Though not its primary spec, experienced welders use E309 as a "high strength" buffer layer on cast iron because it tolerates the high carbon content better than standard electrodes.
GDP E309 refers to a specific type of stick electrode (SMAW – Shielded Metal Arc Welding) used primarily for welding austenitic stainless steels to carbon steels or low-alloy steels. The "GDP" prefix typically denotes a specific manufacturer's brand line (historically linked to companies like Gedik Welding or similar industrial brands in the EU and Asian markets), while "E309" follows the American Welding Society (AWS) classification system.
Under the AWS A5.4 specification, an E309 electrode produces a weld metal that is approximately 23% Chromium (Cr) and 13% Nickel (Ni). This specific chemistry places it between standard 308 (18-8) and 310 (25-20) stainless steels. gdp e309
Before committing to GDP E309 for a structural application, verify the following typical mechanical properties (always check your specific batch certificate):
| Property | Typical Value | | :--- | :--- | | Tensile Strength | 550 – 650 MPa (80,000 – 95,000 psi) | | Yield Strength | 400 – 450 MPa (58,000 psi) | | Elongation | 25 – 35% | | Hardness | ~170-200 HB | | Ferrite Number (FN) | 8 – 20 (FN 10-15 typical) | Though not its primary spec, experienced welders use
Important Note: The tensile strength of E309 weld metal is higher than mild steel (E7018 ~480 MPa). This means the weld itself is stronger than the weaker base metal (usually the mild steel side), which is desirable for dissimilar joints.
Problem: Weld cracking along the toe of the weld.
Cause: Too much dilution from the carbon steel base metal.
Solution: Use a "buttering" technique. Run a thin layer of E309 on the carbon steel edge first, let it cool, then weld the stainless steel to the buttered layer. Under the AWS A5
Problem: "Wagon tracks" or slag inclusions.
Cause: Insufficient interpass cleaning.
Solution: E309 produces a heavy, glassy slag. Use a wire brush or grinder after every pass.
Problem: Spatter sticking to the stainless steel side.
Cause: Amperage too high or arc blow.
Solution: Reduce amperage by 10-15%. Switch to AC if arc blow persists on DC.