Machining of HRSA and Titanium
Heat-resistant superalloys (HRSA) and titanium, with their high hot hardness and strength, make up the ISO S group. HRSA materials can be split into three groups: nickel-based, iron-based and cobalt-based alloys, which can be annealed, solution heat treated, aged, rolled, forged or cast. For HRSA, it is true that increased alloy content (Co more so than Ni), results in better resistance to heat, increased tensile strength and higher corrosive resistance.
The physical properties and machining behavior of ISO S materials varies considerably, due to the chemical nature of the alloy and the metallurgical processing it receives during manufacture.
Annealing and aging are particularly influential for subsequent machining properties. Chip control tends to be difficult, due to segmented chips. The specific cutting force is 2,400–3,100 N/mm² for HRSA and 1,300–1,400 N/mm² for titanium.
Cutting forces and power required for machining are quite high.
The benefits of using these materials also offer up machining challenges, where the right tool coating can make a big difference. Ionbond engineers would be happy to discuss the best solution for your application.
HRSA materials – S 1.0-3.0
HRSA tend to be highly corrosion resistant, retaining their hardness and strength at higher temperatures. The material is used up to 1,000°C and is hardened through an aging process.
Common components made with HRSA are aerospace engine and power gas turbines in the combustion and turbine sections, oil and gas marine applications, medical joint implants and applications requiring high corrosion resistance.
The poor heat conductivity and high hardness of HRSA materials generate high temperatures during machining. The high strength, work hardening and adhesion hardening properties create notch wear at maximum depth of cut and an extremely abrasive environment for the cutting edge.
Titanium – S 4.1-4.4
Titanium has a high strength to weight ratio, with excellent corrosion resistance at 60% of the density of steel. This enables the design of thinner walls. Titanium can be used in very harsh environments that could cause considerable corrosion attacks on most other construction materials. This is because of the titanium oxide (TiO2) layer that forms by itself and immediately rebuilds when damaged. Titanium is suitable for heat exchangers, desalting equipment, jet engine parts, landing gears and structural parts in the aerospace field.
The machinability of titanium alloys is poor compared to both general steels and stainless steels, which places special demands on the cutting tools. Titanium has poor thermal conductivity; strength is retained at high temperatures, which generates high cutting forces and heat at the cutting edge.