low-Cr Steel Research Articles

Properties in Creep of Low Alloy Steels in Relation to their Microstructure

The creep rupture strength of low alloy steels, 1/2Mo, 1Cr-1/2Mo, 21/4Cr-1Mo, 5Cr-1/2 Mo, 9Cr-1Mo was studied in relation to their microstructure.The results obtained are as follows;(1) The intersection of the stress-rupture time curves was observed in a steel with different heat treatment. This was observed also in 1Cr-1/2Mo and 21/4Cr-1Mo steels.(2) High Cr steels (5Cr-1/2Mo, 9Cr-1Mo) show weaker creep strength than low Cr steels (1/2Mo, LCr-1/2Mo, 21/4Cr-1Mo).(3) The Cr content in the residues does not increase by tempering. As for the amount of Mo in the residues, low Cr steels show remarkable increase in Mo content but high Cr steels show slight increase in Mo content.(4) Microscopical observation revealed that N. T. treated specimen contained finer precipitates in the ferrite than Ann. treated specimen. Tempered bainite which was observed in N. T. treated 21/4Cr-1Mo steel was apt to form coarse carbides.In fine the problems with the creep rupture strength of commercial low alloy steels will more clearly be boiled down to alternative between the following two questions:(1) whether or not the low alloy steels contain in their microstructure either bainite or martensite, or (2) whether or not the ferrite is adulterated with carbide particles.

SCr5およびSCM4材における剪断破壊の温度依存性

SCr5およびSCM4材における剪断破壊の温度依存性

アーク熔接法によるレール継目の接合に関する研究(第2報)

This is to report about a welding experiment perform cd in joining heat treated rails with the hardness of 308-390 Hv and high abraision resitance.The following are the results summarized with some comments : -1) In joining heat treated rails by manual arc welding, satisfactory joint strength can be obtained, when the bottom and web are welded with low hydrogen type electrodes, following 90% of the top part welding by means of the same type electrodes, and then the head surface is built up about 10 mm deep with the intention of hardfacing. The joining strength does not change by hard surfacing.2) For padding the employment of Mn Austenite type or Martensite type electrodes cannot be recommended, because of the cracks occurring at the fusion line between padding and base metals. We advise the use of low Cr steel type electrodes whose welding hardness is compatible with that of rail head and the welded metal is difficult to cause cracking.3) By welding, the surface hardness of rail head is softened over the range of about 10 mm from the fusion line. Rails post heated for 30 min. at 600°C immediately after welding tend to be softened down to about 250-280 Hv. over the heating zone, but the micro-structure of the point 50mm apart from the fusion line is not remarkably changed, compared with the base metal structure.4) As the result of passing trains for 80 days, it is recognized that the hardness of welding metal and softening zone of wheel side is inclined to increase by the cold working (train pass load ; 38, 000 ton/day) up to 2 mm depth under the head surface.5) The abraision loss of the base metal, the post heated softening zone and the deposit metal are almost equivalent 2 1/4 years after construction (train pass load 8, 200, 000 ton/year, gradient ; 15/1000, straight track of 348m), and the local abraision can't be observed.It is therefore considered that this weldng procedure can be used practically.

鋼の焼戻脆性に関する研究（第1報）焼戻脆性現象の不規則性

It is said that the degree of temper brittleness of special steel varies in wide range, although their chemical composition is nearly the same. This phenomena is not yet recognized in detail, and also must depend upon the nature of temper brittleness. In this paper the present author proved the variety of temper brittleness of structural special steel (Ni-Cr, Cr, Ni-Mn steel), in the following items. (1) The difference of the degree of temper brittleness in the outer and inner parts of large ingots of Ni-Cr steel, (2) the influence of phosphorus upon the temper brittleness of Ni-Cr steel, (3) the degree of temper brittleness of low phosphorous Ni-Cr, Cr, and Ni-Mn steel. The degree of temper brittleness of Ni-Cr steel is larger in the inner part than the outer part, although the segregation of C, P, S etc. are hardly recognized in any positions. The influence of phosphorous on temper brittleness of specil steel had been examined by many other experimenters. In the same manner as these experiments, our experiments indicated the strong effect of phosphorus on the temper brittleness of Ni-Cr steel. Lastly, it is mentioned especially that the degree of temper brittleness of low phosphorous Ni-Cr, Cr, Ni-Mn steel is much lower than the so-called temper brittleness of steel.

鐵銹の發生機構とその防止

We investigated the mechanism of rust formation on the surface of carbon steel and low Cr-steel in atmosphere and researched its prevention. The results are as follows: 1) Rust particles formed on the polished surface of steel are classified as dotted, granular, thread-like and lumpy rusts in their appearance. The lumpy rusts are produced by a limited number among dew drops condensed on the steel surface and grow rapidly. This is the principal source of rusting. 2) Lumpy rust generally starts in the pearlite area of steel surface, therefore high carbon steels rust more rapidly than low carbon steels. 3) 0.6% C-steel is quenched from 800°C and tempered at various temperatures; the one which is tempered at 450°C is most resistive to rust. 4) About the action of dust adhered to the steel surface, soluble chloride and sulphate particles (NaCl, NH4Cl, MgCl2 and Na2SO4 etc, have strong accelerating action and lumpy rusts start at every particles of them; Fe2O3 particles have nearly the same action; contrary to this, SiO2, Al2O3, CaO particles show no action. 5) If the steel surface initially bears complete oxide film (invisible) it can resist rust; therefore steels finished by proper electrolytic treatment, held in dry air for a long period or immersed in 0.5% K2Cr2O, 1% Na2HPO4 solution show good resistivity. 6) The initial flowing current from the surface of steel wire bearing complete oxide film (that is, having good resistivity to rust) immersed in 1% H2SO4, increases slowly and it requires long time to reach constant current density. Accordingly we can find the resistance to rust formation by measuring the flowing current. 7) Waselin and animal oils have generally greater rust prevention effect than vegetable oils.

鉄銹の発生機構とその防止

We investigated the mechanism of rust formation on the surface of C-steel and low Cr-steel in atmosphere and researched its prevention. The results are as follows: (1) Rust particles formed on the polished surface of steel are classified as dotted, granular, thread-like and lumpy rust in their appearance. (2) The lumpy rusts are produced by a limited number among many dew drops condensed on the steel surface and grow rapidly. This is the principal source of rusting. (3) About the action of dust adhered to the steel surface, soluble chloride and sulphate particles (NaCl, NH4Cl, MgCl2 and Na2SO4 etc.) have strong accelerating action and lumpy rusts start at every particle of them; Fe2O3 particles have nearly the same action; contrary to this, SiO2, Al2O3, CaO particles show no action. (4) Lumpy rust generally starts in the pearlite area of steel surface, therefore, high carbon steels rust more rapidly than low carbon steels. (5) 0.6%C-steel is quenched from 800° and tempered at various temperatures; the one which is tempered at 450° is most resistive to rust. (6) If the steel surface initially bears complete oxide film (invisible) it can resist rust; finished steels held in dry air for long period or immersed in 0.5%K2Cr2O7, 1%Na2HPO4 solution show good resistivity. (7) Waselin and animal oils have generally greater rust prevention effect than vegetable oils.