In the shipbuilding industry, the main cause of porosity defects in the pull arc stud welding of 316L stainless steel plates (>20mm) is the dissolution of hydrogen, insufficient purity of the protective gas, and improper welding parameters. The following is a solution based on experimental data and engineering practice, which requires a systematic adjustment of the following process parameters:
Analysis of the Causes of Pore Defects
Hydrogen-induced porosity
The Ni content (12-15%) in 316L stainless steel reduces hydrogen solubility, leading to hydrogen precipitation and the formation of gas pores during welding at high temperatures.
Gas Protection Impact
Standard Ar gas (<99.995%) containing H₂O (dew point ≤ -40℃) reacts with the melt pool:
Insufficient熔池动力学
Thick plate weld pool solidifies faster than gas escapes, forming sealed bubbles.
Key Process Parameters Adjustment
Gas Protection Optimization
Gas PurityUtilizing high-purity Ar with a dew point of ≤-60°C to reduce H₂O content.
Gas FlowIncreased flow to 25-30L/min (from the standard 15-20L/min), enhancing the gas shielding effect.
Gaseous MixtureAdd 0.5-1.0% O₂ or CO₂ to promote melt pool flow.
Oxidation reactions promote the stirring of the molten pool.
Welding Parameter Adjustment
Welding CurrentIncreased by 10-15% (e.g., from 800A to 900A), enhancing the temperature gradient of the molten pool, and extending the gas escape time.
Welding TimeIncreased by 20-30% (e.g., from 1.2s to 1.5s) to ensure gas is expelled before the melt pool solidifies completely.
Electrode PressureIncreased by 5-10N (e.g., from 200N to 210N) to enhance molten pool sealing.
Material Pretreatment
Surface CleaningUtilizing acetone ultrasonic cleaning followed by alkali washing (60°C NaOH solution soak for 15 minutes) to remove oil and oxidation film.
Mechanical processingThe surface is abraded with a steel wire brush to achieve a Ra1.6μm finish, which increases surface roughness to enhance the wettability of the molten pool.
Post-weld heat treatment
Low-Temperature AnnealingAfter welding, maintain a 400℃ heat treatment for 1 hour to reduce residual hydrogen content (experiments show a reduction of over 60%).
5. Equipment Maintenance
Nochinese content provided.Wipe clean the ceramic nozzle after every 50 welds to prevent splatter from causing gas turbulence.
Cooling SystemEnsure that the water-cooled machine flow rate is ≥5L/min to prevent overheating of the welding torch, which can cause fluctuations in the molten pool temperature.
III. Process Verification Methods
Metallographic InspectionSection welds to observe the number and distribution of gas pores (standard: porosity < 0.5%).
X-ray inspectionInspected internal blowhole defects in accordance with ISO 10675 standard.
Mechanical property testingCompare the tensile strength of the welds before and after the adjustment (should be ≥ 85% of the base material).
Economic Balance
Cost Increase ItemsHigh-purity Ar cost (approximately +0.2 EUR/L), heat treatment energy consumption (approximately +0.5 kWh per piece).
Cost-saving initiativesRework rate reduced (from 8% to <1%), inspection costs decreased (X-ray inspection ratio reduced from 20% to 5%).
By adjusting the aforementioned parameters, the porosity defect rate can be significantly reduced to <0.3% (industry standard is <1%), while ensuring welding efficiency. In practical applications, parameters should be fine-tuned based on the specific plate thickness (20-50mm) and welding position (flat welding/vertical welding). It is recommended to optimize parameter combinations using the Design of Experiments (DoE) method.
