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A. V. Korobka^a, N. N. Vlasenko^a, Yu. K. Sl’usarev^b

 ^aDonetsk National Technical University, ^bSLR “Donpribormash”

 

Studying of interrelation of mechanical properties and coercive force of steel 45 for total non-destructive testing of the quality of rolled stock

 

It is discussed the possibility of the using of the magnetic structuroscopy method for total non-destructive testing of the quality of rolled stock.

testing, rolled stock, coercive force, hardness

The problem of increasing quality of metallurgical product and increase of its field-performance datas puts the more actual problem searching for new, more perfect and reliable methods of the checking its quality. The magnetic methods of the checking get broad spread, they having high efficiency and providing necessary accuracy of the measurements [1]. Besides, that methods allow to reduce the expenseses on fabrication and test samples that particularly currently for rolled stock of the greater sections in connection with increased labour content and duration of the samples fabrication for mechanical test and metallographic studies.

Much works is denoted to the research of the influence of heat treatment on magnetic and mechanical properties of steel, for the reason studies of the possibility of the checking their mechanical characteristics on magnetic. Influencing of temperature of quenching and tempering especially thoroughly was studied. However that heat treatment is used mainly on machine-building enterprises, but in steel production process for obtain of the necessary complex mechanical properties annealing or normalization is used [2]. So presents the practical interest to research the influence of normalizations on magnetic and mechanical properties of steel for the reason of determinations of the possibility nondestructive checking mechanical characteristic in supply condition.

In the first part of work studies of determination intercoupling coercive force with limit of fluidity and relative elongation were conducted on samples which produced from rolled stock by diameter 22 mms from steel 45.

Mechanical test were produced on mechanical test machine EU-40 in accordance with GOST 1497-84 on 18 samples in hot rolling condition and 18 samples after normalization (the temperature of the heating – 860 ^оС, endurance - 30 min., cooling - on air). On these samples coercive force was measured with the help of magnetic structuroscop "POWER" by method of the point pole, which essence is concluded in magnetization of the control product by pole of the electromagnet and measurement of the value of the field remaining magnetization received "spot". The averaged results of the measurements were brought in table 1.

Table 1

Averaged results of the measurements mechanical properties and indications of magnetic structuroscop

From brought data is seen that after normalizations limit of fluidity increases in contrast with hot rolling condition, coercive force and relative elongation herewith increases small that does not give the possibility on importance of the investigation parameter to define this samples were subjected to normalizations or no.

Hereinafter sensitivity of the method magnetic structuroscopy to structure and hardness was researched on samples, which were sliced from rolled stock by diameter 22 mms from steel 45.

             The measurement of hardness produced by method of Rokvell on scale HRB in accordance with GOST 9013-59 on 18 samples in hot rolling condition and 18 samples after normalization (the mode such, either as in the first part of work). Moreover, hardness was measured in cross-sections samples and on lateral surface which were cleaned on depth till 3 mms. On these samples was measured coercive force and remanence after remagnetization, with the help of magnetic structuroscop "POWER". The averaged results of the measurements were brought in table 2.

Table 2

Averaged results of the measurements of hardness and indications of magnetic structuroscop

In addition, metallographic researches were conducted. On the picture 1 the fragments of microstructure of hot rolling steel 45 are resulted both in transversal, and in longitudinal sections.

From results of table 2 it is visible that hardness of hot rolling samples in cross-sections (98 HRBmean) several exceeds hardness of the same samples in longitudal section (94 HRBmean). This fact finds explanation that the structure of ferrit-perlite of samples in the cross-sections has large dispersion (see the fig. 1).

                                     a                                                                                                                  b

Pict.1. Microstructure of rolled stock sample, ×100:

a – a cross-section;  b – longitudal section.

Hardness of the steel after normalization both in longitudal, and in cross-section has the identical values approximately (91 and 92 HRBmean accordingly). This is connected with that structure after normalization more homogeneous on the whole section of rolling stock.

Thus, the executed researches show the presence of definite dependencies between mechanical properties, magnetic features and structure of steel 45 in hot rolling condition and after normalization. These regularities, which being systematized, generalized and complemented, can lie in base of the development of the method nondestructive express-control of quality rolled stock which produced on metallurgical plant.

 

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