65Mn Steel: Composition, Properties, Heat Treatment & CNC Machining

At times a strong and hard yet a tough material is needed for certain applications. Take an example of a survival knife. Even if the blade if sharp but it doesn't show flexibility, it's usage might get limited. 65Mn steel fits perfectly for this application in this sense. It is hard, sharp, tough and flexible. One downside is its susceptibility to rust. But its low cost weighs above this limitation. Certain corrosion protection techniques can be employed to outcome this shortcoming. Let's learn more about this material.

What Is 65Mn Steel?

65Mn steel is a high strength and high elasticity alloy grade of steel. 65Mn steel complies with the Chinese standard GB/T 1222 for spring steels. Due to its ability to retain shape at high stress levels, it is used in a number of tools. Its property of high hardness and edge retention make it worthy for cutting tools and blades.

Medium Carbon Alloy Steel

65Mn steel is a medium carbon alloy steel./ In its nomenclature. “65” denotes a nominal 0.65% carbon content. “Mn”indicates that it has an elevated Manganese content. Other chemical element lie within normal ranges.

Why 65Mn Is Used as Spring Steel

65Mn steel has the ability to store and release energy repeatedly without permanent deformation. It has an high elastic modulus and high yield strength that are characteristics of spring steel.

Pros and Cons

Advantages

1. Its high carbon content give it excellent wear resistance.
2. Good fatigue resistance
3. Less costly than alloy spring steels
4. Good hardenability

Disadvantages

1. Limited corrosion protection
2. Low toughness
3. Susceptibility to crack in some cases

65Mn Steel Chemical Composition & Microstructure

Chemical composition of steel has a dominate role in its microstructure. The useful properties that 65Mn steel has owes to its chemical composition. With the correct balance between different chemical elements, 65Mn steel attains the desired mechanical properties.

Carbon and Manganese Ranges

As the name implies, the carbon content in 65 Mn carbon steel is around 0.65%. It is important to understand that its not a strict number. The carbon content has a range of 0.60-0.70%. Manganese content in 65Mn steel remains higher than most plain carbon steel. It lies in a range of 0.90-1.20% which is higher than the range of 0.3%-0.90% for plain carbon steels.

Role of Silicon, Sulfur, Phosphorus

Silicon plays a vital role in attaining springiness property for 65Mn steel. It discourages the formation of cementite. So, carbon content in pearlite remains high. If heat treated, it spares more carbon for martensite and bainite phases. Presence of Si also modifies the microstructure to the advantage of springiness.

Although S and P content is desired to be kept low in most steels. However, in 65Mn steel, sulphur forms MnS inclusions which increase the machinability of steel. However, phosphorus is considered a detrimental element responsible for cold shortness in steels.

Microstructure After Anneal vs Quench

In the annealed condition, 65Mn steel produces comparatively softer phases like pearlite and ferrite. Whereas, in quenched condition 65Mn steel transforms the softer phases into a very hard Martensite phases. So, it becomes hard, strong and wear resistant.

65Mn Steel Mechanical & Physical Properties

The physical properties of 65Mn steel is comparable to most carbon steels. On the other hand the mechanical properties show high elasticity, high yield strength and high Young's modulus. The mechanical properties are comparable to many spring steels.

65Mn Steel Physical Properties

Density

Similar to most carbon steels, 65Mn has a density of 7.85g/cm³.

Magnetic Properties

Many people ask:“Is 65Mn steel magnetic? The answer is yes. It preserves ferromagnetic behavior in all heat treated states.

Thermal Properties

65Mn steel has a moderate thermal conductivity and a comparatively lower specific heat capacity than most carbon steels. Its thermal expansion is stable for most practical purposes.

65Mn Steel Mechanical Properties

Is 65Mn Steel Hard to Machine?

65Mn steel is considerably difficult to machine alloy. 65Mn steel machining poses problems due to elevated hardness, strong abrasion on cutting tools, and work hardening. 65Mn steel machinability can be improved by annealing, proper tool selection and optimization of feeds and speeds.

Factors Affecting Machining 65Mn Steel

1. Heat Treatment

In contrast to the quenched and tempered state where hardness reaches 50-60 HRC, machining in the annealed state is fairly easier. Most CNC machinists prefer machining in the annealed or as rolled state.

2. Microstructure and Hardness State

65Mn steel comprises of the softer ferrite and pearlite phases in the annealed condition. Whereas, the martensite phases present in the quenched state it very hard to machine. Even the Bainite phase in the tempered state shows considerable difficulty in machining.

3. Section Size and Rigidity

Smaller and thinner sections are often prone to vibration and chatter. On the other hand, larger sections show an acceptable rigidity.

Main Machining Challenges

• High tool wear due to high hardness
• Tendency to work-harden with improper lubrication
• Heat buildup at cutting edge
• Chatter on thin parts
• Difficulty in achieving good surface finishes on hardened material

Tips for Better CNC Machining 65Mn Steel

• Machine in the annealed state whenever possible
• Use carbide or coated carbide tools
• Apply proper coolant to reduce heat
• Apply proper lubrication to prevent work hardening
• Use rigid fixturing
• Reduce cutting speeds but maintain sufficient feed
• Use reinforced cutting geometries to withstand impact loads

Why Choose Heat Treated 65Mn Steel?

Heat treatment is an important step in enhancing the mechanical properties. Heat treatment facilitates 65Mn steel in achieving hardness, strength and wear resistance suitable for springs, blades, and mechanical parts. Conveying the requirements for final hardness helps the CNC manufacturer to modify the heat treatment process.

