Cladding of Continuous Casting Billet Thermal Cutting Shear Blades

Technical Background and Application Context

Continuous casting machines use thermal cutting shears (also known as heat cutters or thermal shear blades) to cut the solidified steel shell of the cast strand at the desired length. These shear blades are subjected to extreme thermal cycling, mechanical impact from the solidifying steel, and abrasive wear from the interaction with the hot metal. The blade edges must maintain their sharpness and dimensional accuracy over extended periods to ensure clean, burr-free cuts that do not damage the downstream processing equipment.

The development of new type cladding technology for continuous casting billet thermal cutting shear blades represents an advancement in extending blade life and improving cutting quality. The cladding layer must provide exceptional thermal stability, abrasion resistance, and resistance to thermal shock at the cutting edge.

Material Design and Cladding Process Selection

Blade Material Architecture

Layer	Material	Function	Typical Thickness
Base	42CrMo / 38CrMoAlA	Structural strength and toughness	40–80 mm
Transition	16MnCr5 equivalent	Gradient transition of thermal expansion	2–5 mm
Cladding (wear layer)	Cr-Co-W-C or Ni-Cr-C composite	Abrasion resistance, thermal stability	1.5–3.0 mm
Edge treatment	High-speed steel equivalent (M2/M35)	Edge hardness and sharpness	0.5–1.0 mm

Cladding Process Comparison for Shear Blades

Process	Heat Input	Dilution	Surface Quality	Deposit Uniformity	Suitability
PTA (Plasma Transferred Arc)	Low-Moderate	Low	Excellent	High	Primary choice for precision blades
Laser Cladding	Very Low	Very Low	Excellent	High	Thin layers, high precision
SAW (Submerged Arc Welding)	High	Moderate	Requires grinding	Moderate	Bulk restoration only
GMAW (MIG)	Moderate	Moderate	Requires grinding	Moderate	General purpose
Cold Spray	None	None	Good	Moderate	Coarse particles, lower bonding

Process Parameters and Optimization

PTA Cladding Parameters for Shear Blades

Parameter	Typical Value	Engineering Significance
Plasma arc current (A)	200–400	Controls melt pool size and penetration
Plasma arc voltage (V)	35–55	Influences arc stability and transfer characteristics
Travel speed (mm/min)	150–400	Balances deposition rate with solidification quality
Powder feed rate (g/min)	50–150	Must match arc energy for complete melting
Gas flow rate (L/min)	50–100	Protects molten pool and powder trajectory
Powder composition	Cr 30%, Co 10%, W 5%, C 2%, balance Fe	Optimized for thermal stability and wear resistance
Preheat temperature (°C)	100–200	Reduces thermal stress in the base material
Interpass temperature (°C)	≤200	Prevents excessive grain growth

Multi-Pass Cladding Strategy

For shear blades requiring a total cladding thickness of 3 mm, a multi-pass strategy is employed:

Bonding pass: Single pass with high current and low travel speed to ensure full fusion at the interface.
Buildup passes: 2–3 passes with optimized parameters to achieve the desired thickness with controlled dilution.
Surface pass: Final pass with low current and high travel speed to achieve a smooth surface with minimal dilution.

Performance Requirements and Testing

Mechanical and Thermal Properties

Property	Requirement	Test Method
Hardness (as-deposited)	75–85 HRC	Vickers or Rockwell C
Hardness (after thermal cycling)	≥70 HRC after 1000 cycles	Thermal cycling test per ASTM F1321
Thermal shock resistance	No cracking after 500 cycles 20°C–1200°C	Thermal shock test
Wear resistance	≥50 mm³/g in pin-on-disk test	ASTM G99
Bond strength	≥300 MPa tensile	Bond strength test per ASTM B108
Edge retention	≥500 cutting cycles without dulling	Simulated cutting test

FMEA Analysis for Cladding Process

Failure Mode	Potential Effect	Severity	Occurrence	Detection	RPN	Mitigation
Crack in cladding layer	Blade failure during cutting	10	3	4	120	Control cooling rate; use preheat; optimize powder composition
Insufficient bond strength	Delamination during service	9	2	3	54	Ensure clean surface; use bonding pass with adequate heat input
Hardness variation	Uneven wear, premature dulling	7	3	3	63	Maintain stable welding parameters; use certified powder
Excessive dilution	Reduced hardness at surface	6	4	3	72	Control heat input; use low-dilution process
Porosity in deposit	Reduced edge strength	8	2	4	64	Ensure proper powder dryness; control gas flow

Engineering Practice Case

A continuous casting plant experienced blade failures every 80 cutting cycles due to edge chipping and thermal cracking. The original blades were made of a single material (42CrMo) with conventional hardening treatment. After implementing PTA cladding with a Cr-Co-W-C composite powder, the blade life was extended to 450 cutting cycles, representing a 5.6-fold improvement. The key factors contributing to this improvement were:

The multi-layer material architecture providing a gradient of thermal expansion coefficients.
The high carbon content in the cladding layer forming stable carbides that resist thermal degradation.
The controlled dilution of the PTA process maintaining the intended composition of the wear layer.

Study Insights and Implications

The cladding of continuous casting shear blades demonstrates the effectiveness of advanced overlay technology in extending the life of critical components subjected to extreme thermal and mechanical loading. The key insight is that the cladding solution must be designed as a multi-layer system that addresses the different functional requirements of each layer rather than relying on a single homogeneous material. The selection of PTA as the primary cladding process is justified by its ability to produce high-quality deposits with minimal dilution and excellent surface finish. Engineers must carefully balance the competing requirements of hardness, toughness, and thermal stability when designing the cladding material system for this application.