Nickel plating is for the water lines in non SS steels.
If you have any metal rubbing or sliding across the 303 it is extremely likely to fuse and make a mess of things. For just two cavities closing in a blow mold it should be fine, ejector pins or slides are a major problem on pre hard 303. The 420-440 are used a lot in injection molds because they are magnetic (you can put them on the surface grinder or edm magnet) and because they act and machine more like tool steels then the gummy 300- SS. One thing to look out for is the fact that P20 has 15-20% better heat transfer then most other tool steels and most of the Stainless steels are 15-20% worse. So you can loose cycle time in a big way, if you design the mold to use the same cooling as you would have with P20 |