A method of processing a substrate, includes: (a) modifying a surface of the substrate into a first oxide layer by supplying, to the substrate, a reactive species generated by plasma-exciting a first processing gas in which oxygen and hydrogen are contained and a ratio of hydrogen in the oxygen and hydrogen of the first processing gas is a first ratio; and (b) modifying the first oxide layer into a second oxide layer by supplying, to the substrate, a reactive species generated by plasma-exciting a second processing gas in which oxygen is contained and hydrogen is optionally contained and a ratio of hydrogen in the oxygen and hydrogen of the second processing gas is a second ratio smaller than the first ratio.

There is provided a metal contamination prevention method performed by passing a metal chloride gas through a metal component having a surface covered with an inactive film formed of a chromium oxide, the method including: generating a chromium chloride (III) hexahydrate by supplying a hydrochloric acid to the inactive film covering the surface of the metal component and allowing the chromium oxide to react with the hydrochloric acid; removing a chromium from the inactive film by evaporating the chromium chloride (III) hexahydrate; and covering a surface of the inactive film with a compound containing a metal contained in the metal chloride gas.

There is provided a metal contamination prevention method performed by passing a metal chloride gas through a metal component having a surface covered with an inactive film formed of a chromium oxide, the method including: generating a chromium chloride (III) hexahydrate by supplying a hydrochloric acid to the inactive film covering the surface of the metal component and allowing the chromium oxide to react with the hydrochloric acid; removing a chromium from the inactive film by evaporating the chromium chloride (III) hexahydrate; and covering a surface of the inactive film with a compound containing a metal contained in the metal chloride gas.

An example component of a machine includes a core layer and an outer layer encasing the core layer. The outer layer has a greater carbon concentration and hardness than the core layer. The outer layer may also be compressively stressed, while the core layer may have tensile stress. The stress and/or hardness profile of the component may enhance its resistance to cracking, particularly in applications where the component is impacted by other object and/or operates at elevated temperatures. The component, such as parts of a fuel injector, may be formed by rough forming the component, carburizing the component, quenching the component, subzero processing the component, and then performing a tempering process. The components may have relatively sharp transition from the high carbon outer layer to the lower carbon core layer. Additionally, the components have a relatively high tempering resistance when used in relatively high temperature environments.

The present, invention includes: an in-furnace atmospheric gas concentration detector configured to detect a hydrogen concentration or an ammonia concentration in a processing furnace; an in-furnace nitriding potential calculator configured to calculate a nitriding potential in the processing furnace based on the hydrogen concentration or the ammonia concentration detected by the in-furnace atmospheric gas concentration detector; and a gas-introduction-amount controller configured to change an introduction amount of each of the plurality of furnace introduction gases except for the ammonia decomposition gas while keeping an introduction amount of the ammonia decomposition gas constant. based on the calculated nitriding potential in the processing furnace and a target nitriding potential, such that the nitriding potential in the processing furnace is brought close to the target nitriding potential.

A raw blank for vacuum carburization is provided. The raw blank for vacuum carburization has a chemical composition containing, by mass, C: 0.13 to 0.28%, Si: 0.01 to 1.20%, Mn: 0.10 to 1.50%, P: 0.030% or less, S: 0.050% or less, Cr: 0.30 to 2.20%, Al: 0.027 to 0.090%, N: 0.0060 to less than 0.0140%, and, as an optional element, Mo: 0.60% or less, the remainder being Fe and unavoidable impurities, and satisfying the following formula (1). AlN precipitates having an equivalent circle diameter of 100 nm or more exist at 1.5 pieces/100 μm.sup.2 or less in a cross section of the raw blank.

Al×N≤0.00090  (1)

It is noted that element symbols in the formula (1) denote a value of content (% by mass) of each element.

A method of preparing an engine valve is provided. The method includes hot forging a heat resistant steel at 1,150 to 1,250° C. to mold a valve, aging the molded valve and hollowed-out processing the aging valve. Additionally, the method includes nitride-heating the hollow valve and grinding a surface of a neck of the nitride-heated valve to remove a nitride layer.

Methods of hardening a case-nitrided metal article, methods of producing a hardened case-nitrided metal article, and hardened case-nitrided metal articles. The methods of hardening a case-nitrided metal article include heating the case-nitrided metal article to an aging temperature, maintaining the case-nitrided metal article at the aging temperature for an aging time, and cooling the case-nitrided metal article from the aging temperature. The methods of producing a hardened case-nitrided metal article include case-nitriding a metal article to produce a case-nitrided metal article and subsequently hardening the case-nitrided metal article. The hardened case-nitrided metal article comprises a body formed of a metal or a metal alloy, a surface surrounding the body, and a nitrided case layer formed in the body and extending inwardly from the surface of the body toward the core that includes a hardness that is greater than that of an otherwise equivalent case-nitrided metal article.

Methods of hardening a case-nitrided metal article, methods of producing a hardened case-nitrided metal article, and hardened case-nitrided metal articles. The methods of hardening a case-nitrided metal article include heating the case-nitrided metal article to an aging temperature, maintaining the case-nitrided metal article at the aging temperature for an aging time, and cooling the case-nitrided metal article from the aging temperature. The methods of producing a hardened case-nitrided metal article include case-nitriding a metal article to produce a case-nitrided metal article and subsequently hardening the case-nitrided metal article. The hardened case-nitrided metal article comprises a body formed of a metal or a metal alloy, a surface surrounding the body, and a nitrided case layer formed in the body and extending inwardly from the surface of the body toward the core that includes a hardness that is greater than that of an otherwise equivalent case-nitrided metal article.

Provided is a method for preparing a metal oxide or a metal hydroxide nano thin-film material by a molten salt method, which mainly comprises the following steps: heating a low-melting-point salt to a molten state, adding a substrate into the molten salt before or after melting for reaction; adding a metal source and continuing the reaction for a period of time; removing the substrate, cooling the substrate to a room temperature, cleaning and drying the substrate to obtain the metal oxide or metal hydroxide nano thin-film material; wherein, the mass ratio of the low-melting-point salt to the metal source is 100-1.5:1. The metal oxide and metal hydroxide nano-film materials with various nano-morphologies prepared by the method of the present application have morphologies that can be regulated and controlled by the types and proportions of the low-melting-point salts and metal sources.