An energy-saving heat treatment device for a metal substrate in a corrosive gas, comprising: a process chamber; a radiation field, arranged in a process space to provide a heat source for the process space; a process frame, arranged inside the process space to accommodate at least one substrate to carry out a rapid heat treatment process, an upper surface of an outer edge of the substrate being covered on the process frame; and a cover, covering a top of the process frame to isolate a space above the substrate from the process chamber; wherein the process frame, the substrate and the cover form a small process volume, and the small process volume reduces an amount of introduction and/or overflow of a process gas exchanged with the process chamber to a limit value; wherein the cover is configured as: 1) being located inside the radiation field and remains stationary; or 2) being located on the process frame and forming an integral structure with the process frame; wherein the outer edge of the lower surface of the substrate is covered by two methods: Mode I): the process frame covers the outer edge of the lower surface of the substrate; or Mode II) the substrate is in contact with a bottom surface of the radiation field so that the bottom surface of the radiation field covers the bottom surface of the substrate; wherein the cover is located between the two outer edges of the substrate, a covering area of the cover is within a range of 1 to 50 mm, and the cover is provided with a photoelectrically inert material; wherein Mode II) comprises: a bottom plate is arranged under the substrate in two forms: Form a): the bottom plate supports the substrate and is located at a bottom end of the process frame and forms an integral structure with the process frame; and Form b): the bottom plate supports the substrate and is installed on the bottom surface of the radiation field;and wherein a sealing member for sealing an upper surface and/or a lower surface of the outer edge of the substrate is arranged in the outer edge of the substrate. a process chamber; a radiation field, arranged in a process space to provide a heat source for the process space; a process frame, arranged inside the process space to accommodate at least one substrate to carry out a rapid heat treatment process, an upper surface of an outer edge of the substrate being covered on the process frame; and a cover, covering a top of the process frame to isolate a space above the substrate from the process chamber; wherein the process frame, the substrate and the cover form a small process volume, and the small process volume reduces an amount of introduction and/or overflow of a process gas exchanged with the process chamber to a limit value; wherein the cover is configured as: 1) being located inside the radiation field and remains stationary; or 2) being located on the process frame and forming an integral structure with the process frame; 1) being located inside the radiation field and remains stationary; or 2) being located on the process frame and forming an integral structure with the process frame; wherein the outer edge of the lower surface of the substrate is covered by two methods: Mode I): the process frame covers the outer edge of the lower surface of the substrate; or Mode II) the substrate is in contact with a bottom surface of the radiation field so that the bottom surface of the radiation field covers the bottom surface of the substrate; Mode I): the process frame covers the outer edge of the lower surface of the substrate; or Mode II) the substrate is in contact with a bottom surface of the radiation field so that the bottom surface of the radiation field covers the bottom surface of the substrate; wherein the cover is located between the two outer edges of the substrate, a covering area of the cover is within a range of 1 to 50 mm, and the cover is provided with a photoelectrically inert material; wherein Mode II) comprises: a bottom plate is arranged under the substrate in two forms: Form a): the bottom plate supports the substrate and is located at a bottom end of the process frame and forms an integral structure with the process frame; and Form b): the bottom plate supports the substrate and is installed on the bottom surface of the radiation field;and Form a): the bottom plate supports the substrate and is located at a bottom end of the process frame and forms an integral structure with the process frame; and Form b): the bottom plate supports the substrate and is installed on the bottom surface of the radiation field;and wherein a sealing member for sealing an upper surface and/or a lower surface of the outer edge of the substrate is arranged in the outer edge of the substrate.