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Project Idea• Application of austempering to martensitic stainless steels should bring some advantages
compared to standard heat treatments.
• Comparison of corrosion behavior of hardened, tempered and austempered samples.
• Application could be interesting, for example, for knives, blades, cutter, …
Austempering of Martensitic Stainless Steels and the Influence to Corrosion Resistance
Matthias SORG, Paul GÜMPEL, Arnulf HÖRTNAGL1Institute for Materials System Technology Thurgau, Tägerwilen, Switzerland, [email protected]
Introduction• Martensitic stainless steels has a wide use, for example for blades, knifes or cutter and also
for valves or shafts, etc.
• Corrosion resistance is an important property of this kind of steels.
• The best corrosion resistance of these materials is in hardened condition, because all
important alloying elements are in solution and the microstructure shows the most
homogeneous condition [1].
• Hardened condition results in a brittle mechanical behavior, so a tempering is normally used
to increase the ductility.
• Tempering precipitate fine carbides, which reduces the corrosion resistance.
• Austempering process can produce excellent mechanical properties like strength, ductility
and better capacity to dynamical stress [2].
• The resulting microstructure after austempering process should also have a better corrosion
resistance like a tempered microstructure, because it is more homogeneous [3].
Experimental Results• Hardness measurements:
• Metallographic investigation:
• Potentiodynamic scans – 0,1 mol/l NaCl, 20°C
• Potentiodynamic scans – 0,1% NaCl, 20°C
Literature[1] P. Gümpel et al., Rostfreie Stähle, expert Verlag, 1996
[2] H.-J. Bargel, G. Schulze, Werkstoffkunde, Springer-Verlag, 2008[3] H. K. D. H. Bhadeshia, BAINITE IN STEELS - Theory and Practice, Maney Publishing, 2015
Conclusions & Future Work• First experimental work shows a reduction of hardness after the austempering process.
→ The ductility should still be tested by means of notched bar impact bending test.
• The metallographic investigation shows a slight reduction of the needle-shaped
microstructure.
→ The bainitic structure should be confirmed by other methods (XRD, EBSD,…).
• The corrosion measurements show a reduction of the CPP for the quenched & tempered
specimens. The CPP of the austempered specimens is similar to the CPP of the hardened
specimens.
→Microscopic investigation of the pitting attack; Immersion corrosion tests.
• Detailed investigation of austempering requirements for martensitic stainless steel.
Experimental• Two similar martensitic stainless steels: 1.4110 (X55CrMo14) & 1.4116 (X50CrMoV15)
• Three kinds of heat treatment:
• Hardness measurements according to Vickers HV1.
• Metallographic investigation of microstructure.
• Potentiodynamic corrosion scans for determination of critical pitting potential (CPP):
• 0,01 mol/l NaCl, 20°C
• 0,01 % NaCl, 20°C
Austenitizing
Fast cooling and tempering
→Martensite
Ductility ↑Hardness ↓Strength ↓
Corrosionresistance ↓
Cooling and holding above MS
→ Bainite ?
Ductility ↑ Hardness ↓Strength ↓
Corrosionresistance ↔ ?
C Si Mn P S Cr Mo V
1.4110 0,583 0,300 0,342 0,030 0,001 14,250 0,640 0,054
1.4116 0,490 0,600 0,410 0,034 0,002 14,400 0,560 0,110
Austenitizing (1050°C) HardenedCooling in water
Austenitizing (1050°C) Tempering (300°C)Cooling in water Cooling in air Quenched and tempered
Austenitizing (1050°C) Holding (320°C)Cooling in salt Cooling in air Austempered
Hardened Austempered Quenched & Tempered