Influence of Partial Replacement of Si by Al on Microstructure and Properties of Nanostructured Martensitic Steel.

Hua Zheng,Feng Hu,Serhii Yershov,Oleksandr Hress,Kaiming Wu,Oleg Isayev,Wen Zhou

doi:10.3390/ma12223718

Abstract

Nanostructured martensitic steels comprising nanoscale-martensite and retained austenite were obtained by quenching–partitioning–tempering (Q–P–T) treatment. The influence of partial replacement of Si by Al on the microstructure and properties were studied. Results showed that with partial replacement of Si by Al, except nanoscale-martensite and retained austenite, a little ferrite was also clearly observed. By contrast, with partial replacement of Si by Al, although the ultimate tensile strength (1392 MPa against 1215 MPa) was slightly lower, the elongation after fracture (16.7% against 19.9%) and the toughness (equivalent to the area under the stress–strain curve) (43.1 × 106 against 37.1 × 106 J/m3) were relatively higher. This was because the retained austenite in the steel with partial replacement of Si by Al had higher carbon content, similar volume fraction of film-like morphology, lower volume fraction of blocky morphology and was surrounded by ferrite, which played significant role in the transformation-induced plasticity (TRIP) effect.

Highlights

Nanostructured martensitic steels with balanced strength and plasticity treated by quenching and partitioning (Q&P) [1,2] or quenching–partitioning–tempering (Q–P–T) [3,4] treatment have attracted attention
The processes of Q&P and Q–P–T, which were distinct from quenching and tempering (Q-T), were used for low/medium-carbon steel to generate microstructure with the nanoscale martensite (M) and retained austenite (RA) combination giving attractive properties
The addition of medium-carbon was for high strength, Mn was for improving hardenability, Si and Al were for preventing the precipitation of cementite, and Ti was for refining the grain

Summary

Introduction

Nanostructured martensitic steels with balanced strength and plasticity treated by quenching and partitioning (Q&P) [1,2] or quenching–partitioning–tempering (Q–P–T) [3,4] treatment have attracted attention. The processes of Q&P and Q–P–T, which were distinct from quenching and tempering (Q-T), were used for low/medium-carbon steel to generate microstructure with the nanoscale martensite (M) and retained austenite (RA) combination giving attractive properties. The element Si was added into the steel with Q&P or Q–P–T treatment to inhibit formation of carbides [5], thereby contributing to the complete diffusion of carbon to untransformed austenite from supersaturated-carbon martensite, increasing stability of RA upon subsequent cooling to ambient temperature. The strong solid solution strengthening of Si can enhance the strength of the steel. High content of Si in steel can lead to the problems of surface quality and coating performance [6], and result in poor weldability.

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Results

Discussion

Conclusion