Development of Innovative Method of Steel Surface Hardening by a Combined Chemical-Thermal Treatment

Abstract

The aim of the article is a hardening of the surface steel layers due to the combination treatment. Samples of steel 38Cr2MoAl were hardened by complex chemical and thermal treatment such as carburizing and subsequent boriding. It was established that surface double-layer hardening for steel 38Cr2MoAl with sequential saturation with atomic carbon (during carburizing) and atomic boron (during furnace boriding) at different temperatures allowed to form a boride layer with transition zone. The obtaining transition zone can improve operational properties of machine parts and tools by micro-friability reduction of diffusion layer. An optimal mode of complex chemical-thermal treatment (CTT) was obtained for the regime, which includes carburizing at 950 °C for 2 hours, boriding at 950 °C for 2 hours, which allows to get the best value for the surface hardness of 22 GPa with a maximum overall diffusion layer 1.4 mm. Due to the technology of combined treatment we can significantly reduce treatment time compared to traditional hardening means and significantly improve product performance properties due to the transition zone between the borides and the matrix of machine elements. The technology can be used in enterprises where there is any hardening furnace without additional installation or conversion of equipment.

Development of an iron-based alloy with a high degree of shape recovery

“…Based on received data (Table 2), we constructed dependences (Figs 1-22) of a value of the shape memory effect and tensile strength on chemical composition of the alloy in the normalized form [24][25][26][27][28]. Experimentally obtained values of chemical composition of the alloy for each element are valid values (Table 2), which for the purpose of subsequent construction of mathematical models were converted to the normalized form.…”

Definition of range of open applications for massive nodes in the stainless steel castings

“…Таким чином, усадочні раковини є результатом взаємозв'язку між фізичним дефіцитом об'єму при кристалізації і можливістю компенсувати її за рахунок додаткової подачі матеріалу [4][5][6].…”

“…Крім загального дефіциту об'єму, його розподілення в тілі відливки і питомого об'єму, види дефектів залежать і від процесу кристалізації. Особливими факторами впливу є зміст газу в сплаві, рух стінок ливарної форми при литті в піщану форму, а також поширення графіту при кристалізації -в разі спеціальних чавунів [5][6][7][8][9].…”

Development of a combined technology for hardening the surface layer of steel 38Cr2MoAl

“…This combination makes it possible to achieve a very high hardening efficiency that cannot be obtained in any single way. Also, the increased interest in combined strengthening technologies is caused by the need of smaller use of alloyed steels because of high cost of alloying metals [7].…”