A case hardening steel material having a chemical composition consists of, by mass percent, C: 0.15 to 0.23%, Si: 0.01 to 0.15%, Mn: 0.65 to 0.90%, S: 0.010 to 0.030%, Cr: 1.65 to 1.80%, Al: 0.015 to 0.060%, and N: 0.0100 to 0.0250%, further containing, as necessary, one or more kinds selected from Cu and Ni of predetermined amounts, the balance being Fe and impurities; 25≦Mn/S≦85, 0.90≦Cr/(Si+2Mn)≦1.20, and 1.16Si+0.70Mn+Cr≧2.20; P, Ti and O in the impurities being P≦0.020%, Ti≦0.005%, and O≦0.0015%; and having a structure consisting of 20 to 70% in an area ratio being ferrite; and the portion other than the ferrite being one or more kinds of pearlite and bainite. The steel material is used suitably as a raw material of the carburized part such as a CVT pulley shaft.

The present invention discloses a method for heat treatment of hypereutectoid steel rail, including the following steps: holding the temperature of the steel rail of which temperature is above 900° C. after finish rolling, conducting a first cooling stage for the steel rail at the first cooling speed after the temperature holding to reduce the temperature of railhead surface layer of the steel rail to 700-750° C., conducting a second cooling stage for the steel rail at the second cooling speed to reduce the temperature of railhead surface layer of the steel rail to 550° C., conducting a third cooling stage for the steel rail at the third cooling speed to reduce the temperature of railhead surface layer of the steel rail to 450° C. or less, and continuing to cool the steel rail in the air. While obtaining good tensile property, the steel rail treated by the method for heat treatment provided by the present invention can effectively reduce secondary cementite and have excellent resistance to abrasion and contact fatigue. The product is particularly suitable for heavy rails.

A process for producing a spring or torsion bar from a steel wire by hot forming may involve providing a steel wire; thermomechanically forming the steel wire; cooling the steel wire thermomechanically; cutting the steel wire to length to give rods; heating the rods; hot forming the rods; and tempering the rods to give a spring or torsion bar, comprising quenching the rods to give a spring or torsion bar to a first cooling temperature, reheating the spring or torsion bar to a first annealing temperature, and cooling the spring or rod to a second cooling temperature. Further, in some examples, the cooling of the steel wire may be cooled to a temperature below a minimum recrystallization temperature such that at least a partly ferritic-pearlitic structure is established in the steel wire.”

Disclosed are a drill bit for drilling and a method for manufacturing same, in which the hardness of a body part of a shank can be selectively improved by performing rapid cooling in a forced cooling method after performing rapid heating selectively only on the body part of the shank in a high-frequency induction heating method after completing infiltration.

A steel wire for drawing includes, as a chemical composition, by mass %: C: 0.9% to 1.2%, Si: 0.1% to 1.0%, Mn: 0.2% to 1.0%, and Cr: 0.2% to 0.6%, limits Al, N, P, and S to be predetermined ranges, and includes one or more selected from the group consisting of Mo: 0% to 0.20%, and B: 0% to 0.0030%, a remainder of Fe and impurities; in which a metallographic structure includes pearlite, a volume fraction of the pearlite is 95% or higher, an average lamellar spacing of the pearlite is 50 nm to 75 nm, an average length of cementite in the pearlite is 2.0 μm to 5.0 μm, and a ratio of the number of grains of cementite with a length of 0.5 μm or smaller to the cementite in the pearlite is 20% or lower.

A forging process is conducted in a temperature range of 350-600° C. on at least a portion that is required to have a fatigue strength in an intermediate forged product having a ferrite and pearlite texture obtained by conducting a hot forging on a steel in which N is not greater than an amount at which N is unavoidably dissolved as a solid, thereby improving strength of the portion that is required to have a fatigue strength. With this, there is provided a forged product having a good strength and a low price.

A manufacturing method and a manufacturing apparatus for a head hardened rail to which various alloy elements are added and which is excellent in hardness and toughness of a head portion surface layer. The method includes, when forcibly cooling at least a head portion of a hot-rolled rail or a heated rail, starting the forcible cooling from a state where a surface temperature of the head portion of the rail is not less than an austenite range temperature, and performing the forcible cooling at a cooling rate of 10° C./sec or more until the surface temperature reaches 500° C. or more and 700° C. or less after the forcible cooling is started.

A rail comprises a predetermined chemical composition. In a hardness distribution in a region from a rail head surface to a depth of 16.0 mm, a part having higher hardness than V1 that is minimum hardness in a first internal region is present in a second internal region, and hardness of the rail head surface is HBW 400 to 520 and average hardness in the region from the rail head surface to the depth of 16.0 mm is HBW 350 or more.

The present invention relates to a wire rod of which softening heat treatment can be omitted, and a manufacturing method therefor. One embodiment of the present invention provides a wire rod of which softening heat treatment can be omitted, and a manufacturing method therefor, the wire rod comprising, by wt %, 0.2-0.45% of C, 0.02-0.4% of Si, 0.3-1.5% of Mn, 0.3-1.5% of Cr, 0.02-0.05% of Al, 0.01-0.5% of Mo, 0.01% or less of N, and the balance of Fe and other inevitable impurities, and having a microstructure consisting of, by area %, 40% or more of proeutectoid ferrite based on an equilibrium phase, 40% or more of regenerated pearlite and bainite, and 20% or less of martensite, and wherein the colony average size of the pearlite in the region amounting to ⅖ to ⅗ of the diameter is 5 μm or less.

Provided is a hot rolled steel sheet comprising a predetermined chemical composition, and a metallic structure comprising, by area ratio, pearlite: 90 to 100%, pseudo pearlite: 0 to 10%, and pro-eutectoid ferrite: 0 to 1%, wherein the pearlite has an average lamellar spacing of 0.20 μm or less, and the pearlite has an average pearlite block size of 20.0 μm or less. Provided is a method for producing a hot rolled steel sheet comprising heating a slab to 1100° C. or more, hot rolling where an exit side temperature of finishing rolling is 820 to 920° C., primary cooling the steel sheet down to an Ae1 point by an average cooling rate of 40 to 80° C./s, then secondary cooling the steel sheet from the Ae1 point down to a coiling temperature by an average cooling rate of less than 20° C./s, and coiling the steel sheet at a coiling temperature of 540 to 700° C.