Lower limit characterization of segregation degree for large-size low-alloy steel.

Based on the original position statistic distribution analysis technique, the characterization method of segregation for large-size metal materials gives significant guidance to the research of material properties and production. However, random errors are inevitably brought into the calculation of segregation degree for materials characterization by the Spark Mapping Analysis for Large Sample (SMALS) technique, resulting in a misguide of the segregation degree. In this paper, we present the lower limit of segregation degree (Ds(L)) method to distinguish the random error from metal material segregation for large-size samples over the SMALS method. The random error of standard material in the 95% confidence interval was utilized as Ds(L) and the method has been applied for macro-segregation quantitative analysis. The precision correlation between Spark Atomic Emission Spectrometry (Spark-AES) and SMALS was established. Furthermore, the functional relationship between the Ds(L) and element content C can be obtained in the SMALS method. The Ds(L) method as the criterion can be used to not only characterize the minimum limit of the segregation degree but also the segregation existence for large-size samples. Applying to low-alloy steel can illustrate the effective performance of the Ds(L) method. Results on both spark mapping analysis and Spark-AES verify the substantial consistency.

Analysis of Ti-inclusions in high carbon chromium bearing steel by laser-induced breakdown spectroscopy.

The presence of Ti-inclusions has a significant impact on the fatigue life of bearing steel. Laser-induced breakdown spectroscopy (LIBS) is a useful tool for analyzing Ti-inclusions, despite the fact that the effective excitation area of LIBS is actually larger than the pre-set spot diameter. The area affected by the LIBS spot ranges from 150 µm to 376.6 µm. A new parameter L has been introduced for better understanding the characterization of Ti-inclusions detected in SEM-EDS and LIBS measurements, When the L threshold falls below the value of 188.3 µm, the SEM-EDS and LIBS data are obtained from the same Ti-inclusion. The study demonstrates that there is a linear relationship between LIBS intensity and Ti-inclusions area, which was tested both theoretically and practically. The analysis of six samples of rolling GCr15 bearing steel with a Cr element content of 1.5% shows that one regression line is enough for analyzing the same type of inclusion processed under the same conditions. This method can significantly reduce the workload and analysis time during the actual analysis process.

Characterization of segregation degree for large size metal component and application on high-speed train wheel.

Elements segregation has a significant impact on the performance of steel products and becomes more serious with the increase of products size. Many studies have been carried out on segregation in solidification. None of the studies on the quantitative analysis of segregation evaluation for the full surface of large-size metal components. In this paper the elements segregation degree (Ds) is used for large size metal component analysis for the first time corresponds to the specification of permissible variations for the final product composition. The permissible variations are able to constrain the upper limit of the segregation degree. Based on the data of non-alloy steel and low alloy steel, alloy steel, stainless steel and heat-resistant steel in ASTM (American Society for Testing and Materials) A29/A29 M and GB/T 222, the correlation between upper and lower permission variation to element content was established and the regression formula was obtained respectively. Each element content was corresponding to a specified permission limit. The segregation degree of steel products was easily evaluated by the formula precisely. The 95% prediction interval was utilized as the upper and lower variation line to evaluate the segregation degree of large-size sample. The method was successfully applied in the full-scale mapping of longitudinal section of the high-speed train wheel by Original Position Analysis for Large Samples (OPA-LS) technique. The negative and positive Ds of Al in high-speed train wheel were over DS(MAX) and the limit specified by GB/T 222, which indicated the Al segregation should be controlled.

[Determination of Acid-Insoluble Aluminum Content in Steel by Laser-Induced Breakdown Spectroscopy].

Laser-induced breakdown spectroscopy (LIBS) has become a very attractive and popular chemical analysis technique in material science for its advantage of rapid analysis, non-contact measurement, micro surface analysis and online analysis. In this paper, LIBS were used to determine insoluble aluminum content by analyzing the scanning data on massive steel samples. Abnormal data were discarded by Nalimov criterion, and the remaining data was used to calculate the average and the standard deviation. The threshold to distinguish acid-insoluble aluminum and soluble aluminum was identified as the average value plus triple standard deviation. Two different mathematical models were proposed to calculate insoluble aluminum content, respectively according to the ratio of the total acid-insoluble aluminium signal strength to total aluminum signal strength and acid-insoluble signal number to total aluminum signal number. The total aluminum content was determined by the calibration curve. Insoluble aluminum content of certified reference materials and plate blank samples obtained by mathematical model is coincident to chemical wet method results. The result according to total acid-insoluble aluminium signal strength is much better. LIBS can be used as a rapid analysis method to characterize insoluble aluminum content in steel samples.

