TRIP-AIDED DUAL-PHASE MARTENSITIC STEEL AND ULTRAHIGH-STRENGTH-STEEL PROCESSED PRODUCT USING SAME

• Main Authors: SUGIMOTO KOH-ICHI, YOSHIKAWA NOBUO, NAKAJIMA YUJI, TAKAHASHI TERUHISA, ARAI GORO, KOBAYASHI JUNYA
• Format: Patent
• Language: English
• Published: 21.08.2014
• Subjects: ALLOYS; BEARINGS; BLASTING; CHEMISTRY; ELEMENTS OR CRANKSHAFT MECHANISMS; ENGINEERING ELEMENTS AND UNITS; FERROUS OR NON-FERROUS ALLOYS; FLEXIBLE SHAFTS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUSMETALS OR ALLOYS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVEFUNCTIONING OF MACHINES OR INSTALLATIONS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; HEATING; LIGHTING; MAKING METAL MALLEABLE BY DECARBURISATION, TEMPERING OR OTHERTREATMENTS; MECHANICAL ENGINEERING; METALLURGY; METALLURGY OF IRON; MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; SHAFTS; TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION; TECHNICAL SUBJECTS COVERED BY FORMER USPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS; THERMAL INSULATION IN GENERAL; TREATMENT OF ALLOYS OR NON-FERROUS METALS; WEAPONS

Provided is a TRIP-aided dual-phase martensitic steel which is excellent in terms of strength-elongation balance and Charpy impact value and has dual-phase martensite composed of a soft lath martensitic structure and a hard lath martensitic structure as a matrix phase, regardless of forging temperature or forging reduction ratio, by controlling heat treatment conditions. The dual-phase martensitic steel contains 0.1-0.7% C, 0.5-2.5% Si, 0.5-3.0% Mn, 0.5-2.0% Cr, 0.5% or less (including 0%) of Mo, 0.04-2.5% Al, and the balance Fe with incidental impurities; has its metallographic structure in which a matrix phase is composed of a soft lath martensitic structure and a hard lath martensitic structure; and obtained by heating its raw steel material to a γ-range, rapidly cooling the heated material to a temperature slightly above a martensite transformation starting temperature (Ms), and then performing an isothermal transformation process the cooled material in the temperature range from Mf to [(Mf)−100° C]. (145 words)