cold work tool steel by NED Students

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Cold Work Tool SteelsTitle:

M.Ahsan (MM-34) Qamar Shafiq (MM-41)Usama Tahir (MM-10)

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Tool Steel:A TOOL STEEL is any steel used to make tools for cutting, forming, or otherwise shaping a material into a part or component for a definite use. The earliest tool steels were simple, plain carbon steels.

Examples of Tool Steel:

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TYPES OF TOOL STEEL:Tool Steel can classified it into following types.

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These steels are used for making tools for cold work applications, when the tool surface temperature does not rise more than 205 to 260 °C (400 to 500 °F). These are characterized by high abrasion & wear resistance , average toughness and heat softening resistance.They are used in production of larger parts or parts that require minimal distortion during hardening.

Cold Work Tool Steel:

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Cold work tool steel are divided into 3 groups:1. Air hardening Steels (grade ‘A’)

2. Oil hardening Steel (grade ‘O’)3. High Carbon , High Chromium Steels(grade ‘D’)

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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˚C.

Applications: Taps Blanking & forging dies Threading dies Expansion reamers.

1.Oil Hardening Steels: (grade ‘O’)

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1.Oil Hardening Steels: (grade ‘O’)Examples:

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It is one of the most well respected oil-hardening tool and die steels. It is easy to machine. Normal care in treatment gives good results in hardening and produces small dimensional changes. It has good abrasion-resistance, and sufficient toughness for normal tool-and-die applications.

AISI 01:

Composition:

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• MachinabilityThe machinability of O1 steels is very good with a rating of 90% that of water hardening low alloy steels.

• HardeningO1 steels should be heated uniformly to 780-820°C (1436-1508°F) until completely heated through. If needed, the steels can be preheated at 300-500°C (572-932°F). About 30 min/per 25 mm of ruling section is to be provided and then the steels should be immediately quenched in oil.

• Dimensional StabilityWhen quenched from the proper hardening temperature this grade normally expands .0015 in./in. plus. In many instances a slight scaling will occur during heat treatment which tends to counteract this expansion. Like all tool steels, hardening of 01 to insure minimum size change careful study of the die or tool and the furnace equipment used for heat treatment.

• Cold WorkO1 steels can be easily cold-worked in the annealed condition .

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1.Oil Hardening Steels: (grade ‘O’)• Heat TreatmentThe heat treatment requires O1 steels to be slowly preheated to 649°C (1200°F) and then heated at 788-816°C (1450-1500°F). Then these steels should be held at the same temperature for 10 to 30 minutes and finally oil quenched.

• AnnealingAnnealing should be performed at 788°C (1450°F) followed by slow furnace cool at a temperature less than 4°C (40°F) per hour.

• TemperingTempering of O1 steels is performed at 177-260°C (350-500°F) to realize Rockwell C hardness of 62 to 57.

• ForgingForging of O1 steels can be performed at 1038°C (1900°F) down to 857°C (1575°F) but not below 816°C (1550°F).• MartemperingMartempering is a substitute hardening procedure which can be used along with suitable salt bath equipment.

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1.Oil Hardening Steels: (grade ‘O’) ApplicationsTypical applications for O1 tool steel include medium run dies, press tools, drawing punches, broaches, bushings,chuck jaws, paper cutting machine knives, plug gauges, thread gauges and precision measuring tools. Also commonly used in applications such as cams, cloth cutting knives, cold taps, reamers, collets, cutting hobs, strip slitting cutters, trimmer dies, tube expander rolls, plastic moulds and woodworking knives.

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Microstructure of AISI O1 1000x

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1.Oil Hardening Steels: (grade ‘O’)Hardness VS Tempering Temp.

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These are hardened by air – quenching and contain Carbon (1.0%) with Manganese , Chromium & Molybdenum and Tungsten. These are characterized by wear resistance and high hardenability , fair red hardness , good toughness & resistance to decarburization..Tempering temperature for these steels varies from 150-425˚C.Applications: Knives Blanking & Trimming dies. Coining dies.

2.Air Hardening Steels: (grade ‘A’)

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• Cold WorkingA2 tool steels are cold worked in the annealed condition.

AISI A2:

• ForgingA2 tool steels are forged between 1093 to 913°C (2000 to 1675°F). These tool steels should not be forged below 899°C (1650°F).• FormingForming of A2 tool steels is carried out by machining or hot forging.

• MachinabilityA2 tool steels have medium machinability.

The data below will provide an overview of A2 air-hardening, medium-alloy, cold-work tool steels.

