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

Literature Overview

This paper by Pan Yubin, Shan Weichun, Tian Baolin, and Liu Chengshan (2000, published in Shandong Metallurgy, Vol. 22, No. 2) addresses a critical maintenance challenge in iron and steel production: the wear of mating surfaces on blast furnace bells and hoppers. The authors describe an automatic submerged arc surfacing (SAW) process that applies a two-layer overlay system—1Cr18Ni9Ti as a transition layer and 3Cr2W8 as the wear-resistant surfacing layer—to restore and enhance the durability of these high-wear components. The publication originates from the Equipment Department and Mechanical Company of Jinan Iron and Steel Group, reflecting a strong engineering practice orientation.

Core Technical Approach

The fundamental problem is that blast furnace bells and hoppers are subjected to continuous abrasive impact from falling ore, coke, and sinter during charging operations. The mating surfaces—where the bell contacts the hopper cone—experience severe sliding wear, leading to loss of dimensional accuracy, increased air leakage, and eventual equipment failure. Traditional replacement or manual welding repairs were costly and resulted in short service intervals.

The authors adopted a layered surfacing strategy:

Layer	Material	Function
Transition layer	1Cr18Ni9Ti (equivalent to 321 austenitic stainless steel)	Buffers the thermal expansion mismatch between the low-alloy base steel and the hard surfacing layer; prevents cracking
Surfacing layer	3Cr2W8 (high-chromium cast iron)	Provides exceptional wear resistance through a high volume fraction of hard carbides (Fe₃W₃C, Cr₂₃C₆)

The use of 1Cr18Ni9Ti is particularly noteworthy. The titanium stabilization prevents chromium carbide precipitation at grain boundaries, which is critical because the transition layer will be exposed to repeated thermal cycling. Without stabilization, sensitization could lead to intergranular cracking during subsequent re-heating events.

Welding Process Details

The automatic submerged arc process was selected for its high deposition rate, deep penetration, and excellent reproducibility compared to manual methods. The paper references both uphill and downhill welding configurations, which is significant for surfacing on curved geometries.

Parameter	Uphill Welding	Downhill Welding
Typical current	400–500 A	500–650 A
Typical voltage	28–32 V	22–26 V
Travel speed	150–250 mm/min	300–500 mm/min
Flux type	Basic (rutile-basic)	Basic
Wire diameter	3.2 mm	3.2 mm

The uphill technique produces a wider, flatter bead profile suitable for the first pass on the transition layer, while downhill welding allows faster deposition with a more convex bead suitable for the surfacing layer. This combination optimizes both wetting and build-up.

Key Process Considerations

Preheating to 150–200 °C is recommended to reduce residual stress in the thick cast iron and low-alloy steel components.
Interpass temperature should be maintained below 250 °C for the transition layer and below 350 °C for the surfacing layer to avoid softening of the 3Cr2W8 carbide structure.
The bell and hopper components typically have wall thicknesses of 40–80 mm, making heat input control critical to prevent distortion of the mating geometry.

Engineering Practice Insights

From a quality control perspective, the critical defects to watch include:

Cracking in the transition layer: This can occur if the carbon equivalent of the base material is too high or if interpass temperatures exceed limits. The 1Cr18Ni9Ti layer acts as a crack arrestor precisely because of its high ductility and thermal expansion coefficient.
Porosity in the surfacing layer: 3Cr2W8 deposits are susceptible to gas porosity due to the high carbon and silicon content. Flux coverage must be maintained, and wire/flux dryness is essential.
Spalling of the surfacing layer: If the dilution ratio exceeds 30%, the hard carbide structure is diluted with softer austenite, leading to premature spalling under impact loading.

The practical benefit reported is a significant extension of service life and maintenance intervals. In the blast furnace context, this translates directly into reduced unplanned shutdowns, which are extraordinarily costly given the need for complete cooling and recharging cycles.

Reflections and Study Value

This paper, while published in 2000, represents a classic application of layered surfacing design philosophy that remains highly relevant today. The two-layer approach—transition layer plus functional layer—is a textbook example of managing metallurgical compatibility in surfacing applications. The selection of 1Cr18Ni9Ti over 304L is a deliberate engineering choice: the titanium stabilizer provides superior resistance to sensitization during the repeated thermal cycles encountered in blast furnace service.

One area where modern practice would differ is in the use of consumable fluxes and wire. Current standards such as AWS A5.18 and ISO 14342 provide more detailed specifications for surfacing consumables, and the availability of low-hydrogen basic fluxes with controlled moisture content has improved porosity resistance. Additionally, modern process monitoring using arc voltage and current feedback control would enhance the reproducibility of the automatic SAW process described here.

For engineers working on similar applications—such as surfacing on mining equipment, cement kiln components, or power plant wear parts—the fundamental design logic remains applicable: always consider the metallurgical compatibility between base metal, transition layer, and functional layer, and always validate the process through full-scale qualification testing under representative service conditions.