Preface to the Special Issue on “Diversified Estimation of Nonmetallic Inclusion Particles in Steel”

Study

Decrement and modification of the nonmetallic inclusion particles and clusters in steel have been required in the refining of steelmaking process. In order to determine the contents of nonmetallic inclusions in steel and guarantee the cleanliness of steel, the analytical researches on the nonmetallic inclusions, whose size was more than a micron order, were carried out in the nonmetallic inclusion conference of 19th Steelmaking Committee, Japan Society for Promotion of Science (1954 to 1974, chair: Hiroshi Sakao). Since much knowledge was previously acquired regarding the generation and the aggregation behavior of nonmetallic inclusions from molten steel to cast ingot, the importance of evaluation of nonmetallic inclusion particles was also becoming significant in order to support those researches. For this purpose, the characterization of nonmetallic inclusions was discussed in the subcommittee on Nonmetallic Inclusion of 19th Steelmaking Committee, Japan Society for Promotion of Science (1990 to 1994, chair: Nobuo Sano) and the Research Group on Ultraclean Steel, ISIJ (1995 to 1998, chief: Hideaki Suito). After then, the characterization and utilization of nonmetallic inclusions were investigated in “Analysis and Estimation of Inclusions and Precipitates in Steel” forum (1997 to 2000, head: Minoru Sasabe), and “Analysis and Control of Inclusions in Steel” forum (2000 to 2005, head: Fumitaka Tsukihashi) and “Advanced Technology for Inclusion characterization” (2005 to 2008, head: Ryo Inoue).

Based on the questionnaire results performed by steelmaking companies in “Analysis and Estimation of Inclusions in Steel” forum (2008 to 2011, head: Ryo Inoue), research group on “Control of Non-metallic Inclusion Properties in Solid Steel” (2008 to 2011, head: Shin-ya Kitamura) and other research committees, the needs for investigations on the characterization of nonmetallic inclusion particles were summarized as the following four items:

1) Evaluation of composition, amount, morphology and distribution of inclusion particles aiming at stable production of clean steel;

2) Rapid, extensive and highly precise evaluation of large inclusion particles;

3) Soluble and insoluble contents of oxide and sulfide inclusion particles;

4) Nondestructive evaluation of full length and full width of steel product.

Recently, since the refinement of steel crystal grain and the improvement in toughness has become possible by using fine nonmetallic inclusion particles, the following has become important:

5) Rapid and highly precise evaluation of fine inclusion particles.

On the other hand, the division of process evaluation and material characterization of ISIJ proposed the following road map:

1) Development of new on-site analytical method

2) Development of the rapid analytical technique of thin film materials

3) Development and standardization of analytical methods of matrix and inclusion

4) Skill free and greening of steel analytical technologies

5) Tradition of analytical techniques

In order to respond to the demands and the ISIJ road map, the ISIJ research meeting on “Diversified Estimation of Nonmetallic Inclusion Particles in Steel” has performed activity from 2010 to 2013. This meeting consisted of 18 researchers (8 from universities and 10 from companies). The characterization of nonmetallic inclusion particles in steel has been carried out from many research viewpoints of three working groups;

(i) Direct evaluation of extracted nonmetallic inclusion particles,

(ii) Improvement of instrumental analysis method for rapid evaluation of nonmetallic inclusions,

(iii) Indirect analysis of nonmetallic inclusions.

As the whole research project, the following was also examined:

(iv) Development of a correction method which changes the two-dimensional value on a polished surface to a three-dimensional value

Many valuable achievements have been obtained during the period of this research project. To summarize those activities, a special issue on “Diversified Estimation of Nonmetallic Inclusion Particles in Steel” was planned with regard to the basic research reports and the application topics of nonmetallic inclusion evaluation. It is my great pleasure to have published 15 papers were submitted not only by the members of this project but also by the domestic and overseas researchers. It is expected that development of process evaluation and material characterization will be more significant when the research field called “nonmetallic inclusion estimation” is recognized widely through this special issue.

Finally, on behalf of the editors of this special issue, I am grateful to all the authors for their contributions.