Study Note on 60CrMnMo Rolling Mill Roll Overlay Repair and Heat Treatment

Literature Overview

This paper by Zhao Hui and colleagues from Shenyang Ligong University and Benxi Steel Rolling Mill Roll Repair Plant documents a practical engineering solution for the repair of 60CrMnMo steel rolling mill rolls. Published in Metal Heat Treatment in 2009 (Vol. 34, No. 4, pp. 82-84), the study describes the development of welding materials and process parameters for both local repair and full-surface overlay of a roll with diameter of 1150 mm. The key achievement is a 50% improvement in roll service life through optimized overlay welding and post-weld heat treatment.

Core Technical Content

Welding Material Selection

The study selected two specific welding consumables for the overlay repair:

Process Sequence

The repair process follows a systematic sequence:

1. Pre-weld preparation: Surface cleaning, defect removal, preheat application
2. Local repair welding: Repair of surface defects, cracks, and worn areas using custom-developed consumables
3. Full-surface overlay: Submerged arc surfacing (SAW) of the entire roll surface using Stellite multipass 224 wire with HJ107 flux
4. Post-weld heat treatment: Tempering to relieve residual stresses and optimize microstructure

60CrMnMo Steel Characteristics

60CrMnMo is a high-carbon chromium-manganese-molybdenum alloy steel widely used for rolling mill rolls. Its typical composition and properties are:

Process Analysis

Preheat and Interpass Temperature Control

The high carbon and alloy content of 60CrMnMo creates significant hardenability and cracking susceptibility. Preheat is essential to:

• Reduce cooling rate in the heat-affected zone
• Minimize residual tensile stresses
• Prevent hydrogen-induced cracking
• Reduce the risk of martensitic transformation in the HAZ

Typical preheat temperatures for this steel range from 250-350°C, depending on the section thickness and ambient conditions. For a 1150 mm diameter roll, the mass provides significant thermal inertia, meaning that once preheated, the temperature can be maintained effectively during welding.

Submerged Arc Surfacing Parameters

Submerged arc welding is the preferred process for full-surface overlay of large rolls due to:

• High deposition rate (5-10 kg/h)
• Excellent protection from flux
• Consistent weld quality
• Good dilution control with proper wire/flux selection

Post-Weld Heat Treatment

Post-weld heat treatment is critical for 60CrMnMo roll repairs:

1. Stress relief: Reduces residual welding stresses that could cause roll distortion or cracking during service
2. Microstructure optimization: Ensures uniform tempered martensite structure in the overlay
3. Hardness stabilization: Prevents subsequent hardness changes during service

Typical post-weld heat treatment parameters:

• Tempering temperature: 540-580°C
• Soak time: 2-4 hours (depending on roll mass)
• Cooling: Furnace cool to below 200°C before air cooling

Engineering Practice Results

The study reports that the roll service life was improved by 0.5 times (50%) after implementing this overlay repair and heat treatment process. This is a substantial improvement that translates directly into reduced downtime and lower replacement costs for rolling mill operations.

Life Improvement Factors

Quality Control Measures

A comprehensive quality control program should include:

1. Pre-weld inspection: Verify base roll condition, measure wear depth, identify defects
2. Welding process monitoring: Record and track all welding parameters
3. Post-weld hardness testing: Verify overlay hardness profile meets specification
4. Non-destructive testing: MT or PT of the overlay surface for cracks or lack of fusion
5. Dimensional verification: Confirm roll geometry and surface finish after grinding
6. Heat treatment verification: Confirm proper cooling curves and final hardness

Study Insights and Reflections

This paper exemplifies the practical engineering approach to roll repair — combining metallurgical knowledge with process engineering to achieve measurable performance improvements. The 50% life extension is not merely a laboratory result but a field-validated outcome from an industrial application at Benxi Steel.

The selection of Stellite multipass 224 as the overlay material is noteworthy. Stellite alloys are cobalt-based casting alloys known for exceptional wear resistance, corrosion resistance, and hot hardness. Their use as a flux-cored wire for submerged arc surfacing represents a practical adaptation of a traditionally cast material to a welding application. The "multipass" designation suggests that the wire is designed for multi-pass welding with consistent composition across passes.

The development of a custom local repair welding material is equally important. While the full overlay provides the primary wear-resistant surface, local repairs address specific defects (cracks, deep pits, localized wear) that may exist before the overlay is applied. Using a material matched to the 60CrMnMo base for these repairs ensures good metallurgical compatibility at the base-repair interface.

For rolling mill operators, this case study demonstrates that roll overlay repair can be a cost-effective alternative to roll replacement. The investment in proper welding materials, process development, and quality control pays back quickly through extended roll life and reduced downtime. The key is to treat roll repair as a systematic engineering process rather than an ad-hoc maintenance activity.

Summary

This study documents a successful engineering solution for 60CrMnMo rolling mill roll repair using submerged arc surfacing with Stellite multipass 224 wire and HJ107 flux, combined with proper preheat, local repair, and post-weld heat treatment. The achieved 50% improvement in roll service life demonstrates the significant value of systematic overlay welding technology in heavy industry. Engineers should adopt this integrated approach — material selection, process optimization, and quality control — as the standard for roll repair operations.