An Investigation on Boron-Treated Steels. I : On the Hardenability of Boron-Treated Medium-Carbon Steels, especially the Effect of Nitrogen-Content in Steels

As fundamental-studies on boron-treated steels, the hardenability and the effect of nitrogen in it were studied with medium carbon steel. The maximum hardenability is obtained with the addition of boron by the order of 0.003%, being decreased sharply with further increase of boron. When the nitrogen content is less than about 0.008%, the effect on the improving action of boron on the hardenability is almost nil, but with increasing of its amount over 0.008% the effect of boron decreases markedly, until the nitrogen content increases up to about 0.02% in which the effect of boron almost diminishes. When steel is strongly deoxidized and denitrogenized by adding aluminium or titanium, prior to boron addition, the effect of boron appears markedly. These results may be attributed to fact that boron accerelates to crystallize out a nitrogen compound during quenching or tempering of steels

On the Mechanism of Boron Hardenability

The adsorptions of boron and other interstitial solute elements in the quenched state could be made well observable by etching the steel with NaOH-NaNO_3 aqueous solution. Boron atoms adsorbed upon a grain surface would fill up the lattice defects or diffusion holes, reducing the internal strains induced by these imperfections ; in other words, these atoms would diminish the unstability of austenite grain boundaries and could suppress the transformation beginning at these places. The decrease of boron hardenability with the increase of the austenitizing temperatures seemed to be caused by the re-dissolution of nitrogen in solid solution

Determination of Condition for Electrolytic Extractions of Nitrides in Steel by Means of Potentiostat

The polarizing characteristics of synthesized nitrides, Fe_3N, Fe_4N, Mn_3N_2 Mo_2N, MoN, Cr_2N CrN, VN, Si_3N_4 AlN, TiN, ZrN and NbN, were studied by means of potentiostat in order to determine the condition for the electrolytic extractions of nitrides from iron and steel. From the results of polarization curves and natural electrode potentials of iron and nitrides, some useful informations were obtained as to the electrolyte and the electrolytic potential for the electrolytic extractions of nitrides contained in iron and steel ; that is, if a suitable electrolytic potential is applied, both acidic and neutral solutions can be used as an electrolyte for the extractions except nitrides of Al, Fe and Mn. For the Fe-nitride, only neutral electrolyte is useful, while for the nitrides of Al and Mn, there seems to be no favorable electrolyte

Nitrogen as Alloying Element in Steels. II : On the Effect of Nitrogen on Blue-Brittleness in Steels

To ascertain the effect of nitrogen on the blue-brittleness in carbon steels, usual tensile tests were carried out at temperatures above room temperature up to 300°, and it was found that nitrogen was the principal cause of this phenomenon, although the brittleness due to carbon was seen at a high temperature range in steels containg low nitrogen

Nitrogen as an Alloying Element in Steel : Effect of Nitrogen on Quench-Aging of Steels

The present investigation was carried out in order to ascertain the effect of nitrogen on the quench-aging of steels containing 0.02～0.03 and 0.15～0.20 per cent carbon. The specimens tempered at 700℃ for 3 hours after quenching at 950℃ were requenched at 300～700℃ after heating for 3 hours at respective temperatures and then aged at 30, 50 and 100℃. From the present investigation the following conclusions were obtained : (1) There is a distinct correlation between the nitrogen in steel and the quench-aging ; (2) By the addition of nitrogen stabilizer such as Al or Ti, or by the fusion in vacuum the aging due to nitrogen is reduced ; (3) The specimens containing less than 0.005 per cent of nitrogen revealed aging due to carbon

Effect of Nitrogen and Few Other Elements on Strain Aging of Steels

Many investigations were carried out on the strain aging of steels but few were reported on commercial steels. In succession to the work on the effect of nitrogen on the strain aging in steels, the effects of Al, Ti, Si, Mn, As and Cu were examined

Sub-Zero Treatment of Quenched Steel. I : On the Stabilization of Retained Austenite

As a fundamental study of sub-zero treatment of steel, the effects of quenching temperature, room temperature aging and tempering on the stabilization of retained austenite were examined. The stabilization of retained austenite was promoted by aging, because the martensite transformation rate due to subsequent sub-zero cooling was increased by the increase in aging, and moreover, when aging increased, the martensite transformation rate passed through a maximum. The martensite transformation due to subsequent sub-zero cooling gave rise to the burst transformation when aging increased to a certain degree. The remarkable increase in the stabilization was caused by the increase in the amount of prior martensite, though the stabilization occurred without prior martensite. It was suggested that the stabilization of austenite was caused by a mechanism similar to age-hardening

Effect of Molybdenum upon the High-Temperature Oxidation and the V_2O_5 Attack on Ni-Cr-Base Alloys

The high-temperature oxidation and the rate of corrosion by the V_2O_5 attack were examined with Ni-Cr-Mo, Ni-Cr-Co-Mo alloys containing about 19 per cent chromium and with some commercial heat-resisting alloys. In addition, the oxides composing thin oxide films or scales in these alloys were identified from observations of electron and X-ray diffractions. Following results were obtained. (1) Addition of molybdenum to Ni-Cr alloys increased the weight loss due to scaling above 1000℃, four sorts of oxides, Cr_2O_3, spinel phase NiOCr_2O_3, NiO and NiOMoO_3, being formed in the scales. Above 1200℃ NiOMoO_3 decomposed soon after the formation, with the volatilization of MoO_3, and thus the oxidation losses remarkably increased in Ni-Cr-Mo alloys. In these alloys, a rapid formation of oxides was observed at 1350℃, owing to the formation of molten phase of NiOMoO_3 in the scales. (2) A rapid oxidation occurred in Ni-Cr-10 Co-5 Mo alloy at 1300℃, owing to the formation of melt of (Ni, Co) OMoO_3 in the scale. The similar rapid oxidation was observed in molybdenum-containing Ni-base, Co-base and Fe-Ni-Co-Cr base heat-resisting alloys, which is considered to be associated with the formation and the fusion of (Ni, Co) OMoO_3, corresponding to nickel and cobalt content. (3) Addition of molybdenum increased the corrosion rate by V_2O_5 attack on Ni-Cr and Ni-Cr-Co alloys. Also the V_2O_5 attack was increased by molybdenum content in commercial heat-resisting alloys. Of the molybdenum-containing Fe-base, Co-base and Ni-base heat-resisting alloys, Ni-base alloys were the most resistant to the attack, Fe-base alloys being the least

Heat-Treatment of Forged Roll Steel

In order to determine the conditions of heat-treatment favorouble to a roll steel containing 0.80 per cent carbon and 1.62 per cent chromium, austempering and martempering were studied, Isothermal transformation curves i. e. S-curves and the hardenability by gradient quenching were determined. Relations between Ar" transformation velocity and quantity of the retained austenite, residual stress as well as quenching crack were studied by various isothermal treatments. Effects of pre-heating on the residual stress were also examined