What tips do you have to solve the defects of high-frequency quenching heat treatment of pins?

The pin is a type of standardized fastener that can be used for static fixed connection or relative movement with the connected parts. It is mainly used at the hinge of two parts to form a hinge connection. The pin is usually locked with a cotter pin, which works reliably and is easy to disassemble. Therefore, the pin has to withstand huge friction during work. Therefore, we often use high-frequency induction hardening power to heat treat the pin. So how to prevent the pin from causing defects during heat treatment and how to solve the defects has become a top priority.

Defects often encountered during heat treatment of pins:

1. Causes and solutions for excessive deformation:

(1) The cooling medium is incorrectly selected, or the cooling method is improper. Choose a reasonable cooling medium and cooling method.

(2) The design of the parts is unreasonable. We should improve the design and make it as symmetrical as possible without defects such as mutations.

(3) The alignment method is improper, which is beneficial to the thermoplastic principle for alignment, or special fixtures are used to strictly temper.

2. Quenching cracking. Quenching cracking is a common defect in the heat treatment of pins. Controlling quenching cracking of pins is also the key to heat treatment. Its causes and solutions:

(1) The cooling medium cools too fast. We can select the appropriate cooling medium according to the hardness and performance requirements of the parts.

(2) The carbon content is above the upper limit, or there is segregation or inclusions exceeding the standard. We select qualified materials and take certain process measures.

(3) The part itself has design defects (cross-sectional mutations, grooves or holes), and we need to improve the design or take necessary preventive measures.

(4) The quenching temperature is high, and we should strictly implement the heating temperature of the heat treatment process.

(5) Improper installation and operation methods cause uneven heating and cooling. We should install the furnace reasonably and standardize the operation.

(6) If there are processing stress, knife marks or printing marks on the surface, stress annealing can be performed to eliminate traces of processing and markings.

(7) When the protective atmosphere is heated, hydrogen penetrates into the surface of the part, and we need to add a low-temperature dehydrogenation annealing (180~220℃).

3. Low hardness. High hardness and low hardness are bad for the workpiece. The causes of low hardness and prevention measures:

(1) When heating causes decarburization or carbon depletion of the surface of the parts, we should perform protective heating, or heat in a neutral or reducing atmosphere to avoid surface decarburization.   

(2) The quenching temperature is low, the austenitizing temperature is not reached or the holding time is short, and the pearlite is not fully transformed. We should strictly follow the process operation.

(3) The hardenability of steel is poor and the cooling rate is too slow. Choose a reasonable cooling medium and cooling method.

(4) The time between heating and quenching is too long, and the temperature of the parts has dropped below the phase transformation point. We should strictly implement the quenching operation specifications to avoid rework defects.

(5) The tempering temperature is high or the tempering time is too long. Lower the tempering temperature and shorten the tempering time.

4. Overheating: Causes and measures for pin overheating:

(1) If the temperature control system (thermocouple damage, etc.) fails or works in the manual position, we should set up an over-temperature alarm device and check the thermocouple regularly.

(2) The quenching temperature is too high or the holding time is too long, and the operation must be performed strictly in accordance with the process operation.

(3) The parts are too close to the heating body or heat source, resulting in high local heating temperature. Therefore, there should be a certain distance between the workpiece and the heating body or heat source (such as furnace wire, salt bath electrode, etc.).

5. High hardness. High hardness is a common defect in heat treatment. Its causes and measures are:

(1) The tempering temperature is low or the tempering is insufficient. Implement correct tempering process parameters and conduct quality inspection.

(2) The quenching temperature is high, we should strictly control the heating temperature and standardize the testing procedures.

(3) The cooling speed is too fast, choose a suitable cooling medium or cooling method.

This is an introduction to the defects that are easy to occur in the heat treatment of pins and some simple solutions. I hope it will be helpful to you. If you would like more detailed information please call us for more detailed information.