thermo mechanical control processing

1. (1)TMCP ?
Thermo-Mechanical Controlled Processing:
(2) Ultra refinement in ferrite grain size by
ultimate utilization of TMCP

2. WHAT IS TMCP?
In the past, the purpose of hot rolling was only to
achieve the nominal dimensions like thickness, width
and length.
when the quality requirement was severe, the off-line
heat treatment such as normalizing or Quench and
Tempering had been added.
But when the quality requirement became severer, the
new process for plate rolling had to be developed.
That is TMCP.
TMCP is a microstructural control
technique combining controlled
rolling and cooling.

3. • For the TMCP process, the total control during reheating of
slab, plate rolling and cooling after plate rolling is important.
• This technology was developed early in 1980’s and it was
introduced to most of Japanese Plate mills and TMCP steels
have been widely applied to Japanese shipyards.
• According to the exact definition of TMCP,
• TMCP includes TMR (Thermo-Mechanical Rolling) and AcC
(Accelerated Cooling).

4. TMCP
Thermo Mechanical Controlled Processing
Controlled Rolling (CR) Accelerated Cooling (AcC)

5. TMCP

6. TMCP

7. The aim of TMCP is to get the fine and uniform microstructure
with fine grains instead of Ferrite/Pearlite banded structure of
conventional steels.
As a result, TMCP steels have higher strength and better
toughness. Fig.3 shows the relationship between tensile strength
and Ceq (Carbon Equivalent). At the same Ceq level, strength of
TMCP steels is higher than those of conventional steels. As shown
in Fig.4, toughness is improved with decrease of the grain size.
Therefore, TMCP steels have the better toughness.
AIM of TMCP

11. Concept of microstructure change during TMCP

12. Microstructure of TMCP steel
20μm 5μm
Conventional rolling TMCP

13. Introduction to Line Pipe Steel
• Line pipe steels are strongly required for pressurized fluid transportation
over long distance.
• The innovative pipeline steel API X80, API X100 and API X120 newly
developed are considering for the new generation of line pipe steels.
• The technical requirements of these steels are the finest combination of
various properties; it includes
i. high strength,
ii. low temperature better toughness,
iii. yield ratio,
iv. high weldability,
v. superior H2S corrosion resistance,
vi.resistance to Hydrogen Induced Cracking (HIC) and
vii.better fatigue behavior etc.

14. • The prime difficulty in adjusting these properties arises
from the fact that, they are inversely linked each other;
for example,
• An increase in strength is achieved at the expenses of
the low temperature toughness and yield ratio and
vice versa.
• Therefore, development of high performance line pipe
steels can be produced by careful control of
“microstructure design”. In turn, the microstructures
are controlled by designing the “fine-tuning of
chemical composition” and “processing route”.
Introduction to Line Pipe Steel…Cont

15. • It is a valid way to achieve excellent mechanical properties of line
pipe steel by improving microstructure and refining grain size by
subjecting to different rolling conditions.
• The Metallurgical Phenomena occur through TMCP provides
different phases such as
i. Polygonal Ferrite (PF),
ii. Banitic or Acicular Ferrite (BF or AF),
iii. Martensite-Austenite Constituent (MA),
iv. Quasi Polygonal Ferrite (QF) or Massive Ferrite (MF), and
v. Granular Banitic ferrite (BF).
However, there are still disagreements and uncertainties on the
metallographical identification and classification of the phases, for
example some time the AF is also considered as banite
Introduction to Line Pipe Steel…Cont

16. Example-1 : API X70 and X80 Grade

18. Resultant Microstructure
The A steel rolled in the single phase region consists of acicular ferrite
(AF) and granular bainite (GB), with the presence of a small amount of
martensite–austenite constituent (MA) .
The B steel rolled in the two phase region is mainly composed of
polygonal ferrite (PF) transformed during finish rolling, with the presence of
AF and upper bainite (UB) and a small amount of MA and cementite.
The C steel, X80 steel rolled in the single phase region, consists of AF and
UB, with a small amount of MA. Table 3 summarizes the basic
microstructures of the three steels and the volume fraction of secondary
phases, such as MA and cementite.

