Ultra-Thick Die Steel Steelmaking Process Research
Executive Summary
FUSHUN SPECIAL STEEL has developed advanced ultra-thick slab continuous casting technology designed by leading metallurgical engineering firms, incorporating state-of-the-art solidification end heavy reduction technology, secondary cooling electromagnetic stirring systems, and crown roll reduction techniques. This comprehensive casting system enables production of slabs with thicknesses of 350mm, 400mm, and 450mm, and widths ranging from 1600-2600mm, including ultra-thick crack arrest steels, high-end hydrogen service vessel steels, and ultra-thick die steels.
Currently, FUSHUN SPECIAL STEEL produces ultra-thick die steel plates reaching maximum thicknesses of 260mm, with ultrasonic testing standards meeting national Grade 1 requirements, enabling stable batch delivery to customers. Ultra-thick die steels including 718 and 2311 grades are typically utilized for large-scale or ultra-large high-precision plastic molds, demanding stringent steel quality requirements including clean steel composition, dense microstructure, narrow hardness ranges with high uniformity, and excellent machinability and wear resistance.
Advanced Casting Technology Overview
Production Challenges and Solutions
Production of ultra-thick die steels presents significant challenges requiring advanced process equipment and resulting in elevated production costs. Prior to FUSHUN SPECIAL STEEL’s ultra-thick slab continuous casting implementation, ultra-thick die steels were typically produced using ingot casting methods with lower yield rates and higher costs. Following ultra-thick continuous casting commissioning, 450mm cross-section slab production has improved production efficiency, enhanced steel plate yield rates, conserved energy, and substantially reduced production costs.
Compared to ingot casting methods, continuous casting advantages include continuous steel pouring capability, high production efficiency, flexible control of slab shape and length, with comprehensive yield rates exceeding ingot casting by over 20%. However, ultra-thick slab continuous casting inevitably encounters center segregation and center porosity issues, combined with minimal rolling compression ratios, creating significant challenges for post-rolling ultrasonic testing compliance.
Continuous Process Development
During 2021-2023, FUSHUN SPECIAL STEEL continuously explored ultra-thick die steel slab steelmaking processes, achieving significant progress in continuous casting technology with ultra-thick die steel ultrasonic testing pass rates stabilized above 95%. This comprehensive development program encompasses advanced refining techniques, optimized casting parameters, and sophisticated quality control measures ensuring consistent product quality.
The systematic approach to process optimization has established FUSHUN SPECIAL STEEL as a leading producer of ultra-thick die steels, meeting demanding industry requirements for precision tooling applications while maintaining cost-effective production through advanced continuous casting technology implementation.
Production Process Flow
Comprehensive Manufacturing Sequence
Ultra-thick die steel production flow encompasses: blast furnace hot metal → converter smelting → LF furnace refining → VD furnace vacuum treatment → ultra-thick slab casting → slab stack cooling → slab flame cleaning → furnace charging and heating → rolling → steel plate surface inspection → steel plate stack cooling → ultrasonic testing → steel plate heat treatment → ultrasonic testing (re-examination) → warehouse storage.
Critical processes include refining, continuous casting, and slab/plate stack cooling operations. Refining provides high cleanliness, low gas content molten steel; continuous casting forms uniform dense internal microstructure slabs; slab and plate stack cooling provides conditions for further hydrogen diffusion. Critical processes require strict quality control, with non-compliant slabs or plates regraded to alternative steel grades. These measures ensure dense steel plate internal microstructure without segregation or minor porosity defects, achieving uniform surface and core hardness.
Chemical Composition Design
Carbon represents a strong interstitial solid solution strengthening element, playing crucial roles in die steel hardness, toughness, and wear resistance. Increased carbon content enhances steel strength, hardness, and wear resistance while negatively impacting steel toughness. Therefore, carbon content control represents a key technical consideration in steel production. Steel wear resistance demonstrates direct correlation with carbon content optimization.
Within steel alloy systems, manganese serves critical functions by dissolving into ferrite and cementite, strengthening steel strength and hardness while combining with sulfur to form high-melting-point manganese sulfides, reducing sulfur’s detrimental effects. Manganese content should be controlled at upper-medium limits to ensure optimal steel performance. Chromium significantly enhances steel hardenability and tempering stability, with secondary hardening effects further improving steel hardness and wear resistance, effectively expanding steel application ranges.
