﻿ Determination of cold brittleness temperature by means of serial dynamic bending tests ﻿

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# Determination of cold brittleness temperature by means of serial dynamic bending tests

The serial dynamic bending (impact toughness) test of notched specimens is the most widespread determination method of temperature critical value (ТCR).

This method is widely used at estimation of steel liability to brittleness while working at low temperatures. Low temperatures increase resistance of metals to plastic deformation and rise metals liability to brittle failure. The main aim of impact bending tests at low temperature is to define the minimal temperature at which the metal can work reliably with a small probability of brittle failure formation.

The information received as a in result of conducting of series of impact bending tests at the gradual decrease of FATT is used at serial curves construction. There is a sudden lowering of impact toughness at a certain temperature (temperature interval) called the critical brittleness temperature. The critical brittleness temperature is a comparative characteristic of metal liability to brittle failure at low temperatures.

The ductile-brittle transition in a short critical temperature interval appears as a result of serial tests of round unnotched specimens (fig. 3.6 a).

The point 1 determines the beginning of transition, and a temperature corresponding to this point is called the upper boundary of cold-brittleness threshold. This temperature is taken as cold-brittleness threshold and is denoted as . The point 2 corresponds to the end of ductile-brittle transition. The temperature at this point is called the lower boundary of cold-brittleness threshold.

While testing of notched specimens, especially specimens made of ductile materials (for example, low-carbon steels), the ductile-brittle transition takes place gradually in a wide temperature interval (fig. 3.6 б). At determination of for such materials some values of impact toughness are used. On the basis of these values a critical temperature is estimated.

Fig. 3.6. Serial curves of smooth (а) and notched (б) specimens test.

The following conditions are used in some cases: аn = nаn (where 0<n<1), usually n = 0,5 or n = 0,8. Critical temperatures obtained on the basis of these criteria are marked as and . The fixed values of impact toughness (equal to 2,5 kg×m/cm2) are also used. These fixed values are mostly used in west-european countries while testing specimens with the notch radius of 0,25 mm, its critical temperature is denoted as . The critical value of ан = 3,0 kg×m/cm2 is used in the Soviet practice, its critical temperature is denoted as .

Appendix 1

 Variant Steel №1 Steel №2 Impact toughness Macroanalysis Microfractography 1. 80С, h/r 20ХГ2Т, h/r KCU KCU х240 2. 80С, h/r 25Г2С, h/r KCU KCU х240 3. 80С, h/r 25Г2С, TS furnace KCU KCU х240 4. 80С, h/r 25Г2С, TS mill KCU KCU х240 5. 80С, h/r 20ХГ2Т, h/r KCV KCV х1000 6. 80С, h/r 25Г2С, h/r KCV KCV х1000 7. 80С, h/r 25Г2С, TS furnace KCV KCV х1000 8. 80С, h/r 25Г2С, TS mill KCV KCV х1000 9. 20ХГ2Т, h/r 25Г2С, h/r KCU KCU х240 10. 20ХГ2Т, h/r 25Г2С, TS furnace KCU KCU х240 11. 20ХГ2Т, h/r 25Г2С, TS mill KCU KCU х240 12. 20ХГ2Т, h/r 25Г2С, h/r KCV KCV х1000 13. 20ХГ2Т, h/r 25Г2С, TS furnace KCV KCV х1000 14. 20ХГ2Т, h/r 25Г2С, TS mill KCV KCV х1000 15. 25Г2С, h/r 25Г2С, TS furnace KCU KCU х240 16. 25Г2С, h/r 25Г2С, TS mill KCU KCU х240 17. 25Г2С, h/r 25Г2С, TS furnace KCV KCV х1000 18. 25Г2С, h/r 25Г2С, TS mill KCV KCV х1000 19. 25Г2С, TS furnace 25Г2С, TS mill KCU KCU х240 20. 25Г2С, TS furnace 25Г2С, TS mill KCV KCV х1000 21. 25Г2С, TS mill 80С, h/r KCV KCV х1000 22. 25Г2С, TS furnace 20ХГ2Т, h/r KCV KCV х1000 23. 25Г2С, TS mill 25Г2С, TS furnace KCU KCU х240 24. 25Г2С, TS furnace 20ХГ2Т, h/r KCU KCU х240 25. 25Г2С, TS mill 25Г2С, TS furnace KCU KCU х240 26. 25Г2С, TS mill 80С, h/r KCU KCU х240

Appendix 2
impact toughness data values after the test of impact specimens

KCU (type Ι)

 Т, °С 80С, h/r 20ХГ2Т, h/r 25Г2С, h/r 25Г2С, TS furnace 25Г2С, TS mill 0,28 0,92 1,54 1,42 2,08 0,17 0,68 1,45 1,4 1,89 0,09 0,63 1,15 1,35 1,06 0,07 0,56 0,82 1,3 0,86 -20 0,06 0,52 0,63 1,17 0,68 -40 0,05 0,42 0,46 0,94 0,53 -60 0,05 0,22 0,3 0,75 0,43 -80 0,03 0,21 0,14 0,63 0,32 -100 0,03 0,2 0,1 0,57 0,23

KCV (type IV)

 Т, °С 80С, h/r 20ХГ2Т, h/r 25Г2С, h/r 25Г2С, TS furnace 25Г2С, TS mill 0,08 0,56 1,12 1,17 1,62 0,06 0,3 0,83 1,18 1,6 0,04 0,2 0,3 1,14 0,82 0,06 0,17 0,22 1,13 0,3 -20 0,03 0,13 0,14 1,07 0,16 -40 0,02 0,08 0,11 0,82 0,13 -60 0,02 0,07 0,08 0,36 0,1 -80 0,02 0,05 0,04 0,27 0,05 -100 0,01 0,04 0,04 0,23 0,05

