Stainless PM steel for both good wear resistance and excellent corrosion resistance associated with high fatigue resistance
TPM NITRION 20 is a nitrogen alloyed tool steel obtained by powder metallurgy. It is characterized by very good wear resistance associated with excellent corrosion resistance and high hardness associated with a high fatigue resistance.
Applications
TPM NITRION 20 is used in high-performance bearings, medical devices, and high-end cutting tools.
TPM NITRION 20 is particularly recommended for tools where high hardness and wear resistance associated with excellent corrosion resistance is required.
TPM NITRION 20 can also be used in molds for glassware.
TPM NITRION 20 is suitable for food and medical applications.
Main properties
- Excellent corrosion resistance
- Good wear resistance
- High hardness
- Good compressive strength
- High fatigue resistance
- Very good strength
Chemical composition (typical)
| C | Si | Mn | Cr | Mo | V | Ni | N |
|---|---|---|---|---|---|---|---|
| 0.40 | 0.50 | 0.40 | 15.5 | 1.70 | 0.3 | 0.50 | 0.20 |
Designation
| Werkstoff Nr | ISO | China GB | JIS Japan | UK | AISI USA | Russia Gost | AFNOR | Other / Special |
|---|---|---|---|---|---|---|---|---|
| 1.4123 | X40CrMoVN16 2 | – | – | – | UNS S42025 | – | – | – |
Structure
The structure of the TPM NITRION 20 is fine and homogeneous without precipitation or alignments of carbides.
Due to its elaboration by powder metallurgy with Hot Isostatic Compression the typical size of the carbides is lower than 5 µm and the level of cleanliness is far better than conventional cold work tool steels.
Corrosion resistance
As shown in the pictures below, the corrosion resistance is significantly better when compared to standard stainless steels X105CrMo17 (440C) and 17 – 4 PH.
TPM NITRION 20 was tested by salt spray test (480 h salt spray (NaCl) exposure.) after the following heat treatment: Austenitization: 1050°C / Tempering: 180°C. Hardness: 59.2 HRC
Hardness at the time of delivery
Annealed for 250 HB max.
Typical mechanical properties in hardened conditions (results from internal tests not indicated on the certificates)
| TS MPa |
YS 0.2% MPa |
Hardness HRC |
KV J 20°C |
|---|---|---|---|
| 2150 | 1602 | 56.5 | 20 |
| 2210 | 1743 | 59.2 | 10.4 |
| 2320 | 1854 | 59.5 | 5.4 |
Physical properties
| Temperature | 20°C |
|---|---|
| Volumic mass kg/m³ | 7700 |
| Young Modulus N/mm² | 195000 |
| Thermal conductivity W/m.K | 25 |
| Coefficient of linear expansion 10-6/K | 10.5 |
Heat treatment
Soft annealing
Temperature: 850 – 870°C, duration 1h + 1h for 25 mm thickness. Slow cooling in the furnace (10 to 20°C / h).
Stress relieving
After machining, it is recommended to perform stress relieving at 650°C for a minimum of 2 hours, followed by slow cooling in the furnace to 450°C.
Austenitization
In order to avoid any risk of cracking it is recommended to preheat in 2 steps.
- 1st preheating step: temperature: 500°C time: 30 s/mm of thickness
- 2nd preheating step: temperature: 875°C time: 30 s/mm of thickness
Recommended austenitizing temperature: 1010 – 1080°C. The holding time should not be too long to avoid a risk of grain coarsening and a loss of toughness. It is recommended to keep the part at the austenitizing temperature 30 minutes per inch of thickness as soon as the temperature of the surface reach the austenitization temperature.
Quenching medium
Oil at 80°C, vacuum (pressure > 6 bars), salt bath 500 – 550°C.
To ensure good toughness, treatment with oil or salt bath is preferable.
Sub zero treatment
For parts that need to have high dimensional stability and to increase wear resistance without reducing toughness, it is recommended to perform a subzero treatment at a temperature between -70°C and -120°C for 1 hour for 25 mm of thickness of the part.
