JP2015215203A - Method of evaluating carburized component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of evaluating a carburized component, configured to analyze carbon concentration after gas carburization with a comparatively simple apparatus.SOLUTION: In evaluating a component with a carburized surface, the surface of the component is subjected to fluorescent X-ray analysis, to measure carbon concentration of the surface. The surface is ground, and the ground surface is subjected to fluorescent X-ray analysis again to measure carbon concentration of the surface. The above operation is repeated, to measure a carbon concentration distribution up to a carburization depth, for evaluating the component.

Description

  The present invention relates to a method for evaluating a carburized part such as an automobile part that has been carburized on a surface in contact with another metal for the purpose of improving fatigue strength.

  Since differential cross joints as automobile parts are used under severe conditions, fatigue strength and hardness are required. For this reason, it forge-molds with the metal excellent in fatigue strength, and the carburizing process is given to the surface for the purpose of surface hardness and fatigue strength improvement on it.

  A differential apparatus using this differential cross joint will be described with reference to FIG.

  FIG. 7 is an exploded perspective view of the differential device 20 in which the differential cross joint 10 is used. 21 is a differential case, 22 and 23 are side gears, 24 is a differential pinion, and 25 is a drive pinion connected to a propeller shaft ( (Not shown), the ring gear 26 is rotated, 26 is a gear case, and 10 is a differential cross joint.

  FIG. 6 is a detailed perspective view of the differential cross joint 10 surrounded by a circle d in FIG. The differential cross joint 10 is configured by integrally providing pins 12 on the outer periphery of the ring 11, and the differential pinion 24 shown in FIG. 7 is pivotally supported on these pins 12, and the differential rotates with the differential. It is supported by a case (not shown).

  Since the differential cross joint (also referred to as a diff spider) 10 in the differential device 20 is used under severe conditions, chromium molybdenum steel such as SCM420 is manufactured by hot forging and supports a pinion gear. The surface of the shaft portion is subjected to gas carburizing treatment in order to improve the surface hardness and fatigue strength.

  SCM420 as chromium molybdenum steel has Fe as a base material, C: 0.17 to 0.23%, Mn: 0.55 to 0.9%, Cr: 0.85 to 1.25%, Mo: 0 .15 to 0.35%, and other components including Si and inevitable metals.

  Using this chromium-molybdenum steel, this is formed into the shape of the differential cross joint 10 shown in FIG. 7 by hot forging, and the surface is machined to a predetermined size, and then subjected to gas carburizing treatment. It has fatigue strength and toughness, the surface is martensitic, the hardness is increased, and the wear resistance of the sliding surface of the pin 12 can be remarkably improved.

  This gas carburizing process is performed so that the surface hardness is Vickers hardness (Hv) and a set value (for example, 600 to 700 Hv) after the differential cross joint is formed by forging.

JP 2008-045975 A Japanese Patent Laid-Open No. 08-094609 JP 2008-292170 A JP 2006-095637 A

  However, the gas carburizing process has different atmosphere control of gas carburizing depending on the component manufacturer, and therefore, it has been found that even if the surface hardness is the same, the pin is cracked.

  That is, it was found that even if the surface hardness is the same, if the carburizing treatment is different, the C concentration distribution in the depth direction changes, and therefore, cracking occurs due to excessive carburization.

  FIG. 8 and FIG. 9 show the results of analyzing the carbon concentration distribution with respect to the surface depth of the pins of the differential cross joints that were gas carburized by different parts manufacturers using EPMA (Electron Probe Microanalyzer). FIG. 8 shows the analysis result of the differential cross joint in which cracking occurred, and FIG. 9 shows the analysis result of the differential cross joint in which cracking did not occur.

  In normal gas carburizing, the surface carbon concentration is said to be 0.8 mass%, but in the differential cross joint of FIG. 8, the carbon concentration of the pin surface is as high as 1.25 mass%, which is the difference in FIG. In the dynamic cross joint, the carbon concentration on the surface of the pin was 0.75 mass%, and the analysis result that it did not reach 0.8 mass% was obtained.

  The differential cross joint shown in the analysis result of FIG. 8 has a surface that is excessively carburized, and a large amount of retained austenite (γ). Therefore, it is considered that a set crack has occurred.

  Further, the differential cross joint shown by the analysis result of FIG. 9 has a carbon concentration of 0.75 mass% and does not crack, but is lower than the ideal carbon concentration of 0.8 mass%, and the carbon concentration is set to 0.00%. There is room to further approach 8 mass%.

  In this way, measurement of the carbon concentration in the depth direction is important to guarantee the quality of the differential cross joint. However, EPMA has a large equipment, requires skill in operation, and is used for quality control on site. It is impossible to adopt.

