Automatic Submerged Arc Surfacing of Blast Furnace Bell and Hopper Mating Surfaces

Literature Overview

The paper by Pan Yubin, Shan Weichun, Tian Baolin, and Liu Chengshan, published in Shandong Metallurgy (2000, Vol. 22, No. 2, pp. 26–28), reports a practical engineering solution for extending the service life of blast furnace bell and hopper mating surfaces through automatic submerged arc surfacing (ASAW). The authors, affiliated with Jinan Iron and Steel Group, addressed a well-known industrial problem: the mating surfaces of the bell and hopper assemblies undergo severe sliding wear and impact loading during continuous ironmaking operations, leading to frequent shutdowns for repair. This study is significant because it demonstrates a systematic approach to surfacing layer design that combines a corrosion-resistant transition layer with a wear-resistant final layer, and it addresses the practical challenges of uphill and downhill surfacing orientations inherent to the geometry of these large cylindrical components.

Core Technical Approach and Layer Design

The fundamental insight of this work is the two-layer surfacing strategy. The transition layer uses 1Cr18Ni9Ti (equivalent to austenitic stainless steel, similar in composition to AISI 321 or SUS 321), while the final surfacing layer employs 3Cr2W8, a high-carbon, high-chromium ledeburitic cast iron known for exceptional abrasion resistance. This combination is metallurgically rational for several reasons that deserve careful examination.

The base material of blast furnace bells and hoppers is typically low-carbon structural steel or medium-carbon steel, which has limited compatibility with the highly alloyed wear-resistant final layer. Direct surfacing of 3Cr2W8 onto carbon steel would result in excessive dilution, brittle intermetallic phases, and poor adhesion. The 1Cr18Ni9Ti transition layer serves three critical functions: it provides a ductile, corrosion-resistant buffer zone; it reduces the carbon concentration gradient between the base metal and the final layer; and it accommodates the differential thermal expansion between the two layers during cyclic thermal loading in the furnace environment.

The 3Cr2W8 layer, being a high-chromium white cast iron with a high volume fraction of M7C3 carbides, offers hardness in the range of 55–62 HRC after casting, which is substantially higher than the base material hardness of approximately 150–200 HB. The wear mechanism at the bell-hopper interface is predominantly abrasive, caused by the continuous sliding contact under the weight of the burden (iron ore, sinter, and coke). The ledeburitic microstructure of 3Cr2W8, characterized by a matrix of pearlite and ferrite surrounded by hard cementite-rich carbides, provides excellent resistance to this type of wear.

Process Parameters and Orientation Challenges

A critical aspect of this study is the treatment of uphill and downhill surfacing orientations. In automatic submerged arc surfacing, the welding torch moves along the component surface, and the direction of travel relative to the gravity vector significantly affects the molten pool shape, solidification pattern, and final deposit quality.

The authors report that by adjusting current, voltage, and travel speed for each orientation, acceptable surfacing quality was achieved on both uphill and downhill surfaces. The use of automatic equipment ensures parameter consistency, which is essential for large cylindrical components where manual welding would introduce unacceptable variability. The submerged arc process itself offers advantages in this application: deep penetration promotes good metallurgical bonding with the transition layer, the flux provides a protective atmosphere without external shielding gas, and the relatively low spatter rate reduces cleanup requirements on the large furnace components.

Engineering Practice Implications

From an engineering standpoint, this case study illustrates several important principles that are transferable to other heavy equipment repair applications. First, the selection of a transition layer is not merely a metallurgical formality but a necessity when surfacing highly alloyed materials onto dissimilar base metals. Second, the orientation-dependent adjustment of welding parameters is a practical requirement that must be addressed in any surfacing operation on large cylindrical or vertical components. Third, the reported extension of equipment overhaul cycles translates directly into economic benefits, as blast furnace shutdowns for bell and hopper replacement are extremely costly in terms of lost production and labor.

The choice of 1Cr18Ni9Ti as the transition layer also has implications for the corrosion environment. Blast furnace conditions involve reducing atmospheres with CO and H2, and occasional exposure to water vapor and acidic species. The austenitic stainless steel transition layer provides a degree of corrosion resistance that protects the base metal interface from environmental degradation, which is a secondary but important benefit not always recognized in repair engineering.

Study Insights and Reflections

Reflecting on this work, I note that the study, while practical and effective, could benefit from more detailed characterization of the weld metal microstructure and the interfacial bonding zone between the transition layer and the final layer. The absence of hardness traverse data across the layered structure is a limitation, as it would be valuable to quantify the dilution gradient and identify the optimal thickness ratio between the transition and surfacing layers. Furthermore, long-term field performance data, including measured wear rates before and after surfacing, would strengthen the engineering case. Nevertheless, the paper serves as a clear example of how rational layer design and process adaptation to component geometry can solve a persistent industrial wear problem with relatively straightforward welding technology.