65Mn Steel VS Heat Treated 65Mn Steel

As a general practice, 65Mn steel is machined before quenching. Only the finished part is subjected to heat treatment. It is because in the as rolled or annealed state the surface hardness is favorable for machining. After quenching and tempering, the surface hardness causes problems like chatter, vibration, surface marks and rapid tool wear.

Spheroidize Anneal For Machinability

Spheroidizing converts lamellar carbides into globular carbides in the microstructure. The globular shape helps 65Mn steel to attain toughness. At the microstructural level, sharp edges are eliminated which spreads load evenly. It increases the machinability dramatically.

Normalize, Austenitize, Quench

Typical Hardness After Q&T

The below table sheds light on important aspects of common heat treatments:

Why 65Mn Steel Is Good for Knives?

65Mn steel is an excellent choice as a knife blade material. It has a good edge retention, high sharpness, high hardness and high elasticity making it highly suitable for knives. After proper heat treatment blades made up of 65Mn steel attain a high durability.

Best Knife Types for 65Mn

Common knife types made up of 65Mn steel are listed below:

• Machetes
• Cleavers and choppers
• Swiss knives
• Bushcraft knives
• Agricultural and forestry blades
• Throwing knives
• Fixed blades and camp tools

Durability and Toughness

After tempering treatment, 65Mn steel imparts an acceptable level of toughness even for impact applications. High wear resistance makes it suitable for frequent use. Heat treated blade can handle conditions ranging from cutting hardwood to light impact tasks without failing.

Springy Performance for Impact Cuts

High elasticity deflects the blades to absorb energy from impact. Similar to spring steel, 65Mn steel has the ability to absorb shocks without breaking. So light to heavy impact blades can be made out of 65Mn steel.

Low Cost and Wide Availability

65Mn is cheaper than tool steels like D2, 440C, or Cr-V steels. It does not require the expensive Nickel content that is necessary for stainless steels. Still it maintains an impressive level of hardness after heat treatment. 65Mn steel is widely available in market at a good price.

What Is 65Mn Material Equivalent to?

65Mn steel complies with the Chinese standard “GB/T 1222 — Spring Steels”. This standard gives requirements for chemical composition and mechanical properties. In order to find equivalence, the chemical composition and mechanical properties are to be compared with other standard systems like JIS, DIN, SAE etc.

Common Standards and Designations

Common Material Equivalents

How they differ in compositions, properties, etc.

• ASTM 1065:It gives a similar carbon content but a lower Manganese content. So, hardenability is a bit less. As MnS inclusion are fewer, machinability also becomes less. But still it is deemed good for spring strips, knives, saw blades, agricultural blades.
• JIS SUP6: It gives a slightly lower carbon content. Buut the addition of silicon improves the elasticity and hardenability. In short JIS SUP6 has more stable quality than 65mn steel.

When to Use Them? When Not?

No grade except for DIN 66Mn4 is truly interchangeable with 65Mn steel. Every grade has its own suitability for a specific application. Whenever, 65Mn steel is explicitly mentioned for a particular use, it must be preferred over other grades. However, in conditions where finding an equivalent grade becomes necessary, llok for the mechanical properties comparison. It is best to consult the manufacturer regarding the equivalence.

65Mn Steel vs Other Steels

65Mn steel belongs to the spring steels classification. Other classifications like tools steels, alloy steels and stainless steels have different functions. However, in some application other steel types can also be put into place is their properties find a suitability.

65Mn vs 1095 Steel

In comparison to 1095 steel, 65Mn has a lesser carbon content. It make 1065 steel more flexible and tougher than 1095 steel. So in applications where flexibility is not required like knives, razors and cutting tools 1095 steel provide more hardness on a lesser cost. On the other hand, 65Mn steel is used in applications like springs, blades, clips and wear tools.

65Mn Steel vs D2 Steel

D2 steel with a higher hardness value than 65 Mn steel is suitable for applications like dies and cutting tools. But D2 steel offers a lower toughness and more brittleness. So, in springy and elastic applications 65Mn is preferred.

65Mn vs Stainless Steel

The basic purpose of stainless steels is corrosion protection. 65Mn steel cannot provide a durable corrosion protective layer on its surface. Some stainless steel grades like 301, 302 and 17-7PH can match the mechanical properties of 65Mn steel.

Applications of 65Mn Steel

Agricultural Machinery

A wide range of agricultural machinery and equipment are being made up of 65Mn steel. This material has the ability to withstand repeated impacts, soil abrasion and bending loads. Tillers, harvesters, plow blades and shovels are extensively being made up of 65Mn steel.

Cutting Tools

65Mn steel maintains a good edge retention at a high sharpness level. It is a lower in cost than other competitive materials. As a result, machetes, axes, saw blades and pruning tools are made up of 65Mn steel.

High Quality Blades

Similar to the cutting tools, survival knives, outdoor blades, camping tools, throwers, and impact blades are being made of 65Mn steel.

Custom Machining Projects

Custom designed parts like springs, clamps, washers, wear plates, industrial and components are requested to be made up of 65Mn steel. Give us your inquiry and get a quote for custom machining projects.

Conclusion

65Mn steel belongs to the spring steels family. It exhibits high hardness, high yield strength, fatigue resistance, high elasticity and good edge retention. Specific heat treatment processes modify the mechanical properties of 65Mn steel in a certain ways. With a combination of good shaping strategies and proper heat treatment several useful parts are made out of 65Mn steel.

FAQs

Does 65Mn rust?

65Mn steel is prone to rusting to the absence of a corrosion protective layer.

Which is the best steel for a katana?

Traditionally, Japanese swordsmiths make a traditional type of steel called “tamahagane” for katana. However, 65mn steel can be used as an alternative material for katana.

Is 65Mn good for knives?

Yes. Properties like high hardness, springiness and edge retention make 65Mn steel suitable for knives.