Nickel-based alloys for bolts

Nickel-based alloys are materials with nickel as the main constituent and additions of chromium, molybdenum, niobium, titanium and aluminium. Depending on the alloy, they are heat-resistant to over 700 °C, resistant to acids and chlorides, or tough down to the temperature of liquefied gases. Well-known trade names are Inconel, Nimonic and Hastelloy; standardised designations include Alloy 718 (2.4668) and Alloy 625 (2.4856). RS Randack uses them to manufacture screws, bolts, studs and nuts to drawing.

Where they are used

Gas turbines and exhaust systems, high-temperature valves, chemical and petrochemical plants with aggressive media, offshore and seawater, refrigeration and cryogenic plants in which materials must remain tough at –196 °C.

What matters in production

Nickel-based alloys are expensive, difficult to machine and work-harden strongly. The first articles are therefore produced with particular care, cutting data and tools are matched to the material, and threads are rolled wherever the strength allows. Age-hardenable alloys such as Alloy 718 are precipitation-hardened after solution annealing; RS Randack has this carried out by qualified partners and verifies it in its own laboratory. Crack testing is carried out using the dye penetrant method, and impact energy at –196 °C is tested through an accredited partner laboratory.

What you should specify

Alloy with material number or UNS number, delivery condition, service temperature and medium, tests and certificate type. As the raw material can have long lead times, it pays to enquire early.