Cracking Failure Analysis of Cladding Layer on Support Rolls

Literature Overview

This 2011 study authored by Wang Hui, Meng Xiaoxia, Yu Zhiwei, Xu Xiaolei, and Guo Xiaoyan from Dalian Heavy Industry Special Spares Manufacturing Co., Ltd. and Dalian Maritime University investigates the cracking failure mechanism of weld overlay cladding layers applied to support rolls in steel rolling mills. Support rolls are critical components in hot rolling mills, subjected to extreme thermal cycling, mechanical loading, and chemical attack from scale and lubricants. The cladding layer is applied to extend service life by providing a wear-resistant and corrosion-resistant surface, yet cracking in these layers represents a major reliability concern.

Core Failure Mechanisms

The study identifies several root causes for cladding layer cracking on support rolls:

Residual stress accumulation: Multi-pass cladding introduces significant longitudinal and transverse residual stresses that can exceed the tensile strength of the overlay material, particularly in the final cooling stages.
Thermal mismatch between substrate and overlay: The coefficient of thermal expansion difference between the base carbon/low-alloy steel roll and the overlay alloy generates interfacial stresses during cooling.
Microstructural incompatibility: Inadequate heat input control can produce brittle phases at the fusion boundary, reducing fracture toughness and promoting crack initiation.
Fatigue loading: Cyclic thermal and mechanical stresses during rolling operations propagate micro-cracks that originate from porosity, inclusions, or intergranular boundaries in the overlay.

Defect Classification and Root Cause Mapping

Defect Type	Primary Cause	Detection Method	Severity Level
Transverse cracks	Excessive residual stress, low ductility of overlay	MT, PT	Critical
Longitudinal cracks	Thermal mismatch, preheating deficiency	MT, UT	High
Interfacial cracks	Poor bond strength, oxide contamination	UT (contact), Bond strength test	Critical
Surface micro-cracks	Thermal cycling fatigue	PT, Microscopy	Moderate
Hot cracks	Sensitive temperature range, high sulfur/phosphorus	PT, RT	High

Process Analysis and Countermeasures

The study emphasizes that proper process control is essential to prevent cracking. Key process parameters and their recommended ranges are summarized below:

Process Parameter	Recommended Range	Rationale
Preheat temperature	200–300°C	Reduces thermal gradient and cooling rate
Interpass temperature	150–250°C	Controls residual stress accumulation
Heat input per pass	1.5–3.0 kJ/mm	Balances dilution and cooling rate
Overlay thickness per pass	1.5–2.5 mm	Minimizes stress per layer
Post-weld heat treatment	600–650°C for 2–4 h	Stress relief, microstructure refinement

Engineering Practice Integration

In my experience with support roll cladding, the most effective strategy combines multi-layer multi-pass welding with controlled heat input and mandatory stress relief. The first pass should use a transition material with good ductility to absorb interfacial stresses. Subsequent passes can employ higher-performance alloys. Preheating must be verified with calibrated thermocouples placed at the roll surface and at a distance of at least 150 mm from the weld zone. Post-weld stress relief is non-negotiable for critical service applications.

Key Reflections

The study reinforces that cladding failure is rarely caused by a single factor. A systematic FMEA approach—identifying failure modes, assigning severity, occurrence, and detection ratings, and prioritizing countermeasures—provides a structured framework for prevention. The collaboration between industry and academia in this work exemplifies the value of integrating metallurgical analysis with field experience. Engineers should always correlate macroscopic failure patterns with microstructural evidence to arrive at accurate root cause conclusions.