Stainless Steel Grades -Nuts, Bolts, Screws, Washers, Studs

Stainless steel fasteners types

Stainless Steel Fastener Grades

Stainless steel fasteners are made from a steel alloy that contains a minimum of 10.5% of Chromium and is also referred to as Inox steel.  There are over 150 different grades and surface finishes of stainless steel fasteners and stainless bolts that are available.  The type of stainless steel fastener used should be engineered for the application/environment that it is being used.  However, the two most common grades are 304 stainless fasteners (commercial grade) and 316 stainless fasteners (marine grade).  For simplicity sake, many treat type 304-ss fasteners and type 18-8 ss and A2 ss fasteners as nearly identical materials and are often used interchangeably / synonyms.

Stainless steel bolting is chosen because primarily of its resistance to corrosion, and not due to its strength.  Stainless steel fasteners are typically unaffected by weak bases, but their resistance to attack by acids is different for each of the grades and is dependent upon variables such as: type of acid, concentration, & temperature.  Similar to steel, it is a “relatively” poor electrical conductor.

Stainless steel is grouped by its crystalline structure.

  • Austentic: When Nickel is added, it stabilizes the steel into an austenite structure thereby making it not magnetic.  However, work hardening can possibly make austentic stainless steel fasteners mildly magnetic.  Adding different amounts of Carbon will then increase its hardness and its ability to be heat treated.
    • 200 Series: A standard purpose stainless that offers little corrosion resistance and is hardened through cold working.
    • 300 Series: 304 stainless steel fasteners, which are the most common type, fall within this category.  They are also known as 18-8 stainless due to its 18% chormium and 8% nickel.  Since precipitation of chromium carbides may occur at grain boundaries if welded, therefore 304L and 316L are “Low” carbon versions that reduce this “sensitaztion effect” from occurring due to having a carbon content less than 0.03%.
  • Ferritic: usually a cheaper form of stainless due to its decreased nickel and choromium content.  These alloys are commonly magnetic, have a body centered cubic crystaline structure, and contain very little nikel and Chromium composition between 27%-10.5%.
  • Martensitic: although not as resistant to corrosion as austentic stainless fasteners, it is magnetic, can be hardened and is easy to machine.Chromium contents (14%-12%) Molybdenum (1%-0.2% )and nickel (<2%).
  • Duplex: this is a type of stainless that is usually a 50/50 mix of austenite and ferrite.  Due to having a tensile strength nearly double of austentic stainless fasteners, it is also very resistant to corrosion, pitting, and stress cracking.  Higher Chromium (32-19%) and Molybdenu (<5%) give duplex stainless fasteners (such as duplex bolt and duplex nuts) their unique characteristics.  Duplex is characterized into 4 subgroupbs based upon their resistance to corrosion and chemical composition.
    • Lean duplex fasteners
    • Standard duplex fasteners
    • Super duplex fasteners
    • Hyper duplex fasteners

Stainless Steel Fastener Grades

SAE Grade

EN – Steel # / DIN

EN Name
UNS
440A 1.4109 X65CrMo14 S44002
440B 1.4112 X90CrMoV18 S44003
440C 1.4125 X105CrMo17 S44004
440F S44020
430 1.4016 X6Cr17 S43000
316 1.4408 G-X 6 CrNiMo 18-10 S31600
409 1.4512 X6CrTi12 S40900
410 S41000
301 1.431 X10CrNi18-8 S30100
301LN 1.4318 X2CrNiN18-7
304L 1.4307 X2CrNi18-9 S3043
304L 1.4306 X2CrNi19-11 S30403
304LN 1.4311 X2CrNiN18-10 S30453
304 1.4301 X5CrNi18-10 S30400
304H 1.4948 X6CrNi18-11 S30409
305 1.4303 X5CrNi18-12 S30500
312 X5CrNi30-9
310 1.4841 X22CrNi2520 S31000
310S 1.4845 X 5 CrNi 2520 S31008
321 1.4541 X6CrNiTi18-10 S32100
321H 1.4878 X12CrNiTi18-9 S32109
316L 1.4404 X2CrNiMo17-12-2 S31603
316 1.4401 X5CrNiMo17-12-2 S31600
316LN 1.4406 X2CrNiMoN17-12-2 S31653
316L 1.4432 X2CrNiMo17-12-3 S31603
316L 1.4435 X2CrNiMo18-14-3 S31603
316 1.4436 X3CrNiMo17-13-3 S31600
316Ti 1.4571 X6CrNiMoTi17-12-2 S31635
316LN 1.4429 X2CrNiMoN17-13-3 S31653
317L 1.4438 X2CrNiMo18-15-4 S31703
2304 1.4362 X2CrNi23-4 S32304
2205 1.4462 X2CrNiMoN22-5-3 S31803/S32205
J405 1.4501 X2CrNiMoCuWN25-7-4 S32760
904L 1.4539 X1NiCrMoCu25-20-5 N08904
1.4529 X1NiCrMoCuN25-20-7 N08926
254SMO 1.4547 X1CrNiMoCuN20-18-7 S31254

 

 

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