The instrumentation technology for process automation in the steel industry has been evolving with the demands of the times, adapting to its production process and its harsh environment as the latest measurement techniques applied by considering the physical measurement principles. Today, the instrumentation technology has become one of the essential technologies to maintain the competitiveness in the steel industry. In this review, the recent development trends and future prospects are described based on lectures and papers on process instrumentation technology published by the Iron and Steel Institute of Japan (ISIJ) in the last decade. The main challenges in recent steel processes were reducing greenhouse gas emissions, supplying high-quality products represented by high-strength steel sheets, and keeping stable operation without skilled workers. To meet these challenges, new measurement techniques that had been advanced in recent years, such as radio waves sensing, image processing, optical fiber sensors, and multivariate analysis, had been applied. The newly obtained process information contributes to further sophisticated processes automation, and is applied to Artificial Intelligence (AI) and Cyber-Physical Systems (CPS). In the next decade, it is hoped that the instrumentation technology will continue to make progress toward the establishment of a sustainable steel industry.

Briquette blending carbonization process is one of the effective cokemaking technologies to increase the blending ratio of semi-soft coking coals. The effect of coal briquette size on coke quality and bulk density in coke oven was studied. It was revealed that coke strength DI¹⁵⁰₁₅ is dependent on the briquette size. DI¹⁵⁰₁₅ shows a maximum, a minimum or monotonic increase with increasing briquette size, which depends on the blend composition of the briquette and the powder coal. The mean size of coke decreases and coal charge bulk density increases with increasing the briquette size. Choice of suitable briquette size is important from the viewpoint of coke quality, productivity and coke oven operation.

We have developed an optimal scheduling method for raw material operations aiming the raw materials cost reduction. In this paper, we report optimization approaches to minimize the cost of ore blending in steel works.

The ore blending problem is to make schedules for the purpose of cost minimization under several constraints such as the stock in yards, ingredients in sintered ore. When formulating as a mathematical model, nonlinearity exists in this problem and make it complicated. However, this problem has characteristic that becomes a linear problem by fixing several key variables as constants. To overcome the nonlinearity, we developed our original Hybrid model that was a combination of Particle Swarm Optimization (PSO) and Linear Programming method (LP). We applied PSO to search the best way of fixing key variables, and obtained blending schedules by solving LPs. Our Hybrid model searched wide area effectively, and derived the solution within 2 minutes. Numerical experiments indicated a cost reduction of secondary materials by 1%.

Thermal Desorption Analysis (TDA) was conducted at multiple research institutions on common specimens, after hydrogen charging with various methods. The specimens were SCM435 steel with/without pre-straining and Vanadium alloyed steel (V steel). Hydrogen charging methods were cathodic charging, soaking in FIP solution and exposure to cyclic corrosion test.

All the TDA spectra (TDA curves) were separated systematically by Gaussian distribution function with unified parameters that are independent to method of hydrogen charging or research institute. They were basically composed of hydrogen trapped by cementite other than dislocation and grain boundary. The pre-strained SCM435 steel contains additional hydrogen trap sites of vacancy and vacancy cluster together with micro-void. The V steel contains further two types of trap sites, regarding two types of V carbide.

The amount of trapped hydrogen was able to be analyzed quantitatively by Fermi-Dirac statistics considering entropy change as pre-exponential factor. It was shown to be controlled mostly by de-trapping process and should be changed according to the binding energy of trap site. This qualitative analysis was favorable for restoring the released hydrogen before TDA measurement.

The elastic-plastic deformation behavior of a 440 MPa hot-rolled steel sheet subjected to many linear stress paths is precisely measured using biaxial tensile tests with cruciform specimens (ISO 16842: 2014) and multiaxial tube expansion tests (Kuwabara and Sugawara, 2013) to determine appropriate material models for finite element analysis (FEA). It was found that the Yld2000-2d yield function (Barlat et al., 2003) correctly reproduces the contours of plastic work (CPW) and the directions of the plastic strain rates (DPSR). Differential hardening (DH) models are determined by changing the values of exponent and material parameters of the Yld2000-2d yield function as functions of reference plastic strain. Moreover, FEA of the hole expansion forming of the test material is performed. The DH model correctly predicts the minimum thickness position that matches the fracture position of the specimen in experiment.

The influence of surface treatment conditions on the welded joint characteristics of aged steel was investigated for verifying the applicability of weld repair to existing steel bridge members. Steel materials with deteriorated paint coatings extracted from an aged bridge that had been in service for a long term were prepared. The weld defects were not observed in the welded joints fabricated by these steels with different surface conditions. Although the tensile strength of welded joints was not affected by the surface treatment conditions, one specimen fractured at the middle in the thickness direction due to non-metallic inclusions. It could be confirmed that sound welded joints could be fabricated by the surface polishing with a disc grinder, which was possible on site, through the experiments by four different aged steels.

