High-grade duplex stainless steel with much suppressed formation of intermetallic phases and having an excellent corrosion resistance, embrittlement resistance castability and hot workability

Inactive Publication Date: 2005-07-21
YONG SO PARK
View PDF7 Cites 39 Cited by
  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0014] The main object of the present invention is to remove brittleness and improve corrosion resistance by reducing a precipitation speed and amount of brittle intermetallic phases, by delaying diffusion and precipitation of inte

Problems solved by technology

However, as compared with commercial PREW 38-level duplex stainless steel such as SAF 2205, the PREW 46-level high-grade duplex stainless steel contains a large amount of Cr, Mo and W which are major elements of sigma and khi phases deteriorating mechanical properties and corrosion resistance, and thus easily forms precipitation phases thereof during the production or application.
Actually, embrittlement by the precipitation phases has been observed in cooling after continuous casting of duplex stainless steel, slow cooling after hot rolling, slow cooling of a heat affected zone after welding, and slow cooling of an ingot center unit after casting.
In addition, Mo for improving local corrosion and SCC resistances among the added alloying elements is a high-priced element facilitating formation of sigma phases and 475° C. brittleness, and thus restrictively used.
But, the conventional research and development have the following problems.
However, it is not relevant to duplex stainless steel containing austenite and ferrite.
The non-metallic inclusions such as oxides and sulfides ar

Method used

the structure of the environmentally friendly knitted fabric provided by the present invention; figure 2 Flow chart of the yarn wrapping machine for environmentally friendly knitted fabrics and storage devices; image 3 Is the parameter map of the yarn covering machine
View more

Image

Smart Image Click on the blue labels to locate them in the text.
Viewing Examples
Smart Image
  • High-grade duplex stainless steel with much suppressed formation of intermetallic phases and having an excellent corrosion resistance, embrittlement resistance castability and hot workability
  • High-grade duplex stainless steel with much suppressed formation of intermetallic phases and having an excellent corrosion resistance, embrittlement resistance castability and hot workability
  • High-grade duplex stainless steel with much suppressed formation of intermetallic phases and having an excellent corrosion resistance, embrittlement resistance castability and hot workability

Examples

Experimental program
Comparison scheme
Effect test

example 1

Method for Manufacturing and Testing Steel of Invention

[0099] A method for designing and manufacturing optimal alloys in accordance with the present invention will now be explained. The method for designing the alloy is obtained by optimally combining alloy design factors such as PREW of equation {circle over (1)}, [PREW(γ)−PREW(α)] for corrosion resistance balance of phases, Creq of equation {circle over (2)}, and Nieq of equation {circle over (3)}, and resultant values are shown in Table 2.

[0100] Creq and Nieq were calculated by the equation {circle over (2)} and {circle over (e)} to determine the composition, the alloying elements are melted in high frequency induction furnace using commercial pure grade of Fe, Cr, Mo, Ni, W, Cu, Si, Mn and Fe—Cr—N as recited in the claims of the invention, and deoxidized according to a common method such as Ti, Mg, Al, Ca or Al+Ca composite deoxidation, samples for casting melted in air, and samples for wrought products were melted in vacuum a...

example 2

Comparison of Microstructures of Aged Products

[0110]FIGS. 1A to 1F are pictures of microstructures showing precipitation of brittle intermetallic phases deteriorating corrosion resistance and mechanical properties, such as sigma and khi of invention steel 4 (FIG. 1A), invention steel 10 (FIG. 1B) and invention steel 36 (FIG. 1C) aging heat-treated at 850° C. for 30 minutes, comparative steel 47 (FIG. 1D), and UR 52N+ (FIG. 1E) and SAF 2507 (FIG. 1F) which are commercial high-grade duplex stainless steels. Bright parts show austenitic phase, and dark parts show ferritic phase decomposed into sigma phase+austenite phase in the aging heat-treatment. The degree of precipitation of the intermetallic phases was ‘invention steel 4=invention steel 10=invention steel 3647’. As a result, invention steels 4, 10 and 36 suppressed precipitation of the intermetallic phases more than commercial steels UR 52+ and SAF 2507 and comparative steel 47, to remarkably improve embrittlement resistance.

