D2 steel hardness, composition, properties, applications

D2 steel hardness | composition | Microstructure | applications

D2 steel belong to the group of cold-worked steel. This group of steel have wide range of application in cold mechanical working like forming dies, and blanking dies. These steels are also termed as non-deforming or non-distortion steels. SKD-11 tool steel is basically high chromium and high-carbon steel. Hudson knives are manufactured most commonly using D2 tool steel.

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UNS Number

T30402

D2 steel composition

Main alloying elements in steel are carbon, chromium, molybdenum and vanadium. High chromium addition improves abrasion and wear resistance. With other alloying elements, these properties get further boost.

Composition of D2 steel is as follows according to ASME tool Steel or SKD 11;

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GradesASME D2 SKD 11                      
Min %Max %Min %Max %
C1.41.61.41.6
Mn0.10.6<0.6
P<0.03<0.03
S<0.03<0.03
Si0.10.6<0.04
Cr11131113
Mo0.5110.20.5
V0.71.20.81.2

D2 steel hardness & D2 tool steel heat treatment

Commonly heat treatment cycle followed for SKD 11 with variant in composition is given below;

CompositionHardnening Temperature (C)Quenching mediumHardness (as-quenched)TemperingHardness (after tempering)
1.50 % C 1.00 % Mo 12.00% Cr 1.00% V980 - 1025Air61 - 63200 - 37558
2.25 % C 12.00% Cr950 - 980Oil62 - 64200 - 37558
1.50 % C 1.00 % Mo 12.00% Cr 3.00% V980 - 1025Air60 - 62200 - 37557
2.35 % C 1.00 % Mo 12.00% Cr 4.00% V1010 - 1065Air63 - 65150 - 250 & 450 - 55063 & 68

Hardness is measured using Rockwell Hardness Tester.

Common defects that you may encounter during heat treatment can be found in the article, “Common defects in heat treatment of steel and their possible remedies“.

As you can see, in composition independent of V and Mo, Austenitizing temperature is less. Alloying elements slow down the diffusion mechanism. Effect of alloying elements can be better understood from the article, “Alloying elements effect on steel” and TTT diagram in steel”.

SKD-11 Microstructure

D2 tool steel, SKD-11
D2 tool steel – SKD-11 microstructure

In D2 tool steel, the addition of high chromium content and carbon content shifts nose in the TTT diagram towards the right and simple air-cooling results in martensitic formation along with carbides of other alloying elements. At 1392 ͦC austenite forms and as the temperature drops to 1242 ͦC, M7C3 carbides start to form on austenite grain boundaries. As the temperature drops austenite fraction is reduced near the eutectoid temperature whereupon reaction austenite is converted to ferrite and M7C3 carbides grow and increase in content.

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It is followed by M23C6 by the dissolution of the M7C3 carbides. Depending on the size and morphology of these different carbides different mechanical properties are inherited in the steel. The Purpose of fine carbides is to resist plastic deformation. While coarse carbides are responsible for higher abrasion and wear resistance. 

SKD-11 Physical Properties

Physical Properties 
Specific Gravity7.83
Density0.283 lb/in3
Melting Point1420 C
Thermal Expansion (/C)10.4 * 10^-6

D2 tool steel Mechanical properties

Mechanical Properties
PropertyUnitValue
HardnessHV748
HardnessHRC62
Impact strengthJ77
Poissons Ratio0.27 - 0.3
Elastic ModulusGpa190 - 210
Compressive StrengthGPa2.76

Decarburization

SKD 11 is cold-worked tool steel containing high carbon concentration. This high carbon concentration makes SKD 11 extremely prone to decarburization. The modern furnaces are equipped with a special atmosphere which protects the SKD 11 steel from decarburization during thermal processing.

Normalizing

High carbon high chromium steels are used for cold-work application and they are practically free from distortion. With faster cooling, chances of stress may cause distortion. So, normalizing should be avoided. Normalizing is also not needed as martensitic formation takes place even in furnace cooling so is also not needed.

Annealing

Annealing is a common practice for SKD 11. For annealing, SKD 11 should be packed in a container consisting of a neutral atmosphere or furnace equipped with protecting the gas atmosphere. Austenitizing temperature for D2 steel should be above 900oC. Below this temperature, the diffusion of alloying elements is limited. After soaking uniformly, steel is cooled slowly. Annealing practice can be studied in the article, “Annealing practice”.

Forging

D2 tool steel forges like high speed steel. Forging temperature should be maintained above 927oC. If temperature of forging drops below 900o C, reheat to maintain the forging temperature uniform.

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During cooling stage, small casting can be easily cooled slowly using furnace cooling. In case of large casting, best practice is to place the steel part in furnace maintained at temperature of 850o C, hold it for some time for uniform temperature distribution and, then, shut off the furnace for slow cooling.

It should be remembered; this is not annealing. After forging, large steel parts should be annealed separately using the annealing cycle mentioned in the Annealing section.

D2 steel welding

D2 steel is considered difficult for welding. The reason for this difficulty is a high concentration of carbon and alloying elements carbides.  Conventional welding processes are not recommended for SKD 11 welding.

A new welding technique called Thixowelding is considered suitable for welding SKD 11 with varying joining temperature and other parameters.

D2 Steel Knife

As discussed earlier, it is high carbon-high chromium non-deformable steel. Low distortion is one of the main characteristics of D2 steel which makes it an ideal choice for knife users.

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Now, the Selection of a knife can be cost dependent. Some knives are costly and you cannot fool around with getting into the guilt of abusing money. Here comes the twist, D2 steel provides all-around performance at a relatively lower cost making it a very optimum choice for blade users.

Here are top D2 blade steel that you must look into. You can purchase them from AMAZON.

  • Ontario Rat II Pocket Knife

This is the RAT II model of the Popular Ontario Blade series. It is considered the successor of RAT 1. The people involved in Hunting and Hiking should really pay extra attention to this knife as its built is designed for heavy-duty cutting power. It’s specially made in such a way to withstand serious abuse. The handle is made of Nylon which is lightweight and corrosion resistance which prolongs the knife usability.

  • ESEE Avispa Folding Knife

If you are not a fan of the Ontario series and interested in something pure steel. This knife is totally built for you. Instead of a Nylon handle, Stainless steel lock has been used maintaining the raw look and elegant design. The blade is again made of D2 making it one of the best steel for the market at a low price.

  • Steel Will Intrigue Flipper

The elegant design and sort of gentlemen’s look make this knife so much desirable. It’s a good alternative for a high pricey knife if the budget is mid-range.

D2 steel Applications

  • Cutting tools e.g. dies and punches
  • Wood working tools
  • Blanking tools
  • Tube Mill Rolls
  • Shear Blades
  • Thread Rolling Dies
  • Dies and Punches
D2 Steel applications
SKD-11 tool steel applications

References

  1. ASME handbook Vol – 4, “Heat Treating