Surfacing Welding Process Optimization for Blooming Mill Rolls Made of 60CrMnMo

Literature Overview

This paper, published in Shanxi Metallurgy (2023, Vol. 46, No. 4), authored by Cao Limei, An Lirong, and Li Qiuhé, addresses the optimization of surfacing welding processes for 60CrMnMo alloy steel rolls used in blooming mills. The study was conducted jointly by Yingkou Institute of Technology and Shigang Jingcheng Equipment Technology Co., Ltd. The authors adopt a systematic approach: using specimen blocks made of the same material and processed by the same method as the actual roll as substitutes, selecting welding consumables that more closely match the roll's performance characteristics, and designing a complete welding process that includes pre-weld preparation, in-process consumable usage, and post-weld heat treatment. The objective is to investigate changes in surfacing layer properties and validate the optimization effects.

Core Technical Analysis

The 60CrMnMo steel is a high-strength, high-toughness alloy steel widely used in heavy-duty roll applications where the surface must withstand extreme contact stress, abrasion, and thermal cycling. The key challenge in surfacing welding such rolls lies in balancing the hardness and wear resistance of the surfacing layer with the toughness and fatigue resistance required to avoid surface cracking and spalling. The authors identify that traditional surfacing approaches often result in excessive dilution from the base metal, which reduces the hardening effect of the alloying elements in the surfacing layer. By selecting welding materials with higher concentrations of alloying elements to compensate for dilution, the authors aim to achieve a surfacing layer hardness that meets or exceeds the original roll surface hardness.

The welding process design involves several critical parameters that warrant close attention from practitioners. Pre-heat temperature is essential to prevent hydrogen-induced cracking in the heat-affected zone, particularly given the high carbon equivalent of 60CrMnMo. The inter-pass temperature must be carefully controlled to avoid excessive grain growth and to maintain the desired microstructure in both the surfacing layer and the HAZ. Post-weld heat treatment, typically involving tempering, is critical to relieve residual stresses and to achieve the target hardness range. The authors emphasize that the welding parameters should be tailored to minimize the dilution rate while maintaining adequate wetting and bond strength between the surfacing layer and the base metal.

Key Process Parameters and Their Influence

Engineering Practice Implications

From a practical standpoint, this study has significant relevance for steel mills and rolling mills that operate blooming mills with 60CrMnMo rolls. The surfacing welding approach offers a cost-effective alternative to full roll replacement, extending roll service life by allowing repeated repairs. However, several practical challenges must be addressed in the field. First, the surface preparation of the roll must be thorough—any residual oxide, scale, or contamination will lead to incomplete fusion and potential delamination. Second, the geometry of the roll surface introduces challenges for maintaining consistent weld bead profiles; automated or semi-automated welding systems are preferred for large-diameter rolls. Third, the thermal distortion caused by surfacing welding must be monitored to ensure that the roll's dimensional accuracy is maintained, particularly the roundness and parallelism of the roll journals.

The study also highlights the importance of metallurgical compatibility between the surfacing material and the base metal. The dilution rate is a critical parameter that directly affects the final composition and hardness of the surfacing layer. In practice, the first surfacing layer typically experiences the highest dilution, often reaching 30–50 percent, which can significantly alter the intended alloy composition. Subsequent layers experience progressively lower dilution rates. Therefore, the selection of welding consumables must account for this progressive dilution effect, and the number of surfacing layers should be sufficient to achieve a composition that is predominantly that of the welding material.

Critical Reflections

One aspect that deserves further investigation is the long-term durability of the optimized surfacing layer under actual rolling conditions. Laboratory specimen testing provides valuable data on hardness, microstructure, and mechanical properties, but it cannot fully replicate the complex stress states, thermal cycles, and mechanical loading experienced by a working roll. A comprehensive evaluation should include fatigue testing, thermal cycling tests, and ideally, field trials on actual rolls under production conditions. Additionally, the study could benefit from a comparative analysis with alternative surface hardening technologies such as induction hardening, plasma nitriding, or laser cladding, which may offer superior performance in certain applications. The integration of non-destructive testing methods such as ultrasonic testing or magnetic particle inspection into the quality control protocol for surfacing welds would further enhance the reliability of the repair process.

Summary

This literature provides a valuable contribution to the field of roll repair and surface hardening, demonstrating that a carefully designed surfacing welding process can effectively restore and even improve the surface properties of 60CrMnMo blooming mill rolls. The systematic approach of using material-matched specimens, optimized consumable selection, and comprehensive process control offers a replicable methodology for similar applications in heavy industry. However, practitioners should remain vigilant about the limitations of laboratory-based validation and ensure that field performance data is collected to confirm the long-term effectiveness of the optimized process.