Tensile Deformation Process and Uniform Elongation of 1700 MPa Grade 18Ni Maraging Steel

The characteristics of plastic deformation of 1 700 N/mm2 grade maraging steel were revealed from the precise true stress-true strain curves and the strain hardening rate-true strain curves, and from the observation of dislocation structure. The factors affecting the uniform elongation were discussed.1) The plastic deformation was mainly composed of the four kinds of fundamental stages.2) In the solution-treated or under-aged steels, the plastic deformation was composed of the first stage which was affected by the martensite transformation and by the aging, and of the third and the fourth stages with linear hardening. The uniform elongation of these steels was determined by the character of the first stage.3) In the over-aged steels, the second stage with high strain hardening rate due to coarse precipitate particles appeared, and so the uniform elongation increased largely.4) The reverted austenite precipitated in over-aged steels increased slightly the uniform elongation.