Topics: Steel, Tensile strength, Materials science Pages: 27 (3634 words) Published: March 26, 2013
No. 10 (Dec. 2007)

Newly-Developed Ultra-High Tensile Strength Steels
with Excellent Formability and Weldability†


TANAKA Yasushi*3

JFE Steel has developed and commercialized ultrahigh tensile strength steel series from TS780 MPa to 1 470 MPa with excellent formability and weldability
which reduces weight and increases safety in collision
when they are applied to the reinforcement parts around
a cabin. Those ultra-high tensile strength steels are
developed by applying JFE Steel’s own technology, continuous annealing line water-quenching facilities which greatly contribute to reduce alloy elements in the steel.
Especially, the TS1180 MPa steel which is expected to
expand in application, excels in elongation. It is 1.5
times larger than the conventional one which is the same
level with 980 MPa, and strech-flangeability has also
been achieved as the same level with TS980 MPa. It is
remarkable work-hardenability and bake-hardenability
make it possible to replace hot-stamping parts.

1. Introduction
In recent years, high strength steel sheets have been
increasingly applied to automobile bodies to improve
crashworthiness so as to secure the safety of the passengers in the automobile and improve fuel economy by reducing automobile body weight in order to reduce CO2
Up to 1990, application of TS440–590 MPa grade
high strength steel sheets (TS: tensile strength) was
studied as a substitute for conventional mild steel sheets.
These steel sheets were improved to overcome problems
such as difficulty of press formability, weldability, and
corrosion resistance, and have played an important role
as front end collision members such as the front side

Originally published in JFE GIHO No. 16 (June 2007), p. 16–20


Dr. Eng.,
Senior Researcher General Manager,
Automotive Sheet Products Res. Dept.,
Steel Res. Lab.,
JFE Steel

member and others which absorb energy by deforming
in a collision.
From the beginning of the 1990s, ultra-high strength
steel sheets of TS780 MPa grade and higher were studied. Conventionally, this type of ultra-high strength steel sheet had been applied in safety reinforcing parts
located away from the cabin, such as bumper reinforcing materials, door impact beams, and the like, but in response to stricter safety and weight reduction requirements, this range has expanded to include pillars and their reinforcing materials and similar parts. This trend

is also clearly shown by the ULSAB (Ultra Light Steel
Auto Body) Project, which was carried out jointly by
32 steel makers in 15 countries beginning in 1994, and
can be interpreted as the future direction for automotive
structural members1).
To meet these needs, JFE Steel, as a total maker
of automotive high tensile strength steels, carried out
product development of automotive steel sheets which
lead the world in responding to the diverse requirements of the automobile market2,3). As part of this effort, the company commercialized high formability ultrahigh strength steel sheets of grades TS780–1 470 MPa utilizing a low alloy composition design and control of

the microstructure, making full use of the continuous
annealing line with a water quench function (WQ-CAL)
process shown in Photo 14) .
This paper introduces JFE Steel’s TS780–1 470 MPa
grade cold-rolled steel sheets, which can contribute to
further weight reduction and improved crashworthiness
in automobile bodies. In particular, the basic concept of
material design and properties are outlined, centering on
TS980 MPa and TS1180 MPa grade steel sheets, which

Senior Researcher Manager,
Automotive Sheet Products Res. Dept.,
Steel Res. Lab.,
JFE Steel


Dr. Eng.,
General Manager, Automotive Sheet Products Res.
Steel Res. Lab.,
JFE Steel


Newly-Developed Ultra-High Tensile Strength Steels with Excellent Formability and Weldability...
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