Abstract
Abstract The type of heat treatment process used is mainly determined by its cooling mode. Hardening is a metal heat treatment during which the most critical operation is cooling. Most quenchants used for steel hardening are vaporizable liquids, such as water, petroleum oils, emulsions, aqueous polymer solutions, or brines. Testing methodologies that include ISO 9950, Industrial Quenching Oils-determination of Cooling Characteristics-Nickel-alloy Probe Test Method, and ASTM Standards: D6200, Standard Test Method for Determination of Cooling Characteristics of Quench Oils by Cooling Curve Analysis, D6482, Standard Test Method for Determination of Cooling Characteristics of Aqueous Polymer Quenchants by Cooling Curve Analysis with Agitation (Tensi Method), D6549, Standard Test Method for Determination of Cooling Characteristics of Quenchants by Cooling Curve Analysis with Agitation (Drayton Unit), and D7646, Standard Test Method for Determination of Cooling Characteristics of Aqueous Polymer Quenchants for Aluminum Alloys by Cooling Curve Analysis, are typically used to evaluate the cooling characteristics of these quenchants or processes. The cooling time–temperature curves obtained by these methodologies traditionally involve three stages of cooling. However, the relationship between this model and heat treatment, especially between hardening theory and practice, has not been satisfactory. Therefore, it is necessary to better understand the relationship between cooling theory and metallurgical behavior to create a new cooling model that achieves zero distortion, zero dispersion of quality, and zero pollution, which are concepts proposed in the “Heat Treating Industry Vision 2020 “and the “Heat Treating Technology Roadmap 2004” by the ASM Heat Treating Society and Materials Treating Institute. The relationship between the physical metallurgical phenomenon of phase transformation of a steel workpiece during quenching after being austenitized and the actual cooling conditions in engineering practice were analyzed and discussed in this report. Additionally, the development of advanced cooling technologies and related quenching equipment are discussed. The evolution from cooling model research to cooling engineering construction represents important progress in heat treatment practice.
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