Cast Steel Quality Upgrade: Clean Steel Refining and Key Material Process Control Points

As downstream equipment becomes larger and more highly parameterized, competition in steel castings is shifting from output to quality, variety and performance. Recent industry literature has accumulated much practical experience on clean-steel refining, production of high-Mn and wear-resistant steels, and the process of martensitic stainless steel castings. This article compiles the key points for technical and management staff of foundries.

Refining Routes for Clean Steel

Clean steel generally means steel castings in which macroscopic oxide inclusions (including sulfide and nitride inclusions) are strictly controlled, typically requiring [S]+[O] (or [N]) below 150 ppm, with ultra-clean steel below 100 ppm. For small and medium foundries using mainly induction furnaces, charge quality and process metallurgy are limited, and argon ladle purification is a cost-effective method: blowing argon through porous plugs at the ladle bottom for stirring and deoxidation can lower oxygen from 120–140 ppm to 30–50 ppm, greatly reducing oxide inclusions. Building on this, Ca-Si and Al-Ca cored-wire feeding stably controls residual Al and raises alloy yield; studies show this reduces casting defects by about 40% on average and up to 60% under optimal conditions. For stainless and special alloy steels, secondary refining such as AOD, VOD, LF and vacuum refining has become mainstream, with over 75% of global stainless steel produced via AOD; LF furnaces under 30 t are limited by lining life and need careful evaluation for batch foundry production.

High-Manganese and Wear-Resistant Steels: Composition Must Match Service Conditions

High-Mn steel (ZGMn13 type) is the best-known wear-resistant material, but it is not "the harder the better." The basic requirement for wear parts is proper matching of hardness and impact toughness; over-emphasizing either high hardness or high toughness backfires. A reasonable composition for high-Mn steel is C 0.9–1.5%, Mn 10–15%, Si≤1%, P≤0.1%; heavy-impact service should use low carbon (0.9–1.05%) for toughness, while non-heavy-impact service can use somewhat higher carbon. Keeping the Mn/C ratio at 8.5–10.2 is appropriate; below this, carbides precipitate after water toughening. For low-energy impact with relatively soft abrasive, ordinary high-Mn steel is actually not wear-resistant; medium-Mn steel (Mn 7.5–8.5%) or alloying high-Mn steel with 1.5–2% Cr performs better. Under strong acidic, alkaline, or corrosion-plus-wear conditions, select chromium-series wear-resistant steel or wear-resistant white cast iron by medium pH and temperature, and avoid blindly choosing high-alloy materials for wet grinding mills.

Martensitic Stainless Steel Castings: Joint Control of Heat Treatment and Composition

Martensitic stainless steels represented by Cr13Ni4Mo have become the preferred material for large hydropower castings (upper crown, lower ring, blades). Key control points include: first, composition optimization—suppress δ-ferrite by controlling the Ni-equivalent to Cr-equivalent ratio (≥0.42), keeping carbon below 0.1% and adding about 0.3% Mo to improve passivation. Second, heat treatment—quench at about 950–1050°C, with spray or forced-air cooling for heavy sections; tempering must begin only after the casting cools below the martensite finish temperature Mf (about 150°C), otherwise retained untempered martensite causes substandard properties. Third, surface quality—resin sand molding may carburize the casting surface; adding about 3% iron oxide powder to the sand significantly mitigates this, while sodium-silicate bonded sand has no carburizing concern. Studies also show that after LF, AOD or VOD secondary refining, the impact toughness of these steels is greatly improved.

Furnace-Side Rapid Detection: Ensuring Process Discipline Is Implemented

Whether controlling oxygen in clean steel, checking the C/Mn ratio in high-Mn steel, or managing pouring temperature for martensitic stainless steel, a stable process depends on fast, accurate furnace-side data. Foundries are advised to pair electric furnaces and ladle stations with fast thermocouples and molten-steel samplers to achieve rapid furnace-side detection of temperature and composition, providing an instant basis for tapping temperature, alloy addition and refining rhythm, turning these process parameters from "experience control" into "data control."

Upgrading steel casting quality is a system project spanning charge, melting, refining and heat treatment. By grasping the three core links—cleanliness, matching composition to service conditions, and the heat-treatment window—and locking process discipline with reliable furnace-side detection, small and medium foundries can steadily improve casting quality and overall benefit without blindly buying large equipment.