Oct 25 2012
Topics Covered
Introduction
Chemical Composition
Physical Properties
Mechanical Properties
Thermal Properties
Other Designations
Fabrication and Heat Treatment
Machinability
Forming
Welding
Heat Treatment
Forging
Cold Work
Annealing
Tempering
Applications
Introduction
High-speed tool steels are of two types, namely molybdenum
high-speed steels and tungsten high-speed steels. The molybdenum
high-speed steels are also referred to as Group M steels. In the United
States, 95% or more of all manufactured high-speed steels are the Group
M steels. The high-speed tool steel types have equal performance but
the molybdenum high-speed steels have relatively lower initial cost. To
enhance performance and tool service life, tools made of high-speed
tool steel can be coated with titanium carbide, titanium nitride, and
other coatings using the physical vapor deposition process.
There are many types of molybdenum high-speed steels. The following
data sheet will provide details relating to M41 molybdenum high-speed
steel. This steel has good hardness and toughness, and costs lesser
than other tungsten tool steels.
Chemical Composition
The following table shows the chemical composition of M41 steels.
| Element |
Content
(%) |
Fe
|
Balance
|
| C |
1.05-1.15 |
| Mn |
0.20-0.60 |
| Si |
0.15-0.50 |
| Cr |
3.75-4.50 |
| Ni |
0.3 |
| Mo |
3.25-4.25 |
| W |
6.25-7.00 |
| V |
1.75-2.25 |
| Co |
4.75-5.75 |
| Cu |
0.25 |
| P |
0.03 |
| S |
0.03 |
Physical Properties
The physical properties of M41 steels are outlined in the following
table.
| Physical properties |
Conditions |
| T
(°C) |
Treatment |
| Density |
8.17 x 1000 kg/m3 |
25 |
- |
| Melting point |
- |
1425 |
- |
Mechanical Properties
The mechanical properties of M41 steels are tabulated below.
| Mechanical properties |
Conditions |
| T
(°C) |
Treatment |
| Poisson's ratio |
0.27-0.30 |
25 |
- |
| Elastic modulus |
27557-30458 ksi |
25 |
- |
Thermal Properties
The table below shows the thermal properties of M41 steels.
| Thermal properties |
Conditions |
| T
(°C) |
Treatment |
| Thermal expansion |
9.7 x 10-6/ºC |
20-200 |
- |
Other Designations
Other designations that are equivalent to AISI M41 molybdenum
high-speed tool steels include:
- AFNOR 07-05-04-04-02
- DIN 1.3246
- ASTM A600
- FED QQ-T-590
- UNS T11341
Fabrication and Heat Treatment
Machinability
The machinability of M41 steels is rated at 55% than that of water
hardening low alloy tool steels.
Forming
The alloy can be formed in annealed condition using conventional
methods.
Welding
M41 type of molybdenum high-speed tool steel is weldable.
Heat Treatment
The M41 steels can be preheated at 788˚C (1450˚F) and then rapidly
heated to 1232˚C ( 2249˚F) for 2-5 minutes followed by air-cooling and
oil and salt bath quenching process.
Forging
M41 steels can be forged at 1149˚C (2100˚F) down to 954˚C (1749˚F).
But they must not be forged below 927˚C (1701˚F).
Cold Work
Conventional methods can be applied for the cold working process
with the alloy in the annealed condition.
Annealing
The M4 has to be annealed at 871– 899˚C (1599-1650˚F) followed by
slow furnace cooling at less than 4˚C (39˚F) per hour.
Tempering
The tempering process can be carried out in the range of 538-593˚C
(1000-1099˚F) for about one hour. It is recommended that this process
be repeated two times for the triple tempering effect. Rockwell C
hardness of the M41 is in the range of 70 to 65.
Applications
The M41 molybdenum high-speed tool steels are mainly used as cutting
tools for machining operations.