Microstructure and Property Comparison of Carrying Roll Cladding Layers After Annealing Treatment with Different Materials

Literature Overview

This 2025 study by Teng Hongyin, Wang Yinyin, and Wu Suotuan from Meishan Steel Co., Ltd. investigates the effects of annealing treatment on cladding layers deposited on carrying rolls using different cladding materials. Carrying rolls in steel mills are subjected to extreme thermal and mechanical loading during hot rolling operations, making the cladding layer critical for roll life and surface quality. The research examines how post-weld annealing treatment affects the microstructure, hardness, and residual stress of various cladding materials.

Technical Context and Material Selection

Carrying rolls support the work rolls during hot rolling and must withstand:

• Temperatures up to 1200°C from contact with hot steel slabs
• Repeated thermal cycling causing thermal fatigue
• Mechanical loading from slab weight and rolling forces
• Abrasive contact with steel scale and oxide layers

The study evaluated multiple cladding material systems:

Annealing Treatment Parameters and Effects

The study applied different annealing regimes to each cladding material system:

The annealing treatment produced significant microstructural changes. For high-speed steel type cladding, the 600°C treatment promoted carbide coarsening and spheroidization, reducing hardness by approximately 100-150 HV while improving toughness. The 800°C treatment caused more extensive carbide dissolution and recrystallization, resulting in greater hardness reduction but potentially better thermal fatigue resistance.

Residual Stress Analysis

Residual stress measurements using the X-ray diffraction method revealed important findings:

• As-welded cladding layers exhibited tensile residual stresses in the range of 200-350 MPa.
• Annealing at 600°C reduced residual stresses to approximately 100-150 MPa.
• Annealing at 800°C reduced residual stresses to below 80 MPa.
• The austenitic cladding material showed the highest residual stress relief due to its superior creep resistance at elevated temperatures.

The residual stress reduction is critical for carrying roll applications because high tensile residual stresses combined with thermal cycling can initiate thermal fatigue cracks at the cladding-substrate interface or within the cladding layer itself.

Microstructural Evolution

Metallographic examination after annealing revealed distinct microstructural responses:

For high-speed steel type cladding, the as-welded structure of fine carbides in a martensitic matrix transformed through carbide coarsening and partial tempering. At 800°C, significant carbide dissolution occurred, with reprecipitation of coarser carbides during furnace cooling. The resulting structure showed improved toughness but reduced wear resistance.

For Stellite type cladding, the annealing treatment promoted homogenization of the cobalt solid solution and reduction of microsegregation. The 1000°C treatment produced a more uniform composition but slightly reduced hardness due to coarsening of the chromium carbide precipitates.

For hardfacing type cladding, the WC particles remained stable during annealing, but the iron-cobalt matrix underwent significant transformation. At 800°C, the martensitic matrix transformed to ferrite-pearlite, significantly reducing hardness while maintaining the WC particle reinforcement.

Engineering Practice Implications

The study provides practical guidance for carrying roll manufacturers:

1. For maximum wear life, high-speed steel type cladding with 600°C annealing offers the best hardness-toughness balance.
2. For applications with severe thermal cycling, Stellite type cladding with 800°C annealing provides superior thermal fatigue resistance despite lower hardness.
3. The hardfacing type cladding requires careful annealing control to avoid excessive hardness reduction that would compromise wear resistance.
4. Austenitic cladding, while offering excellent thermal shock resistance, is not suitable where high hardness is required.

The residual stress relief achieved through annealing is particularly important. Engineers should specify annealing treatment as a mandatory post-weld operation for carrying roll cladding, with the temperature and duration selected based on the specific cladding material and service conditions.

Key Reflections

This study demonstrates the critical importance of post-weld heat treatment in determining the final performance of cladding layers. The as-welded microstructure is rarely optimal for service, and annealing treatment can dramatically alter the balance between hardness, toughness, and thermal fatigue resistance.

The material-specific annealing responses highlight that a one-size-fits-all approach to post-weld heat treatment is inappropriate. Each cladding material system requires its own optimized annealing parameters, and these should be established through process qualification rather than assumed from general metallurgical principles.

The residual stress findings are particularly significant. In carrying roll applications where thermal cycling is severe, high residual tensile stresses can be the primary driver of thermal fatigue cracking. The study confirms that proper annealing can reduce these stresses to acceptable levels, significantly extending roll life.

Summary

The investigation of annealing effects on different carrying roll cladding materials provides comprehensive data for optimizing post-weld heat treatment parameters. The key finding is that annealing treatment is essential for achieving the desired balance of hardness, toughness, and residual stress relief, with optimal parameters being material-specific. Engineers should incorporate annealing into their cladding process qualification and production procedures, selecting parameters based on the specific cladding material and service requirements.