الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Certified reference materials (CRMs) are versatile tools to support quality, correctness and credibility of measurement results. They are used to provide the traceability of the measurement results to the SI unit. CRMs also play important role in verification of the accuracy of analytical measurement results. They are generally used to: 1) assure the quality of the measurement results, 2) establish traceability of the measurement results to the SI units by calibration and 3) to estimate the uncertainty of the measurement results, enabling them to be compared with other results, references, specifications or standards. This work aimed to the production of different types of iron alloys as certified reference materials which are not produced in Egypt or in Middle East. These CRMs enhance the technological innovation and improve competitiveness of the metal alloys industrial sectors in Egypt. Also it aimed to improving awareness of technicians of the iron and steel industrial sectors about the importance of CRMs in enhancing the quality of products.
The production of the certified reference materials of three batches of high alloy steel and seven batches of low alloy steel were done by designing the required composition.
Production technology was developed to guarantee the maximum homogeneity of readability of the chemical composition values. Melting was conducted in a medium frequency electric induction furnace with 100 kg capacity at the Central Metallurgical Research and Development Institute (CMRDI), Cairo, Egypt CMRDI experimental foundry.
For low alloy steel batches, low carbon steel containing ≥ 0.1% carbon was charged at the top of the furnace crucible and was re-melted at certain temperatures. After melting, liquid steel was supposed to contain impurities like sulphur and phosphorus. During the melting process, some elements such as nickel, chromium, manganese, vanadium, tungsten and other elements were added to improve properties of the produced steel. Ferro manganese (Fe- 80 % Mn) containing 6% carbon, Ferro Silicon (Fe-65% Si), pure metallic cupper, pure metallic nickel, ferrochromium (Fe-70% Cr) containing about 8% of carbon, ferrovanadium (Fe- 70% V) and ferromolybdenum (Fe-70% Mo) were added in calculated amounts to de-oxidize the liquid steel. After addition of the desired elements, the furnace temperature was raised up to 1550 °C for 10 minutes. The hot liquid steel was transported into certain thermal crucibles with the addition of 0.02% aluminum to remove oxygen. Specially designed water cooled copper molds were used for steel casting to ensure the maximum cooling rates, to minimize segregation of the alloying elements and to maximize homogeneity of the produced low alloy steel reference materials.
For high steel batches, low carbon steel containing very low carbon content was charged at the top of the furnace crucible and was re-melted at certain temperatures. Ferro manganese (Fe-80 % Mn) containing 0.1 % of carbon, pure metallic cupper, pure metallic nickel, ferrochromium (Fe-70% Cr) containing about 0.5 % of carbon, ferrovanadium (Fe-70% V), ferromolybdenum (Fe-70% Mo) and pure metallic cobalt were added in calculated amounts to de-oxidize the liquid steel. After addition of the desired elements, the furnace temperature was raised up to 1620-1630 °C. The hot liquid steel was transported into certain thermal crucibles with the addition of 0.02% of aluminum to remove oxygen. Specially designed water cooled copper molds were used for steel casting to ensure the maximum cooling rates, to minimize segregation of the alloying elements and to maximize homogeneity of the produced high alloy steel reference material.
The manufactured low alloy steel reference materials were composed of the following elements: Carbon, Silicon, Manganese, Phosphorus, Sulfur, chromium, Nickel, Copper, Molybdenum, Vanadium, Tungsten, Aluminum, Cobalt and Niobium. The composition percentages of these elements were selected in the ranges (%): 0.185-0.596, 0.191-1.000, 0.273-1.510, 0.0010-0.041, 0.002-0.035, 0.170-5.000, 0.040-1.510, 0.009-0.126, 0.001-1.130, 0.004-0.800, 0.008-2.000, 0.020-0.04, 0.001-0.020 and 0.001-0.005 respectively. The three sets of high alloy steel were composed of 0.0189-0.060 of C, 0.400- 1.660 of Si, 0.800-1.860 of Mn, 15.00-24.50 of Cr and 0.260-20.00 of Ni, all in (%). The produced Reference Materials samples were tested for homogeneity using X-ray fluorescence spectrometer and the data was statistically analyzed using one way analysis of variance (ANOVA). It was found that the produced reference materials were homogenous enough. Different methods of analysis in different laboratories were used to quantify the elemental content in each batch of alloys. characterization measurements of the manufactured low alloy steel & high alloy steel reference materials have been performed at four different laboratories using: XRF, OES and AAS and Gravimetric techniques as shown in figures34-35. Each of the randomly selected samples was measured five times by each technique at the four participating laboratories.
The results obtained were tested for normality, outliers, equality of means, and homogeneity of variances at 95% confidence level. The tests indicated that the measurement results were normal after removing the outliers and the method variances were homogeneous. To combine data obtained by the different techniques from the different laboratories, the Paule and Mandel statistical model was used. In this model, the weight of each method mean and the average weighted mean (certified value) were calculated. The weighted uncertainty associated with the average weighted mean was estimated from three sources. These are: uncertainty of the method mean, material variability and the bias allowance. The certified values and their associated expanded uncertainties for each element in low and high alloy steel reference materials batches are shown in the Tables 67 &94.
These alloy steel reference materials are produced and certified in Egypt for the first time and they will be good calibrants for ensuring the quality of low and high alloy steel products.