Evaluation of two AISI 4037 cold heading quality steel wires for improved tool life and product quality

One automobile fastener is manufactured from a cold heading quality (CHQ) steel wire obtained from two different sources. Both wires are spheroidize annealed and phosphate coated. Their microstructures, compositions, and mechanical properties have been evaluated in order to establish the characteristics of a good stock wire that can improve the tool life leading to higher productivity and product quality. The present study revealed that a good quality feed stock for cold heading must be a subtle combination of a uniform microstructure and a phosphate coating without any presence of roll seam and/or rust. The spheroidization ratio indicates the effectiveness of an annealing process. The aspect ratio of cementite as a result of spheroidize annealing influences the mechanical properties of the stock material. The higher the spheroidization ratio (with an aspect ratio of cementite less than 2), the lower will be the flow stress of the material and the better will be its formability. This could improve tool life. Stock wire containing inclusions of MnS-stringers, approximately 30 μm long, and aligned along its length can badly affect the quality of a fastener, and can contribute to an early failure when employed in service. However, small inclusions of both sulphides and oxides, less than 6 μm long, have little influence on product quality.