ALL STAINLESS STEEL RETAINING RINGS ARE NOT CREATED EQUAL

We continue to hear from you concerning the use of retaining rings made from Type 420 stainless steel. In 1987 TRUARC did extensive research comparing 420 stainless steel to PH 15-7Mo stainless steel and published the results. We have updated this information and have republished it for your use and reference.

We are witnessing 420 stainless steel retaining rings being offered in the US market.

Please use caution to assure you are receiving the stainless quality you are paying for.

SUBJECT : Why our PH 15-7 Mo Stainless Steel TRUARC ® Rings are Far Superior to Rings made of Type 420 Stainless

As we've told you in the past:

•  Type 420 rusts in salt spray tests where “H” doesn't. You can show customers and prospects Table 1 to drive home this point.

TABLE 1 : Test Results – Corrosion-Resistance (Standard Salt Spray & Kesternich)

(*) There are no performance specifications for either alloy in either test.

(**) No USA standards for this test. One cycle involves exposure to gas for 8 hours plus 16 hour exposure to normal room atmosphere. Test is designed to simulate industrial atmosphere.

TABLE II : Comparative Corrosion of Mild Steel, Type 420 and AK PH 15-7 Mo Corrosion Rate in Mils per ASTM G 31 (5-48 hour periods)

Additional test results—from a program conducted for one of our customers by an independent testing laboratory—further proved the superiority of PH 15-7 Mo over Type 420 with regard to corrosion resistance. As your can see from Table 2, when Series X5133-6 rings assembled on shafts were tested in a 5% salt solution, in 2520 hours—exactly 105 days—Type 420 rings were found to have severe deterioration and fragmentation.

TABLE III : Test Results – Corrosion-Resistance (Immersion in Salt Solution)

Incidentally, the customer had previously tested PH 15-7 Mo and Type 420 stainless steels in de-ionized water and also soft water—i.e., with minerals removed. After four months, not very long in the life of a product, the Type 420 rings in de-ionized water deformed sufficiently to fall off their shafts, whereas our Type “H” were unaffected. In 4½ months, in the soft water, Type 420 rings again failed and ours were fine.

• There's just no comparison between the two materials in hardness retention under high temperatures. As you can see from Fig. 1, (see next page) Type 420 averaged less than 44 R “C” at 1000ºF in tests and dipped to below 40 R “C” after three hours. After the same period, Type H is still chugging along at a comfortable 47 R “C”.

• And don't forget about embrittlement, to which Type 420 is especially susceptible during heat treatment. As you can see from Table IV, in recently laboratory tests of both internal and radial rings, Type 420 failed across the board—and our PH 15-7 Mo came through unscathed.

• Test conditions were standard Waldes' tests for embrittlement:

Internal rings are closed until lugs touch and held for up to 24 hours.

Radial rings are applied over a shaft whose diameter is one per cent greater than the max. groove dia. specified, and held for up to 24 hours.