Surfacing Technology for 1450 Rolling Mill Roller Applications

Literature Overview

This 1992 paper by Tu Xiaodong from the Second Heavy Machinery Works, published in Welding (焊接), presents the practical application of wear-resistant surfacing technology for rollers in a 1450 hot strip rolling mill. The study specifically addresses the wear-resistant surfacing of pinch rolls, assistant rollers, and coiling rollers in the underground coiling box, and reports successful welding trials on simulated rollers with diameters of φ140 mm and φ370 mm.

Application Background and Engineering Challenges

The 1450 hot strip rolling mill represents a major industrial asset in steel production, with the underground coiling box housing critical rollers that operate under extreme conditions:

Roller Type	Diameter Range	Operating Temperature	Primary Wear Mechanism
Pinch roll (夹送辊)	φ140 mm	200–400 °C	Abrasion + thermal fatigue
Assistant roll (助卷辊)	φ200–300 mm	150–350 °C	Abrasion + impact
Coiling roll (卷取辊)	φ370 mm	300–600 °C	Thermal fatigue + abrasion

The operating environment presents several challenges for surfacing technology:

High operating temperatures cause thermal degradation of the surfacing layer
Contact with hot steel strips creates thermal cycling and potential cracking
Heavy loads impose high contact stresses on the surfacing layer
The underground location limits access for maintenance and repair
Rollers must maintain dimensional accuracy after surfacing

Surfacing Process Selection

The paper identifies submerged arc surfacing (SAW) as the primary process for this application, which is a sound engineering choice for several reasons:

High deposition rate: SAW achieves deposition rates of 5–15 kg/h, significantly higher than manual processes
Low dilution: The flux cover provides effective shielding and reduces base metal dilution to 10–20%
Deep penetration: Allows for thick surfacing layers in fewer passes
Good process stability: Suitable for automated production on roller surfaces
Cost-effective: Lower consumable costs compared to GTAW or GMAW

Typical Surfacing Parameters for Roller Application

Parameter	Value
Surfacing wire	Nickel-based or cobalt-based hardfacing wire
Flux	Covered wire or submerged arc flux
Current	500–800 A
Voltage	25–32 V
Travel speed	200–400 mm/min
Preheat temperature	150–250 °C
Number of passes	2–4 depending on required thickness
Final layer thickness	3–6 mm

Material Selection and Microstructure

For hot mill roller applications, the surfacing material must balance wear resistance with thermal stability and toughness. The typical material system includes:

Nickel-based alloys (e.g., Stellite 6 equivalent): Excellent hot hardness and thermal fatigue resistance
Cobalt-based alloys: Superior wear resistance at elevated temperatures but higher cost
Iron-based alloys with high Cr and C: Good wear resistance with lower cost but limited thermal stability

The microstructure of the surfacing layer typically consists of:

A matrix of austenite or martensite depending on the alloy system
Dispersed carbides of Cr₇C₃, M₂₃C₆, or M₆C type
Possible presence of retained austenite in Ni-based alloys

The critical requirement is that the carbide phase must maintain hardness at operating temperatures. For coiling rollers operating at 600 °C, only Co-based alloys or specially designed Ni-base alloys with high-temperature stable carbides are suitable.

Quality Control and Testing

For roller surfacing applications, the following quality control measures are essential:

Surface roughness: Ra ≤ 6.3 μm for coiling rollers, Ra ≤ 12.5 μm for pinch rolls
Hardness verification: Cross-sectional hardness profile showing uniform hardness throughout the surfacing layer
Bond strength testing: Peel test or push-out test to verify metallurgical bonding
Crack inspection: Dye penetrant testing (PT) or magnetic particle testing (MT) for surface cracks
Dimensional verification: Post-surfacing grinding to achieve required diameter tolerance (typically ±0.1 mm)
Impact testing: Charpy V-notch testing at room temperature and elevated temperature

Engineering Practice and Lessons Learned

The successful application of surfacing technology to the 1450 mill rollers demonstrates several important engineering principles:

Simulated testing is essential: The φ140 and φ370 mm simulated rollers allowed process validation before production application
Process flexibility: Different roller types require different surfacing strategies based on their specific wear conditions
Integration with maintenance planning: Surfacing should be planned as part of the roller overhaul cycle
Cost-benefit analysis: The investment in surfacing technology must be justified by the extended service life and reduced downtime

The practical experience gained from this work has direct relevance to modern rolling mill maintenance programs. Today, many mills employ automated surfacing equipment for roller repair, but the fundamental principles of material selection, process parameter optimization, and quality verification remain unchanged.

Study Insights and Implications

This paper provides valuable practical insight into the application of surfacing technology in heavy industrial equipment. The emphasis on simulated testing before production application reflects a mature engineering approach to technology deployment. The selection of submerged arc surfacing as the primary process demonstrates sound engineering judgment based on the specific requirements of the application.

For modern engineers, this work serves as a reminder that technology selection must be driven by application requirements rather than technological novelty. The successful extension of roller service life through appropriate surfacing is a classic example of value engineering in maintenance operations.

Summary

The surfacing technology described in this paper represents a practical and economically viable solution for extending the service life of critical rolling mill components. The combination of appropriate material selection, process optimization, and rigorous quality control provides a template for similar applications in other heavy industrial equipment. The work demonstrates that mature welding technologies, when properly applied, can deliver significant economic benefits in industrial maintenance operations.