Multi-Functional Roll Body Hardfacing Device Application in Rolling Mills

Literature Overview

This paper by Wang Y. J. from Baosteel Meishan Iron and Steel Co., Ltd. Technical Center, published in the journal Welding (2005, Vol. 10, pp. 60-62), describes the development and field application of a multi-functional roll body hardfacing device at a rolling mill. The device integrates preheating, hardfacing deposition, interpass temperature maintenance, and post-weld heat treatment into a single compact unit. The classification code TG455 places this work squarely within the domain of surfacing welding and overlay technology for industrial equipment restoration.

Core Technical Content

The multi-functional roll body hardfacing device addresses a critical operational challenge in rolling mill maintenance: the restoration of worn or damaged roll surfaces through hardfacing deposition. Conventional approaches often require separate equipment for preheating, welding, and post-weld treatment, leading to thermal cycling issues, extended downtime, and inconsistent quality. This integrated device consolidates all these functions into one platform.

Functional Modules

Function	Purpose	Technical Significance
Preheating	Reduce thermal gradient and prevent cracking	Minimizes residual stress and HAZ hardness
Hardfacing deposition	Restore roll surface geometry and wear resistance	Primary repair function
Interpass temperature maintenance	Control cooling rate between layers	Prevents cold cracking and ensures uniform microstructure
Post-weld heat treatment	Relieve residual stresses	Improves long-term service reliability

Structural and Performance Characteristics

The device is characterized by its compact structure, which allows deployment in confined rolling mill environments where space is limited. The multi-functional integration eliminates the need to move the roll between separate processing stations, reducing logistics complexity and thermal shock from repeated heating and cooling cycles.

Engineering Practice Integration

In rolling mill operations, roll hardfacing is performed to extend service life by restoring worn bearing journals, roll necks, or working surfaces. The key engineering considerations include:

Thermal management: Rolling mill rolls are typically made of high-carbon steel or alloy steel with high hardenability. Without proper preheating (typically 200-300°C for medium carbon steels), the rapid cooling during welding can produce martensitic transformations in the HAZ, leading to hydrogen-induced cracking.
Interpass temperature control: Maintaining interpass temperatures between 200-350°C ensures that each subsequent layer welds onto a sufficiently warm substrate, preventing excessive cooling rates that could exceed the critical cooling rate identified in the CCT diagram of the base metal.
Post-weld heat treatment (PWHT): Temper treatment at 500-650°C for medium carbon steel rolls or 650-750°C for alloy steel rolls relieves residual stresses accumulated during multi-layer deposition. The integrated device performs this treatment immediately after welding, eliminating the risk of stress relaxation during transport.

Application Assessment

The paper reports that the device requires relatively low capital investment compared to purchasing separate preheating furnaces, welding stations, and tempering furnaces. This is particularly significant for smaller rolling mills or for mills with limited maintenance budgets. The compact design also reduces the footprint of the repair facility, which is a practical advantage in space-constrained plant layouts.

Key Technical Insights

The integration of multiple thermal processing functions into a single device represents a systems engineering approach to welding repair. From a metallurgical perspective, the controlled thermal cycle achieved by this integrated system produces hardfacing deposits with more uniform microstructure compared to sequential processing. The elimination of thermal cycling between separate operations reduces the risk of:

Hydrogen-assisted cracking in high-hardness HAZ regions
Transformation-induced plasticity (TRIP) effects from repeated austenitization
Differential stress accumulation from asymmetric thermal gradients

The concept of multi-functional integration is particularly valuable for hardfacing applications where the base metal has high hardenability, such as high-carbon bearing steels (e.g., GCr15) or high-alloy roll steels (e.g., 4Cr5MoSiV). These materials require careful thermal management throughout the entire welding sequence to prevent cracking.

Study Reflection and Implications

This 2005 publication, while focused on a specific device implementation, illustrates a broader engineering principle: the integration of process steps to improve quality consistency and reduce operational complexity. In modern rolling mill maintenance, similar integrated approaches have been adopted for roll machining, heat treatment, and coating applications. The lessons from this work remain relevant for engineers designing maintenance strategies for heavy industrial equipment, particularly where thermal management is critical to repair success.