ABSTRACT

With the rapid development of marine transport in recent years, container ships are becoming larger. In this paper, crack arrest steel plates are developed in micro alloyed route. Uniformly enhanced cooling TMCP technology is used and the rolling technology was controlled at a lower rolling temperature. The grain size of acicular ferrite and bainite are refined to a very low level, which has a advantage effect to the toughness of the matrix. The impact absorbed energy at −40°Care more than 300 J and the Kca value at −10°C are exceeding 8,000N/mm15, which represent a high crack arrestability.

INTRODUCTION

With the rapid development of marine transport in recent years, the size of container ship has been gradually increased for mass transportation and cost reduction in the shipping industry. The largest container ship that have been built in the world can carry 21000 containers. Thus, thick and high strength steel plates are used for the upper deck structure of container ship because of its large hatch openings.

The large container ships have a larger scale and container capacity, and various loads and asymmetrical conditions can easily lead the hatch coaming and upper deck to a high stress state. Therefore, thick plates with excellent crack arrestability need to be used in the hatch side coaming and upper deck to suppress brittle crack propagation (Kazukuni et al., 2015; Yamaguchi Y et al., 2010; Katsuyuki I et al., 2005). The use of crack arrest steel plates can effectively prevent brittle fracture and enhance hull structure strength.

The crack arrestability of thick plate for hull structures is studied and the results have been summarized and incorporated in Class NK "Guidelines on Brittle Crack Arrest Design" (Nippon Kaiji Kyokai, 2009). This crack arrest design situation was concerned and accepted by International Association of Classification Societies (IACS) in January 2013. It explained that the minimum brittle crack arrest toughness, which is marked as Kca, must exceeding 6000 N/mm1.5 at −10°C for steel plate between 50 mm and 80 mm. Due to these design situation, heavy thick high strength steel with excellent crack arrestability has been desired in the field of large container ship building industry.

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