Rolled Rod for Cold-Forged Thermally Refined Article

a technology of cold-forged and thermally refined articles, which is applied in the field of rolling rods, can solve the problems of low hydrogen embrittlement resistance, and achieve the effects of excellent cold workability, excellent hydrogen embrittlement resistance, and high strength

Inactive Publication Date: 2018-12-06
NIPPON STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0023]A rolled rod for cold-forged thermally refined articles according to the present invention has an excellent cold workability and has a high strength and an excellent hydrogen embrittlement resistance when subjected to cold forging and thermal refining.

Problems solved by technology

B increases hardenability of steel, as with the alloying elements such as Mo and V. However, when B containing steels are subjected to cold forging and thermal refining, so as to be used as cold-forged thermally refined articles (e.g., bolts) having tensile strengths of 1000 MPa or more, the B containing steels may have low hydrogen embrittlement resistances.

Method used

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  • Rolled Rod for Cold-Forged Thermally Refined Article

Examples

Experimental program
Comparison scheme
Effect test

example 1

[0132]Molten steels having chemical compositions shown in Table 1 were produced.

TABLE 1Chemical Composition (unit is mass percent; balance is Fe and impurities)SteelCSiMnPSCrAlTiBNOCuNiMoVNbfn1fn2a0.310.420.330.0090.0101.060.0360.0210.00250.00440.0013—————0.661.27b0.370.410.390.0080.0111.160.0380.0190.00190.00320.0012—————0.751.05c0.260.650.250.0060.0091.050.0400.0240.00300.00390.0014—————0.612.60d0.350.800.340.0120.0101.210.0390.0220.00270.00410.00130.020.040.04——0.772.35e0.310.650.240.0110.0051.210.0310.0200.00240.00410.00160.020.060.050.03—0.702.71f0.290.410.310.0100.0091.420.0320.0200.00240.00400.00150.020.030.020.010.030.721.32g0.330.650.550.0110.0090.920.0280.0260.00310.00400.0018—————0.711.18h0.230.410.260.0100.0140.720.0310.0240.00230.00380.0014—————0.491.58i0.391.250.390.0100.0051.260.0320.0210.00150.00400.0013—————0.883.21j0.340.360.380.0110.0090.740.0280.0180.00220.00610.0015—————0.620.95k0.290.350.400.0100.0030.750.0320.0220.00190.00400.0014——0.02——0.580.88l0.360.240.660...

example 2

[Test Method]

[0156]A plurality of blooms of a steel a and a steel grade d were produced. The blooms were heated to at heating temperatures T1(° C.) shown in Table 3 and thereafter subjected to the billeting to produce billets each having a cross section of 162 mm×162 mm. The billets were produced into round bars each having a diameter of 20 mm under producing conditions (heating temperature T2, finishing temperature T3, working rate Z, and cooling rate) shown in Table 3.

TABLE 3F + P Pro-Cooling TotalEutectoidHeatingHeatingFinishingWorkingRateArea ferrite AreaTestTemperatureTemperature TemperatureRate Z(° C. / FractionFractionTSColdNumberSteelT1 (° C.)T2 (° C.)T3 (° C.)( / sec)min)Structure(%)(%)(MPa)WorkabilityRemarks13a125010207956.80.5F + P10038650∘InventiveExample14a105010207926.80.5F + P10038645xComparativeExample15a125011007906.80.5F + P10036705xComparativeExample16a125010207893.40.5F + P10025705xComparativeExample17a125010209006.80.5F + P10024715xComparativeExample18a125010207966....

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Abstract

The rolled rod for cold-forged thermally refined articles according to the present invention has a chemical composition consisting, in mass %: C: 0.22 to 0.40%, Si: 0.35 to 1.5%, Mn: 0.20 to 0.40%, P: less than 0.020%, S: less than 0.015%, Cr: 0.70 to 1.45%, Al: 0.005 to 0.060%, Ti: 0.01 to 0.05%, B: 0.0003 to 0.0040%, N: 0.0020 to 0.0080%, and O: 0.0020% or less, with the balance being Fe and impurities, and that satisfies Formula (1) and Formula (2), wherein a total area fraction of pro-eutectoid ferrite and pearlite is 90% or more, an area fraction of the pro-eutectoid ferrite is 30% or more, and the rolled rod has a tensile strength of 700 MPa or less.
0.50≤C+Si/10+Mn/5+5Cr/22≤0.85  (1)
Si/Mn>1.0  (2)

Description

TECHNICAL FIELD[0001]The present invention relates to a rolled rod that is a steel bar or a wire rod as is hot-rolled (as-rolled member), more specifically to a rolled rod for cold-forged thermally refined articles, which refers to a component subjected to cold forging and thermal refining.BACKGROUND ART[0002]In recent years, components such as shafts, bolts, and the like used for components in various kinds of industrial equipment, automobiles and building structures are in some cases produced by cold forging from the viewpoint of dimensional accuracy, yield, and producing cost. While such cold-forged articles are often used as is cold-worked, they are strengthened by thermal refining (quenching and tempering) when it is desired to provide higher strengths. Among such cold-forged articles, those subjected to the thermal refining are referred to as cold-forged thermally refined articles in the present specification.[0003]As a steel material to be subjected to thermal refining to pro...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C22C38/54C21D9/52C21D6/00C21D8/06
CPCC22C38/54C21D9/525C21D6/004C21D6/005C21D8/065C21D2211/002C21D2211/005C22C38/001C22C38/002C22C38/02C22C38/04C22C38/24C21D8/06C21D2211/009C22C38/06C22C38/28C22C38/32C22C38/42C22C38/44C22C38/46C22C38/48C22C38/50F16B35/00
Inventor SANO, NAOYUKIMATSUI, NAOKINEISHI, YUTAKA
Owner NIPPON STEEL CORP
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