Experimental study on mechanical properties and tightening method of stainless steel high-strength bolts

• Published in: Engineering structures Vol. 290; p. 116176
• Main Authors: Tianxiong, Zhang, Yidu, Bu, Yuanqing, Wang, Zhihua, Chen, Wei, He, Yuekun, Heng
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.09.2023
• Subjects: Curing time; Experiment; High-strength bolts; Lubricant; Stainless steel; Torque coefficient; Curing time; Torque coefficient; High-strength bolts; Stainless steel; Experiment; Lubricant
• ISSN: 0141-0296; 1873-7323
• DOI: 10.1016/j.engstruct.2023.116176

•Tensile strength, shear strength, hardness and preload level of grade 10.9 stainless steel high-strength bolts were obtained and compared with requirements of the conventional grade 10.9 high-strength bolts.•Tightening tests on stainless steel bolts with lubricant were carried out.•The friction-reducing lubrication effect is related to lubricant type as well as the curing time of the lubricant.•The torque coefficient can be reduced to 0.080, with recommended lubricant and curing time, meeting the torque coefficient limit for high-strength bolts. The lack of product specification of stainless steel high-strength bolts has restricted the application of high-strength bolts in stainless steel structures. Existing studies have found that stainless steel bolts experience thread galling during the tightening procedure, making it impossible to apply preload. Different studies have obtained different torque coefficient values. In this paper, a series of tests were carried out on two types of grade 10.9 stainless steel high-strength bolts and two types of ordinary stainless steel bolts, and the tensile strength, shear strength, hardness and preload level were obtained. The results show that the yield strength, tensile strength and elongation after break of the new stainless steel high-strength bolts can reach 1122 MPa, 1147 MPa and 16.3% respectively, proving that the grade 10.9 stainless steel high-strength bolts meet the requirements of the conventional grade 10.9 high-strength bolts. Tightening tests on stainless steel bolts with lubricant were carried out and it was found that the friction-reducing lubrication effect was related to the curing time of the lubricant. The lubricant Molykote D-321R Spray was found to be more effective in reducing friction and preventing thread galling in stainless steel bolts. With the optimum curing time at room temperature of 12 h, the lubricant can reduce the torque coefficient to about 0.080, meeting the torque coefficient limit for high-strength bolts. In the end, the preload level, torque coefficient and torque level for construction for stainless steel high-strength bolts are recommended for engineering applications.