Speaker
Description
Development of Newly Designed Materials for Coiler Roll
in Hot Strip Mill
Akio Sonoda1, Hyo-Gyoung Kang1, Hideaki Nagayoshi1, and Hidenor Era2
1FUJICO Co., Ltd., 1-110-10, Hibiki-machi, Wakamatsu-ku, Kitakyushu-city, Fukuoka, 898-0021, JAPAN
2Kyushu Institute of Technology, 1-1 Sensui-cho, Tobata-ku, Kitakyushu-city, Fukuoka, 804-8550, JAPAN
Abstract
It has been investigated on newly designed materials for improving the properties of corrosion, seize, wear, and heat resistances, aiming at the durable usage of coiler roll in the hot rolling mill. In this study, two types of specimens, i.e., alloys A and B were prepared. Both iron alloys had a hypo-eutectoid composition of C and contained Si, Cr, Ni, Mo, and Mn in common. Alloy A composed of V whereas alloy B was newly designed by addition of Co and Cu aiming at a stability of the matrix and by Nb in place of V so as to exhibit a fine structure during solidification and the subsequent heat treatment. Here, alloy B was designed to have a higher content of C and Cr to show an improved corrosion resistance.
The alloy was melted in an Ar gas atmosphere and cast into a metallic mold at a pouring temperature of 1823 K. The solidified alloy was cut into a cubic shape about 25 mm in size. The cut specimen was solutionized at 1273 K for 72 hrs followed by forced air-cooling. Ageing treatment was conducted at temperatures from 673 to 873 K for 7 hours to obtain some hard phases.
In the as-cast state, both specimens of alloy A and B revealed martensitic structure in addition to austenite phase and minor fraction of M7C3 carbide at grain boundaries of the original austenite phase where the amount of retained austenite was markedly higher in alloy B than alloy A. The martensite in alloy A decomposed to form a coarse bainitic lath during ageing while the martensite and retained austenite in alloy B changed to tempered martensite and re-quenched martensite after ageing, respectively, with finely dispersed M23C6 carbide in the grains and M7C3 carbide at the grain boundaries. Although alloy A after ageing at temperatures of 673 to 873K exhibited higher hardnesses than alloy B, the in situ hardness measurement at such high temperatures yielded that alloy B possessed higher hardnesses than alloy A due to the fine dispersion and more precipitation of the carbides.
Tensile tests were carried out at room temperature and a high temperature of 773 K. The proof and tensile strengths of both alloys exceeded 800 MPa at any temperature and the strengths of alloy B showed further increased values by 100MPa. It was noticed that the reduction area of alloy B at the high temperature exhibited a markedly high value of 10 % while that of alloy A was less than 0.5 %. The fundamental properties in alloy B mentioned above would be suitable for the actual usage of hot rolling process. Other mechanical and physical properties were extensively examined. It was found from the experimental results that the properties such as corrosion, oxidation, seize, wear, heat resistances were much more excellent in alloy B than alloy A. Thus the newly designed materials of alloy B was expected to bear the severe circumstance of hot rolling process.
On-line application tests at the hot strip mill were carried out to confirm the effectiveness of the newly designed materials. The coiler rolls made of alloy A and B were manufactured by the continuous pouring process for cladding, i.e., CPC method. Coiling condition during hot rolling was changed to apply the different levels of the load, i.e., lower and higher than 700 MPa for carbon steel and high alloy steel strip, respectively. It was indicated form the results after usage for 74 or 96 days that the corrosion and wear resistances of the newly developed materials were more excellent over 4 times and 5 times, respectively, than those of the conventional materials. Also, the seize resistance and high temperature oxidation resistance of the developed materials were largely improved. By applying the newly designed and developed material roll to the hot strip mill, a long life over the three times has been achieved compared to the conventional roll.
Keywords: coiler roll, optimum alloy design, heat treatment, corrosion resistance, wear resistance
Corresponding Author: Dr. Akio Sonoda, E-mail: a-sonoda.fujico@kfjc.co.jp
Summary
To improve the corrosion resistance, seize resistance, wear resistance, and heat resistance of the coiler roll for hot rolling, a new materials has been developed by using optimum alloy design, heat treatment technology and the continuous pouring process for cladding (CPC) method. Comparison tests of fundamental physical properties and mechanical properties responding to the working environment in apparatus level were conducted for the conventional and developed materials. In addition, on-line application tests were done at the mills having different load conditions. As a result, the corrosion resistance and wear resistance of the newly developed materials were respectively more excellent over 4 times and 5 times than those of the conventional one. Also, the seize resistance and high temperature oxidation resistance of the developed materials were largely improved. By applying the developed materials to the coiler roll, a high life over three times could be attained.
| Speaker Country | Japan |
|---|