UDC 538.9:621.785.6

Mukazhanov Ye.B.¹

Telebayev Ye.Ye.²

Takenova G.D.³

Tynaliev Bauyrzhan⁴

¹ Doctoral Student, PhD, Associate Professor, Academy of Economics and Law, Zhetysu State University. I.Zhansugurov, Taldykorgan, Kazakhstan

Taldykorgan Polytechnic College

² Taldykorgan Polytechnic College

³ PhD, Associate Professor, Taldykorgan Polytechnic College

⁴ Taldykorgan Polytechnic College

Taldykorgan, Kazakhstan

INFLUENCE OF DIFFERENT MODES TEMPERING ON MECHANICAL PROPERTIES SPRING CR-NI ALLOY

Introduction

Dispersionhardening chromium-nickel alloy 47HNM has high corrosion resistance, low temperature coefficient of the modulus of elasticity nonmagnetic, low hysteresis and elastic springback, high fatigue strength and is used in the industry, not only as a structural material, but also as a spring alloy. For processing the alloy 47HNM recommended modes: hardening of 1250ºC, aging at 700 - 725 ºC, 5H [1]. It is known [1, 2], the technological properties of the alloys depends on the heat-treatment. Therefore, for the selection of optimal processing conditions should be aware of the dependence of the mechanical properties of the alloy hardening behavior in a wide temperature and time interval. However, analysis of the literature showed that almost no information about the mechanical properties of the alloy 47HNM depending on hardening behavior and evidence-based explanations for these changes.

Based on the foregoing, in the objective was to investigate the influence of quenching temperature and exposure time for hardening on the technological properties of the alloy 47HNM.

Experiment

47HNM hardened alloy samples was carried out in water after heating at different temperatures 950-1300ºC. Heating for quenching was carried out in a salt bath of molten BaCl₂, as well as inert gas.

Mechanical testing of samples at room temperature uniaxial tensile carried out on the construction L.I.Vasileva type "POLIYANI" standard procedure. The diagrams were calculated tensile yield strength and durability, as well as determine the elongation of the samples after the break.

Results and Discussion

Effect of quenching temperature on the technological properties of the alloy 47HNM consider the range 950-1300 º C, because below 950 º C intermittent decay begins to develop with the release of α-phase, and above 1300 º C is observed burnout material.

Figure 1 shows the dependence of ductility and resistance to deformation of the alloy 47HNM temperature quenching. The analysis of the dependence can be seen that as the quenching temperature ductility of the alloy is increased, and the flow stress (σ0, 1 - yield stress, σ1 - voltage residual strain of 1%, σV - strength) decrease. Increase in ductility with temperature hardening due not only to the dissolution, but also the processes of coalescence and sferoidezatsii excess α-phase.

Thus, with increasing quenching temperature increases the homogeneity of the solid solution, as the concentration and reduction (healing) defects of the building. It should be noted that a further increase in temperature over 1300 º C leads to a sharp drop in plasticity. The reason for this phenomenon is caused not only by grain growth and the formation of assorted, but fusion α-particle phase near the grain boundaries and the spreading of the liquid phase at the grain boundaries. It is likely that the fused areas there is penetration of components of the furnace atmosphere, leading to the formation of oxides, nitrides or gas bubbles, while it is possible that this may also be the cause embrittlement of the alloy. Therefore, in order to avoid burnout material heating temperature should not exceed 1275 º C.

Figure 1 Dependence of ductility and resistance to deformation of the alloy 47HNM quenching temperature

As the temperature hardening the plastic properties of the alloy decreases, suggesting incomplete dissolution of excess α-phase, and at 950 º C elongation samples to divide half that at high temperature - 1300 º C, at the same time there is a growth of the deforming stress (Fig. 1).]

Consider the change in the technological properties of the alloy on the duration of exposure 47HNM heating temperature before quenching. The studies were conducted in the temperature range 1100-1300 º C, at the same time under quenching is from 1 to 30 minutes. Nature of the change of plasticity and deforming stresses, depending on the length of time before quenching is shown in Fig. 2 - 4.

Analysis of the relationship of technological properties of the holding time at 1300 º C (Fig. 2) and 1250 º C (Fig. 3a) shows that with increasing duration of heat flow stress drops, there is a growth of plasticity. Decrease the resistance to deformation, and increased plasticity involves the dissolution of excess α-phase based on Cr, which has a bcc lattice (Fig. 4). The process starts with the dissolution of dispersed particles, and with increasing exposure time begin to dissolve and larger particles, enriching alloying component solid solution matrix. Growth plasticity with increasing time of homogenization at 1300 º C is up to 30 minutes, inclusive, after which the curve reaches saturation.

