Semi-Finished Steel FAQs | Frequently Asked Questions

Basic Definitions & Distinctions

What is a steel billet?

A steel billet is a semi-finished product with a square or rectangular cross-section, typically ranging from 100 mm to 160 mm per side, though sizes up to 200 mm are produced in some markets. Billets emerge from continuous casting machines as the first solid form molten steel takes, cooled and cut to transportable lengths typically between 6–12 metres.

The compact cross-section makes billets the precursor for long products – they're subsequently reheated to approximately 1200°C and rolled into reinforcing bar, wire rod, light structural sections and merchant bars. A standard 130 mm x 130 mm billet might weigh 1.2–1.5 tonnes per metre of length.

Billets are commodity products that are traded globally, with Middle Eastern producers (Iran, Saudi Arabia, UAE) and CIS countries (Russia, Ukraine, Kazakhstan) particularly active in international billet markets. Chemical specifications remain relatively simple for most billets – carbon content typically 0.18–0.25% for construction grades, with controlled levels of sulphur and phosphorus to ensure weldability and ductility in downstream products.

What is a steel bloom?

A steel bloom is a larger semi-finished long product with cross-sections typically between 200 mm and 400 mm square, occupying the middle ground between billets and the heaviest steel sections. Blooms serve as feedstock for medium and heavy structural sections – H-beams, I-beams, railway rails and heavy merchant bars that require more substantial starting material than billets can provide.

The distinction between large billets and small blooms can be somewhat arbitrary, with the global steel industry generally using 200 mm square as the dividing line, though practices vary by region and mill configuration. Bloom production represents a smaller market segment than billets, as fewer rolling mills specialise in the heavy equipment required to process blooms into finished structural products.

Like billets, blooms are largely commodity items traded on specifications emphasising dimensional accuracy, surface quality and basic chemistry suitable for structural steel grades. Major bloom producers include integrated steel mills with heavy section rolling capabilities, particularly in Europe, Russia and India where demand for heavy structural products justifies the specialised equipment investment.

What is a steel slab?

A steel slab is the flat semi-finished product destined to be rolled further into hot-rolled coil, cold-rolled coil, coated products and plate. Slabs typically measure 150–300 mm thick, 800–2,200 mm wide and 8–12 metres long, with a typical slab weighing anywhere from 25–35 tonnes depending on dimensions.

These massive pieces emerge from continuous slab casting machines, are cooled, scarfed to remove surface defects and either sent directly to hot strip mills for immediate rolling or stockpiled for future processing. The width of the slab determines the maximum width of hot-rolled coil that can be produced – a 1600 mm wide slab might produce 1500 mm finished coil after edge trimming.

Slabs represent a substantial commodity market worth billions of dollars annually, with major export flows from Brazil (particularly from integrated coastal mills), Russia and Ukraine to markets with limited steelmaking capacity but substantial rolling capabilities such as Turkey, Southeast Asia and North Africa. Slab chemistry varies based on intended end use: low-carbon slabs (0.04–0.10% carbon) for deep-drawing automotive applications, medium-carbon for structural uses and specific alloy compositions for electrical steel or tinplate applications.

What differentiates billets, blooms and slabs?

The fundamental difference lies in cross-sectional shape and intended downstream products. Billets and blooms are both square or rectangular sections destined for long products, distinguished primarily by size – billets under approximately 200 mm square feed light sections, rebar and wire rod; whilst blooms above 200 mm square become heavy structural shapes and rails. Slabs are flat products with one dimension (thickness) much smaller than width, exclusively feeding flat-rolled product mills.

Production processes differ accordingly: billet and bloom casters typically produce 4–8 strands simultaneously from a single tundish, whilst slab casters may produce 1–2 wider strands. Market dynamics also vary – billets enjoy the deepest international trade volumes with standardised specifications enabling commodity trading, slabs have substantial but more regionally concentrated trade flows and blooms represent the thinnest market with more bilateral producer-consumer relationships.

Pricing typically sees slabs commanding slight premiums over billets (perhaps US$20–40 per tonne) reflecting their role feeding higher-value flat products, whilst blooms trade similarly to billets. All three serve the critical function of allowing integrated steelmakers with excess casting capacity to supply re-rollers and mini-mills lacking their own melt shops, creating efficient two-tier production structures globally. See Long Steel Products and Flat-Rolled Steel Products for full coverage of downstream finished products.

