THERMAL CRACK IN LAYER DEPOSITION WELDMENTS

ABSTRACT

Thermal cracking is a common defect in welded structures, especially in layer cast welding. They are formed by the rapid heating and cooling processes that occur during welding, resulting in high thermal stresses.

DEPOSITION OF WELDING

In layer deposition welding, multiple layers of weld material are deposited, resulting in complex geometries. This process is usually thermal cracking due to repeated heating and cooling. Thermal cracking in layer deposit welding usually occurs in the heat affected zone (HAZ), where the material undergoes microstructural changes as a result of the welding process.

WELD IRON EXPLODATION

Cavity like cracks: Pit cracks can occur when welding is disturbed. These fissures are usually star-shaped and continue only to the edge of the crater. Such cracks are also called Paw Cracks because of their bird-four shape.

linear weld metal crack:These are the crack usually runs along the weld and looks like a pit.

HOT CRACKS

• Hot-cracks occur when the weld metal is semi-liquid and semi-solid and lacks tensile strength. If not, it happens during hardening.

• Hot cracking occurs mainly in the weld bead but can sometimes occur in the HAZ (Heat Affected Zone)and they are called melting cracks

FACTORS WHICH MAY PROMOTE HOT CRACKING

• Solidification Structure

• Segregation

• High Stress in Weld Metal

• Material Thickness

• Joint Restraint

• Width/Depth Ratio

• Weld Bead Shape

• Material Composition; high Carbon and nickel contents

• Weld Procedure: 1) High Welding Speed, 2) Long arc

• Poor fit-up

CONTRIBUTIONS TO WELC METAL CRACKING

• After cooling of metal when tensile force applied to the weld metal causes the weld metal to crack.

• The susceptibility to cold cracking is proportional to the hydrogen content of the weld state.

• At free pressure hot humid atmosphere has more hydrogen in liquid water then cold dry atmosphere which causes cold cracking

• The occurrence of low temperatures with interruptions in the welding cycle tends to exacerbate cracking problems.

• Welding conditions and their effects on bead size, heat flux, number of passes, etc. have a direct effect on fracture properties.

HOT CRACKING TEST:

1. Varestrant test

2. FISCO test

3. Lehigh Sobriety Test

4. Tekken y-pipeline

METHODS FOR AVOIDING CRACKING

• Dry the electrode or flux according to the manufacturer’s recommendations.

• Reduce stress on welds by avoiding large gaps and high limits.

• Ensure uniform heating on basis of product thickness.

• give heat for some hours after welding.

• Use coated electrodes.

• Clean joint surfaces to remove paint, cutting oil, grease and other contaminants

CONCLUSION

Methods of mitigation Layer deposit welding requires careful control of the system to prevent thermal cracking, including optimizing welding parameters, preheating and postweld heat treatments, and selecting appropriate materials.It is important to understand the formation and prevention of thermal cracking to ensure the integrity and safety of welded products in various industries.

Author Bios :

1. Mr. S.K.Karthikeyan, ASP/Mechanical
2. S. Logasri, II – Mechanical
3. R. Nathish, II – Mechanical
4. S.Madheswaran, II – Mechanical

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