We commonly used carbon steel bolts, in addition to the necessary performance test, 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 play hardness, because we in the production of stainless steel bolts, just changed the appearance of the material, and for its performance parameters did not make any change, a stainless steel bolt finished product.

How its performance, in fact, is the performance of the material. So there is no need to confirm the hardness of the stainless steel bolt, but only need to see what material it is.

So the hardness index is only applicable to carbon steel bolts. The hardness of bolts of different levels is also different.

According to the parameters in the national standard, the hardness of bolts of 4.8 level is the lowest, and the HRC value is 15 degrees, while the bolt of one level higher than it is 6.8 level, and HRC hardness is about 17 degrees.

The next level up is the 8.8 bolt that we use the most, which has HRC hardness around 23 degrees, and the higher level is the 10.9 bolt, which has hardness around 32 degrees.

The last bolt, Grade 12.9, has the highest strength and hardness, with an HRC of about 39 degrees.

Because the shape of the bolt is not a complete plane, the hardness of each part is slightly different. This hardness standard depends on the average value.

Then how to test the hardness of bolts?

Let’s start with Brinell hardness. To measure brinell hardness of bolt, is to use steel ball head or hard alloy head, brinell hardness is suitable for below 450 HBS material.

Can use a steel ball head to measure, and more than 650 HBS material, the alloy head is to be used for measuring, general 12 l15 material brinell hardness test, and bolt has rarely asks of brinell hardness.

The table is a comparison of the old and new standards. In bolt products, the most important parameter is Rockwell hardness, also known as HRC hardness standard.

Rockwell hardness became mandatory in 2004, and six additional hardness indexes and their range of application were added to the previous standard, 15N/30N/45N/15T/30T and 45T. In the old standard, diamond indentation was used

Rockwell hardness, and in the new standard, also can be measured by cemented carbide indentation.

In addition, we also need to refer to the placement environment and temperature changes at that time, and increase the requirement of archiving experiment report, and require the accuracy of experiment results to 0.5hr.