Cr effect on heat treated Fe Cr B C hardfacing overlays

Overview of the study

This study examines four Fe-Cr-B-C hardfacing overlays deposited on Q235 substrate with Cr contents of 12 percent, 14 percent, 16 percent and 18 percent. The overlays were produced by flux-cored wire hardfacing, then heat treated at 600 degrees Celsius. The paper links Cr content to as-welded and heat-treated microstructure, to phase stability, and to abrasive wear resistance.

For pipe and fitting shops, the value of this paper is not that it deals directly with pipe production, but that it clarifies a recurring hardfacing problem. Many wear overlays lose hardness after service heating, stress relief, post-weld heat treatment, or elevated temperature operation. The paper gives a practical warning that Cr content is not just a corrosion or carbide variable. It is a thermal stability variable for the hard phase and the matrix.

Microstructural interpretation

The as-welded overlay contains martensite and retained austenite. This is typical for high-carbon, high-alloy hardfacing metal cooled from a high temperature. Martensite gives high hardness, but retained austenite can reduce wear resistance under severe abrasion because it may transform, deform, or support the hard phase differently during loading. After heat treatment at 600 degrees Celsius, the matrix becomes tempered sorbite. That means the overlay has undergone substantial microstructural adjustment.

The hard phase is described as Fe-Cr carboboride. In practical terms, this phase is the wear skeleton of the overlay. Its shape, continuity, size, and stability during heating determine whether the overlay survives service. The paper states that when Cr reaches 14 percent, the hard phase becomes more stable at high temperature. This is a useful threshold. It suggests that Cr is helping the carboboride resist coarsening, dissolution, or transformation during thermal exposure.

The matrix transformation is also important. Martensite can be very hard, but it is not always stable at 600 degrees Celsius. Tempered sorbite is tougher and more stable, but its hardness is generally lower than fresh martensite. Therefore, a heat-treated overlay cannot rely only on matrix hardness. It must rely on stable hard particles and a matrix that supports them without softening excessively.

Wear performance and engineering meaning

The wear result is the most practical part of the paper. The 12 percent Cr overlay drops from a relative wear resistance of 10.65 in the as-welded condition to 2.08 after heat treatment. That is only 19.5 percent of the original wear resistance. This is a dramatic loss. It shows that a hardfacing alloy can look excellent in the as-deposited condition and then fail quickly if the service temperature or post-treatment temperature is not considered.

The 16 percent Cr overlay retains a relative wear resistance of 9.08 after heat treatment. That is a much more acceptable result. The practical lesson is that Cr content changes the thermal stability of the hard phase. A modest increase in Cr can change the overlay from a room temperature wear metal into a heat-resistant wear metal.

From a pipe fitting and plant maintenance perspective, this matters when hardfacing is applied to valve seats, pump wear plates, screw feeder parts, die faces, guide blocks, and pipe handling tools. If the part will see elevated temperature, stress relief, or repeated welding heat, the alloy selection must be made for the heat-treated state, not only for the as-welded state.

Practice oriented takeaways

A useful screening rule from this paper is to treat 14 percent Cr as a minimum for improved high temperature hard phase stability in this alloy family. If the overlay is expected to operate above moderate temperature, 16 percent Cr or higher should be considered. If the overlay will be heat treated after welding, the supplier should be asked for wear data in the heat-treated condition.

Another practical point is dilution control. The paper used Q235 substrate. In pipe applications, dilution from low alloy or carbon steel substrate can lower Cr, C, and B activity in the overlay. Multiple passes, controlled current, and preheat can help preserve the intended overlay chemistry. A hardfacing alloy selected from a table may still underperform if dilution moves it below the critical Cr stability range.

The study also reinforces the need for proper heat treatment records. A hardfacing layer that has been accidentally heated too high can lose most of its wear advantage. In maintenance work, this can be misdiagnosed as poor welding, wrong filler metal, or poor service conditions. A systematic review should check the actual thermal history, not only the nominal alloy grade.

Summary and study insight

The central insight of this paper is that Cr content controls heat-treated wear resistance more than as-welded hardness alone. The 12 percent Cr overlay loses most of its abrasive wear resistance after 600 degrees Celsius exposure, while the 16 percent Cr overlay remains acceptable. For engineers selecting hardfacing for pipe equipment, dies, wear plates, and valve components, the decisive question is not only how hard the overlay is as welded. The decisive question is whether the hard phase and matrix remain stable after the thermal history the part will experience.