Manufacturing & Technology
Why 8% Chrome Cold Work
Die Steels are the Fastest Growing Tool Steels
Vice President, International Mold Steel, Inc.
In the late 1970's and
early 1980's, the Japanese Specialty Steel industry took a
different direction than their U.S. and European counterparts. The
change in direction was forced by the Japanese auto industry
moving to increase the usage of high strength steels to lighten
vehicle weight. The challenges of forming, cutting, and piercing
the high strength steels were proving too severe for conventional
tool steels, such as D2 (JIS SKD11). Many European and U.S.
producers decided that powder steels would provide the solution.
Daido Steel Co .LTD, a leading Japanese specialty steel
manufacturer (currently with 40% total market share and 60% market
share of specialty die steels) set out to solve the issue in a
Dr. Kunio Namiki, Managing Director
of Daido's Technical Section, Tool Steels was part of the research
team that tackled this problem in the early 1980's. He stated "We
had extensive working knowledge of powder metallurgy, but quickly
rejected powder steels as the solution. The high selling cost of
powder steels was of course attractive to us as a producer.
However, we felt the difficulties in die fabrication, heat
treatment, and the inability to effectively weld repair did not
make them a value to our customers."
Daido developed charts 1 & 2 to identify modes of failure
caused by forming or piercing high strength steel, and the
corrective measures to overcome them. They then began to
design an alloy to out perform D2 uncoated and to supply a
superior substrate for coatings.
An alloy was designed that,
when coupled with proper production techniques would produce a
fine grained steel with carefully controlled carbide size and
dispersion. This resulted in a tool steel with exceptional
impact and fatigue strength. Additional benefits were
exceptional machining and grinding properties. The ability of
this alloy to utilize high drawing temperatures allowed for
high hardness, to HRC 64, and made it a more suitable
substrate for many coatings. The alloys base chemistry is:
1.0% carbon, 8.0% chrome, 2.0% moly, 0.25% vanadium.
Improvements in manufacturing techniques and parameters remain
proprietary information of Daido Steel Co. Ltd. As there was
no A.I.S.I or J.I.S designation for this alloy, it was
assigned the trade name of DC53.
After conducting extensive
trials with Japanese auto producers, Daido introduced DC53 to
the Japanese tooling market in 1987. The performance of DC53
caused sales to explode to 700 tons per month by 1989. Other
Japanese producers were forced to come out with their own
variations of 1% carbon, 8% chrome steels.
Today there are no less than 5
variations (produced by Aichi, Sanyo, Nachi, Hitachi & Koshuha) of
this alloy produced in Japan and it dominates the cold work die
steel market. Daido due to its superior product, remains #1 with
60% market share in 8% chrome die steels. It is noteworthy that
80% of all Toyota under- body components are produced on DC53
Automotive (body and under-body)
Any high strength steel that increases in strength as a result of
a combination of straining and aging at a temperature and time
typical of the automotive paint cycle.
IF Steel (Interstitial Free)
Steels with very low amounts of carbon and nitrogen to which are
added small amounts of elements such as titanium or niobium to
combine with the remaining interstitial elements such as carbon
and nitrogen to remove their strengthening effects.
CP (Complex Phase) Steel
A steel with very fine microstructure of ferrite and a higher
volume fractions of hard phases that are further strengthened by
HSLA (High Strength Low Alloy)
Tensile between 270 and 700 MPa. Yield between 210 and 550 MPa
DP (Dual Phase)
A steel consisting of a ferrite matrix containing a hard second
phase in the form of islands.
(Transformation Induced Plasticity) Steel
A steel with a microstructure of retained austenite embedded in a
primary matrix of ferrite. In addition, hard phases of martensite
and bainite are present in varying amounts. The retained austenite
progressively transforms to martensite with increasing strain.
MART (Martensite type)
During processing the microstructure is transformed almost
entirely to hard martensite.
The 8% chrome revolution has taken
hold in the U.S. Its growth is driven by Japanese transplants and
U.S. manufactures looking for a better way. All of this has made
8% chrome cold work die steels the fastest growing in the U.S.
metal working industry today.