Common defects and countermeasures during heat treatment processes such as quenching and annealing of trapezoidal thread precision hardened lathe screws

The screw is the basic part of the machine tool. Workpieces will always encounter some common defects during heat treatment such as quenching and annealing. Zhengzhou Gou's briefly talks about the defects that are easy to occur in trapezoidal thread precision hardened screws and some preventive measures.

(1) Causes and measures for high hardness after spheroidizing annealing

1. Isothermal temperature affects the precipitation and growth of carbides. If the isothermal temperature is too low, the fine carbide particles precipitated from austenite will have high dispersion and insufficient aggregation, resulting in high hardness after annealing.

2. Improper heating temperature. If the heating temperature is too high, too much or all of the carbides will be dissolved to form uniform austenite, which will make the workpiece harder during the cooling process. If the heating temperature is too low, the carbide will not dissolve enough, causing the carbide sheets to break and form point-like carbides.

3. Improper cooling. The cooling rate determines the size and dispersion of carbide particles. The greater the cooling rate, the finer the carbide particles formed and the greater the dispersion.

If the above defects occur, the process parameters should be strictly controlled and annealed again.

(2) Common defects and preventive measures during quenching

1. Soft spot. That is, the hardness of quenched parts is uneven, which is characterized by obvious high and low hardness on the surface of the parts. This defect may be caused by factors such as the original structure being too coarse and uneven, the quenching medium being contaminated, oxide scale on the surface of the part, or the part not moving properly in the quenching fluid. Perform metallographic analysis and study process execution. Further identify the cause of the waste. Soft spots can be corrected through rework and re-quenching.

2. Oxidation, decarburization and overheating If surface protection is not carried out during the quenching and heating process of parts, defects such as oxidation and decarburization will occur. The consequences will lead to a decrease in surface hardenability of the workpiece and failure to meet technical requirements. Or network cracks form on the surface of the part. And seriously reduce the appearance quality of parts. Increase the surface roughness of the workpiece, so the quenching and heating of finished parts must be carried out in a protective atmosphere or in a salt bath furnace. Cervical cancer products produced in small batches can also be protected with anti-oxidation surface coatings.

Overheating will cause quenching cracks to form or seriously reduce the impact toughness of the quenched parts. Therefore, the quenching heating temperature should be correctly selected, the holding time should be shortened appropriately, and the furnace temperature should be strictly controlled to prevent it. The overheated structure that appears can be re-annealed or normalized if there is sufficient processing allowance. After refining the grain, it is quenched and reworked again.

3. Quenching distortion and quenching cracks. Quenching distortion is an inevitable phenomenon and constitutes a waste product only when it exceeds the specified tolerance or cannot be corrected. Quenching distortion can be effectively reduced or controlled through reasonable material selection, improved structural design, reasonable selection of quenching and tempering methods and specifications, etc. However, quenching cracks are generally irremediable quenching defects. Only active preventive measures can be taken, such as controlling quenching stress, direction, distribution, raw material quality and correct structural design.

4. Insufficient hardness. Insufficient hardness after quenching and tempering is generally caused by insufficient quenching heating, surface decarburization or insufficient tempering. When solving, the causes must be identified and corresponding countermeasures must be taken to prevent them.

Zhengzhou Gou's is a manufacturer specializing in the manufacturing and sales of small induction heating equipment such as high-frequency induction heating equipment, high-frequency welding machines, CNC quenching machine tools, and ultrasonic induction heating equipment. With many years of experience in the industry, Zhengzhou Gou's has considerable experience in heat treatment such as quenching and annealing of workpieces. If you have any questions about the quenching of workpieces, you can contact us freely.