Nippon Steel Sumitomo Metal Corporation

Sumitomo Metal Industries, Inc.

Honda Motor Co., Ltd.

Naoyuki Sano

Tatsuya Hasegawa

Toshiro Tomida

Masayuki Horimoto

Masaki Amano

Akihito Ninomiya

Yoshihiko Kamada

Shigeo Uenoya

Yoshinari Okada

Takayuki Nakatani

Non-post-heat treated steel contains: in mass %, C: 0.27 to 0.40%, Si: 0.15 to 0.70%, Mn: 0.55 to 1.50%, P: 0.010 to 0.070%, S: 0.05 to 0.15%, Cr: 0.10 to 0.60%, V: 0.030% or more and less than 0.150%, Ti: more than 0.10%, not more than 0.200%, Al: 0.002 to 0.050%, and N: 0.002 to 0.020%, and optionally one or more of Cu&#x2264;0.40% and Ni&#x2264;0.30%; the balance being Fe and impurities, wherein [Ti]&#x2212;3.4[N]&#x2212;1.5[S]&#x3c;0, and 0.60&#x3c;[C]+([Si]/10)+([Mn]/5)+(5[Cr]/22)+(33[V]/20) &#x2212;(5[S]/7)&#x3c;0.80. The steel can be used to make a high fatigue strength connecting rod for automobile engines which is fracture-split from a hot forged shape. The non-post-heat treated steel member can have vEof 1.0 to 7.0 J/cm, and &#x3c3;w&#x2265;450 MPa.

Non-post-heat treated steel and non-post-heat treated steel member

A method for producing a carbonitrided member comprising the steps of carburizing a steel part having a composition of, by mass percent, C: 0.10 to 0.35%, Si: 0.15 to 1.0%, Mn: 0.30 to 1.0%, Cr: 0.40 to 2.0%, S: 0.05% or less with the balance being Fe and impurities in a carburizing atmosphere of 900 to 950&#xb0; C. The carburized steel part is carbonitrided in a carbonitriding atmosphere with the temperature of 800 to 900&#xb0; C. and the nitrogen potential of 0.2 to 0.6%. The carbonitrided steel part is qhenched and then shot peened. The shot peening treatment may be further performed while heating to a temperature not higher than 350&#xb0; C. or immediately after heating to a temperature not higher than 350&#xb0; C. After quenching, the shot peening treatment may be further performed after tempering in the temperature range exceeding 250&#xb0; C. and not higher than 350&#xb0; C.

Method for producing carbonitrided member

Non-heat treated steel for soft-nitriding to form parts having high fatigue strength and excellent bend leveling property even in a case of applying soft-nitriding without thermal refining, comprising, by mass %, C: 0.30 to 0.45%, Si: 0.1 to 0.5%, Mn: 0.6 to 1.0%, Ti: 0.005-0.1% and N: 0.015 to 0.030%, and the balance Fe and impurities, having a mixed microstructure of bainite and ferrite whose bainite fraction is 5 to 90% or having a mixed microstructure of bainite, ferrite and pearlite whose bainite fraction is 5 to 90%, the steel could contain one or more of elements of Nb: 0.003 to 0.1% Mo: 0.01 to 1.0%, Cu: 0.01-1.0%, Ni: 0.01 to 1.0%, B: 0.001 to 0.005%, S: 0.01 to 0.1%, and Ca: 0.0001 to 0.005.

Non-heat treated steel for soft-nitriding

(1) A doubly oriented silicon steel sheet having excellent magnetic characteristics in two directions, i.e. in a rolling direction and in a direction perpendicular to the rolling direction, and most suited for use as material for cores of small-sized transformers, and (2) a method for manufacturing the same. The doubly oriented silicon steel sheet as mentioned above in (1) is characterized in that: Si and Mn are contained in amounts which satisfy a predetermined formula of relation; an average crystal grain is as large as 1 to 8 times the thickness of the sheet as measured on a cross section parallel to the surface of the sheet; and at least 60% of all crystal grains have a size of X/3 to 3X, where X is an average grain size. In the doubly oriented silicon steel sheet, preferably, crystal grains having a crystallographic orientation difference within .+-.15 degrees from a cubic orientation of {100}&lt;001&gt; occupy an areal percentage of not less than 70%, or the thickness of a surface oxide layer of the steel sheet is not greater than 0.5 .mu.m. The method for manufacturing a doubly oriented magnetic steel sheet as mentioned above in (2) includes the steps of hot-rolling and cold-rolling steel containing C in an amount of 0.02% to 0.2% and Si and M in amounts satisfying a predetermined formula of relation, wherein annealing is performed at a temperature not lower than 750.degree. C. and through quick application of heat during cold rolling; and the obtained steel sheet is annealed under reduced pressure through use of an annealing separator. In this method for manufacturing a doubly oriented magnetic steel sheet, preferably, a rolling reduction is 40% to 85% in cold rolling performed before and after intermediate annealing.

Doubly oriented magnetic steel sheet and method for manufacturing the

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Takarazuka, Japan

Naoyuki Sano