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首页> 外文期刊>Journal of Research of the National Institute of Standards and Technology >Impact Toughness Modification of NIST Low-Energy Charpy Verification Specimens for Testing at Room Temperature
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Impact Toughness Modification of NIST Low-Energy Charpy Verification Specimens for Testing at Room Temperature

机译：NIST低能量夏比验证试样的冲击韧性改性在室温下进行测试

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摘要

The possibility for the National Institute for Standards and Technology (NIST) to certify Charpy reference specimens for testing at room temperature (21 degrees C +/- 1 degrees C) instead of -40 degrees C was investigated in a previous study, in which a slightly increased likelihood of specimen jamming was observed at the low-energy level (13 J to 20 J). Moreover, there is a concern that the higher impact toughness of low-energy verification specimens at room temperature would not allow the same Charpy machine features to be verified as in the case of low-temperature (-40 degrees C) tests, namely, the linear elastic behavior of the sample and the very high maximum forces (typically larger than 33 kN). In this paper, we report on the change in the mechanical properties (hardness and absorbed energy) of the American Iron and Steel Institute (AISI) 4340 steel low-energy specimens that ensues from the modification of the temperature of the final tempering heat treatment. We established that, if low-energy verification specimens are tempered at 300 degrees C for 2 h and then air cooled, they exhibit equivalent impact toughness (13 J to 20 J) and postimpact behavior (specimen halves projected backward at high speed) at room temperature as compared to specimens currently on sale for testing at -40 degrees C. Their hardness is however increased to above 49 HRC on the Rockwell scale. The minimum hardness requirement for low-energy verification specimens, currently set at 44 HRC in NIST specifications, will have to be increased to 49 HRC.
机译：在先前的研究中研究了国家标准和技术（NIST）国家标准和技术研究所（NIST）的可能性，用于在室温（21摄氏度C +/- 1摄氏度）而不是-40摄氏度的C）而不是-40摄氏度。在低能量水平（13 j至20 j）处观察到样品干扰的略微增加的可能性。此外，担心室温下低能量验证样品的较高冲击韧性不会允许在低温（-40摄氏度）测试的情况下验证相同的夏比机特征，即样品的线性弹性行为和非常高的最大力（通常大于33kN）。在本文中，我们报告了美国钢铁研究所（AISI）4340钢材低能量标本的机械性能（硬度和吸收能量）的变化，从而从最终回火热处理的温度改变。我们建立了，如果低能量验证试样在300摄氏度下进行2小时，然后空气冷却，则它们表现出等效的冲击韧性（13 j至20 j）和底层行为（在高速下延伸的标本半部）在房间与目前销售的试样相比，温度用于在-40摄氏度下进行测试。然而，它们的硬度在罗克韦尔规模上增加到49小时以上。目前在NIST规范中设定为44小时的低能量验证标本的最低硬度要求将不得不增加到49 HRC。

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