Tensile & Yield Strength of Stainless Steel Strip
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1. Definitions: Tensile Strength and Yield Strength
Tensile strength (Rm) is the maximum tensile stress a material withstands before breaking, expressed in megapascals (MPa) or kilopounds per square inch (ksi). Yield strength is the stress at which the material begins to deform permanently without further increase in load. Because most stainless steel grades do not show a sharp yield point, the yield strength is measured at 0.2% offset strain and written as Rp0.2. Yield strength is always lower than tensile strength; the ratio between them, the yield-to-tensile ratio, describes how much deformation warning a material gives before fracture.
2. Why These Values Matter for Strip Users
Strip is supplied in coils and processed by roll forming, bending, stamping and spring manufacture. Three practical consequences follow from the strength values:
Formability: higher yield strength means more force to bend and more springback; a strip that works for a stamping die may not work after a temper change
Load capacity: design stress limits for springs, diaphragms and structural sections are set against yield strength, not tensile strength
Quality control: mill certificates report Rm, Rp0.2 and elongation A%; comparing them against the standard confirms the delivery condition
3. Typical Strength Values by Grade (Annealed Strip)
| Grade | Tensile strength Rm, MPa | Yield strength Rp0.2, MPa | Elongation A, % |
|---|---|---|---|
| 304 (UNS S30400) | 515 min | 205 min | 40 |
| 304L (S30403) | 485 min | 170 min | 40 |
| 316 (S31600) | 515 min | 205 min | 40 |
| 316L (S31603) | 485 min | 170 min | 40 |
| 430 (S43000) | 450 min | 205 min | 22 |
| 301 (S30100), annealed | 515 min | 205 min | 40 |
Values for plate, sheet and strip of the austenitic grades follow ASTM A240/A240M; EN equivalents are in EN 10088-2. The L grades carry lower carbon and slightly lower strength but better weldability.
4. How Cold Work Changes Strength: Temper Designations
Cold rolling increases strength by work hardening. The relationship for austenitic strip is strong: fully hard 301 strip can reach a tensile strength above 1200 MPa, roughly double the annealed value, at the cost of reduced elongation and formability. Temper designations per ASTM A666 use quarter-hard steps:
| Temper | Typical tensile strength (301 strip), MPa |
|---|---|
| Annealed | 515 min |
| 1/4 hard | 860 min |
| 1/2 hard | 1035 min |
| 3/4 hard | 1205 min |
| Full hard | 1275 min |
For 304 strip, cold rolling raises strength less than for 301 because 301 work-hardens faster. Specify the temper precisely: two coils of the same grade in different tempers are different materials for the press.
5. Reading the Mill Certificate and Buyer's Checklist
On an EN 10204 certificate, look for Rm (tensile strength), Rp0.2 (0.2% proof strength), A80 (elongation on 80 mm gauge length), and hardness (HV, HRB or HB). Verify that the values fall within the standard's range for the ordered grade and condition, and that the heat number on the certificate matches the coil marking. If the certificate shows values above the annealed maximums, the strip was probably supplied in a worked condition; confirm this matches the order before accepting.
Specify grade, thickness, width and temper (annealed or hard designation)
State the governing standard: ASTM A240/A480, ASTM A666, EN 10088-2 or GB/T 3280
Define the required strength range if the application is load-bearing
Request the mill certificate and verify Rm, Rp0.2 and elongation
For springs and diaphragms, specify edge condition (slit, deburred, rolled) and surface finish
Agree on hardness testing and PMI for traceability on critical lots
6. FAQ
What is the difference between tensile strength and yield strength?
Tensile strength is the maximum stress before fracture; yield strength (Rp0.2) is the stress at which permanent deformation starts. Yield strength is the design limit for parts that must not deform, while tensile strength describes the ultimate load capacity.
What is the tensile strength of 304 stainless steel strip?
Annealed 304 strip has a minimum tensile strength of 515 MPa and a minimum 0.2% yield strength of 205 MPa per ASTM A240. Cold-rolled tempers raise both values.
Why does cold rolling increase the strength of stainless strip?
Cold working creates dislocations in the crystal lattice that block further slip, a mechanism called work hardening. Austenitic grades work-harden rapidly, which is why 301 strip in full-hard temper reaches over 1200 MPa.
Which stainless steel strip grade has the highest strength?
In the austenitic family, 301 in cold-rolled tempers reaches the highest strength (above 1200 MPa). Precipitation-hardening grades such as 17-4PH or 17-7PH, after age hardening, exceed 1300 MPa but require heat treatment and are supplied as special products.
How do I verify the strength of delivered strip?
Check the mill test certificate for Rm and Rp0.2 against the ordered standard. Independent verification is done with a tensile test on a coupon per ISO 6892-1 or ASTM E8; hardness testing is a faster receiving inspection.
