Abstract
Abstract In order to develop 960MPa grade high strength steel, the effects of cooling rate and austenite deformation on the hardness and the microstructure of high strength steel has been studied by Scanning Electron microscope (SEM), Transmission Electron Microscope (TEM), Gleeble-3500 thermal simulation testing machine and T2500 Vickers hardness tester. The results show that only when the cooling rate was higher than 10∘C/s and the final cooling temperature was lower than 250∘C, the microstructure mainly consists of martensite, and the strength of high strength steel could be above 960MPa; and austenite deformation could effectively refine the width of martensite lath, thus improving the strength and toughness.
Highlights
IntroductionFor reducing self-weight, improving load bearing capacity and reducing manufacturing cost, 960MPa ultra-high strength steel has obtained more and more applications in engineering machinery, coal mining machinery, port machinery and other fields [1]
For reducing self-weight, improving load bearing capacity and reducing manufacturing cost, 960MPa ultra-high strength steel has obtained more and more applications in engineering machinery, coal mining machinery, port machinery and other fields [1].Most of the 960MPa grade steel has been produced via o ine quenching and tempering [2,3,4]
The microstructure mainly consists of lath martensite when the cooling rate exceeds 10∘C/s and the martensite lath would be refined with the increase of cooling rate
Summary
For reducing self-weight, improving load bearing capacity and reducing manufacturing cost, 960MPa ultra-high strength steel has obtained more and more applications in engineering machinery, coal mining machinery, port machinery and other fields [1]. In order to improve the hardenability, some expensive alloys such as Cr, Mo, Cu and Ni were added [5,6,7,8], so the manufacturing costs of the 960MPa grade steel has been increased. In order to reduce the manufacturing cost of 960MPa grade high strength steel, new direct quenching process could be an effective alternative option. Compared with the traditional quenching process [9], DQ omits reheating process, so the energy and production cost could be saved; in the DQ process, the temperature of the billet is so high that the solid solution of alloying elements in austenite could be more uniform, so the hardenability has been improved. In order to develop a 960MPa grade high strength steel, a new composition has been designed and the effect of cooling rate and austenite deformation on the microstructure and hardness of 960MPa grade steel has been studied by gleeble3500 thermal simulator, SEM, TEM and Vickers hardness measurement
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