Bolt hardness testing method

The carbon steel bolts we commonly use, in addition to the necessary performance tests, the bolt hardness standard is also a very important parameter, so how to test the bolt hardness?

First of all, stainless steel bolts do not need to be hardened, because when we produce stainless steel bolts, we only change the appearance of the material, but do not make any changes to its performance parameters. What is the performance of a finished stainless steel bolt? In fact, it is the performance of the material. Therefore, there is no need to confirm the hardness of stainless steel bolts, but only to see what material it is.

Therefore, the index of hardness is only applicable to carbon steel bolts. Different levels of bolts have different hardness. According to the parameters in the national standard, the hardness of 4.8-grade bolts is the lowest, with an HRC value of 15 degrees, while the bolts of a higher grade are 6.8, with HRC hardness. Around 17 degrees. One level higher is the 8.8 grade bolt that we use the most, its HRC hardness is about 23 degrees, the higher level is the 10.9 grade bolt, the hardness is about 32 degrees, and the last one is the 12.9 grade bolt, which has the highest strength. , the hardness is also the highest, the HRC value is around 39 degrees. Since the shape of the bolt is not a complete plane, the hardness of each part is somewhat different, and the hardness standard depends on the average value.

So how to test the hardness of the bolt?

Let's talk about Brinell hardness first. To measure the Brinell hardness of the bolt, it is necessary to use a steel ball indenter or a hard alloy indenter. The Brinell hardness is suitable for materials below 450HBS, which can be measured with a steel ball indenter, while materials above 650HBS, Alloy indenters should be used to measure. Generally, 12L15 materials will be tested for Brinell hardness, while bolts are rarely required to test for Brinell hardness.

The table is a comparison of the old and new standards. In bolt products​, the most important parameter is the Rockwell hardness, which is what we call the HRC hardness standard. Rockwell hardness began to be enforced in 2004, and six hardness indicators and its scope of application were added on the basis of the previous ones, which were 15N/30N/45N/15T/30T and 45T. In the old standard, it was stipulated that diamond The indenter is used to test the Rockwell hardness, and in the new standard, it can also be measured with a carbide indenter. In addition, referring to the storage environment and temperature changes at that time, the experiment report archiving regulations have been added, and the accuracy of the experimental results is required to be 0.5HR.