Provided herein is a high-strength seamless steel pipe, and a method for manufacturing same. A high-strength seamless steel pipe of the present invention has a yield strength of 758 MPa or more, and a K.sub.ILIMIT value of 23.0 MPa√m or more as an evaluation index of sulfide stress corrosion cracking resistance.

Provided herein is a high-strength seamless steel pipe, and a method for manufacturing same. A high-strength seamless steel pipe of the present invention has a yield strength of 758 MPa or more, and a K.sub.ILIMIT value of 23.0 MPa√m or more as an evaluation index of sulfide stress corrosion cracking resistance.

A method for controlling carbide network in a bearing steel wire rod by controlling cooling and rolling, comprises the following steps: rapidly rolling a bar to a wire rod and spinning it into a loose coil, controlling the rolling temperature at 780° C.-880° C.; and the spinning temperature at 750° C.-850° C.; carrying out on-line controlling cooling of continuous loose coils using EDC water bath austempering cooling process, controlling the cooling rate at 2.0° C./s-10° C./s, and controlling the final cooling temperature within 620-630° C.; after EDC water bath austempering cooling, using slow cooling under a cover, and the temperature is controlled to be 400° C.-500° C. when being removed out of the cover; after slow cooling, collecting coils, and cooling in air to the room temperature.

A method for controlling carbide network in a bearing steel wire rod by controlling cooling and rolling, comprises the following steps: rapidly rolling a bar to a wire rod and spinning it into a loose coil, controlling the rolling temperature at 780° C.-880° C.; and the spinning temperature at 750° C.-850° C.; carrying out on-line controlling cooling of continuous loose coils using EDC water bath austempering cooling process, controlling the cooling rate at 2.0° C./s-10° C./s, and controlling the final cooling temperature within 620-630° C.; after EDC water bath austempering cooling, using slow cooling under a cover, and the temperature is controlled to be 400° C.-500° C. when being removed out of the cover; after slow cooling, collecting coils, and cooling in air to the room temperature.

A seamless steel pipe of the present invention is a seamless steel pipe having a composition including, in mass %, C: 0.01 to 0.12%, Si: 0.01 to 0.8%, Mn: 0.10 to 2.00%, P: 0.050% or less, S: 0.040% or less, Al: 0.010 to 0.100%, Cu: 0.03 to 0.80%, Ni: 0.01 to 0.50%, Mo: 0.01 to 0.20%, Sb: 0.002 to 0.50%, Cr: 0.004% or less, W: 0.002% or less, and the balance Fe and incidental impurities, and a structure including a ferrite phase having an area percentage of 50 to 65%, a pearlite phase having an area percentage of 2% or less, and one or both of a bainite phase and a martensitic phase representing the remainder, the seamless steel pipe having a yield strength of 230 MPa or more, and a tensile strength of 380 MPa or more.

A seamless steel pipe of the present invention is a seamless steel pipe having a composition including, in mass %, C: 0.01 to 0.12%, Si: 0.01 to 0.8%, Mn: 0.10 to 2.00%, P: 0.050% or less, S: 0.040% or less, Al: 0.010 to 0.100%, Cu: 0.03 to 0.80%, Ni: 0.01 to 0.50%, Mo: 0.01 to 0.20%, Sb: 0.002 to 0.50%, Cr: 0.004% or less, W: 0.002% or less, and the balance Fe and incidental impurities, and a structure including a ferrite phase having an area percentage of 50 to 65%, a pearlite phase having an area percentage of 2% or less, and one or both of a bainite phase and a martensitic phase representing the remainder, the seamless steel pipe having a yield strength of 230 MPa or more, and a tensile strength of 380 MPa or more.

A flux-cored wire comprising a flux which is a core and a hoop which is an outer skin or sheath is described. The flux includes a strong deoxidizing metal element containing Mg and Al, and a fluoride powder. At least 60 mass % of a strong deoxidizing metal powder related to the strong deoxidizing metal element has a grain size of at most 150 μm. At least 60 mass % of the fluoride powder has a grain size of at most 75 μm. The flux is present at a concentration of 10-30 mass % relative to a total mass of the flux-cored wire. The flux-cored wire also requires a specific composition of elements.

A flux-cored wire comprising a flux which is a core and a hoop which is an outer skin or sheath is described. The flux includes a strong deoxidizing metal element containing Mg and Al, and a fluoride powder. At least 60 mass % of a strong deoxidizing metal powder related to the strong deoxidizing metal element has a grain size of at most 150 μm. At least 60 mass % of the fluoride powder has a grain size of at most 75 μm. The flux is present at a concentration of 10-30 mass % relative to a total mass of the flux-cored wire. The flux-cored wire also requires a specific composition of elements.

A cast steel alloy for an engine of a vehicle is provided. The cast steel alloy comprises 0.29 to 0.65 weight percent (wt %) carbon, 0.40 to 0.80 wt % silicon, 0.6 to 1.5 wt % manganese, up to 0.03 wt % phosphorus, 0.04 to 0.07 wt % sulfur, 0.8 to 1.4 wt % chromium, 0.2 to 0.6 wt % nickel, 0.15 to 0.55 wt % molybdenum, 0.25 to 2.0 wt % copper, up to 0.03 wt % titanium, 0.07 to 0.17 wt % vanadium, 0.02 to 0.06 wt % aluminum, up to 0.03 wt % nitrogen (N), and 0.01 to 0.06 wt % of at least one of cerium (Ce) and lanthanum. The cast steel alloy has unexpected and unconventional results such as reduced ferrite and enhanced strengths.

A cast steel alloy for an engine of a vehicle is provided. The cast steel alloy comprises 0.29 to 0.65 weight percent (wt %) carbon, 0.40 to 0.80 wt % silicon, 0.6 to 1.5 wt % manganese, up to 0.03 wt % phosphorus, 0.04 to 0.07 wt % sulfur, 0.8 to 1.4 wt % chromium, 0.2 to 0.6 wt % nickel, 0.15 to 0.55 wt % molybdenum, 0.25 to 2.0 wt % copper, up to 0.03 wt % titanium, 0.07 to 0.17 wt % vanadium, 0.02 to 0.06 wt % aluminum, up to 0.03 wt % nitrogen (N), and 0.01 to 0.06 wt % of at least one of cerium (Ce) and lanthanum. The cast steel alloy has unexpected and unconventional results such as reduced ferrite and enhanced strengths.