Plain low-carbon steels as substitutes for certain high-strength alloy steels

Conclusions

• 1. Drastic quenching in an 8–10% aqueous solution of NaOH at 10–15°C considerably strengthens steels 10 and 15. The strengthening is due to fixing the carbon in solid solution as well as to distorsionless work-hardening of the ferrite. The steels reached a strength level occasionally exceeding that of steel 30KhGSA and surpassing it in impact toughness. Tempering of specimens at various temperatures changed the properties in a continuous manner which facilitated the selection of the best tempering temperature.

• 2. At equal strengths at room temperature, the elevated-temperature strength of steel 15 was practically the same as that of steel 30KhGSA.

  TABLE 2.

  Steelgrade	Heattreatment	RCkg/sq.mm	Notchductility,ψ, %
  10	Quenched 930°C, tem-pered 300°C	38	11.25
  15	Quenched 900°C, tem-pered 350°C	39	8.46
  50khGSA	Oil quenched, tem-pered at 500°C	40	9.50
  30KhGSA	Oil quenched, tempered at 400°C	42	4.50

• 3. After quenching and tempering of plain low-carbon steel parts, their transition temperature dropped below −70°C, which is very important for parts operating under practical conditions. The considerable amount of ferrite in the center portion of the parts had no effect on embrittlement.

• 4. Hardening to a high strength level of parts and assemblies of low-carbon unalloyed steels enables one in many cases to dispense with alloy constructional steels. Low-carbon plain steels have also processing advantages in view of their good weldability and drawability. The price of low-carbon unalloyed steel is about one-half that of heat-treatable, alloyed constructional steel of the type 30KhGSA.