What is S material group?Within the metal cutting industry, some of the most challenging workpiece materials to machine are heat resistant superalloys (HRSAs) and titanium alloys. Classified as ISO‑S materials or simply S‑materials, these alloys are mainly used for components that need high corrosion and creep resistance, as well as to perform with high strength at extreme temperatures. A high strength‑to‑weight ratio is another important feature that causes titanium to be selected instead of traditional metals.
Within the metal cutting industry, some of the most challenging workpiece materials to machine are heat resistant superalloys (HRSAs) and titanium alloys. Classified as ISO‑S materials or simply S‑materials, these alloys are mainly used for components that need high corrosion and creep resistance, as well as to perform with high strength at extreme temperatures. A high strength‑to‑weight ratio is another important feature that causes titanium to be selected instead of traditional metals.
Components with these characteristics are required in different products, e.g.
- landing gears
- jet engines
- engine mounts
- steam turbines
- oil and gas parts
- implants with biocompatibility requirements, such as knee, hip and dental replacements
Seco focuses strongly on aerospace, energy and medical applications, so as to support customers machining these challenging materials in the most effective and efficient way.
ISO S Material pentagram
Seco classifies the machinability of materials based on 5 important properties: abrasiveness, ductility, strain hardening, thermal conductivity and hardness.
ABRASIVENESS, is defined as variations in hardness caused by alloying elements that are able to form hard carbide, oxide and intermetallic particles. This results in excessive wear on the cutting edges. Some examples of highly abrasive materials are Ni‑ alloys and carbon fibre reinforced plastics.
DUCTILITY, which results in adhesion and built‑up edge, refers to a high elongation at fracture for a material. This is one of the key difficulties in machining aluminiums and titanium alloys.
STRAIN HARDENING occurs when cutting hardens a surface in comparison to the bulk material. This is a well‑known challenge to overcome when machining Ni‑based alloys.
THERMAL CONDUCTIVITY refers to heat conduction of the material. The lower the thermal conductivity of a workpiece material, the more the heat will concentrate on the cutting edge, which results in excessive cutting edge temperatures.
HARDNESS is a material’s resistance to deformation. The higher the hardness, the greater the force needed to deform the material. High hardness results in high heat generation as well.
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Titanium alloys are usually classified as ‘difficult-to-machine’ alloys. But within the group of alloys, there are enormous differences between the alloys and between different variants of heat treatments of the same alloy. The major advantages of titanium alloys are;
- Low density combined with high strength
- Good corrosion resistance
- High melting point
- High fracture toughness
- Good weldability
The far most common titanium alloy is Ti6Al4V, which represents approximately 60 % of the titanium applications. It is commonly referred to as Ti 6-4 and is an α+β alloy (SMG S12). Other common alloys are Ti10V2Fe3Al and Ti5Al5V5Mo3Cr, which are near β alloys (SMG S13) and are used in high strength applications. In aerospace applications, the trend seems to be moving from Ti10V2Fe3Al to Ti5Al5V5Mo3Cr, which is more difficult to machine.
ISO S Titanium pentagram
Basic guidelines for machining ISO S materials, e.g. superalloys machining:
- Very high thermal loads and hard surface scales are your main concern (leading to complex flank and crater wear, notch wear, plastic deformation)
- Use big depth of cut and medium to high feed
- Use cutting speed to balance tool life with economic considerations on the process, but avoid build-up edge window of cutting speeds
- Use dedicated carbide grades and positive cutting geometry (but strong cutting edge geometry) to balance with selected feed
- Rich emulsion (8% – 15%) cooling is advised, JETSTREAM gives excellent results
ISO S Tab extract
Inline Content - Survey
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