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.

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 medical instrument with excellent operability is provided. The medical instrument includes stick-shaped extra-narrow metal members. The extra-narrow member has a hardened layer formed on the surface thereof without losing flexibility.

A workpiece made from a self-passivating metal and having one or more surface regions defining a Beilby layer as a result of a previous metal shaping operation is activated for subsequent low temperature gas hardening by exposing the workpiece to the vapors produced by heating a non-polymeric N/C/H compound.

Provided is steel for nitrocarburizing with excellent surface fatigue strength. The steel has a nitride compound layer with a thickness of 5.0 μm to 30.0 μm and a hardened layer in an order from a steel surface to steel inside, where a thickness of a porous layer on an outermost surface of the compound layer is 3.0 μm or less and 40.0% or less of a compound layer's thickness, the hardened layer has hardness of HV600 or more, HV400 or more and HV250 or more at 50 μm inward from the steel surface, from the steel surface to the steel inside of 400 μm, and from the steel surface to the steel inside of 600 μm, respectively, an unhardened portion excluding the compound and hardened layers has a predetermined chemical composition, and the hardened layer has a chemical composition with a higher N content than the unhardened portion.

Provided is a method and apparatus that can form a metal carbonitride film or a metalloid carbonitride film at low temperature. A metal carbonitride film or a metalloid carbonitride film is formed by supplying onto a film formation object a nitrogen source and a metal source or a metalloid source, the nitrogen source containing a guanidine compound represented by the following general formula (1):

##STR00001##

where a plurality of Rs are the same or different, each represent a hydrogen atom, a linear, branched or cyclic alkyl group of 1 to 5 carbon atoms or a trialkylsilyl group of 1 to 9 carbon atoms, and, depending on circumstances, bond to each other to form a ring.

Provided is a method and apparatus that can form a metal carbonitride film or a metalloid carbonitride film at low temperature. A metal carbonitride film or a metalloid carbonitride film is formed by supplying onto a film formation object a nitrogen source and a metal source or a metalloid source, the nitrogen source containing a guanidine compound represented by the following general formula (1):

##STR00001##

where a plurality of Rs are the same or different, each represent a hydrogen atom, a linear, branched or cyclic alkyl group of 1 to 5 carbon atoms or a trialkylsilyl group of 1 to 9 carbon atoms, and, depending on circumstances, bond to each other to form a ring.

Endodontic instruments for use in performing root canal therapy on a tooth are disclosed. In one form, the instruments include an elongate shank having a cutting edge extending from a distal end of the shank along an axial length of the shank. The shank comprises a titanium alloy, and the shank is prepared by heat-treating the shank at a temperature above 25° C. in an atmosphere consisting essentially of a gas unreactive with the shank. In another form, the endodontic instruments have an elongate shank having a cutting edge extending from a distal end of the shank along an axial length of the shank. The shank consists essentially of a titanium alloy selected from alpha-titanium alloys, beta-titanium alloys, and alpha-beta-titanium alloys. The instruments solve the problems encountered when cleaning and enlarging a curved root canal.

Endodontic instruments for use in performing root canal therapy on a tooth are disclosed. In one form, the instruments include an elongate shank having a cutting edge extending from a distal end of the shank along an axial length of the shank. The shank comprises a titanium alloy, and the shank is prepared by heat-treating the shank at a temperature above 25° C. in an atmosphere consisting essentially of a gas unreactive with the shank. In another form, the endodontic instruments have an elongate shank having a cutting edge extending from a distal end of the shank along an axial length of the shank. The shank consists essentially of a titanium alloy selected from alpha-titanium alloys, beta-titanium alloys, and alpha-beta-titanium alloys. The instruments solve the problems encountered when cleaning and enlarging a curved root canal.

A method for producing a retort for a nitriding furnace, in which metallic workpieces are heat-treated in a pre-determined atmosphere, includes pickling at least the surfaces of the retort, which are configured to come into contact with the pre-determined atmosphere while the nitriding furnace is operating, by using a pickling agent. The pickled surfaces may then be electropolished and passivated. A retort may be produced according to this method and the retort may be used in a nitriding furnace.