Synopsis:Steels containing Te are generally used for free cutting steels. But the effect of Te on mechanical properties and mechanism of grain growth retardation by Te are not well knownyet.The authors have studied the influence of Te on impact properties, tensile properties and austenite grain size of common structural steels at various temperatures.Tellurium compounds were identified by X-ray diffraction with electrolytically extracted residues and by analysis of the compounds using electron probe X-ray microanalyzer.The state of dispersion of telluride was examined by autoradiography using 125m Te isotope. The obtained results are as follows.

The authors made a study on mechanical /Hoperlies and harden ability of medium carbon chromium steel which was developed as corrosion resisling steel under weak acid corrosive atmos/lhere.11 was /l roved that relained hydrogen had an eXlremely bad ejJeel especially on duclility of Ihis steel. Therefore. a process for /lroduclion was invesligated in order to increase duclility. Since the ejJecl qf boron on hardenability depended on the nitrogen contenl ,Ihe relalion between the effeci q! boron and con tenl of such nitride forming elements as aluminum and lilanium was examined.The following resulls were obtained.(1) In order 10 guarantee 8 J 0 of elongalion (JIS No.4 tensile specimen) in steel with 140 kg/mm 2 of tensile slr'ength, hydrogen content was decreased less than] /lpm by slow cooling of bloom after blooming.(2) The effect of boron on hardenability was great in steels containing nitrogen of less than 40 ppm, even if only boron was added 10 the steels.Bul in order 10 make boron to be effective on hardenability, aluminum more Ihan O.O ] O~ and aluminulll more than 0.04";0 or titanium more than 0.02~o were required for steels containing aboul 0 .006 0 0 of nitrogen and for steels containing about 0.0] 00 of nitrogen res/lectively.(3) The effect of boron on hardenability corres/londed with the con lent qf acid soluble boron which was decided by solubility products of (B) (N), (AI) (N ) and (Ti) (N). H owever, the relationship between hardenability and Ihe conlenl of acid soluble boron did nol hold in all cases . T o secure the same hardenability, Ihe content of acid soluble boron , in sleel conlaining aluminum was much smaller than Ih al in steel withoul addition of aluminum .(4) II was proved from the investigalion aboul distribution of boron b), a-lrack method that hardenability was relaled 10 concentralion of boron on /He-auslenite grain boundaries in sleel withou l addition of aluminum.

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