Why do indentations and pores appear on the weld surface?

The causes of indentations and pores on the surface of flux-cored wire welds are often due to multiple factors, including welding process parameters, material properties, and environmental factors. The following are the main causes and their corresponding explanations:

1. Inadequate gas shielding

Improper shielding gas flow

Too low a flow rate: This fails to effectively isolate the air, allowing oxygen and nitrogen to intrude into the weld pool and form pores.

Too high a flow rate: This can disrupt weld pool stability and introduce air (for example, a flow rate of 20-25 L/min is required for CO₂/MAG welding).

Suggestion: Check the gas line for leaks, ensure the nozzle is unblocked, and adjust the flow rate according to the wire diameter.

Shielding gas purity issues

Impurities (such as moisture and oil) decompose at high temperatures to produce hydrogen, which forms hydrogen pores. Use a gas with a purity of ≥99.99% and avoid humid environments.

2. Incompatibility between welding wire and process parameters

Inconsistent wire feed speed and voltage/current

Excessive voltage or fast wire feeding can lead to unstable droplet transfer, rapid weld pool solidification, and insufficient gas escape. Typical symptoms: Surface depressions (indentations) on the weld seam accompanied by dense porosity.

Incorrect polarity selection

Flux-cored wire typically uses direct current reverse polarity (DCEP). Misuse of direct polarity can affect arc stability and increase the risk of porosity.

III. Welding wire or base material contamination

Surface contaminants

Welding wire moisture, rust, or base material contamination with oil, paint, or oxide layers can release gases such as H₂ and CO.

Solution: Clean the wire before welding (grinding, wiping with acetone), and dry the wire at 100-150°C for 1-2 hours.

Moisture absorption by the flux core

Fluorides, carbonates, and other components in flux-cored wire can easily cause porosity when they absorb moisture. Store in a dry environment (relative humidity <60%).

IV. Welding operation issues

Improper arc length control

Excessive arc length (e.g., >10mm) weakens the gas shielding effect and increases the risk of air intrusion.

Tip: Maintain a short arc length, especially for sensitive materials such as stainless steel. Welding Angle and Speed
Excessive inclination angles or high welding speeds may result in inadequate weld pool protection and gas entrapment. The recommended angle is 15-20°, and the speed should be aligned with the weld pool flow.
5. Environmental Factors
Strong wind or excessive ventilation: This can disperse the shielding gas and requires a windbreak.
Low temperature or high humidity: Rapid weld pool cooling or moisture condensation may occur. Preheating the base metal is recommended (e.g., preheating carbon steel to 100-200°C).
Summary of Solutions
Process Optimization: Adjust voltage, current, and wire feed speed to the recommended range (refer to the wire manufacturer's manual).
Strict Cleaning: Thoroughly clean the wire and base metal before welding and control ambient humidity.
Equipment Inspection: Ensure the gas flow is unobstructed and the nozzle-to-workpiece distance is 8-15mm.
Post-weld Inspection: Use X-ray or ultrasonic scanning to check for internal porosity. Perform a process verification test if necessary.
If the problem persists, a welding procedure qualification (WPS) is recommended to systematically eliminate variable factors.