Dictionary SubstancesMetalsAcicular Ferrite Acicular Ferrite Last updated: September 18, 2017 What Does Acicular Ferrite Mean? Acicular ferrite is a microstructure of ferrite in steel that is characterized by needle-shaped crystallites or grains when viewed in two dimensions. The three-dimensional grains have a thin, lenticular shape. This microstructure is advantageous over other microstructures because of its chaotic ordering, which increases toughness. Acicular ferrite is formed in the interior of the original austenitic grains by direct nucleation on the inclusions, resulting in randomly-oriented short ferrite needles with a “basket weave” appearance. Acicular ferrite is also characterized by high-angle boundaries between the ferrite grains. This further reduces the chance of cleavage, because these boundaries impede crack propagation. Advertisement Corrosionpedia Explains Acicular Ferrite In the late 1970s, the importance of an acicular ferrite microstructure in optimizing strength and toughness was identified. Since then, extensive research has been done on acicular ferrite formation and its relation to oxide inclusions, weld metal hardenability and cooling conditions. Acicular ferrite has a microstructure comprised of fine interwoven ferrite laths or plates, and was first recognized in high-strength, low-alloy (HSLA) steel weld metals. This fine interlocking structure was found to be a desirable microstructure in low-carbon steel weldments because it showed improved toughness over that of other transformation products, such as conventional bainite. Acicular ferrite is a fine Widmanstätten constituent, which is nucleated by an optimum intragranular dispersion of: Oxide Sulfide Silicate particles The interlocking nature of acicular ferrite, together with its fine grain size, provides maximum resistance to crack propagation by cleavage. Acicular ferrite has been obtained by both isothermal treatments and continuous coolings in a medium-carbon microalloyed forging steel. Lower cooling rates cause the development of other phases such as allotriomorphic ferrite or pearlite, but a high-volume fraction of acicular ferrite can be achieved using two-stage continuous cooling cycles. A two-stage continuous cooling cycle is the best heat treatment to produce acicular ferrite with a low-volume fraction of other phases such as allotriomorphic ferrite, pearlite, and/or martensite. Advertisement Share This Term> Related Terms Ferrite Free Ferrite Pig Iron Microstructure Crystallites Fracture Toughness Inclusions Pearlite Related Reading VIDEO: The Basics of Corrosion and Protection An Expert Guide To Accurate Cathodic Protection Measurements Leveraging AI for Enhanced Corrosion Control in Oil Pipelines Corrosion Jobs: How to Become a Corrosion Technician in 2023 The 6 Corrosive Components That Can Be Found in Crude Oil Rust in Bolted Systems: Causes and Prevention Tags Hardness Factor Prevention Substrates Abrasion Substances Substances Abrasion Protection Abrasion Management Metals Trending Articles Corrosion An Introduction to the Galvanic Series: Galvanic Compatibility and Corrosion Chemical Compound 5 Most Common Types of Metal Coatings that Everyone Should Know About Asset Management Understanding Aluminum Corrosion Asset Management If Copper is a Noble Metal then Why Are My Pipes Corroding?