How to Avoid Deformation & Intergranular Corrosion In Stainless Steel Welding

1 Stainless Steel Welding Consumable Selection

Stainless steel welding electrodes fall into two main categories per GB/T983-2012 standard: chromium stainless steel and chromium-nickel stainless steel electrodes.

1. Chromium stainless steel electrodes

   Match ordinary chromium stainless steel for power, petroleum and chemical equipment. This material has poor weldability; strict welding heat control and post heat treatment are required to avoid crack defects.

2. Chromium-nickel stainless steel electrodes

   The mainstream choice for medical, food and precision machinery manufacturing, featuring superior corrosion and oxidation resistance. Key operation rule: reduce welding current by roughly 20% compared to carbon steel, shorten arc length and adopt narrow weld beads with fast interlayer cooling to block intergranular corrosion.

2 Core Operation Standards for Stainless Steel TIG Welding

TIG welding fits stainless steel plates under 6mm, delivering smooth welds and minimal deformation. Adopt vertical external characteristic power supply with DC straight polarity (workpiece positive, tungsten electrode negative).

1. Shield gas requirement

   Pure argon with 99.99% purity. Gas flow rate: 8–10 L/min for 50–150A current; 12–15 L/min for 150–250A current.

2. Tungsten electrode extension

   4–5mm for flat welding; 2–3mm for fillet welds with poor shielding; 5–6mm for deep grooves. The distance between nozzle and workpiece shall not exceed 15mm.

3. Arc length control

   1–3mm for stainless steel, shorter than carbon steel welding. Excessively long arc damages argon protection and causes oxidation pores.

4. Pre-weld cleaning

   Completely remove oil, rust and oxide layers on welding seams to avoid internal pores.

5. Back shielding for root pass

   Add argon protection on the back of butt joints to prevent root oxidation and intergranular corrosion.

6. Torch & wire angle

   Maintain 80–85° between tungsten electrode and workpiece; keep filler wire angle below 10° to stabilize the molten pool.

7. Wind isolation

   Set wind barriers for outdoor work. Indoor workshops need ventilation to prevent gas disturbance.

3 Standard Specifications for Stainless Steel MIG Welding

Adopt flat characteristic power supply with DC reverse polarity (wire positive).

1. Shield gas options

   Pure 99.99% argon or mixed Ar+2% oxygen, flow rate controlled at 20–25 L/min.

2. Arc length setting

   Operate under spray transfer mode, adjust voltage to keep arc length 4–6mm.

3. Wind protection

   Even light wind over 0.5m/s creates weld pores; wind baffles are mandatory for open workshop areas.

4 Operation Rules for Stainless Steel Flux-Cored Wire Welding

Ordinary CO2 welding machines can be used, adjust wire feeder pressure slightly looser.

1. Power mode: flat characteristic DC reverse polarity.

2. Shield gas: CO2, flow rate 20–25 L/min.

3. Distance between torch nozzle and workpiece: 15–25mm.

4. Wire extension length: 15mm when current below 250A; 20–25mm when current above 250A.

5 Source Prevention: Eliminate Stainless Steel Welding Deformation

Stainless steel expands far more than carbon steel under heat. Use combined design and process methods to control distortion:

1. Low heat input principle

   Use small current, narrow weld bead, fast travel speed, multi-layer thin pass welding to reduce total heat accumulation. Avoid wide single-pass welds.

2. Fixture clamping

   Fix workpieces with rigid clamps before welding to limit free thermal expansion shrinkage.

3. Symmetric welding sequence

   Adopt skip welding and segmented welding to balance unilateral shrinkage stress.

4. Pre-set reverse deformation

   Reserve reverse offset according to material shrinkage law to counteract post-weld bending.

5. Rapid interlayer cooling

   Cool each weld layer quickly after finishing to shorten high-temperature residence time and reduce residual stress deformation.

6 Fundamental Measures To Prevent Intergranular Corrosion

Intergranular corrosion happens when stainless steel stays at 450–850°C for a long time, causing chromium carbide precipitation at grain boundaries. Core solutions:

1. Strictly limit heat input

   Avoid overheating and slow cooling; complete welding fast and cool the workpiece quickly after welding.

2. Low-carbon welding consumables

   Select ultra-low carbon stainless steel wire/electrode to reduce chromium carbide precipitation risk.

3. Stabilized alloy filling

   Use welding materials containing niobium and titanium to combine carbon elements and protect chromium in the matrix.

4. Post-weld solution treatment

   For high anti-corrosion requirements, conduct high-temperature solution annealing to dissolve precipitated carbides and restore uniform chromium distribution.

7 Conclusion

Deformation and intergranular corrosion are the two most common failure risks in stainless steel fabrication. Reasonable matching of welding consumables, standardized TIG/MIG/flux-cored wire operation parameters, low heat input welding techniques and post-weld heat treatment can fundamentally solve these two major problems. Standardized welding processes not only reduce workpiece scrap rate but also extend the anti-corrosion service life of stainless steel products.

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