Stainless Steel 630
17-4 PH
630 stainless steel, also known as 17-4 PH, is a precipitation-hardening ductile stainless steel that contains copper, nickel, and chromium. Because of this composition, the material can be heat-treated to obtain high mechanical strength while maintaining strong corrosion resistance. Its capacity to modify its characteristics by aging at various temperatures is one of its key benefits, which makes it appropriate for a variety of technical applications. In addition, 630 stainless steel is particularly appealing for components that are subjected to mechanical and environmental stresses since it shows strong machinability in the treatment form and good resistance to fatigue and stress corrosion cracking.
STEP 1: CUTTING THE WORKPIECE
NEXT STEP
Cutting 630 stainless steel requires special care due to its high strength and hardness, particularly in the heat-treated condition, as improper cutting can lead to tool wear and surface damage. We use a Aluminum Oxide and Silicon Carbide cutting wheel specified for cutting ferrous and nonferrous metals.
RECOMMENDED METHOD
Machine: Precision cut-off saw with rigid clamping to prevent vibration
Wheel: Aluminum Oxide and Silicon Carbide (typically 200–300 mm diameter).
Coolant: Abundant water-based coolant to minimize heat and avoid thermal cracks.
Feed Rate: 0.256mm/s.
Blade Rotation Speed: 2800 RPM
Goal: Achieve a flat, undamaged surface with minimal microcracking for subsequent mounting and polishing.
This approach ensures the integrity of the coating and substrate, which is critical for accurate microstructural analysis.
STEP 2: MOUNTING
PREVIOUS STEP. NEXT STEP
The samples for the lapping process were cold-mounted using an epoxy resin mixture with a 1:10 ratio (200 g resin and 20 g hardener), enough for two samples. After cleaning and drying, the samples were placed in molds and completely covered with the resin. The molds were first cured at 60 °C for 30 minutes, then the samples were removed and placed in an oven for a second curing at 80 °C for 8 hours to fully harden the resin. The resulting mounts were solid, uniform, and provided excellent support for subsequent lapping and polishing.
STEP-BY-STEP MOUNTING PROCEDURE FOR CAST IRON SAMPLES
1 Clean the Sample: Remove oil, dust, and debris using ethanol or acetone.
2 Prepare Resin Mixture: Mix epoxy resin and hardener in the recommended ratio (e.g., 10:1 by weight).
3 Pour into Mold: Place the sample in a mold and cover completely with resin.
4 Initial Cure: Heat at 60 °C for 30 minutes to start polymerization.
5 Final Cure: Transfer to an oven at 80 °C for 8 hours for full hardening.
6 Demold and Inspect: Ensure the mount is solid, uniform, and free of bubbles.
7 Proceed to Grinding and Polishing: Start with coarse diamond discs and progress to fine polishing steps.
STEP 3: PLANAR GRINDING AND LAPPING
PREVIOUS STEP. NEXT STEP
If the sample surface is not sufficiently flat after cutting and mounting, planar grinding is performed to achieve uniformity. This step removes excess resin and levels the sample. If the starting surface is already flat, this step can be skipped.
The KGS PROLAP 40 µm disc is used for the initial grinding of the stainless steel 630 sample. This step secure surface flatness and removes initial irregularities.
Figure 1 - PROLAP 40µm (10x)
STEP 4: PRE-POLISHING AND POLISHING
PREVIOUS STEP NEXT STEP
In this stage, the KGS PROLAP 9 µm disc is used to refine the surface and reduce marks left by the 40 µm abrasive (Pre-Polishing Step). The microstructure of cast iron consisting of a metalic matrix with graphite nodules tends to form micro-cavities, therefore, polishing should be light and continuous, with cleaning between steps to avoid contamination by coarser abrasives.
The KGS PROLAP 2 µm disc is used to remove the final marks and achieve a uniform finish. (Polishing Step)
At this stage, the nodular structure can already be clearly observed under the microscope (10×). Avoid overheating the sample and ensure constant lubrication.
Figure 2 - PROLAP 9µm (10x)
Figure 3 - PROLAP 2µm (10x)
STEP 5: FINAL POLISH
PREVIOUS STEP. START AGAIN
The final polishing step is crucial for achieving a flawless surface that is completely free of scratches and deformation. In this stage, the KGS Polishing Pad Viscose White disc is used to gently remove any remaining residues from the previous polishing steps. To enhance the effectiveness of this process, a 0.06 µm colloidal silica suspension is applied as the polishing medium. This extremely fine abrasive not only smooths the surface but also chemically assists in revealing microstructural details, such as grain boundaries and binder phases, which are essential for accurate materialographic analysis. After this step, the sample should exhibit a mirror-like finish suitable for high-resolution microscopic examination.
Figure 4 - Colloidal Silica (10x)
Materialography
The term materialography used today is a factual extension of metallography, which include many other groups of materials, such as ceramics, plastics and composite materials that are examined in the same way. Materialography is the science of examining a material's microstructure, which is its internal composition at a microscopic level. By polishing and analyzing a material's surface, materialography helps engineers understand properties like strength, corrosion resistance, and potential failure points.