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Low alloy steels with ultimate tensile strength greater than 2000 MPa

Hang Chen

Low alloy steels with ultimate tensile strength greater than 2000 MPa.

Rel. Paolo Matteis. Politecnico di Torino, Corso di laurea magistrale in Automotive Engineering (Ingegneria Dell'Autoveicolo), 2022

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In this paper, the current status and latest achievements of ultra-high strength low alloy steels with ultimate tensile strength exceeding 2000Mpa are studied from the aspects of composition, processing, microstructure and mechanical properties, by analyzing the literature. The most conventional heat treatment process for low alloy ultra-high strength steel is quenching and low temperature tempering to obtain lath martensite structure. High carbon chromium bearing steel 100Cr6 is the bearing steel with the largest production volume in the world. If there is no special description for bearing steel, it refers to 100Cr6. Although tempered martensite has high tensile strength, its low toughness can lead to brittle fracture of the material, thus reduce service life. Therefore, on the basis of the conventional quenching and tempering process, the heat treatment process can be improved and steels with lower bainite could be developed. As a typical representative of medium carbon low alloy ultra-high strength steel, AISI4340 steel provided new ideas and directions for the subsequent development of ultra-high strength steel. On the basis of AISI4340 steel, AISI4130, AISI4140, AISI4330 and other modified steels have been successfully developed. In order to increase the tempering temperature range of this type of steel, improve the delayed destructive, and at the same time suppress low temperature tempering brittleness, the chemical composition of the steel can be improved: on the basis of AISI 4340 steel, 300M alloys and D6CA steel, etc. with different alloying elements content are developed. The use of ultra-high strength steel in automobiles is the only way to achieve lightweight and safety at the same time. Boron steel and hot stamping process are currently the most trustworthy materials and process technologies for lightweight of body. Hot-stamped low carbon steels include from conventional 22MnB5 steel to the latest steel grades with ultimate tensile strengths exceeding 2000MPa and higher elongation by changing alloy designs or coupling different processes such as Q&P. Advances in materials and processes allow cars to meet increasingly stringent emissions and safety regulations. The hot stamping process of boron steel is the most important piece of the puzzle. Protecting the vehicle with armor steel over 2000Mpa can achieve protection without making the vehicle too heavy, so that it looks and rides like a normal vehicle. In addition, as a special vehicle steel, the wear resistant steels also have extremely high strength under wear conditions. Developing since the 21st century, in addition to (mainly) tempered martensitic steels listed above, new advanced ultra-high strength steels such as nanobainitic steels and Q&P steels with mixed microstructure have also emerged with considerable ductility and toughness. The research and development of these steels widely used in automobile parts with excellent performance greatly reduces the production cost, providing a broad application forecast and direction for the development of new high-performance materials.

Relators: Paolo Matteis
Academic year: 2021/22
Publication type: Electronic
Number of Pages: 174
Corso di laurea: Corso di laurea magistrale in Automotive Engineering (Ingegneria Dell'Autoveicolo)
Classe di laurea: New organization > Master science > LM-33 - MECHANICAL ENGINEERING
Aziende collaboratrici: UNSPECIFIED
URI: http://webthesis.biblio.polito.it/id/eprint/23683
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