Double-layer centrifugally cast rolls with working layer of high-speed steel. Chemical composition, microstructure and properties.    

     The metal structure of rolls with working layer of high-speed steel has two types of eutectic colonies on the basis of special carbides VC and Cr7C3. Vanadium eutectic with metal matrix forms inverted structure based on Sharpy principle.  Metal matrix after heat treatment is presented tempered martensite-bainite hardened special dispersed secondary carbides of chromium vanadium and molybdenum with increased hardness. After a complicated heat treatment the resulting structure provides the highest heat resistance and wear resistance among all roll materials. High heat capacity (about 500 °C) ensures stable high hardness of body roll material even in accident conditions.
     The core material and necks made of ductile cast iron with nodular graphite and pearlite matrix.


     Field of application of high-speed steel rolls:
        - Work rolls of roughing stands of hot strip mills
        - Work rolls of finishing stands (F1-F4) of hot strip mills
        - Work rolls of roughing stands and pre-finishing stands of narrow strip and middle strip rolling mills.
        - Rolls for cold rolling        


     The metal microstructure of high-speed steel rolls

microstructure of the working layer, х100 microstructure of the core, х100

 

 

Table 1. Chemical compound of metal of working layer and core of high-speed steel rolls.

Pos. Roll execution

Chemical compound, %

С

Si

Mn

P

S

Cr

Ni

Mo

V

no more

1

ЛПХ6НМ5Ф5дц-76

1,5-2,5

0,5-1,0

0,5-1,2

0,1

0,05

5,0-7,0

1,0-1,5

4,0-6,0

4,0-6,0

2

Core of high-strength cast iron

3,0-3,4

1,6-2,4

0,5-1,0

0,1

0,02

до 0,5

0,5-1,5

Cu до 0,2

Mg 0,03-0,06

 

Table 2. Technological and physical-mechanical properties.

Pos. Roll execution Working layer depths, mm Hardness, HS Bending strength, МPа Coefficient of elasticity, GPa Impact strength, Joule/cm2 Heat conductivity, W/m*К Heat capacity, Joule /kg*К

Coefficient of linear extension (20?100 0С) 106/°С

1

ЛПХ6НМ5Ф5дц-76

40-60

75-90

650-800

22-24

3,5-4,5

21-23

420-450

13-15

2

Core of high-strength cast iron

-

35-45

330-460

16-19

4,2-4,6

42-48

550-580

11-12

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19 August 2019

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