  Accordingly, an object of the present invention is to provide a method for evaluating a carburized component that can solve the above-described problems and analyze the carbon concentration after the carburizing process such as gas carburizing with a relatively simple device.

  In order to achieve the above object, the present invention, when evaluating a part whose surface has been carburized, measures the carbon concentration of the surface of the part by fluorescent X-ray analysis, and then grinds the surface again. A method for evaluating a carburized component, characterized in that the carbon concentration of the ground surface is measured by fluorescent X-ray analysis, and this is repeated to measure the carbon concentration distribution up to the carburization depth to evaluate the component. It is.

  The surface of the component is preferably ground with a grindstone that does not contain carbon.

  The grindstone is preferably made of an alumina grindstone.

  It is preferable to grind the surface of the grindstone after grinding with a diamond dresser to remove the carbon adhering to the grindstone surface during grinding, and then perform the next grinding.

  The parts consist of differential cross joints formed by forging chrome molybdenum steel and gas carburized after forging. Evaluation of differential cross joints is based on carburization based on a surface carbon concentration of 0.8 mass%. It is preferable to evaluate whether the depth has reached 1.3 mm.

  When forming a differential cross joint by forging, a test piece is made of chromium molybdenum steel, the test piece is gas carburized along with the differential cross joint, and the gas carburized test piece is subjected to fluorescent X-ray analysis. It is preferable to evaluate it.

  According to the present invention, it is possible to measure the carbon concentration of the carburized component by repeating the fluorescent X-ray analysis of the component surface and the grinding of the measurement surface, and exhibit an excellent effect that the quality can be evaluated.

It is a flowchart which shows one embodiment of this invention. It is a figure which shows the outline of the fluorescent X-ray-analysis apparatus used for this invention. It is a figure which shows the relationship between the energy and X-ray intensity in a fluorescent X ray analyzer. It is a figure which shows the calibration curve for calculating | requiring the carbon concentration in a fluorescent X ray analyzer. In this invention, it is a figure which shows the result of having analyzed the density | concentration distribution of the various metal component with respect to the surface depth of the differential cross joint as components in the fluorescent X ray analyzer. It is a detailed perspective view of the differential cross joint as a component of the present invention. It is an assembly exploded perspective view of a differential device in which a differential cross joint is incorporated. It is a figure which shows the result of having analyzed the carbon concentration distribution with respect to the surface depth of the pin of the differential cross joint by which the excess carburizing process was made | formed by EPMA. It is a figure which shows the result of having analyzed the carbon concentration distribution with respect to the surface depth of the pin of the differential cross joint by which the surface carbon concentration was 0.8 mass% or less and which was carburized, by EPMA.

  A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

  First, the outline of the fluorescent X-ray analyzer will be described with reference to FIG.

  In FIG. 2, when X-rays generated in the X-ray tube 31 are irradiated to the sample 32, the orbital atoms of the inner shell are excited by the interaction with the atoms of the detection element in the sample 32, and fluorescent X-rays are generated. This fluorescent X-ray is split by the spectroscopic crystal 34 through the solar slit 33, and the fluorescent X-rays (mainly Kα rays and Kβ rays) to be measured are spectrally separated and input to the detector 35. Thus, a spectrum of X-ray intensity with respect to energy is detected.

  FIG. 3 shows the spectrum of the X-ray intensity with respect to energy. Based on the spectrum of this Kα ray, the concentration of the component (carbon) of the sample is detected from the calibration curve shown in FIG. That is, the concentration of the measured metal component of the sample can be detected from the peak value of the X-ray intensity based on the calibration curve.

  In this detection, the analysis is performed by automatically replacing the spectral crystal for measuring carbon and the spectral crystal for measuring Mn, Cr, and Mo.

  Now, a method for evaluating a carburized component according to the present invention will be described with reference to the flow shown in FIG.

  First, the part to be measured is the differential cross joint 10 described in FIG.

  Since the surface of the differential cross joint 10 after being carburized is covered with black skin made of carbon, the surface is subjected to fluorescent X-ray analysis after the black skin on the surface is removed by grinding. During measurement, the differential cross joint 10 may be directly set on a fluorescent X-ray analyzer for analysis. However, in order to increase the measurement accuracy, a test piece of 40 mmφ × 30 mmL is prepared, and the differential cross A fluorescent X-ray analysis is performed using a material produced under the same forging conditions as the joint 10 and carburized under the same gas carburizing conditions as the differential cross joint 10. The test piece may be produced by producing chromium molybdenum steel under the same conditions as the forging of the differential cross joint, but may be obtained by cutting a round bar of chromium molybdenum steel.

