1、 Preparation work before welding stainless steel castings

Welding stainless steel castings is a technically demanding process operation, and sufficient preparation work must be done before starting welding.

1.1 Material selection and matching

When welding stainless steel castings, the first consideration is the selection of welding materials. Suitable welding materials should be selected based on the chemical composition and mechanical properties of the base material

For austenitic stainless steel castings such as 304 and 316, welding materials with the same or similar composition are usually used

For duplex stainless steel castings, specialized welding materials that can maintain two-phase balance should be selected

For martensitic stainless steel castings, preheating and post weld heat treatment requirements need to be considered

1.2 Surface cleaning treatment

The surface of stainless steel castings often contains pollutants such as oxide scale and oil stains, which must be thoroughly cleaned before welding

Clean the welding area with a stainless steel specialized wire brush

Remove oil stains with acetone or alcohol

For thick oxide layers, acid washing or mechanical polishing can be used to remove them

The cleaning range should be greater than 20mm on both sides of the weld seam

1.3 Groove preparation

Design appropriate groove form based on casting thickness and welding method:

Thin plates (≤ 3mm) can use I-shaped grooves

Medium thick plate (3-12mm) adopts V-shaped or U-shaped groove

For thick plates (>12mm), it is recommended to use X-shaped or double U-shaped grooves

The bevel angle is generally controlled within the range of 60 °± 5 °

2、 Key control points during welding process

2.1 Selection of Welding Methods

The commonly used welding methods for stainless steel castings include:

SMAW: Suitable for welding in various positions with high flexibility

Tungsten inert gas welding (GTAW): High weld quality, suitable for thin plate and precision welding

Gas Metal Arc Welding (GMAW): High efficiency, suitable for welding medium and thick plates

Submerged arc welding (SAW) * *: suitable for flat welding positions on thick plates

2.2 Welding parameter control

Stainless steel welding requires strict control of heat input:

Using smaller welding current and faster welding speed

During multi-layer and multi pass welding, the interlayer temperature should not exceed 150 ℃

The purity of argon gas during argon arc welding should be ≥ 99.99%

Gas flow control within the range of 8-15L/min

2.3 Deformation control measures

Stainless steel has a high coefficient of thermal expansion and is prone to welding deformation

Adopting a symmetrical welding sequence

Using rigid fixation or anti deformation techniques

Short weld seams are welded using segmented back welding method

Preheating (100-150 ℃) is used during thick plate welding

3、 Post weld treatment and quality inspection

3.1 Post weld heat treatment

Determine whether post weld heat treatment is required based on the type of stainless steel:

Austenitic stainless steel usually does not require post weld heat treatment

Martensitic stainless steel requires tempering treatment (650-750 ℃)

Dual phase stainless steel can undergo solution treatment (1050-1100 ℃)

3.2 Weld cleaning

After welding, the weld seam and heat affected zone should be cleaned in a timely manner:

Remove welding slag and spatter

Acid pickling and passivation treatment to improve corrosion resistance

Polishing treatment improves appearance

3.3 Quality Inspection

After welding stainless steel castings, a comprehensive quality inspection should be carried out:

Appearance inspection: No defects such as cracks, undercutting, lack of fusion, etc

Non destructive testing: RT, UT, PT or MT testing

Mechanical performance testing: Conduct tensile and bending tests if necessary

Corrosion resistance testing: intergranular corrosion test, salt spray test, etc

4、 Common problems and solutions

4.1 Prevention of Hot Cracks

Stainless steel welding is prone to thermal cracking, and preventive measures include:

Strictly control the content of impurities such as S and P

Select appropriate alloying welding materials

Optimize welding sequence and heat input

Avoid excessive constraint stress

4.2 Control of intergranular corrosion

Methods to prevent intergranular corrosion in welded joints:

Select stainless steel with ultra-low carbon or stabilizing elements (Ti, Nb)

Control welding heat input and cooling rate

Perform solution treatment or stabilization treatment after welding

4.3 Measures to prevent air holes

Reduce the generation of welding porosity:

Ensure appropriate purity and flow rate of protective gas

Thoroughly clean the surface of the workpiece before welding

Avoid welding in windy environments

Adopting short arc operation technology

5、 Safety precautions

Special attention should be paid to safety protection when welding stainless steel:

Wear a specialized dust mask to prevent inhalation of chromium compounds

Use protective goggles and face shields to prevent arc light injuries

Maintain good ventilation to avoid the accumulation of harmful gases

Wear protective clothing to prevent metal splashes and burns

Welding stainless steel castings is a process with high comprehensive technical requirements, requiring welders to possess professional knowledge and rich experience. By strictly controlling welding parameters, adopting appropriate process measures, and conducting comprehensive quality inspections, the quality and performance of stainless steel casting welded joints can be ensured to meet usage requirements.