THE INFLUENCE OF THE TYPE OF LASER WORK UPON THE ...metal2014.tanger.cz/files/proceedings/metal_01/papers/165.pdf · METAL 2001 15. - 17. 5. 2001, Ostrava, Czech Republic - 1 - THE

METAL 2001 15. - 17. 5. 2001, Ostrava, Czech Republic

- 1 -

THE INFLUENCE OF THE TYPE OF LASER WORK UPON THECONSTRUCTION OF TOOLING HIGH-ALLOY STEEL’S SURFACELAYER.

a) Józef Jasińskib) Jacek Selejdaka) Wanda Jeziorskaa) Aneta Markuszewskab) Robert Ulewicz

a) Technical University of Częstochowa, Department of Engineering material`sAl. Armii Krajowej 19B, PL 42-200 Częstochowa

b) Technical University of Częstochowa, Department of Management, Divisionof Production Engineering. Al. Armii Krajowej 19B, PL 42-200Częstochowa

AbstractThe work analysed the impact of continuous laser with varied beam velocity from

2.4⋅103 to 13⋅103 W/cm2 upon the structure and properties of the surface layer. Stratifiedconstruction of the surface layer was evaluated based on light and electron microscopy tests,as well as micro-hardness tests. Phase types and distribution were asserted on the basis ofroentgenostructural tests. In order to evaluate the hardening depending on beam power,functional interdependences were asserted.

1. INTRODUCTIONLaser applications in the metallurgical industry are quite universal. Laser beams are

used for cutting, welding, quenching, alloying, and the like. All these operations, in principle,are based upon the heat effect of radiation impact upon metals; but as compared to thetraditional heat processing methods, laser treatment has a number of advantages. Some of themost significant ones are: the operation’s contact-less nature, local character of heating, apossibility to obtain big temperature gradients, and high speeds of heating and cooling. Due tothese specific advantages, laser processing is used for hardening high-load surfaces ofmachines and tools (surfaces of bearings, toothed wheels, blades, etc.). Effects of suchprocessing are dependable upon a number of factors, such as: type of steel, type and densityof radiation power, processing time. Controlling these factors, we can obtain variousstructures, and what follows –various mechanical properties of steel [1, 2].

2. RESEARCH MATERIALIn the analyses, WCL hot-work tooling steel, and SW7M high-speed steel were used.

Tables 1 and 2 present the chemical constitutions of the analysed types of steel.

Table 1.Chemical constitutions of WCL steel

Chemical constitutions

C Mn Si Pmax

Smax

Cr Mo V

0,42 0,57 0,78 0,02 0,026 5,1 1,35 0,41


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Tabela 2Chemical constitutions of SW7M steel

Chemical constitutions

C Mn Si Cr W Mo V0,81 0,45 0,51 4,45 6,23 4,58 1,79

WCL steel analysis input material was a sample in the shape of a plate sized 40 x 15 x5 mm. The sample was cut off from a bar, and subjected to the soft annealing process.. The soft annealing process was conducted with the following parameters:- softening temperature - 8000C (1073 K)- time - 3h (10,8 ks)- cooling -with the furnaceSW7M high-speed tooling steel sample was enriched by diffusion in carbon and nitrogeninside a fluid bed furnace.The process of carbon-nitriding was conducted with the following parameters:- carbon-nitriding temperature - 9800C (1153 K)- time - 1h (3,6 ks)- excess air coefficient - αp=0,22- and ammonia addition into the atmosphere - 2,5 %Fig. 1 presents input microstructures of the materials used in the analyses: a) WCL, b)SW7M.

Fig. 1. Input material’s microstructure:a) WCL steel in the condition after softening, area x 500, etched with nitalb) SW7M steel in the condition after carbon-nitriding, area x 500, etched with natal

The samples were treated with continuous laser beams – 4 paths were madeupon a sample. The paths were arranged at the sample’s width, perpendicular to its length.Distances for steel between the subsequent paths were 8 mm. Fig. 2 presents sample schemeswith paths plotted upon them.

a) b)


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Fig. 2. Sample schemes with paths plotted upon them.

Diameters of laser bundles for the particular re-focusings were calculated according toformula (1), and power density – according to formula (2). Laser treatment parameters arepresented in Table 2.

d = f bf

∆ ∗ (1)

q = 4Qd2Π

(2)

Table 2.Parameters of laser treatment

Variantprocessing

changes offocusing∆f, mm

heat fluxQ, W

Speedtravellingv, mm/s

Laser beamdiameterd, mm

Powerdensity

103 W/cm2

1 12 800 12 2,80 13,00

2 16 800 12 3,73 7,30

3 24 800 12 5,60 3,30

4 28 800 12 6,53 2,40

3. RESEARCH RESULTSAs a result of the analyses conducted, it was found that for WCL steel, with a decrease

in power of a laser bundle, the thickness of a hardened layer increases. Analysing thedistribution of the hardened zone for SW7M steel, it was also found that laser bundle’s powerdensity exerts some influence upon the increase in thickness of the hardened zone; this zone,however, is thicker.

Fig. 3 compares the influence of laser bundle power density upon its interaction withanalysed sample materials.

8mm

5mm

40 mm

15 mm


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Fig. 3. The influence of laser bundle’s power density upon the thickness of a hardened layerof the analysed material.

Micro-hardness analyses were carried out using the Vickers method with the load of0.5 N. Analysed for micro-hardness were samples after laser treatment perpendicular to theirsurfaces, in the middle of a laser bundle’s focus. Fig. 4 presents micro-hardnessmeasurements’ results.

Fig. 4. Micro-hardness distribution in the zone hardened with laser beams perpendicular to thesample’s surface in the focus of the bundle for such materials as: WCL, SW7M.

