Band 61, Heft 2

Ferritic 15 %-Cr steels have better oxidation resistance, due to their higher chromium content, and creep strength, their lower dislocation density and lack of lath microstructure than conventional martensitic steels such as MarBN. Their mechanical properties are sensitive to chemical composition and heat treatment. In this study, we first simulated the formation of stable phases in two ferritic steels containing 2 % nickel (wt.%) and an alloy without nickel using the thermomechanical software MATCALC. Microstructural analysis using scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) reveals the formation of carbides and intermetallic phases after diffusion annealing, both during rapid cooling in oil and slow cooling in the furnace. Dilatometry and XRD studies confirm the gradual phase transformation of ferrite to austenite from 650 °C onwards during heating. Dilatometry also shows that ferritic steels have a lower coefficient of thermal expansion than martensitic steels, austenitic steels, and superalloys, which results in lower thermal stresses during frequent start-up and shutdown of power plants.

The corrosion process of Q345 steel in simulated industrial atmospheric surroundings using NaHSO 3 as the corrosion medium was performed. Corrosion weight loss, X-ray diffraction (XRD), electron probe microanalysis (EPMA), laser scanning confocal microscopy (LSCM), and scanning electron microscopy (SEM) were utilized to investigate the corrosion behavior of Q345 steel samples at various corrosion times. The results indicate that, in the industrial atmospheric acceleration system, the corrosion law of Q345 steel follows an exponential function model and that as the corrosion period lengthens, the rate of corrosion declines steadily. γ-FeOOH, α-FeOOH, Fe 3 O 4 , Fe 3 O 2, and FeO make up the majority of the corrosion products on the surface of rust layer, and the rust layer structure is generally loose in the first stages of corrosion. As the corrosion time lengthens, the corrosion products transform from needle-like to cluster-like and the rust layer will become thicker. In addition, there is a segregation of the elements Cr, S, and O in the rust layer of Q345 steel.

The hitch pin is a critical component between tractor and trailer. The failure of hitch pins is quite frequent and a serious issue which remains unaddressed to a great extent due to limited information on this topic. This paper presents a novel insight into substandard pins manufactured in the informal sector due to non-conformance to any established standard and opens up a new area for further research on this subject. In the present context, risk factors along with reasons of cracks of in-service hitch pins were assessed to enhance the safety of humans. The pin showed signs of a crack, corrosion, scratches, and dents. Notches and scratches acted as stress raisers. Cracks can be seen initiating from the tip of notches. The pin was made of non-standard mild steel and was not heat treated. The study further demonstrates the methods to improve the fatigue life of the pin using numerical simulation. The hardness method was used to collect the cyclic fatigue properties of the commercially available mild steel for different heat-treated samples using the strain life fatigue approach. The casehardened mild steel pin of a case depth of 1.3 mm with a hardness of 30 HRC had considerably increased fatigue properties. Recommendations have been provided to protect humans from these accidents.