Microstructures and Mechanical Properties of an Ultrahigh‐Strength and Ductile Medium‐Carbon High‐Silicon Spring Steel

Abstract

Herein, the microstructure and mechanical properties of medium‐carbon high‐silicon spring steel are studied, which is alloyed and/or microalloyed with Cr, Mo, Ni, Cu, Nb, and V, and subjected to various austenitizing and tempering processes. The steel has a mixed microstructure consisting of fine lath martensite, nanoscale cementite, ε‐carbide, and an amount of retained austenite (10.4 vol%). At room temperature, the steel exhibits ultrahigh tensile strength (2002 MPa) and yield strength (1775 MPa) with total elongation of 11.1%, while a good toughness is obtained characterized by Charpy impact energy as 38 J. The ultrahigh strength of this steel is attributed to the dislocation and precipitation strengthening, while the excellent total elongation is closely associated with the retained austenite. In addition, tempered martensite embrittlement is found in this steel when tempered at 450 °C. This is due to the retained austenite decomposition and cementite coarsening along the prior austenite grain and martensite laths.

Heat Treatment Process, Microstructure, and Mechanical Properties of Spring Steel with Ultra-High Strength and Toughness

“…This process in steel causes the carbon concentration in the supersaturated martensite to decrease, and the cementite content to increase. The calculation formula (8) [13] of solid solution strengthening is as follows:…”

“…Chen et al [12] obtained a new high strength spring steel with a tensile strength and elongation of 2021 MPa and 10.3%, respectively, by implementing a series of heat treatment processes on 55SiCrVNb. Several studies [2,[12][13][14] have shown that the yield strength of spring steel mainly comes from dislocation strengthening and precipitation strengthening. However, the increase in strength causes some decrease in toughness.…”

“…The ultra-high strength spring steel mentioned in Ref. [13] has a tensile strength of 2002 MPa, a yield strength of 1775 MPa, an elongation of 11.1%, a reduction in area of 47%, but an impact energy of only 38 J. In addition, studies such as Refs.…”

Factors Affecting the Cracking Resistances of a Spring Steel Tempered at Different Temperatures

“…[3] Up to now, for automotive leaf spring steels, numerous studies have concentrated mainly on the relationship among the tensile strength, fatigue strength, and microstructures. [4][5][6] However, in actual production process of leaf spring steel, some microcracks introduced by quenching or shot peening processes are inevitable; in this case, the cracking resistance is also one of the crucial indicators of vehicle leaf spring steel for service safety. As a result, it is vital to analyze the cracking resistance of 50CrMnSiVNb steel under different loading conditions.…”

Influence of Nickel on Microstructure and Mechanical Properties in Medium-Carbon Spring Steel

“…Over the past few decades, several approaches have been employed to enhance the strength, ductility, and toughness of spring steel. These include controlling the design of the alloy composition [3][4][5], implementing effective heat treatment [2,[6][7][8][9][10], and utilizing microalloying techniques [11,12]. Medium-carbon spring steel with quenched and tempered lath martensite structures has been widely used as spring steel due to its exceptional strength, ductility, and lower decarburization sensitivity [2,4,7].…”