Boron effect in Fe Cr C hardfacing overlays

Alloy design and hardfacing route

This study prepares high chromium hardfacing overlays with 1.0 to 3.0 percent carbon, 15 to 20 percent chromium, and 0 to 2.0 percent boron. The overlays are deposited using 1.6 mm flux-cored wire with CO2 shielding gas. The paper focuses on the effect of B4C addition on hardness, carbide distribution, and abrasive wear resistance.

This is directly relevant to hardfacing for wear plates, screw conveyors, crusher parts, and heavy service components used around pipe plants. The paper shows that boron is not a minor addition. It changes the morphology and distribution of hard carbides. In practice, this means that a boron-containing hardfacing alloy should be treated as a designed composite wear system, not as a simple high-chromium filler metal.

Microstructure and carbide morphology

The overlay microstructure consists of ferrite, austenite, and Fe-Cr carbide. The paper reports that B4C addition significantly improves the matrix and increases the amount of dispersed carbide. This is a critical observation. Hardness is not the only driver of wear resistance. Carbide size, spacing, and connectivity matter greatly under abrasive loading.

A dispersed carbide structure resists micro-cutting and micro-cracking better than a coarse continuous network. If carbides form as large interconnected networks, they can act as crack initiation sites. If they are fine and evenly distributed, they support the matrix and resist abrasive penetration. Boron appears to promote the favorable condition in this alloy family.

The presence of ferrite and austenite also matters. The matrix must be tough enough to support the hard carbides. If the matrix is too soft, carbides are pulled out. If the matrix is too brittle, the overlay cracks. Boron can improve the balance by modifying carbide formation and matrix structure. This is a good example of why overlay alloy chemistry should be optimized as a system.

Wear behavior and process control

The reported hardness increases from 57.1 HRC to 65.2 HRC, an increase of 14.2 percent. More importantly, relative wear resistance increases from 3.5 times to 18.0 times. That is a much larger gain than the hardness increase alone would suggest. This confirms that wear resistance in hardfacing is controlled by microstructure, not just hardness.

From a shop perspective, the process window must protect the intended boron effect. Flux-cored wire chemistry, dilution, preheat, interpass temperature, and cooling rate can all affect carbide size and distribution. If dilution is too high, the effective boron and carbon activity may drop. If cooling is too slow, carbides may coarsen. If preheat is too high, the overlay may lose the desired fine structure.

The paper also suggests that B4C is effective as an addition route. In practice, powder or wire manufacturers must control particle size, mixing homogeneity, and cored wire packing density. A nonuniform wire can produce local zones with poor boron content and poor carbide distribution. Quality control should include hardness mapping and metallographic inspection of trial overlays.

Engineering practice for pipe and heavy wear parts

For pipe plant wear parts, boron modified Fe-Cr-C overlays can be attractive when the service is severe abrasion and the part can tolerate some brittleness. Examples include chute liners, roller faces, wear plates, and pipe handling dies. However, the design should avoid sharp notches and thick unsupported overlays. The overlay should be kept thin enough to avoid cracking, but thick enough to provide sufficient wear allowance.

A practical qualification approach is to deposit a trial overlay, section it, and evaluate carbide dispersion. The engineer should compare the actual microstructure with the expected dispersed carbide structure. If the carbides are coarse or segregated, the process should be adjusted before production use. This is more meaningful than checking only the HRC number.

The study also warns against using a single hardness value to compare hardfacing alloys. Two overlays with similar hardness can have very different wear life if one has dispersed carbides and the other has coarse carbide networks. Boron can improve dispersion, but only if the welding thermal cycle is controlled.

Summary and study insight

The key insight from this paper is that boron improves abrasive wear resistance mainly by modifying carbide distribution, not merely by raising hardness. The hardness increase is moderate, but the wear resistance increase is substantial. For engineers specifying hardfacing for wear plates, dies, and heavy service parts, the critical control point is the actual overlay microstructure. Process qualification should verify dispersed carbides, acceptable matrix, and consistent overlay chemistry under real welding conditions.