Preparing Surface Treated Steel Samples in Minutes Using the PlanarMet 300 Planar Grinder and EcoMet/AutoMet

Consistent and effective preparation of surface treated steel samples is required for production and quality control setups. Consistent material removal rates and material flatness are vital to gain repeatable results. For surface treated steels, quick material removal and surface planarity can be achieved using the PlanarMet 300. This article discusses a new sample preparation method for microstructure analysis and hardness testing of hardened and nitrided C15E steel, and hardened C45 steel.

Preparation

Sectioning

Hardened zone samples were cut for further mounting processes. Serial sectioning can be carried out at various locations on the sample. The AbrasiMet™ 450 was used for the sectioning process, with abrasive wheels for medium hard ferrous materials.

Mounting

An EpoMet F compression mounting compound was used to mount the surface treated steel specimens on the SimpliMet™ XPS1 (Figure 1). Prior to mounting, the nitrided samples were covered with aluminum foil to prevent the nitrided layer from any damage during preparation. Table 2 shows the equipment and consumables needed for the mounting operation.

Mounted specimens clamped in a central force holder.

Figure 1. Mounted specimens clamped in a central force holder.

 

Grinding and Polishing

Preliminary grinding was performed by using the PlanarMet 300. This shortens the time taken for preparation and produces exceptionally flat samples. The parameters used are listed in Table 3.

Table 1. Grinding and Polishing Parameters

Grinding setting
Load 40.5 lbs [180 N] (for six samples)
Cycle time 1:10min
Head RPM 120
Platen Contra
Wheel Type Aluminum oxide wheel, 120 [P120] grit

For the preliminary grinding stage, a 120 [P120] grit alumina stone was used to achieve a considerable material removal and a distinct surface finish, needed for subsequent steps. This reduced the time taken for the total preparation, with a better preparation of the samples for the later steps.

Polishing of the samples was carried out using the Ecomet/AutoMet 300 and a 12 in [305 mm] platen. The mounted samples were polished in two steps in a central force mode. Table 4 shows the grinding and polishing parameters.

Table 2. 3-Step Method for Medium/Hard (<35HRC) Ferrous Materials using the PlanarMet™ 300 and EcoMet™/AutoM™ 300

Surface Abrasive/Size Load – lbs [N]/Specimen Platen speed [rpm] Head speed [rpm] Relative rotation Time [min:sec]
Alumina Grinding Stone 120 [P120] grit 7 [30] Fixed 120 1:00
Apex™ Hercules S 9µm MetaDiTM Supreme Diamond* 7 [30] 150 60 4:00
MicroFloc 3µm MetaDi Supreme Diamond* 7 [30] 150 60 4:00

= Platen
= Specimen Holder
*Plus MetaDi Fluid Extender as desired

Imaging and Analysis

A Nikon Eclipse MA200 compound microscope with a 3.1MP UEye digital microscopy camera, using bright field illumination (BF), was used to inspect the prepared samples. A magnification range between 50X and 200X was chosen for the eyepiece. The results are depicted in Figures 2 and 3.

Porous and nitrided layer after etching with 3% Nital.

Figure 2. Porous and nitrided layer after etching with 3% Nital.

Vickers hardness testing was carried out using a Wilson® VH3100.

Porous and nitrided layer after etching with 3% Nital.

Figure 3. NHD measurement on nitrided steel to check the nitride-hardened depth on a gear wheel.

Conclusion

Using the PlanarMet 300 grinding stage for less than 2 minutes obtained an ideal surface finish. No further coarse grinding step was required, and ideal flatness was realized on the samples. The 2-step final polishing procedure resulted in a faint grain structure when viewed under BF microscopy. Conventional preparation methods are difficult and time intensive. Buehler’s PlanarMet 300 Planar Grinder avoids these drawbacks, ensures reduction in preparation times, and realizes an ideal surface finish with minimal material deformation.

This information has been sourced, reviewed and adapted from materials provided by Buehler.

For more information on this source, please visit Buehler.

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