ISO 4527 “Autocatalytic (electroless) nickel-phosphorus alloy coatings” is the international standard for electroless nickel plating coatings. The norm defines a standardized designation of the treatment. It defines the specifications and main characteristics of the treatment to be applied on the parts.
The use of this standard allows the designer and the customer to uniquely specify the characteristics of the treatment. This makes it possible to minimize misunderstandings and errors that may occur in the case of unclear treatment specifications.
However, the designation defined by ISO 4527 is not complete and it is necessary to integrate it to better indicate some characteristics, such as the treatment thickness or hardness required.
Designation according to ISO 4527
The designation, to be reported in the technical drawing, is structured as follows:
Autocatalytic nickel coating ISO 4527 – a<b>/NiP(c)d[e(f)g]
The designation consists of a first part, a<b>/ which refers to the basic material, where:
- a: The symbol of the main element of the base material alloy. For example for steels the symbol Fe;
- b: The alloy designation. For example S235JR;
The second part NiP(c)d refers to the deposited electroless nickel layer, where:
- c: The phosphorus content of the coating is indicated as a whole number. By convention the following values are used:
- NiP(7), for medium phosphorous electroless nickel, Niplate 600;
- NiP(11), for high phosphorus electroless nickel, Niplate 500;
- d: Minimum coating thickness in µm indicated as number;
The third part [e(f)g] refers to heat treatment following electroless nickel plating, where:
- e: The type of heat treatment carried out indicated as a symbol:
- ER to indicate the treatment of Embrittlemet Relief
- HT to indicate the hardening Heat Treatment
- f: The temperature of the heat treatment in degrees centigrade expressed in number;
- g: The duration of treatment in hours expressed in number.
The heat treatments usually carried out are the following:
- Embrittlement relief: 180°C x 4h – [ER(180)4)]
- Hardening: 260°C x 8h – [HT(260)8]
- Hardening: 340°C x 4h – [HT(340)4]
A medium phosphorus electroless nickel plating, Niplate 600, with a thickness of 20-25µm with hardening treatment at 340°C for 4 hours to obtain a hardness of 1000±50HV, steel 18NiCrMo5 is designated as follows:
Autocatalytic nickel coating ISO 4527 – Fe<18NiCrMo5>/NiP(7)20[HT(340)4]
Please note that there are two important information missing. The designation according to regulations is deficient and should be supplemented with other indications:
- There is no indication of the maximum thickness. Only the minimum thickness 20µm is indicated in the designation but the maximum thickness is not.
- The indication of the coating hardness is missing.
It is recommended to complete the designation with the missing information as below:
Autocatalytic nickel coating ISO 4527 – Fe<18NiCrMo5>/NiP(7)20[HT(340)4] - Thickness: 20-25 µm – Hardness: 1000±50 HV