ASTM-B733:21 pdf free download – Standard Specification for Autocatalytic (Electroless) Nickel-Phosphorus Coatings on Metal.
6.5 Plating Process:
6.5.1 To obtain consistent coating properties, the bath must be monitored periodically for pH, temperature, nickel and hypophosphite. Replenishments to the plating solution should be as frequent as required to maintain the concentration of the nickel and hypophosphite between 90 % and 100 % of set point. The use of a statistical regimen to establish the control limits and frequency of analysis may be employed to ensure quality deposits are produced.
6.5.2 Mechanical movement of parts, agitation of the bath. and filtration is recommended to increase coating smoothness and uniformity and prevent pitting or streaking due tO hydrogen bubbles.
6.6 Post Coating Treatment for Iron and Steel for Reducing the Risk of I-Ivdrogen Embrittlement—Parts that are made of steel with ultimate tensile strengths of 1000 MPa (corresponding hardness values 300 HV 10. 303 HB, or 31 HRC or greater). as well as surface hardened parts. shall require post coating hydrogen embrittlement relief baking when specified by the purchaser. The tensile strength shall he supplied by the purchaser. Guide B850 contains a list of post treatments, procedures, limitations, and guidelines that are permitted to be used to reduce the effects of hydrogen embrittlement.
6.6. 1 Heat treatment shall be performed preferably within I h, but not more than 3 h, of plating unless the size or weight of the part prevents the initiation of heart treatment within 3 h. in this case, the part shall be heat treated as soon as possible. In all cases, the duration of the heat treatment shall commence from the time at which the whole of each part attains the specified temperature.
6.7 Heat Treatment After Plating to Improve Adhesion—To improve the adhesion of the coating to various substrates, the heat treatments in Table 3 should be performed as soon as practical after plating (see 4.3).
6.8 Heat Treatment After Plating to Increase Hardness:
6.8. 1 To increase the hardness of the coating, a heat treatment of over 260 °C is required. Table 3 describes the heat treatment for maximum hardness. See Appendix X3 and Appendix X4.
6.8.2 A heat treatment at 260 °C for greater than 20 h should be used to reduce the loss of surface hardness and strength of some ferrous basis metals. Avoid rapid heating and cooling of plated parts. Sufficient time must be allowed for large parts to reach oven temperature.
6.8.3 Do not use gas containing hydrogen with high- strength steel parts.
NOTE 7—The length of time to reach maximum hardness varies with the phosphorus content of the deposit. High phosphorus deposits may require longer time or a higher temperature, or both. Individual alloys should be tested for maximum hardness attainable, especially for conditions of lower temperatures and longer times.
NOTE 8—Inert or reducing atmosphere or vacuum sufficient to prevent oxidation is recommended for heat treatment above 260 °C.
7. Requirements
7.1 Process—The coating shall be produced from an aqueous solution through chemical reduction reaction.
7.2.1.2 Imperfections that arise from surface conditions of the substrate which the producer is unable to remove using conventional pretreatment techniques and that persist in the coating shall not be cause for rejection (see 6.1). Also, discoloration due to heat treatment shall not be cause for rejection unless special heat treatment atmosphere is specified (see 5.1.10).