Effect of Intercritical Heat Treatment on Mechanical Properties of Plain Carbon Dual Phase Steel

Abstract

INTRODUCTIONactual distribution between these two phases allows them low yield stress, a smooth flow stress curve, better plasticity and formability with a high strain hardening coefficient [5]. Processing to produce the DP steels is usually done by intercritical annealing from room temperature to two-phase (α + χ) Effect of Intercritical Heat Treatment on Mechanical Properties of Plain Carbon Dual Phase SteelThe mechanical properties of DP steels are directly related to the synergistic effect of two phases present in these steels in which martensite controls the strength of the steel while ferrite is responsible for formability properties [7][8][9]. Numerous studies have reported that the mechanical properties of ferrite-martensite DP steels have been quite [1,3,5-6,8-10,12-13,] suggest that the mechanical behavior of ferrite-martensite DP microstructure cannot be predicted by the general rule of mixture law. These findings are still controversial and no agreement has yet been developed Although many investigations have been made to characterize the microstructure-property relationship of micro alloyed low carbon DP steels, literature pertaining to formation of ferrite-martensite DP microstructure and its effect on mechanical properties of plain low carbon steels has not been well studied.Present study therefore, aims to investigate the effect of intercritical annealing temperature and soaking time on martensite volume fraction and mechanical properties of AISI 1020 plain carbon steel. MATERIALS AND MEHTODChemical composition of a plain carbon steel grade (AISI 1020) used in present study is given in RESULTS AND DISCUSSION MicrostructureThe optical and SEM micrographs of as-received steel specimen are shown in Fig. 1 to which increasing the temperature within ferriteaustenite region increases the amount of austenite which will then transforms into martensite. Increase in grain size was also observed for the specimens soaked for 3hrs due to sufficient time available for grain growth.Also at high magnification, plate type martensite was found in the specimens intercritically heat treated at relatively lower temperatures i.e. 775and 800 o C as shown in Fig. 11(a-b) whereas, lath type martensite was found in the specimens intercritically heat treated at 825 o C as shown in Fig. 11(b). Mechanical PropertiesThe changes encountered in the mechanical properties due to variation of microstructure are summarized in Table 3. Tensile StrengthTS values are listed in Table 3. The higher TS of DP steel specimens is the result of presence martensite phase in the microstructure. Martensite has highly distorted lattice due to entrapment of carbon atoms, making it stronger phase and enabling it to sustain higher load compared to pearlite present in as-received steel. (1) The TS generally increased due to higher volume fraction of martensite formed in DP steel specimens. FIG. 1. MICROSTRUCTURE OF AS-RECEIVED SPECIMEN SHOWS FERRITE (LIGHT) AND PEARLIATE (DARK) (a) OPTICAL (500X) (b) SEM(1000X) FIG. 2. MICROSTRUCT...

Effect of Intercritical Annealing on the Properties of Dual Phase Steel via Finite Element Method

“…Briefly, DP steels with desired properties can be achieved by controlling the alloy chemistry and processing parameters [12][13][14][15]. The effect of the annealing and tempering conditions, phase distribution and different alloy chemistries on the properties of DP steels have been studied extensively [12][13][14][15][16][17][18][19][20][21].…”