The processes leading to hydrogen-related fracture in X80 pipeline steel with stress concentration have been investigated comprehensively through observations of fracture surfaces and subsidiary cracks, a stress analysis, crack initiation and propagation analyses and a crystallographic analysis of fracture surfaces. Fracture morphology showed quasi-cleavage (QC) fracture under various amounts of hydrogen. It was found that QC cracks initiated in the area ranging from the notch tip to 100 µm inside based on interrupted tensile tests just before fracture strength with hydrogen charging. Moreover, fracture surface topography analysis (FRASTA) revealed that QC cracks initiated at the notch tip. A finite element analysis indicated that the equivalent plastic strain was maximum at the crack initiation site at the notch tip. In addition, a backscattered electron image showed that nanovoids of 50-250 µm in diameter were present near the initiation site. Regarding the crack propagation process, field emission scanning electron microscopy (FE-SEM), electron backscattered diffraction (EBSD) and FRASTA results indicated that some microcracks in ferrite grains coalesced stepwise and propagated. Trace analyses using EBSD revealed that the QC fracture surface consisted of {011} slip planes, {001} cleavage planes and non-specific index planes. These findings indicate that QC fracture initiates at the notch tip due to the interaction between dislocations and hydrogen associated with local plastic deformation, and propagates stepwise by coalescence through vacancies, nanovoids and microcracks on various planes associated with/without plastic deformation in ferrite grains.

An elastic-plastic constitutive law embedding cohesive cracks with plasticity-induced damage is proposed to realize degradation of strength and toughness under cyclic loading. A conventional elastic-plastic constitutive law with isotropic and kinematic hardening is combined with our cohesive-force embedding damage model to realize plastic deformation and fracture behavior under monotonic and cyclic loading by solving two kinds of conditional equations. One of them is local balance equation between cohesive traction and principal stress and the other is yield function with nonlinear isotropic and kinematic hardening law. The relationship between the cohesive traction and the crack opening displacement is determined by a cohesive zone model associated with energy release rate to represent process of stress release due to formation of crack surface. In addition, a new plasticity-induced damage is introduced into the cohesive zone model to realize the degradation of the tensile strength and the energy release rate caused by the accumulated plastic strain. On the other hand, the difference of the plastic deformation under various ranges of cyclic loading is represented by additional hardening law depending on a memory surface that is corresponding to plastic strain range. After the material parameters are identified from three experimental results under monotonic and cyclic loading, the capability of our proposed constitutive law is demonstrated by prediction of residual tensile strength and breaking strain of a metal after cyclic loading.

FeCo-2V (Permendur) is one of magnetostirictive alloys, and this alloy is a candidate material for application of vibration energy harvesting. Since their magnetic properties depends on their microstructure, the magnetic properties such as magnetization, magnetostiriction and inverse magnetostriction should be investigated in materials prepared by different processes. In this study, the magnetic properties of FeCo-2V alloy sheets with the different microstructure obtained from a bar were studied, in order to understand influences of the microstructure on the magnetic properties. The results showed that crystalline grains in alloy sheets cut from the bar grow with increasing temperature, while grains in hot-rolled alloy sheets do not grow so much by annealing. It was also shown that inverse magnetostriction in well-annealed alloys reveal good vibration power generation property, and the texture in hot-rolled alloy sheets seems to be unfavorable to the vibration power generation property.

Elastic stiffness c₁₁, c₁₂ and c₄₄ are key parameters in the analysis of elastic deformation behaviors. In order to determine the values of these parameters, Young’s modulus of single crystal; E₁₀₀, E₁₁₀ and E₁₁₁ are needed as well as Young’ modulus Ep and Poisson’s ratio ν in poly-crystal. In this paper, the values of Young’s modulus in single crystalline iron are summarized and then elastic stiffness was estimated for pure iron under the conditions; E_p=208.2 GPa and ν=0.291 that are reliable values for isotropic poly-crystalline iron. As a result, it is found that Young’s modulus of single crystalline iron should be as follows: E₁₀₀=127.8 GPa, E₁₁₀=214.3 GPa, E₁₁₁=276.6 GPa. From these values, elastic stiffness of iron is calculated at c₁₁=228.1 GPa, c₁₂=135.0 GPa, c₄₄=113.2 GPa. Diffraction Young’s modulus of iron can be estimated on the basis of Kröner model by applying the values of elastic stiffness. It is also confirmed that the average value of diffraction Young’s modulus agrees with the value of Young’s modulus E_p (208.2 GPa) of ideal poly-crystalline iron.