General Information for Material Stellite 21
| Material Group |
S - Superalloys (Heat resistant and Titanium) |
| Sub-Group |
Superalloy |
| Hardness |
36.0 HRC |
| Tensile Strength |
[N/mm^2] |
| Machinability Range |
17% |
MACHINABILITY OF STELLITE 21 MATERIAL
Stellite 21 is a cobalt-based heat resistant superalloy (HRSA) material with a machinability rating of 17% and hardness of 36 HRC.
Stellite 21 has 60% cobalt, 2.5% nickel and additional alloying elements per the table below.
Cobalt-based alloys excel in wear resistance and chemical stability in harsh and hot conditions. Therefore, they are mainly used in valves and fittings in an acidic environment and medical implants such as artificial hip joints. In this sub-group, the material standards also define the allowed hardness range, and hardness is a significant factor affecting the machinability (besides the chemical composition). Cobalt-based alloys are the most challenging to machine superalloy sub-group with a poor machinability rating.
Superalloys should be machined with a positive and sharp cutting edges. Geometries that are suitable for austenitic stainless steel will also work well on HRSA. However, quality manufacturers will have in their catalogs additional geometries that are specifically designed for these challenging materials.
SUMMARY:
For general turning of material Stellite 21 at stable conditions use a grade with a very hard substrate and thin PVD coating.
For general milling use a grade with a semi hard substrate and PVD coating.
For detailed carbide grades recommendations, check the table below.
Recommended cutting speed range for turning at stable conditions is 200 - 260 [SFM] / 60 - 80 [m/min].
Consider using CBN inserts. Although they cost more than twice, they enable increasing the cutting speed by 2-4 times (relative to carbide).
Recommended cutting speed range for milling with stable clamping and short overhang is 150 - 200 [SFM] / 45 - 60 [m/min].
For detailed cutting speed recommendations, check the table below.
Equivalent International Designations for Material Stellite 21
Chemical Composition for Material Stellite 21
| Element |
Amount |
| Chromium (Cr) |
27% |
| Cobalt (Co) |
60% |
| Molybdenum (Mo) |
5.5% |
| Iron (Fe) |
3% |
| Nickel (Ni) |
2.5% |
| Carbon (C) |
0.3% |
Cutting Speeds Recomendations for Material Stellite 21
| Application |
Vc (m/min) |
Vc (SFM) |
| Turning |
60-80 |
200-260 |
| Milling |
45-60 |
150-200 |
| Parting |
35-50 |
110-160 |
| Grooving |
50-70 |
160-230 |
| Drilling |
50-70 |
160-230 |
Important! The speed estimation is given for an ideal situation:
- Most suitable carbide grade
- Stable tool clamping
- Stable workpiece clamping
- Good quality raw material
- A short overhang of the cutting tool.
- Nominal hardness of the material.
- etc.
Recommended Carbide Grades for Material Stellite 21
Grade for Milling (Indexable)
Recommended Insert Cutting Edge Geometry for Material Stellite 21
| Honing Size |
0.02-0.05 mm / 0.001-0.002" |
| Rake Angle |
13° -18° |
| Land Angle |
Neutral |
| Land Width |
0.10-0.20 mm / 0.004-0.008" |
| Ground Insert |
Recommended |
