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AssigneeNippon Steel Corporation
InventorsIsamu Takayama, Satoshi Yamamoto, Masanori Kizaki
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Bars of titanium alloys suited for the manufacture of at least the stems (2), (3) of engine valves are mass-producible while maintaining good configurational and dimensional accuracies throughout the valve fabricating process and the wear-resistance imparting processes to at least the stems (2), (3), by surface oxidizing and nitriding. The alloys are of the .alpha.+.beta. type whose microstructure consists of any of an acicular .alpha.-phase consisting of acicular .alpha. crystals having a width of not smaller than 1 .mu.m, an acicular .alpha.-phase consisting of acicular .alpha. crystals having a width of not smaller than 1 .mu.m and dispersed with equiaxed .alpha. crystals, and an equiaxed .alpha.-phase consisting of .alpha. crystals whose diameter is not smaller than 6 .mu.m. Their microstructure may also include one in which the diameter of the pre-.beta. crystals in the acicular .alpha.-phase is not larger than 300 .mu.m and the width of the acicular .alpha. crystals is not smaller than 1 .mu.m and not larger than 4 .mu.m. Selection of these alloys assures very efficient manufacture.
An engine valve of titanium alloy with at least a valve stem thereof having a microstructure consisting essentially of an acicular .alpha.-phase consisting of acicular .alpha. crystals with a width of not less than 1 .mu.m and not more than 4 .mu.m, wherein at least said valve stem has high wear resistance imparted by oxidation or nitriding.
An engine valve of titanium alloy with at least a valve stem thereof having a microstructure consisting essentially of an acicular .alpha.-phase consisting of acicular .alpha. crystals with a width of not less than 1 .mu.m and not more than 4 .mu.m, and pre-.beta. crystals having a grain diameter of not larger than 300 .mu.m, wherein at least said valve stem has high wear resistance imparted by oxidation or nitriding.
In a method of imparting wear resistance to an engine valve of titanium alloy, which comprises subjecting the valve to at least one treatment selected from the group consisting of oxidizing and nitriding, the improvement wherein the valve is made of a titanium alloy having a microstructure consisting essentially of an acicular .alpha.-phase having acicular .alpha. crystals with a width of not less than 1 .mu.m and not more than 4 .mu.m, and said treatment is conducted without thermally deforming the valve.
In a method of imparting wear resistance to an engine valve of titanium alloy, which comprises subjecting the valve to at least one treatment selected from the group consisting of oxidizing and nitriding, the improvement wherein the valve is made of a titanium alloy having a microstructure consisting essentially of an acicular .alpha.-phase consisting of acicular .alpha. crystals with a width of not less than 1 .mu.m and not more than 4 .mu.m, and pre-.beta. crystals having a grain diameter of not larger than 300 .mu.m, and said treatment is conducted without thermally deforming the valve.
Dependencies are inferred from the claim text.