RU2727068C1 - Method for determining limit uniform narrowing - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to determination of plastic properties of metals and can be used for determination of limit uniform reduction without destruction of parts material. Test material is loaded by means of spherical indenter with load in range corresponding to measurement of hardness, depth of imprint on surface of test material is measured and maximum uniform narrowing is calculated from dependence taking into account load on spherical indenter, diameter of spherical indenter, depth of imprint on surface of test material, number π and universal constant for metals.

EFFECT: simple method of determining limiting uniform narrowing and high accuracy thereof.

1 cl, 1 tbl

Description

The invention relates to the field of determining the plastic properties of metals and can be used to determine the limit uniform narrowing without destruction of the material of the parts.

There is a known method for determining the limit uniform narrowing (GOST 1497-84, ISO 6892-84 "Metals. Methods of tensile testing"), which provides for cutting out of a part of blanks for samples and the subsequent manufacture of samples for tensile testing. To determine the limit uniform narrowing, the sample is subjected to Ultimate uniform constriction ψ _B is determined as the ratio of the difference between the initial area F ₀ and the area F _{B of the} sample cross-section (at the end of the stage of its uniform deformation) to the initial cross-sectional area of the sample:

(1) $${\psi }_B=\frac{F_0-F_B}{F_0}.$$

(1)

The disadvantage of this method is that it requires the manufacture of special samples cut from the finished part, which obviously leads to partial or complete destruction of the test part. The disadvantage of this method lies in the high labor costs and material consumption. Thus, this method does not allow promptly and without destruction to determine the limiting uniform narrowing of the material.

It should be emphasized (see, for example, V.M. Matyunin's book "Indentation in the diagnosis of mechanical properties of materials" - Moscow: MPEI Publishing House, 2015. - 288 p. On pp. 179-180) that the value of the ultimate uniform deformation has great practical importance, since the hardenability, plasticity and performance of the material depend on it; in this regard, the ultimate uniform deformation is an important diagnostic parameter of materials and products, characterizing the reliability of their operation.

A known method of measuring the ultimate uniform plastic deformation of the material of the parts (and.with. 557295, IPC G01N3 / 08, G01B5 / 30, publ. 06/30/1977, bul. No. 17), which consists in the fact that from the material used to manufacture the part, a control specimen is made, subjected to uniaxial tension and the ultimate uniform plastic deformation, strength and yield strengths are determined, while the hardness numbers on the part and the control specimen are determined at the strength and yield strengths of conical indenters, the opening angles of which correspond to the strength and yield strains, and the required value is determined as the ratio of the product of the ultimate uniform plastic deformation of the sample by the difference in hardness numbers at the strength and yield strength of the sample to the corresponding difference in hardness numbers found for the part.

The disadvantage of this method is that it also requires additional production of special samples cut from the part, which obviously leads to partial or complete destruction of the test part. Thus, even this method does not allow to quickly and without destruction to determine the limiting uniform narrowing of the material. In addition, this method is very laborious due to the need for the manufacture and subsequent testing of the sample; it cannot be used when it is necessary to control one hundred percent of parts, as well as with small dimensions of parts.

The closest in technical essence is the method for determining the limit uniform narrowing (described in the book by V.M. Matyunin "Indentation in the diagnosis of mechanical properties of materials." - Moscow: MPEI Publishing House, 2015. - 288s., On p. 180), which provides for the construction of a diagram of the penetration of a spherical indenter, which determines the value of the ratio (h / R) _В corresponding to the ultimate strength of the material, that is, the maximum on the penetration diagram (h is the indentation depth corresponding to the maximum on the penetration diagram; R is the radius of the indenter). In accordance with the method, the value of the limiting uniform narrowing ψ _B is determined by means of the formula obtained empirically for a wide range of tested steels

(2) $${\psi }_B\approx 0.4{(h/R)}_B.$$

(2)

The disadvantage of this method is that it provides for the construction of an indenter injection diagram. As the author of this method himself points out (see the above book by V.M. Matyunin on pages 177-178), building an implementation diagram is a rather laborious process, in addition, the maximum on the implementation diagram is determined not by a point, but by a horizontal section, the length of which depends from the mechanical properties of the material. Therefore, it is rather difficult to find the value (h / R) _B corresponding to the maximum of the diagram. The error of this method is about ± 10% (see the above book by V.M. Matyunin on page 180).

Thus, the known methods have a low technical level, since they do not allow quickly and without destruction of the sample to determine the limit uniform narrowing.

In this regard, the most important task is to create a new method for determining the limiting uniform constriction, which would allow quickly and without destruction to determine the limiting uniform constriction.

The technical result is to simplify the method for determining the limit uniform narrowing and increase its accuracy.

The specified technical is achieved in the method for determining the limit uniform narrowing, which consists in the fact that the test material is loaded by means of a spherical indenter with a load in the range corresponding to the measurement of hardness, the indentation depth on the surface of the test material is measured and the limit uniform narrowing is calculated, while the spherical indenter is carried out a single specified load, and the ultimate uniform constriction is calculated from the dependence

where ψ _B is the ultimate uniform narrowing of the test material (%);

F is the load on the spherical indenter (N);

D is the diameter of the spherical indenter (mm);

h is the depth of the impression on the surface of the tested material (mm);

π = 3.14;

0.0041 is a universal constant for metals with a dimension of MPa ^-1 .

The essence of the invention is that a single load on the test material by means of a spherical indenter with a load, the value of which is in the range corresponding to the measurement of hardness, makes it possible to accurately determine the ultimate uniform narrowing of the test material. The proposed method is implemented in a wide range of load values. Each single load on the spherical indenter corresponds to the depth of the indentation of the indenter on the surface of the material under test, which is used to calculate the ultimate uniform constriction.

