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答:用于化学分析的钢铁、合金和铁合金的试样首先必须能代表被测材料的成分.在遇到有特殊涂层、渗层或复合层(如材料表面有喷涂漆层、电镀或化学镀层、渗碳渗硫渗氮、磷化层、堆焊层、复合金属等)时,必须进行预处理.要避免将这些成分混入基体试样中.同时还必须将试样表面可能存在的包砂、氧化皮、油污等不洁物除去.可用砂纸、砂轮或钢丝刷清理到露出金属光泽,油污可用乙醚清洗处理.关于各种材料的取样方法.在各类相关的标准中都有具体规定.球墨铸铁中测定碳用的试样是不能采用钻、铇、车等方式制取样屑,否则由于取样时球状石墨会从基体上脱落、飞散而导致碳结果的严重偏低.即使将钻、铇或车屑筛分再按粗、细比例称样,或者将钻屑全部磨细,混匀后称样也仍然不能避免测定结果的偏低.60年代,在前苏联有人做过以下试验:
A: Specimens for steel, alloy and ferroalloy used in chemical analysis must first represent the composition of the material under test. In the presence of a special coating, coating or composite layer (such as spray paint on the surface of the material, electroplating or chemical Coating, carburizing the infiltration of nitriding, phosphating layer, the welding layer, composite metal, etc.), you must pretreatment to avoid mixing these components into the matrix sample at the same time must also be the sample surface may exist in the package Sand, oxide, oil and other dirty things to remove sandpaper, grinding wheel or wire brush can be cleaned to reveal the metallic luster, oil can be treated with ether cleaning method of sampling on a variety of materials in all relevant standards have specific provisions Sample of carbon in ductile iron can not be made by drilling, grinding, car or other methods, otherwise, the sample will be spheroidal graphite will be off from the matrix, flying and lead to serious low carbon results even if the drill,铇 or car scrap sieve and then press the coarse, thin scale said, or the drill cuttings are all fine, after mixing said the sample still can not avoid the low measurement results in the 1960s, in the Soviet Union someone has done the following test: