Technological Characteristics of a Dual-Phase Steel with 0.09% C and 1.90% Mn Obtained by Intercritical Quenching

Abstract

With this article, the authors present a number of technological characteristics determined for a dual-phase steel with 0.09% C and 1.90% Mn. This steel was obtained through intercritical quenching: heating at 740, 780 and 820 °C, maintaining for 30 minutes and then cooling in water, oil, oil in magnetic field of direct current (DC) and oil in ultrasonic field. It was determined the degree of cold upsetting, the ultimate tensile strength of the resistance butt welded joints and the cutting property based on the study of cutting forces and surface roughness; it was analyzed the influence of heat treatment parameters (heating temperature, quenching medium) and ferrite-martensite structure on these characteristics.

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

“…Comparing the results obtained for the DP 1.90Mn steel (Table 6) with those determined for DP-A and DP-B steels (Tables 2-5), significant differences were observed between the data sets, differences determined, in particular, by the very different manganese content of the two categories of steels [3,25,27,30]. In DP 1.9Mn steel, the position of the critical points A c1 and A c3 led to the obtaining, by intercritical heating, of a higher amount of austenite, which determined the formation, on quenching, of a higher volume fraction of martensite.…”

“…Also, for same heating temperatures, the use of ultrasounds in cooling has led to increasing the volume fraction of martensite (V M ), Tables 2 and 3, Figure 1; for example, in the DP-A steel samples, for T Q = 760 • C, V M increased with 3.55 percent (from 20.19% to 23.74%), and in the samples of DP-B steel, for T Q = 820 • C, V M increased with 4.08 percent (from 38.13% to 42.21%). The ultrasonic quenching medium eliminates one of the most dangerous phases of the cooling (calefaction), enhances heat exchange between product and cooling medium, and reduce the quenching deformations; on the other hand, the additional energy intake increases the volume fraction of martensite formed at quenching and reduces the amount of residual austenite [3,[23][24][25][26][27][28].…”

“…Furthermore, a tendency of their connection and the formation of a network around the ferrite grains are marked [26,28]. and cooling medium, and reduce the quenching deformations; on the other hand, the additional energy intake increases the volume fraction of martensite formed at quenching and reduces the amount of residual austenite [3,[23][24][25][26][27][28].…”

“…This destroys vapor films, thereby ensuring a more prolonged contact between the workpiece and the cooling medium. In this way, the cooling rate is increased, leading to a much stronger cooling, the quenching with ultrasounds being more efficient than the classical one [3,[23][24][25][26][27][28].…”

“…The dual-phase steels have been studied at the "Stefan cel Mare" University of Suceava since 1992, and over the years research has been conducted on several categories of alloys [3,25,27]. In recent years, studies have been carried out on dual-phase steels with low manganese content [26,[28][29][30]; in this article results obtained for two such alloys are presented.…”