Yoshifumi Nakano

Corrosion Resistance of High-Strength Modified 13% Cr Steel

Abstract A new 13% Cr martensitic stainless steel (0.025% C-13% Cr-Ni-Mo) with excellent resistance to carbon dioxide (CO2) corrosion and good resistance to sulfide stress cracking (SSC) was develo...

Behaviour of molten metal and optimum welding conditions for high heat input submerged‐arc welding with flux containing iron powder

Summary The effect of the addition of iron powder to agglomerated flux on welding performance and the optimum welding conditions for high heat input welding were investigated. The main conclusions obtained are as follows: The addition of iron powder to flux increases the deposition rate and improves welding operability.The arc of the leading electrode was generated at a lower point in the molten metal, between the leading and the trailing electrodes, rather than at its top point. The penetration depth was influenced by the ratio of the area of the groove to that of the molten metal on which the leading arc is generated.The cross sectional profile of the bead was influenced by the current ratio of the trailing electrode to that of the leading. The optimum ratio for avoiding weld defects ranged between 0.70 and 0.80.The flux containing iron powder, together with the selection of optimum welding conditions, allowed tandem‐wire one‐pass submerged‐arc welding to be used for 60 mm thick plates.

APPLICATION OF ACCELERATED COOLING FOR PRODUCING 360MPa YIELD STRENGTH STEEL PLATES OF UP TO 150 MM IN THICKNESS WITH LOW CARBON EQUIVALENT

ABSTRACT An accelerated cooling (ACC) process including direct quenching (DQ), which commonly is called TMCP (Thermo-Mechanical Control Process), is a technique which can overcome problems for the production of heavy wall steel plate which meets required strength with a chemistry suitable for low temperature applications. The TMCP process enhances strength properties without sacrificing notch toughness through grain refinement under controlled cooling and introduction of second phase microstructures resulting in the decrease in Carbon equivalent and omission of pre-heating prior to commencement of welding. This TMCP process has been applied to produce heavy wall steel plates for ships, offshore structures and pressure vessels which require high toughness at low temperature and other superior fabrication characteristics. This paper describes the mechanism of TMCP ranging from controlled rolling to accelerated controlled cooling for producing 360MPa yield strength in steel plates of up to 150mm in thickness for diverse use.

A 460MPa YIELD STRENGTH STEEL PLATE PRODUCED BY TMCP FOR ARCTIC USE

ABSTRACT A 460MPa yield strength steel plate was produced. The application of TMCP (thermomechanical control process) and the use of Cu, Ni and a small amount of Nb enabled the production of a high strength steel plate with low carbon equivalent and low Pcm. Appropriate addition of Ti with respect to N and REM controls the growth of grain in fusion boundary and heat affected zone. The reduction of carbon equivalent results in lowering the possibility of forming martensite constituent. As a result, the plate had good weldability and good toughness in welded joint. The multi-pass submerged arc welding joint made with a heat input of 5 kJ/mm gave Charpy impact energy values larger than 41J at −80C. The CTOD value was larger than 0.1mm at −50C. The result indicates a possibility of applying the plate to offshore structures to be used in the arctic region.

Unstable ductile fracture conditions in upper shelf region.

The phenomenon of unstability of ductile fracture in the upper shelf region of a forged steel for nuclear reactor pressure vessels A508 Cl. 3 was studied with a large compliance apparatus, whose spring constants were 100, 170 and 230kgf/mm, at the test temperatures of 100, 200 and 300°C and at the loading rates of 2, 20 and 200mm/min in the crosshead speed. The main results obtained are as follows:(1) The fracture modes of the specimens consisted of (a) stable fracture, (b) unstable fracture which leads to a complete fracture. rapidly and (c) quasiunstable fracture which does not lead to a complete fracture though a rapid extension of ductile crack takes place.(2) Side groove, high temperature or small spring constant made a ductile crack more unstable.(3) High temperature or large spring constant made the occurrence of quasiunstable fracture easier.(4) Quasiunstable ductile fracture took place before the maximum load, that is, at the J integral value of about 10kgf/mm. The initiation of a microscopic ductile crack, therefore, seems to lead to quasiunstable fracture.(5) The concept that unstable ductile fracture takes place when Tapp exceeds Tmat seems applicable only to the case in which unstable ductile fracture takes place after the maximum load has been exceeded.