The declared new dependence (3) for determining the limiting uniform narrowing of the test material establishes relationships between all essential parameters that determine the value of the limiting uniform narrowing: the plastic properties of the material during contact deformation (the indentation depth depends on them), the strength properties of the material (they depend on the value of a single load , which is set in the range corresponding to the hardness measurement). This allows you to quickly and with high accuracy determine the limit uniform narrowing of the test material. This does not damage the part.

The method for determining the limiting uniform narrowing of the test material is implemented as follows.

The material to be tested is loaded once with a spherical indenter with a load in the range corresponding to the hardness measurement. The load value can be selected in accordance with standards providing for hardness control using a spherical indenter, for example, GOST 9012-59. ISO 410-82, ISO 6506-81 Metals. Test methods. Measurement of Brinell hardness "(introduced 01.01.60; last change 12.09.18) or GOST 18835-73. “Metals. Method for measuring plastic hardness "(introduced on 01.07.75; the limitation of the validity period was removed by the Interstate Council for Standardization, Metrology and Certification, protocol No. 3-93, IUS No. 5/6, 1993). A hardened steel ball (with a Vickers hardness of at least HV 850 kgf / mm ² ) is used as an indenter until the hardness of the test material is 4500 MPa; for higher hardness of the test material, use a spherical carbide indenter. A Brinell press can be used as a loading device.

для определения предельного равномерного сужения. Постоянная 0,0041 МПа^-1 – является универсальной для металлов, π = 3,14, D – диаметр используемого сферического индентора (мм).The value of the load F on a spherical indenter with a diameter D is set using a Brinell press. The depth h of the indentation on the surface of the test material is measured. The depth of the residual indentation can be measured with a dial gauge (1 μm graduation) mounted on the dial. The known values of the parameters are substituted into the dependence

to determine the limit uniform contraction. The constant 0.0041 MPa ^-1 is universal for metals, π = 3.14, D is the diameter of the spherical indenter used (mm).

An example of the implementation of the proposed method.

Determination of the limiting uniform narrowing was carried out on samples made of carbon and alloy structural steels of various levels of strength and ductility.

A hardened steel ball 5 mm in diameter was used as an indenter, and for steels with a plastic hardness greater than 4500 MPa, a spherical indenter made of hard alloy.

The table shows the mechanical properties of the tested materials. For the reference (comparison standard), the values of the limiting uniform narrowing of the material ψ _{I, E} (%), determined according to GOST 1497-84 (ISO 6892-84) “Metals. Tensile test methods ". The limiting uniform narrowing ψ _B (%) was determined by dependence (3).

Table

Sample number steel grade Load F, N Imprint depth h, mm Limiting uniform restriction ψ _B ,% Limiting uniform narrowing ψ _{V, E} ,%

Error

1 Steel 20 4905 0.200 13.505 13.9 2.88 2 Steel 35 4905 0.138 9,725 10.1 3.71 3 Steel 20X 4905 0.053 3.973 3.8 -4.55 4 Steel 45X 4905 0.063 4.687 5.0 6.26 five Steel 38X 4905 0,071 5.251 4.9 -7.16 6 Steel 40ХН 2453 0.031 4.627 4.8 3.60 4905 0.064 4,476 6.75 7358 0.098 4.627 3.6

Tensile tests were carried out using the software and hardware complex for metal testing (equipped with a personal IBM compatible computer) IR 5143-200.

In this case, the ultimate uniform narrowing of the material was determined according to GOST 1497-84 (ISO 6892-84) “Metals. Tensile Test Methods ”, adopted as a reference method.

As can be seen from the table, when using the proposed method, the error in determining the limiting uniform narrowing in comparison with the reference method according to GOST 1497-84 (ISO 6892-84) does not exceed (3 ... 7)% and has the character of two-sided spread. Note that, as indicated above, the error in determining the limiting uniform narrowing according to the prototype method is ± 10%.

In contrast to the prototype method, the indentation depth h does not require repeated measurements with rigidly fixed loads on the indenter, that is, a single load is sufficient and its value can be any. As can be seen from the table, for the example of steel 40XN (sample No. 6), a change in the load on the indenter in a fairly wide range (3 times) practically does not affect the values of the limiting uniform narrowing determined by the proposed method.

Thus, the proposed method is easy to use and provides the following advantages:

- has a higher accuracy in comparison with the known method: the error in determining the limit uniform narrowing does not exceed (3 ... 7)% in a wide range of changes in the plastic and strength properties of the material;

- does not require material destruction and can be used to control the plastic properties of the material of various machine parts.

является простым, не требует разрушения испытуемой детали и обеспечивает повышение точности определения предельного равномерного сужения.Thus, the method for determining the limit uniform narrowing, which consists in the fact that a single specified load F of the test material is carried out by means of a spherical indenter with a load in the range corresponding to the measurement of hardness, the indentation depth on the surface of the test material h is measured and the limit uniform narrowing is calculated according to the dependence

is simple, does not require destruction of the tested part and provides an increase in the accuracy of determining the limit uniform narrowing.

Claims (8)

The method for determining the limit uniform narrowing, which consists in the fact that the test material is loaded by means of a spherical indenter with a load in the range corresponding to the measurement of hardness, the depth of the indentation on the surface of the test material is measured and the limit uniform narrowing is calculated, characterized in that the spherical indenter is subjected to a single specified load, and the ultimate uniform constriction is calculated from the dependence

where ψ _B is the ultimate uniform narrowing of the test material (%); F is the load on the spherical indenter (N); D is the diameter of the spherical indenter (mm); H is the depth of the impression on the surface of the tested material (mm); π = 3.14; 0.0041 is a universal constant for metals with a dimension of MPa ^-1 .