High-hardenability, medium-carbon, low-alloy round steel for fasteners and the manufacturing method thereof

a technology of low-alloy round steel and high-hardenability, which is applied in the field of high-hardenability, medium-carbon, low-alloy round steel for fasteners and the manufacturing method thereof, can solve the problems of increasing the transition temperature of ductile-brittle, reducing plasticity and toughness, and achieving the effect of improving the hardenability of steel bars and reducing the manufacture cost of alloy raw materials

Inactive Publication Date: 2019-09-19
JIANGYIN XINGCHENG SPECIAL STEEL WORKS CO LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0017]Compared with prior arts, the advantages of present invention focus on: taking a very small amount of alloy elements B and Ti to replace parts of noble metal elements Mo and Ni so as to improve hardenability of steel bar, manufacturing the fasteners with maximum diameter up to 65 mm, and on the basis of satisfying the mechanical and physical requirements of quenched martensite content in steel core being more than 90%, difference of the hardness of the whole cross-section being within 30 HV, impact energy measured at −20° C. being z,28 27 J in standard ISO 898-1, obviously reducing the manufacture cost of alloy raw material.

Problems solved by technology

C is used for improving hardenability, strength and hardness, but it decreases plasticity and toughness, and increases ductile-brittle transition temperature.

Method used

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  • High-hardenability, medium-carbon, low-alloy round steel for fasteners and the manufacturing method thereof
  • High-hardenability, medium-carbon, low-alloy round steel for fasteners and the manufacturing method thereof

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embodiment 1

[0022]The diameter of the steel for fastener relating to the present embodiment is 64 mm, and the steel is processed with heat treatment according to the requirements of 10.9 grade fastener, the chemical constituents by mass percentage are as follows: C: 0.42%, Si: 0.25%, Mn: 0.95%, Cr: 1.10%, Mo: 0.10%, Ni: 0.12%, Cu: 0.12%, Al: 0.018%, B: 0.0020%, Ti: 0.025%, the balance is Fe and unavoidable impurity elements.

[0023]The manufacturing processes are as follows: the main raw materials are processed, in sequence, by electric furnace smelting, LF refining, VD degassing to obtain molten steel, feeding Ti wires and ferroboron after LF refining; the molten steel is casted into a continuous casting billet by adopting low superheat degree of 15˜30° C. and under a full argon protection, the continuous casting billet is slowly cooled for 32 hours; the continuous casting billet is heated to 1250° C. and kept warm for 4 hours in the furnace, and then is taken out of the furnace; after high-pres...

embodiment 2

[0024]The diameter of the steel for fastener relating to the present embodiment is 54 mm, and the steel is processed with heat treatment according to the requirements of 10.9 grade fastener, the chemical constituents by mass percentage are as follows: C: 0.37%, Si: 0.22%, Mn: 0.95%, Cr: 1.10%, Mo: 0.08%, Ni: 0.10%, Cu: 0.10%, Al: 0.022%, B: 0.0023%, Ti: 0.028%, the balance is Fe and unavoidable impurity elements.

[0025]Above round steel is processed, in sequence, by electric furnace smelting, LF refining, VD degassing to obtain molten steel, feeding Ti wires and ferroboron after LF refining; the molten steel is casted into a continuous casting billet by adopting low superheat degree of 15˜30° C. and under a full argon protection, the continuous casting billet is fed warmly at a temperature of 400° C.; the continuous casting billet is heated to 1200° C. and kept warm for 4 hours in the furnace, and then is taken out of the furnace; after high-pressure water descaling, the continuous c...

embodiment 3

[0026]The diameter of the steel for fastener relating to present embodiment is 48 mm, and the steel is processed with heat treatment according to the requirements of 8.8 grade fastener, the chemical constituents by mass percentage are as follows: C: 0.36%, Si: 0.21%, Mn: 0.92%, Cr: 1.08%, Mo: 0.08%, Ni: 0.06%, Cu: 0.08%, Al: 0.023%, B: 0.0025%, Ti: 0.026%, the balance is Fe and unavoidable impurity elements.

[0027]Above round steel is processed, in sequence, by KR pre-treatment, converter smelting, LF refining, RH degassing to obtain molten steel, feeding Ti wires and ferroboron after LF refining; the molten steel is casted into a continuous casting billet by adopting low superheat degree of 15˜30° C. and under a full argon protection, the continuous casting billet is fed warmly at a temperature of 400° C.; the continuous casting billet is heated to 1200° C. and kept warm for 4 hours in the furnace, and then is taken out of the furnace; after high-pressure water descaling, the contin...

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Abstract

The present invention relates to a high-hardenability, medium-carbon, low-alloy round steel for fasteners, the chemical constituents by mass percentage are as follows: C: 0.36˜0.44%, Si: 0.15˜0.40%, Mn: 0.80˜1.00%, Cr: 1.00˜1.15%, Mo: 0.05˜0.25%, Ni: 0.05˜0.25%, Cu: 0.05˜0.25%, Al: 0.015˜0.050%, B: 0.0010˜0.0050%, Ti: 0.020˜0.050%, the balance is Fe; the maximum diameter of the round steel is 65 mm. The manufacturing process are as follows: the raw materials are processed, in sequence, by converter smelting, LF refining, RH/VD degassing to obtain molten steel, feeding Ti wires and ferroboron, continuous casting, rolling into the bar, obtaining the quenched and tempered round steel after quenching and tempering treatment; the quenched and tempered round steel is able to be directly used in processing fasteners which meet ISO 898-1 standard for grade 10.9, such as bolts and the like.

Description

TECHNICAL FIELD[0001]The present invention relates to a field of manufacturing special round steel, and specially relates to a high-hardenability, medium-carbon, low-alloy round steel, which satisfies the mechanical performance requirements of Ø65 mm fasteners after quenching and tempering treatment, and the manufacturing method thereof.BACKGROUND ART[0002]At present market, the fasteners are manufactured mostly according to the requirements of standard ISO898-1: Mechanical properties of fasteners—Part 1: Bolts, screws and studs. The table 3 of this standard puts forward very strict requirements of mechanical and physical performance for fasteners, wherein the difficulties are: {circle around (1)} after quenching, the martensite structure in core of the steel should be 90% or more; {circle around (2)} on the basis of satisfying the strength and the hardness in each strength grades, the difference of HV 0.3 hardness between surface and core should be less than 30 HV; {circle around (...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C21D6/00C22C38/54C22C38/50C22C38/44C22C38/42C22C38/06C22C38/04C22C38/02C21D1/18
CPCC22C38/50C22C38/54C22C38/02C22C38/06C22C38/04C22C38/44C21D1/18C21D6/005C21D6/004C22C38/42C21D6/008C21D2211/008C21D8/065C21D9/0093C21D9/525
Inventor JI, LINGXU, XIAOHONGHUANG, ZHENSHAO, SHUYANLIU, XUEWENKONG, XIANGWEIHU, SHAOXINZHANG, XUDONG
Owner JIANGYIN XINGCHENG SPECIAL STEEL WORKS CO LTD
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