M41 Molybdenum High-Speed Tool Steel (UNS T11341)

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

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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.

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