CLADDING TECHNOLOGY SHANXI CO., LTDCladding Technology Summary for 750 Roughing Mill Rolls
Application Context and Requirements
The 750 roughing mill is a primary rolling mill used in steel production to reduce the cross-section of hot slabs (typically 150–250 mm thick) into strip or bloom sections. The work rolls and backup rolls in this mill experience extreme conditions: temperatures of 800–1,200 °C from the hot metal, severe mechanical loading (rolling forces of 800–1,500 kN per roll pair), and abrasive wear from scale and oxide particles. Roll life is typically measured in terms of tonnage rolled or meters of steel processed, with target lives ranging from 50,000 to 150,000 tons depending on the product and roll material.
The literature under review summarizes the cladding technology program implemented for 750 roughing mill rolls, covering the selection of overlay materials, process optimization, quality control, and field performance evaluation. The program encompasses both work rolls (diameter 450–550 mm, barrel length 1,200–1,500 mm) and backup rolls (diameter 900–1,100 mm, barrel length 1,800–2,200 mm).
Overlay Material Selection
The selection of overlay material is governed by the competing requirements of hardness (for wear resistance), toughness (for impact resistance), and thermal stability (for high-temperature service). The following table presents the materials evaluated and their performance characteristics:
| Material Type | Composition (wt%) | Hardness (HV) | Hot Hardness (900°C) | Toughness | Application |
|---|---|---|---|---|---|
| High-speed steel (W6Mo5Cr4V2) | W6, Mo5, Cr4, V2, C0.85 | 650–700 | 500–550 | Medium | Work rolls, finish passes |
| Cr-Mo cast iron (C-8 type) | C3.5–4.5, Cr2.0–3.0, Mo1.5–2.5 | 550–650 | 450–500 | High | Backup rolls, rough passes |
| High-carbon chromium alloy | C0.8–1.2, Cr8–12, Mo2–4 | 600–700 | 480–530 | Medium-High | Work rolls, general use |
| Ni-Cr alloy (Ni-30Cr) | Ni30, Cr15, C0.5–1.0 | 550–600 | 450–500 | High | Backup rolls, heavy load |
| Composite (carbide-reinforced) | Ni-Fe matrix + WC/TiC | 700–850 | 550–600 | Low-Medium | Work rolls, abrasive wear |
The selection criteria for each roll type are:
- Work rolls: Require high hardness for wear resistance and sufficient toughness to resist chipping from scale and impact. High-speed steel and high-carbon chromium alloys are preferred.
- Backup rolls: Require high toughness for impact resistance and good thermal stability. Cr-Mo cast iron and Ni-Cr alloys are preferred.
- Finish pass rolls: Require excellent surface finish and dimensional stability. High-speed steel with fine grain structure is preferred.
Cladding Process Technology
Submerged Arc Welding (SAW) for Backup Rolls
SAW is the primary process for backup roll cladding due to its high deposition rate and good penetration. The following parameters are typical:
| Parameter | Value |
|---|---|
| Wire diameter | φ3.2 mm (solid) or φ1.6 mm (flux-cored) |
| Current | 450–550 A |
| Voltage | 28–34 V |
| Travel speed | 250–400 mm/min |
| Wire feed speed | 8–12 m/min |
| Flux coverage | 3–5 mm |
| Layers | 8–15 (total thickness 20–30 mm) |
| Interpass temperature | 200–300 °C |
The roll is mounted on a specialized cladding machine that synchronizes the wire feed with the roll rotation. The machine ensures consistent bead height, spacing, and overlap across the entire roll circumference.