The 10.9 grade bolt is a popular flat head hexagonal screw. Due to its high hardness, it is often used in applications such as precision machinery and grinding tools. So what is the hardness of grade 10.9 bolts? In this article, we will comprehensively analyze the hardness of grade 10.9 bolts, hoping to provide reference for everyone.
Firstly, let's take a look at the hardness of grade 10.9 bolts.
According to the standard, the hardness of grade 10.9 bolts should be HV320-380 or HRC34-40. In actual production, the manufacturer immerses the bolts in quenching oil heated to 850 degrees Celsius for 30 minutes. After quenching, the bolts will be tempered for 120 minutes. This process is crucial for producing the required hardness.
Next, let's delve deeper into the process of 10.9 grade bolts.
Process 1
For the 35CrMo process, it is required to use 40Cr material to make bolts. The bolt has a diameter of 22mm and a length of 114mm, used for truck tires. After quenching and tempering, the hardness should be HV320-380 or HRC34-40, the tensile strength should be 1040MPa, and the microstructure should be tempered with sorbite.
Process 2
Test process 1 adopts hot forging forming followed by machining, and heat treatment is carried out in a mesh belt furnace. The quenching temperatures in zones 1-4 are (860-870-870-860), and the quenching time is about 90 minutes. The quenching oil is used for cooling, and the hardness after quenching is HRC49-52; The tempering temperature range 1-3 is 510, and the hardness after tempering is HRC32-35. However, the inspection results indicate that the process cannot meet the requirements.
Test process 2 underwent annealing, phosphating, and cold extrusion forming. The heat treatment was carried out in a mesh belt furnace, with quenching temperatures ranging from 860-870-870-860 in zones 1-4. The quenching time was about 90 minutes, and the quenching oil was used for cooling. The hardness after quenching was HRC49-52; A tempering temperature range of 480 in the 1-3 zones, with a hardness of HRC34-38 and a tensile strength of 1005MPa after tempering, as well as a small amount of ferrite; The other type of tempering temperature ranges from 1 to 3, with a hardness of HRC36-40 and a tensile strength of 960MPa after tempering. The entire process fully utilized the material properties and achieved the required performance.
In summary, the hardness of 10.9 grade bolts on the market is usually HV320-380 or HRC34-40. For the manufacturing of 10.9 grade bolts, it should be carried out on the basis of holding at 850 degrees Celsius for 60 minutes, carbon potential of 0.45, isothermal graded quenching oil, oil temperature of 100 degrees Celsius, quenching time of 30 minutes, tempering at 480 degrees Celsius, and 120 minutes. In addition, if a small amount of ferrite is produced in the bolt after tempering, its tensile strength is also acceptable.
