Weather resistant structural steels

Usage

Photo of building, which made use of Allwesta

These weather-resistant structural steel grades are used for manufacturing welded, riveted or bolted structures, e. g. in bridge, façade and vehicle construction. In general, the specific rust-building properties of Allwesta steel grades make surface protections of structures built of this steel grade unnecessary, provided that the 'Stahl-Eisen-Werkstoffblatt' (Iron and steel material sheet) 087 ‘Wetterfeste Baustähle, Richtlinien für die Lieferung, Verarbeitung und Anwendung’ (weather-resistant structural steel, guidelines for delivery, processing and application) is observed.

The user of these steel grades must make sure that his calculation, design and processing methods are appropriate for the material and comply with the state-of-the-art. The good properties of Allwesta steel grades are not negatively affected by cold or hot-forming. The minimum bending radii according to table 6 of DIN EN 10025-5 are recommended for cold-forming. Suitability for cold-forming must be agreed upon in the order.

If mechanical properties have been significantly modified by heavy cold-forming, either stress relief annealing or normalized may be applied. Normalized should also be applied following hot-forming outside of the temperature range of 750 - 1.050 °C and after overheating.

Standards

Europe Material no. DE FR GB US JP Salzgitter Flachstahl FK1)
EN 10025-5 SEW 087 NFA 35-502 BS 4360 ASTM JIS G 3114
S235J0W 1.8958 - E 24 W 3 - - - Allwesta 360 A
S235J2W 1.8961 WTSt 37-3 E 24 W 4 - - - Allwesta 360 F A
S355J0WP 1.8945 - E 36 WA 3 WR 50 A - - Allwesta 510 P B
S355J2WP 1.8946 - E 36 WA 4 - A 242 Type 1 - Allwesta 510 FP B
S355J0W 1.8959 - E 36 WB 3 WR 50 B A 588 SMA 50 AW Allwesta 510 B
S355J2W 1.8965 WTSt 52-3 E 36 WB 4 WR 50 C - SMA 50 CP Allwesta 510 F B
S355K2W 1.8967 - - - - - Allwesta 510 F 40 B
  1. FK = Tensile strength class

Chemical composition in percent by weight [%] (Heat analysis)

Grade C Si Mn P S N Cr
max. max. max. max.
S235J0W1) 0.13 0.40 0,20 - 0,60 max. 0,035 0.035 0,0092) 3) 0,40 - 0,80
S235J2W1) 0.13 0.40 0,20 - 0,60 max. 0,035 0.030 – 4) 0,40 - 0,80
S355J0WP1) 0.12 0.75 max. 1,0 0,06 - 0,15 0.035 0,0093) 0,30 - 1,25
S355J2WP1) 0.12 0.75 max. 1,0 0,06 - 0,15 0.030 – 4) 0,30 - 1,25
S355J0W1)5) 0.16 0.50 0,50 - 1,50 max. 0,035 0.035 0,0092) 3) 0,40 - 0,80
S355J2W1)5) 0.16 0.50 0,50 - 1,50 max. 0,030 0.030 – 4) 0,40 - 0,80
S355K2W1)5) 0.16 0.50 0,50 - 1,50 max. 0,030 0.030 – 4) 0,40 - 0,80
  1. The steel contains a maximum of 0.25 to 0.55 % Cu and a maximum of 0.65 % Ni.
  2. Exceeding the specified maximum value is permitted if the phosphorous content remains below the maximum value by 0.005 % for each 0.001 % of nitrogen; however, the nitrogen content must not
 exceed 0.012 % in the heat analysis.
  3. The maximum nitrogen content shall not apply if the steel grades contain at least 0.020 % Altotal or sufficient quantities of other nitrogen-fixing elements. .
  4. The steel grades contain at least one of the following elements: Altotal: ≥ 0.020 %, Nb: 0.015 - 0.060 %,
 V: 0.02 - 0.12 %, Ti: 0.02 - 0.10 %. If a combination of these elements is present, at least one of them is contained with the specified minimum content.
  5. The steel may contain a maximum of 0.65 % Ni, 0.30 % Mo and 0.15 % Zr.

