Alloy makeup of MS21250 bolt 2

[danielcompton]

I want to know how to find the specific percentages of alloying properties in a bolt......specifically MS21250. Can this be accomplished with only a P/N? Do I need to know the manufacturer, lot#, batch#, etc.? I am helping research whether any of a group of particular bolts have been negitivly affected by hydrgen embrittlement due to a neglected step in a cadmium plate process.

 

[CoryPad]

MS 21250 Bolt, Tension, Steel, External Wrenching, Flanged, 12-Point, 180 Ksi Ftu, 450F has been superseded by NASM 21250 Bolt, Tension, Steel, External Wrenching, Flanged, 12-Point, 180 Ksi Ftu, 450F. The allowable compositions are shown in this document, which is available for purchase at:

http://www.techstreet.com/aiagate.html

The basic composition specified in the governing document will determine whether a part is susceptible to Hydrogen Embrittlement or not. The lot, batch, etc. will help in identifying how many parts did not receive the appropriate treatment(s).

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[rerig]

MS21250
1. Material: Steel Alloy, MIL-S-5626 (AISI 4140), MIL-S-5000 (AISI 4340), MIL-S-6049 (AISI 8740), MIL-S-8503 (AISI 6150)

So, your % of alloy will depend on which of the materials this Spec. Bolt was made from.
You are probably correct about needing the MFG & Lot/batch# to determine % alloy.

 

[israelkk]

MIL-B-8831 is the procurement specification for MS21259. This document only define bolt strength, fatigue etc. requirements, metalurgical and finish properties. As rerig mentioned MS 21250 can be manufactured from the following alloys MIL-S-5626 (AISI 4140), MIL-S-5000 (AISI 4340), MIL-S-6049 (AISI 8740), MIL-S-8503 (AISI 6150) to satisfy MIL-B-8831 requirements. The larger the bolt the more alloyed steel is needed to achieve the the bolt requirements due to quenching depth requirements. Therefore, you probably can not figure out the composition unless you can trace the specific bolt history back to the base metal manufacturer heat lot number and batch number.

 

[yates]

Several things are going to get in the way of attempting to correlate chemical composition and susceptibility to hydrogen embrittlement in MS21250 bolts:
a) As pointed out by israelkk, quench response is not the same for the different steels authorized by the standard, and many manufacturers switch grades somewhere up the diameter scale.
b) One of the preponderant factors in the NASM8831 requirements is the double shear strength requirement - there is a lot less spare strength here than in tensile, which is another reason to switch grades with varying diameter (really a special case of a)
c) By far the greatest influence upon hydrogen embrittlement in my view would be the variation in the cad. plate process. Some proprietary mixes of cad. plate chemicals contain brightening agents which can have a significant effect upon embrittlement
d) MS21250 is a very widely used bolt in the aerospace field, and is a perfect candidate for sale by distributors. Some odd diameters and lengths may have been on their shelves for some time, and it should be noted that the embrittlement relief treatment duration has been changed a few times over the life of the QQ-P-416 cad plate standard.
e) Last but not least, how do you intend quantifying hydrogen embrittlement ? Often times, without any noticeable difference in structure under an electron microscope, fatigue testing will give better results before cad. plate than after.