19. • EBSD = Electron Backscattered Diffraction

23. Thermo-mechanical control processing (TMCP) refers to a
multi-stage deformation schedule, both above and below the
non-recrystallization temperature (Tnr), followed by accelerated
cooling.
Repeated recrystallization above the Tnr produces fine
austenite grains which are subsequently rolled below the Tnr to
obtain pancake shaped austenite grains which can then
transform into very fine ferrite or bainite following the fast
cooling.
Example-2

24. The steel used in this study was laboratory made by hot rolling
of a 5 in. thick ingot. The alloy contained 0.056%C, 1.97%Mn,
and 0.41%Mo, microalloyed with Nb + Ti + V (less than 0.13%).
Four thermomechanical cycles were designed as shown in Fig.
1.

26. Above mentioned TMCP Cycle:
Four thermo-mechanical cycles are shown in Fig. 1.
The slab was reheated at 1180 ◦C for 2.5 h and then rolled in two stages;
rough rolling and finish rolling followed by accelerated cooling and then
slow cooling to simulate the coiling process.
An overall grain refinement was expected by rolling above Tnr temperature
(Tnr temperature 924 ◦C). Rolling was finished in the austenite region
(above Ar3, 698 ◦C). The rough rolling was started at about 1125 ◦C and∼
finished 1010 ◦C. Finish rolling was performed at various temperatures∼
(between about 875 and 700 ◦C) in several passes. The rolled steels were
then cooled to about 450 ◦C at 30 ◦C/s (Ar1 = 368 ◦C). The rolled materials
were finally furnace cooled and had a thickness of 14 mm.

27. Application of TMCP steels

28. Historical progress of TMCP
C.Ouchi:ISIJ Int., 41,(2001),542.

29. Though metallurgical phenomena such as recovery,
recrystallization, precipitation, and transformation are
individually simple, as described in the textbooks, the
infinite combinations of these phenomena and
processing parameters are believed to further improve
the various properties of advance steel plates.

30. What would be happened
by ultra refinement in grain size?
20μm 5μm
Conventional
rolling
TMCP
1μm
UFG

32. Advantages and technical problems
involved in ultrafine grain steels
Advantage Technical problem
Increase of yield strength
Improvement of toughness
Increase of fatigue strength
Improvement of corrosion resistance
property
Improvement of grain boundary failure
resistance property
Increase of yield ratio
Decrease of uniform elongation
Properties of weld and HAZ
High temperature properties
Creation of ultrafine grain in heavy
section products
C.Ouchi:CAMP-ISIJ vol ,(1998), .

33. International projects involved in
ultrafine grain steels
・ Japan
1) Ferrous Super Metal Project
2) STX 21
・ China
・ Korea HIPERS 21
Univ. of Manchester (U.K.)
Univ. of Deakin and BHP (Australia)

34. Ferrous Super Metal Project
(1) Objective:
Ultra refinement of grain size under 1μm,
in carbon/low alloy steel
(2) Key technology:
Large-strain deformation higher than 50% per pass
(3) Fund:
＄ 15M Japanese government
(4) Participants:
Nippon Steel, NKK, Kawasaki Steel,
Sumitomo Metal Industries, Kobe Steel

35. Three types of
large-strain deformation
Ar1
Ar3
Conventional TMCP
Ar1
Ar3
TypeⅠ
Ac3
Ac1
TypeⅡ
Ar1
Ar3
Reverse transfomation
after heavy deformation
in α region
Transformation/
recrystrallization
after heavy deformation
in (α +γ ) or (α +θ )
region
Transformation
after heavy deformation
in extremely under cooled
γ region
TypeⅢ
Ultimate utilization of TMCP

36. Achievement in
the Ferrous Super Metal Project
Some interesting metallurgical phenomena caused by heavy deformation has been found
out
1) Strain assisted low temperature diffusional transformation
2) Spontaneous reverse transformation due to adiabatic deformation heating
M.Niikura et al: Jour. of Mat. Proc. Tech,117 (2001), 341.