Microstructure and Wear Resistance of Fe-Cr-C-Ti Overlay Alloy

Literature Overview

This study investigates the microstructural characteristics and tribological performance of Fe-Cr-C-Ti based overlay alloys, which represent a class of hardfacing materials designed for severe abrasive wear applications. The addition of titanium to the conventional Fe-Cr-C system introduces new carbide-forming capabilities and microstructural refinement mechanisms that can significantly enhance wear resistance. The research examines the effects of titanium content, carbon content, and cooling rate on overlay microstructure, hardness, and wear behavior under various wear mechanisms.

Core Technical Points

Alloy Design and Phase Constitution

The Fe-Cr-C-Ti overlay alloy system offers several advantages over conventional Fe-Cr-C hardfacing alloys:

Component	Conventional Fe-Cr-C	Fe-Cr-C-Ti Alloy	Performance Impact
Cr content	10-25 wt%	8-18 wt%	Maintains oxidation resistance
C content	2.5-4.0 wt%	2.0-3.5 wt%	Optimal carbide density
Ti content	0-0.5 wt%	2.0-5.0 wt%	Refines microstructure, forms TiC
Base matrix	Ferrite/martensite	Ferrite/martensite/austenite	Improved toughness

The titanium addition promotes the formation of TiC and Ti4C3 carbides, which are extremely hard (3000-3500 HV for TiC) and contribute significantly to wear resistance. Additionally, titanium acts as a grain refiner for the ferrite/martensite matrix, reducing grain size from 20-50 μm to 5-15 μm, which improves both hardness and toughness.

Microstructural Evolution with Titanium Content

The study systematically varies titanium content from 0 to 6 wt% and examines the resulting microstructural changes:

0% Ti (baseline): Coarse blocky Cr7C3 carbides (10-30 μm) in martensitic matrix, hardness 650-700 HV
2% Ti: Refinement of Cr7C3 carbides (5-15 μm) plus TiC particles (1-3 μm), hardness 750-800 HV
4% Ti: Significant TiC formation (2-5 μm), reduced Cr7C3 size (3-10 μm), hardness 850-900 HV
6% Ti: Excessive TiC formation, possible Ti-rich phases, hardness 900-950 HV but reduced toughness

The optimal titanium content appears to be 3-4 wt%, providing the best balance between hardness and toughness for most abrasive wear applications.

Wear Mechanism Analysis

The study employs multiple wear testing methods to characterize the overlay's performance under different wear conditions:

Wear Test Method	Wear Rate (mm³/N·m)	Wear Mechanism	Optimal Ti Content
Pin-on-disk (Al2O3)	0.5-0.8	Abrasive (two-body)	3-4 wt%
Three-body abrasion (quartz sand)	1.2-1.8	Abrasive (three-body)	4-5 wt%
Dry sliding (steel pin)	0.3-0.5	Adhesive + abrasive	2-3 wt%
Erosive wear (SiC particles)	0.8-1.2	Erosive-abrasive	3-4 wt%

The results demonstrate that the Fe-Cr-C-Ti overlay with 3-4 wt% Ti achieves wear rates 40-60% lower than conventional Fe-Cr-C alloys with equivalent hardness, attributed to the combined effect of fine TiC carbides and refined matrix microstructure.

Process Parameters and Microstructure Control

Welding Process Selection

Process	Cooling Rate (°C/s)	Matrix Structure	Carbide Size (μm)	Hardness (HV)
SAW	5-15	Coarse martensite	10-30	650-700
GMAW	15-40	Medium martensite	5-15	700-780
GTAW	30-80	Fine martensite	3-10	750-830
PTA	50-150	Fine martensite/austenite	2-8	800-900
Laser cladding	100-500	Very fine martensite	1-5	850-950

The study demonstrates that higher cooling rates consistently produce finer microstructures and higher hardness, but with diminishing returns above 100°C/s cooling rate. PTA and laser cladding processes offer the best microstructural refinement while maintaining reasonable deposition rates.

Recommended Process Parameters for PTA Cladding

Parameter	Value	Rationale
Arc current	150-200 A	Optimal penetration for dilution control
Powder feed rate	40-60 g/min	Ensures adequate deposition
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