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Hardness testing as a method to identify the
highest-temperature
combustion zone
in
transport fires
Galina Sikorova1*, Nikolay Chumakov2, Maxim Tumanov 3, Sergey Zhikharev4, and Sergey
Panov5
1
Saint - Petersburg University of the State Fire Service of of EMERCOM of Russia, 196105 Saint
Petersburg Russia
2
Higher School of Technosphere Safety of Peter the Great St. Petersburg Polytechnic University,
195251 Saint Petersburg, Russia
3
Saint - Petersburg Mining University, 199106 Saint Petersburg, Russia
4
Mining Institute of the Ural Branch of the Russian Academy of Science, 614007 Perm, Russia
5
Saint-Petersburg State University of Industrial Technologies and Design, 191186 Saint Petersburg,
Russia
Abstract. This article presents some results on the selection of the
necessary micro-hardness tester for the purposes of research. In accordance
with the objectives, namely the scientifically based choice of a hardness
meter for the purposes of fire-technical examination and evaluation of its
capabilities, aimed primarily at the possibility of identifying the most hightemperature combustion zone in fires in transport. The selection of a device
for measuring microhardness was carried out in accordance with current
methods for measuring microhardness, first of all for determination of
microhardness for products based on metals and their alloys, as well as
materials found in vehicles. The paper describes the main types of hardness
testers and their applications. On the basis of the analysis programmable
electronic small-sized hardness tester TEMP-4 was chosen. This device met
all the requirements on the decision of set tasks of research connected with
express researches both laboratory and industrial conditions, and the field at
the decision of tasks of fire-technical examination directly on a place of
ignition of the transport unit. Experimental results of nondestructive express
measuring of various metal samples are described. Metal fasteners and
supporting constructions are chosen as samples for research. The thermal
effect on the test specimens was carried out in a thermostat chamber
allowing for an impact heating rate. The results, testifying about change of
microhardness of metal products as a result of influence of a hightemperature field are received.
*
Corresponding author: sikorova.g@igps.ru
© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative
Commons Attribution License 4.0 (https://creativecommons.org/licenses/by/4.0/).
E3S Web of Conferences 402, 11019 (2023)
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1 Introduction
At the present time fires on transport arising for various reasons, including because of various
kinds of accidents except for the big material and ecological damage do irreparable damage
to the population of Russia [1, 2, 3]. Besides, the available statistical data does not allow us
to cover in full the whole list of transport means: sea, air, railway, cargo, including the
specialized transport serving quarries and open-cast mines of mineral raw materials complex
of Russia, and also automobile transport [1, 3]. The statistical data given in table 1, provided
by the Ministry of Transport of Russia (Rostransnadzor), only confirms the necessity of
carrying out this kind of researches. They are aimed both at developing measures to reduce
accidents and at establishing the true causes and locations of hotbeds of combustion, as well
as the dynamics of flame spread through the main communications and structures of vehicles
operating on different types of fuel.
Table 1. Statistics on transport fires and fatalities
Type of vehicle
Truck
Passenger car
Number of fires, units
2018
2019
2020
2051
2237
2191
12839
13613
12756
Number of fatalities, people
2018
2019
2020
14
13
10
77
81
89
One of the methods for determining the location of combustion and the dynamics of
propagation of the combustion front as part of complex techniques, as shown by our research,
can be a method of non-destructive express control of hardness of the metal included in the
structural composition of vehicles [3, 4, 5]. Depending on the instrumentation used hardness
meters can measure the hardness of a number of other materials included in the composition
of vehicles besides metals [1, 6, 7].
2 Materials and methods
In carrying out the research work, some of the results of which are discussed in this article,
micro-hardness methods were chosen as methodological and logistical support, and several
types of micro-hardness meters were used in the instrumentation [4, 8, 9].
The most common micro-hardness testers, depending on their operating principle, can be
ultrasonic (UHT), dynamic (DHT) or universal micro-hardness tester [3, 9, 10]. The basis of
operation UHT is the contact ultrasonic impedance method (UCI method). In contrast to
UHT, DHT works according to the Leeb method. It takes into account the relationship
between the rebound velocity and the falling velocity of a carbide-tipped indenter and the
hardness of the material being tested [11, 12, 13].
Whereas, in the early days of metal hardness research, Rockwell and Super Rockwell,
Brinell, Shore and Vickers hardness testers were used, each with its own hardness scale. The
micro-hardness scales were named after their inventors, e.g. the Vickers hardness tester had
a Vickers scale of HV.
With the development of technology and scientific knowledge, i.e. the development and
improvement of instruments in modern types of hardness testers, it is now possible to
interpret the data obtained from these scales [12, 13, 14].
The metal hardness results presented in this article were obtained by using a microhardness tester TEMP-4 (electronic compact portable programmable hardness tester). The
choice of this type of micro-hardness tester is justified by its versatility and the possibility, if
necessary by programming the built-in scales, to extend the capabilities of the device and
examine not only a wider range of metals, including cast iron, but also some non-metals, such
as rubber. Besides, this type of device allows it to be used by various specialized services
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(for example, during express fire-technical data collection directly on the fire place), i.e. in
field conditions, as well as in laboratory and production conditions at enterprises of wide
technical profile. The objects to be measured can be of different shapes and thicknesses [12,
14, 15].
This type of instrument was used in various modes of operation during the research work.
The main purpose was to carry out express measurements of the micro-hardness of steels in
a non-destructive way. In this article the determination of the micro-hardness of steels should
also be understood to mean that the authors measured not only "pure" metals, but also their
alloys and their welds and joints.