Semi-Finished Steel Products Comparison

Key Differences: Billets and blooms are square sections for long products (distinguished by size), slabs are flat sections for flat-rolled products. Continuous casting replaced ingot casting for 96%+ of production due to superior yield (95–98% vs 85–90%), lower energy consumption and better surface quality. Billet market has deepest international trade (~50+ million tonnes annually), followed by slabs (~40+ million tonnes), whilst bloom trade is limited.

Production Process & Technology

How are semi-finished steel products made?

Modern semi-finished steel production overwhelmingly uses continuous casting, which replaced older ingot casting methods during the 1970s-1990s. The process begins when molten steel at approximately 1550–1600°C flows from a steelmaking furnace (BOF or EAF) into a ladle, then through a tundish (an intermediate vessel) into water-cooled copper moulds.

The moulds are open-bottomed with an oscillating motion that prevents the steel shell from sticking. As molten steel enters the mould, the outer surface immediately solidifies against the cooled walls, forming a shell that's progressively withdrawn downward at controlled speeds of 0.5–6 metres per minute depending on section size. Water sprays cool the emerging strand as solidification progresses inward toward the centre.

Once fully solidified – this might occur 8–15 metres below the mould depending on section thickness and casting speed – the continuous strand is cut to transportable lengths by high-speed oxygen torches or mechanical shears. Multiple strands (4–8 for billets, 1–2 for slabs) can be cast simultaneously from a single tundish.

The entire process runs continuously for 4–12 hours per sequence, with ladles exchanged whilst casting continues, achieving equipment utilisation rates of 85–95% in well-operated facilities. Capital costs for casting equipment are covered in our EAF Capital Investment data and Steel Plant Equipment guide.

What is continuous casting and why did it replace ingot casting?

Continuous casting revolutionised steelmaking by eliminating the batch process of ingot casting and primary rolling.

The old ingot method involved pouring molten steel into large moulds (ingots) weighing 5–25 tonnes each, allowing them to solidify completely over several hours, stripping the moulds, reheating the solid ingots to rolling temperature, then using massive primary mills (slabbing mills or blooming mills) to reduce the ingots to semi-finished sections – an energy-intensive process with typical yields of only 85–90% due to surface defects requiring cropping and scarfing.

Continuous casting achieves several critical advantages: yield increases to 95–98% as the process eliminates ingot cropping and surface conditioning steps; energy consumption falls by 0.5–1.0 GJ per tonne by eliminating reheating; capital costs decrease by removing primary rolling mills; and surface quality improves through controlled cooling.

The transition occurred gradually between 1970–2000, with continuous casting rising from under 10% of global steel production in 1970 to over 96% today. Only specialty products requiring specific solidification characteristics or extremely large cross-sections still use ingot casting, representing perhaps 3–4% of total production. The efficiency gains were so compelling that continuous casting capability became essential for competitive steelmaking.

🎧 Yield Loss Economics: The casting-stage crop losses, scale formation and batch sizing decisions that determine whether semi-finished yield reaches 95–98% or falls short are explored in Podcast Episode 6: Understanding Steel Mill Yield Losses (19 minutes).

What quality issues affect semi-finished steel?

Surface defects represent the most common quality concern in semi-finished products, arising from mould powder entrainment (slag inclusions trapped in the surface), mould sticking causing cracks or star cracks, or oscillation marks that create periodic surface depressions. Internal defects include centre-line segregation where alloying elements concentrate along the final solidification zone, porosity from trapped gases and internal cracks from thermal stresses during cooling.

Chemical composition variations occur if ladle mixing proves insufficient or if residual elements from scrap vary between heats. Dimensional deviations – thickness variations, width inconsistencies or crown (thickness difference between centre and edges in slabs) – affect downstream rolling efficiency and yield.

Quality control systems include continuous mould monitoring, strand surface inspection using cameras or laser systems, ultrasonic testing for internal soundness on critical products, and spectrographic analysis verifying chemistry. Modern plants achieve surface quality levels where 90–95% of cast surface reaches the downstream mill without requiring scarfing (flame cleaning) or grinding.

However, the commodity nature of most semi-finished products means buyers tolerate minor surface imperfections that don't affect final product quality – specifications typically allow surface defects up to 1–2 mm deep over 5% of surface area.

How does casting speed affect semi-finished product quality?

Casting speed fundamentally balances productivity against quality, with faster speeds increasing throughput but raising defect risks. Billet casters might operate at 3–5 metres per minute for 130 mm sections, whilst large slab casters run 0.8–1.5 metres per minute due to greater thermal mass requiring longer solidification times.