Appendix 3
macrophotographs of fractures

Test temperature: +100°С

 Steel grade KCV(type IV) KCU(type I) 80С, h/r 25Г2С, h/r 25Г2С, TS furnace 25Г2С, TS mill

Test temperature: + 60°С

 Steel grade KCV(type IV) KCU(type I) 80С, h/r 25Г2С, h/r 25Г2С, TS furnace 25Г2С, TS mill

Test temperature: + 20°С

 Steel grade KCV( type IV) KCU(type I) 80С h/r, 25Г2С, h/r 25Г2С, TS furnace 25Г2С, TS mill

Test temperature: 0°С

 Steel grade KCV(type IV) KCU(type I) 80С, h/r 25Г2С, h/r 25Г2С, TS furnace 25Г2С, TS mill

Test temperature: - 20°С

 Steel grade KCV( type IV) KCU( type I) 80С, h/r 25Г2С, h/r 25Г2С, TS furnace 25Г2С, TS mill

Test temperature: - 40°С

 Steel grade KCV(type IV) KCU( type I) 80С, h/r 25Г2С, h/r 25Г2С, TS furnace 25Г2С, TS mill

Test temperature: - 60°С

 Steel grade KCV(type IV) KCU(type I) 80С, h/r 25Г2С, h/r 25Г2С, TS furnace 25Г2С, TS mill

Test temperature: - 80°С

 Steel grade KCV(type IV) KCU(type I) 80С, h/r 25Г2С, h/r 25Г2С, TS furnace 25Г2С, TS mill

Test temperature: – 100°С

 Steel grade KCV(type IV) KCU(type I) 25Г2С, TS furnace 25Г2С, TS mill

Appendix 4
microphotographs of fractures

Steel 80С, hot-rolled

t=+20°C, х240 t=+20°C, х240

t=+20°C, х1000 t=+20°C, х1000

Steel 20ХГ2Т, hot-rolled

t=+20°C, х240 t=+20°C, х240

t=+20°C, х1200 t=+20°C, х1000

Steel 20ХГ2Т, hot-rolled

t=+20°C, х1000 t=-20°C, х240

t=-20°C, х1000 t=-60°C, х240

Steel 20ХГ2Т, hot-rolled

t=-60°C, х240 t=-60°C, х1000

t=-60°C, х1000 t=-60°C, х1000

Steel 25Г2C, hot-rolled

t=+20°C, х240 t=+20°C, х240

t=+20°C, х1000 t=+20°C, х1000

Steel 25Г2C, hot-rolled

t=-20°C, х240 t=-20°C, х240

t=-20°C, х1000 t=-20°C, х1000

Steel 25Г2C, hot-rolled

t=-60°C, х240 t=-60°C, х1000

t=-60°C, х1000 t=-60°C, х1000

Steel of 25Г2C, TS furnace

t= +20°C, х240 t= +20°C, х240

t= +20°C, х1000 t= +20°C, х1000

Steel 25Г2C, TS mill

t= +20°C, х240 t= +20°C, х240

t= +20°C, х1000 t= +20°C, х1000

Steel 25Г2C, TS mill

t= -20°C, х240 t= -20°C, х240

t= -20°C, х1000 t= -20°C, х1000

Steel 25Г2C, TS mill

t= -60°C, х240 t= -60°C, х240

t= -60°C, х1000 t= -60°C, х1000

Appendix 5
design regulations of the course paper

The explanatory note to the course paper is conventionally subdivided into:

- introduction;

- main part;

- appendix.

Introduction

Introduction contains the following structural elements:

- title page;

- task for the course paper;

- abstract;

- contents;

- list of conventional signs, symbols, contractions, terms.

Title page

A title page contains information that should be represented in the following sequence:

a) information about the ministry, higher educational establishment, department;

b) complete name of document. The division of words in the heading of title page is forbidden;

c) signatures of supervisors, tutors and the student who executed this the course paper. The signatures of responsible persons are placed in the following order: to the left there should be the white space for the personal signatures. To the right of this white space the posts, surnames, names and patronymics should be pointed in appropriate lines. Below the personal signatures, there should be pointed the dates of signing in Arabic numerals in the following sequence: year, month, date. For example, December, 26, 2002 should be designed as: 2002.12.26. or 02.12.26., verbally-digital dates design is also possible: December, 26, 2002.

d) year of explanatory note drawing up.

The supervisor formulates and gives the task.

There should be the topic of the course paper, data values, list of questions that should be studied in the task. The timetable of work stages preparation can also be shown in the task.

Abstract

An abstract is intended for getting acquainted with a work. It is prepared in the official (Ukrainian) language.

The abstract should be brief, informative and it should contain all necessary information that allows making the decision about the expedience of all explanatory note or report reading.

The abstract is placed directly after a title page. It begins from a new page.

The abstract should contain:

- information about the note volume, quantity of illustrations, tables, appendixes, resources quantity in accordance with the list of references;

- text of the abstract;

- list of keywords.

The text of the abstract of the course paper should reflect the information given in the explanatory note in the following sequence:

- object or research of the development;

- purpose of the work;

- research methods and equipment;

- results and their novelty;

- the main structural, technological and operational data and indices;

- recommendations of the work data use;

- economic efficiency;

-summary.

The abstract should contain one A4 page. The keywords are placed after the abstract text. The quantity of keywords should be from 5 to 15 words (word-combinations). The keywords should be written in capital letters in a line with commas.

Contents

The contents are placed right after the abstract. It begins from a new page. The contents include: introduction; all sections titles consequently listed, subsections titles; conclusions; list of references; appendixestitles and number of pages which the next material begins from.

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