Manganese Steel

MANGANESE STEEL. In modern steels manganese is used as a strengthener and toughener; carbon-free alloys are remark ably ductile in a wide range ; while cast manganese steel con taining over io% of manganese is the toughest material known. Crucible or electric steels can be properly deoxidized without manganese, consequently high carbon steels have a sharply limited quantity. Bessemer or open-hearth steels require at least 0.3% manganese to counteract the effect of oxygen and sulphur; a slight excess also improves the rolling properties. For these rea sons the tonnage steels contain from 0.3% to 0.9% manganese. Increasing wheel loads have caused a demand for harder rails to resist the wear. Recent American specifications for 120 to 140-lb. rails call for carbon 0.72 to 0.89, manganese 0.5 to 0.9 and silicon more than 0.15%.

A new high strength boiler plate and

structural steel has been produced, misnamed in America "silicon steels." This and the ex cellent ship-building material (D-Quality Structural Steel) of this general type, used by the British admiralty since the Wash ington conference, is described in the article on STEELS, ALLOY. Continental engineers favour even higher silicons. The "Freund" or "F" steel produced in Germany contains 0.13 to 0.57 carbon, 0.90 to 1.20 silicon, and 0.7 to 1.0 manganese. Freund steel's ulti mate strength is somewhat less than that of D-steel, and the elongation correspondingly higher. Most leaf springs for vehicles are made with a "silico-manganese" steel containing 0.45 to 0.60 carbon, 1.8 to 2.2% silicon and o.6 to 0.9 manganese. European practice favours the lower chemical ranges. Such steels permit a wider temperature range in forming the hardening than high car bon spring steels. "Non-deforming" steels for gauges, master tools, intricate dies, and broaches contain 0.80 to 0.95 carbon and 1.5 to 1.75 manganese. For any of these steels a heat treatment schedule can be fixed so that the principal dimensions will be the same after hardening, drawing, and polishing off the scale as when the piece left the machine tool. High strength steel castings, made

in America since 1909, contain 0.20 to 0.30 carbon and 1.10 to 1.40 manganese. Such castings when properly made approach D-steel and are used for artillery mounts, freight car couplers, and places where the maximum quality is desired.

Manganese acquired a bad reputation as an alloying element, except in large quantities, from Hadfield's early experiments wherein carbon always increased with the manganese. When ferro manganese with low carbon became available, its moderate use had no bad effects-quite the contrary. (Commercial production of electrolytic manganese in 1939 presages an entirely new alloy family of hitherto unattainable properties.) Hence we find wide use for plain carbon steels, strengthened by 1% manganese rather than the ordinary 0.5% for deoxidation ; LI% manganese added to free-cutting steels with high sulphur to improve their toughness; 14% manganese added to medium carbon steels (0.30 to 0.50% carbon) for a type of true alloy steel, for such important parts as automobile axles, oil quenched forgings, steam valves, rifle barrels, cylinders for compressed gas; and the same with 0.15% vanadium for forgings too large to be effectively quenched. Man ganese, properly proportioned to the carbon, in a well-made steel will increase its hardenability in a very useful way. Mass pro duction also approves of the low cost of this alloying element. Development of special open-hearth furnace techniques, and especially of new deoxidizers and addition agents, produces these medium manganese steels of fine grain, and therefore of unusually good toughness added to inherent strength. For these reasons American use is rapidly growing at the expense of alloy steels con taining the more expensive nickel and chromium. (E. E. T.)