Abstract: Disclosed is a copper-infiltrated valve seat insert of an iron-base sintered alloy having a two-layer structure formed by integrating a functional member side layer and a supporting member side layer across a boundary, and the thermal conductivity rate at 300° C. is 25 W/m·K or more in the functional member side layer and 60 W/m·K or more in the supporting member side layer.

Abstract: A valve seat insert made of an iron-base sintered alloy is configured to have a structure in which the base matrix phase is a fine carbide precipitation phase in which a fine carbide being 10 ?m or less in size is precipitated and which has a hardness of 550 HV or more in Vickers hardness; and in the base matrix phase, hard-particles having a hardness of 650-1200 HV in Vickers hardness are dispersed in an area percentage of 20-40%, a diffusional phase is formed in an area percentage of more than 0% and not more than 5%, and solid-lubricant particles are dispersed in an area percentage of 0-5%. Even if a valve having a high face hardness of 400 HV or more, or 600 HV or more is used, a facing valve seat insert wears only slightly, improving valve train durability.

Abstract: Provided is a valve seat insert made of an iron-base sintered alloy, in which a base matrix part that includes a base matrix phase and hard particles, has a base matrix part composition containing, in % by mass, 0.5%-2.0% of carbon and 10%-70% in total of one kind or two or more kinds selected from nickel, cobalt, chromium, molybdenum, vanadium, tungsten, manganese, silicon and sulfur, with the balance being iron and unavoidable impurities, and Co-base hard particles having a composition containing, 1.0% or less of C, 25%-50% of Mo, 5%-15% of Cr, Si as an impurity in a content adjusted to be 0.3% or less, with the balance being Co, and having a Vickers hardness of 500 to 1,500 HV, are dispersed as hard particles in the base matrix phase in an amount of 10%-60% by mass with respect to the total amount of the valve seat insert.

Abstract: A valve seat insert made of an iron-base sintered alloy is configured to have a structure in which the base matrix phase is a fine carbide precipitation phase in which a fine carbide being 10 ?m or less in size is precipitated and which has a hardness of 550 HV or more in Vickers hardness; and in the base matrix phase, hard-particles having a hardness of 650-1200 HV in Vickers hardness are dispersed in an area percentage of 20-40%, a diffusional phase is formed in an area percentage of more than 0% and not more than 5%, and solid-lubricant particles are dispersed in an area percentage of 0-5%. Even if a valve having a high face hardness of 400 HV or more, or 600 HV or more is used, a facing valve seat insert wears only slightly, improving valve train durability.

Abstract: Provided is a valve seat insert made of an iron-base sintered alloy, in which a base matrix part that includes a base matrix phase and hard particles, has a base matrix part composition containing, in % by mass, 0.5%-2.0% of carbon and 10%-70% in total of one kind or two or more kinds selected from nickel, cobalt, chromium, molybdenum, vanadium, tungsten, manganese, silicon and sulfur, with the balance being iron and unavoidable impurities, and Co-base hard particles having a composition containing, 1.0% or less of C, 25%-50% of Mo, 5%-15% of Cr, Si as an impurity in a content adjusted to be 0.3% or less, with the balance being Co, and having a Vickers hardness of 500 to 1,500 HV, are dispersed as hard particles in the base matrix phase in an amount of 10%-60% by mass with respect to the total amount of the valve seat insert.

Abstract: A steel product having a composition which contains by mass C: 0.01 to 1.9%, Si: 0.01 to 1.9%, Mn: 5.0 to 24.0% with balance consisting of Fe and unavoidable impurities and a steel product described above which further contains Cr: 18.0% or below and/or Ni: 12.0% or below in addition to the above essential elements. The above steel products may each further contain Al: 1% or below and/or N: 0.3% or below and the above steel products may each further contain one or more elements selected from among Nb, Ti, Zr, Mo and Cu in a total amount of 4.0% or below. The steel products can sufficiently follow the thermal expansion of a cylinder made of an aluminum alloy and thus enables the production of a piston ring which is suitable for use as a piston ring to slide on the inner face of a cylinder bore made of an aluminum alloy in an internal combustion engine and which can retain excellent sealing properties.