Faster casting reduces the time available for solidification, potentially creating thinner solid shells at critical points where support rollers apply pressure, increasing breakout risk (catastrophic failure where molten steel escapes containment). Speed increases also amplify the tendency for centre-line segregation and porosity, as the final solidification occurs more rapidly with less opportunity for micro-shrinkage to be fed by surrounding liquid.

Surface quality generally improves with moderate speed increases (up to a point) because the faster shell formation can reduce mould powder entrainment, but excessive speeds cause oscillation marks to deepen and increase star cracking risk. Modern electromagnetic stirring systems partially mitigate these issues by improving internal soundness at higher speeds.

Mills optimise casting speed based on steel grade – clean low-carbon steels might cast 15–20% faster than high-carbon or alloy grades more prone to cracking. Commercial pressures constantly push toward higher speeds, with incremental improvements in mould design, cooling water control and electromagnetic stirring enabling 20–30% speed increases over the past two decades whilst maintaining quality levels.

Market Dynamics & Trading

Why do semi-finished steel products get traded internationally?

The international semi-finished market exists because steelmaking (melting and casting) and steel rolling (producing finished products) require different optimal scales and can be geographically separated for economic advantage. Integrated mills with large blast furnaces and BOFs achieve the lowest costs at scales of 5–10 million tonnes annually, often exceeding local finished product demand or having product mix imbalances – excess casting capacity for billets but insufficient long product rolling capacity, for instance.

Simultaneously, EAF-based rolling mills in import-dependent regions might lack economical access to scrap or prefer semi-finished feedstock for quality consistency. This creates natural trade flows: CIS countries with large integrated plants and limited local demand export billets and slabs; Brazilian coastal mills with advantageous iron ore costs export slabs to Mediterranean re-rollers; Middle Eastern plants built around cheap energy export billets to South and Southeast Asia.

Transportation costs of US$30–60 per tonne for inter-regional shipment remain economical against building duplicate steelmaking facilities in import markets. Trade also balances seasonal or cyclical demand variations – a mill might export excess production during soft domestic markets whilst importing to supplement capacity during peaks. The semi-finished market thus provides flexibility and efficiency to global steel supply chains, with annual trade volumes exceeding 100 million tonnes for billets and slabs combined.

Which countries are major exporters of billets and slabs?

Russia and Ukraine historically dominated CIS semi-finished exports, though Ukrainian volumes collapsed following the 2022 invasion. Russian producers including NLMK, Severstal and MMK maintain substantial billet and slab exports despite sanctions complicating logistics and payments. Iran emerged as the world's largest billet exporter during the 2010s, with annual exports reaching 5–8 million tonnes, though US sanctions periodically disrupt trade flows.

Turkey serves as both major importer (processing CIS and Iranian billets into rebar and sections) and re-exporter of finished products. Brazil's coastal integrated mills – particularly CSN and Usiminas – are major slab exporters, with advantageous iron ore costs supporting competitiveness despite high labour costs. Middle Eastern producers in UAE (Emirates Steel) and Saudi Arabia (various mini-mills) export billets regionally.

China's position fluctuates dramatically – the country can swing from being the world's largest semi-finished importer during construction booms to a major exporter when domestic demand softens, causing significant market disruption. India maintains modest slab exports during periods of domestic overcapacity. See our global steel trade statistics for current import and export data.

Southeast Asian countries (Indonesia, Malaysia, Vietnam) import billets and slabs for re-rolling, with limited domestic steelmaking. This trade geography reflects the fundamental economics: low-cost steelmaking in resource-rich or energy-advantaged locations supplies re-rolling capacity in import-dependent markets.

How are semi-finished steel products priced?

Semi-finished products typically price as a discount to finished products, reflecting their intermediate position in the value chain. Billet pricing commonly references finished rebar prices minus a conversion margin of US$80–120 per tonne – this spread compensates re-rollers for reheating, rolling, cutting and bundling operations plus normal profit margins. When Turkish rebar exports trade at US$530 per tonne CFR Mediterranean, Black Sea billets might trade at US$450 per tonne CFR.

Slab pricing similarly references hot-rolled coil prices minus rolling margins typically US$100–140 per tonne, though this spread compresses when slab supply tightens or hot strip mill utilisation rates fall. Index-linked pricing predominates in international trade, with contracts specifying "Platts index minus $X" or "CRU price plus $Y" to reduce both parties' price risk. However, spot market transactions occur for immediately available material, often at significant premiums or discounts to indices depending on supply-demand balance.

