Cooperative effort Norway - Japan on a new type of steel

By Jan Erik Kaarø
Photo: Jens Søraa

The Japanese doctoral student Takehiro Inoue and Professor Christian Thaulow intently study the fracture surface on a piece of steel that has been tested using NTHΔs large scale tensile testing machine

The Japanese have developed steels with a much higher strength and easier welding potential than today´s material.

The Norwegian steel industry are advanced users of these modern steels and are now, in cooperation with NTH/SINTEF, testing the steels. The cooperative effort also includes Osaka University in Japan and Fundia Norwegian Iron Works located in the city of Mo in northern Norway. Among other things, Fundia has access to the latest technology for producing ship profiles, the iron work´s main product. The engineering workshops Haugesund Mekaniske Verksted, Kværner-Rosenberg and Aker Verdal are also involved in the project. Never before has the gigantic Japanese steel industry allowed potential European competitors to tread so freely on their turf.

Three conditions have enticed the Japanese northward: Because of the offshore industry, Norway is considered a pioneer in testing new types of steel. In addition, the world´s largest tensile testing machine and a Cray super computer are found at NTH´s Gløshaugen campus in Trondheim.

With a force of up to 10,000 tons, the iron jaws in the tensile testing machine reduce a 15 cm thick steel beam to pieces. As part of a cooperative research effort, a similiar series of tests has been done in Trondheim over the last few years. NTH Professor Christian Thaulow and the Japanese doctoral student Takehiro Inoue have been surveying the "damage" being done in NTH´s laboratory. They personify the close cooperation which has been initiated between steel researchers in the two countries. Inoue will be residing in Norway for two years. Actually, he is one of 40,000 employees working at one of Japan´s largest steel producers - Nippon Steel Company. Similarly, group leader Mons Hauge from SINTEF is residing in Japan.

A new generation of steel, produced by the so-called ThermoMechanically Controlled Process (TMCP) and which was originally developed in Japan, is the object of this intense cooperative research effort. Instead of increasing the content of alloying elements, the steel is produced in a continuous and meticulously controlled process. The manufacturer uses factors such as time, temperature, deformation and chemistry as tools for steering the production and to obtain the derived material´s properties. With this process it is possible to produce high strength steel with a yield point of over 500 MPa. In other words, the steel can withstand a load of up to five tons per square centimetre before it is deformed, while steel produced in a more traditional manner has a yield limit of approximately 350 MPa. It was during the construction of the Oseberg oil platform that TMCP steel was first utilized in Norway.

The steel samples were manufactured in Japan and then sent to Norway. Using various techniques, some of the samples are welded both in Japan and at the three Norwegian offshore workshops that are involved in the project. The last stop is NTH/SINTEF where the weldments are subjected to a long series of tests.

"First and foremost, the material researchers want to find the fracture resistance of the weldments. However, factors such as mechanical properties and crack arrest properties are also investigated," explains Professor Christian Thaulow.

"Our philosophy is to be able to test the steel on the micro-level before it is used on the macro-level. For example, by fracture mechanics testing of a steel beam that is to be used in a structure, we can give a rather precise rundown of the structure´s overall specifications," stresses Thaulow.

Researchers at NTH/SINTEF have been asked to draw up guidelines for the requirements the new steel must meet. This fundamental work is done partially with the help of statistic fracture mechanics and partially by understanding the conditions that are responsible for a catastrophic fracture. Researchers have two important devices to assist them in this task. One is the large scale tensile testing machine, which has been a tremendous success since in was installed at Gløshaugen in 1989. The machine is booked solid until the early part of 1995. The results from these tests will be verified through calculations done on the Cray super computer. Some of these computer simulations require up to 15 hours of simulation time.

The results of the Japanese/ Norwegian cooperative venture will have major consequences for offshore structures, but among other things, it will also have an effect on ship and bridge construction.

"The cost of producing high strength steel is approximately the same as traditional steel. With increased strength the structures can be slenderized and the weight reduced, thus reducing the total construction costs. Aker Engineering have examined the advantages of increasing the yield strength in the deck of the Sleipner platform from 350 to 500 MPa yield strength. The analysis shows that compared to using ordinary steel, the weight and the costs would be reduced 20% and 13%, respectively," Professor Thaulow reports.

The NTH professor has been the front figure in the contact with Japan, but he emphasizes that it took a long time to build up a truly trustful research alliance. Contact was first established with Professor Masao Toyoda at Osaka University in 1985. The project with the five Japanese steel manufacturers started in 1989 and will continue until 1994.

"We have tried to overcome our cultural differences. It took six or seven years before I felt that we had managed to achieve a state of mutual respect and understanding. A substantial effort on the part of both parties is needed when researchers from two countries with different backgruonds are working together," the professor emphasizes. Both he and a number of the other seven NTH/SINTEF researchers involved in the project have several research sojourns behind them. Likewise, several of Takehiro Inoues´ colleagues have resided for a time in Trondheim.