In industrial production, stainless steel bolts, as key fasteners, their quality is directly related to the safety and stable operation of equipment. When we observe a stainless steel bolt that seems normal in quality with the naked eye through a magnifying glass, we may find that its surface shows an obvious loose feeling. In severe cases, there will also be bubbles similar to air filling and white spots. These phenomena are important factors leading to the substandard strength of stainless steel bolts, and we call this situation the material structure loose segregation defect syndrome.
At present, the usage rate of stainless steel bolts in the entire fastener products has reached about 30%, and it still maintains an upward trend. In order to ensure the rational use and quality stability of stainless steel bolts, it is crucial to accurately judge their non - conventional quality problems. The non - conventional quality problems mentioned here do not refer to rare situations, but rather those quality hidden dangers that are easily overlooked, such as the segregation defects mentioned above.
The production materials of stainless steel bolts need to go through a series of process flows such as cold rolling, pickling, and polishing before processing. Some materials, after rough grinding, also need to go through a fine sand grinding process to remove surface burrs to ensure surface smoothness. The material looseness problem that occurs at this time refers to the insufficient density of the material itself. This is mainly due to excessive impurities in the local area, and after long - term corrosion, bubbles gradually appear. If this phenomenon occurs on the cross - section of the bolt, the impact is relatively small; but if it occurs on the straight line of the bolt shank, it indicates that the central part of the bolt may have developed looseness. At this time, professional testing instruments must be used to determine the degree of damage to the bolt strength.
So, what is segregation? Simply put, segregation is the uneven distribution of various elements in the material. Observed through a microscope, the internal structure of the material shows a dendritic criss - cross pattern, and there are also irregular shapes such as squares and dots. With the continuous progress of China's material technology, dot - shaped segregation has become relatively rare. The common dendritic distribution is caused by temperature changes during the material formation process. When there is a temperature difference, the material distribution will show uneven thickness traces. With repeated temperature changes, more lines will be derived from the initial segregation line, and finally a dendritic distribution is formed. Although segregation is difficult to completely eliminate, overly severe segregation will significantly affect the bolt strength.
Bubbles and small hole residues are small voids formed during the condensation process of the material. Individual bubbles are a normal phenomenon, but the appearance of honeycomb - like bubbles belongs to a quality problem. Due to continuous temperature changes, the condensation time of each molecular structure of the material is slightly different. When there are stains in the material, white stains or bubbles will form. In addition to temperature changes, the formation of bubbles is mostly caused by inclusions in the material. Bolt materials are synthesized by high - temperature smelting of various alloys. The melting points of different alloys vary. During the melting and synthesis process, high - melting - point alloy materials are likely to remain, thereby triggering the formation of bubbles. Therefore, the smelting environment of bolt materials is very important. We must not ignore the large number of adverse factors in the open environment. Large - particle dust and metal particles in the environment are important inducements for quality problems.
When the bolt surface is severely affected, not only white spots will appear, but obvious cracks may also occur. Such cracks have a great impact on the mechanical properties of the bolt and are problems that must never occur during material smelting. To ensure that there are no cracks on the bolt surface, professional ultrasonic instruments should be used to detect whether there are abnormalities in the internal structure of the bolt. This is a crucial testing link.
In conclusion, for stainless steel bolts, segregation, white spots, and cracks are all quality problems that are absolutely not allowed to occur. When materials enter the factory and finished products leave the factory, strict testing systems and high - standard quality judgment mechanisms must be established. Only by giving top priority to quality problems can enterprises achieve healthy development.
