This work presents a detailed study directed to supermartensitic stainless steels (SMSS) alloyed to nitrogen (UNS S41425) and vanadium (UNS S41427), showing comparison between them by varying their tempering temperature, evaluating the behavior in its mechanical properties, presenting a fractographic and microstructural analysis between these alloys, besides to demonstrate techniques for modeling these strain-hardening results with best coefficients that determine these materials with good predicted values. The Hollomon, Voce and Chaboche models were determined, using an iterative regression method (R2) in order to obtain the best coefficients for each analysis condition. This work concludes by presenting graphic results of the effect of tempering temperature increase on the final mechanical properties, evaluates the differences obtained between these materials and presents an evaluation of the behavior of each coefficient of the models presented separately, showing the best R2 fitting results. With the models determined, it is possible to use the results in this work to perform numerical simulations and meet the needs of the engineering on industry.

Maraging steels are ferrous alloys with Ni, Co, Mo, and Ti additions. These materials are a special class of ultra high mechanical strength steels with wide and special applications in strategic areas, which makes their knowledge very valuable. Computational advances allowed to analyze the behavior of these materials numerically, using the finite element method and developing mathematical models that can represent numerically its mechanical behavior. The present work has the objective of surveying the mechanical properties of maraging steels 300 and 350 by slow strain rate tensile (SSRT) tests, after the solution treatment at 1183K for 1h. Additionally, it was evaluated the hydrogen embrittlement in samples tested by SSRT under cathodic protection with a potential -1.2 VSCE in 3.5% NaCl solution. The study was complemented with detailed fractographic analysis. This work also presents the analysis of representative models by use of Hollomon, Swift, Voce and coupled Swift-Voce equations to describe the strain-hardening behavior. Compared to the others, the Voce’s model was the one which best fitted the experimental results, with values of R2 higher than 0.992. Through the variation of the chemical composition found in the different grades of maraging steels, this work contemplates the creation of a generalized Voce model based on the variation of the Ti content. The work concludes presenting the generalized Voce model proposed and a numerical analysis of the SSRT results with a good accuracy of the strain-hardening response.

Abstract Supermartensitic steels represent a new sub-class of martensitic stainless steels with higher toughness and corrosion resistance than conventional grades. These properties were improved by the drastic reduction of carbon content, and the addition of nickel and molybdenum. These chemical composition changes also increased the weldability of these steels, since the soft and ductile martensite formed is not susceptible to cold cracking during welding. However, post weld heat treatment may be necessary for uses in sour, aggressive and embrittlement environments. This work investigates the mechanical properties of a weld produced by gas tungsten arc welding (GTAW) of a pipe of 12%Cr supermartensitic stainless steel with 625 nickel alloy as filler metal. The response of the weld metal to post weld heat treatments at 650oC was also evaluated.