An austenitic steel sheet excellent in resistance to delayed cracking is provided. The composition of said steel comprises in weight: 0.35%C1.05% 15%Mn26% Si3% Al0.050% S0.030% P0.080% N0.1%, at least one metallic element X chosen among vanadium, titanium, niobium, molybdenum, chromium 0.050%V0.50%, 0.040%Ti0.50% 0.070%Nb0.50% 0.14%Mo2% 0.070%Cr2%. The composition may optionally include B, Ni and/or Cu. The remainder of the composition includes iron and unavoidable impurities inherent to fabrication, including hydrogen. The quantity Xp of the at least one metallic element under the form of carbides, nitrides or carbonitrides is, in weight: 0.030%Vp0.40% 0.030%Tip0.50% 0.040%Nbp0.40% 0.14%Mop0.44% 0.070%Crp0.6%. The hydrogen content Hmax designating the maximal hydrogen content that can be measured from a series of at least five specimens, and the quantity Xp, in weight, is such that: $1000\frac{H_{\max }}{X_P}3.3.$

A gas quenching method of the present invention includes a first stage (t1 to t2) at which a workpiece is subjected to a rapid cooling by forcibly circulating a cooling gas, a second stage (t2 to t3) at which the circulation of the cooling gas is stopped and pressure is reduced inside the furnace to conduct heat insulation, and a third stage (as from t3) at which the workpiece is cooled again by the cooling gas. At the second stage, the workpiece is maintained at an intermediate temperature that is higher than martensite transformation start temperature, and, during this, temperature throughout the workpiece is made uniform. Therefore, it is possible to achieve a uniform quenching and suppress distortion caused by difference of the cooling speed.

A thermal scavenging system to remove remnant lubricants from interior of bright annealing steel tubes is provided. The system is retrofitted to bright annealing furnace with a conveyer belt and hydrogen gas source and comprises hydrogen-blowing rack, flexible rubber hoses and a lighter. The tubes are placed on the conveyer belt. The hydrogen-blowing rack comprises a hydrogen gas manifold and outlet nozzles connected to tailing ends of the tubes by flexible rubber hoses. At the leading ends of the tubes, a lighter ignites the hydrogen gas to insure all tubes are filled with hydrogen gas, instead of atmospheric air. Then rubber hoses are unplugged from the leading ends and the hydrogen-filled tubes are fed into the furnace for heat treatment. At high annealing temperature, lubricant remnants are burned off the tube's interior surfaces. A negative difference in atmospheric pressure, combustion products of hydrocarbons are scavenged out from the tailing ends.

A thermal scavenging system to remove remnant lubricants from interior of bright annealing steel tubes is provided. The system is retrofitted to bright annealing furnace with a conveyer belt and hydrogen gas source and comprises hydrogen-blowing rack, flexible rubber hoses and a lighter. The tubes are placed on the conveyer belt. The hydrogen-blowing rack comprises a hydrogen gas manifold and outlet nozzles connected to tailing ends of the tubes by flexible rubber hoses. At the leading ends of the tubes, a lighter ignites the hydrogen gas to insure all tubes are filled with hydrogen gas, instead of atmospheric air. Then rubber hoses are unplugged from the leading ends and the hydrogen-filled tubes are fed into the furnace for heat treatment. At high annealing temperature, lubricant remnants are burned off the tube's interior surfaces. A negative difference in atmospheric pressure, combustion products of hydrocarbons are scavenged out from the tailing ends.

A process for fabricating a steel sheet is provided. The process includes soaking a steel sheet. The steel has a composition including iron, carbon, manganese, silicon, aluminum, sulfur, phosphorus and nitrogen and at least one metallic element X chosen among vanadium, titanium, niobium, molybdenum, and chromium. A quantity X.sub.p of metallic element under the form of carbides, nitrides or carbonitrides is, by weight:
0.030%V.sub.p0.40%;
0.030%Ti.sub.p0.50%;
0.040%Nb.sub.p0.40%;
0.14%Mo.sub.p0.44%; or
0.070%Cr.sub.p0.6%.
The soaking step occurs under a pure nitrogen or argon atmosphere with a dew point lower than 30 C. at a soaking temperature between 250 and 900 C. and with a dynamic circulation of a regenerated atmosphere.

A process for fabricating a steel sheet is provided. The process includes soaking a steel sheet. The steel has a composition including iron, carbon, manganese, silicon, aluminum, sulfur, phosphorus and nitrogen and at least one metallic element X chosen among vanadium, titanium, niobium, molybdenum, and chromium. A quantity X.sub.p of metallic element under the form of carbides, nitrides or carbonitrides is, by weight:
0.030%V.sub.p0.40%;
0.030%Ti.sub.p0.50%;
0.040%Nb.sub.p0.40%;
0.14%Mo.sub.p0.44%; or
0.070%Cr.sub.p0.6%.
The soaking step occurs under a pure nitrogen or argon atmosphere with a dew point lower than 30 C. at a soaking temperature between 250 and 900 C. and with a dynamic circulation of a regenerated atmosphere.

A batch furnace for annealing material, in particular a single chamber furnace or single coil furnace, with a furnace housing. The batch furnace has a closable charging opening, a receiving chamber for receiving furnace material, and a device for convective heat transfer onto the furnace material by a heat transfer medium. The batch furnace includes at least one fan, which is arranged in the furnace housing, at least one heating device for the heat transfer medium and/or at least one inlet for an externally heated heat transfer medium, wherein the heating device and/or the inlet is arranged directly in front of the intake side or directly behind the pressure side of the fan or circumferentially in an annular gap between the fan and the furnace housing, and a receiving chamber for the furnace material, which is arranged on the pressure side of the fan.

A batch furnace for annealing material, in particular a single chamber furnace or single coil furnace, with a furnace housing. The batch furnace has a closable charging opening, a receiving chamber for receiving furnace material, and a device for convective heat transfer onto the furnace material by a heat transfer medium. The batch furnace includes at least one fan, which is arranged in the furnace housing, at least one heating device for the heat transfer medium and/or at least one inlet for an externally heated heat transfer medium, wherein the heating device and/or the inlet is arranged directly in front of the intake side or directly behind the pressure side of the fan or circumferentially in an annular gap between the fan and the furnace housing, and a receiving chamber for the furnace material, which is arranged on the pressure side of the fan.

This heat treatment apparatus is configured such that a treating target is conveyed via an intermediate conveyance chamber and accommodated in a heating chamber. The heat treatment apparatus is provided with a gas cooling chamber that is disposed adjacent to the intermediate conveyance chamber and in which the treating target is cooled using a cooling gas containing an oxidizer.

A device for tempering an object includes a chamber for receiving the object, wherein the chamber is surrounded by a chamber casing, a base element and a cover element, a heating element, a rotor for circulating a first gas, wherein the rotor is arranged in the chamber, and a rotor drive with which the rotor is made to rotate. The heating element is formed by the rotor with the rotor drive.