With the development of energy-saving, environmentally friendly, lightweight, and miniaturized automotive products, high-strength fasteners for automobiles have received increasing attention. Automotive fasteners are the main connecting parts of automobiles, accounting for almost half of the total number of automotive parts.
The research and development of high-strength automotive fasteners in China is still relatively backward compared with developed countries.
So what is the key point in producing high-strength fasteners for automobiles? One is the choice of fastener materials, and the other is the heat treatment process of fasteners. No matter which point is not good, the performance of high-strength fasteners of automobiles will be invalid, which will bring safety hazards to driving.
Automobile high-strength fasteners must obtain tempered sorbite and tempered torsite structure with good comprehensive mechanical properties, provided that the quenching is to ensure the martensite structure of the core, which is closely related to the hardenability of the steel. Related.
Whether it is carbon steel or alloy steel, in the case of complete hardening, when the fasteners are tempered at high temperature to obtain finished products of the same hardness, their mechanical properties such as strength, ductility and toughness are similar.
However, if it is not completely hardened, even if the hardness after tempering is the same as that after tempering, the yield strength, elongation after forging, area shrinkage and impact toughness are lower, and the degree of reduction is The degree of hardening increases and decreases.
The quenching heating temperature is mainly determined according to the chemical composition of the steel in combination with a specific process.
The energy-saving and lightweight development of automobiles puts forward higher requirements for the design of engines and power systems. As the strength increases, the fracture caused by hydrogen embrittlement is mainly the quenched and tempered martensitic steel, which occurs in yielding. For high-strength materials with a strength > 620 MPa and a hardness value > 31 HRC, the higher the tensile strength, the more sensitive it is to hydrogen embrittlement. The easier the material is to absorb hydrogen, the more difficult it is to drive hydrogen.
The sensitization of tempered martensite, upper bainite, lower bainite, sorbite, pearlite and austenite to hydrogen embrittlement is successively reduced.
Car fastener quenching and tempering heat treatment is carried out at high temperature. In order to reduce the formation of surface oxidation during heat treatment, a protective atmosphere is often added to the heating furnace. If the protective atmosphere contains hydrogen compounds, it is possible to absorb hydrogen during the heat treatment and increase the risk of hydrogen embrittlement of the fasteners.
In order to prevent hydrogen embrittlement, high-strength fasteners of 1000 to 1300 MPa must drive hydrogen after electroplating.
Under certain conditions, the quality of raw materials will affect the selection of fastener production process parameters, and directly affect the comprehensive performance and safety of high-strength fasteners for automobiles. During the assembly process of automobiles, the development and application of high-strength fasteners for automobiles also present challenges from raw material suppliers and manufacturing.
Fastener manufacturers must continuously improve their production processes and technologies in order to meet the needs of the ever-developing fastener market. Especially in today's deepening reform, we must strictly control the production process and improve the product quality level in order to tighten in the future. Survival in the firmware market competition!
We should strengthen the research and development of automotive fastener products, learn advanced production technology, and enhance our country's self-development and innovation capabilities.