Integrated vs. Mini Mills

Introduction

For procurement professionals, engineers, and supply chain decision makers, knowing the impact of steel sourcing is crucial. The choice between integrated mills and mini mills has typically revolved around cost, lead times, sustainability goals, and performance.

Because of these factors, it has long been debated which sourcing option is superior. In this blog, we will break down the key differences between integrated and mini mills, highlighting how each mill's processes impact product quality, flexibility, and environmental footprint.

When making supply decisions, turn to the experts at Worthington Steel, a steel service center, who not only understand the difference in steel mills but also know how to leverage those distinctions creatively to meet your specific needs, efficiently and reliably.

In this guide, we'll explore the following key topics to help you make informed sourcing decisions. You can read it straight through or jump to the sections most relevant to your needs.

• The Basics of Steel Production
• What Buyers Need to Know
• Product Characteristics
• Application Factors
• Cost and Price Considerations
• Evolving Steel Industry

The Basics of Steel Production: Integrated Vs. Mini Mills

What are Integrated Mills?

Integrated mills are traditionally large industrial complexes that handle the entire steelmaking process, from raw materials and scrap to finished steel coils. Designed to produce massive quantities of steel, they supported the infrastructure and manufacturing boom in the 20th century to become an industrial staple.

Most integrated mills use traditional technology like blast furnaces and basic oxygen furnaces (BOFs) to produce steel from raw materials, and 25-30% steel scrap. Over time, to match the competition, the facilities upgraded technology by retrofitting equipment, like replacing blast furnaces and basic oxygen furnaces with EAFs (covered in the next section), leading to less optimized run times.

Despite the emergence of mini mills, integrated mills remain competitive due to their ability to handle complex chemistries, treat steel surfaces, allow more reduction from slab to final thickness, and their reliability in the steel industry.

What are Mini Mills?

Mini mills offer a more modern, flexible approach to steelmaking, using 100% scrap instead of raw materials, which emerged in the late 20th century. They became popular by reducing production complexities, increasing efficiency, and requiring less capital to start up. Initially, mini mills had challenges with surface quality and defects compared to integrated mills, but advancements in technology have largely leveled the playing field.

Mini mills use electric arc furnaces (EAFs) instead of blast furnaces and BOFs, relying almost entirely on recycled steel and electricity rather than raw materials. With newer equipment, mini mills can run optimally without retrofitting. They are competitive in the market due to better gauge control, uniform temperatures, tighter tolerances, lighter gauges, and greater efficiency in production and capital usage.

Now that we have an overview of integrated and mini mills, we can divide into specific comparisons regarding products, quality differences, and price considerations.

What Steel Buyers Need to Know

Over the last 20 years, the distinctions between integrated and mini mills have blurred. Mini mills have improved their internal cleanliness and surface management, while integrated mills have upgraded casting equipment and adopted newer steelmaking technologies, such as EAF replacements of BF/BOFs.

There are still more key differences between the two when needing specific parameters. The chart below highlights where the key differences lie - and if you're curious about the reasoning behind these assessments, they are explained in more detail in the following sections.

If you are unsure which mill is the best fit for you, Worthington Steel, with 70 years of industry experience, can help guide you through your options based on capabilities, availability, lead times, pricing, and other procurement considerations. Our goal is to help businesses achieve their desired specifications, regardless of mill type.

Product Characteristics: Quality, Tolerances, Grades

The main difference between the mill types relates to hot rolled steel, while cold rolled or coated steel products depend more upon the additional processing procedures performed after the hot roll coil is produced. Keep this in mind as you read the following sections.

What is the Difference in Surface Quality?

Twenty years ago, the industry consensus was that integrated mills produced superior surface quality. One key reason was slab thickness, as integrated mills cast slabs at 8-10 inches thick, compared to 2-3.5 inches in mini mills. The additional thickness allows for more reduction during rolling, helping eliminate surface imperfections.

Integrated mills also employ scarfing, a process that removes 2-6 mm from the surface of slabs before hot rolling. This further enhances surface quality by minimizing irregularities in the final coil.

Common steel surface imperfections include scale pitting, laminations, cracks, seams, and caster folds. These can often be corrected during rolling, but again, thinner slabs from mini mills offer fewer opportunities for removal. Smaller cross-sections increase the risk of flaws forming during solidification, which integrated mills are better equipped to manage.

Because of the reliance on scrap from mini mills, the steel may have a higher value residual element than the virgin steel created by integrated mills. The higher content may lead to surface imperfections in addition to the reduced slab thickness.

Despite these limitations, mini mills have rapidly advanced in both operations and technology. Today, they can generally match integrated mills in surface quality across most applications.

Verdict: Surface quality is rarely a determining factor for Worthington Steel in sourcing selection; integrated and mini mills are considered on par for most applications.

What is the Difference in Thickness Tolerances?

Mini mills typically achieve tighter thickness tolerances than integrated mills because they cast directly to sheet thickness, avoiding the cooling and reheating steps required by integrated mills, which cast thicker slabs and roll them into sheet products later.

Tighter hot roll tolerances at mini mills also stem from newer processing technologies. Their equipment is typically 20-30 years old, compared to the 50-60-year-old, retrofitted machinery used by integrated mills.

