The equilibrium relations between the dissolved sulphur in molten iron and gaseous sulphur, and sulphur dioxide were established by means of some thermodynamic calculations. From these relations, the pressures of sulphur gases and sulphur dioxide in equilibrium with molten iron as well as the heats of vaporization of sulphur from the bath were determined. It was also proved that sulphur gas would behave in atomic state in the case of a bath containing a small amount of the sulphur at a high temperature such as in steelmaking practice.
Mild steels in contact with molten copper-tin alloys embrittled severely in the range of 0-80%Sn, but did not embrittle in the range of 90-100% Sn.As the tin percentage in the alloys was increased and the melting point of the alloys was lowered, the embrittling temperature range was extended down to lower temperature. Mild steel was not embrittled by pure tin, but embrittled by pure zinc and more easily by tin-zinc alloy. Mild steel in contact with the alloys containing 50% zinc and 50% tin respectively was embrittled at a temperature higher than 500°C.The cracks ran along to ferrite-grain boundaries at below A1 point.Mild steel was embrittled severly by molten copper-zinc alloy that is a brazing solder, but was not embrittled by a tin-lead solder.Some steels in contact with molten iron sulphide were embrittled.
There has been no method to distinguish exactly and conveniently whether materials are composed of grains of uniform size or grains of mixed sizes.The authors analysed theoretically the size and its distribution of the grains appeared on a sectional plain of the material and presented a method for that purpose, and then experimentally comfirmed this method to be suitable one. According to the authors'calculation, when the material are composed of grains of uniform size, on a sectional plain of the material, the percentage.of area (R), occupied by grains having the area ranged from the area of large circle of the grain to its 75%, must be nearly 70%.Then if the measured value is nearly 70%, the material may be defined to be composed of grains of uniform size, and, if not, grains of mixed sizes. Experimental results indicates that the above consideration is correct, i.e., the measured value of R on a sample of carbon steel, which is confirmed to be duplex-grain structure by three dimensional measurment, is only a few percent.
Carbide segregation in ball-bearing steel has been said to be harmful in their life. But unfortunately there is no concrete experimental data on this problem. In order to see the effect of this segregation, flattening test which proved the strength at room temperature, and a life test were performed. Test pieces were taken from each ingot belonging to the same heats. These ingots were heated at high temperature for different durations. Concequently the grades of segregation in each ingot were found different. The ring made of the ballbearing steel were quenched, tempered and flattened between the two arms of a physical test machine. Carbide segregation slightly affected the flattening strength of the ring. But from the practical point of view, these effects could be neglected. A life-test machine was invented by the Government Mechanical Laboratory. The small needle cut from the tube were rolled between three rolls. Their life was proved by the noise caused by the flaking on the suface of the needle. Microscopic segregation did not affect on the life of the ball-bearing steel.
To investigate the influence of P on properties of 13 Cr stainless steels, which were widely used for kitchen utensils, medical instruments, high-temperature duties and otheruses. The authors measured the transformation temperatures, the hardness change, the mechanical properties at room and elevated temperatures and studied the corrosion resistance to 40% boiling nitric acid and to 5% acetic acid at room temperature and boiling. The results obtained were as follows: (1) The Ac transformation temperatures were raised but the Ar beginning points were lowered by P addition. (2) The as-annealed hardness of these steels and of cold-drawn materials were increased with P contents. The as quenchd hardness was subjected to the influence of quenching temperatures but was not affected by P content. The resistance to softening by tempering were enhanced by P addition (3) The tensile and yield strengths at room and elevated temperatures were increased by P addition, but elongation and reduction of area at room temperature were slightly degreased. The impact strength were lowered with P content. (4) The corrosion resistance to 40% boiling nitric acid was enhanced by less than 0.05% P, but the resi stance to 5% boiling acetic acid was decreased by P addition.
Studies have been made on the formation of the nitrogen-bearing austenite in 20% Cr-Ni-Fe alloys containing nickel up to 10% by the authors' nitrogen-absorption method and the thermal behavior of the formed austenite. The corrosive resistivity and the elevated temperature spring property obtained by this treatment have also been investigated. The results obtained are as follows: 1) Austenite containing about 0.4% of nitrogen is formed in 20% Cr-Ni-Fe alloys by nitrogen-absorption treatment at 1250°C. for 4 hours. The depth of the nitrogen-bearing austenite zone from the surface is widened with increase of the nickel content of alloys, while the nitrogen content of this zone is lowered gradually as the nickel content is raised in the alloys containing 4% or more of nickel. 2) When the nickel content of the alloys is 2% or more, the nitrogen-bearing austenite is retained by the quenching in water. In the alloys containing 6% or more of nickel, no martensite is formed even by the subzero-treatment using the liquid oxygen. 3) In the nitrogn-absorbed alloys the lamellar phase is developed at grain boundaries during the aging at 700°C. The fine precipitants are also found within grains after the prolonged aging if the nickel content of alloys is higher than about 6%. The hardness of the aged alloys up to 780 hours is always kept to be higher than that of the alloys before the aging. 4) The hardness of the nitrogen-absorbed alloys in both water-quenched and cold-rolled conditions is appreciably higher than that of alloys before the absorption, and the softening temperature of the cold-rolled alloys on heating is raised markedly by nitrogen-absorption treatment. 5) The spring prbperty at elevated temperatures of the nitrogen-absorbed 20% Cr-Ni-Fe alloys containing 4% nickel is superior to that of 18-8 steel or 17-7 PH steel. 6) The corrosive resistivity of 20% Cr-Ni-Fe alloys against aqueous solutions of 65% HNO3, 5% H2SO4 and 1% HCl in respective boiling conditions is improved remarkably by nitrogen-absorption treatment; the nitrogen-absorbed alloys containing 2-3% nickel is found to have nearly the resistivity equivalent to that of 18-18 steel. 7) The resistivity to intergranular corrosion of the nitrogen-absorbed alloys is superior to that of carbon-free 18-8 steel.