1450 Mill Roller Cladding Technology

Literature Overview and Industrial Context

This 1992 publication from the Second Heavy Machinery Factory (Erzhong) documents the cladding technology applied to rollers of a 1450 mm hot strip rolling mill — a critical piece of equipment in steelmaking operations. The 1450 mill refers to the maximum width of hot rolled strip that the mill can process, indicating a large-scale industrial installation. Rollers (backup rolls and work rolls) in hot strip mills endure extreme operating conditions including temperatures exceeding 800°C, heavy rolling loads, severe abrasive wear from scale and oxide debris, and cyclic thermal loading. The cladding of these rollers represents a cost-effective strategy for restoring worn surfaces or enhancing the wear resistance of new rollers without replacing the entire roll body.

The Second Heavy Machinery Factory, located in North China, was one of China's premier heavy equipment manufacturers during this period, producing large forging equipment, rolling mills, and heavy machinery components. Their involvement in roller cladding reflects the integrated approach to equipment maintenance and surface engineering that was essential for maintaining productivity in China's rapidly growing steel industry.

Roller Cladding Process Selection and Parameters

For 1450 mill rollers, several cladding processes were evaluated and applied, with the selection depending on the specific service requirements of work rolls versus backup rolls.

The typical cladding alloy compositions for mill roller applications include:

• High-carbon martensitic alloys (C 2.0–4.0%, Cr 15–25%): Provide high hardness (60–65 HRC) and excellent abrasion resistance for work rolls in contact with hot steel.
• Medium-carbon ferritic alloys (C 0.3–0.8%, Cr 8–12%): Offer balanced hardness and toughness for backup rolls subjected to high compressive loads.
• High-chromium white cast iron alloys (C 3.0–4.0%, Cr 26–30%): Used for severe abrasion conditions where hardness exceeds 65 HRC.
• Nickel-iron alloys (Ni 30–40%, Fe balance): Provide good thermal fatigue resistance for rolls experiencing rapid temperature cycling.

Metallurgical Challenges and Quality Control

The cladding of large-diameter rollers presents unique metallurgical challenges that must be carefully managed:

1. Residual stress management: The thermal gradient between the cladding layer and the base roll generates significant residual stresses that can cause cracking, distortion, or premature failure during service. Mitigation strategies include:

• Preheating the roll to 200–400°C depending on base material
• Interpass temperature control (150–250°C)
• Post-weld heat treatment (PWHT) at 550–650°C for stress relief
• Spiral welding sequence to distribute heat input uniformly
• Backing pressure welding to reduce penetration and dilution

2. Interface bonding quality: The bond between the cladding alloy and the base roll material (typically 42CrMo or similar medium-carbon alloy steel) must withstand the combined action of rolling loads, thermal cycling, and abrasive forces. Bond strength testing in accordance with ASTM A263 or equivalent standards is essential, with minimum shear strength typically specified at 200–250 MPa.

3. Cracking susceptibility: High-carbon martensitic cladding alloys are inherently susceptible to cold cracking due to high carbon content and the formation of hard martensite during rapid cooling. Countermeasures include:

• Strict control of hydrogen pickup through flux and electrode drying
• Preheating to reduce cooling rate below the critical cracking temperature
• Use of low-hydrogen fluxes and electrodes
• Post-weld tempering to transform martensite to tempered martensite

4. Dilution control: Excessive dilution from the base material reduces the hardness and wear resistance of the cladding layer. For high-carbon overlay alloys, dilution must be limited to below 30% to maintain adequate hardness. This is achieved through:

• Multi-pass welding with thin individual layers
• Use of backing strips to control penetration
• Selection of consumables with sufficient alloying content to compensate for dilution

Performance Assessment and Service Experience

The effectiveness of roller cladding is evaluated through multiple criteria:

Field service experience with cladded 1450 mill rollers typically demonstrates a 2 to 4 times extension of roller life compared to uncladded base material rollers. The economic benefit is substantial, as roller replacement involves significant downtime, and cladding can be performed during scheduled maintenance windows without removing the roller from the mill housing.

Study Insights and Engineering Recommendations

This research underscores the importance of systematic approach to roller cladding technology. The success of cladding operations depends not only on the selection of appropriate alloy compositions but also on meticulous attention to process parameters, preheat and interpass temperature control, welding sequence optimization, and post-weld heat treatment.

For modern rolling mill operators, the following recommendations emerge from this study and subsequent engineering practice:

1. Establish a roller cladding qualification program based on NB/T 47014 or equivalent standards, documenting process variables, consumable specifications, and acceptance criteria for each roller type and service condition.
2. Implement routine metallographic examination of cladding layers to monitor microstructure evolution, detect incipient cracking, and verify hardness profiles across the overlay thickness.
3. Develop alloy selection guidelines that match cladding composition to specific wear mechanisms — abrasion (high-carbon martensitic), adhesion (nickel-based), corrosion-abrasion (high-chromium), and thermal fatigue (nickel-iron).
4. Consider advanced cladding technologies such as laser cladding or plasma arc cladding for critical applications where lower dilution, higher precision, and superior surface quality are required.

The legacy of this 1992 work lies in its demonstration that systematic application of cladding technology to large industrial rollers can deliver substantial economic and operational benefits, a principle that remains valid in contemporary steel manufacturing operations worldwide.