Bolts are classified by different strength levels, and bolts of corresponding material grades should be selected according to different design requirements, which cannot be taken lightly. There is no need to elaborate on the materials of ordinary bolts, as most types of ordinary bolts are readily available on the market. Moreover, there is basically no incentive for material fraud with ordinary bolts-after all, it makes no sense to counterfeit ordinary bolts with a cost of 100 yuan just to sell them for 90 yuan. Haha. Therefore, we will mainly focus on the relevant knowledge of high-strength bolts.
The differences between high-strength bolts and ordinary bolts lie first in raw materials, and then in the heat treatment processes applied during production. Standard high-strength bolts are far superior to ordinary bolts in terms of torque resistance and other mechanical properties. The quenching process for high-strength bolts is a highly rigorous procedure, with extremely precise requirements for furnace temperature and quenching duration. In industry practice, the commonly recognized high-strength bolts do not include Grade 8.8 medium-carbon steel bolts; high-strength bolts mainly refer to two categories: Grade 10.9 and Grade 12.9. Before delivery to customers, these two grades of high-strength bolts must undergo strict inspections, including verification of quenching parameters, surface hardness testing, and even tensile strength tests, to ensure compliance with standards.
Grade 10.9 high-strength bolts are typically manufactured from 40CrMo alloy steel. Their yield strength ranges from 390 MPa (for bolts with diameter d ≥ 30 mm) to 430 MPa (for bolts with diameter d < 30 mm), with a nominal tensile strength of 1000 MPa. This grade of bolts is not designed for heavy load applications. If higher load capacity or surface hardness is required for specific working conditions, bolts of a higher strength grade should be selected as a replacement.
A special category is Grade 12.9 bolts made from 42CrMo alloy steel. Compared with 40CrMo steel, 42CrMo steel produces bolts with higher strength, better toughness, and excellent high-temperature resistance. As a result, these bolts are widely used in demanding industries such as pressure vessel manufacturing and chemical furnace construction.
From the perspective of raw material costs, ordinary bolts are usually made from carbon steels such as Q235, 45# steel, or 35# steel. These materials are produced and sold by most steel mills in China, leading to intense market competition and a supply surplus relative to demand. Thus, the costs of these raw materials are relatively controllable. In contrast, high-strength bolts are made from alloy steels such as 40CrMo and 35CrMo. The number of steel manufacturers producing such special alloy steels is limited, and most of them are large-scale enterprises. Purchasers and market forces have little influence on the pricing set by these steel mills, resulting in significantly higher raw material costs for high-strength bolts compared to ordinary bolts.
The production process of high-strength bolts is intricate and imposes high requirements on manufacturing equipment, with most manufacturers relying on imported machinery for production. To fully meet the requirements of national standards or customer specifications, strict quality control must be implemented starting from the first step of raw material procurement. In the subsequent stages, establishing a reasonable safety stock, optimizing transportation solutions, and standardizing sales processes are essential to effectively control overall costs, enabling the provision of high-quality products to customers at competitive prices.