As a result of SW7M steel metallographic analysis conducted, cracks were observed inthe zone of heat impact, which arose due to the occurrence of heat stresses, at the border of

0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0200

400

600

800

1000

12001300

Sample no 1, WCL, power density 13*103W/cm2

Sample no 2, WCL, power density 2,4*103W/cm2

Sample no 1, SW7M, power density 13*103W/cm2

Sample no 2, SW7M, power density 2,4*103W/cm2

Har

dnes

s H

V 0

05

Distance from the surface, mm

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0

0,1

0,2

0,3

0,4

0,5

0,6

0,7Th

ick

of h

arde

ned

laye

r, m

m

13*10E3 7,3*10E3 3,3*10E3 2,4*10E3

Power density W/cm

��WCL

��SW7M

2


carbide releases. Carbide releases have a striped morphology[3]. Fig. 5 presents characteristiccracks at the border of carbides’ striped releases. Analysing the structure of WCL steel heatinfluence after laser treatment, no occurrences of cracks were observed.

F

pow

F

b

a

a)

- 5 -

ig. 5. SW7M steel structure in the heat influencea) area x 100 etched with nital,b) area x 1000 etched with nital

Fig. 6 shows the SW7M steel surface awer density. Together with an increase in p

ider.

ig. 6. Sample surface at spots of a laser bundle a) sample no 1, area 35 x, power density 13 x b) sample no 2, area 35 x, power density 7.3 xc) sample no 2, area 35 x, power density 2.4 x

c)

)

zone with heat cracks shown:

fter passage of a laser bundle with varyingower density, the paths become wider and

b
)
i1

)

mpact:03 W/cm2,103 W/cm2,103 W/cm2


At Fig. 6 one can see, in the central part of the “path”, some arches that emerged as aresult of material shift caused by the movement of the laser radiation bundle. This effect canbe compared to the effect of a padding weld.

SW7M material’s stratified structure can be described using control model 4:- the first stratum arose as a result of re-melting of the material,- the second one is the stratum of partial melting of the material,- the third one – hardened material,- the fourth one – tempered material.

In effect of WCL steel’s surface treatment by means of continuous laser beams, a 3-stratum structure of the top layer was observed:- a bright white stratum,- having arisen from the re-melting of the material;- a hardened warp stratum;- and an intermediary stratum.Fig. 7 presents the stratified structure of WCL and SW7M steels.

F

4.Inth

F

b

a

a)

- 6 -

ig. 7. Stratified structure of the top layer of steea) WCL after treatment with continuous laser bb) SW7M after treatment with continuous laser

RECAPITULATION the course of the analyses conducted, it was noe analysed materials. Fig. 8 illustrates the struc

ig. 8. Scanning micro-structure etched with nitaa) WCL,b) SW7M

)

)

l:eams, beams

ted that re-melting zones occurred in both ofture of the analysed steels.

)
b
l area x 3500.


Fig. 8a shows partial meltings upon surfaces of the treated materials. As a result of avery fast disposal of heat, fine-acicular martensite and residual austenite arose. Also, thereappeared a process of coagulation of carbides, and a process of increasing their size. Lookingat Fig.6b, one can notice some very small releases in the acicular form. Due to the carbon-nitriding process carried out earlier, these could be needle-shaped releases of carbide nitrides.Carbides that can be seen at this photo are very fine and rather uniformly arranged.

Fig. 9 a, b depict the occurrence of a dendritic structure in the stratum of SW7M steelafter laser processing. Micro-hardness analyses results suggest that the heat impact zone waslimited by striped releases of carbides that did not allow the heat impact field to extend insteel SW7M, which was not observed in the case of steel WCL. Based upon the results aslisted at Fig 4, it is easy to see the increase in micro-hardness inside the hardened zone, at acertain distance from the surface for steel SW7M, whereas in the case of steel WCL, hardnessdecreases together with an increasing distance away from the surface.

Fiw

mphmSuloty

L1.

2.

3.

) b
a
- 7 -

g. 9. Dendritic micro-structure for steel SW7Mith bundle density 2.4*10W/cm2.

The structure as shown at Fig. 9b was acheltings, using nital. One can easily see dark gases. Dark areas are most probably martensite,ay be some releases of cementite eutectic (carface areas in other samples also posses the s

cated deeper away from the surface, a layer pical for a quick-cooled material. The micro-str

ITERATURE Zenker R., Reisse G., Zenker U.: „Niektóre

Konferencja Obróbki Cieplnej, Karl-Materiałoznawstwo i obróbka cieplna, nr 83-8

Serżysko J., Sobusiak T., Sokołow K. N.strukturę i własności stali szybkotnących”, Mpowierzchni, nr 99-100, 1989.

Kusiński J. Naprężenia własne w konstrlaserowej obróbce cieplnej, Materiały konOgólnopolska Konferencja Naukowa Kule 13

)

etched with nital, hardened with laser beams

ieved as a result of very strong etching of re-rains isolated from one another with white and the white phase in between these grainsrbides) at the borders of martensite grains.ame cellular structure. Looking at the areaswas obtained having a dendritic structure,ucture of this zone is illustrated at Fig. 9a.

aspekty laserowej obróbki cieplnej stali”, IIMarx-Stadt 1985, tłum. Strauss J.,4, 1986.

: „ Wpływ obróbki cieplnej laserowej naetaloznawstwo i obróbka cieplna, Inżynieria

ukcyjnych stalach chromowych poddanychferencyjne „Obróbka Powierzchniowa” II-15.10.1993.

THE INFLUENCE OF THE TYPE OF LASER WORK UPON THE ...metal2014.tanger.cz/files/proceedings/metal_01/papers/165.pdf · METAL 2001 15. - 17. 5. 2001, Ostrava, Czech Republic - 1 - THE

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