Low Sulfur Material Research Articles

Quenching cracks in medium carbon steel initiated at manganese sulfide inclusions

Abstract Quench crack propensity has been investigated for two identical medium carbon steels (50CrMo4) which only differed in sulfur content. The standard variant of the material was affected by manganese sulfide inclusions whereas the low sulfur material was essentially free of sulfides. 80 mm, cylindrical test specimens were used. The test specimens had been cut out of cross rolled steel plates in which the manganese sulfide were flattened to discoid shape. The specimen orientation was in direction of principal deformation where the flattened sulfides were aligned with the test specimen axis. The largest sulfides reached lengths of 150 μm. Both materials were austenitized at 850 °C for 60 minutes, quenched in a salt-bath at 180 °C and immediately annealed at 425 °C for one hour. It turned out that the standard material developed quench cracks which initiated at manganese sulfide. No cracks could be found in the low sulfur material. Thermal and transformational stresses, which develop during quenching, aggravate the stress situation around the manganese sulfide and cause the cracking. The results are interpreted in fracture mechanical terms.

Pyrite utilization in the carboniferous region of Santa Catarina, Brazil - Potentials, challenges, and environmental advantages

Abstract The main coal seams explored in the coal region of Santa Catarina are Barro Branco (BB) and Bonito (BO). Owing to the association with the mineral matter, the tailings generated in the beneficiation are arranged in disposal areas, and subject to the generation of acid mine drainage (AMD). The objective of this study was to evaluate the use of pyrite present in the coal rejects of the BB and BO seams and the environmental gains with desulfurization. For this purpose, densimetric separability test, ash, sulfur, and AMD generation analyses were performed. In addition, the amount of pyritic concentrates and sulfuric acid were estimated considering the current level of production. Three densimetric fractions were obtained: less than 2.2 (energetic material), between 2.2 and 2.7 (low sulfur material), and greater than 2.7 g cm-3 (pyrite concentrate). The results revealed that the two seams could be beneficiated by gravimetric processes, obtaining pyrite concentrates with approximately 60% pyrite. By converting pyrite to sulfuric acid would represent an increase of 500,000 tons per year in the Brazilian production of this material and, in environmental terms, a reduction of up to 90% of the acidity potential to be disposed in the environment in the case of the BB seam and 65% for the BO seam. It was also observed that the “desulfurized” fraction of the BO had higher levels of pyrite and a higher potential for acidity generation than the BB seam, implying greater risks of environmental contamination and higher acid water treatment costs.

Effects of Sulfur Level and Anisotropy of Sulfide Inclusions on Tensile, Impact, and Fatigue Properties of SAE 4140 Steel

During metal forming processes such as rolling and forging, deformable manganese sulfide (MnS) inclusions become elongated. Such elongated MnS inclusions can have considerable adverse effects on mechanical properties, if the inclusions are not aligned with the loading direction. The objectives of this study were to evaluate and compare fatigue, monotonic tensile and CVN impact behavior of SAE 4140 steel with high (0.077% S), low (0.012% S) and ultra low (0.004% S) sulfur contents at two hardness levels (40 HRC and 50 HRC). The longitudinally oriented samples at 40 HRC, where MnS inclusions were oriented along the loading direction, did not exhibit any significant sensitivity of tensile or fatigue properties to the sulfur content. For the transversely oriented MnS inclusions, however, the monotonic tensile test results indicate very low ductility of the high sulfur material at both hardness levels, where specimens failed shortly after yielding. The yield strength of the materials, however, did not differ significantly with the sulfur content. With regards to fatigue strength, the high sulfur material had up to 25% lower fatigue strength than the ultra low sulfur material under transverse loading. The scanning electron microscopy (SEM) inspection of failed fatigue test specimens revealed that the fracture topography of the high sulfur material were very rough and jagged, indicating several cracks originating from MnS inclusions. The fracture surfaces of the other two materials with lower sulfur content exhibited typical fatigue fracture surfaces with clear initiation and final fracture regions.

