|
High Chrome, Double Pour
|
 |
 |
Double Pour, Flake or Nodular Core
Developed for use as work rolls in the early finishing stands of hot strip mills, High Chrome rolls are centrifugally cast double poured and consist of a shell which is essentially a high chromium white iron with journals and barrel axis of cast iron.
This type of shell material combines very good wear properties with an excellent resistance to fire cracking and banding, and also has good hot hardness characteristics. Thus the rolls are very resistant to both surface deterioration and damage in service leading to high tonnage output, good stock finish and extended mill availability.
The structure of the shell metal consists of discontinuous primary chromium carbides in a matrix which is normally acicular with fine globular carbides. In softer rolls some pearlite may be present.
High chrome rolls have also proved to be very successful as cold mill work rolls as they offer a number of advantages. As well as their excellent grip properties which greatly facilitate 'threading' of the mill, High Chrome rolls have much higher wear resistance which leads to higher tonnage outputs. Other factors are that High Chrome rolls show little fall off in hardness to discard so that expensive re-hardening is not required. Their lower residual stress and relatively high toughness make the rolls much more resistant to damage from mill incidents.
High Chrome rolls for cold mills can be supplied with a hardness of up to 95o Shore C.
The core material for any Double Poured High Chrome roll can be either flake or nodular core according to requirements. In general the flake core will display better thermal properties while the nodular iron achieves greater mechanical strength. The extra strength has become increasingly important in mills using work roll bending and shifting systems.
|
|
Applications
|
|
| Product |
Type of Mill |
Position |
| Wide Strip |
4 High |
Roughing/Finishing |
|
Typical Mechanical Properties
|
|
|
Barrel |
Journal & Axis |
|
| Property |
|
Flake Core |
Nodular Core |
| Tensile Strength |
850 |
240 |
425 |
| Bending Strength |
1300 |
350 |
835 |
|
Typical Hardness Gradient
|
|
|
|
|
Micrograph
|
|
Shell x 100
Flake Core x 50 Nodular Core x 50
|
|
Typical Analysis
|
|
| Code |
Leeb E |
Shore C |
C |
Si |
Mn |
Ni |
Cr |
Mo |
| HC |
680-845 |
65-88 |
2.4/3.0 |
0.5/1.1 |
0.7/1.5 |
0.7/1.5 |
14/20 |
0.7/3.5 |
|
