A 1040mpa grade weather-resistant bolt with anti-delayed fracture

Abstract

Provided is a delay-fracture-resisting 1040 MPa-grade weather-proof bolt. The Delay-fracture-resisting 1040 MPa-grade weather-proof bolt is prepared from the chemical ingredients including, by mass percent, 0.21% to 0.32% of C, 0.10% to 0.50% of Si, 0.60% to 1.00% of Mn, 0.008% to 0.020% of P, not larger than 0.005% of S, 0.82% to 1.20% of Cr, 0.25% to 0.50% of Ni, 0.25 to 0.50% of Cu, 0.05% to 0.20% of Mo, 0.015% to 0.060% of Nb, 0.015% to 0.090% of V, 0.008% to 0.035% of Ti, 0.0008% to 0.0035% of B, 0.015% to 0.040% of Al, 0.003% to 0.007% of Ca, 0.015% to 0.045% of Zr, 0.010% to 0.045% of Re and the balance Fe and inevitable impurities. According to a method for preparing the bolt, the conventional high-purity smelting-continuous casting-rolling technology is mainly adopted, and metal raw materials are prepared into a steel material for the delay-fracture-resisting weather-proof bolt; and raw material acid pickling, steel pulling, blanking, end face chamfering, head cropping, head forming, head chamfering, shot blasting, semi-finished product surface treatment, hole shrinking, thread rolling, thermal treatment and finished product surface treatment are carried out according to aconventional method. The bolt is resistant to delay fractures and atmospheric corrosion and relatively low in cost.

Description

technical field [0001] The invention belongs to the technical field of fasteners, in particular to a 1040MPa grade (10.9 grade) weather-resistant bolt. Background technique [0002] At present, the high-strength bolts used in infrastructure facilities such as steel structure bridges and electric towers are mainly grade 10.9. + , O 2- , Cl - Plasma penetration, ordinary 10.9 high-strength bolts will be severely corroded. At present, the main measure is to carry out surface treatment before the bolts leave the factory, but this cannot guarantee the long-term corrosion resistance requirements of the bolts. Corrosion will occur, and it is still necessary to repeatedly paint or replace the bolts. At the same time, since the minimum tensile strength of 10.9 high-strength bolts reaches above 1040MPa, the problem of delayed fracture becomes very prominent. Generally speaking, the higher the strength, the higher the delayed fracture sensitivity of the bolt, especially when the te...

AI Technical Summary

Problems solved by technology

The C content of Japan's weather-resistant bolt products is strictly controlled. While ensuring the strength of the bolt, it avoids the hidden dangers of weather resistance and delayed fracture resistance that may be caused by high C content. However, due to the absence of Mo, Nb, Insufficient content of V, Ti or C, only by controlling C content cannot make bolt products have delayed fracture resistance

Up to now, there are no clear standards at home and abroad or the inclusion of delayed fracture resistance, but there are invention patents for the delayed fracture of high-strength steel or high-strength bolts, but because the weather resistance of bolts is not considered, these inventions are difficult to resist atmospheric corrosion. Therefore, it is difficult to apply to structural connections in the harsh environment of steel structure facilities

[0004] The atmospheric corrosion resistance index of the coating-free weathering steel currently used in China is I ≥ 6.5 (the atmospheric corrosion resistance index calculated based on the chemical composition of raw materials I = 26.01 (% Cu) + 3.88 (% Ni) + 1.20 (% Cr) + 1.49 (%Si)+17.28(%P)-7.29(%Cu)(%Ni)-9.10(%Ni)(%P)-33.39(%Cu) 2 , the larger the I value, the higher the atmospheric corrosion resistance (that is, the higher the weather resistance). Compared with that, because its atmospheric corrosion resistance corrosion index I is difficult to meet the minimum requirement of 6.5, it will inevitably become a corrosion weak area of ​​the steel structure. In addition, the bolts are located at the connection nodes, which will cause greater hidden dangers to the safety performance of the steel structure.

The content of Mo, Nb, V, and Ti microalloying elements added to the existing 10.9 grade bolts for delayed fracture resistance is unbalanced, and there is a problem of incomplete addition of microalloying elements, which will inevitably lead to a decline in the delayed fracture resistance of bolts

Therefore, the composition of the existing 10.9 high-strength bolts cannot take into account delayed fracture resistance, weather resistance and economy. It is difficult to ensure the service performance of high-strength bolts while being easy to manufacture and popularize related products. The weather-resistant steel structure needs high-strength bolts with good delayed fracture resistance and weather resistance

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