The Effect of Cooling Rate on the Microstructure Evolution and Mechanical Properties of Ti-Microalloyed Steel Plates

Abstract

Ti-bearing microalloyed steel plates with a thickness of 40 mm were subjected to ultra-fast cooling (UFC) and traditional accelerate cooling after hot-rolling, aiming to investigate the effect of cooling rate on the microstructure and mechanical properties homogeneity, and thus obtain thick plates with superior and homogeneous mechanical properties. Yield strength, tensile strength, and elongation were 642 MPa, 740 MPa, 19.2% and 592 MPa, 720 MPa and 16.7%, respectively, in the surface and mid-thickness of the steel with ultra-fast cooling, while in the steel with traditional accelerate cooling, 535 MPa, 645 MPa, 23.4% and 485 MPa, 608 MPa, 16.2% were obtained in the surface and mid-thickness of the plate. The yield strength has been greatly improved after UFC, for the refinement of grain and precipitates produced by UFC. In addition, the equivalent grain size and precipitates size in the thick plate with UFC are homogeneous in the thickness direction, leading to uniform mechanical properties. The crystallographic characteristics of different precipitates have been studied. The precipitates formed in the austenite deformation stage obey Kurdjumov–Sachs orientation relationship with the ferrite matrix, while the fine precipitates formed in the ferrite obey [112]MC//[110]α and (1¯1¯1)MC//(1¯12)α orientation relationship with the ferrite matrix.

Hot Ductility, Homogeneity of the Composition, Structure, and Properties of High-Strength Microalloyed Steels: A Critical Review

“…The problem of increasing the homogeneity of the composition, structure, and properties of metal in modern metallurgical technologies is one of the most important, since it largely controls the properties and quality of steel. It applies to all stages of the metal, from smelting to the production of finished metal products [20,21,32,33,[97][98][99]. For example, in [100], based on the testing of samples taken from four places within the product, i.e., front-centre, back-centre, centre-centre and centre-edge, it was shown that there was at least 10% variation in mechanical properties within one roll.…”

“…In the work [98], sheet steel with the composition, wt.%: 0.15 C-0.98 Mn-0.28 Si-0.02 Al-0.08 Ti-0.0027 N with a thickness of 40 mm was studied. It was found that the near-surface layer and the mid-thickness region differed both in grain size and in the size of titanium carbide precipitates.…”

Effect of Zr on static recrystallization of deformed austenite and strain-induced precipitation in Ti microalloyed steel

“…In recent years, with the development of steel production technology towards high quality, efficiency, low consumption, and low cost, the microalloyed element Ti has been increasingly valued. 1 The low cost and excellent performance of Ti microalloyed steel are increasingly evident, which makes Ti microalloyed steel have broad application prospects. 2 Due to the high sensitivity of TiC precipitation to temperature and cooling rate, it is easy to cause fluctuations in the mechanical properties of different parts of the steel plate.…”