Analysis of precipitates in the hottest gh9158 iro

Analysis of precipitates in gh9158 iron base superalloy

Abstract: Objective To study the distribution and concentration change of alloy elements in the precipitates of gh9158 alloy. Methods electrolytic extraction phase analysis was used. Results the type, quantity, composition and structure of precipitates at different aging temperatures were measured and calculated. Conclusion the precipitated phases M6C and Laves are stable during aging at (720 ~ 820) ℃

key words: iron base superalloy; Phase analysis; Laves phase; M6C phase

introduction

gh9158 iron base superalloy is developed by North China Institute of technology. It is a new type of hot work die material strengthened by Cr, Ni, W, Mo and other multi-element composite. After solid solution and aging treatment, austenite matrix and dispersed precipitates are obtained, which makes the alloy have good thermal strength, thermal stability and oxidation resistance. At present, the alloy has been used as a large-scale elastic body forming and drawing die ring, and the production practice has proved that the effect is remarkable [1]. During the development of the alloy, the author studied the type, quantity and composition of precipitates in the alloy under different aging treatment conditions, as well as the distribution and concentration of alloy elements in each precipitate, which is of great significance for determining the amount of alloy elements, selecting the alloy heat treatment system and studying the alloy strengthening mechanism [2]

1 test conditions and methods

1.1 preparation of samples

the test material is a cast blank, hot rolled into a round steel with a diameter of 18 mm, and processed into a diameter of 14 mm after solution treatment (1 180 ℃ heating, holding for 2 hours, water cooling) × For 100 mm round bar, three aging treatment temperatures are adopted: 1 # sample 720 ℃, 2 # sample 770 ℃, 3 # sample 820 ℃, and the time is 2.5 h. The treated sample is polished with sandpaper and ready for use after rough electrolysis

1.2 electrolytic conditions and X-ray phase analysis of electrolytic extracts

two kinds of electrolytes are used for electrolytic extraction of samples, and the conditions are shown in Table 1. The anodic precipitates of each sample were qualitatively analyzed by d/max-rb X-ray diffractometer. The results showed that the precipitates under three aging conditions were M6C phase and Laves phase (i.e. AB2 phase). Table 1 electrolytic extraction conditions [3]

composition of electrolyte electrolytic system 14% sulfosalicylic acid, 1% LiCl, 5% glycerol methanol solution current density i=0.05 a/cm2, temperature (-7 ~ -5) ℃ 25% HCl, 5% glycerol, 2% citric acid methanol solution current density i= (0.05 ~ 0.1) a/cm2, Temperature (-5 ~ 0) ℃

1.3 phase separation and phase element determination

1.3.1 AB2 phase and M6C phase separation

after washing and drying a certain amount of anode precipitation obtained by electrolysis, soak it in chemical separation solution cuilixin, chairman of Shandong innovation group: build the "small workshop" into a large domestic aluminum alloy material production base (the composition of separation solution is 10%kio3+5%h2so4+2% potassium sodium tartrate + water), and keep it at 95 ℃ for 1.5 h [3]. At this time, M6C phase is dissolved and AB2 phase is quantitatively retained

filter the solution and wash the sediment with 1% citric acid aqueous solution to wash KIO3

1.3.2 determination of elements in M6C and AB2 phases

put the precipitate obtained by electrolysis and the precipitate obtained by separation of AB2 phase into 30 ml porcelain crucible respectively, incinerate and burn (650 ℃), and add potassium pyrosulfate to melt. Soak the frit with 100 ml of 5% NaOH aqueous solution, place it for several hours, wait for the hydroxide of Fe, Mn, Cr, Ni to precipitate, filter it in a 200 ml volumetric flask with dense filter paper, wash the precipitate with 1% NaOH aqueous solution for more than 10 times, and dilute it to the scale. The solution is used for the determination of W, Mo, V and other elements. Put the precipitation into the original beaker together with the filter paper, add 10ml concentrated sulfuric acid, add HNO3 to dissolve the precipitation, decompose the filter paper until smoking, make a transparent solution, add water to dissolve it, transfer it into another 200ml volumetric flask, dilute it with water to the scale, and this solution is used to determine Fe, Cr, Mn, Ni and other elements

phase is determined by conventional colorimetric analysis. M6C phasor = (m6c+ab2) total -ab2 phasor

