Embodiments of the present disclosure are directed to coiled steel tubes and methods of manufacturing coiled steel tubes. In some embodiments, the final microstructures of the coiled steel tubes across all base metal regions, weld joints, and heat affected zones can be homogeneous. Further, the final microstructure of the coiled steel tube can be a mixture of tempered martensite and bainite.

A welded steel part with a very high mechanical strength is provided. The welded steel part is obtained by heating followed by hot forming, then cooling of at least one welded blank obtained by butt welding of at least one first and one second sheet. The at least one first and second sheets including, at least in part, a steel substrate and a pre-coating which includes an intermetallic alloy layer in contact with the steel substrate, topped by a metal alloy layer of aluminum or aluminum-based alloy. A method for the fabrication of a welded steel part and the fabrication of structural or safety parts for automotive vehicles are also provided.

A brazed joint having excellent tensile strength (TSS and CTS) and a method of production of the same are provided. A sheet combination 200 comprised of steel sheets 210, 220 between which a brazing filler metal 230 is clamped is heated at a temperature of the Ac3 point of the steel sheet (matrix material) or more. The Ar3 point of the regions near the brazing filler metal at the steel sheets is made higher than the Ar3 point of the steel sheets (matrix material), then the quenching start temperature X is made a temperature of the Ar3 point of the steel sheet (matrix material) or less and hot stamping is performed to produce a brazed joint.

A steel plate comprising, by mass %: C: 0.03% to 0.12%, Si: 0.5% or less, Mn: 1.0% to 2.0%, P: 0.015% or less, S: 0.0005% to 0.0050%, Al: 0.005% to 0.060%, Ni: 0.5% to 2.0%, Ti: 0.005% to 0.030%, N: 0.0015% to 0.0065%, 0: 0.0010% to 0.0050%, Ca: 0.0005% to 0.0060%, and optionally one or two or more of Cu and the like. Ti/N, Ceq, Pcm, and ACR are in particular ranges, a base metal of the plate has an effective grain size of 20 μm or less at half the thickness of the plate, and the plate contains a particular number of complex inclusions at ¼ and ½ of the thickness of the plate. The complex inclusions comprise a sulfide containing Ca and Mn and an oxide containing Al and having an equivalent circular diameter of 0.1 μm or more.

A welded steel part with a very high mechanical strength is provided. The welded steel part is obtained by heating followed by hot forming, then cooling of at least one welded blank obtained by butt welding of at least one first and one second sheet. The at least one first and second sheets including, at least in part, a steel substrate and a pre-coating which includes an intermetallic alloy layer in contact with the steel substrate, topped by a metal alloy layer of aluminum or aluminum-based alloy. A method for the fabrication of a welded steel part and the fabrication of structural or safety parts for automotive vehicles are also provided.

A martensitic steel including the following elements, expressed in percentage by weight 0.1%≤C≤0.4%; 0.2%≤Mn≤2%; 0.4%≤Si≤2%; 0.2%≤Cr≤1%; 0.01%≤Al≤1%; 0%≤S≤0.09%; 0%≤P≤0.09%; 0%≤N≤0.09%; and can contain one or more of the following optional elements 0%≤Ni≤1%; 0%≤Cu≤1%; 0%≤Mo≤0.1%; 0%≤Nb≤0.1%; 0%≤Ti≤0.1%; 0%≤V≤0.1%; 0.0015%≤B≤0.005%; 0%≤Sn≤0.1%; 0%≤Pb≤0.1%; 0%≤Sb≤0.1%; 0%≤Ca≤0.1%; the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of said steel having microstructure by area percentage including cumulative presence of residual austenite and bainite between 0% and 25%, the remaining microstructure being martensite at least 70%, and with an optional presence of ferrite between 0% and 10%.

The present invention relates to a steel material used as materials for building structures, ship structures, offshore structures, or the like and, more specifically, to a steel material having low yield ratio and excellent weld heat affected zone toughness and a manufacturing method therefor.

This application relates to a resistance spot weld, a resistance spot welding method, a resistance spot welded joint, and a method for manufacturing the resistance spot welded joint. In the resistance spot weld, at least one of steel sheets is a high-strength steel sheet having a prescribed chemical composition. In at least one of a nugget edge region corresponding to a faying interface, the nugget edge region has a metal microstructure including tempered martensite as a main phase. The hardness Hv of the nugget edge region and the hardness Hmw of martensite in the nugget as a whole satisfy formula (4). In at least one of a strong HAZ region corresponding to the faying interface, the hardness Hh of the strong HAZ region and the hardness Hmh of martensite in a prescribed steel sheet satisfy formula (8).

[00001]$\begin{array}{cc}\mathrm{Hv}\le \mathrm{Hmw}-40& \left(4\right)\\ \mathrm{Hh}<\mathrm{Hmh}-25& \left(8\right)\end{array}$

A system for air quenching a heat treated element comprises a tubular component, an internal air quench device moveably disposed within the interior of the tubular component, and an external air quench device moveably disposed about the tubular component. The internal air quench device comprises a nozzle configured to induce an airflow within the tubular component. The external air quenching device can comprise an annular ring disposed about the tubular component that is configured to generate a cone of air about the tubular component.

The present disclosure relates to the technical field of rails welding, and particularly to a method for optimizing microstructure of a rail welded joint, the method comprises the following steps: step 1): subjecting a rail web area of a to-be-cooled welded joint which is obtained by flash butt welding to an accelerated cooling by means of an accelerated cooling device and by using compressed air as a cooling medium, measuring and monitoring temperature of a central position of the rail web of the welded joint while cooling; step 2): stopping the accelerated cooling when the temperature of the central position of the rail web drops to a preset temperature, then placing the welded joint in air and naturally cooling to room temperature, wherein the rail is a pearlite rail having a carbon content of 0.6-0.9 wt %.