Технические науки/1.Металлургия

Bogomolov A.V., Kanayev A.T.

Pavlodar State University named after S. Toraigyrov, Kazakhstan

Kaken A.S.

Innovative University of Eurasia, Kazakhstan

INFLUENCE OF SILICIUM ON OPERATIONAL PROPERTIES OF ACCESSORIZED STEEL.

In determining of a chemical composition of a material for mass production of thermally strengthened fittings from rolling heating plays a role of an effective alloying and a micro alloying. The widest distribution has received silicium because of relative availability and low cost in metallurgy which is entered into steel as a deoxidant and the alloying element.

Cubic face-centered diamond-type crystal lattice of silicium - (figure 1).

Figure 1 - Crystal lattice of metal silicium

Silicium besides ability to oxidize steel actively, due to the ease of transfer of its valence electrons from an external cover 5s23p2 to the atoms of oxygen having an external electronic cover 2s22p with achievement of steady electronic configurations 2s22p6 as a result of it. There is an available very useful property for alloys hardening: ability to raise firmness of martensite against tempering.

Silicium makes difficult and ambiguous impact on toughness, plasticity and impact strength of iron and steel. This influence changes depending on the content of the silicium, other alloying elements in steel and nature of its thermal processing.

The majority of researchers [1] express unanimous opinion that silicium at its contents to 1,5 — 2 %, as well as manganese, makes strengthening effect on iron and steel, practically without worsening thus plasticity. However, the estimate of influence of silicium on impact strength and resilience to fragile destruction of iron also became considerably more contradictory. A.P.Guljaev has showed that in pure (0,002 % C) iron of vacuum smelting adding 1 % of Si is essentially reduce T_cr and only during further increasing of its concentration in an alloy, It is observed the increasing of the temperature, though at 2 % of Si iron appears even less inclined to fragility, than in its absence. This positive effect is connected with oxidize effect of silicium in steel.

M. P. Brown considers that silicium, especially in a complex with manganese and lame, provides significant reinforcement while saving high plasticity and viscosity if the content of carbon isn't higher than 0,25 %. while working with steel 0,35% С, in the tempered and high-released condition it was found out that unlike manganese, when we increase the content of silicium to 2,5 % plasticity continuously improves. The presence of silicium in high-thermo strengthened steels is obligatory, in connection with its beneficial effect on sub-structure of martensite. There is data that silicium (under 2%) reduces a tetragonality of initial martensite lattice and reduces tendency to formation of hardening cracks as reduces a sample deformation during hardening.

At the same time, there are also other estimates of influence of silicium on properties of iron and steel. So, increase of the content of silicium up to 0,6 % doesn't influence on impact strength of technical (0,05 % C) cast iron, but at further growth its concentration it sharply decreases L.I.Gladstein and D.A.Litvinenko have noted the increase T_cr in the normalized construction steel from 1,46 % of Si. It is specified (K.Taffner, K.Meyer) that at the contents over 0,5 % silicium makes negative impact on T_cr of hot-rolled construction steel, and at the contents over 0,37 % silicium makes an adverse impact on work of distribution of cracks in normalized and improved steels with 0,15 — 0,20 % of C.

Provided analysis of the researches results from various authors testifies that influence of silicium on a ratio of durability, plasticity and tendency of iron and steel to fragile destruction is ambiguous. It is in a difficult dependence on the content of carbon, other elements in steel, technology of its production and thermal processing. Therefore according to data it is not possible to choose the optimum maintenance of these elements.

Systematic researches were required[2] in this field, especially when we know the specificity of the final product — high-strength fixture steel of periodic profile which has active-operating concentrators of tension (system of cross-section and longitudinal edges of rigidity) and testing difficult influence of external and internal forces during a work in preintense beton.

As a result of the carried-out laboratory researches of fixture steel of 35 GS at increase in the content of silicium up to 1,5 % on weight strength goes up to 100-140 MPas, a fluidity limit goes up to 50-120 MPas, relative lengthening reduces to 2,4-2,9%.

Dependence of the strong properties and plasticity of fixture steel from nuclear concentration of silicium is expressed by the following equations of regression:

s_Т=334+38Si

s_в=509+41Si

d₅=36-1,5Si

With the growth of the content of silicium from 0,21 % to 1,5 % with weight (0,43-3 % ат.) the ratio of s_Т\s_в changes slightly and is in limits 0,66 - 0,70.

Figure 2 - Influence of silicium on the microhardness of ferrite and pearlite

On the figure 2 there is data on influence of silicium on microhardness of ferrite and a pearlite hot-rolled fixture steel; each point — on average from 200 measurements. If we express, concentration of these elements in nuclear percent that is the most reasonable from physics point of view.

This article was prepared within the program of basic and applied researches of the Ministry of Education and Science of the Republic of Kazakhstan on a subject from 1796\GF «Development of technology of the integrated production of high-strength fixture hire from continuously cast preparations» (Doctor of Technical Sciences, Professor A.T. Kanayev).

References:

1. High-strength fixture steel. Kugushkin A.A., Uzlov I.G., etc.- Moscow: Metallurgy, 1986, 272s.

2.Kanayev A.T., A.V. Bogomolov, E.N. Reshotkina T The research of defects and thermal hardening of fixture rolling from the continuously cast preparations / / Steel, № 6, 2010 - Moscow, p. 87-91.