Spot weldability of TRIP assisted steels with high carbon and aluminium contents

Abstract

We examine here the spot welding characteristics of transformation induced plasticity assisted steels, which contain d-ferrite as a consequence of their aluminium concentrations of 3?5 or 5?6 wt-% and which also have high carbon contents of 0?3 or 0?4 wt-% when compared with conventional automotive steels. The resistance spot welds are tested in both shear and crosstensile tests in order to determine the so called ductility ratio, which is a parameter associated with the fitness of such welds for automotive applications. With an increase in the d-ferrite fraction from 0?19 to 0?5, the hardness variation across the weld and heat affected zone is decreased approximately from 400 to 150 HV. It seems that the presence of stable d-ferrite is helpful in reducing hardness variations and in achieving a significant ductility ratio of 0?39.

Relationship between microstructure and mechanical properties in Nb–V microalloyed TRIP steel

“…8,9 However, in the first generation AHSS, which includes regular TRIP steels, where fully martensitic fusion zones become unavoidable, the C content should be kept ,0?25 wt-%. 10 Therefore, in these steel grades, microalloying seems to be the easiest way to reach a product of R m xA 80 exceeding 16 000 MPa %, set out by the automotive industry, while maintaining an appropriate spot weldability.…”

Retention of δ-ferrite in aluminium-alloyed TRIP-assisted steels

“…Recent attempts, at designing low-alloy steels in which the microstructure retains a large fraction of d-ferrite, have come up against Yi et al (2010) difficulties in which the quantity of d-ferrite is sometimes grossly overestimated using standard phase diagram calculations (Yi et al 2010), thus necessitating the empirical study of a series of seven alloys with varying aluminium contents (Yi et al 2011b;Jung et al 2012). An attempt was made to explain the discrepancies using kinetic simulations and microanalytical data, resulting in a conclusion that the problem arises owing to the inadequate partitioning of substitutional solute as austenite grows from d-ferrite.…”

Avaliação Da Homogeneidade Microestrutural Em Aços Com Alto Alumínio E Distintas Adições De Carbono E Nióbio Forjado a Quente

“…Assim sendo, o material em estudo foi elaborado com alto teor de alumínio com o intuito de verificar a possibilidade de obter ferrita delta em sua microestrutura, uma adição de nióbio para observar sua contribuição em relação as propriedades devido favorecer a estabilidade da austenita retida, além de uma variação no teor de carbono. A escolha das composições foi baseada no trabalho de Jung [17] e em simulações no Thermo-Calc realizadas por Botelho (2018), autor do trabalho que desenvolveu as ligas em estudo. Botelho almeja como produto final uma liga passível de efeito TRIP com possibilidade de aplicação na indústria automobilística devido suas características microestruturais e propriedades mecânicas [18].…”