The Effect of Strength and Work Hardening Characteristics on the Headability of Austenitic Stainless Steel Wires

Abstract

There have been studied the effects of volume fraction of martensite, stacking fault energy, austenite grain size and solid solution hardening on the strength, work hardening behavior and other mechanical properties of austenitic stainless steel wires. We tried to evaluate systematically the headability of the relationship between the mechanical and physical properties and the headability.
The main results are as follows:
(1) The work hardening behavior (n-value) is mainly decided by volume fraction of martensite and stacking fault energy, that is, steel KSS 70 containing 3% Cu (18Cr-9Ni-3Cu) and SUS 384 (16Cr-18Ni) show lower n-value than SUS 305 J 1 (18Cr-13Ni) as a result of high stacking fault energy even in the presence of strain induced martensite.
(2) The yield strength becomes higher with the increase of solution elements such as C, N, and Mo and with the decrease of austenite grain size following the Petch relationship.
(3) In SUS 304-7 (18Cr-8Ni), the n-value and elongation decrease slightly with the increase of austenite grain size. On the other hand, a contrary tendency is seen in the stable alloys such as SUS 384, 385, 305 J 1 and etc. In the tensile test, the reduction of area gradually decreases with the increment of grain size.
(4) There can be seen an obvious relationship between the headability of each specimen ranked from 1st to 8th and the hardening factor H. F., defined as yield strength times n-value, that is, the low hardening factor results in an excellent headability.
(5) Factors affecting headability can be classified to two groups such as;(i) strain induced martensite, stacking fault energy, and grain size which affect headability as a result of the change in yield strength and n-value, (ii) inclusion, surface scratch, and heading technique which affect headability without change in yield strength or n-value.