1. The document discusses the Schaeffler diagram, which is used to predict the microstructure of stainless steel welds based on their composition. It also discusses modifications to the diagram by Delong. 2. The M3 concept for developing third generation advanced high strength steels is described, which aims to achieve ultrahigh strength and ductility through a multi-phase, meta-stable, multi-scale microstructure. 3. Quenching and partitioning heat treatments are summarized as a novel method to produce multi-phase steels with significant retained austenite through quenching to form martensite and austenite, followed by an isothermal treatment to partition carbon into the a

1. 1. Schaeffler diagram
2. M3 Concept
3. Quenching & Partitioning Heat Treatments
1
Lecture Series- C

2. 2
• The Schaeffler diagram is an important tool for predicting the constitution
of austenitic Cr-Ni steel welds with carbon contents up to 0.12%. However,
it does not allow determination of the composition and volume
• of the carbide phase.
• This Schaeffler diagram is especially suited to weld metals in order to
predict the structure.
Schaeffler diagram

3.  Schaeffler and Delong diagrams are used to predict structure on the basis
of alloying elements. (Stainless Steel Weld)
 Plots the compositional limits at room temperature of austenite, ferrite
and martensite, in terms of nickel and chromium equivalents
 The Cr and Ni equivalent can be empirically determined as:
Cr equivalent = (Cr) + 2(Si) + 1.5(Mo) + 5(V) + 5.5(Al) + 1.75(Nb) + 1.5(Ti) +
0.75(W)
Ni equivalent = (Ni) + (Co) + 0.5(Mn) + 0.3(Cu) + 25(N) + 30(C)

4. 4
Chrome and nickel are among the most important alloying elements
here. All ferrite formers have a chromium equivalent and all
austenite formers a nickel equivalent.

5. Schaeffler
diagram

6. Modified Schaeffler diagram
 Delong modified the schaeffler diagram
 Ferrite No.(FN) is also plotted on schaeffler diagram
Widely use in predicting phase-structure in weld metal
 Also include calculation of volume and composition of
carbide phase

7. Modified Schaeffler diagram
 FN can be roughly determine by:
FN = 3.34 Creq – 2.46 Nieq – 28.6
--> FN between 3-7 (max.) is preferred
Solidification mode of S.S. during casting or welding can be
predicted roughly as under:
 Creq/Nieq < 1.5 (Austenitic)
 Creq/Nieq > 2.0 (Ferritic)
 In b/w 1.5 and 2.0 is the mixed structure

8. 8

9. Schaeffler-Delong diagram
FN = Ferrite No.
Low %ferrite
leads to
solidification
cracking in weld
metal, but low
%ferrite
render/reduce
Stainless steel
more corrosion
resistant

10. Schaeffler
-Delong
diagram

11. M3 Concept

12. 12
• The performance of steel products is closely related to the
constitutes and morphology of microstructures.
• The characterization and effective control of microstructure
are now from micron scale to nano scale steadily (to be in
nano order).
• The properties have been raised from the order of 106 to 109
unit (to be in Giga order).
Future Perspective of Steels

13. Future Perspective
Tensile
Strength
Fatigue
Strength
Fatigue
cycles
Creep
strength
Improved from
MPa to GPa order
Improved from
MPa to GPa order
Improved from
Mega cyles to Gega
Cycles
Improved from
Mega secs to
Giga secs

14. Third Generation Steels
Toughness ≥ 200 J
Ductility ‘A’ ≥ 20 %
Y.S. ≥ 800-1000 MPa
Target Values
Mass production
on existing mills !

15. M3 Concept
Fig. – The performance of steels are associated with the
microstructure, characterized by Multi-phase, Meta-stability and
Multi-scale

16. M3 Concept
Multi-phase
Meta-stability
Multi-scale
Mixture of
Bainite,
Martensite,
Retained austenite
Stability of austenite
Strain-induced
Martensite (SIM)
UFG, Ultra Fine Grain
Nano-laths martensite
Nano-Bainite

17. M3 Concept
Schematic of Research Targets and Future Directions
 Third generation AHSS with improvednductility and reduced cost.
 Third generation martensitic steels for improved creep strength.

18. 18
Quenching & Partitioning
Heat Treatments

19. Quenching & Partitioning
A Novel method, proposed by G. Speer, for the development of multiphase
steels with considerable retention of austenite in the microstructure.
The Q&P process consists of a first quench (quenching step) to a
temperature below the Ms but above the Mf to form a mixture of martensite
and austenite.
Subsequent isothermal treatment (partitioning step) at the same
temperature (one-step treatment) or at a higher temperature (two step
treatment), in order to transfer the C from the supersaturated αM into the γ.
Final structure = Decarburized (carbon depleted) martensite + C enriched
austenite + Fresh martensite.

20. Quenching & Partitioning
Fig. – Schematic representation of
One and Two step Q&P process

21. Quenching & Partitioning
In addition to carbon partitioning into austenite,
other processes that could occur during the ‘‘partitioning’’ step are:
 Tempering of Martensite
 Carbon trapping at dislocations and interfaces in the martensite
 Formation of carbides (both transition carbides and/or cementite)
 Decomposition of the austenite to bainite or other transformation
products
Competition occurs b/w theses processes.
*Bainite has been recognized as a potential constituent particularly at increased quench
temperatures where the amount of martensite is limited and bainite transformation kinetics
are more rapid than at a lower temperature.

22. Quenching & Partitioning
Fresh martensite is formed after quenching from partitioning temperature to
room temperature, b/c of unstable austenite.
This microstructure can lead to an interesting combination of mechanical
properties.
Good formability, as a result of the TRIP effect from the retained austenite,
and a strength higher than that of conventional TRIP steels due to martensite.

23. Q&P – Design Requirements
(a) Absence of ferrite and/or pearlite formation during the quenching step.
(b) Retardation or inhibition of bainite formation, in order to minimize
possible overlapping of carbon partitioning and formation of bainite.
(c) Retardation or minimization of the precipitation of carbides, which
consumes carbon that is then no longer available for carbon enrichment
of the austenite.
(d) A sufficiently high carbon content for thermal stabilization of a
considerable fraction of retained austenite at room temperature.

24. Q&P Steel - Microstructures
Fig. - Light optical
micrograph of Q&P
microstructure in AISI 9260
steel quenched to 190°C
and partitioned at 400°C.
Nital etch; retained
austenite appears white.
Fig. – SEM micrograph
showing blocky austenite
within the martensite
matrix formed during Q&P
heat treatment.

25. Q&P Steel - Microstructures
Fig. - Field emission scanning electron micrographs of medium
carbon low alloy steel samples quenched at 180 ◦C, partitioned at
300 ◦C for (a) 30 s (b) 120 s and (c) 900 s respectively.

26. Q&P Steels - Properties
Fig. - Comparison of impact toughness at room temperature
between Q&P and Q&T at various partitioning (or tempering)
temperatures.

27. Q&P Steels - Properties
Fig. - Comparison of the engineering stress-strain curves
and strain hardening of Q&P and Q&T