Mechanical properties1)

Grade Position of sample Min. yield strength2) Tensile strength2) Min. total elongation2)
[MPa] [MPa] [%] [%]
L0 = 80 mm L0 = 5,65 √S0
e ≤ 16 e > 16 e<3 e ≥ 3 e≤2 2< e < 2,5 2,5 < e < 3 e ≥ 3
S235J0W l/t 235 225 360 - 510 360 - 510 19/17 20/18 21/19 26/24
S235J2W l/t 235 225 360 - 510 360 - 510 19/17 20/18 21/19 26/24
S355J0WP l/t 3553) - 510 - 680 4703) - 6303) 16/14 17/15 18/16 22/203)
S355J2WP l/t 3553) - 510 - 680 4703) - 6303) 16/14 17/15 18/16 22/203)
S355J0W l/t 355 345 510 - 680 470 - 630 16/14 17/15 18/16 22/20
S355J2W l/t 355 345 510 - 680 470 - 630 16/14 17/15 18/16 22/20
S355K2W l/t 355 345 510 - 680 470 - 630 16/14 17/15 18/16 22/20
  1. The tensile test values given in the table apply to longitudinal samples; in case of strip and sheet steel of widths of ≥ 600 mm, transverse samples should be taken.
  2. e = Nominal thickness in mm
  3. S355J0WP and S355J2WP: e ≤ 12 mm

Notch impact energy in condition of delivery (minimum values obtained using Charpy-V samples)

Grade Temperature [°C] Notch impact energy1) [J]
S235J0W  0 27
S235J2W -20 27
S355J0WP  0 27
S355J2WP -20 27
S355J0W  0 27
S355J2W -20 27
S355K2W -20 40
  1. Average values of 3 samples; one individual value may fall short of the required minimum value by not more than 30 %. The sample width shall equal the product thickness if the latter is between 5 - 10 mm, the tests being performed using samples which are similar to Charpy-V samples. The values specified in the table above are to be reduced proportionally to the sample width.

Formation of a protective coating

Graphic corrosion mechanism
Corrosion mechanism for non-alloy structural steels and weather resistant structural steels

Unlike unalloyed constructional steels, when copper is added as an alloy in weather-resistant steels, a barrier layer forms when the steel comes into contact with the atmosphere. This layer contains alkaline copper sulfate (see diagram).

In the case of the phosphorous-alloyed steel grades Allwesta 510 P and Allwesta 510 FP (S355J0WP and S355J2WP), the barrier layer is also strengthened by alkaline copper phosphate.

Depending on the environmental conditions, the formation of this barrier layer takes approx. 1,5 - 3,5 years and prevents water, oxygen and sulfur dioxide from coming into contact with the surface of the steel. There is then no further corrosion.

The prerequisites for the formation of the protective coating are as follows:

  • No permanent moisture
  • Uniform run-off of rainwater
  • Avoidance of small cracks (capillary formation)
  • Protective coating to protect against condensation water on the inside
  • Absence of chlorides (seawater, near to the coast)
  • Permanent fluctuation between moisture and dryness
  • Avoidance of electrochemical local elements

As the protective coating forms, the color changes from light brown to brown to brown-violet; the surface becomes dark brown / violet and grainy. The color changes, depending on the incidence of light and the weather conditions.

Salzgitter Flachstahl should like to point out that, during the formation of the protective coating, specks may form as a result of the washout of rust; this should be taken into account in the design.

Welding

The steel grades of the Allwesta series can be perfectly welded both manually and using automatic equipment by means of all known welding processes. However, the quality of the weld joint depends on the welding process, the welding conditions and the selection of the correct filler metals. Suitably alloyed filler metals shall be used if the same requirements regarding weather resistance are made on the basic material and the weld metal and if the structure is not to be provided with a painting coat.

In general, pre-heating prior to welding or torch-cutting is not necessary. Only when external temperatures drop below -5 °C should the metal be pre-heated to approx. 150 °C.

Condition of delivery, scope of testing and certificate

Flat products made of Allwesta steel grades have the condition of delivery +N (normalized rolled). The provisions of EN 10025-5 shall apply for delivery and inspection.

Certificates according to DIN EN 10025-5 can be supplied as follows: IT, DUN, FAX, e-mail, paper.