Grade 10.9 bolts are a popular type of flat head hex 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 conduct a comprehensive analysis of the hardness of grade 10.9 bolts, hoping to provide a reference for everyone.
First, let's 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, manufacturers soak the bolts in quenching oil heated to 850 degrees for 30 minutes. After quenching, the bolts will be tempered for 120 minutes. This process is critical to producing the required hardness.
Next, let's take a deeper look at the process of grade 10.9 bolts.
Craft 1
For the 35CrMo process, it is required to use 40Cr material to make bolts. Bolt diameter is 22mm, length is 114mm, for truck tires. After quenching and tempering, the hardness should be HV320-380 or HRC34-40, the tensile strength should be 1040MPa, and the structure should be tempered sorbite.
Craft 2
Test process 1 adopts hot forging and then lathe processing. The heat treatment is in a mesh belt furnace. The quenching temperature in zones 1-4 is (860-870-870-860). The quenching time is about 90 minutes. The quenching oil is cooled. The hardness after quenching is HRC49. -52; the tempering temperature in zones 1-3 is 510, and the hardness after tempering is HRC32-35. However, the inspection results showed that the process could not meet the requirements.
In test process 2, annealing, phosphating, and cold extrusion were carried out. The heat treatment was in a mesh belt furnace. The quenching temperature in zones 1-4 was (860-870-870-860). The quenching time was about 90 minutes. The quenching oil was cooled and quenched. The hardness after tempering is HRC49-52; one tempering temperature zone 1-3 is 480, the hardness after tempering is HRC34-38, the tensile strength is 1005MPa, and there is a small amount of ferrite; the other tempering temperature is 1 The -3 zone is all 460, the hardness after tempering is HRC36-40, and the tensile strength is 960MPa. The entire process takes full advantage of material properties and achieves the required performance.
To sum up, the hardness of grade 10.9 bolts on the market is usually HV320-380 or HRC34-40. For the manufacturing of grade 10.9 bolts, it should be carried out on the basis of insulation at 850 degrees for 60 minutes, carbon potential 0.45, isothermal graded quenching oil, oil temperature 100 degrees, quenching time 30 minutes, tempering 480 degrees, 120 minutes. In addition, if the bolt produces a small amount of ferrite after tempering, its tensile strength is acceptable.
