Nippon Steel Corporation

Honda Motor Co., Ltd.

Yusuke Miyakoshi

Motoki Takasuga

Tatsuya Hasegawa

Hideki Matsuda

Isamu Saito

Masashi Kawakami

A steel bar for hot forging according to the present disclosure has a chemical composition consisting of, in mass percent, C: 0.05 to 0.40%, Si: 0.05 to 0.50%, Mn: 1.51 to 3.50%, P: 0.010 to 0.100%, S: 0.30% or less, Cr: 0.05 to 2.50%, V: 0.10 to 0.75%, Ti: 0.005% to 0.250%, Al: 0.005 to 0.060%, and N: 0.002 to 0.020%, with the balance being Fe and impurities, and satisfying Formula (1). A number density of TiNs having a circle equivalent diameter of not less than 20 &#x3bc;m in steel is 0.3 to 4.0/mm:0.48&#x2264;C+0.11Mn+0.08Cr+0.75V+0.20Mo&#x2264;1.50&#x2003;&#x2003;(1)where, symbols of elements in Formula are to be substituted by contents of corresponding elements (in mass percent).

Steel bar for hot forging

A non-heat treated steel bar according to the present disclosure has a chemical composition consisting of, in mass percent, C: 0.39 to 0.55%, Si: 0.10 to 1.00%, Mn: 0.50 to 1.50%, P: 0.010 to 0.100%, S: 0.040 to 0.130%, Cr: 0.05 to 0.50%, V: 0.05 to 0.40%, Ti: 0.10% to 0.25%, Al: 0.003 to 0.100%, and N: 0.020% or less, with the balance being Fe and impurities, and satisfying Formula (1). A number density of AlO-based inclusions in each of which AlOis contained at 70.0% or more in mass % and &#x221a;AREA is not less than 3 &#x3bc;m is 0.05 to 1.00/mm.0.60&#x2264;C+0.2Mn+0.25Cr+0.75V+0.81Mo&#x2264;1.00&#x2003;&#x2003;(1)

Non-heat treated steel bar

A rolled steel material for fracture splitting connecting rods consists of, C: 0.30 to 0.40%, Si: 0.60 to 1.00%, Mn: 0.50 to 1.00%, P: 0.04 to 0.07%, S: 0.04 to 0.13%, Cr: 0.10 to 0.30%, V: 0.05 to 0.14%, Ti: more than 0.15% to 0.20% or less, N: 0.002 to 0.020%, and optionally may contain Cu, Ni, Mo, Pb, Te, Ca, and Bi, with the balance being Fe and impurities. fn1, defined by Formula (1), ranges from 0.65 to 0.80. Relative to the V content in the steel material, a V content in coarse precipitates having a particle size of 200 nm or more is 70% or less, and relative to the Ti content in the steel material, a Ti content in the coarse precipitates is 50% or more.1=C+Si/10+Mn/5+5Cr/22+(Cu+Ni)/20+Mo/2+33V/20&#x2212;5S/7&#x2003;&#x2003;(1)

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Tokyo, Japan

Yusuke Miyakoshi