An NPR non-magnetic steel material for rock bolt and a production method thereof are disclosed. The NPR non-magnetic steel material for rock bolt has a composition, in weight percent, consisting of: C: 0.4-0.7%, Mn: 15-20%, Cr: 1-18%, Si: 0.3-3%, Ca: 0.05-0.15%, Cu: ≤0.03%, Ni: ≤0.02%, S: ≤0.001%, P: ≤0.001%, and the rest being Fe and unavoidable impurity elements. The NPR non-magnetic steel material for rock bolt and the production method thereof effectively solve the problems of steel materials for rock bolt in the prior art such as strong magnetism, low tensile strength and low effective elongation. The NPR non-magnetic steel material for rock bolt has a fully-austenitized structure and is non-magnetic, its yield strength is adjustable in the range of 600-1000 MPa, and its elongation is adjustable in the range of 20-60%.

A method of heat treating a fastening member having a head portion, a shank portion, and a thread portion includes hardening the fastening member to a first hardness value. Hardening of the fastening member includes heating the fastening member at a first pre-set temperature value. The method also includes tempering the fastening member at a second pre-set temperature value to a second hardness value. The method further includes induction tempering the thread portion of the fastening member. Induction tempering of the thread portion includes heating the thread portion at a third pre-set temperature value to a third hardness value. The third hardness value of the thread portion is less than the second hardness value of the head portion and the shank portion.

A steel for a high-strength bolt that includes from 0.50 mass % to 0.65 mass % carbon, from 1.5 mass % to 2.5 mass % silicon, 1.0 mass % or more chromium, 0.4 mass % or less manganese, greater than 1.5 mass % molybdenum, 0.03 mass % or less phosphorus and sulfur combined, and balance iron and inevitable impurities.

A method for producing a bimetallic screw with a tip element and a drive element, in which a first blank comprising a steel with 0.07 to 0.14% by weight carbon, 13 to 15% by weight chromium, 1.3 to 1.7% by weight molybdenum, 1.5 to 2.0% by weight nickel and 1.0 to 1.5% by weight manganese is provided and the tip element is made from the first blank. A bimetallic screw with a tip element and a drive element is also provided, the tip element and the drive element having a different material composition, and the tip element comprising at least in some areas a steel with 0.07 to 0.14% by weight carbon, 13 to 15% by weight chromium, 1.3 to 1.7% by weight molybdenum, 1.5 to 2.0% by weight nickel and 1.0 to 1.5% by weight manganese.

A mine bolt includes an elongated body having a first end and a second end positioned opposite the first end, with the elongated body having a first threaded section, a second threaded section, and a non-threaded section positioned between the first threaded section and the second threaded section. The non-threaded section is configured to yield under loading when the mine bolt is installed with grout in a bore hole.

The present disclosure provides a wire rod for cold heading that can shorten the spheroidizing heat treatment time, processed products using the same, and manufacturing method thereof. A wire rod for cold heading according to an embodiment of present disclosure includes, in percent (%) by weight of the entire composition, C: 0.15 to 0.5%, Si: 0.1 to 0.4%, Mn: 0.3 to 1.5%, Cr: 0.1 to 1.5%, Al: 0.02 to 0.05%, N: 0.004 to 0.02%, at least one selected from the group consisting of Nb: 0.001 to 0.03%, V: 0.01 to 0.3%, Mo: 0.01 to 0.5%, Ti: 0.001 to 0.03%, and the remainder of iron (Fe) and other inevitable impurities, and the microstructure has a long and short axis ratio of cementite present in pearlite colonies of 200:1 or less.

A bolt of the present invention is a high-strength bolt of high-carbon steel having a tempered martensite structure, wherein the composition of the bolt comprises: 0.50 mass % or more and 0.65 mass % or less of carbon (C); 1.5 mass % or more and 2.5 mass % or less of silicon (Si); 1.0 mass % or more and 2.0 mass % or less of chromium (Cr); 0.2 mass % or more and 1.0 mass % or less of manganese (Mn); and 1.5 mass % or more and 5.0 mass % or less of molybdenum (Mo); a total content of impurities being phosphor (P) and sulfur (S) is 0.03 mass % or more; and the remaining is iron (Fe). Furthermore, the carbon concentration satisfies the following Formula (1): 0.75X<1 . . . Formula (1) wherein, in Formula (1), X represents surface carbon concentration/inner carbon concentration. Therefore, the bolt of the present invention has low quench cracking susceptibility and excellent delayed fracture resistance, because an increase in temperature at which martensite transformation occurs (Ms point) on the surface side is held down.

An NPR steel material for rock bolt and a production method thereof are disclosed. The NPR steel material for rock bolt has a composition, in weight percent, consisting of: C: 0.4-0.7%, Mn: 15-20%, Si: 0.1%, Cu: 0.03%, Cr: 0.01%, Ni: 0.02%, S: 0.001%, P: 0.001%, and the rest being Fe and unavoidable impurity elements. The NPR steel material for rock bolt and the production method thereof effectively solve the problem that rock bolts in the prior art have low tensile strength and low effective elongation. The NPR steel material for rock bolt has a yield strength adjustable in the range of 500-1100 MPa, and an elongation adjustable in the range of 10-80%.

A bolt of the present invention has a composition comprising: 0.50 mass % or greater and 0.65 mass % or less of carbon (C), 1.5 mass % or greater and 2.5 mass % or less of silicon (Si), 1.0 mass % or greater and 2.0 mass % or less of chromium (Cr), 0.2 mass % or greater and 1.0 mass % or less of manganese (Mn), 1.5 mass % or greater and 5.0 mass % or less of molybdenum (Mo), wherein a total amount of phosphorous (P) and sulfur (S) as impurities is 0.03 mass % or less, the remaining is iron (Fe), and the bolt comprises an iron based oxide film with a film thickness of 3 m or greater and 20 m or less on the surface thereof. The bolt has excellent delayed fracture resistance and reliably provides a fastening axial force.

When a rod-shaped workpiece (W) having an outer peripheral surface with a circular cross section is inductively heated to a quenching temperature while being conveyed at a predetermined velocity along an axial direction of the rod-shaped workpiece (W), the rod-shaped workpiece (W) being currently conveyed is heated to a predetermined temperature equal to or lower than the quenching temperature by a first heating coil (2A), which is electrically connected to a first high-frequency power supply (3) and has a constant output. Then, the rod-shaped workpiece (W) being currently conveyed is heated so as to be maintained at the quenching temperature by a second heating coil (2B), which is electrically connected to a second high-frequency power supply (4) and has a constant output.