Abstract:Due to the difference in chemistries and manufacturing processes applied, the microstructure and mechanical properties of DP780 steel produced by different production lines may be inconsistent. Annealing experiments are designed and carried out in the laboratory based on the actual industrial production process in order to investigate the effects of continuous annealing process parameters on the microstructure and mechanical properties of DP steel quantitatively. The results show that the effect of intercritic… Show more
“…Our results showed that during the austenite grain refining process and the precipitation mechanisms, the presence of Nb, V, and Ti formed particles of carbides, nitrides, or a combination of both. This result, combined with the formation of precipitated carbonitrides, creates a fine dispersion in the matrix [36][37][38][39][40][41]. The presence of precipitates was confirmed by the presence of Nb, V, Ti, C, and N peaks using the XRD technique.…”
Section: Discussionmentioning
confidence: 93%
“…The vapor phase is eliminated using different cooling rates combined with polymeric solutions, directly causing boiling and convection, increasing the cooling rate. In this way, the microstructures of two-phase steel can be guaranteed [20,35,38,[40][41][42][43][44].…”
Due to its combination of high mechanical properties, good formability, and low production cost, steel is a key material with potential for improvement in the metallurgical industry. Based on these conditions, this research evaluated the influence of material composition and incomplete austenitization parameters on the final metallurgical and mechanical properties of high-strength microalloyed steels after cooling in a medium with high severity. The applied cycle was based on the intercritical thermal treatment of microalloyed steels with niobium (Nb) and titanium (Ti) to increase the mechanical resistance and guarantee the tenacity of the material. An experimental study was carried out testing three intercritical temperatures, 806 °C, 775 °C, and 740 °C, with subsequent cooling in polymeric solutions in water. The studies showed that the intercritical temperature variation directly contributed to the difference in the second phase microstructure present in the samples. The heat treatment findings resulted in a microhardness of 434.2 HV0.01, characterizing the low-carbon martensite. The presence of a matrix consisting of ferrite and a second phase of low-carbon martensite promoted the typical behavior of dual phase steel. In the x ray diffraction, the presence of retained austenite was not evidenced, indicating the efficiency of the cooling rate. The experiments confirmed the influence of different engineering parameters and intercritical treatment on the mechanical properties. The study enriches the current knowledge about the development of variables for the development of dual phase steel from microalloying elements.
“…Our results showed that during the austenite grain refining process and the precipitation mechanisms, the presence of Nb, V, and Ti formed particles of carbides, nitrides, or a combination of both. This result, combined with the formation of precipitated carbonitrides, creates a fine dispersion in the matrix [36][37][38][39][40][41]. The presence of precipitates was confirmed by the presence of Nb, V, Ti, C, and N peaks using the XRD technique.…”
Section: Discussionmentioning
confidence: 93%
“…The vapor phase is eliminated using different cooling rates combined with polymeric solutions, directly causing boiling and convection, increasing the cooling rate. In this way, the microstructures of two-phase steel can be guaranteed [20,35,38,[40][41][42][43][44].…”
Due to its combination of high mechanical properties, good formability, and low production cost, steel is a key material with potential for improvement in the metallurgical industry. Based on these conditions, this research evaluated the influence of material composition and incomplete austenitization parameters on the final metallurgical and mechanical properties of high-strength microalloyed steels after cooling in a medium with high severity. The applied cycle was based on the intercritical thermal treatment of microalloyed steels with niobium (Nb) and titanium (Ti) to increase the mechanical resistance and guarantee the tenacity of the material. An experimental study was carried out testing three intercritical temperatures, 806 °C, 775 °C, and 740 °C, with subsequent cooling in polymeric solutions in water. The studies showed that the intercritical temperature variation directly contributed to the difference in the second phase microstructure present in the samples. The heat treatment findings resulted in a microhardness of 434.2 HV0.01, characterizing the low-carbon martensite. The presence of a matrix consisting of ferrite and a second phase of low-carbon martensite promoted the typical behavior of dual phase steel. In the x ray diffraction, the presence of retained austenite was not evidenced, indicating the efficiency of the cooling rate. The experiments confirmed the influence of different engineering parameters and intercritical treatment on the mechanical properties. The study enriches the current knowledge about the development of variables for the development of dual phase steel from microalloying elements.
“…As a DP steel is heating up to its soak temperature, the relative proportion of ferrite to austenite will change. At the lower soak temperature, it would be expected that a lower proportion of austenite would be present leading to a lower volume fraction of martensite in the final microstructure, whilst higher soak temperatures will increase the austenite formation and subsequent martensite volume fraction in the final microstructure [18]. The light microscope images below show the initial cold-rolled microstructure in Figure 2, whilst Figure 3 shows the effect of changing soak temperature on the microstructure. Figure 2. Initial cold-rolled microstructure before annealing.…”
Section: Resultsmentioning
confidence: 99%
“…Increasing the intercritical temperature increases austenite formation, which can lead to an increase in the final martensite start temperature [17,18]. This start temperature is important for austenite transformation, and whether it transforms to martensite or bainite on rapid cooling [19].…”
A dual-phase steel chemistry has been processed with varying intercritical annealing temperatures and the properties investigated. It was found that increasing the temperature in the intercritical region led to an increase in the volume fraction (52%-65%) and grain size (1.8-3.3 µm) of martensite whilst the volume fraction and grain size of ferrite decreased. The highest tensile strengths were found at low intercritical temperatures, achieving 935 MPa whilst the highest elongation values of 21% were achieved at the highest intercritical temperatures.
“…Continuous annealing process is critical to the final properties during dual phase steel manufacturing [9]. The dual-phase microstructure is obtained when it is annealed within its intercritical annealing temperature range and suitably quenched.…”
DP980 is a promising light-weightening material in car body. To avoid high investment of strong cooling system, a new DP980 steel with low cooling rate requirement was developed. The mechanical properties and microstructure were analyzed under different manufacturing process. It could be concluded that the chemical composition design should be reasonable and of low cost to achieve both high strength and also austenite to martensite transformation at low cooling rate. Strength increased with coiling temperature decreasing during hot rolling, and higher annealing temperature and lower over aging temperature were favourable to higher strength. The austenite-martensite transforming could be completed at even lower rapid cooling rate of 20°C/s. Through optimized manufacturing process parameters, the new DP steel product with good mechanical properties could be obtained successfully, which provided a new option for normal production line to produce ultra high strength steel.
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