Chinese domestic prices for billets and slabs effectively set floors for global markets – when Chinese construction activity slows and domestic prices fall, export offers emerge that pressure international prices downward. Regional price differentials persist due to transportation costs, quality perceptions (CIS material might trade US$10–20 per tonne below equivalent Middle Eastern material due to surface quality reputation) and geopolitical factors (Iranian material trades at discounts reflecting payment difficulties and sanctions risk).

Current market prices are tracked on our Semi-Finished Steel Prices page – see also Steel Pricing for broader context.

What role do traders play in the semi-finished steel market?

Steel traders serve as crucial intermediaries in semi-finished markets, particularly for buyers lacking established relationships with producing mills or seeking smaller parcels than mills prefer to sell directly. Large international trading houses – Trafigura, Stemcor, Duferco, Metinvest – maintain extensive producer networks, credit facilities and logistics capabilities enabling them to bridge geographical and commercial gaps.

Traders provide several key functions: they aggregate small mill outputs into full shipments, warehouse material to provide immediate availability, extend credit to buyers who might struggle to secure payment terms directly from mills and navigate complex sanctions and compliance requirements (particularly important for Iranian or Russian material). Trading margins typically range from US$8–25 per tonne depending on transaction complexity, payment terms and services provided.

Some steel traders operate on a purely merchant basis, buying and selling for profit, whilst others work on commission representing either producers or consumers. The rise of Chinese trading companies during the 2010s added considerable liquidity to semi-finished markets, with firms like Shagang and HBIS trading hundreds of thousands of tonnes monthly alongside their own production.

However, traders face constant pressure from direct mill-to-consumer relationships that bypass intermediaries, requiring them to add value through financing, technical services or market intelligence rather than simple product movement.

Specifications & Standards

What chemical specifications apply to billets for rebar production?

Billets destined for construction reinforcing bar typically specify relatively broad chemical ranges optimised for strength, weldability and cost rather than stringent composition control. Carbon content commonly ranges 0.18–0.25% for Grade 420 rebar (420 MPa yield strength) or 0.20–0.28% for Grade 500, providing adequate strength whilst maintaining good weldability. Manganese typically sits between 0.60–1.40%, contributing to strength through solid solution hardening without excessive hardenability that would impair weldability.

Sulphur and phosphorus are restricted – usually maximum 0.050% each, sometimes 0.045% – as these elements reduce ductility and increase hot shortness risk during rolling. Silicon ranges broadly from 0.15–0.50%, serving as a deoxidising agent. Residual elements from scrap use – copper, nickel, chromium, tin – are tolerated at levels up to 0.30% combined, though excessive residuals can cause surface cracking during hot rolling.

Nitrogen content matters for microstructure, with specifications typically limiting it to 0.012% maximum. Some markets specify minimum carbon equivalent values (CEV) to ensure consistent strength, whilst others rely on mechanical property testing of finished rebar. The relatively loose specifications reflect rebar's commodity nature – as long as the finished bar achieves required yield strength, tensile strength, elongation and bend test performance, precise billet chemistry is secondary.

This tolerance enables efficient scrap-based EAF production without expensive refining. The economics of converting billets to rebar are modelled in our Rebar Cost Model.

How do slab specifications differ for automotive versus construction steel?

Slabs destined for automotive applications demand substantially tighter chemistry control and lower residual elements compared to construction-grade material. Automotive deep-drawing steels require ultra-low carbon (0.003–0.08% depending on grade), achieved through secondary refining processes including vacuum degassing and sometimes ladle furnace treatment. Sulphur must stay below 0.015%, often below 0.010%, to prevent inclusions that create surface defects or formability issues – construction slabs might tolerate 0.040–0.050% sulphur without consequence.

Nitrogen control proves critical for automotive grades, requiring levels below 0.005% to prevent strain ageing and ensure consistent forming behaviour, achieved through aluminium killing (0.020–0.060% aluminium addition). Residual copper should remain under 0.08%, nickel below 0.06%, to avoid hot shortness and surface quality issues – residuals matter less for structural products where surface appearance is secondary. Automotive slabs typically specify inclusion ratings using microscopic examination methods, rejecting material with excessive oxide or sulphide inclusions that might cause defects during stamping.

Silicon content requires tighter ranges (0.01–0.03% for interstitial-free steels versus 0.10–0.40% for structural grades) to optimise forming characteristics. Continuous casting parameters differ too – automotive slabs often use electromagnetic stirring throughout solidification and careful cooling control to minimise centre-line segregation, whilst construction slabs tolerate more segregation.

