INCREASING THE ACCURACY OF CALCULATION OF THE AVERAGE DIAMETER OF GRAINS OF STRUCTURAL STEELS
Authors:   Lviv Polytechnic National University, Zhuravel I. M. 
Published: April 2021

It is well-known that the­re is a cle­ar cor­res­pon­den­ce bet­we­en the qua­li­ta­ti­ve cha­rac­te­ris­tics of the me­tal un­der study and its in­ter­nal struc­tu­re. This ma­de it pos­sib­le to eval­ua­te the mec­ha­ni­cal pro­per­ti­es of a me­tal thro­ugh the analysis of its in­ter­nal struc­tu­re. In many ca­ses the si­ze of the gra­in is used as the ma­in pa­ra­me­ter of the me­tal in the analysis of its in­ter­nal struc­tu­re, be­cau­se it has a sig­ni­fi­cant ef­fect on the pro­per­ti­es of the me­tal. In this appro­ach to re­se­arch in­te­res­ting from the po­int of vi­ew of ma­te­ri­al sci­en­ce is to study the ki­ne­tics of gra­in growth of the ma­te­ri­al un­der the influ­en­ce of so­me fac­tors of ex­ter­nal influ­en­ce, such as tem­pe­ra­tu­re. Dif­fe­rent appro­ac­hes are used to de­ter­mi­ne gra­in si­ze. Among them are the met­hod of de­ter­mi­ning the gra­in si­ze on the ba­sis of com­pa­ri­son with the re­fe­ren­ce sca­les, the met­hod of co­un­ting gra­ins and the met­hod of cal­cu­la­ting the in­ter­sec­ti­ons of gra­in bo­un­da­ri­es. The abo­ve met­hods ha­ve a num­ber of sig­ni­fi­cant draw­backs, among which are the fol­lo­wing. First, in the abo­ve met­hods and in ot­her appro­ac­hes of this type, they ope­ra­te on ave­ra­ge sta­tis­ti­cal val­ues, and the ob­ject of analysis is not in­di­vid­ual gra­ins, but so­me, so­me­ti­mes qui­te lar­ge, gro­up of gra­ins. Sin­ce on the thin sec­ti­on may be gra­ins of dif­fe­rent si­zes, this le­ads to a met­ho­do­lo­gi­cal er­ror in cal­cu­la­ting the ge­omet­ri­cal pa­ra­me­ters of the gra­in. Se­cond, the met­hods con­si­de­red are sui­tab­le for the analysis of gra­ins of con­vex sha­pe only. When the sha­pe of the gra­ins dif­fers from the con­vex one, it will al­so gi­ve ri­se to ad­di­ti­onal met­ho­do­lo­gi­cal er­ror. Third, the met­hods descri­bed in the pa­per are not au­to­ma­ted, which req­ui­res ad­di­ti­onal ti­me to cal­cu­la­te the num­ber of gra­ins, the num­ber of po­ints of in­ter­sec­ti­on of li­nes and bo­un­da­ri­es of gra­ins, etc. The pa­per analyzes one of the most com­monly used appro­ac­hes to cal­cu­la­ting the ave­ra­ge di­ame­ter of ste­el gra­ins ba­sed on me­tal­log­rap­hic ima­ges. It is a met­hod of cros­sing gra­in bo­un­da­ri­es, ba­sed on the req­ui­re­ments of re­gu­la­tory do­cu­ments. It is es­tab­lis­hed that the ave­ra­ge di­ame­ter of the gra­ins of me­tal in the pla­ne of thin sec­ti­on cal­cu­la­ted ac­cor­ding to this met­hod do­es not cor­res­pond to the re­al ave­ra­ge di­ame­ter of the gra­ins in three-di­men­si­onal spa­ce. An er­ror analysis is per­for­med, which is that the sa­me cross sec­ti­ons in the pla­ne of the thin sec­ti­on do not al­ways cor­res­pond to re­al gra­ins of the sa­me si­ze in three-di­men­si­onal spa­ce. To over­co­me this draw­back, a met­hod using a cor­rec­ti­on co­ef­fi­ci­ent is pro­po­sed, the val­ues of which de­pend on the num­ber of gra­ins used in the cal­cu­la­ti­on of the ave­ra­ge di­ame­ter. In ge­ne­ral, the pro­po­sed met­hod will impro­ve the ac­cu­racy of the cal­cu­la­ti­ons of the ave­ra­ge di­ame­ters of the me­tal gra­ins.