The performance of metal materials is generally divided into two categories: process performance and use performance. The so-called process performance refers to the performance of metal materials under the specified cold and hot processing conditions during the processing and manufacturing of mechanical parts. The process performance of metal materials determines its adaptability in the manufacturing process. Due to the different processing conditions, the required process performance is also different, such as casting performance, weldability, forgeability, heat treatment performance, machinability, etc. The so-called performance refers to the performance of metal materials under the conditions of use of mechanical parts, which include mechanical, physical, and chemical properties. The performance of the metal material determines its use range and service life.
In the machinery manufacturing industry, general mechanical parts are used in normal temperature, normal pressure and non-strongly corrosive media, and each mechanical part will bear different loads during use. The ability of metal materials to resist damage under load is called mechanical properties (or mechanical properties). The mechanical properties of metal materials are the main basis for the design and selection of parts. The nature of the applied load is different (such as tension, compression, torsion, impact, cyclic load, etc.), and the required mechanical properties of the metal material will also be different. Commonly used mechanical properties include: strength, plasticity, hardness, toughness, multiple impact resistance and fatigue limit. The various mechanical properties will be discussed separately below.
Strength refers to the ability of metal materials to resist damage (excessive plastic deformation or fracture) under static load. Since the load acts in the form of tension, compression, bending, shearing, etc., the strength is also divided into tensile strength, compressive strength, bending strength, and shear strength. There is often a certain relationship between various strengths, and tensile strength is generally used as the most basic strength index in use.
Plasticity refers to the ability of metal materials to produce plastic deformation (permanent deformation) without damage under load.
Hardness is a measure of the hardness of metal materials. At present, the most commonly used method for determining hardness in production is the indentation hardness method, which uses an indenter of a certain geometric shape to press into the surface of the metal material to be tested under a certain load, and the hardness value is determined according to the degree of indentation.
Commonly used methods include Brinell hardness (HB), Rockwell hardness (HRA, HRB, HRC) and Vickers hardness (HV).
The strength, plasticity, and hardness discussed above are all mechanical properties of metals under static load. In fact, many machine parts are working under cyclic loads, under which conditions the parts will fatigue.
5. Impact toughness
The load acting on the machine at a very high speed is called impact load, and the ability of metal to resist damage under impact load is called impact toughness.