The price differential for automotive-quality slabs over construction grades can reach US$80–150 per tonne, reflecting both chemical purity costs and the tighter process control required. The economics of converting slabs to hot-rolled coil are covered in our HRC Cost Model.

What dimensional tolerances apply to semi-finished products?

International standards specify dimensional tolerances balancing production capability against downstream processing requirements. For billets, typical tolerances include: cross-sectional dimensions ±2 mm for sides under 150 mm (so a 130 mm billet might range 128–132 mm), thickness variation within a single billet limited to 1.5 mm maximum, out-of-square limited to 1.5 mm (all corners should be close to 90 degrees) and length tolerances of +100 mm/-0mm (no short pieces, modest overlength acceptable). Surface concavity or convexity should not exceed 0.8% of the side dimension.

For slabs, thickness tolerances tighten: ±4 mm for slabs 200–250 mm thick, with crown (centre thickness exceeding edge thickness) limited to 5–8 mm depending on width. Width tolerances typically allow ±5 mm for slabs under 1800 mm wide. Length tolerances are more generous at ±200 mm since slabs get crop-sheared before rolling.

Blooms follow similar principles to billets but with slightly looser absolute tolerances given their larger size. These tolerances matter because downstream mills design their rolling schedules around expected input dimensions – a billet consistently 3 mm oversize forces the rolling mill to take heavier reductions in early stands, potentially causing excessive roll wear or productivity losses.

Conversely, undersize material might not fill the final finishing stands properly, creating dimensional problems in finished products. Modern casting equipment with automatic width control and online thickness measurement achieves these tolerances routinely, with 95%+ of production falling within specified ranges.

What surface quality requirements apply to semi-finished steel?

Surface quality specifications balance the cost of defect removal against downstream processing requirements and final product appearance needs. Semi-finished products destined for rebar or structural sections – where surface finish doesn't affect end-use performance – tolerate relatively rough surfaces with minor defects.

Typical specifications allow: surface cracks up to 2 mm deep over 5% of surface area, provided individual cracks don't exceed 150 mm length; transverse cracks limited to 0.5 mm depth; isolated pits or scabs up to 3 mm deep across 2% of surface; mild longitudinal seams or slivers not exceeding 1 mm deep.

However, slabs for cold-rolled automotive products demand near-perfect surfaces, often requiring scarfing (flame removal of 1–2 mm surface layer) or grinding to eliminate all visible defects. Specifications for these premium slabs might limit surface defects to 0.3 mm depth, essentially requiring defect-free casting or complete surface conditioning.

Inspection methods vary by criticality: visual inspection suffices for construction-grade material, whilst automated surface scanning systems using cameras or laser triangulation check premium products continuously during casting. Some mills classify semi-finished products into multiple quality tiers – Prime material with minimal defects commands standard pricing, whilst Secondary material with acceptable but more numerous defects sells at US$20–40 per tonne discounts to re-rollers producing less critical applications.

This grading allows mills to monetise production that doesn't meet Prime specifications rather than scrapping or downgrading to lower-value uses.

Economics & Value Chain

What profit margins do steelmakers earn on semi-finished products?

Margins on semi-finished products remain thin due to their commodity nature and intense competition, particularly from low-cost producers in CIS and Middle East. In stable market conditions, integrated producers might achieve EBITDA margins of US$30–60 per tonne on billet or slab exports – total costs of US$420–480 per tonne yielding revenues of US$450–540 per tonne. However, these margins compress dramatically during oversupply periods when Chinese exports flood markets or when raw material costs spike faster than selling prices adjust.

During 2015–2016 when Chinese billet exports surged, international margins fell to US$10–20 per tonne with some producers operating at cash-cost breakeven simply to maintain mill utilisation. Conversely, during tight supply periods (2021–2022 post-pandemic boom), margins expanded to US$80–120 per tonne as buyers competed for limited availability. EAF-based producers using scrap feedstock show more margin volatility since scrap prices fluctuate widely with steel cycles, whilst integrated producers using iron ore have more stable (but not necessarily higher) margins.

The marginal producer – typically defined as a CIS integrated mill with depreciated assets and low labour costs – can survive at margins near US$15–25 per tonne, setting effective market floors. This thin margin structure means semi-finished producers depend on volume throughput rather than per-tonne profitability, driving the constant push for higher casting speeds, longer casting sequences and maximum equipment utilisation to spread fixed costs across more tonnes.

For broader cost context see Steel Production Costs and Steel Market Outlook.