The ASTM A532 Class III A specification refers to a group of high chrome white irons (HCWI) with at least at least 23% Cr. This category of cast iron has been manufactured to offer high abrasion and corrosion resistance with high toughness particularly in corrosive environments. High chromium cast iron with more than 25% Cr, also known as tough chromium cast iron, has a combination of abrasion resistance with higher toughness. These alloys are used for thicker section castings that are exposed to a high impact, erosive and corrosive environment.
High chromium cast iron is heat treatable and generally produced in ferritic, martensitic and austenitic matrices. Their microstructure consists of a stainless steel-like matrix enclosed by hard chromium carbides (M23C6, M7C3, M3C). A key factor to their properties is a presence of hard Cr carbides within the ferrous matrix. Castings poured with this alloy can be machined in the annealed condition and usually avoids the need for drilling and tapping.
Abreco®produces modified high chromium cast irons with hypo-eutectic and hypereutectic chemistry for applications that require extreme wear to extreme corrosive materials with high fracture toughness.
Hypereutectic chemistry in HCWI has high carbide volume fraction (CVF) (Up to 45%) with martensitic matrix and has high hardness and abrasion resistance. Hypoeutectic chemistry has high Cr content with the ferritic (delta ferrite) matrix which increases corrosion resistance in oxidizing acids but not particularly in reducing acids. These categories are well known for their excellent corrosion and abrasion resistance. Figure -1 shows the typical microstructure of martensitic HCWI.
Mechanical and abrasion properties of these categories as a ratio function of matrix volume, chromium carbides type and volume fraction of carbides could be changed. Toughness and abrasive resistance can be modified by adjusting proportions, shapes and types of carbides.
Abreco® has performed extensive research and development to manufacture HCWI under strictly controlled foundry and heat treatment conditions delivering excellent and consistent wear and corrosion life in castings for industry. Abreco® cast chromium iron provides excellent resistance to shock and impact during its service life.
Tables 1-2-3 show typical chemical compassion and mechanical and abrasion resistance of HCWI.
Table-1 Chemical Composition (ASTM A532-III A)
Table-2 Mechanical and Physical Properties
Table-3 Wear and Abrasion Resistant Properties
High Chromium cast iron alloys have a good combination of wear, corrosion and mechanical properties. This family is suitable for the high-impact wear application since they have the highest fracture toughness in their family. These materials are used extensively in ground engaging wear applications and in the mining and aggregate industries such as self-mounted mining crusher liners, chute liners, slurry pumps, dredge impellers, pump housings, blow bars, Oil Sands/tailings pipe and separators applications.
High Chromium cast iron alloys produced in a wide range of mechanical and chemical properties in as-cast, Stress Relieved (SR), heat-treated condition.
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