Abstract
The stamps for hot deformation are widely adopted in industry. In use they are affected by high temperatures, tension (close to a fluidity limit) and variable thermal loadings. High-hardenability tool steels with high mechanical characteristics are used for stamps production. In this article, the possibility of use of 5KhNM steel for this goal is considered. One of technological operations at production of stamps is training in oil. It is rational to apply volume and superficial hardening, in particular chemical heat treatment, to improve operational characteristics of stamps, including wear resistance. The way of superficial hardening by the combined heating under chemical and thermal and heat treatment is presented. As a superficial way of hardening of largesize stamps of hot deformation, it is offered to use borating. Optimum temperature and time parameters of heating under the combined heat treatment are chosen and confirmed. The offered mode of chemical heat treatment allows receiving the necessary thickness of the borated layer providing high hardness and corrosion resistance in the working range of temperatures of a stamp. Also the influence of heat treatment on structure and grain size of the samples has been researched. It is shown that with increase in temperature and hold time, the size of grain increases. It leads to decrease in strength, fluidity, hardness and impact strength that can negatively influence operational properties of stamps. For definition of mechanical characteristics, the samples (in the studied range of temperatures and excerpts) have been tested for stretching and impact strength. All tests were carried out according to the existing state standard specifications. On the basis of these results, temperature and time of borating are chosen providing high mechanical properties and thickness of a borated layer. The offered approach has allowed reducing economic costs of stamps production from 5KhNM steel by exception from technological process of repeated heating for training with saving the required operational characteristics of largesize stamps.
Highlights
The stamps for hot deformation are widely adopted in industry
In use they are affected by high temperatures, tension and variable thermal loadings
High-hardenability tool steels with high mechanical characteristics are used for stamps production
Summary
Предложенный подход позволил значительно сократить экономические затраты на изготовление штампов из стали 5ХНМ за счет исключения из технологического процесса повторного нагрева для проведения закалки при сохранении требуемых эксплуатационных характеристик крупногабаритных штампов. В процессе эксплуатации штампы горячего деформирования находятся под воздействием высоких температур нагрева и знакопеременных механических и термических нагрузок, значительного уровня напряжений, близкого к пределу текучести штамповых сталей [1, 2]. Технологический процесс термической обработки штампов и деталей оснастки состоит из закалки для образования мартенсита и отпуска с целью получения структуры сорбита или троостита [2, 3, 6, 7]. Целью проведения настоящей работы является получение исходных данных для разработки совмещенного процесса объемного и поверхностного упрочнения, исключающего необходимость применения контейнеров для борирования штампов и проведения повторного нагрева для их закалки. Триэтаноламин при нагреве свыше 500 °С разлагается по реакции (С2Н4ОН)N3 → 2СН4 + 3СО + НСN + 3Н2
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