Why Martensitic Stainless Steel Tube Welding is Highly Susceptible to Cold Cracking

In the stainless steel family, Martensitic Stainless Steel Tube is widely utilized in oil, chemical, and mechanical manufacturing sectors due to its exceptional strength and hardness. However, during the welding process, this material frequently encounters a challenging issue—Cold Cracking, also known as delayed cracking. These cracks typically appear during the cooling process to room temperature or after a period of time post-weld, making them highly concealed and destructive.

This article provides an in-depth explanation of the underlying causes of cold cracking in martensitic stainless steel tube welding from the perspectives of material science and welding thermal cycles.

Hardenability and Brittle Microstructure

The core characteristic of Martensitic Stainless Steel is its high hardenability. Due to the high concentrations of Carbon and Chromium in its chemical composition, the weld metal and the Heat Affected Zone (HAZ) are extremely prone to forming coarse martensitic structures after the high-temperature heating of the welding thermal cycle, even when cooled in air.

While this as-quenched martensitic microstructure possesses extremely high hardness, its Ductility and toughness are remarkably low, resulting in significant brittleness. When a welded joint lacks sufficient deformation capacity to absorb thermal stress, minor triggers can lead to brittle fracture, which serves as the physical foundation for cold cracking.

The Mechanism of Hydrogen-Induced Embrittlement

In the field of welding, Hydrogen-induced Cracking is the most common manifestation of cold cracking. Martensitic stainless steel is highly sensitive to hydrogen:

Sources of Hydrogen: During welding, moisture in the arc, damp electrode coatings, or the decomposition of oil stains on the bevel can introduce large amounts of atomic hydrogen into the molten pool.

Hydrogen Accumulation: As the temperature decreases, the solubility of hydrogen in steel drops sharply. Due to the severe lattice distortion in the martensitic structure, hydrogen atoms easily diffuse and accumulate in areas of stress concentration, such as the weld toe or root.

Pressure Effect: Accumulated hydrogen atoms combine into hydrogen molecules at microscopic defects, generating immense molecular pressure. When superimposed with residual welding stress, this directly induces crack initiation.

Significant Residual Welding Stress

Welding is a non-uniform process of localized heating and cooling. Martensitic Stainless Steel Tube possesses low thermal conductivity and a high coefficient of thermal expansion.

During cooling, there is a large temperature gradient between the inner and outer walls of the tube. Furthermore, since the martensitic transformation is accompanied by volume expansion, complex phase transformation stresses occur. For thick-walled tubes, the Restraint stress of the joint is extremely high. When the tensile stress caused by thermal contraction and phase change exceeds the instantaneous fracture strength of the material, cold cracks initiate and propagate instantly.

2026 Martensitic Stainless Steel Application and Welding Trends

As global industry moves toward precision and intelligence, the market in 2026 demonstrates the following trends:

Popularization of Super Martensitic Steel: To solve the welding difficulties of traditional martensitic steel tubes, low-carbon, high-nickel Super Martensitic Stainless Steel is becoming mainstream. This material significantly reduces hardening tendencies through compositional optimization, greatly improving the welding stability of long-distance pipelines in the field.

Automation and Laser Hybrid Welding: With the maturation of robotic welding technology in 2026, laser-arc hybrid welding is being widely applied to high-grade martensitic tubes. This high-energy-density process shortens the residence time in the heat-affected zone, reducing the generation of coarse microstructures.

Digital Hydrogen Content Monitoring: New intelligent welding machines can now monitor humidity and hydrogen content in the welding atmosphere in real-time. They use data models to predict cold cracking risks, achieving zero-defect production at the source of the process.