The properties of metal materials are generally divided into process properties and service properties. The so-called technological performance refers to the performance of metal materials under the specified cold and hot working conditions during the processing and manufacturing of mechanical parts. The technological performance of metal materials determines its adaptability to processing and forming during the manufacturing process. Due to different processing conditions, the required technological properties are also different, such as casting performance, weldability, malleability, heat treatment performance, machinability, etc. The so-called service performance refers to the performance of metal materials of mechanical parts under service conditions, including mechanical properties, physical properties, chemical properties, etc. The service performance of metal materials determines its service range and service life.
In the machinery manufacturing industry, general mechanical parts are used in normal temperature, normal pressure and non-strong corrosive media, and each mechanical part will bear different loads in the process of use. The resistance of metal materials to failure under load is called mechanical property (or mechanical property).
The mechanical properties of metal materials are the main basis for the design and material selection of parts. The mechanical properties required for metal materials will vary with the nature of the applied load (such as tension, compression, torsion, impact, cyclic load, etc.). Common mechanical properties include strength, plasticity, hardness, impact toughness, multiple impact resistance and fatigue limit. The process performance and mechanical performance will be introduced respectively.
The technological performance of materials is the synthesis of physical, chemical and mechanical properties, and refers to the adaptability of materials to various processing technologies. It mainly includes casting performance, forging performance, welding performance, cutting performance and heat treatment performance. The quality of process performance will directly affect the processing quality and production cost of parts, so the selection of materials and the formulation of part processing technology must be considered during design.
Different materials correspond to different processing technologies. The technological performance of materials plays a decisive role in the degree of difficulty, production efficiency and production cost of parts processing. Therefore, process performance is another important factor that must be considered at the same time when selecting materials. The technological properties of materials mainly include the following aspects:
Refers to the ability of metal to obtain qualified castings by casting.
Refers to the difficulty of obtaining high-quality welded joints under certain welding conditions.
Pressure processing Properties:
Including forging performance, cold stamping performance, etc. If the material has high plasticity and good formability, the surface quality after pressure processing is good and it is not easy to produce cracks.
Refers to the difficulty of accepting cutting processing and becoming a qualified workpiece.
Heat treatment process Properties:
Mainly including hardenability, hardenability, deformation cracking tendency, temper brittleness, temper stability, oxidation decarburization tendency, etc.
Strength refers to the resistance of metal materials to failure (excessive plastic deformation or fracture) under static load. Since the action mode of load includes tension, compression, bending, shear, etc., the strength is also divided into tensile strength, compressive strength, bending strength, shear strength, etc. Various strengths are often related to each other, and tensile strength is generally used as the most basic strength indicator.
Plasticity refers to the ability of metal materials to produce plastic deformation (permanent deformation) without damage under load.
Hardness is a pointer to measure the hardness of metal materials. At present, the most commonly used hardness measurement method in production is the indentation hardness method, which is to press the surface of the metal material to be tested with an indenter of a certain geometric shape under a certain load, and determine its hardness value according to the degree of indentation.
The 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 indicators of mechanical properties of metals under static load. In fact, many machine parts work under cyclic load, in which case the parts will produce fatigue.
5. Impact toughness
The load acting on the machine at a great speed is called impact load, and the ability of metal to resist damage under impact load is called impact toughness.