RU2041267C1 - Method for making white deformable cast iron - Google Patents

Abstract

FIELD: ferrous metallurgy. SUBSTANCE: one or more elements of 0.3 10 wt. Ni, 0.2 1.5 wt. Si, 0.05 0.5 wt. Al are added to a melt comprising carbide generating elements soluble in cementite chosen of the following group: Mo, Cr, Mn, W, V, Ti, Nb, Ta, Zr, Hf, U. Then an ingot is produced, and annealing, further heating up to temperature of hot working, plastic deformation, cooling, additional heating up to a temperature by 80 400 C as low as solidus temperature are performed followed by plastic deformation with successive cooling. EFFECT: high quality of cast iron. 2 tbl

Description

 The invention relates to ferrous metallurgy, and more particularly to a method for the production of white wrought iron.

 The invention can be used to obtain products from white cast iron by plastic deformation.

 Most effectively, the invention can be used for the manufacture of products requiring for the manufacture of large degrees of reduction, for example, sheets up to 2 mm thick, wires with a diameter of up to 2 mm and the like.

 Cast white cast iron alloyed with carbide-forming elements has high hardness and wear resistance, however, it has low mechanical properties and fatigue strength. In industrial conditions, the plastic deformation of white cast iron is difficult due to its low ductility, which is due to the presence of a eutectic in the structure, which is formed on the basis of a brittle carbide phase.

 A known method for the production of white wrought iron, containing 2.0-3.7 wt. carbon, including alloying the molten iron with carbide-forming elements soluble in cementite, obtaining an ingot, annealing it, heating and plastic deformation, followed by cooling of the deformed ingot.

 The specified method allows you to deform white cast iron on crimping mills, however, as a result of the specified plastic deformation, the necessary level of ductility for rolling cast iron with high compression ratios on high-quality and sheet mills cannot be achieved, which makes it impossible to obtain products of small thickness and diameter, such as sheet up to 2 mm thick and wire up to 2 mm in diameter.

 The aim of the invention is to increase the plastic properties of white cast iron.

This is achieved by the fact that in the method for the production of white wrought iron, containing 2.0-3.7 wt. carbon, including alloying the molten iron with carbide-forming elements soluble in cementite, selected from the group of Mn, Cr, Mo, W, V, Ti, Ni, Ta, Zr, Hf, U, taken separately or in combination in an amount that allows the selection of carbides of these elements from cementite, preparation of an ingot, annealing of the obtained ingot, its heating and plastic deformation followed by cooling of the deformed ingot, according to the invention, Ni, Si, Al, taken separately or in combination in quantity, are introduced into the melt simultaneously with these elements TBE: Ni 0,3-10,0 wt. Si 0.2-1.5 wt. Al 0.05-0.5 wt. wherein after cooling of the deformed billet is heated again to a temperature of 80-400 ^{° C} below the solidus temperature and its plastic deformation is carried out, followed by cooling.

 The introduction of Ni, Si, Al increases the density of dislocation-free special carbides of dislocations, and thereby contributes to the implementation of polygonization and recrystallization in cementite. This leads to an increase in the ductility of pre-deformed cast iron, since cementite is divided at this stage by shifting along grain and subgrain boundaries, i.e. it becomes possible to conduct subsequent plastic deformation of a previously deformed ingot to large degrees of compression.

 Ni, introduced into the melt in the indicated amounts, displaces carbide-forming elements from the solid solution into cementite, increasing their effective concentration in cementite. Thus, the decomposition of cementite during firing and subsequent deformation is facilitated. The ductility of white cast iron is greatly increased.

 When the Ni content is less than 0.3 wt. in the alloy, its effect on the carbide transformation becomes imperceptible, and the increase in ductility is negligible.

 Ni content of more than 10 wt. leads to the formation of graphite in cast iron during plastic deformation and a decrease in its ductility.

 Doping with silicon within the specified limits increases the activity of carbon in cast iron and accelerates the formation of special carbides in cementite. The ductility of white cast iron is significantly increased.

 When the Si content is less than 0.2 wt. the above effect is imperceptible, and when the Si content is more than 1.5 wt. the ductility of the metal base of cast iron decreases, and the overall ductility of white cast iron ceases to increase.

 The introduction of Al within the indicated limits enhances stresses at the boundary of the metal based cementite. This facilitates the generation of dislocations in cementite and the nucleation of special carbides in it. The consequence is an increase in ductility of white cast iron.

 When the Al content is less than 0.05 wt. the indicated effect is invisible.

 The introduction of more than 0.5 wt. Al is not technologically advanced due to the formation of a large amount of aluminum oxide. As a result of this, the metal continuity at the grain boundaries is violated, and, in addition, the aluminum content in the solid solution does not increase further.

