Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/18—Hardening; Quenching with or without subsequent tempering
  • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching

Definitions

• the invention is for a method of hardening steel.
• Hardening is generally employed to enhance the strength of the steel, by which is understood also tensile strength and yield strength, and its hardness.
• a general problem in connection with employment of hardened steel components is that the steel's toughness generally decreases when the strength and hardness are increased by various hardening methods.
• tempering will generally enhance the toughness of the steel at the expense of its strength and hardness.
• the grain size of the steel after hardening is chiefly determined by the grain size in a heated condition at the hardening temperature before hardening. In this condition the grain structure of the steel is known to practitioners of the art as austenite.
• the martensite structure is a series of fine needles or plates formed within the individual austenite grain, in such a manner that the martensite grain size is determined by the austenite grain size before hardening.
• the austenite grain size varies greatly according to the steel type and the holding temperature/ holding times at which the steel is at high temperature and has an austenitic structure.
• a particularly coarse austenitic structure is obtained if the steel is heated above the temperature that produces granulation.
• the steel has in the prior art been allowed to cool to room temperature followed by a new heating and hardening, that is, heating to hardening temperature and sudden cooling. This, however, involves heavy energy expenditure in that the steel must be reheated.
• the grain structure of the steel moreover, does not become particularly fine as a result of the afore-mentioned procedure, as the austenite grain structure is formed by the transformation of a relatively coarse structure formed by the slow cooling to room temperature.
• the purpose of the invention is to supply a method for hardening of steel in which the grain size of the steel is reduced and which, when the method is employed together with the heat treatment of steel, will enable energy savings to be made.
• the purpose is achieved according to the invention by causing a transformation of the steel in a temperature range between the hardening temperature and the critical temperature for formation of martensite.
• the transformation is achieved by cooling the steel from an austenitic state through or holding it at that temperature at which its transformation to ferrite, pearlite or bainite occurs most rapidly. After the transformation has taken place to a sufficient degree, a rapid heating to hardening temperature is performed, with a brief holding at that temperature before the steel is hardened in the conventional manner in a suitable hardening medium. Heating and hardening times are made short to avoid new unwanted grain growth.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Strip Materials And Filament Materials (AREA)
• Heat Treatment Of Steel (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Applications Claiming Priority (2)

Publications (2)

Family

ID=19888566

Family Applications (1)

Country Status (3)

Citations (5)

• 1985
  • 1985-11-05 NO NO854396A patent/NO854396L/no unknown
• 1986
  • 1986-10-31 DK DK522586A patent/DK522586A/da not_active Application Discontinuation
  • 1986-11-05 EP EP86850388A patent/EP0221874A3/de not_active Withdrawn

Patent Citations (5)

Non-Patent Citations (2)

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