Yoshiyuki Saito

COMPUTER SIMULATION OF MICROSTRUCTURAL CHANGES IN THERMOMECHANICAL PROCESSING OF 18Cr-8Ni AND 9Cr-1Mo-V-Nb STEELS

This paper describes an extensive study on microstructural changes in thermomechanical process in 18Cr-8Ni and 9Cr-1Mo-V-Nb steels by computer simulation. Kinetics of recrystallization and grain growth, carbonitride precipitation and deformed structure formation are predicted by the models which are essentially identical to those employed for conventional structural steels. The computed microstructures show good agreement with the experimental results. The computer simulation method is considered to be effective to the optimization of chemistry and manufacturing process for alloy steels produced by thermomechanical control process.

MONTE CARLO SIMULATION OF MICROSTRUCTURAL EVOLUTION IN STEEL

The temporal evolution of microstructure during thermomechanical processing of steels is simulated by Monte Carlo simulation techniques. In the simulation of normal grain growth, the anisotropy of the grain boundary energy is incorporated into the model. Compared with the case in which no anisotropy of boundary energy is assumed, the suppression of grain growth was observed and the grain size distribution became broad. The effect of dispersed particles on growth kinetics is also studied by the model. The simulation of restoration kinetics after hot deformation is conducted by a model which incorporates the effect of stored energy by deformation into the free energy term. The difference of site energies between austenite and ferrite is incorporated into the free energy of the system in the simulation of austenite to ferrite phase transformation. Nucleation of proeutectoid ferrite was observed to predominate the progress of transformation in the initial stage and ferrite grain growth became dominant in the subsequent stage.

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.