Nippon Steel & Sumitomo Metal Corporation

Nippon Steel Corporation

Junji Haji

Osamu Kawano

Kaoru Kawasaki

Kiyokazu Ishizuka

Yuzo Takahashi

Ikuo Kikuchi

Kazumi Nishimura

Daisuke Maeda

Kenichi Yamamoto

Tatsuo Yokoi

Hideaki Yamamura

Yoshihiro Suwa

Teruaki Yamada

Fuminori Tasaki

Kohsuke Kume

Satoshi Horioka

Tooling used in a punching process which uses a die and projecting punch to form a worked material of steel sheet into a predetermined outer shape, in which tooling for punching, a radius of curvature Rd of a die cutting edge is from 0.03 mm to 0.2 mm and an angle (&#x3b1;) formed by a tangent drawn from a punch cutting edge to a projection shoulder and a direction perpendicular to a direction of movement of the punch is from 12&#xb0; to 72&#xb0;, and a punching method and shaping method using the same, are provided. Further, when making the die cutting edge (shoulder R part) a two-stage R of radii of curvature Rand Rand making a slant of a line passing through the centers of Rand R&#x3b2;, by making 0.03 mm&#x2264;R&#x2264;0.2 mm, 1&#x2264;R/R&#x2264;5, 0&#x2264;R(1&#x2212;sin &#x3b2;1)&#x2264;0.3t, and 30&#xb0;&#x2264;&#x3b2;&#x2264;90&#xb0;, punching hole expandability can be improved.

Tooling for punching steel sheet and punching method

A hot-rolled steel sheet includes, as a chemical composition, by mass %, C: 0.030% to 0.10%, Mn: 0.5% to 2.5%, and Si+Al: 0.100% to 2.5%, in which the steel sheet has a microstructure including, by area fraction, ferrite: 80% or more, martensite: 3% to 15.0%, and pearlite: less than 3.0%, in which a number density of martensite having an equivalent circle diameter of 3 &#x3bc;m or more at a position which is at a depth of &#xbc; of the steel sheet thickness from the surface of the steel sheet, is 5.0 pieces/10000 &#x3bc;mor less, and the following Expression (1) is satisfied.&#x2265;1.00&#x2003;&#x2003;Expression (1) Here, R is an average martensite interval (&#x3bc;m) defined by the following Expression (2), and Dis a martensite average diameter (&#x3bc;m).={12.5&#xd7;(&#x3c0;/6)&#x2212;(&#x2154;)&#x2003;&#x2003;Expression (2) Here, Vis a martensite area fraction (%) and Dis the martensite average diameter (&#x3bc;m).

Hot-rolled steel sheet and method for producing same

The present invention provides a method of production of hot dip galvannealed steel sheet with excellent workability compared with the Sendzimir method or non-oxidizing furnace method and further with excellent powdering or slidability, that is, a method of production of hot dip galvannealed steel sheet with excellent workability, powdering, and slidability characterized by processing a slab containing, by mass %, C: 0.01 to 0.12%, Mn: 0.05 to 0.6%, Si: 0.002 to 0.1%, P: 0.05% or less, S: 0.03% or less, sol. Al: 0.005 to 0.1%, and N: 0.01% or less and having a balance of Fe and unavoidable impurities by hot rolling, pickling, cold rolling, then annealing at 650 to 900&#xb0; C., cooling to 250 to 450&#xb0; C., holding at said temperature range for 120 seconds or more, then cooling to room temperature, pickling, preplating Ni or Ni&#x2014;Fe without intermediate temper rolling, heating by 5&#xb0; C./sec or more down to 430 to 500&#xb0; C., galvanizing in a galvanization bath, wiping, then heating by a rate of temperature rise of 20&#xb0; C./sec or more up to 460 to 550&#xb0; C., not providing any soaking time or holding for soaking for less than 5 seconds, then cooling by 3&#xb0; C./sec or more, and final temper rolling by a 0.4 to 2% elongation rate.

