Four ways of strengthening steel metal materials (Chapter One)

 1. Deformation strengthening (or strain strengthening, work hardening)

01. Definitions

After the yield of the steel material, with the increase of the degree of deformation, the strength and hardness of the material increase, and the plasticity and toughness decline.

02. Mechanism

With the progress of plastic deformation, the dislocation density continues to increase, so the mutual delivery of dislocation in motion is intensified, resulting in fixed step cutting, dislocation entanglement and other obstacles, so that the dislocation movement resistance increases, resulting in increased deformation resistance, causing difficulties to continue plastic deformation, thereby improving the strength of the metal

Rule: The degree of deformation increases, the strength and hardness of the material increase, the plasticity and toughness decrease, and the dislocation density continues to increase

The strength is proportional to the half power of ρ of the dislocation density. The larger the Bergdahl vector b of the dislocation, the more significant the strengthening effect is.

03. Methods

Cold deformation, such as cold pressing, rolling, shot peening, etc.

04. Examples

Cold-drawn steel wire can multiply its strength.

05. The practical significance of deformation strengthening (advantages and disadvantages)

(1) Advantages:

Deformation strengthening is an effective way to strengthen the metal, for some materials that can not be strengthened by heat treatment, the strength of the material can be improved by deformation strengthening, which can increase the strength exponentially.

②It is an important factor in the processing and forming of some workpieces or semi-finished products, so that the uniform deformation of the metal, so that the forming of the workpiece or semi-finished products is possible, such as cold drawn steel wire, stamping of parts.

(3) Deformation strengthening can also improve the safety of parts or components in the process of use, some parts of the stress concentration or overload phenomenon, so that there is plastic deformation, due to work hardening to stop the deformation of the overload part to improve safety.

(2) Disadvantages:

Deformation strengthening also brings trouble to the production and use of materials, deformation increases the strength and reduces the plasticity, and it is difficult to continue deformation, requiring more power consumption.

In order to allow the material to continue to deform, recrystallization annealing is required in the middle, so that the material can continue to deform without cracking, increasing the production cost.

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