For cold-rolled steel, both mill types show similar capabilities in holding tighter tolerances, as the cold roll gauge is made on the cold mill, independent from the hot mill processes. It is largely influenced by additional processing done after casting.

Verdict: Mini mills tend to have tighter thickness tolerances than integrated mills for hot rolled steel, but are generally the same for cold rolled steel.

What is the Difference in Grade Availability?

Integrated mills are preferred for producing steels with more complex chemistries, known as peritectic grades (0.08-0.17% carbon content, such as 1010, 1012, 1015). This is due to their superior control over solidification in thin casting. These harder grades are more susceptible to cracking and deformation, which integrated mills are better equipped to manage.

Mini mills have yet to master producing complex peritectic grades because of challenges in controlling the heat generated during the solidification of peritectic reaction (the shell that starts to form remelts and cracks). Integrated products take advantage of a hotter reduction to final thickness and can run slower to avoid those breakouts.

However, mini mills have grades like extra deep drawing steel (EEDS) and drawing steel type B (DS) that are not quite as formable as integrated but are very close. Advancing technologies may eventually enable mini mills to produce peritectic grades in the future.

Verdict: For steels that fall within the peritectic grade range, integrated mills may be the choice compared to mini mills.

Choosing the Right Mill Based on Application Factors

At Worthington Steel, we are agnostic about sourcing from integrated or mini mills in most cases. Our priority is to meet customer specifications with timely delivery, competitive pricing, and technical precision guided by our experienced metallurgical team by leveraging the strengths of each mill matched to our customers' end uses.

That said, when it comes to specialized needs like precise surface finishes, advanced material grades, or exceptional formability, one option may still outperform the other. A good example is the automotive industry, where various components demand these characteristics. For instance, exposed body panels require smooth surface finishes, lightweight oil pans benefit from high formability, and deep-drawn parts often call for superior internal cleanliness. These are all areas where integrated mills may have a distinct edge.

In addition to special application requirements, the automotive industry has increasing concerns about its environmental footprint, from cradle to grave. Because of this, mini mill sourcing may be more advantageous in the near term to meet their environmental goals, as the steel is nearly 100% recycled steel, and their processes are more efficient, requiring less energy. To compete, most integrated mills have set 2050 goals for carbon neutrality.

Regardless of the application or industry pressures, Worthington Steel is uniquely positioned to help you navigate sourcing decisions - whether you are in automotive, heavy trucks, agriculture, construction, energy, or countless other industries. Our strong relationships across both mill types ensure you receive the optimal material solution tailored to your business needs.

Cost and Price Considerations in Steel Production

There is no definitive, consistent, or advertised price advantage between integrated and mini mills, as pricing is influenced by various factors, including:

• Fluctuations in steel scrap pricing
• Raw materials harvesting
• Labor costs
• Market health
• Supply chain fluctuations
• Regional Variances

Mini mills are generally cheaper to operate, have a smaller environmental footprint, and require fewer staff, making their production costs lower than those of integrated mills. Consequently, recent investments in the steelmaking industry have favored mini mills, while integrated mills have been retrofitted or shuttered.

An Evolving Steel Industry

The steel industry is undergoing a notable transformation after decades of relative stability. Traditionally, integrated and mini mills served distinct roles, one offering superior chemistry control and surface finish while the other delivering operating cost-efficiency and sustainability. However, these boundaries are rapidly dissolving.

One of the first integrated steel mills with an electric arc furnace was introduced in the U.S. this year. At the same time, mini mills continue to improve quality control, steel internal cleanliness, and surface quality, which were once areas of limitations. This convergence of capabilities is reshaping sourcing strategies, as buyers are no longer confined to a single mill type for specific applications.

Meanwhile, broader industry trends are accelerating this shift. Green hydrogen initiatives, AI-driven quality monitoring, and real-time analytics are being piloted across facilities to reduce carbon emissions, enhance process control, and improve overall yield. Though it's still uncommon for steel companies to operate both mill types under one roof, strategic acquisitions and partnerships may make this dual model more prevalent in the coming years.

For buyers, this evolution means expanded sourcing flexibility, greater emphasis on mill transparency, and new opportunities to align material procurement with sustainability and performance goals.

Conclusion

While integrated and mini mills offer some distinct advantages, there is no one-size-fits-all solution. For most applications, the performance gap has narrowed significantly, making procurement a much easier task. However, for more specialized needs, such as critical surface finishes, complex grades, or high formability, one type may still outperform the other.

Understanding these nuances is essential for making informed sourcing decisions. If you are unsure which mill is best suited for your application, Worthington Steel is here to help. With deep industry expertise and strong relationships across both integrated and mini mills, we will work with you to navigate these choices and ensure you get the right material to support your performance, timing, and business goals.

About Worthington Steel

Since 1955, Worthington Flat Roll Steel has been delivering top-quality service that enables our customers to do the same for themselves. Our steel processing capabilities serve a variety of markets, including automotive, heavy trucks, agriculture, energy, construction, and many others.

Our commitment to our customers' business goes far beyond supplying steel. We provide advanced material support, price risk management, supply chain solutions, and the highest level of customer service and collaboration.

If you are interested in learning more about us at Worthington Steel, want to view our capabilities, or have a question that we can help you answer, please explore our website or call us at 1.800.944.3733. We are here to be partners for your manufacturing goals.