JPS61261431A - Manufacture of high strength and toughness steel having high yield strength ratio - Google Patents

Abstract

PURPOSE:To manufacture the titled steel independently of components contained with a conventional equipment for manufacturing a steel bar by hot rolling a steel contg. a prescribed amount of C, forcing the steel to be cooled under specified conditions, allowing it to cool, and carrying out finish rolling by a specified extent of stretch. CONSTITUTION:A steel contg. >=0.30wt% C is heated, hot rolled and forced to be cooled for 1-10sec. This cooling is stopped before a supercooled structure is produced, and the steel is allowed to cool to obtain a steel having a uniform ferrite-pearlite structure. The steel is then subjected to finish rolling by 0.5-5% extent of stretch. By this method, a high yield ratio suitable for the manufacture of a PC steel bar, a high strength bolt or the like as well as high strength and toughness can be provided to a bar steel or an unrefined steel.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing high-strength, high-toughness steel with a high yield strength ratio, and more specifically, a method for manufacturing high-strength, high-toughness steel with a high yield strength ratio, which is suitable for long steel bars, non-tempered steel bars, etc. This invention relates to a method for manufacturing high-strength, high-toughness steel.

[Prior art 1] In general, non-tempered steel bars contain V, Nb, etc. to improve and ensure strength and toughness, and to increase the yield strength of steel, stretching is , drawing, heat treatment, etc. are performed, but these treatments are performed outside the series of manufacturing steps.

Furthermore, conventional non-tempered steels have low yield strength, and PCC steel bars, which require high yield strength, for example, cannot be used for applications such as high-strength bolts.

[Problems to be Solved by the Invention] As explained above, the present invention has been developed in view of the fact that conventional steel bars or non-tempered steels have low yield strength, and methods for improving yield strength are inconsistent. As a result of intensive research conducted by researchers, it has been found that regardless of the content, and by simply using conventional steel bar manufacturing equipment, it is possible to produce a PC steel bar with a high yield strength ratio (and high strength and high toughness), such as a PC steel bar. They developed a method to manufacture steel suitable for high-strength bolts and high-strength bolts through a series of processes.

[Means for Solving the Problems] The method for producing high-strength, high-toughness steel with a high proof stress ratio according to the present invention is characterized by: heating steel containing 3011 t% or more of CQ, and after hot rolling. Forced cooling is performed for 1 to 10 seconds, and the forced cooling is stopped before supercooled tissue formation and allowed to cool. Next, the amount of stretching is 0.
The purpose is to perform finish rolling of 5 to 5%.

The method for producing high-strength, high-toughness steel with a high proof stress ratio according to the present invention will be described in detail below.

First, the structural requirements of the method for producing high-strength, high-toughness steel with a high proof stress ratio according to the present invention will be explained.

C is necessary to obtain high strength as a ferrite pearlite structure, and such an effect cannot be expected if the content is less than 0.30 wt%. Therefore, the C content is 0.30
wt% or more.

Forced cooling after hot rolling is performed by water cooling for 1 to 10 seconds, because if the time is less than 1 second, the internal heat will re-austenite and the stretching performed in the subsequent process will not be effective.
In addition, if the time exceeds 10 seconds, it is difficult to prevent the surface layer from cooling properly, and furthermore, forced cooling must be stopped and allowed to cool before the steel has a suitable cooling structure, resulting in uniform ferrite pearlite formation. It is set as mm.

As described above, finish rolling is performed on steel with a uniform ferrite-pearlite structure with a stretching amount of 0.5 to 5%, but if the stretching amount is less than 0.5%, the yield strength will not be improved enough, Furthermore, if the amount of stretch exceeds 5%, the yield strength improvement effect is saturated, and the diameter of the steel material becomes narrower.

[Example 1] An example will be described regarding the method for producing high-strength, high-toughness steel with a high proof stress ratio according to the present invention.

Example (1) Sample material CO, 60wt%, Si 0024wt%, Mn 1,
36wt%, CrO, 98wL%, balance Fe and impurities (2) Rolling conditions Normal heating (980℃) ↓ Rolling (rough row, middle row) 32φ 1 Rolling end temperature 920″C ↓ Forced cooling (intermediate water cooling) 2. 4 seconds cooling 1 Surface temperature 390°C (Ms point 266°C) ↓ Surface temperature after stretch recuperation by finishing rolling mills (4 units) 520°C Stretch amount 0%, 0.5%, 1.0%, 2.1% ,
5.4% The structure of the test piece thus produced was a small amount of ferrite pearlite structure.

Table 1 shows the mechanical properties and dimensional loss due to stretching of this test piece.

In addition, when the above-mentioned sample material was forcedly cooled for 12 seconds, the surface temperature was 80°C, a martensitic structure, and the surface temperature after reheating was 180°C.

The steel obtained by the method for manufacturing high-strength, high-toughness steel with a high proof stress ratio according to the present invention has a high proof stress ratio (and high toughness) even when rolled, and can be JIS G grade without being subjected to heat treatment.
3109 PC steel bar type B or JISB1051 10.
Can be used for 9 volts.

[Effect of the invention 1 As explained above, the method for manufacturing high strength, high toughness steel with a high proof stress ratio according to the present invention has the above configuration, so that the long steel, non-tempered steel, for example, It has the excellent effect of providing high strength and high toughness with a proof stress ratio suitable for manufacturing PC steel bars, high-strength bolts, and the like.

Claims (1)

[Claims] Steel containing 0.30 wt% or more of C is heated, forced cooling is performed for 1 to 10 seconds after hot rolling, cooling is stopped before the formation of supercooled structure and allowed to cool, and then the amount of stretch is 0.5 ~5
A method for producing high-strength, high-toughness steel with a high yield strength ratio, which comprises performing finish rolling of 1.5%.