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2.Air Hardening Steels: (grade ‘A’)• Heat Treatment1.Annealing—Heating slowly and uniformly to 845~870℃, furnace cooling to 540℃ at a rate 8~15℃/h. Hardness max. HB 248 2.Stress Relieving —Heat to 650~675℃, furnace cooling. 3.Hardening— Preheating: Heat to 790℃, holding 20 minutes per 25 mm. Austenitizing: Heating to 925~980℃, holding 20 minutes per 25 mm. Quenchant: By air. 4.Tempering— Heating to175~540℃, holding 30 minutes per 25 mm. Air-cooling. Hardness HRC 63 to HRC 54

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A2 MicroSturcture 1000x

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2.Air Hardening Steels: (grade ‘A’)Applications Of Air Hardening Steels:

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2.Air Hardening Steels: (grade ‘A’)PROPETIES:Group A tool steels exhibit minimum distortion and the highest safety (least tendency to crack) in hardeningchromium, and molybdenum are the principal alloying elements used to provide this deep hardening moderate resistance to softening at elevated temperatures.

CLASSIFICATION:A2, A3, A7, A8, and A9 contain a high percentage of chromium (5%), which provides moderate resistance to softening at elevated temperatures. Types A4, A6, and A10 are lower in chromium content (1%) and higher in manganese content (2%). They can be hardened from temperatures about 110 °C (200 °F) lower than those required for the high-chromium types, further reducing distortion and undesirable surface reactions during heat treatment.

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2.Air Hardening Steels: (grade ‘A’) Silicon is added to type A8 To improve toughness, both silicon and nickel are added to types A9 and A10 Because of the high carbon and silicon contents of type A10, graphite is formed in the microstructure; as a result,

A10 has much better machinability when in the annealed condition, and somewhat better resistance to galling and seizing when in the fully hardened condition, than other group A tool steels.

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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 from showing Grain coarsening (upto 1040˚C). Chromium imparts non-deforming properties. Tempering of these steels results in high hardness, wear & abrasion resistance.Tempering temperature for these steels varies from 150-375˚C.

Applications:

Mandrel for tube rolling by Pilger rolls. Blanking & piercing dies, Coining dies, Drawing dies.

3.High Carbon, High Chromium Steels: (grade ‘D’)

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3.High Carbon, High Chromium Steels: (grade ‘D’)AISI D2 :

• Machinability:D2 has a machinability rating of 65, as compared with a rating of 100 for a 1 pct carbon tool steel. • Dimensional StabilityTests on this grade normally show a slight amount of contraction after hardening with the part in the as-quenched condition or tempered below 900F. Tempering at approximately 925F usually eliminates this contraction and brings the part virtually back to its original size. D2 has the minimum distortion in heat-treatment as compared with other tool steels.

• Description: D2 is a high carbon, high chromium alloy tool steel. It is a tool steel with high dimensional stability in heat treatment. A microstructure with coarse complex carbides provide a steel with high wear resistance and good toughness. • Compositio

n:

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3.High Carbon, High Chromium Steels: (grade ‘D’)• Annealing : Use a controlled-atmospheric furnace or pack in some inert material in a sealed container to prevent decarburization. To anneal, heat slowly to approximately 1600°F to 1650°F and hold at temperature for 1-1/2 hours for each inch of greatest thickness. Cool slowly at a rate of 20 degrees per hour to 900°F, after which the steel may be allowed to cool down with the furnace. Resulting hardness will be Brinell 217 max. • Hardening: Hardening should be done in neutral salt bath, fluidised bed or other controlled atmosphere furnaces. Preheat slowly to 300-800°C then raise to 980-1020°C, followed by air cooling. It is essential to soak at hardening temperature for 10-20 minutes. Obtainable hardness 63 – 65 HRC.

• Tempering: Tempering should be carried out immediately on completion of quenching. For maximum hardness and abrasion resistance heat to 150-250°C holding at temperature 1 hour for each 25mm of section. Tempering curve given indicates typical values obtained from air cooling from 1010°C. Nitriding treatment for improved retention of hardness is recommended for certain applications.

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Microsturture of AISI D2:

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Hardness VS Tempering Temp.

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3.High Carbon, High Chromium Steels: (grade ‘D’) APPLICATIONS: High duty cutting tools (dies and punches), long run form rolls, tube mill rolls, deep drawing tools for sheet and strip, shear blades, circular shears, thread rolling dies, small moulds for plastic industries and pressing tools for ceramic industries.

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APPLICATIONS OF AISI D2:

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cold work tool steel by NED Students

Engineering

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