Cold working of the stainless will increase its strength, but don't know if it will go that high in your application.  An alternative would be a duplex steel, 2205 is close to your range and 2507 should excede it.

You can get 316 fasteners in the strength you are looking for.  I assume from your units you are looking for metric, 316 would be A4-50 for 500 MPa proof strength and you get get up to 700 MPa (A4-70) fairly easily depending on the size you need.

Mike Bensema
www.dutchmenservices.com

I will take a closer look at duplex Steel thankyou.

I was of the understanding that A4-70 as specified in ISO 3506 (which i have not viewed a copy of as yet)was an Ultimate Tensile Stress of 700 MPa and a value for the proof stress would be in the range of 500 MPa, although this is a not characteristic value simply an indicative one not to be used as a design basis.

Are these grade of fasteners available off the shelf or do they require special fabrication and machining. All suppliers i have contacted are not certain of the properties of (readily available) fasteners and they appear to be of the 200 MPa grade.

scottoc,

You can obtain stainless steel bolts/screws with the strength that you have indicated.  The fasteners will need to be solution annealed (carbide solution treatment) and strain hardened (cold worked).  ISO 3506 or ASTM A 193M are appropriate standards.

Regarding specific grades & designations, you were correct that A4-70 indicates a minimum TENSILE STRENGTH of 700 MPa-- the minimum yield strength would be 450 MPa.  A4-80 has minimum requirements of 800 MPa for tensile strength and 600 MPa for yield strength.

The ASTM standard is similar, but not identical.  Class 2 fasteners are the higher strength (solution annealed + strain hardened), and Type 316 (referred to as Grade B8M) has minimum requirements of 760 MPa for tensile strength and 665 MPa for yield strength.  Type 316N (Nitrogen strengthened) is called Grade B8MN can also meet these properties.

Sorry, I misspoke, you are correct, I looked in the wrong column.  -70 is the tensile strength, yield would be approx 450 for A4-70.  Nuts classified as A4-70 do have a proof strength of 700 MPa though.  A4-80 has a rated yield strength of 600 MPa, not always easy to find though.  The 200 MPa fasteners you are talking about are most likely the A4-50 which are rated for 210 MPa and everyone seems to carry.

I have not had trouble finding fasteners up to about M20 in A4-70.  A4-80 is more difficult to get, but you might try calling Brikksen www.brikksen.com they only sell to manufacturers and distributors, but should be able to send you in the right direction.  You can also try McMaster-Carr, they don't list A4-80 in the book, but they are good at getting what you need.

Mike Bensema
www.dutchmenservices.com

It might be hard to find a strained hardened bolt above 40mm.  Most people who used to call out strained hardened bolts have changed their specifications to non-strain hardened above 1". Also look at using a standard 316 nut as many of the others that are modified are going to be hard to find and costly.  I’m familiar with several people that use this combination especially up to one 1” with no problems.
Most of these applications were for flanges.

A lot of people are going to A453 Gr660 on critical connections.