Especially the Transformation of Austenite in High-Strength Cast Iron during Processing With Continuous Cooling

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Especially the Transformation of Austenite in High-Strength Cast Iron during Processing With

Continuous Cooling

R K Hasanli, S N Namazov

To cite this version:

R K Hasanli, S N Namazov. Especially the Transformation of Austenite in High-Strength Cast Iron during Processing With Continuous Cooling. Mechanics, Materials Science & Engineering Journal, Magnolithe, 2017, 8, �10.2412/mmse.34.581.343�. �hal-01500629�

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Especially the Transformation of Austenite in High-Strength Cast Iron during Processing With Continuous Cooling

R.K. Hasanli ^1,a, S.N. Namazov ^2,b

1 – Associated professor, Dr., Azerbaijan Technical University, Baku, Azerbaijan 2 – Professor, Dr., Azerbaijan Technical University, Baku, Azerbaijan

a – hasanli_dr@mail.ru

b – subhan_namazov@daad-alumni.de

DOI 10.2412/mmse.34.581.343 provided by Seo4U.link

Keywords: high-strength cast iron, spherical graphite, the transformation of austenite, economical alloying, chill casting, heat treatment, structure, austenite, bainite, properties.

ABSTRACT. The peculiarities of the transformation of austenite in high-strength cast iron with spherical-eminent graphite when machining with continuous cooling. The possibility of obtaining a bainite structure economically-alloyed with nickel and copper, and molded in a metal mold of high strength cast iron with continuous cooling. It is established that in high-strength cast iron processed by bainite, graphite inclusions should have a spherical shape. The amount of vermicular graphite may be in the range of 10-20%.

Introduction.The aim of this work is to study the peculiarities of the transformation of austenite in high-strength nodular cast iron when machining with continuous cooling. According to the literature recommendations, cast iron subjected to heat treatments continuous cooling to ensure it bainite structure should contain additives of Ni, Cu and Mo [1, 2]. The lack of Mo in the composition of the investigated cast irons has demanded carrying out of special research.

Analyses of the Especially the Transformation of Austenite in High-Strength Cast Iron during Processing With Continuous Cooling. It is possible to assume, that the continuous air-cooling economically-alloyed cast iron   – transformation occurs at temperatures of 450-350⁰C (not lower than 350⁰C). The real strength of cast iron after such treatment may be 800-1100 MPa, which satisfies these requirements. Rightly considered, that the bottleneck for high-strength cast irons are a lack of ductility and toughness. However, it was found that using the chill casting method largely facilitates the solution of this problem [3-12].

Comparison of properties of high-strength cast irons carried out the casting in the mold and sandy- argillaceous form an integrated doped Ni - Cu additives or Ni. Heat treatment of castings is carried out in the following mode. Heating was carried out up to temperatures of 870±10⁰C and 900±10⁰C with excerpts 15 and 40 min. The cooling was carried out on the tranquil air and accelerated with a blowing air jet. Quality heat treatment were evaluated by hardness and obtain the structure of the matrix. After air-cooling in the design of all cast irons are observed more or less large areas of ferrite around the graphite inclusions are spherical (Fig. 1). Such areas are enriched in silicon and this is why the process of saturation with carbon is inhibited.

It is established that the increase in time of exposure at a temperature of austenitization slightly reduces the size of the ferritic regions. Determined that a small amount of ferrite (2-3%) are located on the boundaries of the secondary grains, have no detrimental effect on the tribological properties

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with continuous cooling, the dwell time of 30-40 min, cooling, vacation with heating for 3 hours to a temperature of from 200 to 400⁰C (see table 1).

a)

b)

c) d)

Fig. 1. Microstructure of non-alloy iron after normalization 900⁰C, exposure 15 min.: a, b - chill casting; and b - x100; c, d - casting in sand-clay the form of a; b, d - x600.

As studies have shown, a vacation at 200⁰C contributes to the improvement of impact strength of not less than 20% without visible changes in structure. Vacation at 300⁰C reduces the toughness of all investigated cast irons, while not significantly affecting the wear resistance [6, 7]. Vacation in 400⁰C promotes the release of fine carbides, also resulting in a significant increase in toughness as Nickel and Nickel - copper cast irons, lower (3-5%) to their durability.

