Surfacing Materials and Process Development for Long-Life Continuous Casting Rolls

Literature Overview

Published in Journal of Northeastern University (Natural Science) (Volume 29, Issue 5, 2008, pp. 693-696) by Sun Dale, Li Xiaobing, Yao Lisong, and Liu Chengmin from Northeastern University and Baosteel Research Institute, this paper addresses the development of surfacing materials and processes for large slab continuous casting (CC) rolls. The research is supported by the National Natural Science Foundation of China (Project 50674022) and a major Baosteel research project (ZA9815), reflecting the industrial significance of extending CC roll service life in China's steel industry.

Service Environment and Failure Analysis

Large slab continuous casting rolls operate under extreme and complex conditions:

The primary failure modes of CC rolls include:

1. Thermal fatigue cracking — Repeated heating and cooling causes surface cracking
2. Hot cracking — Cracking during contact with molten steel due to thermal stresses
3. Cold cracking — Cracking during rapid water cooling due to thermal gradients
4. Abrasive wear — Contact with oxide scale and inclusions on slab surface
5. Contact fatigue — Rolling contact fatigue leading to surface spalling

Surfacing Material Development

The base material selected is 1Cr13NiMo, which is a martensitic stainless steel known for its good combination of hardness, toughness, and corrosion resistance. The development work involved adding functional alloying elements to improve specific performance characteristics:

The new surfacing weld strip and matched sintered flux were developed to achieve the following improvements over imported materials:

• Superior microstructure with finer and more uniformly distributed hard phases
• Higher strength and hardness in the as-welded condition
• Enhanced hot and cold thermal fatigue resistance
• Better bonding strength with the roll substrate

Process Parameter Optimization

The study investigates the effects of two critical process parameters:

Interpass Temperature

The interpass temperature between successive surfacing passes significantly affects:

Post-Weld Heat Treatment Temperature

Post-weld heat treatment is critical for optimizing the final properties:

The study demonstrates that there exists an optimal combination of interpass temperature and post-weld heat treatment temperature that produces the ideal microstructure and mechanical properties. This optimal window represents a balance between hardness (for wear resistance) and toughness (for thermal fatigue resistance).

Microstructural Design Philosophy

The microstructural design for CC roll surfacing must accommodate multiple, often competing, requirements:

1. Hardness for wear resistance — Requires hard carbide and boride phases in a hard matrix
2. Toughness for thermal fatigue resistance — Requires a ductile matrix that can accommodate thermal strain cycling
3. Corrosion resistance — Requires sufficient chromium for passive film formation
4. Oxidation resistance — Requires alloying elements that form protective oxide scales
5. Bonding strength — Requires good metallurgical bonding with the roll substrate

The achieved solution involves a tempered martensitic matrix with finely dispersed carbide and boride phases. The tempering reduces the brittleness of as-quenched martensite while maintaining adequate hardness. The fine dispersion of hard phases provides wear resistance without creating the large, interconnected hard phase networks that would act as crack initiation sites.

Performance Validation

The new surfacing material and process were validated through:

• Microstructural examination confirming the designed phase composition and morphology
• Mechanical property testing demonstrating superior strength and toughness compared to imported materials
• Thermal fatigue testing showing improved resistance to both hot and cold cracking
• Service trials demonstrating extended roll life compared to imported alternatives

The result of extended service life represents significant economic benefit, as CC roll replacement is a major cost and production interruption factor in steelmaking operations.

Engineering Practice Integration

For implementation in production environments, the following considerations are essential:

• Welding procedure specification — Precise control of all welding parameters within validated windows
• Operator training — Ensuring consistent execution of the surfacing procedure
• Quality monitoring — Regular microstructural and mechanical property verification
• Equipment maintenance — Ensuring stable welding power sources and powder/strip feeding systems
• Substrate preparation — Proper cleaning, preheating, and surface preparation of the roll

Study Insights

This research demonstrates a systematic approach to solving a complex engineering problem through material development, process optimization, and performance validation. The integration of functional alloying elements into a proven base composition (1Cr13NiMo) provides a practical pathway to performance improvement without requiring fundamentally new metallurgical concepts. The emphasis on both material development and process parameter optimization reflects the holistic approach required for successful industrial implementation. For engineers working on CC roll refurbishment programs, this work provides a validated technology that extends roll life while reducing dependence on imported materials. The methodology of systematically investigating the effects of interpass temperature and post-weld heat treatment is directly transferable to other surfacing applications where thermal cycling resistance is critical, such as reheating furnace rollers, heat exchanger tubes, and turbine components.