On 2018-08-08 14:48:54
Arrangement of heat treatment process
A metal heat treatment process that changes the mechanical properties of steel surface by heating and cooling the steel surface. Surface quenching is the main content of surface heat treatment, its purpose is to obtain high hardness of the surface layer and the favorable distribution of internal stress, in order to improve the wear resistance and fatigue resistance of the workpiece. The strengthened metal heat treatment process on the surface of the workpiece is widely used in the requirements of not only the surface with high wear resistance, fatigue strength and large impact load, but also the overall requirements of good plasticity and toughness of the parts, such as crankshaft, camshaft, transmission gear. Surface heat treatment can be divided into surface quenching and chemical heat treatment.
As the heat treatment process arrangement has a great impact on the turning process, it is more important that the reverse of the heat treatment process arrangement often makes the workpiece unable to continue processing, and the waste products are often irreparable. Therefore, the arrangement of heat treatment process should be understood and attention should be paid to it.
The following are the common heat treatment methods, the purpose and the arrangement of the process location:
Preliminary heat treatment
Preliminary heat treatment includes annealing, normalizing, tempering and aging. The purpose of this type of heat treatment is to improve machining performance, eliminate internal stress and prepare the organization for final heat treatment. Annealing, normalizing and tempering processes are mostly before and after rough machining. Aging treatment is generally arranged after rough machining and semi-finished machining and before finishing.
1. Annealing and normalizing
The aim is to improve the cutting performance, eliminate the internal stress of the blank, refine the grain and even the structure. Prepare for future heat treatment. For example, carbon steel and alloy steel with a carbon content of more than 0.7% can be annealed in order to reduce the hardness. Carbon less than 0.3% of low carbon steel and low alloy steel, in order to avoid hard over the low cutting stick, and the adoption of normalizing to improve the hardness.
Generally used for forgings, castings and welds. Annealing is generally arranged in the blank after manufacturing, before rough machining.
The purpose is to obtain better mechanical properties of the material in terms of strength, plasticity and toughness, and to prepare for later heat treatment.
Used for various medium carbon structural steels and medium carbon alloy steels. Tempering is generally arranged after the rough machining, before the semi - finishing machining. Tempering is the most commonly used heat treatment process. Most of the parts are through the tempering treatment to improve the comprehensive mechanical properties of the material, that is, to improve the tensile strength, yield strength, reduction of area, elongation, impact work. Tempering and tempering can greatly improve the tensile strength and yield strength of the material, improve the flexural ratio and impact work, and make the material have a good combination of strength and plasticity. Due to the increase of yield strength, fatigue strength and impact strength, smaller material section can be adopted in the design of parts, thus reducing the overall weight of mechanical equipment, saving parts occupied space and energy consumption. So in some cases in order to reduce the mechanical space and mechanical weight in the design process to consciously use the tempering process.
3. Aging at low temperature (drying)
For all kinds of precision parts to eliminate machining stress, keep the dimensional stability. Generally arranged after the semi - fine car, or rough, semi - fine grinding, grinding before.
Final heat treatment
1. The quenching
The purpose is to improve the hardness, strength and wear resistance of the material. For structural and tool steels above medium carbon.
2. High (medium) frequency surface quenching
The purpose is to improve the surface hardness and wear resistance of the parts, while the heart to maintain good plasticity and toughness. The depth of quenching is generally: 1 ~ 2mm high-frequency quenching; Medium frequency quenching 2 ~ 6mm.
Generally used in the above - carbon structural steel and alloy steel spindle, gear and other parts. When the workpiece quenching, the surface hardness is high, in addition to grinding, generally can not be other cutting processing. Therefore, the process should be as far as possible behind, generally arranged in the semi-finished machining, grinding before.
3. The carburizing
The carbon content of the surface layer of low carbon steel is increased to 0.85 ~ 1.10%, and then treated with quenching and tempering, so that the surface layer of steel has a high hardness (HRC≥59), increasing wear resistance and fatigue strength. And the heart still retains the original plasticity and toughness.