Impact strength is the ability of various materials to absorb impact energy, which is one of the most important indicators of strength. The impact strength of a particular material is most often determined by impact bending of a rectangular sample of material, and the work before breaking or breaking a particular sample under impact loading is evaluated, which is an indicator of impact strength. Its definition is carried out on a special device - a pendulum head. A sample of material with a notch in the middle is tested by hitting it with a pendulum knife. Testing this indicator of metal can be carried out at temperatures from -100 ° C to 1200 ° C, depending on the metal and the purpose of the test. The impact strength of metals is an indicator of the reliability of a particular material, indicates its ability to resist destruction caused by tensile stress between atoms.
The impact strength of steel is determined by the magnitude of the work that is sufficient to destroy a sample of this steel. It is denoted by a combination of letters and numbers. The first two letters are a symbol of impact strength (COP). The third letter shows the type of hub. Then come the numbers. The first of them shows the maximum energy from the impact of the pendulum, the second indicates the depth of the concentrator, and the third indicates the width of the test sample. If the sample was tested at low or high temperature, then an additional digital index is indicated, indicating the level of temperature at which the test was carried out.
A drop in the toughness of metals with a large decrease in temperature is an indicator of their cold brittleness. Cold brittleness is an increase in the level of brittleness of metals with decreasing temperature. Low- alloy steels and some other metals, such as tantalum, tungsten, chromium, and molybdenum, which consist of a body-centered cubic lattice of metal atoms, are susceptible to such a phenomenon as cold brittleness. The impact strength of metals depends primarily on temperature.
The impact strength of steel is determined by the structure of the test steel, including the size of its grains and is a good indicator of the quality of the metal. Therefore, the impact test is widespread. The temperature range in which the toughness of steel drops sharply is called the temperature brittleness region. And it is necessary that this region of thermal brittleness does not coincide with the temperature of the steel. In other words, the working temperature of metal products should be higher than the threshold beyond which the temperature fragility region begins. This is necessary so that the material of the part does not begin to crack and in the end does not undergo destruction. The criterion of temperature brittleness is closely related to the level of toughness of metals.
Optimum toughness of steel is possessed by heat-treated steel and quiet open-hearth steel, the indices of the area of thermal brittleness of which allow them to possess such characteristics. For each type of steel, GOST sets its own temperature at which impact strength is determined, as well as the temperature that is optimal for working with a particular type of steel. The impact strength of steel depends not only on temperature, but also on various impurities, the presence of alloying elements and the composition of the steel itself. The formation of hardening structures in steel products seriously reduces the toughness of steel. For example, if martensite formed during welding with a certain violation of the work technology, the toughness of the metal in the welding zone may decrease by 13 times.