Quenching cracks in medium carbon steel initiated at manganese sulfide inclusions

Abstract Quench crack propensity has been investigated for two identical medium carbon steels (50CrMo4) which only differed in sulfur content. The standard variant of the material was affected by manganese sulfide inclusions whereas the low sulfur material was essentially free of sulfides. 80 mm, cylindrical test specimens were used. The test specimens had been cut out of cross rolled steel plates in which the manganese sulfide were flattened to discoid shape. The specimen orientation was in direction of principal deformation where the flattened sulfides were aligned with the test specimen axis. The largest sulfides reached lengths of 150 mm. Both materials were austenitized at 850°C for 60 minutes, quenched in a salt-bath at 180°C and immediately annealed at 425°C for one hour. It turned out that the standard material developed quench cracks which initiated at manganese sulfide. No cracks could be found in the low sulfur material. Thermal and transformational stresses, which develop during quenching, a...

Ｈｏｌｌｏｗ Ｃａｔｈｏｄｅ Ａｒｃ溶接現象に関する基礎的研究

Hollow Cathode Arc (HCA) is a low-pressure arc discharge, which is formed in vacuum by supplying a very small quantity of gas from the tip of hollow cathode. The purpose of this work is to elucidate the HCA characteristics as a welding heat source. In the present work, arc voltage-current characteristics of HCA and its melting characteristics have been discussed. As a result, it is made clear that the HCA process is very sensitive to arc parameters, such as gas flow rate, arc length, electrode shape, and ambient pressure. The results of the present work are summarized as follows.(1) The voltage of HCA increases with the increase of electrode inner diameter and the decrease of Ar gas flow rate.(2) The penetration in HCA melting is extremely deep and huge under the condition that Ar gas flow rate is low and arc length is long.(3) The penetration in HCA melting is sensitive to the minor elements in base metal such as sulfur. Even in the low sulfur material, a deep penetration is formed under high speed and high current conditions. The above results suggest that HCA method is promising as the heat source of welding in space or welding on the earth.

Fundamental characteristics of hollow cathode arc welding

Hollow Cathode Arc (HCA) is a low-pressure arc discharge, which is formed in vacuum by supplying a very small quantity of gas from the tip of hollow cathode. The purpose of this work is to elucidate the HCA characteristics as a welding heat source. In the present work, arc voltage-current characteristics of HCA and its melting characteristics have been discussed. As a result, it is made clear that the HCA process is very sensitive to arc parameters, such as gas flow rate, arc length, electrode shape, and ambient pressure. The results of the present work are summarized as follows.(1) The voltage of HCA increases with the increase of electrode inner diameter and the decrease of Ar gas flow rate.(2) The penetration in HCA melting is extremely deep and huge under the condition that Ar gas flow rate is low and arc length is long.(3) The penetration in HCA melting is sensitive to the minor elements in base metal such as sulfur. Even in the low sulfur material, a deep penetration is formed under high speed and high current conditions. The above results suggest that HCA method is promising as the heat source of welding in space or welding on the earth.

圧力容器用低合金鋼の高温高圧水中疲労き裂伝ぱ挙動に及ぼす流速の影響

Effect of water flow rate on fatigue crack growth behavior in high temperature water simulating BWR environments was examined by using a flow rate change test method. Materials used in this work were two types of low alloy pressure vessel steels A533B cl 1; one was medium sulfur material (S=0.014 wt%) and the other low sulfur material (S=0.004 wt%). Corrosion potentials during the tests were successfully measured in the relevant conditions.As a result, the fatigue crack growth rate in high temperature water was more accelerated with decreasing flow rate, and this trend was more striking for the medium sulfur material compared to the low sulfur material. Change of corrosion potential during the tests showed a good correlation with the change of water flow rate.

Influence of Sulfur on Initial Permeability of Commercial 49% Ni–Fe Alloys

Attainment of high initial permeability in commercial 49% Ni–Fe alloys is shown to be a function of the sulfur content and grain size. Low sulfur material was obtained by desulfurization during melting or by strip annealing. μ40 of the low sulfur material was significantly higher than that of normal commercial material at annealing temperatures below 1200°C. When annealed at 1200°C, μ40 for the initially low sulfur material was slightly lower because of a smaller grain size or a higher final sulfur level. Analysis of sulfur content of annealed material by the methylene-blue technique allowed a direct correlation between μ40 and sulfur content in secondary recrystallized structures. In general, μ40 values in excess of 10 000 cannot be obtained unless final sulfur content is less than 12 ppm. Highest initial permeabilities result from a coarse-grained secondary recrystallized structure and low impurity contents.