Machine structural steel product

A steel product for machine structural use having a Nd-free chemical composition comprising, in mass percent, C:

• 0.05% to 0.43%;
• Si:
• 0.50% to 2.5%;
• Mn:
• 0.33% to 1.00%;
• P:
• not greater than 0.035%;
• S:
• 0.005% to 0.080%;
• Cu:
• 0% to 1.5%;
• Ni:
• 0% to 2.0%;
• Cr:
• 0% to 2.0%;
• Mo:
• 0% to 1.5%;
• V:
• 0% to 0.50%;
• Nb:
• 0% to 0.1%;
• Ti:
• 0% to less than 0.04%;
• B:
• 0% to 0.01%;
• Al:
• 0.010% to 0.04%;
• N:
• not greater than 0.015%:
• Bi:
• 0% to0.10%;
• Ca:
• 0% to0.05%;
• Pb:
• 0% to0.12%;
• Te:
• 0% to 0.05%;
• Se:
• 0% to 0.5%;
• value of fn1 represented by equation (1) below being not less than 0;
• value of fn2 represented by equation (2) below being not less than 3.0;
• value of fn3 represented by equation (3) below being not greater than 100;
• balance being Fe, incidental impurities and inclusions;
• an area percentage of a ferrite phase in a microstructure being 10% to 80%;
• and Hv hardness being 160 to 350;
• fn1=−23C+Si(5−2Si)−4Mn+104S−3Cr−9V+10 (1)
• fn2=3.2C+0.8Mn+5.2S+0.5Cr−120N+2.6Pb+4.1Bi−0.001α2+0.13α (2)
• fn3=100C+11Si+18Mn+32Cr+45Mo+6V (3)
• where an element symbol appearing in equation (1), (2) or (3) represents the content in mass percent of the corresponding element, and α represents the area percentage in % of the ferrite phase in the microstructure.

A steel product for machine structural use having a Nd-free chemical composition comprising, in mass percent, C:

• 0.05% to 0.43%;
• Si:
• 0.50% to 2.5%;
• Mn:
• 0.15% to 1.06%;
• P:
• not greater than 0.035%;
• S:
• over 0.080% to 0.2%;
• Cu:
• 0% to 1.5%;
• Ni:
• 0% to 2.0%;
• Cr:
• 0% to 2.0%;
• Mo:
• 0% to 1.5%;
• V:
• 0% to 0.50%;
• Nb:
• 0% to 0.1%;
• Ti:
• 0% to less than 0.04%;
• B:
• 0% to 0.01%;
• Al:
• not greater than 0.04%;
• N:
• not greater than 0.015%;
• Bi:
• 0% to 0.10%;
• Ca:
• 0% to 0.05%;
• Pb:
• 0% to 0.12%;
• Te:
• 0% to 0.05%;
• Se:
• 0% to 0.5%;
• value of fn1 represented by equation (1) below being not less than 7.5;
• value of fn2 represented by equation (2) below being not less than 3.0;
• balance being Fe and incidental impurities;
• an area percentage of a ferrite phase in a microstructure being 10% to 80%;
• and Hv hardness being 160 to 350;
• fn1=−23C+Si(5−2Si)−4Mn+104S−3Cr−9V+10 (1)
• fn2=3.2C+0.8Mn+5.2S+0.5Cr−120N+2.6Pb+4.1Bi−0.001α2+0.13α (2)
• where an element symbol appearing in equation (1) or (2) represents the content in mass percent of the corresponding element, and a represents the area percentage in % of the ferrite phase in the microstructure, the balance of the microstructure consisting essentially of pearlite, bainite and martensite.

A steel product for machine structural use having a Nd-free chemical composition comprising, in mass percent, C:

• 0.05% to 0.43%;
• Si:
• 0.50% to 2.5%;
• Mn:
• 0.33% to 1.00%;
• P:
• not greater than 0.035%;
• S:
• 0.005% to 0.080%;
• Cu:
• 0% to 1.5%;
• Ni:
• 0% to 2.0%;
• Cr:
• 0% to 2.0%;
• Mo:
• 0% to 1.5%;
• V:
• 0% to 0.50%;
• Nb:
• 0% to 0.1%;
• Ti:
• 0% to less than 0.04%;
• B:
• 0% to 0.01%;
• Al:
• 0.010% to 0.04%;
• N:
• not greater than 0.015%:
• Bi:
• 0% to 0.10%;
• Ca:
• 0% to 0.05%;
• Pb:
• 0% to 0.12%;
• Te:
• 0% to 0.05%;
• Se:
• 0% to 0.5%;
• value of fn1 represented by equation (1) below being not less than 0;
• value of fn2 represented by equation (2) below being not less than 3.0;
• value of fn3 represented by equation (3) below being not greater than 100;
• balance being Fe, incidental impurities and inclusions;
• an area percentage of a ferrite phase in a microstructure being 10% to 80%;
• and Hv hardness being 160 to 350;
• fn1=−23C+Si(5−2Si)−4Mn+104S−3Cr−9V+10 (1)
• fn2=3.2C+0.8Mn+5.2S+0.5Cr−120N+2.6Pb+4.1Bi−0.001α2+0.13α (2)
• fn3=100C+11Si+18Mn+32Cr+45Mo+6V (3)
• where an element symbol appearing in equation (1), (2) or (3) represents the content in mass percent of the corresponding element, and a represents the area percentage in % of the ferrite phase in the microstructure, the balance of the microstructure consisting essentially of pearlite, bainite and martensite.