Hydrogen-Induced Cracking Initiation and Propagation in 10CrNi3MoV Steel Under Gas Metal Arc Welding

Literature Overview

The paper by Wei Jinshan, Zhang Tianhong, and Fang Hongyuan, published in the Journal of Welding in 2002 (Vol. 23, No. 1, pp. 53–56), addresses a critical defect mechanism encountered in the welding of 590 MPa-class high-strength marine steel 10CrNi3MoV. The study investigates the initiation and propagation behavior of hydrogen-induced cracking (HIC) when welding without preheating, using WM960-S electrode wire and an Ar + 20% CO2 shielding gas mixture under GMAW (gas metal arc welding). The authors employed the small iron weldability test method under controlled environmental conditions of −5°C and 80% relative humidity, which deliberately accelerates hydrogen embrittlement to reveal cracking susceptibility in a laboratory setting.

Core Technical Findings

The study establishes several key observations regarding the cracking behavior of 10CrNi3MoV steel under GMAW conditions. The material is a quenched-and-tempered low-alloy high-strength steel containing chromium, nickel, molybdenum, and vanadium, designed for marine applications requiring high yield strength combined with adequate toughness. The absence of preheating, combined with the cold and humid test environment, creates the worst-case scenario for hydrogen accumulation in the weld and heat-affected zone.

Single-Pass versus Multi-Pass Cracking Behavior

The most significant finding concerns the difference in cracking behavior between single-pass and double-pass welds. Single-pass welds exhibited a higher crack rate, with hydrogen-induced cracks propagating along grain boundaries (intergranular mode). In contrast, double-pass welds demonstrated significantly improved crack resistance, with any cracks that did form propagating in a transgranular manner. This distinction in crack propagation mode is not merely academic; it has profound implications for the severity and detectability of cracking in service conditions.

Intergranular cracking is generally more dangerous because it requires less energy to propagate and can initiate at lower stress levels. Transgranular cracking, while still undesirable, typically requires higher driving forces and is more readily detectable through non-destructive testing methods. The improvement in crack resistance with multi-pass welding is attributed to the thermal cycling effect of the second pass on the heat-affected zone of the first pass.

Microstructural Mechanism of Improved Crack Resistance

The authors identify the coarse grain zone (CGHAZ) of the first pass as the critical region. During the first pass, the CGHAZ develops coarse austenite grains due to the peak temperatures exceeding the recrystallization temperature. These coarse grains create long, continuous grain boundaries that serve as preferential paths for hydrogen-induced intergranular cracking. When the second pass is deposited, its welding thermal cycle acts as an additional heat input on the CGHAZ of the first pass. This secondary thermal cycle promotes the formation of fine grains along both sides of the coarse grain boundaries.

These newly formed fine grains effectively interrupt the continuous intergranular paths, forcing any hydrogen-induced cracks to change their propagation mode from intergranular to transgranular. This mechanism is essentially a localized grain refinement effect achieved through the thermal cycling of subsequent weld passes, which is a well-known but often underappreciated phenomenon in multi-pass welding of high-strength steels.

Engineering Practice Implications

For engineers working with 590 MPa-class high-strength steels in marine or offshore applications, this study provides actionable guidance. The data strongly supports the use of multi-pass welding procedures even when single-pass welds might appear adequate from a penetration or efficiency standpoint. The crack resistance improvement is substantial and comes without additional material cost, only a marginal increase in welding time.

In practical terms, the findings suggest that for 10CrNi3MoV and similar high-strength steels, the welding procedure specification (WPS) should mandate multi-pass welding sequences. The first pass should be designed to leave a root that allows the second pass to thermally cycle the CGHAZ effectively. This may require careful consideration of the interpass temperature and the spacing between passes to ensure adequate thermal overlap.

The study also reinforces the importance of preheating as a fundamental crack prevention measure. While the study deliberately omitted preheating to create a worst-case scenario, in actual production welding, preheating to temperatures typically in the range of 100–150°C for this steel grade would substantially reduce hydrogen diffusion rates and further suppress cracking susceptibility.

Key Reflections and Study Insights

One of the most thought-provoking aspects of this research is the demonstration that microstructural evolution in the HAZ can be deliberately manipulated through welding sequence design. The concept that the second pass acts as a beneficial thermal treatment for the first pass's HAZ is a powerful insight that bridges welding process engineering and materials science. It suggests that welding procedure optimization should not focus solely on achieving full penetration and adequate mechanical properties, but should also consider the metallurgical benefits of multi-pass thermal cycling.

From a quality control perspective, the distinction between intergranular and transgranular cracking modes has implications for non-destructive testing strategy. Intergranular cracks may be more difficult to detect with magnetic particle testing because they follow grain boundaries that may not be aligned with the surface. Transgranular cracks, being more randomly oriented, are generally more amenable to detection by various NDT methods.

The environmental sensitivity demonstrated in this study also underscores the importance of controlling hydrogen sources during welding. Wire selection, shielding gas composition, and joint cleaning all contribute to the hydrogen budget. The WM960-S wire was specifically designed for low-hydrogen welding, yet cracking still occurred under the harsh test conditions, indicating that even low-hydrogen consumables require complementary process controls for high-strength steels.

This study remains highly relevant to modern welding practice, particularly in the context of high-strength steel applications in shipbuilding, offshore platforms, and heavy machinery where 590 MPa-class steels are commonly specified. The fundamental metallurgical mechanisms identified are independent of the specific equipment used, and the principles apply to both conventional and advanced welding processes. Engineers should treat this literature as a foundational reference for understanding hydrogen cracking mechanisms and for justifying multi-pass welding procedures in their WPS documentation.