A case hardening steel having excellent fatigue resistance is provided at relatively low production cost. A case hardening steel has a chemical composition containing C: 0.10% to 0.30%, Si: 0.10% to 1.20%, Mn: 0.30% to 1.50%, S: 0.010% to 0.030%, Cr: 0.10% to 1.00%, B: 0.0005% to 0.0050%, Sb: 0.005% to 0.020%, and N: 0.0150% or less in a predetermined range, and further containing Al: 0.010%≤Al≤0.120% in the case where B−(10.8/14)N≥0.0003%, and 27/14[N−(14/10.8)B+0.030]≤Al≤0.120% in the case where B−(10.8/14)N<0.0003%.

A case hardening steel having excellent fatigue resistance is provided at relatively low production cost. A case hardening steel has a chemical composition containing C: 0.10% to 0.30%, Si: 0.10% to 1.20%, Mn: 0.30% to 1.50%, S: 0.010% to 0.030%, Cr: 0.10% to 1.00%, B: 0.0005% to 0.0050%, Sb: 0.005% to 0.020%, and N: 0.0150% or less in a predetermined range, and further containing Al: 0.010%≤Al≤0.120% in the case where B−(10.8/14)N≥0.0003%, and 27/14[N−(14/10.8)B+0.030]≤Al≤0.120% in the case where B−(10.8/14)N<0.0003%.

The present invention relates to a zinc plated steel sheet having excellent surface quality and spot weldability, and a manufacturing method therefore. A zinc plated steel sheet according to one aspect of the present invention comprises a base steel sheet and a zinc-based plating layer formed on the surface of the base steel sheet, wherein the GDOES profile of oxygen, which is measured in the depth direction from the surface of the base steel sheet, has a form in which a local minimum point and a local maximum point alternately appear in the depth direction from the surface, and the difference (a local maximum value—a local minimum value) between the oxygen concentration (a local minimum value) at the local minimum point and the oxygen concentration (a local maximum value) at the local maximum point can be 0.1 wt % or more.

Provided are a non-heat treated wire rod having high drawability and impact toughness, and a method for manufacturing the non-heat treated wire rod. The non-heat treated wire rod includes, by wt%, C: 0.02% to 0.30%, Si: 0.05% to 0.8%, Mn: 0.5% to 2.0%, Cr: 1.0% or less, P: 0.03% or less, S: 0.03% or less, sol.Al: 0.01% to 0.07%, N: from greater than 0.01% to 0.02%, Nb: 0.1% or less, V: 0.5% or less, and Ti: 0.1% or less, and a balance of Fe and inevitable impurities, wherein the non-heat treated wire rod has a microstructure including ferrite and pearlite.

Provided are a non-heat treated wire rod having high drawability and impact toughness, and a method for manufacturing the non-heat treated wire rod. The non-heat treated wire rod includes, by wt%, C: 0.02% to 0.30%, Si: 0.05% to 0.8%, Mn: 0.5% to 2.0%, Cr: 1.0% or less, P: 0.03% or less, S: 0.03% or less, sol.Al: 0.01% to 0.07%, N: from greater than 0.01% to 0.02%, Nb: 0.1% or less, V: 0.5% or less, and Ti: 0.1% or less, and a balance of Fe and inevitable impurities, wherein the non-heat treated wire rod has a microstructure including ferrite and pearlite.

This application provides Fe—Mn—Al—C lightweight steel, including: Fe, wherein a weight percentage of the Fe is greater than or equal to 50.4 wt %; Mn, wherein a weight percentage of the Mn is 25-35 wt %; Al, wherein a weight percentage of the Al is 6-12 wt %; C, wherein a weight percentage of the C is 0.8-2.0 wt %; and O, wherein a weight percentage of the O is 0.005-0.6 wt %. This application further provides a terminal to which the Fe—Mn—Al—C lightweight steel is applied, a production method for the Fe—Mn—Al—C lightweight steel, a steel mechanical part, and an electronic device. The lightweight steel in this application has low density, high strength, and high elongation.

An anti-collapse oil casing with high strength and a manufacturing method therefor, comprising the following chemical elements in percentage by mass: C:0.08%-0.18%; Si:0.1%-0.4%; Mn:0.1%-0.28%; Cr:0.2%-0.8%; Mo:0.2%-0.6%; Nb:0.02%-0.08% b; V:0.01%-0.15%; Ti:0.02%-0.05%; B:0.0015%-0.005%; and Al:0.01%-0.05%. The manufacturing method for the anti-collapse oil casing with high strength comprises the steps of: (1) smelting and continuous casting; (2) perforating, rolling, and sizing; (3) controlled cooling: the initial cooling temperature being Ar3+50° C. and the final cooling temperature being ≤80° C.; the cooling step being performed only to the outer surface of the casing without performing to the inner wall of the casing; and the rate of the controlled cooling being 30-70° C./s; (4) tempering; and (5) thermal straightening. The anti-collapse oil casing with high strength according to the present invention has reasonable chemical composition and process design, which not only has excellent economic efficiency, but also has high strength, high toughness and high anti-collapse performance.

Provided is a steel component with excellent surface fatigue strength. The steel component has a nitride compound layer with a thickness of 5.0 μm to 30.0 μm and a hardened layer in an order from a component surface to a component inside, where a thickness of a porous layer on an outermost surface of the nitride compound layer is 3.0 μm or less and 40.0% or less of a thickness of the nitride compound layer, and the hardened layer has a hardness of HV600 or more at a position of 50 μm inward from the component surface, a hardness of HV400 or more at a position from the component surface to the component inside of 400 μm, and a hardness of HV250 or more at a position from the component surface to the component inside of 600 μm.

Provided are a hot-dip zinc plated steel material and a method for preparing same, the hot-dip zinc plated steel material comprising: base iron comprising 0.01-1.6 wt % of Si and 1.2-3.1 wt % of Mn; a Zn—Al—Mg alloy plating layer; and an Al-rich layer formed on the interface of the base iron and Zn—Al—Mg alloy plating layer, wherein the rate of occupied surface area of the Al-rich layer is 70% or higher (including 100%).

Disclosed are a pressure vessel steel sheet and a method for manufacturing the same, the steel sheet comprising: by wt %, 0.10-0.20% of C, 0.15-0.40% of Si, 1.15-1.50% of Mn, 0.45-0.60% of Mo, 0.03-0.30% of Cu, 0.025% or less of P, 0.025% or less of S and 0.005-0.06% of sol. Al; two or more selected from the group consisting of 0.03-0.30% of Cr, 0.002-0.025% of Nb and 0.002-0.025% of Zr, and the balance of Fe and inevitable impurities, wherein the structure comprises a mixture structure of ferrite, perlite and tempered bainite after post weld heat treatment (PWHT) for 60 hours at 600-660° C., and the area fraction of the tempered bainite is at least 10% (excluding 100%).