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 // orientation relationship with the ferrite matrix.
Highlights
During recent decades, the adjustment and upgrade of steel products have always been essential tasks in the iron and steel industry under the pressure with respect to resources, energy, and environment
The thermomechanical controlled processing (TCMP) technique has been proposed and studied extensively. Wang and his group at Northeastern University studied the effect of TMCP parameters, including hot-rolling temperature [2,3], cooling rate [3], and finish cooling temperature [4,5,6], on the mechanical properties of medium thickness microalloyed steel plates
We focus on comparing the effect of ultra-fast cooling (UFC) and traditional accelerated cooling on the homogeneity of microstructure and mechanical properties of thick plates, and investigate the correlation between microstructure and mechanical properties
Summary
The adjustment and upgrade of steel products have always been essential tasks in the iron and steel industry under the pressure with respect to resources, energy, and environment. The thermomechanical controlled processing (TCMP) technique has been proposed and studied extensively Wang and his group at Northeastern University studied the effect of TMCP parameters, including hot-rolling temperature [2,3], cooling rate [3], and finish cooling temperature [4,5,6], on the mechanical properties of medium thickness microalloyed steel plates. Based on the above problem, new generation TMCP (NG-TMCP), that is TMCP involving ultrafast cooling (UFC) technology, is currently being applied to industrial production [19,20,21], aiming to reduce the consumption of expensive alloying elements, improve the homogeneity of the steel plate, and make the steel making process economically visible [15,22,23,24]. The precipitation behavior in different regions of the thick plate is studied, with a particular focus on the crystallographic characteristic
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