CLADDING TECHNOLOGY SHANXI CO., LTDStudy Note on Cladding Process and Performance of 45Cr4NiMoV Roll Electrode
Literature Overview
The paper titled "Research on Cladding Process and Performance of 45Cr4NiMoV Roll Electrode" addresses a critical industrial challenge in rolling mill operations: restoring or enhancing the surface hardness, wear resistance, and service life of work rolls made from 45Cr4NiMoV steel through shielded metal arc welding (SMAW) cladding. 45Cr4NiMoV is a high-carbon, high-chromium hot work tool steel widely used in medium and heavy plate mills, where the roll surface is subjected to extreme thermal cycling, mechanical abrasion, and chemical attack from scale and lubricants. The literature investigates the electrode selection, welding parameters, heat input control, interlayer temperature management, and post-weld heat treatment needed to achieve a cladding layer with hardness exceeding 55 HRC while maintaining adequate toughness and resistance to thermal fatigue cracking.
Core Technical Points
The fundamental metallurgical challenge in cladding 45Cr4NiMoV rolls lies in the mismatch between the base metal composition and the desired overlay properties. The base steel contains approximately 0.45% C, 4.0% Cr, 1.0% Mo, 1.0% Ni, and 0.15% V, which gives it a hardenability that makes it susceptible to cracking during rapid cooling. The cladding electrode must therefore be carefully selected to balance carbon content, alloy additions, and dilution from the base metal.
Electrode Selection and Composition Design
The study evaluates electrodes based on a modified high-carbon chromium type, typically containing 5–7% Cr, 0.6–1.2% C, with additions of Mo, V, and W to form stable carbides. The key design principle is to ensure that after dilution with the base metal, the cladding layer still achieves the target hardness. Dilution in the first pass is typically 30–40%, dropping to 10–15% in subsequent passes.
| Parameter | Base Metal (45Cr4NiMoV) | Cladding Electrode | Target Cladding Layer |
|---|---|---|---|
| C (%) | 0.42–0.48 | 0.8–1.2 | 0.6–0.9 |
| Cr (%) | 3.8–4.2 | 5.5–7.0 | 4.5–6.0 |
| Mo (%) | 0.9–1.1 | 0.5–1.0 | 0.6–0.9 |
| Ni (%) | 0.9–1.1 | 0.2–0.5 | 0.4–0.7 |
| V (%) | 0.12–0.18 | 0.3–0.6 | 0.2–0.4 |
| Target Hardness (HRC) | 45–52 | 58–62 (as-welded) | ≥55 |
Welding Process Parameters
The literature emphasizes that heat input must be tightly controlled to prevent excessive grain growth and cracking in the hardened base metal. The recommended parameters for a typical 6 mm diameter electrode are as follows:
| Parameter | Recommended Range |
|---|---|
| Current (A) | 160–220 |
| Arc voltage (V) | 24–30 |
| Travel speed (mm/min) | 80–120 |
| Heat input (kJ/cm) | 4–8 |
| Interlayer temperature | ≤200 °C (first layer), ≤300 °C (subsequent) |
| Preheat temperature | 150–250 °C |
| Number of passes | 2–4 |
The interlayer temperature is particularly critical. Exceeding 300 °C in the base metal can cause tempering of the hardened case, reducing hardness by 5–10 HRC and increasing susceptibility to thermal fatigue. Conversely, too low an interlayer temperature increases residual stress and the risk of cold cracking due to the high carbon equivalent of the base metal.
Post-Weld Heat Treatment
A critical finding of the study is that post-weld stress relief alone is insufficient. The recommended procedure involves:
- Stress relief at 580–620 °C for 2 hours per 25 mm of section thickness, followed by furnace cooling to prevent cracking.
- Optional surface quenching and tempering (Q&T) of the cladding layer to refine the microstructure and improve wear resistance.
- The tempering temperature is typically 550–600 °C for 1–2 hours, which reduces hardness slightly (to 50–55 HRC) but significantly improves toughness and thermal fatigue resistance.
Defect Analysis and Countermeasures
The literature identifies several common defects and their root causes:
| Defect | Root Cause | Countermeasure |
|---|---|---|
| Transverse cracking in base metal | High Ceq, rapid cooling, excessive heat input | Increase preheat, reduce travel speed, use low-hydrogen electrode |
| Cracking in cladding layer | High carbon, brittle martensite | Add Ni or reduce C in electrode, increase tempering temperature |
| Excessive dilution | Too wide bead, high current | Reduce current, use narrower electrode, increase travel speed |
| Incomplete fusion | Low heat input, poor joint preparation | Increase current, clean base surface, ensure proper groove geometry |
| Hardness below target | Excessive dilution, insufficient alloying | Increase passes, adjust electrode composition, verify dilution |
Engineering Practice Insights
In my experience with roll cladding operations at medium plate mills, the most frequently encountered problem is thermal fatigue cracking after 200–500 hours of service. This is directly related to the microstructure of the cladding layer. A purely martensitic structure with coarse carbides is brittle and prone to microcracking under thermal cycling. The study's recommendation to balance hardness with toughness through proper tempering is well-founded.
A practical approach that has proven effective in our shop is to use a two-electrode strategy: the first pass with a low-carbon, high-nickel electrode (e.g., ENiCrMo-16 equivalent) to reduce dilution-induced hardness and improve weldability, followed by subsequent passes with the high-carbon, high-chromium electrode to build up the target hardness. This approach reduces the risk of base metal cracking while still achieving ≥55 HRC in the final cladding layer.
Another practical consideration is the surface preparation. Roll surfaces often have residual scale, oxide, and lube deposits that must be completely removed by grinding before cladding. Incomplete cleaning leads to porosity and lack of fusion, which are difficult to detect without ultrasonic testing.
Study Insights and Implications
The literature provides a systematic approach to roll cladding that bridges the gap between metallurgical theory and shop-floor practice. The emphasis on dilution control, interlayer temperature management, and post-weld heat treatment reflects a mature understanding of the problem. However, I believe the study could benefit from more quantitative data on thermal fatigue life under simulated rolling conditions. Understanding the relationship between cladding microstructure, hardness profile through the thickness, and fatigue life would enable more rational process optimization.
The concept of designing the cladding layer for a specific service environment—rather than simply maximizing hardness—is a philosophy that should be adopted more broadly in the industry. For hot strip mills with aggressive thermal cycling, a slightly lower hardness (50–53 HRC) with higher toughness may provide longer service life than a 58 HRC layer that cracks prematurely.