There is provided a method of manufacturing a high nitrogen duplex stainless steel sheet through a twin roll strip casting process without the occurrence of surface swelling on the high nitrogen duplex stainless steel sheet.

[Summary]

[Assignment] A precipitation hardening martensitic stainless steel having superior strength and improved welding properties.

[Solution] In mass %, C: 0.030 to 0.065%, Si: 1.0 to 2.0%, Mn: 0.51 to 1.50%, P: not more than 0.04%, S: not more than 0.0020%, Ni: 4.0 to 10.0%, Cr: 11.0 to 18.0%, Mo: 0.1 to 1.50%, Cu: 0.30 to 6.0%, Al: 0.005 to 0.2%, Sn: 0.003 to 0.030%, N: 0.001 to 0.015%, Ti: 0.15 to 0.45%, Nb: 0.15 to 0.55%, Ca: not more than 0.0025%, Mg: 0.0001 to 0.0150%, O: not more than 0.01% and Fe and inevitable impurities as a remainder, and satisfying the following formula (1). and cal. (vol. %) defined by the formula (2) is in a range of 1.0 to 9.0.

Sn+0.009Cu0.06(1)

cal. (vol. %)=4.3(1.3Si+Cr+Mo+2.2Al+Ti+Nb)3.9(30C+30N+Ni+0.8Mn+0.3Cu)31.5(2)

In a continuous casting apparatus 100 for casting a stainless steel billet 3c, a long nozzle 2 extending into a tundish 101 is provided at a ladle 1 for pouring a molten stainless steel 3 in the ladle 1 into the tundish 101. Further, a nitrogen gas 4 is supplied as a seal gas around the molten stainless steel 3 in the tundish 101, and continuous casting of the stainless steel billet 3c is performed, in which, while immersing the spout 2a of the long nozzle 2 into the molten stainless steel 3 in the tundish 101, the molten stainless steel 3 is poured through the long nozzle 2 into the tundish 101 and the molten stainless steel 3 in the tundish 101 is poured into a casting mold 105.

There is provided a method for manufacturing a duplex stainless steel sheet having reduced inclusions through argon oxygen decarburization (AOD), ladle treatment (LT), and twin roll strip casting. The method includes deoxidizing molten steel using silicon (Si) during the AOD, wherein the molten steel has a silicon (Si) content of 0.55 wt % to 0.75 wt % at the end of the AOD.

A manufacturing method for strip casting 550 MPa-grade high strength atmospheric corrosion-resistant steel strip, comprising the following steps: 1) smelting, where the chemical composition of a molten steel is that: C is between 0.03-0.08%, Si0.4%, Mn is between 0.6-1.5%, P is between 0.07-0.22%, S0.01%, N0.012%, Cu is between 0.25-0.8%, Cr is between 0.3-0.8%, and Ni is between 0.12-0.4%, additionally, also comprised is at least one micro-alloying element among Nb, V, Ti, and Mo, where Nb is between 0.01-0.08%, V is between 0.01-0.08%, Ti is between 0.01-0.08%, and Mo is between 0.1-0.4%, and where the remainder is Fe and unavoidable impurities; 2) strip casting, where a 1-5 mm-thick cast strip is casted directly; 3) cooling the strip, where the cooling rate is greater than 20 C./s; 4) online hot rolling the cast strip, where the hot rolling temperature is between 1050-1250 C., where the reduction rate is between 20-50%, and where the deformation rate is >20 s.sup.1; austenite online recrystallizing after hot rolling, where the thickness of the hot rolled strip is between 0.5-3.0 mm; and, 5) cooling and winding, where the cooling rate is between 10-80 C./s, and where the winding temperature is between 570-720 C. The microscopic structure of a steel strip acquired is primarily constituted by fine polygonal ferrite and pearlite.

The present invention pertains to a hot-rolled ferritic stainless steel sheet having excellent formability, which has an R-bar value of at least 1.08 and satisfies TS/YS1.5 representing the ratio of tensile strength (TS) to yield strength (YS) after a steel, containing 0.001-0.1% of C, 10.0-14.0% of Cr, 0.001-0.5% of Ti, 0.001-0.5% of Nb, 0.001-1.5% of Ni, 0.001-1.5% of Mn, 0.001-1.0% of Cu, 0.001-2.0% of Si, 0.001-0.1% of N, and 0.1% or less of Al, with the remainder comprising Fe and inevitable impurities, is hot-rolled and then pre-rolled at a reduction ratio of 30% or more.

A method for manufacturing a plate, a band, or a coil of hot-rolled steel is provided. The method includes providing an ingot or a slab of steel with a desired composition and a microstructure composed of austenite and 35 to 65% ferrite by volume and hot rolling the ingot or slab at a temperature between 1150 and 1280 C. to obtain a plate, a band or a coil. A method for manufacturing a hot-rolled bar or wire of steel, a steel profile and a forged steel piece are also provided.

In a continuous casting method for casting aluminum-deoxidized molten stainless steel 1 by using a continuous casting apparatus 100 in which a long nozzle 3 extending into a tundish 101 is provided at a ladle 2, the molten stainless steel 1 is poured into the tundish 101 through the long nozzle 3, while the spout 3a of the long nozzle 3 is being immersed in the molten stainless steel 1 that has been poured, and the molten stainless steel 1 in the tundish 101 is poured into a casting mold 105. A TD powder 5 is sprayed so that the powder covers the surface of the molten stainless steel 1 in the tundish 101, and nitrogen gas is supplied around the molten stainless steel 1. A calcium-containing material is added to the molten stainless steel 1 in a state other than a state of retention in the tundish 101.

In a continuous casting method for casting an aluminum-deoxidized molten stainless steel 1 by using a continuous casting apparatus 100 in which a long nozzle 3 extending into a tundish 101 is provided at a ladle 2, the molten stainless steel 1 is poured through the long nozzle 3 into the tundish 101, while immersing a spout 3a into the poured molten stainless steel 1, and the molten stainless steel 1 in the tundish 101 is poured into a casting mold 105. A TD powder 5 is sprayed so that the powder covers the surface of the molten stainless steel 1 in the tundish 101, a nitrogen gas is supplied around the molten stainless steel 1, and a calcium-containing material is added to the molten stainless steel 1 in the tundish 101. The surface of the molten stainless steel 1 after casting is ground.

This disclosure is directed at methods for mechanical property improvement in a metallic alloy that has undergone one or more mechanical property losses as a consequence of forming an edge, such as in the formation of an internal hole or an external edge. Methods are disclosed that provide the ability to improve mechanical properties of metallic alloys that have been formed with one or more edges placed in the metallic alloy by a variety of methods which may otherwise serve as a limiting factor for industrial applications.