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VACCUM HARDENING PROCESS

Hot-worked Tool Steels

  • Carbon-content =0.3-0.5%.These Steels are used for high temperature metal forming operation (except cutting), where the temperature is around 200-800 degree Celsius.
  • These are characterized by high hot yield strength, high red hardness, wear resistance, toughness, erosion resistance, resistance to softening at elevated temperatures, good thermal conductivity.
  • These are divided into 3 groups depending on the principle alloying elements:
    1. Chromium-based [H11-H19]
    2. Tungsten-based [H20-H26]
    3. Molybdenum-based [H41-H43]

Chromium-based

  • Contains Chromium (>=3.25%), and small amounts of vanadium, Tungsten, and molybdenum.
  • These are characterized by High red Hardness & high hardenability.
  • Oil quenching is required when dimensional stability is not of prime importance. Tempering temperature for these steels varies from 550-675 degree Celsius.
  • Applications:
    1. Hot dies for extrusion, forging, mandrels, punches.
    2. Highly stressed structural parts of supersonic aircrafts.
    3. Hot work steels

Tungsten based

  • Contains Tungsten (=9.00%) & Chromium (2.0 -12.0%), and low carbon %.
  • These are characterized by resistance to high temperature softening.
  • Tempering temperature for these steels varies from 550-675 degree Celsius.
  • Applications:
    1. Punches
    2. mandrels
    3. Extrusion dies for Brass, Steel &Nickel alloys.

Molybdenum based

  • Contains Molybdenum (8.00%) & Chromium (4.0-12.0%), and some tungsten and vanadium.
  • These are characterized by high toughness & high heat check resistance.
  • Tempering temperature for these steels varies from 550-650 degree Celsius.

Vacuum-Hardening of Hot-Work Tool Steel

 


Microstructure of H-13 Tool Steel (1000x)

 


Microstructure of Annealed H-13 Tool Steel

 


NADCA Specification #207-2006


Banding/Microsegregation Chart


 

Annealed Quality Microstructure chart


Heat Treatment Quality Microstructure Chart



Cold-worked Tool Steels

  • These steels are used for making tools for cold work applications, when the tool surface temperature does not rise more than 200 degree Celsius.
  • These are characterized by high abrasion & wear resistance, higher toughness and high impact resistance.
  • These steels are also called “Non-distorting steels”, as they show little change in dimension during heat treatment.
  • These are divided into 3 groups:
    1. Oil hardening Steels [GRADE ‘O’]
    2. Air hardening Steels [GRADE ‘A’]
    3. High Carbon, High Chromium Steels [GRADE ‘D’]

Oil-hardening Steels

  • These are hardened by oil-quenching & contain high carbon with manganese, chromium, molybdenum.
  • These are characterized by high machinability, wear resistance, and non-distorting properties.
  • Tempering temperature for these steels varies from 100-425 degree Celsius.
  • Applications:
    1. Taps
    2. Blanking and forging dies
    3. Threading dies
    4. Expansion reamers

 Air-hardening steels

  • These are hardened by air-quenching & contain carbon (1.0%) with manganese, chromium, molybdenum & tungsten.
  • These are characterized by high wear resistance & high hardenability, fair red hardness, good toughness and resistance to decarburization.
  • Tempering temperature for these steels varies from 150-425 degree Celsius.
  • Applications:
    1. Knives
    2. Blanking and Trimming dies
    3. coining dies

 High Carbon, High Chromium Steels

  • These are hardened by oil- or air-hardening & contain carbon (1.4-2.3%) & chromium (12-14%), with molybdenum, cobalt, vanadium.
  • Vanadium prevents these steels form showing grain coarsening (up to 1040 degree Celsius). Chromium imparts non-deforming properties. Tempering of these steel results in high hardness, wear & abrasion resistance.
  • Tempering temperature for these steels varies from 150-375 degree Celsius.
  • Applications:
    1. Mandrel for tube rolling by pilger rolls.
    2. Blanking and piercing dies, coining dies, drawing dies




 

High Speed Tool Steels

  • These are highly alloyed tool steels developed initially to do high speed metal cutting. Now they used in a wide variety of machining operations.
  • These are characterized by high hardness (60-65 HRC at 600-650 degree Celsius), high red hardness, wear resistance, reasonable toughness and good hardenability.
  • They contain 0.6% carbon, 4% chromium, 5-12% cobalt.
  • Carbon imparts hardness of at-least 60 HRC of martensite formed. Chromium increase hardenability & corrosion resistance. Cobalt increases the thermal conductivity, melting point, red hardness & wear resistance of high speed steels.
  • These are divided into 2 groups depending upon the principal alloying elements & the composition:
    1. Molybdenum high speed steel [GRADE ‘M’]

(Contain molybdenum, tungsten, chromium, vanadium & sometimes cobalt)

    1. Tungsten high speed steel [GRADE ‘T’]

(Contain high amount of tungsten with chromium, vanadium and some cobalt)

  • Application:
    1. End mills, drills, lathe tools, planar tools.
    2. punches, reamers
    3. Routers, taps, saws
    4. Broaches, chasers, and hobs.

Typical heat treatment cycle for HSS



 



 

Note: Photographs and illustrations are more for clarity and educative purpose of the business we do and not necessarily in original form of our service centers

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