Jul 16 2012
Topics Covered
IntroductionOverviewPropertiesComposition Applications
Introduction
Hot work tool steels are known as Group H steels. They are designed to resist high pressure, heat and abrasion caused during manufacturing operations performed at 480 to 760°C (900 to 1400°F). They are further classified into three subgroups:
- Chromium hot-work steels
- Tungsten hot-work steels, and
- Molybdenum hot-work steels
They consist of tungsten, molybdenum, and chromium class H alloys. They have 0.35 to 0.45% of carbon, and 6 to 25% of tungsten, chromium, vanadium and molybdenum.
Tools made from the hot work tool steels possess good wear resistance, high strength and toughness in order to successfully perform different processes for shaping and forming hot metals. Hot work tool steels have high productivity and high operational efficiency. Hot work steels exhibit good red hardness and high softening resistance to withstand high temperatures.
Overview
Molybdenum is a carbide former and a silvery white metal, which is alloyed with other elements. It has good weldability and secondary hardening characteristics. It promotes formation of fine grain and also increases temper brittleness.
Molybdenum hot work steels include types H42 and H43. They contain chromium, molybdenum, carbon, tungsten, and vanadium. H42 is a principal alloy of molybdenum hot work steel. The composition of molybdenum hot work steels is similar to that of molybdenum high-speed steels. Applications and characteristics of molybdenum hot-work steels are similar to that of tungsten hot-work steels. In order to avoid decarburization, extreme care should be taken during heat treatment.
Properties
Molybdenum hot work tool steels have good shock resistance and high deformation and wear resistance under normal working temperature. They have excellent machinability in the annealed condition. They also exhibit high temperature strength, high tempering resistance and high-temperature toughness.
Composition
The following table shows the composition limits of the H42 molybdenum hot work steel.
| Designation |
Compositionx, % |
| AISI |
UNS |
C |
Mn |
Si |
Cr |
Ni |
Mo |
W |
V |
Co |
| H42 |
T20842 |
0.55-0.70a |
0.15-0.40 |
- |
3.75-4.50 |
0.30 max |
4.50-5.50 |
5.50-6.75 |
1.75-2.20 |
- |
xExcept group W, all steels contain 0.03 max S, 0.03 max P and 0.25 max Cu; group W contain 0.025 max S, 0.025 max P, and 0.20 max Cu. As mentioned, amount of sulfur may be increased from 0.06% to 0.15% to enhance the machinability of group A, M, T, H and D steels.
aAvailable in several carbon ranges.
Applications
The applications of the molybdenum hot work steels are as follows:
- Die casting, forging, piercing, heading, extrusion, and trimming purposes
- Hot-shear and punching blades.