Steelmaking Innovation by Better Refractories

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1 Steelmaking Innovation by Better Refractories Prof. Dr. H. Jansen REFRATECHNIK Steel

2 World refractory Consumption The Dominating Role of Iron- and Steelmaking 4 % 7 % 2 % Iron and Steel Non Ferrous Cement Lime Glas Ceramic Energy 68 % Chemistry Incineration Rest

3 Requirements of the Steelmaking Industry in the Refractory Makers Refractories play an important role in steelmaking processes This is why the performance of refractories is essential to fulfil targets and goals of the steelmakers in terms of: Output and Quality Safety Environment and Sustainabikity Innovation of Steel Products

4 Consequences of a ladle break through Outflow of ~ 50 to of liquid steel Destruction of equipment and constructions Downtime of the steel plant Damages worth millions

5 The Magnesia-Carbon Brick (MgO-C): The standard and state-of-the-art refractory material in the steel industry: High refractoriness Good compatibility with basic slags Non wettability properties of the graphite High flexibility and thermal shock resistance Availability

6 The Magnesia-Carbon Brick (MgO-C): Features: Unfired, organically bonded Based on magnesia grades with 94 to 99 % MgO Graphite contents between 3 and 25 % Possible addition of additives like antioxidants or steel fibers Post-treatments like surface coating, pitch or resin impregnation Available in ~ 500 different shapes and ~ 150 different grades (combinations of MgO grade, graphite content, additives etc.)

7 1 st Example Demand for Safe and Reliable BOF-Service Very often only one or two BOF are available in a steelplant, i.e: Cycling between operation, dismantling and relining has to be well adjusted. Premature shut down of a BOF leads to tremendous problems in the supply chain from blast furnace to rolling mill. So, the reliability and performance of the refractories in a BOF are essential not only for the steelplant, but for the whole production site. Often the scrap-impact, a zone of extreme wear, limits the total lifetime of the refractory lining and is responsible for shutdowns before time.

8 The Scrap Impact Zone of a BOF Zone of maximum load in terms of: mechanical stress slagging thermal stress

9 Solution: Steelfibre-Reinforced MgO-C-Bricks Fibre reinforcements generally increase the toughness and tolerance against damage of any kind of materials. But: The temperatures in a BOF of 1750 C exceed the maximum application temperatures of any stainless steelfibre. Solution: The fibres have to be protected against meltout by a ceramic coating

10 Steelfibre-Reinforced MgO-C-Bricks The fibre-addition modifies the crack pattern in the brick: without fibres macro-cracks fibre-reinforced: micro-cracks

11 Steelfibre-Reinforced MgO-C-Bricks Cross-section of a stainless-steel-fibre after 85 heats in a steel ladle Magnesia Dense Layer Stainless Steel Droplets

12 Steelfibre-Reinforced MgO-C-Bricks Formation of a protective coating: Reactions between fibres, refractories and atmosphere during the steel-making process: Stainless Steel Fibre Air Oxygen Scale (1) (2) (Cr x,fe y ) + n O 2 Internal Reaction in the MgO-C-Brick Cr x Fe y O 2n Appr C MgO + C Mg (gas) + + CO (3) Cr x Fe y O 2n + 2n Mg (gas) 2n MgO + (Cr x,fe y ) Scale + Magnesium Vapour Magnesia Dense Layer Stainless Steel Droplets

13 Steelfibre-Reinforced MgO-C-Bricks Influence of Stainless Steelfibres on the Properties of MgO-C-Brick cold hot Standard with Steelfibres Young's Mod. CCS opor HMOR WOF Displacement

14 2 nd Example: Demand for Steel-Ladle-Linings with High Performance and Lowest Smoke Emissions During Preheating In comparison to ceramic refractories MgO-C bricks leave the factory and are installed in an unfinished state: Most of volatile components from the binder are still in the brick due to low temperature treatment. The bricks do not exhibit their final properties (strength, open porosity, etc.) yet.

15 Emissions [kg/to.] Properties of Ordinary MACARBON Bricks Emissions Of Resin-Bonded MgO-C Bricks During Coking Between 20 C and 1000 C maximum minimum H2 CH4 CO CO2 CxHy H2O Phenole Aromates Benzo- (a)- pyrene Carbon Soot

16 CCS, Young's Modulus [MPa] op [%] Properties of Ordinary MACARBON Bricks Properties as a function of treatment temperature CCS [MPa] Young's Modulus [MPa] Open Porosity [%] Treatment Temperature / Max. Temperature Level [ C]

17 Fireclay 40 MgO brick, resin bonded MgO ramming mix Temperature [ C] Temperature Profile in a Ladle preheating to 1100 C preheating to 1200 C after first heat 50 mm wear 100 mm wear 150 mm wear 200 mm wear Distance from ladle shell [mm] MgO-C (5-7 % C) wear lining

18 Ceramically Bonded MACARBON (CBMC) Bricks Features: CBMC bricks are prefired at elevated temperatures and reducing atmosphere by a special new firing technology. Volatile components are completely removed from the bricks and combusted inside the kiln to water and carbon oxides, resulting in a real Zero-Emission-Brick. The firing leads to a partially ceramised MgO-C brick with a unique combination of flexible graphitic bond and a rigid and durable ceramic bond. The ceramic bond equalizes the varying strengths and the decline of carbon-bond dependant on the thermal history of the MgO-C-brick.

19 Ceramically Bonded MACARBON (CBMC) Bricks The ceramic bond in MACARBON Bricks cannot be generated by a solid-state reaction like ordinary ceramics, because carbon does not have any sintering properties. Sintering is maintained by internal redox-reactions, that take place between MgO and carbon: MgO + C -> Mg (g) + CO Reoxidation: 2 Mg (g) + O 2 -> 2 MgO This phenomenon is well-known in literature as MgO Dense Layer by reoxidation of Mg on the surface of MgO-C-bricks. In Ceramically Bonded MACARBON Bricks these reactions provide ceramic linkages within the brick.

20 Ceramically Bonded MACARBON (CBMC) Bricks Microphoto of an MgO-C brick (tempered 6h at 1650 C, embedded in coke) Light grey particles are periclase (MgO), darker grey matrix is graphite (C)

21 CCS [MPa] Ceramically Bonded MACARBON (CBMC) Bricks Properties as a function of treatment temperature CBMC ordinary MgO-C brick Treatment Temperature [ C]

22 Ladle Lifetime [number of heats] Results in VOD-Steel Ladle Linings Approx. 10 % higher lifetime in Stainless Steel Ladles CBMC ordinary MgO-C brick

23 Steelmaking Innovation by Better Refractories Summary: Although the share of costs of refractories is relatively low (appr. 4 %) they have a tremendous impact on quality, performance and safety of steelmaking processes. Advanced refractories can improve steelmaking processes. Our message to all steelmakers: Choose for the best and most suitable refractories to outperform old fashion processes and increase your benefit!