升温模式对高氮不锈钢粒样中氮元素测定的影响

粒状样品是炉前实验室测定氮含量的常用样品形态,但用于测定高氮不锈钢过程中经常出现鼓泡状熔体现象,严重影响氮含量分析准确性。实验对氧氮分析仪测定粒状高氮不锈钢样品中氮含量的影响因素进行了探讨,分析了影响样品脉冲熔融状况和高含量氮元素测定结果准确性的相关因素,认为待分析样品形态、样品中气体元素总量和成分特殊性是主要的内在影响因素,而脉冲熔融升温速度的快慢是外在影响因素。在原因分析的基础上,对脉冲炉升温程序进行试验,提出了适用于高氮不锈钢粒状样品中氮含量测定的阶梯升温模式:用时25s,脉冲炉功率由1 452W升至2 176W,然后快速升温,5s内功率由2 176W升至4 500W。将确定的阶梯升温模式用于耐热不锈钢、双相不锈钢及高强度无磁不锈钢中氮含量的测定,与常规方法的屑状样品测定结果比较,差值小于国家标准方法的重复性限r。

Influence of heating pattern on the determination of nitrogen in stainless steel granular sample containing high content nitrogen

Granular sample is common sample state for the determination of nitrogen content in laboratory on-the-spot analysis. However, bubble melt phenomena often appear during the analysis of stainless steel containing high content nitrogen, which seriously influences the determination accuracy of nitrogen. The factors influencing the determination of nitrogen content in granular stainless steel samples containing high content nitrogen by oxygen-nitrogen analyzer were discussed. The parameters those influenced the pulse fusion status of sample and determination accuracy of high content nitrogen were analyzed. It was found that the state of testing sample, total contents of gaseous elements in sample and the particularity of chemical components are major inherent influencing factors, which the heating rate in pulse fusion was an extrinsic influencing factor. Based on the analyses above, the heating procedures of pulse furnace were tested. The step heating mode which was suitable for the determination of nitrogen content in granular stainless steel sample containing high content nitrogen was proposed: the power of pulse furnace was increased from 1452W to 2176W within 25s; then the power was rapidly increased from 2176W to 4500W within 5s. The proposed step heating mode was applied for the determination of nitrogen content in heat-resisting stainless steel, duplex stainless steel and high strength non-magnetic stainless steel. Compared with the determination results of scrap samples by conventional methods, the difference value was less than repeatability limit r in national standard method.