In addition to sufficient strength and plasticity, metal materials also require sufficient toughness during use. Toughness is the ability of a metal to absorb deformation energy before fracture. The toughness of a metal 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 when subjected to low temperatures or impact loads. Toughness is a comprehensive reflection of the strength and plasticity of a material. 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 is impact toughness.

According to GB10623-1989 "Terminology for 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. The impact absorption work on the 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.

Impact testing, in order to sensitively display the impact of small changes in the chemical composition, metallographic structure, and processing technology of electric control valve materials on their toughness, should be conducted in a semi brittle state with a transition between toughness and brittleness. Therefore, notched specimens are usually used to fracture under impact load to obtain the impact toughness of the material.