The temperature range from -70°C up to -120°C (named cold treatment of steel) leads to the complete transformation of austenite into martensite and as a consequence to better stability associated with improved hardness and better wear resistance.
This treatment is optional for common applications.
Tempering
To ensure a minimum residual austenite rate as well as greater tool stability, it is essential to perform double (better triple) tempering. Each tempering is followed by a cooling under 100°C. For optimal corrosion resistance avoid to perform the tempering in the temperature range of 400 to 550°C.
Depending on the use of the final part the following tempering temperatures are recommended:
| Austenitizing temperature | Tempering temperature | Hardness | Properties |
|---|---|---|---|
| 1050°C * | 180°C | 59 HRC | Optimized hardness and corrosion resistance |
| 1010°C | 180°C | 56.5 HRC | Good corrosion resistance and good toughness |
| 1075°C* | 500°C | 59.5 HRC | For tools working at high temperature with high hardness and moderate corrosion resistance. |
* Subzero treatment is recommended to lower the retained austenite content.
Each tempering time must be at least equal to 1h + 1h for 25 mm of thickness of the treated part (equivalent thermal thickness).
Surface treatment
Nitriding
TPM NITRION 20 is a stainless steel and cannot be nitrided.
PVD, CVD
TPM NITRION 20 is suitable for all kind of PVD and CVD treatment as soon as the treatment temperature is 30°C lower than the last tempering temperature.
Surface hardening
TPM NITRION 20 is suitable for surface hardening by induction or laser.
It is recommended to do the heat treatment of the “bulk” tool with an austenitization temperature of 1050°C and a double tempering at 650°C to reach a “bulk” hardness of 35 – 37 HRC. After surface hardening by induction or laser the surface hardness will be at 55 – 58 HRC on a depth of 2 mm for induction hardening and 1 mm for laser hardening. After hardening a stress relieving at 150°C for 2 h minimum is mandatory.
Machining
The machining parameters below are given for information only and must be adapted according to the equipment and usual machining conditions.
Turning in annealed conditions
| Carbide tool | ||
|---|---|---|
| Rough machining | Finishing | |
| Cutting speed m/min | 60 – 70 | 70 – 80 |
| Feed mm/r | 0.4 – 0.6 | 0.1 – 0.2 |
| Depth of cut mm | 2 – 4 | 0.3 – 0.5 |
Grinding in annealed conditions
| Carbide insert | Solid tool | |
|---|---|---|
| Rough machining | Finishing | |
| Cutting speed m/min | 60 – 70 | 50 – 90 |
| Feed mm/r | 0.15 | 0.10 – 0.15 |
| Depth of cut mm | 2 – 3 | 0.1 |
Drilling in annealed conditions: carbide drill
| Solid | |
|---|---|
| Cutting speed m/min | 40 |
| Feed mm/r | 0.15 |
HSS twist drill
| Drill diameter mm | Cutting speed m/min | Feed mm/r |
|---|---|---|
| < 5 | 7 | 0.10 |
| 5 – 10 | 0.20 | |
| 10 – 15 | 0.30 | |
| 15 – 20 | 0.35 |
Fine grinding
General indications for grinding wheels to be used on TPM NITRION 20 in the heat treated condition.
Usually, rather soft vitrified aluminum oxide grinding wheels (grades G for plane grinding to K for cylindrical grinding) are used.
Particular attention will be paid to effective cooling of the surface during grinding to prevent degradation of the material surface.
Electro-discharge machining
TPM NITRION 20 is also suitable for EDM machining (wire or electrode). Preferably, the machining will be carried out with a low current density and a high frequency in order to limit the thickness of the white layer as much as possible.
Then it is necessary to carry out a stress relieving at 25°C below the last tempering in order to reduce the level of residual stresses (which could lead to a risk of cracking) and to carry out a polishing to completely remove the white layer formed during the discharge machining process.
Avoid to perform the stress relieving in the range 400 – 550°C if a good corrosion resistance is required.
Download the TPM NITRION 20 datasheet (PDF)
More grades: Cold Work Tool Steels. Where to buy: Service Network.
