There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

The purpose of the present contribution is to review the current knowledge about the relationship between the micro-structure of cold rolled intercritically annealed low alloy TRIP-aided sheet steels and their mechanical properties from a materials engineering point of view. The focus is on their production in existing industrial lines and on their application in the manufacture of passenger cars with a body-in-white which offers an improved passive safety. The review aims to make clear that although low alloy TRIP-aided sheet steel is by now starting to be an established structural material in BIW manufacturing, there is still room for the further optimization of the composition and the processing. In addition, there are still a number of problems related to their physical metallurgy that require a better fundamental understanding.

Structure–properties relationship in TRIP steels containing carbide-free bainite

The effect of morphology on the stability of retained austenite in a quenched and partitioned steel

Carbon partitioning to austenite from martensite or bainite during the quench and partition (Q&P) process: A critical assessment

Austenite stability of ultrafine-grained transformation-induced plasticity steel with Mn partitioning

Conventional CMnSi transformation-induced plasticity (TRIP)-aided steels are a promising solution for producing lighter, crash-resistant car bodies, due to their high-strength and large uniform elongation. The CMnSi TRIP-aided steels, with more than 1 mass pct Si, have the drawback of poor galvanizability due to the presence of complex Si-Mn oxides on the surface. The full substitution of the Si by Al in cold-rolled and intercritically annealed TRIP-aided steels, therefore, was evaluated in detail. The phase-transformation kinetics during the intercritical annealing and the isothermal bainitic transformation were investigated by means of dilatometry. The allotropic phase-boundary was determined both by thermodynamic calculations and the experimental determination of the C content in the retained austenite. The results imply that short isothermal bainitic transformation times are sufficient to obtain the TRIP microstructure and that the processing of CMnAl TRIP-aided steels in a continuous annealing line not equipped for overaging is possible. The mechanical properties were evaluated for CMnAl TRIP-aided steels obtained using an industrial thermal cycle: the properties matched those of the conventional CMnSi TRIP-aided steels, where it was found that the high-Al CMnAl TRIP-aided steel had a high strain-hardening coefficient of 0.25, which was stable up to a true strain of 0.25.

Phase Transformation and Mechanical Properties of Si-Free CMnAl Transformation-Induced Plasticity-Aided Steel

Galvanizability of high-strength steels for automotive applications

Transformation induced plasticity (TRIP) steels are a promising solution for the production of cars with low body mass because of the combination of high strength and large uniform elongation that ...

Galvanisability of silicon free CMnAl TRIP steels

The processing of cold rolled intercritically annealed steels which exhibit transformation induced plasticity (TRIP) requires the precise determination of equilibrium parameters, the kinetics of the intercritical γ phase formation and the kinetics of the isothermal bainitic transformation. In addition, the aging phenomena associated with the bainitic transformation must be taken into account. A detailed analysis of the kinetics of the combination of both transformations carried out in succession has hitherto not been reported. The present contribution proposes an empirical method to study these transformations in low C intercritically annealed TRIP steels: a standard CMnSi TRIP steel and a CMnAlSi TRIP steel in which part of the Si is replaced by Al. The latter TRIP steel is more likely to be used in continuous galvanising lines. Dilatometry was used to determine the soaking time necessary to obtain the equilibrium phase distribution during the intercritical annealing. Furthermore, the transformat...

Empirical microstructure prediction method for combined intercritical annealing and bainitic transformation of TRIP steel

By means of surface characterization and subsequent hot-dip galvanizing tests, both Al-alloyed TRIP grades showed good galvanizability.

Jan Mahieu

Papers

Phase Transformation and Mechanical Properties of Si-Free CMnAl Transformation-Induced Plasticity-Aided Steel

Galvanizability of high-strength steels for automotive applications

Galvanisability of silicon free CMnAl TRIP steels

Empirical microstructure prediction method for combined intercritical annealing and bainitic transformation of TRIP steel

Hot Dip Galvanising of Al Alloyed TRIP Steels.