Development of Si-alloyed steels Summary of on-going work about - - PowerPoint PPT Presentation

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Development of Si-alloyed steels Summary of on-going work about - - PowerPoint PPT Presentation

Dec 17, 2022 148 likes •295 views

Development of Si-alloyed steels Summary of on-going work about steels with austenitic-ferritic structure Esa Vuorinen Austempered Si-alloyed steel Austempering of Si-alloyed steels creates a carbide-free structure consisting of austenite

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Development of Si-alloyed steels

Summary of on-going work about steels with austenitic-ferritic structure Esa Vuorinen

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Austempered Si-alloyed steel

Austempering of Si-alloyed steels creates a carbide-free structure consisting of austenite and ferrite

Ausferrite

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Fine grained carbide-free micro-structure consisting of retained austenite and ferrite, achieved by austempering at 340oC for two hours Steel 55Si7

Ausferrite

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SLIDE 4

Work performed

  • Mechanical properties
  • Sliding wear resistance
  • Laser hardening
  • Rolling-sliding wear resistance
  • High-temp in-situ X-ray study of

austempering process

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Austempering of Si-alloyed Steels

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Hot rolled Austempering, 340oC, 2h Yield strength, Rp0.2 612 MPa 1047 MPa 338 HV0.3 13 % 40 % 12 J Ultimate strength, Rm 1240 MPa 1530 MPa 485 HV0.3 12 % 58.5 % Hardness Elongation, A10 Reduction in area, Z Impact energy, KV 20 J

Effect of Heat Treatment

Improved mechanical properties, with maintained ductility

Fe-0.56C-1.90Si-0.84Mn-0.19Cr-0.11Ni

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SLIDE 7

Toughness

  • Impact toughness

KV = 20 J at T = -40 0C for Rm > 1500 MPa (values for a steel with 0.55%C, 1.9%Si) Ductile fracture

  • Fracture toughness

KIC = 50-85 MPa(m)½ for castings (litterature- values) KIC < 130 MPa(m)½ for rolled and heat treated steels (litterature -values)

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Wear resistance

  • Strain hardening & transformation of

austenite to martensite contributes to the wear resistance of this group of steels

  • Better wear resistance in comparison to

boron-steels with same hardness.

  • Good tempering resistance.
  • Surface hardened components with high

core strength can be produced

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SLIDE 9

In-situ X-ray observation C Xiang

Experiments with low C (0.32wt% and high C (0.83 wt%) has been performed

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In-situ X-ray observation

  • The amount of

ferrite as a function

  • f time at different

temperatures has been measured

  • The carbon content
  • f ferrite and

austenite has been determined as a function of time

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SLIDE 11

In-situ X-ray observation

  • The austenite amount

decreases with transformation temperature from 400oC to 240oC

  • C-content in austenite

increases from 240oC to 320 oC but decreases then sharply for 360 oC and 400 oC

  • 0.9%C 1.1%C
  • 0.5%C and 0.3%C
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SLIDE 12

On-going work

  • Wear resistance as a function of the amount of

austenite in the ausferritic structure;

– Transformation at different temperatures – Different amount of austenite – Rolling-sliding test – Microstructural changes

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SLIDE 13

New projects 2008-11

  • RFCS

Low C-Si Steels

  • Div of Eng Materials

& Mat Mechanics

  • Goal:

– Ductility – Weldability – Strength & Toughness

  • RFCS

High C-Si Steels

  • Div of Eng Materials

& Solid Mechanics & Machine Elements

  • Goal:

– Fatigue resistance – Wear resistance – Strength & Toughness