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Steels with excellent toughness for welding heat affected section and method of producing the same

A manufacturing method and technology of steel, applied in the direction of manufacturing tools, heat treatment furnaces, temperature control, etc., can solve the problems of low yield ratio, easy occurrence of brittle fracture, insufficient research on HAZ toughness, etc., and achieve the effect of suppressing deviation

Inactive Publication Date: 2012-06-20
KOBE STEEL LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, the improvement of HAZ toughness when performing welding of 50kJ / mm or more has not been sufficiently studied, and it is desired to realize a high-strength steel material that is excellent in both characteristics of low yield ratio and HAZ toughness
[0007] On the other hand, high strength is also required for steel used in ships and the like, but if the steel is made higher in strength, the yield strength is higher than the brittle fracture strength, and brittle fracture is likely to occur during elastic deformation

Method used

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  • Steels with excellent toughness for welding heat affected section and method of producing the same
  • Steels with excellent toughness for welding heat affected section and method of producing the same
  • Steels with excellent toughness for welding heat affected section and method of producing the same

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0167] In the following experimental examples 1-1 and 1-2, using the same steel grade, the HAZ toughness of the steel and its deviation (experimental example 1-1) and the strength and yield ratio of the rolled steel product (experimental example 1- 2) Research was carried out to evaluate the properties of steel materials (rolled steel products) comprehensively in Experimental Example 1-1 and Experimental Example 1-2.

experiment example 1-1

[0168] [Experimental Example 1-1 (Evaluation of HAZ Toughness and Its Variation)]

[0169] After primary refining of molten iron in a 240-ton converter, steel is tapped from the converter into ladles, and secondary refining is performed while adjusting composition and temperature.

[0170] In the ladle, while deoxidizing with Si and Mn, adjust to the total oxygen amount [O] shown in Table 1 below. 1 While adjusting the chemical composition. Total oxygen [O] 1 It means the total amount of oxygen contained as dissolved atoms in the molten steel and the oxygen contained as oxide-based inclusions. The oxygen contained as dissolved atoms in the molten steel is oxygen using a solid electrolyte. The sensor is used for measurement, and the total oxygen content is measured by a general inert gas fusion-infrared absorption method. Also, in Table 1 below, except for the total oxygen amount [O] 1 In addition, the amount of dissolved oxygen in the molten steel before adding REM and Zr ...

experiment example 1-2

[0204] [Experimental Example 1-2 (Evaluation of Tensile Strength and Yield Ratio of Base Material)]

[0205] The slabs (steel grades a1 to o1) obtained by casting under the conditions described in Experimental Example 1 above were hot-rolled so that the finishing temperature of finishing rolling became the temperature shown in Table 5 below. 3 The hot-rolled material obtained by quenching in the temperature region above the point. Quenching is to perform direct quenching (expressed as DQ in Table 5 below) from the quenching start temperature shown in Table 5 below after hot rolling, or to heat the hot-rolled material obtained by hot rolling to the temperature shown in Table 5 below. Quenching was performed after the indicated quenching start temperature (expressed as RQ in Table 5 below).

[0206] After quenching, heated to Ac 1 point ~Ac 3 The temperature area of ​​the point is maintained and quenched from this temperature area. Hold time is 5 minutes. The heating temper...

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Abstract

The present invention provides steels reducing HAZ toughness deviation. The steels comprise foreign materials of REM and Zr, and also comprises solid solution REM that is below 0.0010% without 0% and solid solution Zr that is 0.0010% without 0%. First steel rolled product made from the steels, forming a yield ratio reduced lower than 80%, contains bainite and / or martensite and ferrite, the ferrite occupies 4% to 24% area of an entire tissue, when the metal tissue of the steels are observed by using an electron backscatter pattern (EBSP) analyzing method, a formula (I) is satisfied. In the formula (1), D is an average equivalent roundness diameter (mum) of crystal particles enclosed by high-angle crystal boundary with a crystal azimuth difference bigger than 15 DEG, wherein, the azimuth difference of two adjacent crystals is measured by using the EBSP method. 35<=D...(1). In addition, when the metal structure of the second steel rolled product with improved low-temperature flexibility is observed by using the EBSP method, wherein, the second steel rolled product is made from the steels, the formulas (2) and (3) are satisfied. In formula (3), M is an occupying area ratio (%) of crystal particles enclosed by high-angle crystal boundary with a crystal azimuth difference bigger than 55 DEG in the entire steel issue. D<=30...(2); 50<=M...(3).

Description

technical field [0001] The present invention relates to steel materials used in structures such as bridges, high-rise buildings, ships, etc., and specifically relates to the toughness of parts affected by heat during welding (hereinafter referred to as "welding heat-affected zone" or "HAZ") Improved steel materials and methods for their manufacture are provided. Background technique [0002] In recent years, the properties required of steel materials used in structures such as bridges, high-rise buildings, and ships have become increasingly strict, and in particular, good toughness is required. These steel materials are generally joined by welding, but the welded joint portion, especially the HAZ, is affected by heat during welding, and there is a problem that the toughness tends to deteriorate. This deterioration in toughness becomes more pronounced as the heat input during welding increases, and the reason for this is considered to be that when the heat input during weldi...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C22C38/14C22C38/58C22C38/54C21D9/52B21B37/74B21B37/56
CPCC21D1/25C21D8/0226C22C38/00C22C38/001C22C38/002C22C38/005C22C38/04C22C38/12C22C38/14C22C38/16
Inventor 山口彻雄出浦哲史杉村朋子金子雅人
Owner KOBE STEEL LTD