Very hard surface layer
Very hard surface layer
(OP)
I have come accross an item (a spiral bevel gear set), which has been reportedly made of 17NiCrMo6 (1.6566) carburizing steel and the surface hardness is 68 HRc, while a typical would be around 58-62 HRc. Does anybody know how did they achieve 68 HRc on this steel?
Here's more information:
The items were checked with two different Rockwell Hardness Testers and the result was always 68 HRc. Then the gears were sent out to a laboratory for a material analyzis. They have reported a microhardness HV 0.8N (80G) at distance from the surface .05-2.0 mm as follows:

The chemical composition:

The surface layer structure:

The surface layer:

Based on these results they have indentified the material as 17NiCrMo6 after carburizing. A 1 mm thickness of the layer with minimal hardness of 550HV has been reported and that the maximum hardness of 940 uHV equals to approx. 68 HRc.
Here's more information:
The items were checked with two different Rockwell Hardness Testers and the result was always 68 HRc. Then the gears were sent out to a laboratory for a material analyzis. They have reported a microhardness HV 0.8N (80G) at distance from the surface .05-2.0 mm as follows:

The chemical composition:

The surface layer structure:

The surface layer:

Based on these results they have indentified the material as 17NiCrMo6 after carburizing. A 1 mm thickness of the layer with minimal hardness of 550HV has been reported and that the maximum hardness of 940 uHV equals to approx. 68 HRc.





RE: Very hard surface layer
RE: Very hard surface layer
Below there's a tempering curve for the 17NiCrMo6, showing that the surface hardness can reach 64 HRc max.
Is there a special process required to reach 68 HRc, e.g. higher quenching temperature?
If so, is this special process common?
Thanks in advance.
RE: Very hard surface layer
RE: Very hard surface layer
RE: Very hard surface layer
RE: Very hard surface layer
The thermal capacity of the part will impact on the cooling rate needed for complete transformation as will the influence of the Austenite Grain Size.
Austenitic carbonitriding can typically develop case depths of up to 1mm (0.7 is commonplace) and produces harder layers than carburising.
Ferritic Nitrocarburising also known as Tuftriding or Tenifer treatment is a much lower temperature process and case depths of 0.05mm would be more common.
RE: Very hard surface layer