The heating of the deformed billet to a temperature of 80-400 ^{° C} below the solidus temperature prepare white iron structure to deform plastically deformed before the ingot, which leads to the formation in its strukture fine carbides dispersed in the base metal. This provides the deformed cast iron with high strength and ductility.

When white cast iron is heated before plastic deformation to a temperature lower than the solidus temperature by more than 400 ^о С, microstructure is formed in the structure of cast iron during deformation, which reduces its strength and ductility. In white cast iron heated above the solidus temperature greater than 80 ^{° C,} due to reflow heating localized areas arise in the plastic deformation, whereby the ductility is reduced.

 Thus, the proposed method is characterized by significant differences and novelty, consisting in a certain selection and regulation of alloying elements, which, in combination with the specified additional technological operations, can significantly increase the plastic properties of cast iron, as a result of which it becomes possible to manufacture products that require high degrees of production crimping, for example a sheet up to 2 mm thick, a wire with a diameter of up to 2 mm.

 The proposed method is as follows.

 In the induction furnace create a molten iron containing 2.0-3.7 wt. carbon.

 Alloying carbide-forming elements soluble in cementite, selected from the group of Mn, Cr, Mo, W, V, Ti, Nb, Ta, Zr, Hf, U, taken separately or in combination in an amount providing the possibility of carbide precipitation of these elements are introduced into the melt from cementite.

 At the same time, Ni, Si, Al, taken separately or in combination in an amount of Ni: 0.3-10.0 wt. Si 0.2-1.5 wt. Al 0.05-0.5 wt.

The alloyed melt is held for 15 minutes to completely assimilate the alloying elements, then it is poured into molds to obtain ingots. The resulting ingots weighing 25 kg is annealed at regime 950 ^{° C} for 2 hours and slowly cooled to perlitizatsii austenite. This operation can be repeated many times to better prepare the structure of cast iron for plastic deformation. Then, the ingots are heated to a temperature of 80-400 ^{° C} below the solidus temperature and incubated for 30-120 min to reduce the stresses in the deformed ingot.

 Then, plastic deformation of the deformed ingot heated to the indicated temperature is carried out by any known method, including at high-speed mills, and it is cooled.

 PRI me R s 1-5.

 The method was carried out in a technological sequence similar to that described previously.

 The amount of introduced Ni, Si, Al, the chemical composition of the obtained ingots, the modes of technological operations of the method are given in table 1.

 From the obtained ingot, samples were prepared that were tensile.

 The test results, clearly characterizing the level of ductility obtained as a result of the implementation of the proposed method of white cast iron, are also shown in table 1.

 PRI me R s 6-12.

For comparison, examples 6–9 show a method in which Ni, S, and Al were introduced within a range outside the range of the proposed values, in examples 10, 11, at temperatures outside the range of the proposed values, and example 12 shows a method in which not carried out the heating of the deformed billet to a temperature of 80-400 ^{° C} below the solidus temperature of its plastic deformation and subsequent cooling (prototype).

 From the obtained in examples 6-12 ingots were made samples that were tested in tension.

 The amount of introduced Ni, Si, Al, the chemical composition of the obtained ingots, the modes of its technological operations and the test results are given in table. 2.

 A comparison of the parameters is given in table 1, with the parameters given in table. 2, clearly illustrates the advantages and significant differences of the proposed method, since the ductility of white cast iron obtained by the proposed method is approximately 1.5 times higher than the ductility of white cast iron obtained by a known method, as well as in the case of non-compliance with the proposed technology and the boundary values of the components.

 Economic efficiency.

 Using the proposed method makes it possible to produce products from wrought white cast iron such as sheets up to 2 mm thick, wire with a diameter of up to 2 mm and the like, which reduces their cost by 2-5 times compared to similar products made of steel. Therefore, the replacement of alloyed grades of steel with white cast iron provides a significant economic effect in the national economy.

Claims (1)

METHOD FOR PRODUCING WHITE DEFORMABLE IRON containing 2.0 3.7 wt. carbon, including alloying the molten iron with carbide-forming elements soluble in cementite, selected from the group of Mn, Cr, Mo, W, V, Ti, NB, Ta, Zr, Hf, U, taken separately or in combination, in an amount that allows the allocation carbides of these elements from cementite, ingot preparation, annealing, heating and plastic deformation followed by cooling of the deformed ingot, characterized in that, in order to increase the ductile properties of cast iron, Ni, Si, Al taken separately are introduced into the melt simultaneously with alloying with the indicated elements dissolved in combination, in an amount of 0.3 10.0 wt. Ni, 0.2 1.5 wt. Si, 0.05 to 0.5 wt. Al, in this case, after cooling the deformed ingot, it is heated to a temperature of 80 - 400 ^o C below the solidus temperature and plastic deformation is carried out, followed by cooling.

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