An Introduction to the Strength of Heat-Treated Fastener Raw Materials

When selecting carbon steel fasteners, the raw material grade directly determines the mechanical strength rating of the screws after heat treatment. Different wire materials undergo heat treatment processes such as quenching and tempering, resulting in significant variations in the performance standards they can achieve. This is a key reference for fastener selection and custom manufacturing. Jiaxing Aoke has specialized in fastener production for many years. Leveraging our mature heat treatment production lines and material R&D expertise, we can match the appropriate raw materials based on customers’ operating conditions and strength requirements. We offer customized carbon steel screws and stainless steel fasteners of various grades, and support production based on customer drawings or samples.

I. 1010/1018/1022 Low-Carbon Steel Wire Rod

1010, 1018, and 1022 are standard low-carbon steel materials. Without heat treatment for hardening, the finished screws can only achieve a strength grade of 4.8 or lower. Due to differences in carbon content among these three wire types, there are slight variations in the tensile strength of the finished products. If 1010 and 1018 low-carbon steel screws undergo heat treatment, the surface hardness of the product can be increased to meet Grade 6.8 standards. However, due to the low-carbon nature of the raw material, heat treatment only hardens the surface layer of the screw, with little to no improvement in the core’s microstructure or hardness. For this type of low-carbon fastener, the industry typically uses surface Vickers hardness (HV) as the basis for strength evaluation.

II. 10B21 Boron-Carbon Steel

10B21 is a commonly used boron-carbon steel raw material for mass-produced fasteners. After full-body heat treatment and hardening, the finished screws consistently meet Grade 8.8 or higher standards. Both surface and core Rockwell hardness (HRC) can be fully tested, and the hardness values for both the interior and exterior meet national acceptance standards. It is the mainstream material for mass-producing Grade 8.8 bolts and machine screws.

III. CM435 Medium-Carbon Alloy Steel

CM435 features an excellent overall carbon-manganese ratio. After quenching and tempering, fasteners made from this material can meet high-strength standards such as Grade 10.9 and Grade 12.9. It exhibits uniform hardening throughout the cross-section, and both surface and core HRC hardness values can be verified through compliant testing. It is widely used for high-strength fasteners in high-pressure equipment and construction machinery.

IV. 45K Quenched and Tempered Carbon Steel

45K wire rod undergoes quenching and tempering (a dual heat treatment process of quenching and high-temperature tempering) prior to shipment. The steel’s strength, toughness, and ductility are optimized, significantly reducing the risk of deformation during subsequent secondary processing and heat treatment. Combined with a preheating process during production, the finished screws can reliably achieve Grade 8.8 strength without the need for additional deep hardening, making them suitable for high-volume, standardized bolt production.

V. Other Metal Materials Capable of Heat Treatment Hardening

In addition to mainstream carbon steel materials, 410 and 430 stainless steels, as well as 7-series aluminum alloys, are also suitable for heat treatment hardening. From a metallurgical perspective, surface hardening can be achieved for the vast majority of metal materials using a ternary boron-carbon-nitrogen co-diffusion process. However, due to the high production costs and complex manufacturing procedures associated with this process, as well as constraints related to pricing and processing difficulty, this hardening method is typically reserved for small-batch, custom-made fasteners.