  In FIG. 1, when analysis is started (step S1), a component (test piece) is set in a fluorescent X-ray analyzer. In this case, if it is a test piece, the surface is lightly ground until the black skin disappears. Thereafter, the X-ray fluorescence analysis of the carburized surface of the set part (test piece) is performed (step S2). Next, the part is taken out from the fluorescent X-ray analyzer, and the measurement surface is ground by about 0.2 mm with a grindstone not containing carbon (alumina-based grindstone) (step S3), and the part is set in the fluorescent X-ray analyzer again. Then, the fluorescent X-ray analysis of the grinding surface of the part is performed (step S5). Before and after this, the grinding powder containing C adheres to the grinding wheel after grinding. The surface is cut and cleaned with a grindstone or the like (step S4).

  Thereafter, in step S6, it is measured whether or not the grinding depth has reached a predetermined depth (about 1.5 mm) that is equal to or greater than the carburized depth (1.3 mm). S5 is repeated, and the measurement surface is repeatedly ground by about 0.2 mm, and fluorescent X-ray analysis of the ground surface is performed at each grinding depth (about 7 to 10 times).

  In this manner, after the analysis up to a predetermined depth including the carburization depth is finished in Step S6 (Yes), the analysis is finished (Step S7).

  In this flow, if the grindstone for grinding the measurement surface is a grindstone containing carbon like silicon carbide abrasive grains, the abrasive powder adheres to the grinding surface, and C contained in the abrasive grains is included in the analysis results. Reflected, the accurate C concentration analysis cannot be performed. Therefore, for the grinding, a brown alumina-based, white alumina-based, single crystal alumina-based, or zirconia alumina-based alumina-based grindstone is used. Also, when grinding with an alumina grinding wheel, the grinding powder of the parts adheres to the grinding wheel surface, and the carbon contained in this grinding powder is reflected in the analysis results during subsequent grinding. By grinding with a diamond grinder and cleaning, carbon contamination on the surface to be analyzed can be prevented and accurate carbon concentration analysis can be performed.

  In addition, although the above flow has been described in the analysis for measuring the carbon concentration, the spectral crystal described in FIG. 2 is automatically changed by a fluorescent X-ray analyzer, so that other metal components (Mn, Cr, Mo) can also be analyzed simultaneously in relation to depth to measure these concentrations.

  FIG. 5 shows the results of measuring the concentration distribution (from the surface to a depth of 1.5 mm) of various components (C, Mn, Cr, Mo) with respect to the surface depth of the carburized chromium molybdenum steel.

  In FIG. 5, although the carbon concentration distribution changes, the concentration distribution of Mn, Cr, and Mo coincides with the components of the chromium-molybdenum steel that is the raw material. It can be seen that the concentration is also consistent with the C component of chromium molybdenum steel, and the carburization depth is up to 1.3 mm.

  Moreover, when the carbon concentration on the surface is observed, it is found that the carbon concentration is 0.9 mass% or more with respect to an appropriate carbon concentration of 0.8 mass%, and the carburizing treatment is slightly excessive.

  Therefore, based on this result, in the gas carburizing process, the surface carbon concentration can be adjusted to a concentration closer to the target of 0.8 mass% by adjusting the atmospheric conditions, quenching temperature, processing time, and the like.

  Thus, by making the carbon concentration on the surface of the part close to 0.8 mass% and carburizing the carburized depth to 1.3 mm, the produced part can be evaluated and its quality is reliably guaranteed. It becomes possible.

10 Differential cross joint (parts)
30 X-ray fluorescence analyzer 32 Sample

Claims (6)

  When evaluating a carburized component, the surface of the component is measured for surface carbon concentration by fluorescent X-ray analysis, and then the surface is ground and again subjected to fluorescent X-ray analysis. A method for evaluating a carburized component, characterized in that the carbon concentration is measured, and the following is repeated to measure the carbon concentration distribution up to the carburization depth to evaluate the component.   The method for evaluating a carburized component according to claim 1, wherein the grinding of the surface of the component is performed with a grindstone not containing carbon.   The method for evaluating a carburized component according to claim 2, wherein the grindstone is an alumina grindstone.   The evaluation of the carburized part according to any one of claims 1 to 3, wherein the surface of the grindstone after grinding is shaved with a diamond dresser to remove carbon adhering to the grindstone surface during grinding, and then the next grinding is performed. Method.   The parts consist of differential cross joints formed by forging chrome molybdenum steel and gas carburized after forging. Evaluation of differential cross joints is based on carburization based on a surface carbon concentration of 0.8 mass%. The method for evaluating a carburized component according to claim 1, wherein the evaluation is performed based on whether the depth reaches 1.3 mm.   When forming a differential cross joint by forging, a test piece is made of chromium molybdenum steel, the test piece is gas carburized along with the differential cross joint, and the gas carburized test piece is subjected to fluorescent X-ray analysis. The method for evaluating a carburized component according to claim 5, wherein