In the steel rolling industry, semi-steel rolls have become essential spare parts for hot rolling mills due to their excellent wear resistance and resistance to thermal cracking. So, what are the basic steps involved in producing semi-steel rolls? This article will systematically outline the complete process flow from smelting to the finished product.
Smelting and Deoxidation: The First Step in Molten Steel Purification
The production of semi-steel rolls begins with electric arc furnace (EAF) smelting. Taking an 8-ton EAF as an example, the quality of the molten steel directly determines the final performance of the rolls. Among these steps, the final deoxidation stage is particularly critical.
Traditional processes often use aluminum ingots for deoxidation inside the furnace or in the ladle, but this method has obvious drawbacks: significant aluminum burn-off and a tendency to produce hard, brittle oxide inclusions that compromise the roll’s toughness. Modern advanced processes employ a combination of argon (Ar) blowing in the ladle and aluminum wire feeding. Practice has proven that this combined process is effective.
It significantly reduces the total oxygen content in molten steel.
It also decreases the size of inclusions.
Furthermore, it improves the dispersion of inclusions.
Data from a certain steel mill supports these findings.
Before argon blowing and wire feeding, the average maximum equivalent diameter of inclusions was 11.85.
The average minimum equivalent diameter was 13.3 before treatment.
After treatment, these values dropped to 7.09 and 2.12 respectively.
This demonstrates a significant purification effect.
Next is the pouring process, which includes the selection of top pouring.
Pouring Process: Selection of Top Pouring vs. Bottom Pouring
Semi-steel materials are characterized by a wide liquid-solid phase line interval. Conventional monolithic casting is prone to producing coarse dendrites and compositional segregation; when carbon content is high, network-like carbides may form along grain boundaries, thereby degrading toughness.
Regarding pouring methods, while the traditional bottom-pouring process is common, it involves lengthy mold opening and cleaning times, causing the roll temperature to drop too rapidly, which is detrimental to subsequent hot-loading furnace treatment. In contrast, the top-pouring process is simple to operate, effectively shortens the time required for mold removal and cleaning, and facilitates the timely entry of the roll into the heat treatment furnace.
Furthermore, using a heat-insulating riser sleeve made of microspherical sand improves the riser’s thermal insulation properties, promotes sequential solidification of the roll, ensures effective shrinkage compensation, and simultaneously reduces the riser height, thereby conserving molten steel.
Hot-Loading into the Furnace and Heat Treatment: The Core Steps in Crack Prevention
To achieve optimal heat treatment results and prevent cracks and roll breakage, semi-finished steel rolls must undergo hot-loading into the furnace—that is, immediately after casting, before the roll temperature drops below 650°C, the mold must be opened, cleaned, and the roll loaded into the heat treatment furnace.
Typical heat treatment processes include:
High-temperature diffusion annealing: Eliminates dendritic segregation.
Spheroidizing annealing: Improves carbide morphology.
Spray quenching: Enhances surface hardness.
Tempering: Eliminates internal stresses and stabilizes the microstructure.
Although this process involves a long cycle time, high technical difficulty, and high manufacturing costs, it is an indispensable key step in ensuring the performance of semi-steel rollers.
Centrifugal Composite Casting: A Breakthrough in Next-Generation Technology
In recent years, centrifugal composite casting technology has gradually become widespread in the production of semi-steel rolls. Compared to traditional monolithic casting, it offers distinct advantages:
Significantly improved metal yield: Reduces alloy waste.
Low-cost core filling: Uses relatively inexpensive molten iron to fill the core, saving a significant amount of alloy.
Refined as-cast microstructure: No complex heat treatment is required; normalizing and tempering alone are sufficient to meet service requirements.
Practical application cases demonstrate that a certain steel company adopted centrifugal composite casting for semi-steel rolls in the F1-F3 stands of the finishing section of a 1700mm hot rolling mill. The service life of these rolls was comparable to that of traditional solid cast rolls, with a rolling volume of 3,800 tons per millimeter, while the production cost of steel strip was reduced by 10%–20%.
Summary
The basic production process for semi-steel rolls can be summarized into several steps.
These steps include smelting and deoxidation.
Next comes pouring and molding, using top pouring with a heat-retaining riser.
Then, the roll is hot charged into the furnace.
After that, heat treatment is performed.
Heat treatment consists of diffusion annealing, spheroidizing annealing, spray quenching, and tempering.
With the widespread adoption of centrifugal composite casting technology, the process has been simplified.
This simplification has significantly reduced costs.
As a result, steel rolling mills now have a more economical and efficient option.
For roll manufacturers, strictly controlling the parameters and quality of each process step—particularly during deoxidation and heat treatment—is key to ensuring the service life of semi-steel rolls and rolling safety.