Abstract
New flat-oval groove rolling process of multi-direction deformation is proposed to manufacture ultra-fine grain bar. Application of new groove series can introduce uniform large plastic strain into whole cross section of the material, and meanwhile satisfy the requirements of shape and size. Principle of grain refinement, based on experimental research of small specimen, is that grain refinement of ferrite is mainly dynamic recrystallization when low-carbon alloy steel is at low temperature deformation. Relationship of grain size and z-factor is also obtained through experimental research, as well as ultra-fine ferrite grain less than 1 micron. To predict strain, shape, dimensions and grain size of the material in rolling process, numerical simulation model of the warm groove bar rolling process is established via nonlinear finite element method, and distribution of grain size of the final section is obtained via finite element subroutine. The result indicates that ultra-fine grain bar rolling can accomplish at low temperature region.
Highlights
After entering the 21st century, countries in the world begin to concentrate on the study of fine-grain strengthening, such as “Super Steel” Project in Japan, “Highperformance Structural Steel in 21st Century” Project in Korea, and the national 973 project “Major Basic Research of New Generation Steel and Iron Materials” and et al in China [1], which have made great breakthroughs in theory, and achieved a high degree of economic efficiency
Shape, dimensions and grain size of the material in rolling process, numerical simulation model of the warm groove bar rolling process is established via nonlinear finite element method, and distribution of grain size of the final section is obtained via finite element subroutine
The blank of square steel with side of 24 mm, flipped 90 ̊ after first of flat-oval groove, passed into the second pass of square groove with side of 18 mm, flipped 45 ̊ passed into the third pass of flat-oval groove, flipped 90 ̊ passed into the fourth pass of square groove with side of 13 mm, and flipped 45 ̊ passed into the fifth pass of precision rolling of flat-oval groove, and flipped 90 ̊ passed into the round groove to finish the bar rolling
Summary
After entering the 21st century, countries in the world begin to concentrate on the study of fine-grain strengthening, such as “Super Steel” Project in Japan, “Highperformance Structural Steel in 21st Century” Project in Korea, and the national 973 project “Major Basic Research of New Generation Steel and Iron Materials” and et al in China [1], which have made great breakthroughs in theory, and achieved a high degree of economic efficiency. In order to obtain ultra-fine grain steel products, added alloying elements and controlled method implementations are used, such as mild cooling-controlled process on grain refinement and strength [12]. Similarity of these researches is in high temperature austenitic region, while there has been rare report of obtaining smaller ultra-fine grains products by grain refinement in bar rolling process via warm processing method in ferrite region [14]. Based on finite element analysis model of bar continuous rolling warm forming, deformation evolution rules of traditional groove and new flat-oval groove in rolling process are compared to conclude that the new type of flatoval groove can better introduce large strain into center of the section than the traditional groove, and its multidirectional plastic strain value meets conditions of ultrafine grain
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