Research and Application of Cladding Materials for Slag Mill Roller Surface

Literature Overview

The paper by Zhang Haiyan, Wei Wei, Yang Wei, and Zhang Yongsheng from Zhengzhou Mechanical Research Institute Co., Ltd., published in New Century Cement Herald in 2021, addresses a practical and increasingly critical challenge in cement grinding operations: the selection and application of weld overlay materials for slag mill roller surfaces. Slag grinding mills operate under severe abrasive and impact conditions, where the roller surface is subjected to continuous contact with hard slag particles. The conventional repair cycle is short, leading to high downtime costs and reduced production efficiency. This literature reviews the metallurgical behavior of various cladding materials and provides application data from field trials.

Core Technical Points

Material Selection Criteria

The study evaluates multiple weld overlay consumables including high-chromium cast iron types (Cr15, Cr20, Cr26), carbide-containing alloys (WC-based, Cr3C2-based), and martensitic stainless steels. The key selection criteria are summarized below:

Material Category	Typical Hardness (HV)	Key Alloying Elements	Wear Mechanism Resistance	Typical Application Zone
High-Cr Cast Iron (Cr15)	550-650	Cr 15%, C 2.5-3.5%	Abrasive + moderate impact	Low-impact grinding zones
High-Cr Cast Iron (Cr26)	700-800	Cr 26%, C 2.0-3.0%	Severe abrasion	High-abrasion roller body
WC-Reinforced Alloy	1000-1400	WC 20-40%, Cr 12-18%	Extreme abrasion	Critical wear hotspots
Martensitic SS (D2/440C)	550-620	C 1.0-1.6%, Cr 12-18%	Abrasion + moderate corrosion	Mixed service environments

Metallurgical Considerations

The fusion zone between the base steel (typically Q345 or 45# carbon steel) and the overlay layer is the weakest link in terms of mechanical integrity. The study highlights that the dilution rate in single-pass cladding can reach 30-50%, significantly altering the intended microstructure of the overlay. Multi-pass welding strategies with controlled interpass temperature (80-150°C) are recommended to maintain carbide distribution and hardness uniformity.

The microstructure of the high-chromium alloy layer typically consists of a martensitic matrix with dispersed M7C3 and M23C6 carbides. The WC-reinforced variant introduces tetragonal WC particles that act as hard second phases, dramatically improving abrasion resistance but potentially increasing brittleness. The optimal carbon equivalent and cooling rate must be balanced to avoid excessive white cast iron formation at the fusion boundary.

Process Parameters and Engineering Practice

Recommended Welding Parameters

Parameter	Value Range	Notes
Welding method	SMAW (stick) or SAW (submerged arc)	SAW preferred for thick overlays
Wire diameter (SAW)	2.0-3.2 mm	Larger for higher deposition rate
Current	250-450 A	Depends on wire size and flux
Voltage	28-36 V	Maintain stable arc
Travel speed	80-200 mm/min	Slower for better dilution control
Layer thickness per pass	3-6 mm	Multi-pass for total 15-25 mm
Interpass temperature	80-150°C	Prevent excessive cooling rate
Post-weld treatment	Normalizing 850-900°C × 1-2h	Relieve residual stress

Field Application Results

Based on the reported field data, the application of Cr20 high-chromium overlay on slag mill rollers extended service life from approximately 3-4 months (uncladded base steel) to 12-18 months. The WC-reinforced overlay achieved the longest service life at 18-24 months but at significantly higher material and fabrication cost. The economic analysis in the paper suggests that for most cement plants operating with standard slag feed, the Cr20 overlay offers the best cost-benefit ratio.

Key Defects and Countermeasures

Defect Type	Cause	Detection Method	Countermeasure
Cracking in overlay	High cooling rate, excessive carbon	MT / PT	Preheat to 150°C, use low-hydrogen flux
Poor fusion at interface	Base surface contamination	UT (angle beam)	Thorough grinding and cleaning
Hardness drop at fusion zone	High dilution (>40%)	Hardness traverse test	Multi-pass with reduced first-pass penetration
Spalling / delamination	Residual stress, thermal mismatch	UT (toe angle)	Post-weld stress relief, controlled cooling

Study Insights and Engineering Implications

This literature provides valuable practical data that bridges the gap between laboratory material characterization and real-world industrial application. The key insight is that material selection alone does not guarantee service life improvement; the welding process parameters, particularly dilution control and interpass temperature management, are equally critical. Engineers working on similar applications in grinding mills, ball mills, and vertical roller mills should pay close attention to the fusion zone metallurgy, as this is where most premature failures originate. The economic analysis framework presented—comparing material cost, welding labor, downtime reduction, and extended service intervals—provides a replicable methodology for justifying cladding investments to plant management.