The effect of quenching and defects size on the HCF behaviour of Boron steel
Abstract This work investigates the effect of natural and artificial surface defects and quenching on the fatigue strength of a Boron steel (22MnB5). A vast experimental campaign has been undertaken to study the high cycle fatigue behaviour and more specifically the fatigue damage mechanisms observed in quenched and untreated materials, under different loading conditions and with differents artificial defects sizes (from 25 μm to 370 μm radius). In order to test the sheet metal in shear an original test apparatus is used. The critical defect size is determined to be 100 ± 50 μm. This critical size does not appear to depend on the loading type or the microstructure of the material (i.e. ferritic–perlitic or martensitic). However, for large defects, the quenched material is more sensitive to the defect size than the untreated material. For a defect size range of 100–300 μm the slope of the Kitagawa–Takahashi diagram is approximately −1/3 and −1/6 for the quenched and untreated materials respectively. A probabilistic approach that leads naturally to a probabilistic Kitagawa type diagram is developed. This methodology can be used to explain the relationship between the influence of the heat treatment and the defect size on the fatigue behaviour of this steel.
Determination of boron in steel by HNO 3 -NH 4 HF 2 digestion and ICP-MS
Various studies have been done to improve the properties of the steel by adding boron to the steel. Some studies have reported on the analysis of the boron in steel by AAS (atomic absorption spectrometry), ICPOES(inductively coupled plasma-optical emission spectrometry), ICP-MS (inductively coupled plasma/mass spectrometry). The volatile loss of boron of steel in sample digestion and the separation procedure for avoiding matrix effect by high concentration of iron are difficulties for determination of boron in steel. The method to determine boron in steel by ICP-MS was developed without volatilization of boron in sample digestion step with HNO3-NH4HF2 digestion method, and the additional separation process for avoiding matrix effect. Complete decomposition of steel with HNO3-NH4HF2 digestion method, and boron determination by ICP-MS in the matrix of high concentration of iron were possible. Quantitative recoveries of boron in certified standard steel by new method in this study were 103 to 111%, and the relative standard deviation is less than 5%. The method detection limit was 1.17 μg/g. 요 약: 최근 붕소를 철강에 첨가함으로써 철강의 성질을 개선시키는 여러 연구들이 알려져 있다. 이러 한 연구를 위하여 원자 흡광광도법, ICP-OES, ICP-MS에 의한 철강 중 붕소 분석 방법에 관한 연구들이 보고되고 있으며, 철강 중 붕소 정량 시 붕소의 휘발 손실 및 고농도 철 매트릭스로 인한 붕소 분석 방 해 등의 어려움이 알려져 있다. 이 연구에서는 붕소의 휘발 손실을 억제 가능한 철강 시료 분해 방법 및 매트릭스 분리과정 없이 ICP-MS에 의하여 철강 내 붕소를 정량할 수 있는 방법을 연구하고자 하였다. 질산-이플루오린화 암모늄을 이용하여 철강 시료 중 붕소의 휘발 손실을 억제하고 시료의 완전 분해가 가능하였으며, ICP-MS에 의하여 다량의 철 매트릭스 중 붕소 정량이 가능하였다. 서로 다른 붕소 함량 의 철강 표준물질을 대상으로 시료 분해 및 ICP-MS에 의한 붕소 정량 결과 회수율은 103~111%, 상대표 준편차는 5% 이하였으며, 방법검출한계(MDL)는 1.17 μg/g 이었다.
Experimental investigation of the geotechnical properties and microstructure of lime-stabilized saline soils under freeze-thaw cycling
Abstract The Song-Nen Plain in northeastern China holds one of the three largest expanses of soda saline-alkali soil in the world. Due to its disadvantageous geotechnical properties, the saline soil in this area is unable to meet the needs of construction projects. This study evaluates the stabilizing effect of adding lime to such soils. Specifically, it investigates how the physicochemical and mechanical properties and microstructure of soda saline-alkali soil are altered by lime and how these changes are affected by both freeze-thaw cycling and the duration of curing. The results reveal that adding lime to saline soil transforms clay particles into sand and silt particles and causes the pore size distribution (PSD) to become bimodal, with small-pore and macropore populations. An increase in lime content leads to an increase in the unconfined compressive strength (UCS) but a gradual decrease in both the cation exchange capacity (CEC) and plastic index. Freeze-thaw cycles break up coarse particles and aggregate finer particles, increasing the diameter of macropores and decreasing the USC; however, the effect on specimens with >9% lime is negligible. It is further shown that the geotechnical properties of the soil change immediately after the addition of lime, indicating that the cation exchange reaction takes place very quickly. Furthermore, the pozzolanic reaction leads to an increase in the percentage of sand-sized particles and a decrease in porosity after 28 days of curing. Overall, these results indicate that it is feasible to use lime to improve the engineering properties of soda saline-alkali soil in this area.