Figure 2. The dependence of the technological properties (ductility and resistance to deformation δ σ) alloy 47HNM the time of exposure at 1300 º C

The nature of technological change in the properties as a function of exposure time at 1250 º C and 1225 º C (Fig. 3a, b) subject to the same laws as at 1300 º C, but occurs at a lower intensity.

a) b)

Figure 3 Dependence of technological properties (ductility and resistance to deformation δ σ) alloy 47HNM the exposure time of a - at 1250 º C; b - at 1225 º C

а) b) c)

Figure 4 47HNM microstructure of quenched from 1250 º C: and -1 min, b - 5 min, c - 10 min.

It is interesting to consider the dependence of the technological properties of the alloy from the holding time at a temperature of 1200 º C (Fig. 5a). The presented data show that with increasing time of homogenization of the alloy mechanical properties fall, but to a much lesser extent, with the yield strength and tensile strength increased by more than 10 kg/mm2 compared to the temperature range 1300-1250 º C.

a) b)

Figure 5 The dependence of the technological properties (ductility and resistance to deformation δ σ) alloy 47HNM the time of exposure: a - at 1200 º C; b - at 1250 º C, the pre-treated at 1100 º C, 5 hours

Nature of the change of plasticity changes dramatically, the expected growth of plasticity with increasing heating time observed her fall. The reason for this phenomenon has not been established, although the nature of the structural studies of fracture patterns in cross-section show the presence of the so-called structure of the "slate" kink. It is considered that the "slate" of the structure is not a marriage of heat treatment, but it is possible that this may be one of the reasons why the ductility and toughness of the alloy.

Creation of a "slate" of the structure of fracture, apparently, could be due to non-uniform distribution of particles α-phase (Stroke) that the homogenization of the alloy leads to the dissolution of most of dispersed particles to form microvoids. Eliminate the "slate" can be prolonged homogenization of the alloy, but it is necessary to monitor the oven temperature to avoid burnout.

Should point to a rather large variations in the ductility and strength testing samples quenched from 1200 º C. Apparently, the spread of values affects not only the heterogeneity structure, but also the partial melting of the α-phase particles located at the grain boundaries and the presence of non-dissolving particles, which are stress concentrators. All these factors lead to the formation of micro-cracks, reducing the ductility and toughness of the alloy.

Conclusions

Thus, hardening alloy 47HNM spending below 1225 º C is not advisable, as it is the deformation leads to the formation of micro-cracks, reducing the ductility and toughness of the alloy.

With the increase of quenching temperature increases homogeneity of the solid solution, as the concentration and reduction defects of the building. The increase in temperature over 1300 º C leads to a sharp drop in ductility, melting due to α-phase particles on the basis of Cr and a spreading of the liquid phase at the grain boundaries.

With the increase of the heating time for hardening flow stress drops, there is a growth of plasticity, which is associated with the dissolution of excess α-phase. In samples quenched from 1200 º C, the variation of plasticity changes dramatically, the expected growth of plasticity with increasing heating time observed her fall. It is assumed that this is caused by the presence in the structure of the "slate" kink.

literature

1 Molotilov BM Precision alloys. - Moscow, Metallurgy, 1974. - 448.

2 Erbolatuly D. Features of formation of fine structures and their influence on the superplastic properties of alloys and 40HNYU 67KN5B / / Proceedings of the Intern. Research School conference. "Physics and chemistry of nanomaterials." - Tomsk, 2005. - P.52-55.

INFLUENCE OF DIFFERENT MODES TEMPERING ON MECHANICAL PROPERTIES SPRING CR-NI ALLOY

The nature of technological change and the strength of the alloy 47HNM by quenching in a wide temperature and time interval. Shown to increase the hardening temperature of the alloy up to 1300 º C reduces the mechanical properties and improved ductility. Found that above 1300 º C ductility decreases sharply, due not only to grain growth and the formation of assorted, but fusion α-particle phase based on Cr and a spreading of the liquid phase at the grain boundaries. With the increase of the heating time for hardening flow stress drops, there is a growth of plasticity, which is associated with the dissolution of excess α-phase.