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    DARI JOURNAL : TEKNOLOGI MATERIAL PROSES.

    EFEK HEAT TREATMENT PADA MIKROSTRUKTUR DAN PROPERTI

    MEKANIK PADA CR-V-MOSTEEL MELALUI METODE RAP

    (RECRYSTALIZATIONANDPARTIALMELTINGMETHODE)

    NAMA : HENGKI IRAWAN

    NRP : 2714201002

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    1. INTRODUCTION

    Excellent mechanical properties, such as hardness, toughness,

    strength, and corrosion resistance, are the most important criteria

    in evaluating tool steels owing to the wide utilization of these steels

    in machine tools and dies.

    microstructure containing a fine-grained martensite matrix with auniform carbide precipitation distribution is a guarantee of highquality

    tool steel products

    The conventional multipass hot rolling method consumes large

    amounts of energy and time in the long process chain of manufacturing

    steel for machine tools and dies

    a new processing route with lower time and energy consumption is

    required. The recrystallization and partial melting (RAP) method invented

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    CONTINUED

    The characteristic microstructure of a semisolid metal, i.e., equiaxed solid

    particles surrounded by a liquid matrix affects its forming behavior and the

    distribution of alloying elements in the alloy billet showed that RAP involves

    the partial melting of recrystallized metal slurry

    The capability of the RAP method, which entails cold or warm working to

    introduce a critical strain into an alloy and heating the alloy to above thesolidus temperature, for fabricating tool steel slurries has been investigated

    and verified by Meng et al. (2012). In the improved tool steel manufacturing

    route proposed by Meng et al. (2013), a RAP-processed material is

    deformed in the semisolid state and then subjected to heat treatments.

    investigated the microstructure and mechanical properties of semisolid

    X210CrW12 tool steel treated under various heat treatment conditions and

    pointed out that complex multiphase microstructures with excellent wear

    resistance and hardness can be achieved by adjusting the cooling rate and

    the time of isothermal aging.

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    CONTINUED

    The microstructural evolution of cast CrVMo steel (JIS SKD61, AISI

    H13, DIN 1.2344) during various heat treatments was clarified. Vickers

    hardness measurements, tensile tests, and Charpy impact tests were carried

    out to determine the effects of heat treatments on the mechanical properties

    of semisolid treated CrVMo steel.

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    2. EXPERIMENTALPROCEDURE

    2.1. Material

    o Melting material then cast to block which size 180 mm dia and 200 mm height machines the matluntill size 50 x 20 x 10 mm then compressed to 50% height

    reduction at 300 oC , partially melted at 1385 oC for 20s and cooled in cold water.

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    2.2 HEATTREATMENT

    Various heat treatments were performed using a resistance furnace,as shown

    in Fig. 2. The specimens were protected by ceramic wool. In the annealing

    treatment, all of the RAP-processed specimens were held at 850 C for 3 h

    and then cooled in a furnace

    Thesubsequent quenching was carried out by heating the specimens to 950,

    1000, 1050, or 1100 C and cooling them in air after isothermal holding for

    480 s

    Following the quenching treatment, specimens were tempered twice at

    temperatures ranging from 200 to 800 C for 1.5 h and subsequently cooled

    in air

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    2.3. MEASUREMENTOFMECHANICAL

    PROPERTIES

    Vickers hardness

    Tensile strength and elongation

    High temperature wear test (ASTM D 5707-11)

    Impacted test

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    2.4. METALLOGRAPHYOBSERVATIONS

    Scanning Electron Microscopy (SEM)

    Energy-dispersive X-Ray (EDS)

    X-ray Diffraction (XRD)

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    3. RESULT

    3.1. Starting Material

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    3.2. QUENCHING

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    CONTINUED

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    3.3. TEMPERING

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    CONTINUED

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    CONTINUED

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    CONTINUED

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    CONTINUED

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    4. DISCUSSION

    4.1. Effect of quenching

    Calculate the Ms start and Ms Finish material

    according to the result of EDS Analysis.

    Microstructure effect : large tensile residual stress

    cause higher hardness and lower ductility, large

    ammount retained austeniet cause lower high temptwear strength, large ammount chain like carbide

    have lower tensile and elongation strenght and

    decrease impact value.

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    CONTINUED

    Various quenching temp results various average hardness , when

    quenching temperatur is increased from 950 to 1050, more carbide

    dissolve in the austenitic matrix because of the number possiblity

    position of carbon atoms increase at higher temp. , thus :specimen

    quenched at 1050 is harder than the others.

    On the other hand execesice austenization at a higher temp increasethe alloying element content of austenite cause lower martensite

    temp and more retained austenite.

    A higher temp quenching also cause grain growth, a coarsed grain,

    more retained austenite means lead to lower hardness and low

    tensile strenght.

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    4.2. EFFECTOFTEMPERING

    The purpose of tempering is to reduce the residual stress an

    dtransform retained austenite to martensite

    Temper 200 400 oC : diffusion alloying element too weak for

    transformation retained austenite to martensite, recovery of

    dislocation in martensite, the presipitation of carbide from martensite

    and coarse tempered martensite structure.

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    CONTINUED

    Tempering 400-600 oC

    Causes microstructural evolution in both the former liquid-phase and

    solid-phase regions and changes the morphology and distribution of

    carbides. In the former solid-phase regions, martensite is transformed to

    tempered martensite and secondary carbides

    In the former liquid-phase regions, diffusion eliminates chain-like carbidesand decreases the alloying element content of the retained austenite.

    A lower alloying elements results in a higher martensite starting

    temperature. The retained austenite partially transforms to martensite

    and secondary carbides

    The homogenization of alloying elements shown in Fig. 13b is attributedto the precipitation of carbides from the initial martensite and the diffusion

    of alloying elements at higher tempering temperatures

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    CONTINUED

    The precipitated secondary carbides and newly formed martensite

    increase the hardness of the specimen, as shown in Fig. 14. This

    phenomenon, which occurs during the tempering of high-alloy tool steels

    is called secondary hardening

    the release of residual stress and the microstructural evolution caused by

    tempering. The elimination of chain-like carbides in the former liquid-phase regions and the decreased residual stress improve the ductility and

    impact toughness of the specimen

    The decrease in the amount of retained austenite and the homogeneous

    distribution ofcarbides result in better resistance to high-temperature wear

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    CONTINUED

    Temp ecceeds 600 oC : almost all the retained austenite transforms to

    martensite. Grain growth and the combination of carbides occur at high

    temperatures.

    Large amounts of alloying elements are distributed at the boundaries of

    martensite grains The coarsening of the microstructure leads to low tensile

    strength but high elongation

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    5. CONCLUSION

    1. After quenching, the RAP-processed specimen exhibited high but

    inhomogeneous hardness owing to its inhomogeneous microstructure. Its

    low ductility, poor impact toughness, and poor resistance to high-

    temperature wear were mainly attributed to retained austenite and chain-

    like carbides in the former liquid-phase regions.

    2. The specimen quenched from 1050 C exhibited better mechanicalproperties than the specimens quenched from other temperatures. The

    inhomogeneous hardness could not be eliminated by adjusting the

    quenching temperature.

    3. The hardness of the tempered specimen changed nonlinearly with

    increasing tempering temperature. The tempering treatment resulted in a

    uniform distribution of alloying elements and homogeneous hardness.

    4. The microstructural evolution caused by tempering improved the ductility of

    the tempered specimens. When the tempering temperature was 560 C, a

    good combination of mechanical properties was achieved.

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    THANKYOU