example 3

X-ray Diffraction Analysis Test

[0111]FIGS. 2A to 2D are graphs of X-ray diffraction analysis test results showing precipitation of brittle intermetallic phases deteriorating corrosion resistance and mechanical properties, such as sigma and khi of invention steel 4 (FIG. 2A) aging heat-treated at 850° C. for 30 minutes, comparative steel 47 (FIG. 2B), and UR 52N+ (FIG. 2C) and SAF 2507 (FIG. 2D) which are commercial high-grade duplex stainless steels. As compared with comparative steel 47 and commercial steels UR 52+ and SAF 2507, invention steel 4 did not precipitate sigma phase, and precipitated little khi phase, to considerably improve embrittlement resistance.

the structure of the environmentally friendly knitted fabric provided by the present invention; figure 2 Flow chart of the yarn wrapping machine for environmentally friendly knitted fabrics and storage devices; image 3 Is the parameter map of the yarn covering machine
Login to view more

PUM

PropertyMeasurementUnit
Fractionaaaaaaaaaa
Fractionaaaaaaaaaa
Fractionaaaaaaaaaa
Login to view more

Abstract

Formation of intermetallic phases such as sigma (σ) and khi (χ) shows detrimental effects on the corrosion and mechanical properties of high-grade duplex stainless steel. The present invention provides high-grade duplex stainless steel with much suppressed formation of intermetallic phases, of which the chemical composition consists essentially, on a weight basis, of: Cr: 21.0%˜38.0%, Ni: 3.0%˜12.0%, Mo: 1.5%˜6.5%, W: 6.5% or less, Si: 3.0% or less, Mn: 8.0% or less, N: 0.2%˜0.7%, C: 0.1% or less, at least one element selected from the group consisting of Ba: 0.0001˜0.6% and one or more elements of Mischmetal (MM) and Y: 0.0001˜1.0% in total, and a balance of Fe and incidental impurities. The pitting resistance equivalent has a value of 40≦PREW≦67 defined by the following formula (1):
PREW=wt. % Cr+3.3(wt. % Mo+0.5 wt. % W)+30 wt. % N  ((1)
The present high-grade duplex stainless steel exhibits an excellent corrosion resistance, embrittlement resistance, castability and hot workability.

Description

TECHNICAL FIELD [0001] The present invention relates to duplex stainless steel having excellent corrosion resistance, and more particularly to, high-grade duplex stainless steel having excellent corrosion resistance, embrittlement resistance, castability and hot workability by suppressing formation of intermetallic phases, such as sigma (θ) and khi (χ), formed during the production (casting, hot rolling or welding). BACKGROUND ART [0002] Duplex stainless steel where austenite (γ) phase providing high workability and ferrite (α) phase providing high corrosion resistance are minutely combined has higher strength than austenitic stainless steel by at least 1.7 times, and also shows high pitting resistance and high stress corrosion cracking (SCC) resistance. Commercial high-grade duplex stainless steels having a pitting resistance equivalent (PREW=wt % Cr+3.3(wt % Mo+0.5wt % W)+30wt % N) of about 46, such as SAF 2507 (UNS S32750), UR 52N+ (UNS 32550) and ZERON 100 (UNS 32760) have been ...

Claims

the structure of the environmentally friendly knitted fabric provided by the present invention; figure 2 Flow chart of the yarn wrapping machine for environmentally friendly knitted fabrics and storage devices; image 3 Is the parameter map of the yarn covering machine
Login to view more

Application Information

Patent Timeline
no application Login to view more
IPC IPC(8): C22C38/00C22C38/42C22C38/44C22C38/58
CPCC21D2211/001C21D2211/005C22C38/001C22C38/58C22C38/005C22C38/42C22C38/44C22C38/002
Inventor PARK, YONG-SOOKIM, SOON-TAELEE, IN-SUNG
Owner YONG SO PARK
Who we serve
  • R&D Engineer
  • R&D Manager
  • IP Professional
Why Eureka
  • Industry Leading Data Capabilities
  • Powerful AI technology
  • Patent DNA Extraction
Social media
Try Eureka
PatSnap group products

Browse by: Latest US Patents, China's latest patents, Technical Efficacy Thesaurus, Application Domain, Technology Topic.

© 2024 PatSnap. All rights reserved.Legal|Privacy policy|Modern Slavery Act Transparency Statement|Sitemap