According to ISO 898-1 2013, the performance of bolts are divided into more than 10 grades including 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, etc. Grade 8.8 bolts are bolts with tensile strength minimum 800 MPA, yield strength minimum 360 MPA, bolts hardness from HRC 22 to HRC 34. It is a comprehensive performance grade for bolts. The specific mechanical properties of grade 8.8 bolts varies with the bolts sizes. Here is a reference for mechanical properties range for different sizes in below chart.

Grade 8.8 Bolts are manufactured using medium carbon steel or alloy steel. Regular materials adopted for grade 8.8 bolts production include 1035ACR, 1040ACR, CH38F, 1045ACR, 1039, 10B21, 10B33, 10B38 etc. They will be quenched and tempered after cold forming. Grade 8.8 bolts are generally applied in railroad equipment, motors, engines and processing equipment, grade 8.8 bolts exhibit good tensile strength and perform well in most environments.

The most common problem for grade 8.8 bolts manufacturing are hydrogen embrittlement and dark spots after heat treatment. Hydrogen embrittlement occurs when metals become brittle as a result of the introduction and diffusion of hydrogen into the material. The degree of embrittlement is influenced both by the amount of hydrogen absorbed and the microstructure of the material.It is because hydrogen is included in processes like heat treatment, plating, acid washing, welding etc.They may penetrate into the bolts during these process.Dark spots are generally oxide skins formed during heat treatment. If they are not removed properly after the process, dark spots will show in the finished bolts which leads to the appearance failure.
Peak Fasten Tech are professional and experience manufacturer for custom bolts, we are adopting clean material, low acid washing, baking bolts properly after zinc plating, no-oxide heat treatment process etc to avoid such problem in the production of specialty fasteners like bolts, nuts ,rivets etc.Finished fasteners or parts are properly packed to protect them from possible injury during shipping.

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