influence of surface hardening method on wear...

18. - 20. 5. 2011, Brno, Czech Republic, EU

INFLUENCE OF SURFACE HARDENING METHOD ON WEAR BEHAVIOURS OF 1.2311 AND 1.2379 STEELS

Pavla KLUFOVÁ a, Jiří HÁJEK b, Antonín KŘÍŽ c, Stanislav NĚMEČEK d

a UNIVERSITY OF WEST BOHEMIA IN PILSEN, Faculty of Mechanical Engineering, Univerzitní 22, 306 14 Pilsen, Czech republic, [email protected]

b UNIVERSITY OF WEST BOHEMIA IN PILSEN, Faculty of Mechanical Engineering, Univerzitní 22, 306 14 Pilsen, Czech republic, [email protected]

c UNIVERSITY OF WEST BOHEMIA IN PILSEN, Faculty of Mechanical Engineering, Univerzitní 22, 306 14 Pilsen, Czech republic, [email protected]

d MATEX PM, s.r.o, Rokycanská 58, 301 00 Plzeň, Czech republic, [email protected]

This paper was prepared in the framework of a project entitled “Mobile Station for Laser Treatment of Steel”

supported by the Ministry of Industry and Trade of the Czech Republic under the Operational Programme

Industry and Enterprise, Innovative Action Pilot Project – Knowledge Transfer Support.

Abstract

This paper deals with wear behaviour of laser-hardened steels No. 1.2311 and 1.2379 as evaluated by pin-

on-disk test. In order to obtain comparison with other treatment methods, both steels were treated by laser

hardening, induction hardening and through hardening with heating in furnace. The goal of the paper is to

give comparison of wear behaviour of materials upon different surface hardening treatments: laser and

induction hardening.

Keywords: laser-hardening, induction-hardening

1. EXPERIMENTAL

The steels 1.2311 and 1.2379 were heat treated using the following methods:

laser hardening

high-frequency induction hardening

through hardening

Heat-treated steels were examined by metallographic methods, surface hardness measurement and by pin-

on-disk wear test.

Laser hardening was used to obtain continuous hardened layer on the surface. As measurement in the areas

of overlap between hardening passes would make evaluation and comparing with the other hardening

methods much more difficult, the tribological test track was in all cases laid right over the hardening pass and

not in the overlap area (see Fig. 1).


The resulting tribological test track was observed in a Carl Zeiss light microscope which was capable of

accurately positioning the specimen and offering readings of the “z” coordinate of the distance from the

specimen surface plane. The total of 4 measurements were made in A, B, C and D regions of each

tribological test track (see Fig. 2).

Measured values for 4 tribological test track profiles in various locations were converted into arithmetic

average values and plotted in graphs in sections 2 and 3.

Fig. 1 Location of the tribological test tract between overlaps of laser hardening passes

Fig. 2 Areas of measurement of the tribological test track profile


2. EXPERIMENTAL RESULTS – 1.2379 STEEL 2.1 Microstructure and surface hardness HV 10

Fig. 3 Steel grade 1.2379 upon laser hardening,

3% nital etch

499 ± 53 HV 10

Fig. 4 Steel grade 1.2379, induction hardened,

3% nital etch

Fig. 5 Steel grade 1.2379, through hardened,

3% nital etch

456 ± 10 HV 10

792 ± 68 HV 10


Comparison of micrographs in Figures 3 through 4 and HV 10 surface hardness values reveal the effects of

heating rate and holding time at austenitizing temperature before quenching upon dissolution of carbon and

alloying elements in the matrix. Laser and induction hardening are accompanied by negligible redistribution

of carbon. This is thanks to high heating rates and short austenitizing times. On the other hand, the matrix of

through-hardened 1.2379 shows much greater level of carbon saturation. This is reflected in measured HV10

hardness values. Microstructures shown in Figures 3 and 4 contain carbides, retained austenite, martensite

matrix but also tempered martensite and sorbite. Tempered microstructure resulted from insufficient heat

dissipation during surface hardening.

2.2 Wear evaluation – Pin-on-Disk method

Curves in Fig. 6 show the differences between wear behaviours of laser-hardened and induction-hardened

surfaces and through-hardened steel 1.2379. Very interesting aspects are the different depths and widths of

tribological test tracks in laser and induction-hardened samples. These notable differences were caused by

different orientations of carbides in the parent metal. Values in the graph in Fig. 6 indicate the ratios between

the cross-sections of test tracks and the total image area. The total image area was adapted using Axiovision

software for Carl Zeiss microscope to the size of 1024×768 pixels.

Fig. 6 Tribological test track profile

4,6 %

9,5 %

25,9 %


3. EXPERIMENTAL RESULTS – 1.2311 STEEL

3.1 Microstructure and surface hardenss HV 10

Fig. 7 Steel grade 1.2311 upon laser

hardening, 3% nital etch

Fig. 8 Steel grade 1.2311, induction hardened,

3% nital etch

655 ± 31 HV 10

767 ± 62 HV 10

539 ± 19 HV 10


Microstructures of 1.2311 steel in Figs. 7 through 9 are mostly mixed-type structures. Martensite, bainite and

retained austenite can be found in all micrographs. The microstructures mostly differ in the bainite and

martensite proportions and their grain sizes. This causes different HV10 surface values.

3.2 Wear evaluation – Pin-on-Disk method

The lowest wear values (smallest area above the curve in Fig. 10) were found in the induction-hardened

1.2311 steel. The amounts of wear of induction-hardened and through-hardened specimens were virtually

identical, although the difference in their surface hardness was about 150 HV10. This was due to differences

between their microstructures and grain sizes.

CONCLUSIONS

Results of wear testing of 1.2379 steel proved the importance of orientation of carbides in the microstructure

on the tribological behaviour of material. Whereas the laser-hardened 1.2379 steel exhibited high wear

resistance, the induction-hardened steel showed much greater amount of wear in pin-on-disk test.

In case of 1.2311, the difference between amounts of wear of laser and induction-hardened surfaces was not

as evident as in the 1.2379 steel, but it was still substantial and measurable, resulting from differences

between the microstructures.

Fig. 10 Tribological test track profile

6,6 %

9,7 %

9,6 %

influence of surface hardening method on wear...

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