1.1 本规程涵盖通过使用高速膨胀计技术测量作为时间和温度函数的线性尺寸变化，并以数值或图形形式将结果报告为线性应变，来确定亚共析钢的相变行为。 1.2 本规程适用于具有可编程热剖面和数字数据存储和输出能力的高速膨胀测量设备。 1.3 本规程适用于在等温和连续冷却条件下测定钢的相变行为。 1.4 本规程包括获取金相信息的要求，这些信息将用作膨胀计测量的补充。 1.5 以国际单位制表示的数值应视为标准。本标准中不包括其他计量单位。 1.6 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的使用者有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 1.7 本国际标准是根据世界贸易组织技术性贸易壁垒委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认的标准化原则制定的。 ===意义和用途====== 5.1 本规程用于提供数值模型所需的钢相变数据，用于预测钢制造、锻造、铸造、热处理和焊接过程中的微观结构、性能和变形。或者，该实践通过确定规定热循环产生的微观结构，为钢和预制钢产品的最终用户提供了为给定应用选择钢种所需的相变数据。 5.1.1 有几种计算机模型可用于预测钢的微观结构、机械性能和变形，作为热处理循环的函数。 它们的使用是基于准确和一致的热应变和转变应变数据的可用性。热循环过程中产生的应变，包括热应变和变形，是用于预测微观结构和性能以及估计变形的参数。应该指出的是，这些模型正在不断发展。该过程旨在建立钢中应变离散值和特定微观结构成分之间的直接联系。本规程描述了在规定的热循环期间测量应变的标准化方法。 5.1.2 本规程适用于为钢铁制造、锻造、铸造、加热控制中使用的计算机模型提供数据- 处理和焊接工艺。它还可用于提供预测微观结构和性能的数据，以帮助选择最终用途的钢合金。 5.1.3 这种做法适用于提供构造转换图所需的数据，转换图将钢热处理过程中形成的微观结构描述为时间和温度的函数。这些图表提供了热循环变化对钢微观结构影响的定性评估。 附录X2 描述了这些图的构造。 5.2 应该认识到，钢在热循环过程中产生的热应变和转变应变对化学成分很敏感。 因此，化学成分的各向异性会导致应变的可变性，并会影响应变测定的结果，尤其是体积应变的测定。冷却过程中确定的应变对奥氏体的晶粒尺寸很敏感，而奥氏体的晶粒大小是由加热循环决定的。当奥氏体晶粒尺寸保持在5至8的ASTM晶粒尺寸之间时，获得了最一致的结果。最后，共析碳含量定义为0.8 % 用于碳钢。合金元素的添加可以改变这个值，同时Ac 1. 和Ac 3. 温度。如下所述，需要采用加热循环，以确保在冷却期间的应变测量之前完全形成奥氏体。

1.1 This practice covers the determination of hypoeutectoid steel phase transformation behavior by using high-speed dilatometry techniques for measuring linear dimensional change as a function of time and temperature, and reporting the results as linear strain in either a numerical or graphical format. 1.2 The practice is applicable to high-speed dilatometry equipment capable of programmable thermal profiles and with digital data storage and output capability. 1.3 This practice is applicable to the determination of steel phase transformation behavior under both isothermal and continuous cooling conditions. 1.4 This practice includes requirements for obtaining metallographic information to be used as a supplement to the dilatometry measurements. 1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 5.1 This practice is used to provide steel phase transformation data required for use in numerical models for the prediction of microstructures, properties, and distortion during steel manufacturing, forging, casting, heat treatment, and welding. Alternatively, the practice provides end users of steel and fabricated steel products the phase transformation data required for selecting steel grades for a given application by determining the microstructure resulting from a prescribed thermal cycle. 5.1.1 There are available several computer models designed to predict the microstructures, mechanical properties, and distortion of steels as a function of thermal processing cycle. Their use is predicated on the availability of accurate and consistent thermal and transformation strain data. Strain, both thermal and transformation, developed during thermal cycling is the parameter used in predicting both microstructure and properties, and for estimating distortion. It should be noted that these models are undergoing continued development. This process is aimed, among other things, at establishing a direct link between discrete values of strain and specific microstructure constituents in steels. This practice describes a standardized method for measuring strain during a defined thermal cycle. 5.1.2 This practice is suitable for providing data for computer models used in the control of steel manufacturing, forging, casting, heat-treating, and welding processes. It is also useful in providing data for the prediction of microstructures and properties to assist in steel alloy selection for end-use applications. 5.1.3 This practice is suitable for providing the data needed for the construction of transformation diagrams that depict the microstructures developed during the thermal processing of steels as functions of time and temperature. Such diagrams provide a qualitative assessment of the effects of changes in thermal cycle on steel microstructure. Appendix X2 describes construction of these diagrams. 5.2 It should be recognized that thermal and transformation strains, which develop in steels during thermal cycling, are sensitive to chemical composition. Thus, anisotropy in chemical composition can result in variability in strain, and can affect the results of strain determinations, especially determination of volumetric strain. Strains determined during cooling are sensitive to the grain size of austenite, which is determined by the heating cycle. The most consistent results are obtained when austenite grain size is maintained between ASTM grain sizes of 5 to 8. Finally, the eutectoid carbon content is defined as 0.8 % for carbon steels. Additions of alloying elements can change this value, along with Ac 1 and Ac 3 temperatures. Heating cycles need to be employed, as described below, to ensure complete formation of austenite preceding strain measurements during cooling.