January 30, 2008
  • JFE Steel Corporation

Development of HITEN “JFE-HYD1100LE” Ultra High Strength Steel Plate with High Resistance to Delayed Fracture
- Expands Lineup of HOP-produced HITEN Plate Products -

TOKYO — JFE Steel Corporation has announced the development of HITEN “JFE-HYD1100LE”1), a new ultra high strength steel plate for use in construction and industrial machinery. Samples are already being shipped. The new product features high resistance to delayed fracture and is the first steel plate of this strength level to be manufactured on a rolling line. JFE Steel has developed a proprietary “HOP”2), online steel plate heat treatment facility, the first of its kind in the world, and uses it to manufacture high-end steel products, including its HITEN lineup, and line pipe materials. JFE-HYD1100LE is a new product made possible by the application of this innovative HOP technology.

JFE-HYD1100LE is an ultra high strength steel plate with minimum yield strength of 1,100 MPa and minimum tensile strength of 1,180 MPa. It guarantees low temperature toughness value at -40°C. JFE-HYD1100LE has many revolutionary features including superb resistance to delayed fracture3), which is one of the most important factors for safe usage of ultra high strength steels.

Toughness and delayed fracture resistance generally deteriorate as steel materials are strengthened. In order to solve these issues, two advanced technologies are applied to the microstructure control of JFE-HYD1100LE:

  1. Innovative rolling and cooling conditions to achieve the ausforming effect4) by directly quenching work-hardened austenite5) and transforming it into martensite6),
  2. and

  3. Application of HOP to achieve rapid heating and tempering.

JFE Steel pursued microstructure refinement and cementite7) refinement to the extreme by combining these advanced microstructure control technologies to ensure excellent low temperature toughness and high resistance to delayed fracture. In addition, the application of these technologies improves the strength/toughness balance of the steel, making possible a low-alloying design that exhibits better welding properties than conventional steel plates.

Demand for materials with higher strength and lighter weight is one of the most pressing needs in the construction and industrial machinery market. JFE Steel has already developed and commercialized “JFE-HITEN780LE”8) with 780 MPa class tensile strength and “JFE-HYD960LE” with 960 MPa class yield strength, and has produced a cumulative total of 100,000 tons of these HOP-based HITEN products for construction and industrial machinery. The addition of the 1,100 MPa class yield strength ultra high strength steel plate to the lineup of the HOP-produced HITEN plate products will satisfy an even wider range of customer requirements.

Notes:

1)HYD: High Yield Strength Steel, LE: Leading-Edge
2)HOP (Heat-treatment On-line Process): The first process in the world that enables continuous heat treatment of steel plates on a rolling line
3)Delayed fracture: A sudden fracture caused by hydrogen that occurs a certain amount of time after the application of load
4)Ausforming effect: Achievement of high strength and excellent toughness by quenching work-hardened austenite to cause a martensite transformation
5)Austenite: The name of a high temperature steel phase in carbon steel
6)Martensite transformation: Quenching austenite steel to transform into martensite, which shows a hard low temperature transformation structure
7)Cementite: A form of iron carbide expressed as Fe3C
8)JFE-HITEN780LE: Awarded the 28th Technical Development Prize by the Japan Institute of Metals for “Development of High Strength Steel Plates with Excellent Toughness by Controlling Morphology of Carbides through HOP (Heat-treatment On-line Process)”

Fig.1 Layout of HOP
Fig.1 Layout of HOP


Fig. 2 Heat treatment process of quenched/tempered steel
Fig. 2 Heat treatment process of quenched/tempered steel


RQ-FT: Reheat Quenching and Furnace Tempering
DQ-FT: Direct Quenching and Furnace Tempering
DQ-HOP: Direct Quenching and HOP Tempering


Fig.3 Refinement of cementite by ausforming and HOP rapid heating and tempering
Fig.3 Refinement of cementite by ausforming and HOP rapid heating and tempering


Fig.4 Improvement of resistance to delayed fracture by ausforming and HOP rapid heating and tempering

Fig.4 Improvement of resistance to delayed fracture by ausforming and HOP rapid heating and tempering


Table 1 Example of chemical composition of HYD1100LE steel
Table 1 Example of chemical composition of HYD1100LE steel


Table 2 Example of mechanical properties of HYD1100LE steel
Table 2 Example of mechanical properties of HYD1100LE steel