Designation System for Stainless Steel (ISO 3506 1979)
Composition Groups
Austenitic
Ferritic
Martensitic
Identification of Steel Grades
A1, A2, A4
F1
C1, C4
C3
Property Class
50
70
80
45
60
50
70
80
Soft
Cold- Worked
High- Strength
Soft
Cold-Worked
Soft
Hardened and Tempered
Hardened and Tempered
Stainless Steel Properties
Extract from DIN 267 Part 11 - Chemical Composition of austenitic chromium-nickels steels in % by weight
Austenitic Grade
Material No. to AISI
C
Si
Mn
P
S
Cr
Mo
Ni
A1
303
0.12
1.0
2.0
0.20
0.15 to 0.35
17.0 to 19.0
0.6
8.0 to 10.0
A2
304
0.08
1.0
2.0
0.05
0.03
17.0 to 20.0
-
8.0 to 13.0
A4
316
0.08
1.0
2.0
0.05
0.03
16.0 to 18.5
2.0 to 3.0
10.0 to 14.4
Maximum values unless otherwise stated.
Types A2 and A4 may contain up to a maximum of 4% copper.
The selection of steel grades within a group is the prerogative of the manufacturer, unless the purchaser has specified particular steels to ISO or national standards.
Different grades of steel may be used as long as all physical and mechanical properties and the corresponding corrosion resistance of the finished product are achieved. Only when all these conditions are fulfilled may finished articles be marked in accordance with DIN 267 Part 11.
Mechanical Properties-Austenitic Grades
Bolts, Screws and Studs
Grade
Property Class
Tensile Strength Rm MPa (N/mm2) minimum
Yield Stress Rp 0.2 Mpa (N/mm2) minimum
Elongation AL Minimum
Proof Load Stress Sp Mpa (N/mm2) minimum
Diameter Range
A2 and A4
70
700
450
0.4d
700
=
80
800
600
0.3d
800
=
Comparison: US and ISO (DIN) Stainless Steels
Tensile Load
A2 and A4 as compared to 304 and 316
Percent difference from US - Stainless Steel
up to M20
44% higher
M22 and over
6% lower
Selection of Diameters Tightening Torques, Loads
Guideline values for screws in steel groups A2-70 and A4-70 with standard metric threads to DIN 13
Diameter
Load 1) Force at 0.2% yield point N
Initial Stressing Force N
Tightening Torque Nm
Force in service N
Axial Static
Axial Dynamic
Radial Static or Dynamic
M3
2250
1420
0.9
610
360
120
M4
3960
2490
2.2
1070
640
210
M5
6390
4030
4.3
1730
1040
350
M6
9040
5700
7.3
2440
1470
490
M8
16470
10380
17.7
4450
2670
890
M10
26100
16440
35.5
7050
4230
1410
M12
37930
23900
61.3
10240
6150
2050
M16
70650
44510
147.1
19080
11450
3820
M20
110250
69460
285.1
29770
17860
5950
1)The values correspond to 100% of the 0.2%
Notes on application:
When selecting the correct screw diameter it should be ensured that the total load on the screw does not exceed 90% of the standardized 0.2% yield stress. Care should be taken to ensure correct initial tensioning, with a torque wrench wherever possible.
Experience has shown that a utilization of 70% of the total load is reasonable average for the initial stressing force to allow additional forces in service to be taken up.
**The table above is only intended as an aid for quick comparison**
