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

PhD Project

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

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

Background  What is a Nanobainitic or ausferritic Steel?  Developed by HK. Bhadheshia and co-workers  Theoretically created grades  Austempering at low Temperature  Extremely fine Microstructure Taken from: F.G. Caballero et al.  / Materials and Design 30 (2009) Si content ~1,5% 2077–2083  Carbide free  Outstanding Mechanical properties

Background  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 m 1/2  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

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

R&D Plan  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

Ongoing Research Activities  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

Results Frictional Behaviour 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 ~0,18 ~0,08 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 6,00E ‐ 04 Test 2 Test 1 5,00E ‐ 04 Specific Wear Rate (mm3/N.m) Austempering Temperature 4,00E ‐ 04 300 °C 3,00E ‐ 04 Austempering Austempering Temperature Temperature 250 °C 2,00E ‐ 04 250 °C 1,00E ‐ 04 0,00E+00 0,8C 1C Bainitic Pearlitic 60SiCr7 60SiCr7 Specific wear rates of different steels tested under the same conditions

Results and Publications  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 of 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