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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.

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.

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.