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Stainless steel CNC manufacutring hardening: reasons, characteristics, and countermeasures

Stainless steel is widely used in various fields due to its excellent corrosion resistance and durability. However, one of its characteristics is' manufacturing hardening '. manufacturing hardening refers to the hardening phenomenon that occurs during the processing of materials. If appropriate measures are not taken, it can lead to a decrease in processing efficiency and product defects. This article will elaborate on the reasons and characteristics of stainless steel manufacturing hardening, its impact on processing, and specific countermeasures.

What is manufacturing hardening of stainless steel? The manufacturing hardening of stainless steel refers to the phenomenon in which the internal crystal structure of the material changes during plastic deformation, thereby increasing its hardness and strength. This phenomenon is also found in ordinary metals, but is particularly significant in stainless steel. The manufacturing hardening effect of austenitic stainless steel (such as SUS304 and SUS316) is particularly strong, which may lead to problems during machining, stamping, and bending processes.

As manufacturing hardening progresses, the material exhibits the following characteristics:

An increase in hardness can lead to accelerated wear of cutting tools.

Bending and shaping become difficult.

Increased risk of cracking and surface damage

Although manufacturing hardening can sometimes improve material strength, its impact on processing efficiency and product quality cannot be ignored.

manufacturing hardening mechanism

The mechanism of manufacturing hardening is mainly due to the distortion of crystal structure. When stainless steel undergoes plastic deformation, the number of dislocations in the lattice increases. These dislocations intertwine with each other, hindering atomic movement and causing the material to harden.

In austenitic stainless steel, not only manufacturing hardening but also stress-induced martensitic transformation (SIM transformation) may be involved. This phenomenon refers to the stress generated during the machining process causing some austenite to transform into martensite, resulting in local hardening. Therefore, in some cases, manufacturing hardening may occur rapidly.

Types of stainless steel and their manufacturing hardening properties

Stainless steel is mainly divided into three types: austenite, ferrite, and martensite. The manufacturing hardening performance of each type is different, so the processing methods and countermeasures are also different.

Austenitic stainless steel

Austenitic stainless steel (such as SUS304 and SUS316) is the most commonly used type. Its characteristics include:

Excellent corrosion resistance

It has high ductility and is prone to plastic deformation.

The phenomenon of manufacturing hardening is very obvious.

During mechanical processing, the hardened layer often thickens, leading to increased tool wear; Therefore, appropriate cutting conditions and tool selection are crucial. Sheet metal processing and bending processing are also prone to cracking due to hardening.

Ferritic stainless steel

Ferritic stainless steel (such as SUS430) is a relatively hard and magnetic type.

Compared with austenitic materials, its manufacturing hardening phenomenon is not very obvious.

It is very brittle and prone to cracking when bent.

Hardness is a major challenge in mechanical processing.

For ferritic materials, cooling and cutting tool conditions are more important than manufacturing hardening in preventing cracking and chipping.

Martensitic stainless steel

Martensitic stainless steel (such as SUS410 and SUS420) is a type of stainless steel that can be hardened (quenched).

Tool wear is a major challenge faced during cutting and grinding processes.

Easy to crack when bent or stamped.

Due to the difficulty in processing martensitic materials after hardening, it is crucial to plan the processing sequence

The influence of manufacturing hardening on the machining process

The manufacturing hardening of stainless steel has multiple impacts on processing efficiency and product quality.

The impact on cutting technology

As manufacturing hardening progresses, chips will pass through the hardened layer and apply significant loads to the cutting tool. This will result in the following issues:

Blade wear and chipping

Increased cutting resistance

Surface roughness deterioration

Processing deformation increases

Especially for austenitic stainless steel, hardening occurs under initial cutting conditions, so it is necessary to remove the hardened layer during precision machining.

The impact on bending and pressing processes

The degree of hardening of materials during bending and compression is directly proportional to their elongation. If manufacturing hardening is carried out too quickly, the following problems may occur:

Cracks and crevices

Adjusting the bending radius is difficult

Enhanced spring rebound force after processing

Especially for austenitic stainless steel sheets, it is recommended to undergo softening treatment (annealing) before bending.

The impact on welding nozzles

manufacturing hardening may occur even near the weld seam. Especially friction welding and laser welding are prone to forming localized hardening layers, leading to cracks and stress concentration. Therefore, appropriate heat treatment before and after processing is crucial.