The Brinell scale (HB) and other types of scales, namely Vickers (HV), Shore (HSD) and
Rockwell (HRC), are primarily used for micro-hardness determination. In addition, it can be
used to determine the ultimate tensile strength of steels, Rm. The TEMP-4 thus allows you
to obtain hardness results directly in hardness numbers (HV, HRC, HSD and HV).
One of the main aims of this research work, some of the results of which are summarised
in this article, was to determine the capability of the device to operate under various
conditions when carrying out fire technical examinations.
3 Results
The test specimens (nails and screws) were placed one after the other in a furnace heated to
a preset temperature and kept there for 15 minutes each, then cooled down naturally.
The temperature is monitored and controlled by an electronic regulator. The maximum
annealing temperature was 1200°С.
The samples were then heated over a temperature range of 100 to 1000°C. For each new
sample, the temperature was increased by 100°C, with an oven dwell time of 15 minutes.
After the heat treatment the samples were cooled down naturally.
A visual analysis of the surface changes of the samples after the heat treatment is shown
in Figures 1 and 2.
The visual analysis of the examined samples showed that it is possible to distinguish
clearly between the changes occurring to the samples depending on the exposure temperature.
Fig. 1. Steel angles after firing in the kiln (G. Sikorova)
Metal corners when heated to a certain temperature and allowed to stand for 15 minutes:
100÷200 °C - There is no visible change.
300 °C - The steel corner has turned yellow-brown.
400 °C - The corner has taken on a dark brown colour.
500 °C - The grey is now a shade darker.
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600 °C - The metal is blackened and scale has started to form.
700 °C - Black colour and a more pronounced layer of scale.
800 °C - Metal has taken on a blue-grey colour, a layer of scale.
900 °C - Black colour, scale starting to flake off.
1000 °C - Deep black colour, descaling.
Fig. 2. Steel screws after firing in kiln (G. Sikorova)
Metal screws when heated to a certain temperature and allowed to stand for 15 minutes:
100÷300 °C - There are no visible changes to the facilities.
400 °C - The colour of the metal is darker.
500 °C - The metal has taken on a light grey colour.
600 °C - The metal's colour has turned grey and scale has started to form.
700 °C – Metal started to take on a grey-black colour, scale formation.
800 °C - The metal became even blacker, the scale.
900 °C - The screw has turned black and the scale is flaking off.
1000 °C - Gained a deeper black colour, flaking of scale.
The results of the post-firing micro-hardness of the metal angles and screws are shown in
Table 2 and, for better visualisation, additionally represented by the graphs for the metal
angles in Fig. 3 and for screws in Fig. 4.
Table 2. Micro-hardness test results for steel angles
Free-cooling samples
Micro-hardness, HB (kgf/mm2)
2
3
4
5
6
7
8
9
10
100
510
516
503
449
521
521
520
510
510
508
507
21
200
521
522
487
516
524
499
499
501
508
515
509
12
300
501
501
491
492
500
515
510
496
506
507
502
8
400
487
483
485
504
508
512
479
499
492
487
494
11
500
Average
RCS
Value
1
511
503
483
479
481
493
494
490
501
489
492
10
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600
510
507
484
481
476
490
491
477
481
484
488
12
700
486
490
493
502
481
478
480
484
480
482
486
7
800
480
483
487
503
493
494
477
478
480
485
486
8
900
473
478
480
476
474
471
476
472
470
473
474
3
1000
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474
470
466
471
468
472
469
467
464
470
469
3
Fig. 3. Diagram of micro-hardness variation of steel angles as a function of firing temperature.
Fig. 4. Diagram of micro-hardness variation of steel screws as a function of firing temperature.
As a result of the research work, some of the results presented above have shown that the
dependencies shown in Figures 3 and 4 are true for all metal products present in trucks and
cars.
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4 Conclusion
Several conclusions can be drawn from the experiments carried out and the experimental data
obtained.
As a field device, the development of a small portable programmable TEMP-4 hardness
tester was scientifically justified. This device proved itself well, especially in experimental
studies of steel products, cold-deformed products subjected to thermal effects, similar to the
rate of temperature increase in a hydrocarbon fire.
According to the obtained dependencies on the change in the micro-hardness of the
samples on the exposure temperature, it was found that the data obtained in the interval from
600 till 1000 0С coincide well with the results of changes in the magnetic characteristics of
similar materials after exposure to high temperatures. In this range, the recrystallisation
process results in a decrease in hardness of the investigated metallic samples and materials.
We consider that application of a micro-hardness metre of the given type or not inferior
on tactical and technical characteristics, type of execution and functional opportunities,
undoubtedly, will expand a set of devices applied for the purposes of fire-technical expert
examination. This applies to technical measuring instruments that are used directly on site,
i.e., in the field, and serve both to locate the initial origin of the fire, i.e., to help establish the
location of the fire, and indirectly to determine the cause of the fire. Thus, measuring the
microhardness of large metal parts (steel bodies) of burnt-out vehicles will provide the
necessary data to assess the rate and time of heating. In addition, it will identify
(determine/identify) the areas subjected to the highest temperature impact, which is
particularly relevant for load-bearing steel structures.
The results obtained by the authors do not contradict the available data and are in good
agreement with the results of other researchers [1, 8, 12, 14]. The authors suggest that this
kind of research and its results are of some interest to specialists in the field of fire expertise,
so the work in this direction will continue.
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