Investigation on Nonmetallic Inclusions in Ultra-Low-Oxygen Special Steels
- PDF / 5,117,348 Bytes
- 14 Pages / 593.972 x 792 pts Page_size
- 65 Downloads / 220 Views
ECIAL steel parts used as bearings, springs, gears, etc. require excellent fatigue resistance properties. As nonmetallic inclusions can easily be the origins of fatigue fractures, their existence in special steels must be well controlled, including their population, size, morphology, etc. As early as the 1980s, the Sanyo Special Steel Co. discovered that the fatigue life span of bearings would be significantly increased by decreasing the total oxygen (TO) in steel to an ultra-low level of about 0.0004–0.0007 mass pct.[1–4] Since then, achieving ever lower TO has been a goal during the production of special steel. At present, TO in special steels such as bearings, springs, and gears can be controlled in this JIN ZHU LI and XIAO-FEI HE, Ph.D Candidates, MIN JIANG, Assistant Professor, and XIN-HUA WANG, Professor are with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing, People’s Republic of China. Contact e-mail: [email protected] WEI SUN, Professorial Senior Engineer/Senior Director of Technology, is with the Technology Centre of Maanshan Iron and Steel Co. Ltd., Maanshan, An-hui Province, People’s Republic of China. Manuscript submitted October 4, 2015. Article published online May 16, 2016. 2386—VOLUME 47B, AUGUST 2016
range of 0.0004–0.0007 mass pct in most Chinese special steel plants. However, for high-quality special steels requiring stable and high-fatigue life cycles, a decrease in TO content is far from enough. In recent years, control of large-sized inclusions in special steels has become really important, and this topic has aroused ever more attention, especially in China.[5–9] It lies in the fact that micro-inclusions in larger sizes from several tens to several hundreds of microns have always been detected in the final product despite low TO content. The problem is that the population of these catastrophic inclusions is limited and, therefore, very difficult to inspect well with conventional testing methods such as optical microscopy detection after the ASTM E-45 standard. Nevertheless, these scarcely distributed large particles are regarded as the main reason for the scattered life span of steel parts,[5,9] which means deteriorated stability in quality control. To solve this problem, the Sanyo Special Steel Co. of Japan proposed the concept of premium cleanliness steel during the production of bearings, which requests not only ever lower TO content but also a minimized size for the inclusions, which decreases the chances of large inclusions.[5,6]
METALLURGICAL AND MATERIALS TRANSACTIONS B
Unfortunately, the current steelmaking process is long and involves many facility units (ladle furnace, RH/VD degasser, tundish, mold, casting machines, etc.) and operations (de-oxidation, slag-making, gas bubble stirring, etc.). And a couple of metallurgical phenomena (slag-steel reaction, collision/agglomeration among inclusions, solidification of liquid steel, interaction of inclusion particles and solidifying frontiers, etc.) and sometimes unexpected inc
Data Loading...
