Dining and/or serving cutlery made of ferritic stainless steel with a martensitic boundary layer
The invention relates to dining and/or serving cutlery made of a steel material which is formed from a ferritic core with an essentially martensitic boundary layer. In the dining and/or serving cutlery of the invention, the surface hardness of the boundary layer, determined according to the hardness test according to Vickers HV 3, is thereby greater by 30 to 300% than the lowest hardness of the core, likewise measured according to Vickers HV 3.
1. A dining and/or serving cutlery made of a ferritic steel material with a boundary layer which is formed by a heat treatment with nitriding and subsequent cooling and is essentially martensitic, having the proviso that the surface hardness of the boundary layer, determined according to the hardness test according to Vickers HV 3 (DIN ISO EN 6507), is greater by 30 to 300% than the lowest hardness of the core measured according to HV 3, wherein the steel material is selected from 1.4016 (AISI 430), 1.4000 (AISI 410) and 1.4024 (AISI 403).
2. The dining and/or serving cutlery according to claim 1 , wherein the hardness difference between the surface hardness of the boundary layer relative to the lowest hardness of the core is 80 to 250%.
3. The dining and/or serving cutlery according to claim 2 , wherein the surface hardness of the boundary layer is in the range of 320 to 650HV 3 and the lowest hardness of the core is in the range of 160 to 260 HV 3.
4. The dining and/or serving cutlery according to claim 1 , wherein the boundary layer is defined by a hardness penetration depth (HPD) which progresses from the lowest hardness of the core, measured according to HV 3, +30% up to the surface of the boundary layer.
5. The dining and/or serving cutlery according to claim 4 , wherein the HPD is in the range of 0.005 mm to 1.00 mm.
6. The dining and/or serving cutlery according to claim 1 , wherein the martensitic boundary layer has a modulus of elasticity in kN/mm 2 which is greater by 1 to 100% than the modulus of elasticity in kN/mm 2 of the material core.
7. The dining and/or serving cutlery according to claim 4 , wherein the modulus of elasticity of the martensitic boundary layer is greater by 1 to 50% than the modulus of elasticity of the core.
8. The dining and/or serving cutlery according to claim 1 , wherein within the martensitic boundary layer, the hardness and/or the modulus of elasticity reduces starting from the surface towards the core.
9. The dining and/or serving cutlery according to claim 1 , wherein the surface of the martensitic boundary layer is roughened and/or made matte.
10. The dining and/or serving cutlery according to claim 9 , wherein the surface roughness is in the range of 1.5 μm to 4.0 μm, measured according to DIN ISO EN 4287.
11. The dining and/or serving cutlery according to claim 1 , wherein particles at the surface of the martensitic boundary layer have no chromium carbide precipitations at the their boundaries.
12. The dining and/or serving cutlery according to claim 1 , wherein particles at the surface of the martensitic boundary layer have a higher particle size in comparison with those in an unhardened surface.
13. The dining and/or serving cutlery according to 1 , wherein it is a knife, a fork or a spoon.
14. The dining and/or serving cutlery according to claim 1 , wherein the hardness difference between the surface hardness of the boundary layer relative to the lowest hardness of the core is 100 to 250%.
15. The dining and/or serving cutlery according to claim 4 , wherein the HPD is in the range of 0.01 mm to 0.4 mm.
16. The dining and/or serving cutlery according to claim 4 , wherein the HPD is in the range of 0.01 to 0.3 mm.