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07421 Fabricating Nickel Alloy Products to Avoid Stress Relaxation Cracking

Various alloys subjected various heat treatments were examined in-service and tested to determine their susceptibility to stress relaxation cracking.

Product Number: 51300-07421-SG
ISBN: 07421 2007 CP
Author: Lewis E. Shoemaker, Gaylord D. Smith, Brian A. Baker, and Jon Poole
Publication Date: 2007
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Nickel-chromium alloys for service at elevated temperatures are generally solution annealed prior to service to coarsen their grain size to enhance their high temperature strength and resistance to creep and rupture. Alloys for high temperature are often supplied from the producing mill as solution annealed. However, this large grain condition is not optimum for fabrication as it can compromise weldability and the large grain material is subject to stress relaxation cracking when annealed after heavy cold forming. Ideally these alloys are supplied after a lower temperature heat treatment that anneals the product but avoids substantial grain growth. Such fine grain material is more readily formed and much more resistant to stress relaxation cracking when solution annealed after forming. While the example of alloy 800HT is used to demonstrate the advantage of this processing sequence, the technique can be applied to essentially any alloy or stainless steel that is to be used for applications at highly elevated temperatures.

Key Words: Alloy 800HT, UNS N08811, Alloy 800H, UNS N08810, Alloy 617, UNS N06617, Alloy 601, UNS N06601, Cracking, Fabrication, Welding, Heat Treatment, Annealing, Stress Relaxation, Pipe, Strain-Age Cracking, SAGBO

 

Nickel-chromium alloys for service at elevated temperatures are generally solution annealed prior to service to coarsen their grain size to enhance their high temperature strength and resistance to creep and rupture. Alloys for high temperature are often supplied from the producing mill as solution annealed. However, this large grain condition is not optimum for fabrication as it can compromise weldability and the large grain material is subject to stress relaxation cracking when annealed after heavy cold forming. Ideally these alloys are supplied after a lower temperature heat treatment that anneals the product but avoids substantial grain growth. Such fine grain material is more readily formed and much more resistant to stress relaxation cracking when solution annealed after forming. While the example of alloy 800HT is used to demonstrate the advantage of this processing sequence, the technique can be applied to essentially any alloy or stainless steel that is to be used for applications at highly elevated temperatures.

Key Words: Alloy 800HT, UNS N08811, Alloy 800H, UNS N08810, Alloy 617, UNS N06617, Alloy 601, UNS N06601, Cracking, Fabrication, Welding, Heat Treatment, Annealing, Stress Relaxation, Pipe, Strain-Age Cracking, SAGBO

 

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