Method of production of hot dip galvannealed steel sheet with excellent workability, powderability, and slidability

A hot rolled steel sheet includes, as a chemical composition, at least one selected from Ti, REM, and Ca, and includes, as a metallographic structure, a ferrite as a primary phase, at least one of a martensite and a residual austenite as a secondary phase, and plural inclusions, wherein a total length in the rolling direction of both inclusion-cluster whose length in the rolling direction is 30 &#x3bc;m or more and independent-inclusion whose length in the rolling direction is 30 &#x3bc;m or more is 0 mm to 0.25 mm per 1 mm.

Hot rolled steel sheet and method of producing same

The present invention provides a high-strength steel sheet including: C: 0.03 to 0.25 mass %, Si: 0.1 to 2.0 mass %, Mn: 0.5 to 3.0 mass %, P: not more than 0.05 mass %, T.O: not more than 0.0050 mass %, S: 0.0001 to 0.01 mass %, N: 0.0005 to 0.01 mass %, acid-soluble Al: more than 0.01 mass %, Ca: 0.0005 to 0.0050 mass %, and a total of at least one element of Ce, La, Nd, and Pr: 0.001 to 0.01 mass %, with a balance including iron and inevitable impurities, in which the steel sheet contains a chemical component on a basis of mass that satisfies 0.7&#x3c;100&#xd7;([Ce]+[La]+[Nd]+[Pr])/[acid-soluble Al]&#x2266;70 and 0.2&#x2266;([Ce]+[La]+[Nd]+[Pr])/[S]&#x2266;10, the steel sheet contains compound inclusion including a first inclusion phase containing at least one element of Ce, La, Nd, and Pr, containing Ca, and containing at least one element of O and S, and a second inclusion phase having a component different from that of the first inclusion phase and containing at least one element of Mn, Si, and Al, the compound inclusion forms a spherical compound inclusion having an equivalent circle diameter in the range of 0.5 &#x3bc;m to 5 &#x3bc;m, and a ratio of the number of the spherical compound inclusion relative to the number of all inclusions having the equivalent circle diameter in the range of 0.5 &#x3bc;m to 5 &#x3bc;m is 30% or more.

High-strength steel sheet exhibiting excellent stretch-flange formability and bending workability, and method of producing molten steel for the high-strength steel sheet

Exemplary embodiments of the present invention can provide a method for producing hot dip galvannealed steel sheet which exhibits high strength, high ductility, and a significant degree of alloying. Such exemplary method can be applied to, e.g., a pickled hot rolled steel sheet or an annealed and pickled cold rolled steel sheet containing between about 0.02% and about 0.2% C and between about 0.15% and about 2.5% Mn, and may include one or more procedures for rinsing the sheet, preplating the sheet with Ni, rapidly heating the sheet in a nonoxidizing atmosphere to a sheet temperature of about 430&#xb0; C. to 500&#xb0; C., then hot dip plating the sheet in a galvanizing bath containing between about 0.05% and about 0.2% Al, and then immediately heating the sheet rapidly for an alloying treatment. Such exemplary method can provide an improved alloying speed, improved plating appearance and better plating adhesion.

Method for producing high-strength hot-dip galvannealed steel sheet

On a cross section with a sheet width direction of a high-strength hot-rolled steel sheet set as a normal line, with regard to an inclusion having a major diameter of 3.0 &#x3bc;m or more, a maximum of a major diameter/minor diameter ratio expressed by (a major diameter of the inclusion)/(a minor diameter of the inclusion) is 8.0 or less, and a sum total of a rolling direction length per 1 mmcross section of a predetermined inclusion group composed of plural inclusions each having a major diameter of 3.0 &#x3bc;m or more and a predetermined extended inclusion having a length in a rolling direction of 30 &#x3bc;m or more is 0.25 mm or less. The plural inclusions composing the predetermined inclusion group congregate in both the rolling direction and a direction perpendicular to the rolling direction 50 &#x3bc;m or less apart from each other. The predetermined extended inclusion is spaced over 50 &#x3bc;m apart from all the inclusions each having a major diameter of 3.0 &#x3bc;m or more in at least either the rolling direction or the direction perpendicular to the rolling direction.

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Tokyo, Japan

Junji Haji