Remelted cold working tool steel for both very good wear resistance and very high toughness
TGX8 is an 8% Cr cold working steel with a specific elaboration that achieves very high cleanliness and a very fine structure.
Applications
TGX8 has very good dimensional stability (it can be used for measuring instruments), good compressive and abrasion resistance as well as good resistance to chipping, very good resistance to brittleness and tempering. It also has good machinability and suitability for grinding and processing such as gas, ionic or salt bath nitriding, as well as PVD or CVD coatings.
TGX8 can be used for: cutting tools (punches and dies), cutting tools, punching and drilling tools, cold heading tools (punches and dies), stamping tools, cold spinning and extrusion tools, thread rolling tools, reamers, shear blades, cold working rolls (rolling or straightening).
TGX8 can also be used for mold injection cavities and thresholds for plastics and in some cases for hot work tools thanks to its high hot hardness.
TGX8 can be considered as a steel that pushes the limits of cold-working steels at 12% chromium.
TGX8 is an excellent solution for improving the service life of tools in 1.2363, 1.2550 or 1.2842 when they reach their end of life due to wear and for tools in 1.2379 or 1.2380 when they reach their end of life due to breakage.
TGX8 is delivered in the annealed condition and in use it should be treated to a hardness of 58 to 60 HRC.
Main properties
- Very good wear resistance
- Very good toughness
- High hardenability
Designation
| ISO |
|---|
| X110CrMoV8-2 |
Chemical composition (typical)
| C | Mn | Si | P | S | Cr | Mo | V |
|---|---|---|---|---|---|---|---|
| 1.08 | 0.40 | 0.30 | < 0.03 | < 0.005 | 8.50 | 2.00 | 0.50 |
Structure
The structure of the TGX8 is fine and homogeneous without precipitation or alignments of carbides. The size of the primary carbides is by far smaller than those in the conventional grade 1.2379.
The cleanliness of TGX8 which is an electro slag remelted steel (ESR) is very high and according to ASTM E 45 – 95 method A it is at most equal to: fine series: A0.5 – B0.5 – C0 – D1.5 / thick: A0.5 – B0.5 – C0 – D1 and B + C + D less than 2.5
Hardness at the time of delivery
Annealed for 255 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 |
KU J à 20°C |
|---|---|---|---|
| ≥ 2000 | ≥ 1600 | ≥ 56 | ≥ 20 |
Physical properties
| Temperature | 20°C | 200°C | 300°C |
|---|---|---|---|
| Volumic mass kg/m³ | 7750 | 7670 | 7630 |
| Young Modulus N/mm² | 205000 | 192000 | 185000 |
| Thermal conductivity W/m.K | 16 | 23 | 2 |
| Coefficient of linear expansion 10-6/K | 12 | 12.2 | 12.5 |
Heat treatment
Soft annealing
Temperature: 840 – 850°C, duration 1h + 1h for 25 mm thickness. Slow cooling in the furnace (10 to 20°C/h). The atmosphere in the furnace must be reducing to avoid decarburization of the steel.
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: 550°C time: 30 s/mm of thickness
- 2nd preheating step: temperature: 750°C time: 30 s/mm of thickness
Recommended austenitizing temperature: 1030 – 1050°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 -190°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 and the temperature range from -135°C down to -190°C (named cryotreatment of steel) leads also to the complete transformation of austenite and also the the precipitation of ultrafine carbides improving a lot the wear resistance without modification of the toughness. 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 a double tempering. Each tempering is followed by a cooling under 100°C.
Each tempering time must be at least equal to 1h + 1h for 25mm of thickness of the treated part (equivalent thermal thickness).
The minimum deformations (the deformations are negative (narrowing) ≈- 0.05%) are obtained for tempers between 350 and 450°C and an austenitization temperature of 1030°C.
Surface treatment
Nitriding
TGX8 can be nitrided at temperatures less than or equal to 20°C below tempering temperatures without risk of deterioration of the mechanical characteristics.
PVD, CVD
TGX8 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.
Polishing
TGX8 is perfectly suitable for polishing in the heat treated condition and can be used for applications requiring a good level of polish (total roughness Rt ≈ 4 μm, CNOMO level 1.5, roughness N5).
Optimal polishing is achieved by performing consecutive stages of roughness that are close enough and stopping each step as soon as the last scratch from the previous step disappears.
Surface hardening
The surface of the TGX8 can be hardened by induction, laser or torch heating.
By induction it is typically possible to achieve a surface hardness of the order of 62 HRC at a depth of 2 mm (1 mm by laser). This hardening must be followed by a low-temperature tempering to release the stresses induced by the treatment and to adjust the hardness.
By using an oxyacetylene torch with heating to 1000°C followed by air quenching, it is quite possible to obtain a surface hardness of 60 to 62 HRC.
Machining
The machining parameters below are given for information only and must be adapted according to the equipment and usual machining conditions.
Turning
| Carbide tool Rough machining |
Carbide tool Finishing |
HSS tool Finishing |
|
|---|---|---|---|
| Cutting speed m/min | 100 – 140 | 160 – 210 | 17 – 22 |
| Feed mm/r | 0.2 – 0.4 | 0.1 – 0.2 | 0.1 – 0.3 |
| Depth of cut mm | 2 – 4 | 0.5 – 2 | 0.5 – 2 |
Milling: surfacing
| Milling with carbide tools Rough machining |
Solid tool Finishing |
|
|---|---|---|
| Cutting speed m/min | 110 – 160 | 180 – 220 |
| Feed mm/r | 0.2 – 0.4 | 0.1 – 0.2 |
| Depth of cut mm | 2 – 4 | 0.5 – 2 |
End milling
| Milling with carbide tools Solid carbide |
Milling with carbide tools Carbide indexable insert |
HSS milling tool | |
|---|---|---|---|
| Cutting speed m/min | 100 – 120 | 110 – 10 | 12 – 19 |
| Feed mm/teeth | 0.02 – 0.2 | 0.07 – 0.2 | 0.05 – 0.3 |
Drilling: HSS twist drill
| Drill diameter mm | Cutting speed m/min | Feed mm/t |
|---|---|---|
| < 5 | 14 – 16 | 0.05 – 0.15 |
| 5 – 10 | 14 – 16 | 0.15 – 0.20 |
| 10 – 15 | 14 – 16 | 0.20 – 0.25 |
| 15 – 20 | 14 – 16 | 0.25 – 0.30 |
Drilling: carbide drill
| Carbide type | Indexable insert | Solid carbide | Carbide tip |
|---|---|---|---|
| Cutting speed m/min | 210 – 230 | 80 – 100 | 70 – 80 |
| Feed mm/t | 0.05 – 0.10 | 0.10 – 0.25 | 0.15 – 0.25 |
Fine grinding
General indications for grinding wheels to be used on TGX8 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
TGX8 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.
Download the TGX 8 CORVI datasheet (PDF)
More grades: Cold Work Tool Steels. Where to buy: Service Network.
