IC
WEAR in HSM
R&D
DEPT
ABRASIVE WEAR
by HARD ASPERITY (2-body wear) by PARTILES LOCATED between 2 SURFACES (3-body wear)
REMOVAL of MATERIAL
OXIDE SCALE
1
2
3
IC
WEAR in HSM
R&D
DEPT
LOADS & STRESSES
WEAR RATE is DIRECTLY PROPORTIONAL to NORMAL PRESSURE on ROLL SURFACE
ROLLING PRESSURE RANGE
100-300 MPa
CYCLIC STRESSES (also THERMAL) IRREGULAR PRESSURE DISTRIBUTION
For both systems
COOLING
LUBRICATION
EFFICIENCY & WORKING REGULARITY GIVE a LONGER ROLL LIFE
IC
WEAR in HSM
R&D
DEPT
ROLL MATERIALS
LOW SURFACE ROUGHNESS
LOW CRACKING SENSITIVITY
IC
WEAR in HSM
R&D
DEPT
FRICTION & ROUGHNESS
m INCREASE with ROLL ROUGHNESS
FRICTION IS CORRELATED to DEFORMATION WORK GENERATED in ASPERITY SMOOTHING
IC
WEAR in HSM
OXIDE FILM STABILITY on ROLL SURFACE
FeO ACTS AS A LUBRIFICANT
IC
WEAR in HSM
R&D
DEPT
TERTIARY SCALE in FINISHING GROUP
HOT-ROLLED STEEL
but another theory exists also LOOKED in LABORATORY TESTS
by SPECIFIC MILL CONDITIONS
IC
MECHANISM AFFECTS by CONTACT COMPATIBILITY of SURFACES
IC
WEAR in HSM
R&D
DEPT
FATIGUE WEAR
CYCLICAL LOADING
MECHANICAL THERMAL
microcracks
(flat sheet-like particle detachment)
Carbon (%)
MECHANISM AFFECTS by ROLL HARDNESS
IC
WEAR in HSM
R&D
DEPT
ADHESIVE WEAR
JUNCTIONS (MICRO WELDING) GENERATED by PLASTIC DEFORMATION of ASPERITY SEPARATION or BREAKING MAY LEAD LOSS of MATERIAL
Genarally HSS shows a friction up to 30% higher but…
IC
WEAR in HSM
R&D
DEPT
FRICTION & ROLL MATERIALS
…the way to reduce m of HSS exists
Low amount of MC Carbides
cracks
firecrack pattern
delamination
PITTING, SPALLING…
IC
WEAR in HSM
R&D
DEPT
CHEMICAL WEAR
LOSS of MATERIAL
TRIBOCHEMICAL REACTIONS
ROLL STRIP
due to
LUBRIFICANT
±500 MPa
NON UNIFORM WEAR
IC
WEAR in HSM
R&D
DEPT
FRICTION
NEEDFUL to ROLLING
ESTABILISH the ROLLING POWER CONSUMPTION
IMPORTANT for STRIP SURFACE QUALITY
ROLLING SPEED
R&D
DEPT
FRICTION & ROLL MATERIALS
HARDNESS
CARBIDES SHAPE
m
CARBIDES AMOUNT
CARBIDES TYPE
IC
WEAR in HSM
R&D
DEPT
FRICTION & ROLL MATERIALS
m DECREASES as the TOTAL CARBIDE
WEAR in HSM
R&D
DEPT
CLASSIFICATION of WEAR
• ABRASIVE WEAR • ADHESIVE WEAR • FATIGUE WEAR • CHEMICAL WEAR
LOSS of TOOL MATERIAL during DEFORMATION
SKETCHS of MECHANISMS
m
ROUGHNESS
REDUCTION TEMPERATURE
IC
WEAR in HSM
R&D
DEPT
FRICTION & REDUCTION
THERE IS a SLIGHT DIRECT CONNECTION SURFACE CONDITION INFLUENCE THIS RELATIONSHIP
50 mm
10-11% of Carbides mainly M2C
MICROSTRUCTURE of LOW FRICTION HSS
IC
WEAR in HSM
R&D
DEPT
FRICTION & ROLL MATERIALS
LABORATORY RESULTS
0.6
0.5
0.40-0.46 0.46
IC
WEAR in HSM
R&D
DEPT
TERTIARY SCALE in FINISHING GROUP
HOT-ROLLED STEEL
CONTROLLING STRIP TEMEPERATURE below 950°C IMPROVES ROLL PERFORMANCE
THERMAL FATIGUE
FRACTION INCRቤተ መጻሕፍቲ ባይዱASES
MC CARBIDES MAY LEAD HIGHER FRICTION COEFFICIENT
(SPIKE EFFECT)
IC
WEAR in HSM
R&D
DEPT
FRICTION & ROLL MATERIALS HSS – HCrI m of these MATERIALS DIFFER
in ROLLING SPEED but ROLLING SPEED AFFECTS STRAIN HARDENING of STEEL ALSO
FRICTION & ROLLING SPEED GENERALLY m DECREASES with an INCREASE
IC
WEAR in HSM
Above 950°C SCALE SHEARS INTERNALLY: WEAR & FRICTION DECREASE
Below 950°C WEAR INCREASE with TEMPERATURE: ROLL SOFTENING & HARDER SCALE
WEAR SHOWS a MAXIMUM at 900-950°C
ENVIRONMENT
IC
WEAR in HSM
R&D
DEPT
ROLL WEAR
COMPLEX PHENOMENON SEVERAL MECHANISM ACTING at the SAME TIME…
MECHANICAL FATIGUE
ABRASION
CORROSION
THERMAL FATIGUE
IC
WEAR in HSM
R&D
DEPT
HOT-ROLLED STEEL
CHEMISTRY & MECHANICAL PROPERTIES HAVE a STRONG EFFECT on WEAR
DEFORMATION RESISTANCE
WEAR
TEMPERATURE CONTROLS GROWTH & TYPE of OXIDE SCALE
IC
WEAR in HSM
R&D
DEPT
ROLL WEAR
ROLLING PARAMETERS
IC
WEAR in HSM
R&D
DEPT
FACTORS INFLUENCING ROLL WEAR
LOADS & STRESSES
FRICTION