Papers by Keyword: Low Alloy Steel

Abstract: Welding at high humidity is frequently needed for the harbor hoisting machinery of steel structures in the coastal port city. A computational procedure is proposed for analyzing residual stress and temperature distributions induced by the T-joint welding in two types of St52-3 high strength low alloy steel plates both 6 mm in thickness. The relative humidity conditions varied from 75 to 90% at constant pressure. The finite element models are employed to evaluate the transient temperature and the residual stress during welding. According to the analysis results, the higher residual stress and the highest concentration of hydrogen are distributed in and surround the heat affected zone (HAZ), and vary with different humidity.

Abstract: The full scale evaluation test of a set of API Q125 high strength low alloy steel casing specimens was conducted. With the tension increasing to failure, the abnormal fracture occurred on each specimen. A series of testing and analysis including fracture observation, chemical composition analysis, mechanical properties testing, metallographic analysis and SEM analysis were made for the specimen with abnormal spiral fracture. The geometry measurement, visual examination, mechanical properties testing and metallographic analysis were conducted for a new specimen. The mechanical properties of the two specimens are in compliance with the specified material specification. The new specimen has lower external diameter ovality and higher wall thickness eccentricity. The smaller wall thickness is distributed in a spiral shape, similar with the abnormal fracture. The fracture originated in the middle of casing wall, and the fracture position had obvious necking. According to fractography and fracture mechanics analysis, the abnormal spiral fracture was attributed to the metallurgical and geometry imperfection grown out of tubing processing process.

Abstract: In this paper the emphasis is focused upon nitriding effect on corrosion fatigue strength of Cr-Mo low alloy steel in 1% HCl aqueous solution.Corrosion fatigue strength enhancement of Cr-Mo low alloy steel by nitriding is discussed on the basis of the corrosion fatigue testing results on gas and ion nitrided Cr-Mo low alloy steel plate specimen with 3.5mm thickness in 1%HCl aqueous solution. It can be concluded that residual compressive stress distributed on the nitrided specimen surface caused improvement of corrosion fatigue strength of Cr-Mo low alloy steel.

Abstract: In this paper, the empirical kinetics models for athermal martensite transformation in plain carbon and low alloy steels were reviewed. Four models based on an exponential function were selected and evaluated by comparing with the published values of M₅₀ and M₉₀ temperatures. It was confirmed that the model proposed by Lee and Van Tyne resulted in more accurate predictions of athermal martensite transformation kinetics by considering the composition dependent parameters and the exponent term to express a sigmoidal shaped curve.

Abstract: This paper presents the results of research influence nitriding in electrolytic plasma on the tribological properties of low-alloy 40Cr steel. It is shown that the process of electrolytic plasma nitriding can significantly increase the wear resistance of the samples 40Cr steel. Found that after nitriding component adhesive wear mechanism is changed to abrasion.

Abstract: Dual phase (DP) steel is a high strength steel for auto-panel. In this paper, mechanical property, forming ability of high strength steel DP450 are studied by experiments and compared with those of steel MS6000. And theoretical research on predicting the forming limit of steel DP450 by the NADDRG model. The established mathematic model for relativity is of practical usefulness. Experimental results reveal that the yield strength of steel DP450 is about 7.2% lower than the MS6000, and the break strength increases by 18.9%, while the elongation increases by 19%. The results show that mechanical property of high strength steel DP450 is better than that of MS6000, while forming ability of DP450 is not lower than that of MS6000.

Abstract: The metallurgy quality of the steel was improved greatly by calcium treatment which was a technique developed for a long time. The Mn steels treated with calcium, carbon-manganese steels and nickel-chromium steels were collected and their corrosion behaviors were investigated. The results showed that the corrosion resistance of the Mn steel is lower than that of the Ni-Cr steel. The shape of the inclusions can be modified and quality of the steels can be enhanced by the calcium treatment, and the corrosion resistance of the steel treated with calcium is higher than that of the common carbon-Mn steel, and near to that of the NiCr steel.

Abstract: Aimed at improving mechanical properties of high strength low alloy steel welds, oxides with high melting point and high stability were added into steel liquid. By thermodynamics calculation and thermal simulating technology, phase transformation characteristics of low alloy steel weld with TiO₂ addition were investigated. The results showed that TiO₂ added in welds led to the decrease of phase transformation temperature and the wideness of γ→α transformation temperature range. The starting and finishing transformation temperature of ferrite respectively dropped about 311K and 486K on the cooling condition of 373K/s. Moreover, the complex inclusions of TiOx-MnO-SiO₂-MnS with spherical shape and 0.67μm mean size formed in weld metal. In addition, only acicular ferrite existed in the titanium oxide added welds. So it was concluded that titanium oxide can effectively be used to control phase transformation and then achieve fine and favorable microstructure.

Abstract: EDXRF analysis provides several important advantages such as simultaneous determination of the elements present, analyses of wide concentration ranges, and fast analysis with no sample preparation. The paper relates a comparative quantitative analysis using regression and modified Fundamental Parameter Technique FPT methods in the determination of minor elements present in low alloy steel. Regression was developed by plotting calibration graphs using low alloy reference standards while the modified FPT method involves incorporation of pure metal spectrum to the existing equation to improve on the accuracy of the analysis. Discrepancy tests carried out for the two methods showed that the error ranges were 0.3-6.5% and 1.2-7.9% for regression and modified FPT analyses, respectively. This makes the FPT method more acceptable for quantitative analysis of elements present in low alloy steel.

Abstract: Wear is a common problem for engineering components subjected to dynamic loading. Surface modification is mostly applied to reduce the wear. An exploratory research is conducted to form a composite coating on AISI 4340 steel surfaces by incorporating a mixture of TiC and hexagonal Boron Nitride (h-BN) particulates using powder placement and TIG torch melting techniques. Initial results show the evidence of TiC incorporation in all tracks but the presence of h-BN is limited in a few tracks. However, processing conditions are identified that can produce composite coatings incorporating both TiC and h-BN particulates. The melt microstructure consists of a small amount of un-melted TiC and h-BN, partially melted TiC particulates with eutectic structure containing precipitated TiC and TiB2 particles. Hardness of the coating is found to fluctuate along the melt depth. However, the maximum hardness of the coating is about 3 times the base hardness of 250 HV.