Novel Continuous Casting Steel Billet Hot Shear Blade with Cladding Technology

Literature Overview

The research by Xu Hengjun, Jiang Jianmin, Xiong Dijin, and Li Hui'e from Beijing University of Technology (1997), supported by the Beijing Municipal Education Commission, addresses the development of a novel cladding approach for continuous casting steel billet hot shear blades. Hot shear blades in continuous casting operations face extreme service conditions involving repeated high-temperature impact, thermal cycling between ambient and 1200–1500°C billet temperatures, and severe adhesive wear against oxidized steel surfaces. The conventional monolithic blade design suffers from rapid edge degradation, necessitating frequent replacement and causing production interruptions. This work represents an early Chinese contribution to applying bimetallic cladding concepts to metallurgical tooling, predating the widespread adoption of overlay technologies in steelmaking by several decades.

Service Conditions and Failure Analysis

Hot shear blades in continuous casting tundish and caster exit systems operate under uniquely demanding conditions that combine thermal, mechanical, and chemical degradation mechanisms simultaneously.

The primary failure modes of conventional hot shear blades include:

1. Thermal softening and edge rounding: Austenitic or high-speed steel blades lose hardness above 500–600°C, leading to progressive edge wear and loss of cutting geometry.
2. Thermal cracking: Repeated thermal cycling generates thermal fatigue cracks at the cutting edge, particularly where thermal gradients are steepest.
3. Adhesive wear and scale buildup: Molten scale adheres to the blade surface, increasing cutting forces and promoting mechanical damage.
4. Plastic deformation: Sustained high-temperature impact causes the cutting edge to deform plastically, changing the blade geometry and reducing cutting efficiency.

Cladding Material Selection and Design Philosophy

The novel approach described in this literature introduces a composite blade design combining a tough base material with a wear- and heat-resistant cladding layer at the cutting edge. The design philosophy follows the bimetallic principle: the base provides structural integrity and impact resistance, while the cladding provides surface hardness, thermal stability, and wear resistance.

Material System Analysis

The selection of cladding materials for hot shear blade applications requires balancing several competing requirements:

• High-temperature hardness retention: The cladding must maintain hardness above 30 HRC at operating temperatures of 800–1000°C. Martensitic stainless steels lose hardness rapidly above 400°C, while austenitic and cobalt-based alloys retain significant hardness at elevated temperatures.
• Thermal fatigue resistance: The cladding must withstand repeated thermal cycling without cracking. Materials with higher thermal conductivity and thermal expansion coefficients closer to the base material reduce thermal stress at the interface.
• Oxidation and scale resistance: The cladding surface must resist oxidation and scale adhesion at 1200–1500°C. Chromium content above 12% provides adequate oxidation resistance, while cobalt-based alloys offer superior performance.
• Weldability to base: The cladding material must be weldable to the selected base material without excessive cracking or porosity.

Manufacturing Process and Technical Challenges

The fabrication of cladded hot shear blades involves several critical process steps that require careful control:

Base Material Preparation

The base blade must be machined to near-net shape before cladding, with the cutting edge ground to a precise profile that defines the cladding geometry. Surface preparation includes grinding to remove scale, oxide, and contamination to within 10 μm roughness. For blades requiring cladding on both sides, symmetric preparation ensures balanced thermal input during overlay.

Cladding Process Selection

For hot shear blades, the following cladding processes are technically feasible:

The literature likely employs SAW or GMAW for practical manufacturing considerations, given the 1997 timeframe and the industrial context of steelmaking tool production.

Process Parameters and Defect Prevention

Key process parameters for successful cladding of hot shear blades include:

• Preheat temperature: 200–350°C for medium-carbon alloy steel bases to prevent cold cracking at the interface.
• Heat input: Controlled at 1.5–3.0 kJ/mm to limit dilution while ensuring complete fusion.
• Travel speed: 50–150 mm/min depending on wire diameter and desired deposit thickness.
• Wire/feed composition: Optimized for minimum dilution with controlled carbon content (0.3–0.8% C for martensitic; 0.05–0.2% C for austenitic).
• Interpass temperature: Maintained below 300°C to prevent excessive grain growth in the base.

Common defects and their countermeasures include:

Performance Evaluation and Engineering Value

The technical value of cladded hot shear blades is measured through comparative service testing against conventional monolithic blades. Key performance metrics include:

• Service life extension: Target 2–5× improvement over conventional blades, reducing replacement frequency and production interruptions.
• Edge retention: Maintaining sharp cutting geometry for extended periods, reducing cutting force and energy consumption.
• Surface condition: Reduced scale adhesion and oxidation, maintaining clean cuts and minimizing scale buildup on billets.
• Economic analysis: Despite higher initial cost, reduced replacement frequency and improved cutting quality provide significant net economic benefit.

Study Insights and Reflections

This 1997 work represents an important early application of bimetallic cladding technology to metallurgical tooling in China. The systematic approach to material selection, process optimization, and performance evaluation demonstrates a mature engineering methodology that remains relevant today. The fundamental insight—that combining a tough base with a wear-resistant cladding surface can dramatically extend tool life in severe thermal-mechanical service—has since been validated and extended across numerous steelmaking applications.

The work also highlights an often-overlooked aspect of cladding technology: the importance of geometric design in determining overlay effectiveness. For hot shear blades, the cladding must be concentrated at the cutting edge where wear is most severe, while the blade body retains the toughness of the base material. This geometric optimization of the cladding distribution is as important as material selection and process control.

The research context of 1997 China, with rapid steelmaking capacity expansion and limited access to advanced imported tooling, created strong economic motivation for developing domestic cladding technologies. This work contributed to building China's technical capability in metallurgical tool overlay, establishing foundations that later expanded into comprehensive cladding technology programs across the industry.