heat treatment

Put the workpiece in the medium containing active elements for heating and heat preservation, make the active atoms in the medium penetrate into the surface layer of the workpiece or form a covering layer of some compound, so as to change the structure and chemical composition of the surface layer, so that the surface of the part has special mechanical or physical chemical properties. For example, nitriding treatment, nitriding treatment refers to a kind of chemical heat treatment process in which nitrogen atoms penetrate into the surface of workpiece in a certain medium at a certain temperature. The products treated by nitriding have excellent wear resistance, fatigue resistance, corrosion resistance and high temperature resistance.

Contact resistance heating and quenching

A voltage less than 5 V is applied to the workpiece through the electrode, which flows through a large current at the contact between the electrode and the workpiece, and generates a large amount of resistance heat, so that the surface of the workpiece is heated to the quenching temperature, and then the electrode is removed, and the heat is transferred into the interior of the workpiece and the surface is cooled rapidly, which achieves the purpose of quenching.

Electrolytic heating quenching

Place the workpiece in the electrolyte of acid, alkali or salt aqueous solution, connect the workpiece to the cathode, and connect the electrolyzer to the anode. After the direct current is connected, 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, which becomes a resistor and generates heat. The surface of the workpiece is heated to the quenching temperature rapidly, and then the power is cut off. The gas film disappears immediately, and the electrolyte becomes the quenching medium, which makes the surface of the workpiece cool and harden rapidly.

Laser heat treatment

The application of laser in heat treatment began in the early 1970s, and then from laboratory research stage to production application stage. When the focused high energy density (10W / cm) laser irradiates the metal surface, the metal surface rises to the quenching temperature in a few percent or even a few thousandths of a second.

Electron beam heat treatment

Electron beam surface quenching should be carried out in vacuum, other characteristics are the same as laser. When the electron beam bombards the metal surface, the bombardment point is heated rapidly. The depth of the electron beam through the material depends on the accelerating voltage and the density of the material.

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