Solid state phase transformations in Advanced Steels

In order to achieve progress in Advanced Steels development came more emphasis in solid state phase transformations are received. For achieving the desired mechanical and corrosion resistance properties in Duplex Stainless Steels (DSS), a precise knowledge of the precipitation kinetics of secondary phases, the morphology of the precipitates and effects of the alloying elements on different properties is needed. A complicated chemical composition and the production technology route make each grade of DSS a unique object for a study. Besides, when the market needs to reduce weight and increase product durability by utilizing Advance Strength Steels, a deeper understanding of their transformations is required. The aim of the present work was to study the main features of phase precipitation in diverse Duplex Stainless Steels grades, including Lean Duplex, Standard and Superduplex. Beside analyze the effects of metallurgical features on the properties of DSS and Advanced High Strength Dual Phase (DP) steels. One of the tasks was to study the effects plastic deformation after heat treatment in diverse duplex grades

Microstructural Development in a TRIP-780 Steel Joined by Friction Stir Welding (FSW): Quantitative Evaluations and Comparisons with EBSD Predictions

The present work describes the effect of FSW on the result microstructure in the stir zone (SZ), thermo-mechanically affected zone (TMAZ), heat affected zone (HAZ) and base metal (BM) of a TRIP-780 steel. X-ray diffraction (XRD), optical microscopy (OM) and EBSD were used for determinations retained austenite (RA) in the SZ, It was found that the amount of RA developed in SZ was relatively large, (approximately 11% to 15%). In addition, recrystallization and the formation of a grain texture were resolved using EBSD. During FSW, the SZ experienced severe plastic deformation which lead to an increase in the temperature and consequently grain recrystallization. Moreover, it was found that the recrystallized grain structure and relatively high martensite levels developed in the SZ lead to a significant drop in the mechanical properties of the steel. In addition, microhardness profiles of the welded regions indicated that the hardness in both the SZ and TMAZ were relatively elevated confirming the development of martensite in these regions. In particular, to evaluate the mechanical strength of the weld, lap shear tensile test was conducted; exhibited the fracture zone in the SZ with shear fracture with uniformly distributed elongation shear dimples

Solid state phase transformations in Advanced Steels

In order to achieve progress in Advanced Steels development came more emphasis in solid state phase transformations are received. For achieving the desired mechanical and corrosion resistance properties in Duplex Stainless Steels (DSS), a precise knowledge of the precipitation kinetics of secondary phases, the morphology of the precipitates and effects of the alloying elements on different properties is needed. A complicated chemical composition and the production technology route make each grade of DSS a unique object for a study. Besides, when the market needs to reduce weight and increase product durability by utilizing Advance Strength Steels, a deeper understanding of their transformations is required. The aim of the present work was to study the main features of phase precipitation in diverse Duplex Stainless Steels grades, including Lean Duplex, Standard and Superduplex. Beside analyze the effects of metallurgical features on the properties of DSS and Advanced High Strength Dual Phase (DP) steels. One of the tasks was to study the effects plastic deformation after heat treatment in diverse duplex grades.Con lo scopo di ottenere progressi industriali nello sviluppo di Advanced Steels, specie quando le necessità di mercato richiedono una riduzione di peso e un aumento della durabilità è fondamentale una più profonda comprensione delle loro trasformazioni di fase allo stato solido. Nel caso di acciai Inossidabili Duplex (DSS), per raggiungere le proprietà meccaniche desiderate e le proprietà di resistenza alla corrosione, è necessaria la precisa conoscenza della cinetica di precipitazione di fasi secondarie, la morfologia dei precipitati e gli effetti degli elementi alleganti su diverse proprietà. La complessa composizione chimica e la tecnologia di produzione rendono ciascuna tipologia di DSS come un caso di studio unico. L’obbiettivo del presente lavoro è stato quello di studiare le principali caratteristiche delle precipitazioni di fasi secondarie in diversi tipi di acciai inossidabili duplex, comprendendo i Lean Duplex, Standard e altamente legati duplex, ed inoltre di analizzare gli effetti delle caratteristiche metallurgiche sulle proprietà degli Acciai Duplex e Advanced High Strength Steels

Innovative Coatings for Materials Subjected to Aggressive Environments

Aggressive environments require durable materials or excellent coatings to improve their performance and life service [...

Detrimental Cr-rich Phases Precipitation on SAF 2205 Duplex Stainless Steels Welds After Heat Treatment

Abstract The austeno-ferritic Stainless Steels are commonly employed in various applications requiring structural performances with enhanced corrosion resistance. Their characteristics can be worsened if the material is exposed to thermal cycles, since the high-temperature decomposition of ferrite causes the formation of detrimental secondary phases. The Submerged Arc Welding (SAW) process is currently adopted for joining DSS owing to its relatively simple execution, cost savings, and using molten slag and granular flux from protecting the seam of atmospheric gases. However, since it produces high contents of δ-ferrite in the heat affected zone and low content of γ-austenite in the weld, high-Ni filler materials must be employed, to avoid excessive ferritization of the joint. The present work is aimed to study the effect of 3 and 6 hours isothermal heat treatments at 850°C and 900°C in a SAF 2205 DSS welded joint in terms of phases precipitation. The results showed the presence of σ-phase at any time-temperature combination, precipitating at the δ/γ interphases and often accompanied by the presence of χ-phase. However, certain differences in secondary phases amounts were revealed among the different zones constituting the joint, ascribable both to peculiar elements partitioning and to the different morphology pertaining to each microstructure

Microcracks Reduction in Laser Hardened Layers of Ductile Iron

A study of surface hardening of Ductile Iron (DI) with and without austempering heat treatment was developed. The chemical composition of the material contains alloying elements such as Cu and Ni, that allow to obtain a Ductile Iron Grade 120-90-02, based on ASTM A536, which was heat treated to be transformed to Austempered Ductile Iron (ADI). Specimens of 10 × 10 × 5 mm3 were obtained for application of surface hardening by Nd:YAG UR laser of 150 W maximum power. The parameters used were advance speed of 0.2 and 0.3 mm/s and power at 105, 120, 135 and 144 W; the departure microstructures were fully pearlitic in the samples without heat treatment, and ausferrite for austempered samples. Microstructural characterization of hardened samples was performed were analyzed and martensite and undissolved carbides were identified in the pearlitic samples, while in ausferrite samples it was found finer martensite without carbides. The depth of hardened surface to different conditions and their respective microhardness were measured. The results indicate that the surface hardening via laser is a suitable method for improving wear resistance by means of hardness increment in critical areas without compromising the core ductility of DI components, but the surface ductility is enhanced when the DI is austempered before the laser hardening, by the reduction of surface microcracks

Acciaio inossidabile effect of gas tungsten arc welded 308 and 409 stainless steels on their mechanical properties

Stainless steels (SS