[Progress in the application of laser ablation ICP-MS to surface microanalysis in material science].

In the present paper, apparatus and theory of surface analysis is introduced, and the progress in the application of laser ablation ICP-MS to microanalysis in ferrous, nonferrous and semiconductor field is reviewed in detail. Compared with traditional surface analytical tools, such as SEM/EDS (scanning electron microscopy/energy dispersive spectrum), EPMA (electron probe microanalysis analysis), AES (auger energy spectrum), etc. the advantage is little or no sample preparation, adjustable spatial resolution according to analytical demand, multi-element analysis and high sensitivity. It is now a powerful complementary method to traditional surface analytical tool. With the development of LA-ICP-MS technology maturing, more and more analytical workers will use this powerful tool in the future, and LA-ICP-MS will be a super star in elemental analysis field just like LIBS (Laser-induced breakdown spectroscopy).

[Element distribution analysis of welded fusion zone by laser-induced breakdown spectroscopy].

Over the past decade there has been intense activity in the study and development of laser-induced breakdown spectroscopy (LIBS). As a new tool for surface microanalysis, it caused widespread in materials science because of the advantage of rapid and high sensitivity. In the present paper, the distribution of Ni, Mn, C and Si near weld fusion line was analyzed on two kinds of weld sample. Line scanning mode analysis was carried out by three different kinds of methods, namely laser-induced breakdown spectroscopy (LIBS), scanning electron microscope/energy dispersive spectrometer (SEM/EDS) and electron probe X-ray microanalyser (EPMA). The concentration variation trend of Ni and Mn acquired by LIBS is coincident with SEM/EDS and EPMA. The result shows that the content of Ni and Mn was significantly different between weld seam and base metal on both the samples. The content of Ni and Mn was much higher in weld seam than in base metal, and a sharp concentration gradient was analyzed in the fusion zone. According to the distribution of Ni and Mn, all the three methods got a similar value of welded fusion zone width. The concentration variation trend of C and Si acquired by LIBS is not coincident with SEM/EDS and EPMA. The concentration difference between weld seam and base metal was analyzed by LIBS, but had not by SEM/EDS and EPMA, because of the low concentration and slight difference. The concentration gradient of C and Si in fusion zone was shows clearly by LIBS. For higher sensitivity performance, LIBS is much more adapted to analyze low content element than SEM/EDS and EPMA.

[Segregation bands analysis of steel sample using laser-induced breakdown spectroscopy].

In the present paper, under optimum experimental condition, two middle-low alloy slab and homogeneous samples were analyzed under the condition of spatial resolution about 100 microm by scanning mode. Element 2D intensity distribution can be converted into 2D concentration distribution via establishing calibration curve. The results showed that there is a central segregation for C, Si, Mn, P, S and Cu for 86 # slab sample, and C, Si, P and Ti for 174 # slab sample, the width of segregation band was estimated, and it agrees well with metallographic analysis. Homogeneous sample was analyzed by scanning mode, the result showed that C, Si, Mn, P, S and so on are well distributed, and there is no segregation band existing. 2D distribution of element intensity or concentration can be used to indirectly reflect sample's homogeneity. Compared with traditional metallographic analysis, LIBS can not only show central segregation bands position and width, but also provide 2D concentration distribution for C, Si, Mn, P, S etc in detail. This method can be used to characterize segregation band position and its width rapidly, and provide theoretical guidance for improving metallurgical process.

[Application progress of laser-induced breakdown spectroscopy for surface analysis in materials science field].

As a truly surface analytical tool, laser-induced breakdown spectroscopy (LIBS) was developed in recent ten years, and in this paper, fundamental theory, instrumentation and it's applications in material science are reviewed in detail. Application progress of elemental distribution and depth profile analysis are mainly discussed in the field of metallurgy, semiconductor and electronical materials at home and abroad. It is pointed out that the pulse energy, ambient gas and it's pressure, and energy distribution of laser beam strongly influence spatial and depth resolution, and meanwhile a approach to improving resolution considering analytical sensitivity is provided. Compared with traditional surface analytical methods, the advantage of LIBS is very large scanning area, high analytical speed, and that conducting materials or non-conducting materials both can be analyzed. It becomes a powerful complement of traditional surface analytical tool.