Metal materials require not only sufficient strength and plasticity, but also sufficient toughness during use. Toughness is the ability of a metal to absorb deformation energy before fracture. The toughness of metals usually decreases with increasing loading speed, decreasing temperature, and increasing stress concentration.

Toughness is a mechanical performance indicator that measures the sensitivity of a material to notches, especially reflecting its sensitivity to notches at low temperatures or under impact loads. Toughness is a comprehensive reflection of the strength and plasticity of materials. Steel with good plasticity generally has better toughness. Control valve materials with high strength and good plasticity have better toughness. The commonly used testing method and indicator currently is impact toughness.

According to GB10623-1989 "Terminology for Testing Mechanical Properties of Metals", impact toughness is defined as the work absorbed by a specimen of a specified shape and size when it breaks under a single impact test force, which is called the impact absorption work. The impact absorption energy per unit cross-section at the bottom of the notch of the impact specimen is called impact toughness. Impact toughness is a mechanical performance index used to evaluate the impact resistance of metal materials under dynamic loads.

In order to sensitively display the impact of small changes in the chemical composition, metallographic structure, and processing technology of the electric control valve material on its toughness, the impact test should be conducted with the material in a semi brittle state of transition between toughness and brittleness. Therefore, notched specimens are usually used to fracture under impact load to obtain the impact toughness of the material.
Experiments have shown that impact values are highly sensitive to tissue defects and can sensitively reflect minor changes in material quality, macroscopic defects, and microstructure. Impact testing is an effective means of testing the metallurgical quality and brittleness tendency of materials, and pneumatic control valves.