PhD Project PhD Project Wear and fatigue properties of novel - - PDF document

PhD Project

Wear and fatigue properties of novel nanostructured bainitic steel grades for high performance components

• PhD student: Alejandro Leiro
• Main Supervisors: Braham Prakash, Karl-Gustaf Sundin
• Associate Supervisor: Esa Vuorinen

PhD Project

• Background
• Aim and Scope of work
• R&D plan 2009-2011
• Ongoing research activities
• Results and Publications

Outline

• What is a Nanobainitic or ausferritic

Steel?

• Developed by HK. Bhadheshia and co-workers
• Theoretically created grades
• Austempering at low Temperature
• Extremely fine Microstructure
• Si content ~1,5%
• Carbide free
• Outstanding Mechanical properties

Background

Taken from: F.G. Caballero et al. / Materials and Design 30 (2009) 2077–2083

• Why are they Interesting?
• Small amount of alloying elements
• Austempering treatment done at low temperatures (200-300 Celsius
• Allows bigger sections than Q&T steels
• Very cheap steels
• Outstanding mechanical properties
• UTS in the range of 1600–1700 MPa.
• Toughness values of 130 MPa m1/2
• Show promise in industrial applications

Background

• Research Gaps
• A lot of attention has been directed towards the

alloying of these steels. Bhadeshia, Caballero, Putatunda.

• Typical mechanical properties (UTS, YS, Charpy,

etc.) have been studied

• More complex properties (Fatigue, Wear, etc.) are

yet to be evaluated

Background

Aim and Scope of Work

• Wear behaviour of ausferritic steels
• Rolling-Sliding
• Pure sliding
• Wear in corrosive environments
• Understanding the wear mechanisms
• Fatigue Properties
• Standing contact fatigue
• Rotating bending
• Fretting?
• Correlating properties to Microstructure
• Austenite content
• Grain/lath size

• 2009
• Wear properties and behavior of bainitic and

commercial steels (reference group)

• Wear properties and behavior of ausferritic steels

with different carbon contents (extended to 2010)

• 2010
• Standing contact fatigue evaluation of nanobainitic

steels

• Pure sliding behaviour of ausferritic steels
• Rotating-Bending fatigue evaluation of nanobainitic

steels

• 2011
• Fretting behavior
• Wear in corrosive environments

R&D Plan

• Metalography and hardness measurements
• Quantitative XRD analysis
• Austenite content
• Carbon content in the austenite and ferrite
• SEM and EDS
• Microstructure characterization
• Wear mechanism identification
• Rolling-sliding behaviour of ausferritic steels
• Standing contact fatigue properties of

ausferritic steels

Ongoing Research Activities

Results

Frictional Behaviour

~0,18 ~0,08

The higher hardness of the Ausferritic steel prevents the oxidized wear debris from being crushed into the surface, providing a more stable frictional behaviour over time

Conventional Bainitic steel New Ausferritic Carbide free steel

Results

Wear Resistance

Ausferritic Steels with carbon contents of 0,8% and 1% seem to perform better unde rolling-sliding conditions than conventional steels and 60CrSi with an ausferritic microstructure

Specific wear rates of different steels tested under the same conditions

0,00E+00 1,00E‐04 2,00E‐04 3,00E‐04 4,00E‐04 5,00E‐04 6,00E‐04

0,8C 1C Bainitic Pearlitic 60SiCr7 60SiCr7 Specific Wear Rate (mm3/N.m)

Test 2 Test 1

Austempering Temperature 250 °C Austempering Temperature 300 °C Austempering Temperature 250 °C

• 2009
• So far ausferritic steels seem to outperform the conventional

steels that they have been compared against, as well as other ausferritic steels

• 2010
• Fatigue and further wear behaviour studies will provide more

information about the potential of these steels in industrial applications

• A contribution to the NordTrib Conference on the wear behaviour
• f ausferritic micro-structures has been reviewed and accepted

by the comitee

• Fatigue studies are planned for the 2nd half of 2010
• 2011
• The fretting and corrosion behavior under rolling sliding or pure

sliding contacts will give the more complex properties of these materials and will complement the previous studies

Results and Publications