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The medium carbon steel and low alloy SAE 4340 has undergone several changes in this development process came 300M steel, from this ultra-high strength steel. With similar resistance and higher ductility to the steel 300M, the maraging steel can replace conventional steels in various applications. This study aims to evaluate and compare the microstructure and mechanical strength of SAE 4340 steel, 300M and Maraging 18Ni 300, underwent the procedure of autogenous laser welding.

Search for alloys with improved high temperature specific strength and creep resistance properties for aerospace applications has led in the last decades to sustained research activities to develop new alloys and/or improve existing ones. The maraging steels evoked tremendous interest, especially in the aerospace world. Extra low carbon, high nickel, iron based alloys held great promise of providing an extraordinary combination of structural strength and fracture toughness. Applications of this alloy include aircraft structural components and rocket engine case for Satellite Launcher Vehicles. The objective of this work is to study the creep behavior of a solution treated Maraging 300 alloy. Constant load creep tests were conducted with this alloy at 550°C and in a stress range of 200 to 500 MPa. The creep parameters are determined. Samples with a gage length of 18.5 mm and a diameter of 3.0 mm were used for all tests.

The aim of the present work is to analyse the microstructural changes caused by distinct heat treatments and their relationships with the mechanical properties of a recently developed microalloyed steel with 0.08%C-1,5%Mn. This steel, designated as B550, is being considered as a promising alternative to replace the low carbon steel in some wheel`s components for the automotive industry. Various multiphase microstructures with different amounts of ferrite, martensite, bainite and retained austenite were obtained by means of heat treatments conducted at distinct temperatures. Tensile tests allowed evaluating the mechanical properties of the various material conditions. The experimental results showed that water quench from 800°C results in a better combination of mechanical properties of strength, hardenability and ductility.

Applying the Heat Tinting Technique the microestrutural characterization of a 300M steel (medium carbon steel) was accomplished. The steel was austenitized for 20 min to 900°C, followed by holding at 400°C (in the bainitic temperature), with maintenance time of the material in the temperature of 1min, 5min and 30min, aiming at the formation of a multiphase structure. Through the metallographic analysis it is verified that, with the use of this technique, it is possible the determination of the volume fraction of the present phases in the 300M steel, especially in the identification and quantification of the retained austenite.

In this work five methods of heat treatments are investigated in order to obtained convenient volume fractions of ferrite, bainite, martensite and retained austenite, starting with a low carbon steel and seeking the distinction of the phases, through optical microscopy. Specific chemical etching is improved. The results in tensile and fatigue tests were accomplished and the results were related with the microstructural parameters. The results show that the mechanical properties are closely related with the phases, grains size and the phases morphology.