Structures and Mechanical Properties of Some Dual-Phase Steels with Low Manganese Content

Constantin Dulucheanu,Traian Lucian Severin,Luminita Irimescu,Delia Aurora Cerlinca

doi:10.3390/met12020189

Constantin Dulucheanu, Traian Lucian Severin + Show 2 more

Open Access

https://doi.org/10.3390/met12020189

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Journal: Metals	Publication Date: Jan 20, 2022
Citations: 5	License type: CC BY 4.0

Affiliation: Ştefan cel Mare University of Suceava

Abstract

In recent years, to reduce cars costs, research has been conducted on dual-phase steels with low manganese content (below 1.0%). This study investigated the influence of technological parameters of heat treatment (heating temperature and cooling medium) on such steels’ structures and mechanical properties. The ferrite-martensitic structures, specific for dual-phase steels, were obtained by intercritical quenching: heating of samples (made of alloys with 0.511% Mn, respectively 0.529% Mn) to temperatures located between critical points Ac1 and Ac3, followed by cooling in water without mechanical agitation and in water activated with ultrasounds at the frequency of 59 kHz. Through metallographic analyses and tensile tests, it was possible to determine the volume fraction of martensite, the ferrite microhardness, the ultimate tensile strength, the total elongation, and with the obtained data, their variations with the heating temperature and the cooling medium were established. Raising the heating temperature (between 760 °C and 820 °C) and using ultrasounds at cooling increased the volume fraction of martensite and the ferrite microhardness. This fact has increased the mechanical strength and reduced the deformability of the studied dual-phase steels. Intercritical quenching in water activated with ultrasounds provided values of structural characteristics and mechanical properties very close to those obtained by quenching in water without mechanical agitation, but was accomplished using a higher-temperature heating. The results obtained were compared with those determined in previous research, performed on dual-phase steel with 1.90% Mn.

Highlights

The dual-phase steels are metallic materials increasingly used by the automotive industry to make some structural car body components that can be damaged during an accident
These steels’ structure is formed by a soft and ductile ferrite matrix in which martensite (10 to 35%) and a small amount of residual austenite (1 to 2%) are homogeneously dispersed. They have, in general, a percentage of carbon less than 0.12%, a content of manganese between 1.0% and 3.5%, and elements such as V, Cr, Mo, Si, Nb, Ti are to be found in chemical composition in proportions situated below 1%; in the recent years, to reduce cars costs, research has been conducted on dual-phase steels in which the manganese content was less than 1% (0.5 to 1% Mn) [1,2,3,4,5,6,7,8,9,10,11,12,13,14]
One of the technologies applied to produce these steels is intercritical quenching; the structure obtained, for the given chemical composition, is the result of combined action of the technological parameters of heat treatment, their influence on the structure is directly reflected on mechanical properties as well

Summary

Introduction

The dual-phase steels are metallic materials increasingly used by the automotive industry to make some structural car body components that can be damaged during an accident.

Results

Conclusion