The influence of the size of the cross section was investigated on samples with a diameter of 10 and 20 mm. found that in sections of 20 mm or more it is possible to obtain bainite structure by using the analyzed heat treatment in industrial conditions under a powerful fan. In the laboratory banana structure can be reliably obtained in the samples with cross-section not exceeding 10 mm if sufficient quantities of alloying elements (Fig. 2). If the cross section of the part is 20 mm, cast iron acquires the structure of pearlite with different number of top bainite (Fig. 3).

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Table 1. The influence of the mold and heat treatment on the structure of the doped Ni (1.0%) and Cu (0.5%) cast iron.

Material and mold Heat treatment Hardness,,

HRC

Structure

Steel 40KH Hardening 49 M+B

Ductile iron cast in metal mold

Normalization with 870⁰C, excerpt 15 min.

53 B+F(2%)

53 B

54 B+F(5%)

Normalization with 900⁰С, excerpt 40 min.

51 B+F(3%)

Ductile iron, cast in sand form

50 B+P(40%)+Ф(15%)

47 B+F(30%)

52 B+P+F(20%)

47 B+F (10%)

The amount of alloying elements and their composition determine the homogeneity of the structure and structural components formed in the cast iron after to normalize. Nickel - copper cast irons, containing 1.0% of Ni and 0.5% Cu, in laboratory conditions, tended to lower the needle bainite (Fig. 4).

On the calm air in these alloys is formed pearlitic-bainitic structure (Fig. 5, b). In cast iron, only Nickel doped (2%) after heat treatment with rapid cooling in the laboratory is produced bainite the top, in the factory, the lower needle bainite. A decrease in doping leads to the fact that in the cast iron with the addition of 1.5% Ni in the laboratory it is practically impossible to fully bantou structure.

Typically, a mixture of perlite with a small amount bainite.

At low doping (1% Ni) observed the presence of ferrite on the boundaries of the secondary grains.

The matrix is mostly pearlite, sometimes with insignificant portions of the upper bainite (Fig. 2, a).

The mutual arrangement of the structural components (perlite and bainite) reflects the kinetics of recrystallization alloy. Often bainite is around the perlite at the grain boundaries (Fig. 3, b), or around graphite inclusions radiating rays (Fig. 5, a).

Thus, it can be argued that in traditional cast iron silicon largely localized around graphite inclusions (Fig. 6). In pearlitic-bainitic cast iron, formed during the slow cooling, lower bainite is located in characteristic alternating strips. It is important to cast iron, processed by bainite, graphite inclusions were globular form, allowed a small amount of vermicular graphite in the range of 10-20%.

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а) b)

c) d)

Fig. 2. The microstructure of alloyed 1% Ni +0.5% of Cu metal after normalization a-870⁰C, casting in sand-clay the form; b-900⁰C, the same; c-935⁰C, the same; d-900⁰C, chill casting. x600. Cross- section 10 mm.

а) b)

c)

Fig. 3. The microstructure of alloyed 1% Ni +0.5% of Cu metal after normalization a - 870⁰C; b- 900℃; c-935⁰C. x600. Section 20 mm.

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Fig. 4. The microstructure of alloyed 1% Ni +0.5% of Cu metal after normalization with the blowing.

x600. Cross-section 10 mm.

а) b)

Fig. 5. Microstructure of alloy cast iron after normalization on the tranquil air: a-1% Ni-0,5% Cu;

b-1.5% of Ni+0,5% Cu. x600. Cross-section 10 mm.

Fig. 6. The microstructure of alloyed 1% Ni-0,5% Cu iron after normalization with the blowing. x600.

The cross section of 20 mm.

Summary. Thus, the peculiarities of the transformation of austenite in high-strength cast iron when machining with continuous cooling. It is revealed that the pearlite-bainite cast iron, formed during the slow cooling, lower bainite is located in a characteristic alternating bands corresponding to the axes of the dendrites. The possibility and efficiency of producing bainite structure in the economically alloyed with Nickel and copper in cast iron, cast in the mold using continuous cooling. Determined that the cast iron processed by bainite, graphite inclusions should have a spherical shape, with perhaps

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