ASTM A532/A532M-10(2023) is the standard specification for abrasion-resistant cast irons, grouping white cast irons engineered for mining, milling, earth-handling and manufacturing service [S1].
The standard organizes these alloys into three classes and several types, with the high-chromium group (Class III) running 11% to 30% Cr and delivering Brinell hardness from roughly 550 BHN up past 680 BHN depending on chemistry and heat treatment [S2][S4].
Class I Ni-Hard: nickel-chromium baseline
Class I Type A Ni-Hard 1 has been in production the longest of any ASTM A532 alloy and is the lower-cost option when nickel pricing is favorable [S2]. Pacific Alloy and other North American foundries cast Ni-Hard for low-impact sliding abrasion, both wet and dry, with typical service in mill liners, mixer tips, slurry pumps, brick and asphalt, cement, concrete, rock, sand and gravel handling [S3].
The Class I family also includes Type D Ni-HiCr, a nickel-chromium grade carrying 7% to 11% Cr and offering a higher hardness ceiling than classic Ni-Hard, which makes it a common pick for crusher wear parts and grinding mill components [S6]. When toughness, abrasion resistance and any corrosion resistance are required together, the high-chrome group of white irons is generally considered superior to Ni-Hard [S3].
Class II medium-chromium: 12% to 20% Cr
Class II covers medium-chromium white irons sitting between Ni-Hard and the high-chromium family, and is split into Type A (12% Cr), Type B (15% Cr-3% Mo, also called 15-3) and Type D (20% Cr-1% Mo, also called 20-1) [S4].
Type A 12% Cr is widely used for chute liners, small wear pumps and recycling parts such as paddle blades; Type B 15-3 trades some carbide content for additional toughness, which puts it into ball mill liners and dredging components; Type D 20-1 adds roughly 1% Mo to preserve hardness through thicker sections, suiting it to mining and crushing castings [S4].
Class III Type A: the high-chromium workhorse
Class III Type A is the most common high-chromium white iron, with Cr content from 11% to 30% and hardness levels that start around 550 BHN and run well above that with adjusted chemistry and heat treatment [S4].
Within this single type foundries offer differentiated grades: a "softenable" variant machinable in the annealed state and then hardened beyond 600 BHN for pump volutes, impellers and hydraulic fracturing liners; a 25% Cr grade typically supplied at greater than 650 BHN for slurry pumping and crushing; a higher-carbide grade usually exceeding 680 BHN for chute liners and blow bars; and a toughened 25% Cr grade engineered for through-hardness in thick sections like gyratory crusher concaves [S2].
Hardness, abrasion resistance and toughness in this class are functions of matrix volume, chromium carbide type (M23C6, M7C3, M3C) and carbide volume fraction, with hypereutectic chemistries reaching carbide volume fractions up to 45% in a martensitic matrix [S5]. High-chromium iron is heat-treatable and is generally produced in ferritic, martensitic or austenitic matrices, and castings can be machined in the annealed condition to avoid field drilling and tapping [S5].
Where each class actually gets specified
Ni-Hard Class I stays the default for handling cement slurry, raw mix and clinker in cement plants, and for low-impact mill liner and mixer tip service [S3]. Class II medium-chromium grades are typically specified for ball mill liners, dredge pumps, paddle blades and chute liners where some toughness is needed but full high-chrome cost is not justified [S4].
Class III Type A is specified for the harshest combined-abrasion jobs: slurry pump liners and impellers, cyclone components, crusher liners, blow bars, oil sands hydrotransport piping, tailings lines and pump boxes, plus shredder and hammermill parts in recycling [S2][S3][S5]. When corrosion is part of the service, a 30% Cr variant (related family, not the main A532 classes) is chosen for flue-gas desulfurization and other oxidizing environments, with the trade-off of slightly lower abrasion resistance versus 25% Cr grades [S4].
Foundry reality: casting and machining constraints
High-chromium white iron is not a drop-in for gray or ductile iron: it shrinks more, demands careful gating and risering, and is difficult to machine because the same carbides that deliver wear resistance also dull tooling fast [S4]. Foundries mitigate this by pouring certain grades in an annealed, machinable condition, then heat-treating to final hardness after drilling, tapping or broaching [S2][S4]. White iron cannot be made machinable by any downstream thermal treatment without converting it to malleable iron, which destroys its wear resistance, so the anneal-then-harden route is the only practical path for finished machined parts [S7].
Specifications for these castings, including impact and wear test requirements, are also covered under ASTM A532 alongside chemistry and hardness, and buyers should pin the Class/Type designation plus any supplementary hardness or impact callouts on the purchase order rather than relying on trade names alone. For broader wear-component selection context, see the comparison of grinder sizes and materials in angle grinder cutting capacity and selection map.
The underlying component specifications are covered under cast iron, high voltage tester, and pressure transmitter.