Effect of Welding Materials on the Wear Resistance of Chromium Carbide Surfacing Composite Steel Plates

Literature Overview

This paper by Li Tieying from Tianjin Jinghua Petrochemical Co., Ltd., published in Welding Technology (2014, Vol. 43, No. 7, pp. 48-51), investigates the influence of welding consumable selection on the sliding wear resistance of chromium carbide surfacing composite steel plates. Two welding wires are compared: a conventional iron-based chromium carbide wire and a boron-modified chromium carbide wire. The study employs ASTM G65 sliding wear testing and correlates wear performance with microstructural features, carbide volume fraction, and surface hardness.

Core Technical Content

The study addresses a practical problem in industrial processing applications where sliding wear causes severe component degradation. Surfacing plates offer an economical and practical solution by providing a hard, wear-resistant surface layer on a tougher substrate. The key findings are summarized below:

The paper establishes that wear resistance of the surfacing layer is primarily determined by the volume fraction of carbides, surface hardness, and alloy composition. The boron addition promotes austenite matrix formation, which provides additional chromium carbide nucleation sites through the formation of fine boron carbide particles. This increases both the number and volume fraction of chromium carbide grains, resulting in superior wear performance.

Metallurgical Analysis

The metallurgical mechanism described in this paper is particularly instructive. The addition of boron to the chromium carbide system introduces a secondary carbide phase (B4C) with a different crystal structure and lattice parameter than chromium carbides. These fine boron carbide particles serve as heterogeneous nucleation sites for chromium carbide precipitation during solidification. The result is a finer, more uniformly distributed carbide structure in the boron-modified variant.

The formation of an austenite matrix in the boron-modified composition is significant. Austenite provides a more ductile matrix that can accommodate the volume changes associated with carbide precipitation, reducing the risk of microcracking. Additionally, the retained austenite in the as-welded condition can transform to martensite during use, providing additional hardening.

The finding that wear resistance correlates linearly with carbide volume fraction but not strongly with surface hardness is a crucial insight. This suggests that for wear-resistant surfacing applications, the priority should be maximizing carbide content and dispersion rather than simply achieving the highest possible hardness value. A material with slightly lower hardness but significantly higher carbide volume fraction may exhibit superior wear resistance.

Standards and Testing Methodology

The ASTM G65 sliding wear test is the appropriate standard for evaluating sliding wear resistance in industrial applications. This test measures material removal under controlled conditions of normal load, sliding distance, and counterface material. The results are typically expressed as wear volume or mass loss per unit sliding distance.

The optimal w(Cr)/w(C) ratio of 4.1 identified in this study is a critical design parameter. This ratio determines the relative amounts of chromium and carbon available for carbide formation during solidification. Below this ratio, excess carbon may form free graphite or cementite, which are detrimental to wear resistance. Above this ratio, excess chromium may form chromium-rich phases that are less hard than chromium carbides.

Engineering Practice Implications

For engineers specifying wear-resistant surfacing overlays on equipment components, this study provides several actionable recommendations:

• When selecting surfacing consumables for sliding wear applications, boron-modified chromium carbide wires should be considered as a preferred option over conventional chromium carbide wires.
• The w(Cr)/w(C) ratio should be maintained near 4.1 to maximize carbide formation and wear resistance.
• Surface hardness alone should not be used as the sole criterion for evaluating surfacing layer performance; carbide volume fraction and morphology are equally important.
• The austenite matrix formed with boron addition provides a more crack-resistant microstructure, which is beneficial for components subjected to impact loading.

The practical application of these findings in petrochemical equipment maintenance can extend the service life of components such as slide plates, guide shoes, and conveyor components that experience severe sliding wear.

Key Questions and Reflections

The study raises several questions that warrant further investigation:

1. How does the wear resistance compare under abrasive sliding versus adhesive sliding conditions?
2. What is the effect of heat treatment on the microstructure and wear performance of the boron-modified surfacing layer?
3. How does the dilution rate from the base metal affect the carbide volume fraction and wear resistance?

The linear relationship between wear resistance and carbide volume fraction is a valuable design principle. It suggests that future developments in wear-resistant surfacing alloys should focus on maximizing carbide content through careful composition design and process optimization.

Summary

This paper provides a clear demonstration that the addition of boron to chromium carbide surfacing consumables significantly enhances sliding wear resistance through the formation of fine boron carbide particles that promote chromium carbide nucleation. The finding that wear resistance correlates with carbide volume fraction rather than surface hardness alone offers a valuable design principle for surfacing alloy selection. Engineers involved in specifying wear-resistant overlays should consider boron-modified chromium carbide consumables as a cost-effective solution for extending component life in sliding wear applications.