1. Surface Alloying of Mild Steel and Advanced Characterization of the Alloyed Surface
Kaustubh K. Rane
Department of Materials Science and Engineering,
University of Wisconsin-Milwaukee
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2. Introduction:
Aim: Replace the use of expensive alloys by surface micro-alloying of mild steel
Motivation: Reduce the cost of as-cast products, reduce the use of alloying elements and offer a variety of micro-alloying solutions for wide range of products.
Difference: Current processes are performed after casting the product. Our process aims at in- situ surface micro-alloying during the casting process.
Importance: Reduces time required for post-processing, saves labor costs, saves energy, and reduces expenses on resources.
Outcomes: Current experiments aimed at improving wear resistance of mild steel. Future experiments will explore other alloying systems.
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3. Experimental Procedure
Grinding, Polishing, and Etching
Metallographic Preparation
Optical Microscopy
Elemental Scans (EDS)
Hardness Measurements
X-Ray Diffraction
Metallographic Preparation: Most important step (probably). Samples have to polished and etched (3% Nital, 5 seconds) to perfection.
Optical Microscopy: Identify defects such as blow holes, porosities, inclusions, etc., in the alloyed layer. Confirm phases in the base metal and quantify thickness of alloyed layer.
Elemental Scans: Confirmed presence and uniform distribution of micro-alloying elements along the alloyed layer.
X-Ray Diffraction: Identify phases in alloyed layer to understand effects of varying quantities of micro-alloying elements.
Hardness Measurements: Compare hardness of alloyed layer, base metal and interface. Alternatively, use to measure Young’s Modulus.
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4. Results:
Microstructural Analysis: Dendritic microstructure of alloyed layer indicates complete melting and solidification.
Alloying Element Diffusion: SEM images show a visible interface separating the alloyed layer and base metal. EDS scans confirm the presence of alloying elements only in the alloyed layer.
X-Ray Diffraction: Yarlongite is primary phase observed along with nitrides of alloying elements.
Residual Stress: Minimal quantity of residual stresses, 3.5 Mpa. Measured using d vs sin2ψ method.
Hardness Measurements: Increase in hardness of alloyed layer as compared to base metal implying an increase in wear resistance.
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5. Surface Alloyed Layer
Substrate
Graph 1. EDS line scan for elemental distribution analysis
Sample
Surface (GPa)
Base (GPa) 5
5.5
4.2 6
5.34
3.9 7
5.17
4.27 8
6.78
4.28
Interface
Figure 1. Dendritic Microstructure of surface alloyed layer in as-cast sample
Table 1. Comparison of nano-indentation results of alloyed layer and base metal
Graph 2. XRD plot confirming presence of Yarlongite in the surface alloyed layer
Sample
Surface (HV)
Base (HV) 1
510.22
292.86 2
314.16 3
433.9
382.1 4
540.16
418.02
Sample
Residual Stress (Mpa) 1
3.5 2
3.446
Table 3. Quantification of residual stresses in alloyed layer
Table 2. Comparison of Vicker’s Microhardness of alloyed layer and base metal
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6. Conclusions:
Surface alloying improved the hardness of the as-cast samples.
Residual stress was measured to be 3.5 MPa (compressive), which is not high enough to cause significant machining issues.
Distribution of alloying elements in the surface alloyed layer is uniform
Dendritic microstructure suggests complete melting and solidification of mild steel and alloying elements.
XRD indicates presence of desirable Fe phases.
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7. Conclusions:
Surface alloying improved the hardness of the as-cast samples.
Residual stress was measured to be 3.5 MPa (compressive), which is not high enough to cause significant machining issues.
Distribution of alloying elements in the surface alloyed layer is uniform
Dendritic microstructure suggests complete melting and solidification of mild steel and alloying elements.
XRD indicates presence of desirable Fe phases.
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8. Thank You! Any Questions?
Yup, that’s me heating steel!
Yes, all safety standards are followed.
Thank You!
Any Questions?
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