03-07-2012, 04:44 PM
Material used for making dies for forging
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INTRODUCTION
Die material selection is possibly the biggest factor that affects the life of dies in a hot or
warm forging operation. There is a large variety of tool steels available in the market
that can be used for hot and warm forging applications. These steels could be
categorized as low alloy tool steels (Groups 6G, 6F, 6H), air-hardening medium alloy
tool steels (A2, A7-A9), chromium hot work steel (H-10 – H-19), tungsten hot work
steels (H20-H26), and molybdenum hot work steels (H41-H43).
Selection of die material grade (steel composition and microstructure distribution) and
subsequent heat treatment play a key role in failure of dies. These properties completely
define the thermal and mechanical properties that affect the mode of failure and the
rate of tool failure. In this section, we will go over the main classifications of tool steel
grades and characteristics of incoming tool steel – alloying composition, physical and
mechanical properties.
HOT WORK DIE STEELS
Hot work die steels are classified into 3 different categories based on their alloy content.
Chromium based
Tungsten or Molybdenum based
Steels where tungsten and chromium are approximately in equal proportion
Most hot work steels are low carbon steels with medium or high alloying elements.
SUPERALLOYS
Nickel, cobalt and iron based superalloys are another group of die materials that has
excellent potential in hot precision forging. This group of materials have extremely high
temperature strength and thermal softening. Like maraging steels, this group of
materials gets its strength from precipitation strengthening of intermetallic compounds
like Ni3Al.
Iron-based alloys. This group comprise of die steels like H-46 and Inconel 706 and contain over 12% of Chromium. Small amounts of Molybdenum and Tungsten
Provide the matrix with high temperature strength. Iron based superalloys also include
austenitic steels with high chromium and nickel content. This group can be used in
applications where dies could heat up to 1200°F.
Nickel-Iron based alloys. This group of alloy contains 24-27% nickel, 10-15% chromium and 50-60% iron along with small quantities of Molybdenum,
Titanium and Vanadium. The carbon content in these alloys is very small, typically less than .1%.
Nickel based alloys. This group of alloys contains virtually no iron. The primary constituent of these alloys are nickel (50-80%), chromium(20%) and combination of
molybdenum, aluminum, tungsten, cobalt and columbium. These grades again, get
their strength from solid solution strengthening and can be put to service at
temperatures up to 2200° F.