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AssigneesJapan Casting & Forging Corporation, Nippon Steel Corporation
InventorsSeinosuke Yano, Koh Moriyama, Takashi Harabuchi, Yoshikazu Nakano, Hiroshi Mochiki, Kimio Nagata
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The present invention provides hot rolled steel plates and sheets having a tensile strength of 34 to 62 kgf/mm.sup.2 and excellent in a uniform elongation even after cold working the steel plates and sheets to give round and square tubes, shapes, sheet piles, etc., to such an ordinary degree that the productivity is not lowered, and a process for producing the hot rolled steel plates and sheets. The hot rolled steel plates and sheets contain from 0.04 to 0.25% of C, from 0.0050 to 0.0150% of N and from 0.003 to 0.050% of Ti, also contain from 0.0008 to 0.015% of TiN having a particle size exceeding 1 .mu.m and dispersed in the matrix thereof, and have Ceq. (WES) of 0.10 to 0.45%. The process comprises heating a steel slab containing the constituents as mentioned above to 1,000 to 1,300.degree. C., starting to roll the steel slab subsequently and finishing rolling at a temperature of at least the Ar.sub.3 transformation point, and air cooling from a temperature of at least 500.degree. C. or coiling at a temperature of at least 500.degree. C. and air cooling, the resultant steel structure having a pearlite phase in an amount of 5 to 20% in terms of area fraction.
High strength hot rolled steel plates and sheets excellent in uniform elongation after cold working, containing from 0.04 to 0.25% by weight of C, from 0.0050 to 0.0150% by weight of N and from 0.003 to 0.050% of Ti, having a carbon equivalent (Ceq.) defined by the formula described below of 0.10 to 0.45% and a pearlite phase in an amount of 5 to 20% in terms of area fraction, and containing from 0.0008 to 0.015% by weight of TiN having an average particle size exceeding 1 .mu.m and dispersed therein:
A process for producing high strength hot rolled steel plates and sheets excellent in uniform elongation after cold working, which comprises heating a steel slab containing from 0.04 to 0.25% by weight of C, from 0.0050 to 0.0150% by weight of N and from 0.003 to 0.050% by weight of Ti, and having a carbon equivalent (Ceq.) of 0.10 to 0.45% to a temperature from 1000.degree. to 1300.degree. C., starting to roll the heated steel slab and finishing rolling at a temperature of at least the Ar.sub.3 transformation point, and air cooling from a temperature of at least 500.degree. C.
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