2 analysis results

2.1 the number and composition of precipitated phases

the weight percentage of each element in the precipitated phase in the alloy and the content of precipitated phase in the alloy are shown in Table 2 and table 3. Table 2 analysis results of M6C phase

sample No. M6C phasor (weight ratio) phase composition structural formula femnvcrniwmosic* Σ 1 × 2.210.050.140.650.223.761.640.450.2269.35 (fe0.35mn0.01v0.03ni0.03

cr0.11w0.18mo0.15si0.14) 6c2 × 2.230.050.150.630.283.791.730.460.2319.55 (fe0.34mn0.01v0.02ni0.04

cr0.11w0.18mo0.16si0.14 6c3 × 2.240.050.150.590.434.541.960.500.25110.71 (fe0.32mn0.01v0.02ni0.06

cr0.09w0.20mo0.16si0.14) 6cc * calculated value; Σ Total phase

Table 3 analysis results of AB2 (Laves) phase

sample No. AB2 phasor (weight ratio) phase composition structural formula femnvcrniwmo Σ 1 × 1.630.030.200.360.172.021.035.44 (fe0.67mn0.01v0.09cr0.16ni0.07) 2 (w0.51mo0.49) 2 × 1.770.030.210.390.192.191.115.89 (fe0.67mn0.01v0.09cr0.16ni0.07) 2 (w0.51mo0.49) 3 × 1.890.030.230.420.202.341.186.29(Fe Yulian group deepening reform and innovative development 0.67mn0.01v0.09cr0.16ni0.07) 2 (w0.51mo0.49)

2.2 phase composition structural formula

2.2.1 M6C phase composition structural formula

m6c carbide system interstitial phase, Its composition can be roughly divided into a3b3c, a2b4c, a4b2c types, in which a atom is mainly Fe, Cr, Mn, Ni, Co, V, etc. of transition metals, and B atom is composed of Mo, Zr, Nb, Ta, Ti, etc. with large atomic radius. M6C has a complex face centered cubic structure, with 96 metal atoms and 16 carbon atoms per unit cell [4]. According to the measured composition of M6C phase elements, calculate the structural formula of M6C phase composition of each sample, as shown in Table 2

2.2.2 Laves (AB2) phase composition structural formula

laves phase, also known as AB2 phase, is a topologically dense phase (TCP), which has three structures: mgcu2 type complex cubic lattice, mgzn2 type complex hexagonal lattice; Mgni2 complex hexagonal lattice. Mgzn2 type AB2 phase appears in multicomponent alloys and steels, in which a is composed of Ti, Zr, W, Mo and other elements with large atomic radius, and B is composed of Fe, Cr, Ni, Mn and Si [4]. At present, AB2 phase is widely used in the research of heat-resistant steel to strengthen medium and high alloy heat-resistant steel, which has high thermal stability and can maintain the long-term endurance strength at a high level [5]. According to the composition of AB2 phase elements measured, the structural formula for calculating the AB2 phase composition of each sample is shown in Table 3

3 conclusion

(1) with the increase of aging temperature, the total amount of precipitated phase increases, the precipitation rate of M6C phase is accelerated above 750 ℃, and the Laves phase changes gently

(2) with the increase of aging temperature, the composition structural formula of M6C phase changes slightly, while the composition structural formula of Laves phase remains unchanged, indicating that the two precipitates have high thermal stability, which has a good effect on the thermal strength and thermal stability of gh9158 superalloy

(3) the contents of W and Mo in the precipitated phases (M6C and Laves) account for about 82% and 75% of the amount added in the alloy, that is, W and Mo are the main alloying elements forming M6C and Laves phases in the alloy; Si does not participate in the formation of Laves phase, but its content in M6C is large. When aged at 820 ℃, about 62.5% enters M6C, indicating that Si significantly increases the formation speed and stability of M6C

(4) more than 90% of Ni and Cr in the alloy are solid soluble in the matrix, which is also the main element of solid solution strengthening in addition to ensuring that the alloy obtains a single austenite matrix. It has beneficial effects on the thermal strength and oxidation resistance of the alloy

ministry level "Eighth Five Year Plan" pre Research Fund funded project

Cao Shirui (1955-), male, lecturer Major: metal heat treatment

Cao Shirui (Department of material engineering, North China Institute of technology, Taiyuan 030051, Shanxi)

Hao Yao (Department of material engineering, North China Institute of technology, Taiyuan 030051, Shanxi)

Lu cuifen (General Iron and Steel Research Institute, Beijing 100081) Zhou Xiuchuan (Department of material engineering, North China Institute of technology, Taiyuan 030051, Shanxi)

Hu Jianyong (Department of material engineering, North China Institute of technology, Taiyuan 030051, Shanxi)

References:

[1] Hao Yao, Cao Shirui. Study on aging strengthening mechanism of austenitic iron-based alloy

[2] phase analysis group of chemical analysis room of iron and Steel Research Institute of the Ministry of metallurgy. Element composition of the second phase in steel and alloy

[3] General Iron and Steel Research Institute of the Ministry of metallurgy. Physical and chemical phase analysis of steel and iron nickel base alloys

[4] Lu Jinsheng, Wang Biao, Yao Yingcheng. X-ray Identification Manual of common phases in steel and alloy

[5] zhangshouhua. Alloy steel (e third party product certification is one of the important rings nd)