A ferritic stainless steel and a heat exchanger using the ferritic stainless steel are provided. The ferritic stainless steel includes, in mass %, C: 0.030% or less, N: 0.020% or less, Si: 0.5% or less, Mn: 1.0% or less, P: 0.05% or less, S: 0.01% or less, Cr: 16% to 25%, Nb: 0.05% to 1.0%, Al: 0.003% to 0.20%, and a balance comprising Fe and unavoidable impurities. The Al oxide is present on the surface of the material, the surface coverage ratio by the Al oxide is 5% to 70%, the surface roughness in Ra measured by red laser is 0.010-0.15 μm, and the thickness from the surface to the point, which includes the value of a half peak of the Al content on the surface, satisfies 300 nm or less, the value of a half peak of the Al content in an elemental profile expressed by a cation ratio.

The invention describes a method of heat-treating an article, which includes a first step of heating the article to a temperature of 400° C. to 500° C. at a pressure of 1 to 3 millibar in an atmosphere comprising hydrogen for a period of 0.1 to 50 hours to produce a hot article, a second step of heating the hot article at a temperature of 400° C. to 500° C. at a pressure of 1 to 3 millibar in an atmosphere comprising at least one of hydrogen, argon, and nitrogen, for 0.1 to 50 hours to produce a preliminary heat treated article, and a third step of heating the preliminary heat treated article at a temperature of 400° C. to 500° C. at a pressure of 1 to 3 millibar in an atmosphere comprising at least one of hydrogen, nitrogen, and a hydrocarbon gas, for 0.1 to 50 hours; to produce a heat-treated article.

Low temperature gas carburization of stainless steel using acetylene as the carburizing specie is carried out under soft vacuum conditions in the presence of hydrogen or other companion gas. Carburization is made to go faster by including HCl or other carbon-free, halogen-containing activating compound in the carburizing gas being fed to the carburization reactor.

Low temperature gas carburization of stainless steel using acetylene as the carburizing specie is carried out under soft vacuum conditions in the presence of hydrogen or other companion gas. Carburization is made to go faster by including HCl or other carbon-free, halogen-containing activating compound in the carburizing gas being fed to the carburization reactor.

A plastic single-axis zero-expansion composite material and a preparation method thereof are provided, featuring incorporating an α-Fe second phase into a matrix of R.sub.2Fe.sub.17-type intermetallic compound, in which R refers to a rare earth element with a low atomic content of 4%. The material has simple synthesis steps and can be easily implemented, and the phase interface formed by the eutectic reaction is more stable than the composite structures obtained by the traditional solid-phase sintering, thereby realizing the regulation of the thermal expansion, and significantly improving the mechanical properties.

A plastic single-axis zero-expansion composite material and a preparation method thereof are provided, featuring incorporating an α-Fe second phase into a matrix of R.sub.2Fe.sub.17-type intermetallic compound, in which R refers to a rare earth element with a low atomic content of 4%. The material has simple synthesis steps and can be easily implemented, and the phase interface formed by the eutectic reaction is more stable than the composite structures obtained by the traditional solid-phase sintering, thereby realizing the regulation of the thermal expansion, and significantly improving the mechanical properties.

Embodiments of the disclosure provide a system including: an enclosure having an interior sized to enclose and the workpiece and form a vacuum and pressurized atmosphere within the interior. A plurality of thermal applicators may be in thermal communication with first and second portions of the interior. First and second thermal applicators may independently heat and cool the first and second portions of the interior. The first thermal applicator may apply a first thermal treatment to a first portion of the workpiece in the first portion of the interior. A second thermal applicator may apply a second thermal treatment to a second portion of the workpiece in the second portion of the interior independently of the first thermal treatment.

A process for manufacturing a high nitrogen stainless steel pipe material includes keeping an outside surface and/or an inside surface of an austenite stainless steel pipe material in contact with a substance that becomes a nitrogen (N) source, heating the steel pipe together with the nitrogen source substance at a temperature of 800° C. to 1100° C. in a range of temperatures not higher than the critical temperature for crystal grain enlargement of the steel pipe material to cause nitrogen to be absorbed into the surface of the pipe and diffused into the steel solid phase, and applying to the heat-treated pipe material annealing treatment in the range of temperatures in vacuum, inert gas including argon gas or an atmosphere of a gas with a reducing substance including H.sub.2 gas added thereto, to result in a decrease of nitrogen concentration gradient.

A process for manufacturing a high nitrogen stainless steel pipe material includes keeping an outside surface and/or an inside surface of an austenite stainless steel pipe material in contact with a substance that becomes a nitrogen (N) source, heating the steel pipe together with the nitrogen source substance at a temperature of 800° C. to 1100° C. in a range of temperatures not higher than the critical temperature for crystal grain enlargement of the steel pipe material to cause nitrogen to be absorbed into the surface of the pipe and diffused into the steel solid phase, and applying to the heat-treated pipe material annealing treatment in the range of temperatures in vacuum, inert gas including argon gas or an atmosphere of a gas with a reducing substance including H.sub.2 gas added thereto, to result in a decrease of nitrogen concentration gradient.

Disclosed are a continuous heat treatment device and method for a sintered Nd—Fe—B magnet workpiece. The device comprises a first heat treatment chamber, a first cooling chamber, a second heat treatment chamber, and a second cooling chamber continuously disposed in sequence, as well as a transfer system disposed among the chambers to transfer the alloy workpiece or the metal workpiece; both the first cooling chamber and the second cooling chamber adopt a air cooling system, wherein a cooling air temperature of the first cooling chamber is 25° C. or above and differs from a heat treatment temperature of the first heat treatment chamber by at least 450° C.; a cooling air temperature of the second cooling chamber is 25° C. or above and differs from a heat treatment temperature of the second heat treatment chamber by at least 300° C. The continuous heat treatment device and method can improve the cooling rate and production efficiency and improve the properties and consistency of the products.