1. Specifications & Capability
FUSHUN METAL forges back-up rolls in Cr3/Cr4/Cr5-series steel (MC3/MC5 types) and 86CrMoV7-class steel, 600-1200 mm body diameter and up to 100 t single weight. These are the largest forged rolls, produced from vacuum-cast ingots with hydrogen controlled to 1.2 ppm or below to prevent flaking.
The roll body is differentially quenched to a surface hardness with a body hardness uniformity of 2 HSD or better, giving the contact-fatigue and wear resistance a strip-mill back-up roll demands.
| Grade | Standard | Uniformity |
|---|---|---|
| Cr5 type (MC5) | User specification | 2 HSD max |
| Cr3/Cr4 type (MC3) | User specification | 2 HSD max |
2. Components & Service Conditions
The back-up roll supports the work rolls and absorbs the full rolling force in a strip mill, so it is the largest and most heavily loaded roll in the stand. It must resist contact fatigue and surface wear against the work rolls, while the body must be sound enough to carry very high bending loads.
Because the back-up roll is so large, its soundness depends on forging practice that closes the central porosity of the ingot. FUSHUN METAL uses KD/WHF consolidation forging on an 80 MN press to compact the core, then vacuum casting to keep hydrogen low enough to prevent flaking in the 100 t section. The differential quench produces a hard surface over a tough core, with hardness uniformity controlled to 2 HSD across the body.
3. Grade Equivalents – Cr5 / MC5
| Designation | Standard | Notes |
|---|---|---|
| Cr5 type (MC5) | User specification | 5% Cr back-up roll steel |
| Cr3/Cr4 type (MC3) | User specification | 3-4% Cr back-up roll steel |
| 86CrMoV7 / 1.2327 | EN ISO 4957 | High-carbon roll steel option |
| 70Cr3Mo / 45Cr4NiMoV | GB/T 1299 | Reference only, not used in certification |
| Grade | C | Si | Mn | Cr | Mo | V |
|---|---|---|---|---|---|---|
| Cr5 type (MC5) | 0.50-0.60 | 0.40-0.70 | 0.50-0.80 | 4.50-5.50 | 0.80-1.20 | 0.10-0.30 |
| Cr3 type (MC3) | 0.35-0.45 | 0.30-0.60 | 0.50-0.80 | 2.80-3.50 | 0.40-0.70 | – |
Composition is agreed to the user specification; the chromium and molybdenum give the hardenability and temper resistance required for the 2 HSD body uniformity.
4. Manufacturing Process
Melting & casting. FUSHUN METAL vacuum-casts the ingots with hydrogen controlled to 1.2 ppm or below, preventing the flaking that threatens very large roll sections.
Forging. The roll is forged on an 80 MN fast forging press using KD/WHF consolidation to compact the core and close the central porosity of the ingot.
Heat treatment. The roll is quenched and tempered, then differentially quenched on the body to a surface hardness with uniformity controlled to 2 HSD.
Testing. UT to SEP 1921, hardness and uniformity verification, with full traceability from ingot to final machining.
5. Standards & Certification
Back-up rolls are supplied to the user specification with ultrasonic testing to SEP 1921 and inspection certificates under EN 10204 3.1. FUSHUN METAL holds ISO 9001 and AS9120B certification.
Related forgings: work rolls and intermediate rolls.
6. Typical Applications
Hot strip mills
Back-up rolls for hot strip mill finishing stands.
Cold strip mills
Back-up rolls for cold rolling mill stands.
Plate mills
Large back-up rolls for heavy plate mills.
Roll blanks
Rough or finish-machined roll blanks to drawing.
7. Inquiry Essentials
To quote your back-up roll, please provide the body diameter and length, the required surface hardness in HSD, the hardening depth, and whether you need a rough blank or a finished roll.
