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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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