The present invention provides a novel heat exchange medium to replace lead. A carbon-steel wire 1A heated in a heating furnace 11 is passed through a bath 12A filled with a liquid-phase Mg—Al—Ca alloy 20 obtained by melting a Mg—Al—Ca alloy in which the main constituent elements are Mg (magnesium), Al (aluminum) and Ca (calcium). When it passes through the bath 12A, the carbon-steel wire 1A, which has been heated for example to about 950° C. in the heating furnace 11, is cooled to about 550° C. The Mg—Al—Ca alloy is non-toxic and has no environmental impact as well.

The present invention relates to a steel material for a pressure vessel, which is used in a hydrogen sulfide atmosphere, and, more specifically, to a steel material having excellent hydrogen induced cracking (HIC) resistance, and a manufacturing method therefor.

Provided are a gradient steel material having a surface layer with ferrite and an inner layer with ferrite+pearlite, and a manufacturing method, the weight percentages of the components are: C≤0.15%, Si≤1%, Mn≤1.5%, the balance of Fe and inevitable impurities, and the surface layer of the steel material is ferrite, the inner layer is ferrite+pearlite. The manufacturing method thereof includes: smelting, casting, rolling, heat treatment; wherein, in the heat treatment step, the steel material is heated above the austenitizing temperature Ac3, and hold at the temperature more than 3 min to ensure that the material is completely austenitized; subsequently, it is cooled to a temperature below Ar1 at a cooling rate lower than 0.5° C./s. The present steel material does not need to be obtained by means of the compound preparation of different materials, and is only processed and prepared by a single material, the process is short, the procedure is simple, and the cost is low.

A high-strength steel sheet having a microstructure represented by, in area %, martensite: 5% or more; ferrite: 20% or more; and pearlite: 5% or less. A ratio of the number of bulging type martensite grains to the number of martensite grains on grain boundary triple points of a matrix is 70% or more, wherein: the bulging type martensite grain is on one of the grain boundary triple points of the matrix; and at least one of grain boundaries of the bulging type martensite grain, the grain boundaries connecting two adjacent grain boundary triple points of the bulging type martensite grain and grains of the matrix, has a convex curvature to an outer side with respect to line segments connecting the two adjacent grain boundary triple points. An area ratio VM/A0 is 1.0 or more.

A hot rolled steel having a composition including comprising of the following elements 0.01%≤Carbon≤0.1%, 0.2%≤Manganese≤2%, 0.2%≤Silicon≤1.5%, 0.01%≤Aluminum≤2%, 0.1%≤Tin≤1%, 0.1%≤Copper≤0.5%, 0.001%≤Niobium≤0.1%, 0.002%≤Phosphorus≤0.02%, 0%≤Sulfur≤0.005%, 0%≤Nitrogen≤0.01%, with 0.3%≤Sn+Cu≤1.2% and can contain one or more of the following optional elements 0%≤Titanium≤0.1%, 0%≤Vanadium≤0.1%, 0%≤Chromium≤1%, 0%≤Molybdenum≤0.5%, 0%≤Calcium≤0.01%, 0%≤Boron≤0.01%, 0%≤Magnesium≤0.05%, 0%≤Calcium≤0.01%, 0%≤Cerium≤0.1%, 0%≤Boron≤0.05%, 0%≤ Nickel≤0.01%, the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of said steel sheet including in area fraction, 75% to 95% Ferrite, 1% to 15% Pearlite and optionally Bainite is between 0% and 25% wherein the average grain size of all the microstructural constituent is less than 15 microns.

The invention relates to a steel sheet for tool, and method for manufacturing thereof. An embodiment of the present invention is a steel sheet for a tool comprising 0.4 to 0.6 wt % of C, 0.05 to 0.5 wt % of Si, 0.1 to 1.5 wt % of Mn, 0.05 to 0.5 wt % of V, 0.1 to 2.0 wt % of at least of one or two components selected from the group comprising Ni, Cr, Mo, and combinations thereof, and the balance of Fe and inevitable impurities, with respect to 100 wt % of the total steel sheet, and provides a steel sheet for a tool of which the deviation of Rockwell hardness by the position in the width direction is within 5 HRC, and the ratio of those having a wave height in the longitudinal direction within 20 cm is 90% or more with respect to the wave height per 1 m of the steel sheet comprising the central portion in the longitudinal direction of the steel sheet for a tool.

A hot-press molding method of the present disclosure includes a first heating process in which a steel plate is heated and the entire steel plate becomes austenite, a first cooling process in which a cooling rate of the steel plate after the first heating process is partially changed, a first region which is a part of the steel plate is transformed into martensite, and a second region other than the first region remains as austenite, a second heating process in which the entire steel plate is reheated and the first region becomes tempered martensite, and a second cooling process in which the entire steel plate after the second heating process is cooled. At least one of the first cooling process and the second cooling process is performed during a molding process in which the steel plate is press-molded on a molding die.

The invention relates to a 9Ni steel plate for ship LNG storage tank with high strength and low yield ratio. According to the mass percentage, the chemical constituents are C: 0.02-0.05%, Si: 0.10-0.30%, Mn: 0.50-0.80%, Ni: 8.90-9.50%, P: ≤0.0070%, s: ≤0.0020%, Cr: 0.10-0.25%, Alt: 0.010-0.035%, Nb: 0.010-0.020%, Ca: 0.0005-0.0030%, O: ≤0.0012%, N: ≤0.004%, H: ≤0.00015%, and the balance is Fe and unavoidable impurity elements. The production process flow is: smelting in a converter or electric furnace->RH vacuum degassing->LF refining->RH high vacuum degassing->Ca Treatment->continuous casting->slab slow cooling treatment->slab surface cleaning->heating->rolling ->quenching->tempering. For the 9Ni steel, especially the 9Ni thin steel plate, the invention adopts the constituents design of low C, 9% Ni, addition of Nb and Cr. The steel plate is subject to high-temperature hot rolling, and then QLT heat treatment process to obtain 9Ni steel with good strength, toughness and low yield ratio.

This hot-rolled steel sheet has a predetermined chemical composition, in a microstructure, in terms of area%, residual austenite is less than 3.0%, ferrite is less than 15.0%, and pearlite is less than 5.0%, an E value that indicates periodicity of the microstructure is less than 10.7, and an I value that indicates uniformity of the microstructure is less than 1.020, a standard deviation of a Mn concentration is 0.60 mass% or less, and a tensile strength is 780 MPa or more.

An upper member of a steel piston has a chemical composition which consists of, in mass %, C: 0.15 to 0.30%, Si: 0.02 to 1.00%, Mn: 0.20 to 0.80%, P: 0.020% or less, S: 0.028% or less, Cr: 0.80 to 1.50%, Mo: 0.08 to 0.40%, V: 0.10 to 0.40%, Al: 0.005 to 0.060%, N: 0.0150% or less, O: 0.0030% or less, and the balance: Fe and impurities, and satisfies Formula (1) and Formula (2), in which, at a cross section parallel to the axial direction of the upper member, the number of Mn sulfides is 100.0 per mm.sup.2 or less, the number of coarse Mn sulfides having an equivalent circular diameter of 3.0 μm or more is within a range of 1.0 to 10.0 per mm.sup.2, and the number of oxides is 15.0 per mm.sup.2 or less.
0.42≤Mo+3V≤1.50  (1)
V/Mo≥0.50  (2)