近年来,钢铁行业需求量快速上升,竞争也变得更加激烈.为了得到性能可靠的产品,钢铁车间在生产工艺方面需要进一步严格控制好产品的生产规格.在这种背景下,为了严格控制好生产工艺的密封性并保证产品所期望的特性(尤其是其韧性和机械加工性方面),精确地进行氮的分析必不可少.在过去几年中,经典燃烧技术(CC)已广泛应用于鉴定钢中的碳、硫和氮元素.而火花发射法因其性能改进、耗材成本(燃烧技术方面)降低以及在分析时间缩短等方面的优势,也在氮分析方面得到了应用,并且应用越来越广泛.本项研究的目的在于通过火花发射光谱仪(OES)对氮分析进行优化.研究是在巴西塞拉的阿塞洛米塔尔图巴朗钢铁集团的化学分析实验室进行,利用DMAIC方法学(一种用于改进生产工艺质量的研究方法)[1],对潜在的影响因素(包括漂移、样品和周期)进行了分析,并确定和优化了影响氮分析精度的根本原因.在实施该计划后,对结果的精度(基于内标物的标准偏差)和准确性(通过与OE认证的参考物质和力可交叉核验结果进行比较)进行了评估.在本研究项目之前,通过光发射法测得的氮元素的标准偏差高达0.004 0％.阿塞洛米塔尔图巴朗钢铁集团利用光谱仪完成所有的研究计划后,试验表明,其测定标准偏差低达0.000 5％,充分展现了该技术的潜力.本研究对这一标准偏差进行了监测,频率为每周一次,监测期为3个月.结果发现,该标准偏差在0.000 3％到0.000 5％之间波动,表明稳定性较好.由此可见,火花发射光谱技术是氮分析的一种较有前途的方法.%In the latest years, as steel industry becomes more demanding and competitive, steel shop process has an increasing need to control the production specifications on time with reliable results. In this context, accurate nitrogen results are essential to control process sealing and to guarantee desired product characteristics (especially tenacity and machinability). Clearly, classical combustion techniques (CC) have been widely used in past years for determining carbon, sulfur and nitrogen in steel. However, spark emission has also been used and has been gaining popularity as a result of improved performances, reduction in consumables costs (associated with CC) and time gains. This work aimed to optimize nitrogen analysis by optical emission spectrometry (OES) in the Steel Chemical Analysis Laboratory of ArcelorMittal Tubarao located in Serra, Brazil and was performed according to DMAIC methodology (specific tool to improve the quality of processes)[1]. The potential influence variables were analyzed (shift, sample and period) , the basic causes related to nitrogen precision were identified and prioritized. After that the action plan was implemented and the results were evaluated focusing in precision (evaluated based on an internal reference material standard deviation) and accuracy (evaluated comparing with OE certified reference material and LECO cross checks). Before this project development, nitrogen standard deviation by optical emission reached 0. 004 0%. The trials made after the implementation of all planned actions in one of ArcelorMittal Tubarao's spectrometers showed the potential of this technique, since a standard deviation of 0. 000 5% was achieved. This result was monitored weekly during 3 months, floating from 0. 000 3 to 0. 000 5% what demonstrate its stability. Therefore,optical emission technique appears as a promising method to perform nitrogen analysis.
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