Why does machining need heat treatment?

This is a very good problem. It is a puzzle for many new people who have just joined the industry. It is also a problem that many people with considerable experience have not thought deeply about. Today, we are here to unify science popularization.

The heat treatment requirement of machining is actually a technical requirement in the design process. If you are a mechanical structure design engineer, you need to have cognitive ability in this respect. If you do not have such a consciousness, you are not a qualified design engineer, at least not a very comprehensive design engineer.

The cognition of heat treatment design requirements of parts is basically based on the cognition of the change of material use and processing, so this is a very systematic knowledge structure, which does not exist in isolation.

First of all, we need to know how many kinds of heat treatment methods are included in the so-called part machining process? In view of the frequency and importance of various methods in the process of machining, we choose the following methods for analysis, that is, focused analysis.

In the machining process, we use the most four heat treatment methods: annealing, normalizing, quenching and tempering. The following analysis is made.

01 annealing

Definition of annealing treatment: a metal heat treatment process in which metal parts are heated to a certain high temperature, kept for a period of time, and then allowed to cool naturally.

Its main function:

A. Reduce the hardness of parts and improve the cutting performance;

B. Eliminate the residual stress, stabilize the size, reduce the probability of deformation and crack;

C. Refine the grain, adjust the structure and eliminate the material defects;

D. Homogenize the structure and composition of the material, improve the performance of the material or prepare the structure for the subsequent heat treatment process.

02 normalizing treatment

The definition of normalizing treatment is to heat metal parts to a certain high temperature for a period of time, then let them be cooled by spraying water and spray blowing in the air, which is different from the annealing process. The cooling speed is faster, so the material obtained is finer and the mechanical properties are improved.

Its main function:

A. Remove the internal stress of materials;

B. Reduce the hardness and improve the plasticity of the material;

03 quenching treatment

Definition of quenching treatment: heat the metal parts to the critical temperature above AC3 or AC1, keep them for a period of time, austenite them in whole or in part, and then cool them to the martensitic transformation below ms at the cooling speed faster than the critical cooling speed.

Its main function:

A. Greatly improve the rigidity, hardness, wear resistance and fatigue strength of the parts;

B. It can satisfy the physical and chemical properties of some special steels such as ferromagnetism and corrosion resistance.

04 tempering treatment

Definition of tempering treatment: it refers to that the steel after quenching and hardening or normalization treatment is immersed for a period of time below the critical temperature

After cooling at a certain speed to increase the toughness of the material.

Its main function:

A. Eliminate the residual stress produced during quenching to prevent deformation and cracking;

B. Adjust the hardness, strength, plasticity and toughness of the workpiece to achieve better performance requirements;

C. Stable structure and size, ensure accuracy;

D. Improve and improve processing performance.

As a mechanical design engineer, when heat treatment is needed for the parts we design, there are only the following requirements:

A. The purpose of eliminating casting stress is to obtain more stable machining size and precision;

B. The purpose of improving the cutting performance of parts is to improve the machining efficiency, quality and cost;

C. There is no need to explain how to improve the rigidity, hardness and wear resistance of parts.

Our heat treatment requirements for most parts are designed around the above three major aspects, so you only need to use the above four heat treatment methods according to your requirements

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