VDM® Alloy 718 is a heat-treatable nickel-chromium-iron-molybdenum alloy. According to the manufacturer, heat-treatability is achieved by the addition of niobium, titanium and aluminium. The alloy is characterised by high thermostability up to 700° C, excellent oxidation and corrosion resistance as well as good workability. Initially, the material was developed and used for the aerospace industry, where there are high requirements regarding creep resistance and fatigue behaviour, especially for rotating applications.
"We carried out a number of important test procedures on test specimens prior to production of the pipes in pipe size 6" Sch 80S (168.3 x 10.97 mm) and extensively tested the material with regard to forming and heat treatment," explains Tobias Krebiel, Head of Sales Special pipes. The welding tests were conducted using Plasma and TIG arc welding processes, using a welding additive of the same type.
The test specimens were then subjected to a multi-stage heat treatment. This showed that the material VDM® Alloy 718 is easy to process in the solution-annealed state. The non-destructive testing of the joining area by means of visual, dye penetration and radiographic examination confirmed the good weldability.
"The achievable strength properties in the weld area are at a high level and are comparable to those of the parent metal. This means there was nothing preventing us from manufacturing BUTTING pipes using VDM® Alloy 718," sums up Stefan Bartholomäus, Welding supervisor.
For many years, BUTTING has maintained a cooperative relationship with its customers and suppliers such as VDM Metals, which has its headquarters in Germany. In recent years, a number of joint projects have been implemented. A highlight of our cooperation was the development of the BUTTING HeRo®, which is a heat-resistant furnace roller used in roller hearth furnaces in the steel industry for the production of long and flat products. Depending on the annealing task, this is also manufactured from special alloys such as Alloy 602 CA, 601 H or 800 H.
BUTTING – Progress by Tradition