When a piece of equipment handles rocks, slurry or any other abrasive material, the parts inside take a beating. Chutes wear thin. Pumps lose their walls. Impellers erode down to nothing. Regular steel does not last long in these conditions, which is why foundries turn to high chrome white iron. The specification that covers this family of alloys is ASTM A532.
What Is ASTM A532?
ASTM A532 is the standard specification for abrasion-resistant cast irons. These are not the gray irons used for engine blocks or the ductile irons used for heavy truck parts. High chrome white irons are built for one job: standing up to wear. They contain between 11% and 30% chromium, along with other elements that form hard carbides inside the metal. These carbides act like tiny armor plates throughout the casting, stopping abrasive particles from tearing into the surface.
The standard is broken down into classes and types. Each one has a different chemistry and hardness range. Choosing the right one depends on the application, the type of wear and whether corrosion is also a factor.
Class I: Ni-Hard
Class I covers nickel-chromium irons – commonly called Ni-Hard. These alloys have been around the longest and they offer good abrasion resistance at a lower cost when nickel prices are favorable. Ni-Hard is often used for handling cement slurry and other moderately abrasive materials. It does not, however, have the same level of hardness or corrosion resistance as the higher chrome classes.
Class II: Medium Chrome
Class II alloys contain less chromium than Class III but still offer solid wear resistance with improved toughness. The Type A (12% Cr) works well for chute liners, small wear pumps and recycling parts like paddle blades. Type B (15-3) has slightly fewer carbides, which gives it a bit more toughness for ball mill liners and dredging components. Type D (20-1) adds molybdenum to maintain hardness and is a good fit for thicker castings in mining and crushing.
Class III Type A: High Chrome White Iron
Class III Type A is the most common high chrome white iron. It contains 11% to 30% chromium and delivers hardness levels that typically start at 550 BHN and go up from there. Foundries can adjust chemistry and heat treatment to produce different grades for different jobs within this single type.
Where ASTM A532 Gets Used
High chrome white irons show up wherever materials move against metal. Mining operations use these castings for slurry pumps, cyclones and crusher parts. Oil sands producers rely on them for hydrotransport lines and pump boxes. Recycling facilities put them in shredders and hammermills. Even cement plants use Ni-Hard for handling raw mix and clinker.
The common thread is abrasive wear. If the material being processed contains sand, rock, ore or any other sharp particle, an ASTM A532 casting will outlast carbon steel by multiple times.
What About 30% Chrome?
Some applications need corrosion resistance along with abrasion resistance. The 30% chrome white iron sits outside the main A532 classes but falls under the same family. It offers the best corrosion resistance of any high chrome white iron, making it a good fit for flue-gas desulfurization systems and other environments where oxidation is a problem. The trade-off is slightly lower abrasion resistance compared to the 25% chrome alloys.
Working with ASTM A532
Not every foundry pours high chrome white iron. The material behaves differently than gray or ductile iron. It shrinks more and requires careful gating and risering. Machining is difficult because the carbides that provide wear resistance also dull cutting tools quickly. Some grades of ASTM 532 are designed to be machined in a soft state before being heat treated to final hardness.
MACA Casting pours ASTM A532 alloys for customers who need parts that last. If your pumps, chutes or crushers are wearing out too fast, talk to us about high chrome white iron.