FUSHUN SPECIAL STEEL Ultra-Thick Die Steel Chemical Composition (wt%)
Smelting Process Control
Ultra-thick die steel composition complexity remains moderate, requiring no special hot metal composition requirements, typically utilizing high-quality self-produced scrap steel. Blowing endpoint requires P content ≤0.015% before tapping, with tapping processes employing slag detection and tapping temperatures ≥1615°C. During tapping, alloys and aluminum-based deoxidizers are added with steel flow for deoxidation and alloying, with aluminum-based deoxidizer additions at (1.1-1.2) kg/ton steel.
LF furnace refining requires circulation ladles, prohibiting major repair ladles due to extended station smelting times, avoiding exposed tapping effects on molten steel cleanliness. Flow sand requires chromium-based flow sand with silicon-based flow sand covering. Steel ladle station operations require adequate smelting time (generally ≥50min), employing high slag volume slag-making processes with rapid white slag formation and white slag maintenance time ≥15min.
Continuous Casting Technology
Production Preparation and Conditions
Ultra-thick slab continuous casting machine characteristics require comprehensive pre-production preparation. Before casting machine startup, adequate time must be coordinated for casting machine precision inspection and secondary cooling nozzle compliance verification, ensuring optimal production conditions. Each ultra-thick die steel production campaign requires casting machine roll gap inspection, examining segment and bending section roll gaps and arc connections, with standard roll gap settings of ±0.5mm, requiring immediate adjustment or replacement of deviated roll gap points.
For ultra-thick die steels, internal slab quality receives priority consideration, with surface quality addressable through downstream flame cleaning processes. Therefore, casting machines employ low casting speed modes with typical strand drawing speeds of (0.425-0.450) m/min, roll gaps utilizing “450 high carbon steel” mode, and mold reverse taper of 1.3% (m⁻¹). These parameters ensure optimal internal quality characteristics while maintaining production efficiency requirements.
Electromagnetic Stirring Technology
Electromagnetic stirring effectiveness varies according to installation position differences, with current installations primarily encompassing mold electromagnetic stirring (MEMS), secondary cooling zone electromagnetic stirring (SEMS), and solidification end electromagnetic stirring (FEMS). MEMS typically employs rotational stirring methods, promoting inclusion and bubble convergence toward center regions and flotation for absorption by molten protective slag, reducing inclusion and bubble quantities in slab surface and subsurface regions while ensuring uniform shell growth and reducing breakout accident probability.
SEMS technology primarily utilizes steel stirring to fracture previously formed columnar crystals, integrating them with molten steel, with fractured columnar crystals subsequently becoming equiaxed crystal formation nuclei. This zone electromagnetic stirring core objective enhances equiaxed crystal proportions while optimizing segregation conditions. Slab production utilizing light reduction technology with significant liquid core length differences when casting different steel grades makes solidification end electromagnetic stirring technology applications less common for large slabs.
FUSHUN SPECIAL STEEL Electromagnetic Stirring Process Parameters
Solidification End Reduction Technology
Continuous casting solidification end reduction technology was developed by Japanese companies to address ultra-thick continuous cast slab center porosity issues. This method establishes reduction rolls at continuous casting machine segment ends, applying heavy reduction forces when slab center solid fraction exceeds 80%, reducing slab center porosity severity and decreasing rolling reduction ratio requirements.
This process produces slabs achieving excellent internal quality ultra-thick steel plates under 1.5-2.5 compression ratio rolling conditions, effectively reducing thick slab center porosity and shrinkage cavity issues. 450mm slabs produced using this process achieve maximum rolled product thicknesses reaching 260mm. FUSHUN SPECIAL STEEL’s ultra-thick slab continuous casting machine incorporates solidification end heavy reduction technology from initial design, with segments 10, 11, 12 providing maximum 5mm single-segment reduction and segments 13, 14, 15 providing maximum 10mm single-segment reduction.
FUSHUN SPECIAL STEEL Production Parameters and Quality Results
Slab Stack Slow Cooling Process
Hydrogen Control Fundamentals
In steel materials, hydrogen represents a critical factor affecting steel quality. Hydrogen causes steel white spots, hydrogen embrittlement, and hydrogen-induced cracking, severely compromising quality and performance. For small-dimension steel plates, minimal hydrogen effects remain insignificant; however, in thick-specification steel plates, hydrogen diffusion and elimination prove extremely difficult, causing internal plate testing non-compliance and reduced Z-direction performance deterioration.
During medium and heavy plate production, effective hydrogen content control represents critical technical considerations. Comprehensive hydrogen diffusion process research, clarifying diffusion patterns, and subsequently developing efficient hydrogen removal processes hold significant importance for medium and heavy plate production. FUSHUN SPECIAL STEEL’s systematic approach to hydrogen management ensures superior product quality across thick section applications.
