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Forged steel cold-rolled rolls include cold-rolled work rolls and backup rolls. The purpose of forged steel cold-rolled backup rolls is mainly to support the work rolls. Compared with the work rolls, the on-machine time is longer, usually more than 4 times that of the work rolls. It is in rolling contact with the work roll or intermediate roll for a long time, so the back-up roll body is required to have high rigidity, wear resistance and high contact fatigue strength.
At the same time, because the backup roller has a long machine cycle and the roll neck is subjected to alternating bending stress for a long time, it is required to have a good combination of strength and toughness.
1. Chemical composition
Steel grade | C | Si | Mn | P | S | Cr | Ni | Mo | V | Cu |
45Cr4NiMoV | 0.40-0.50 | 0.40-0.80 | 0.60-0.80 | ≤0.025 | ≤0.025 | 3.50-4.50 | 0.40-0.80 | 0.40-0.80 | 0.05-0.15 | — |
50Cr5MoV* | 0.40-0.60 | 0.40-0.80 | 0.50-0.80 | ≤0.025 | ≤0.025 | 4.50-5.50 | ≤0.60 | 0.40-0.80 | ≤0.30 | — |
40Cr3MoV | 0.35-0.45 | 0.40-0.80 | 0.50-0.80 | ≤0.025 | ≤0.025 | 3.00-4.00 | ≤0.30 | 0.50-0.80 | ≤0.30 | |
9Cr2Mo | 0.85-0.95 | 0.25-0.45 | 9.20-0.40 | ≤0.025 | ≤0.025 | 1.70-2.10 | — | 0.20-0.40 | — | ≤0.25 |
70Cr3NiMo | 0.65-0.75 | 0.40-0.70 | 0.50-0.90 | ≤0.025 | ≤0.025 | 2.00-2.70 | 0.40-0.60 | 0.40-0.60 | — | ≤0.25 |
70Cr3Mo | 0.58-0.75 | 0.40-0.70 | 0.50-0.80 | ≤0.025 | ≤0.025 | 2.00-3.50 | ≤0.60 | 0.25-0.60 | — | ≤0.25 |
55Cr | 0.50-0.80 | 0.20-0.40 | 0.35-0.65 | ≤0.025 | ≤0.025 | 1.00-1.30 | — | — | ≤0.25 | |
35CrMo | 0.32-0.40 | 0.20-0.40 | 0.40-0.70 | ≤0.030 | ≤0.030 | 0.80-1.10 | — | 0.15-0.25 | ≤0.25 | |
Note 1: 45Cr4NiMoV, 50Cr5MoV, 40Cr3MoV, 9CY2Mo, 70Cr3NiMo, and 70Cr3Mo are used for monolithically forged backup rollers and nested backup rollers. Note 2: 55Cr and 35CrMo are used for inserting the support roller core shaft. | ||||||||||
*50Cr5MoV Ni can be adjusted. When using VOD, Si≤0.1%. | ||||||||||
2.surface hardness
Usage | Roller body hs | Roll neck (bearing part)) Hs | ||
A | B | C | ||
Hot rolled | 60~70 | 50-60 | 40-50 | 35-50 |
Cold rolled | 65-75 | 60-70 | 55-65 | |
3.Effective hardened layer depth of roller body
Hardness HS | Steel grade % | |||
9Cr2Mo、70Cr3Mo | 50Cr5MoV | 45Cr4NiMoV | 40Cr3MoV | |
40-50 | ≥70 | — | — | ≥90 |
50-60 | ≥65 | ≥80 | ≥70 | ≥80 |
60-70 | ≥60 | ≥75 | ≥65 | — |
65-75 | ≥55 | ≥70 | ≥60 | — |
4.Allowable soft belt width on roll body surface
Roller length mm | ≤1500 | >1500-2000 | ≥2000 |
Allowed soft band width (not greater than) mm | 60 | 80 | 100 |
5. Ultrasonic flaw detection
5.1 No cracks or white spots are allowed in any part of the entire roll.
5.2 For forged backup rollers, the surface layer 100mm deep from the surface of the roller body is not allowed to have defects greater than the equivalent diameter φ2mm.
5.3 Within the scope of other ultrasonic inspection areas, when a single defect wave continuously maintains F>1/2, the defect area of the defective part with a bottom wave B≤1/2 shall not be larger than 25cm'.
Note: F is the height of the defective wave, and B is the height of the bottom wave of the defective part.
5.4 For the roll sleeve of the inlaid backup roller, when a defect wave occurs, the AVG method should be used to calculate the size of the defect in the surface layer 100mm deep from the surface of the roll sleeve, and within the remaining depth range, which is the same as 4.4.2, and it should not be larger than the equivalent diameter. 3mm. 4.4.5 For support rollers without center holes, when excessive defects appear in the center, they can be removed by drilling a center through hole.
6 Surface quality
The surface of the roll should not have any visible defects such as dents, non-metallic inclusions, etc., and should comply with the surface roughness specified in the drawing.