FUSHUN SPECIAL STEEL Hydrogen Content vs. Testing Pass Rate Analysis
Stack Cooling Implementation
Ultra-thick die steel production requires tundish molten steel hydrogen content monitoring, with statistical analysis revealing direct correlation between tundish hydrogen content and ultrasonic testing pass rates. Lower tundish hydrogen content results in higher ultra-thick die steel testing pass rates. Ultra-thick die steel slabs require specific stack cooling periods after strand exit, utilizing insulation covers for slow cooling while maintaining slab temperatures above 300°C for adequate hydrogen diffusion and elimination.
Following slab temperature cooling completion, stack dismantling and conditioning occur with conditioning depths generally exceeding 5mm, checking for surface cracks and other defects. When tundish hydrogen content exceeds 0.00020%, extended stack cooling periods or slow cooling pit applications become necessary for adequate hydrogen removal. This systematic approach ensures consistent product quality meeting demanding ultrasonic testing requirements.
Research Conclusions and Industrial Implementation
Key Technical Achievements
Primary Finding:
Ultra-thick die steel plate production utilizing 450mm cross-section continuous cast slabs requires refining processes providing high-quality molten steel and reasonable continuous casting reduction process settings, prioritizing slab internal quality assurance. This comprehensive approach ensures consistent achievement of demanding quality specifications.
Process Optimization Discovery:
Secondary cooling electromagnetic stirring processes improve slab low magnification center segregation conditions but adversely affect slab center porosity characteristics. Ultra-thick die steels prove unsuitable for secondary cooling electromagnetic stirring technology applications, requiring alternative process approaches for optimal quality achievement.
Critical Quality Control:
Ultra-thick die steels demand extremely strict hydrogen content requirements, with tundish molten steel hydrogen content targets ≤0.00015% and maximum limits not exceeding 0.00020%. Exceeding these limits requires corresponding slab hydrogen removal measures including extended stack cooling or specialized slow cooling pit applications.
Industrial Production Benefits
FUSHUN SPECIAL STEEL’s ultra-thick die steel production achievements demonstrate significant industrial benefits including improved production efficiency, enhanced yield rates, reduced energy consumption, and substantially lower production costs compared to traditional ingot casting methods. The systematic approach to process optimization has established reliable production protocols ensuring consistent quality achievement.
Comprehensive yield rates exceeding ingot casting by over 20% combined with 95%+ ultrasonic testing pass rates validate the effectiveness of advanced continuous casting technology implementation. These achievements position FUSHUN SPECIAL STEEL as a leading producer of ultra-thick die steels for demanding precision tooling applications.
Future Development Directions
Continued research and development initiatives focus on further optimization of solidification end reduction technology, enhanced hydrogen control measures, and advanced quality monitoring systems. Integration of artificial intelligence and machine learning technologies promises additional improvements in process control precision and product quality consistency.
Collaboration with customers and research institutions continues advancing ultra-thick die steel applications, expanding grade varieties, and developing specialized compositions for emerging high-precision tooling requirements. FUSHUN SPECIAL STEEL’s commitment to innovation ensures continued leadership in ultra-thick die steel manufacturing technology.
Conclusions and Technical Impact
FUSHUN SPECIAL STEEL’s comprehensive research and development of ultra-thick die steel steelmaking processes has established new industry benchmarks for continuous casting technology application in specialized steel production. The systematic approach to process optimization, incorporating advanced solidification end reduction technology, optimized electromagnetic stirring protocols, and precise hydrogen control measures, ensures consistent production of ultra-thick die steels meeting the most demanding quality specifications.
The achievement of 95%+ ultrasonic testing pass rates with maximum plate thicknesses reaching 260mm demonstrates the effectiveness of integrated process control strategies. These technological advances enable cost-effective production of high-quality ultra-thick die steels for precision tooling applications while maintaining superior internal quality characteristics.
Through systematic research, process optimization, and continuous improvement initiatives, FUSHUN SPECIAL STEEL has transformed ultra-thick die steel production from traditional ingot casting limitations to advanced continuous casting capabilities, providing enhanced production efficiency, improved yield rates, and superior product quality for demanding industrial applications.
FUSHUN SPECIAL STEEL’s innovative approach to ultra-thick die steel manufacturing represents a significant contribution to global steel industry advancement, establishing new standards for quality, efficiency, and technological excellence.
