Hot working of the hottest 1Cr11Ni2W2MoV steel bla

2022-08-06
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Hot working process and mechanical properties of 1Cr11Ni2W2MoV steel blade Abstract: the relationship between hot working process and mechanical properties of aviation 1Cr11Ni2W2MoV steel blade was discussed. The process test results show that the mechanical properties of the steel are mainly related to the degree of forging deformation, size effect, temper brittleness and δ- F organization and other factors

key words: aeroengine blade; Mechanical properties; Forging; Heat treatment

1. Preface

1cr11ni2w2mov steel is a new martensitic heat-resistant stainless steel obtained by adding a large number of ferrite forming elements such as W, Mo and V to low-carbon 12%cr steel to reduce the austenite phase zone, so that the steel has the ability of martensitic transformation hardening. The steel has good comprehensive mechanical properties, and has been widely used in the aviation industry to manufacture engine blades, discs, shafts and other important parts working below 600 ℃

this paper mainly discusses the relationship between hot working process (forging and heat treatment) and mechanical properties of aviation 1Cr11Ni2W2MoV steel blade

II. Raw materials and process equipment

aviation 1Cr11Ni2W2MoV steel blade is an important secondary forging. The raw material electroslag steel hot-rolled bar for forgings must comply with the technical standards such as Yb stainless steel and heat-resistant steel bars for aviation and Hb high quality stainless steel bars for rotating parts of aircraft engines and the provisions of relevant issued technical conditions; The raw materials can be put into use only after they pass the re inspection and the surface defects are removed. The chemical composition after re inspection is shown in Table 1, and the final mechanical properties of the blade shall meet the provisions in Table 2. Table 11cr11ni2w2mov steel chemical composition (wt%)

element csimncrniwmovsp content 0.10 ~ 0.16 ≤ 0.60 ≤ 0.6010.5 ~ 12.01.40 ~ 1.801.50 ~ 2.000.35 ~ 0.500.18 ~ 0.30 ≤ 0.020 ≤ 0.030 recheck 0.130.220.5111.601.781.850.470.23/

table 21cr11ni2w2mov steel final mechanical property requirements

heat treatment system mechanical properties ≥ quenching and tempering σ b(MPa) σ 0.2(MPa) δ 5(%) ψ (%) hrcak (kj/m2) 1000 ~ 1020 ℃

oil or air quenching 660 ~ 690 ℃ air cooling 0~35.~ Air cooling at 600 ℃ 5 ~ 41.5685 qt31-wy 5 ~ 33.5685

1cr11ni2w2mov steel blade hot working process test heating equipment adopts rjx- and rjx- industrial electric furnaces. Before raw materials are loaded into the furnace, the foreign matters in the electric furnace shall be completely removed, the mixing of materials shall be avoided, and the temperature control instrument shall be calibrated according to the process requirements; In order to improve the uniformity of furnace temperature, the asbestos insulation grid of furnace door can be used, and the effective rate is ≥ 87%

III. process test

the formulation of hot working process specification for aviation 1Cr11Ni2W2MoV steel blade shall be carried out in strict accordance with the technical provisions in Hb aviation steel forgings, and finally meet the mechanical properties required in Table 2

1. Forging process

1cr11ni2w2mov steel blade forging process test scheme is shown in Table 3. Table 31cr11ni2w2mov steel blade forging process test

blade number forging size raw material size deformation degree

(forging ratio) forging process number 0t × fifty-two × one hundred and thirty-eight φ fifty × 1001.57F10T φ seventy-five × 1303.54F20T × seventy-five × one hundred and seventy-five φ ninety-five × 1601.96/1.84F30T φ one hundred and ten × 1202.63/1.840T2324 × fifty-two × one hundred and fifteen φ sixty-five × 1402.65F20T6322 × thirty-eight × one hundred and seventy-five φ fifty-three × 752.63F10T6422 × forty × one hundred and forty-five φ fifty-three × 652.50f1

in the table: F1 - single blank forged in one heat

f2 - forged in one heat and then cut evenly into three pieces

f3 - two fire forging forming, i.e. cutting evenly into three pieces after pre forging, and then heating for final forging forming

at high temperature, the structure of 1Cr11Ni2W2MoV steel blade is austenite (a) and a small amount of δ- Ferrite (f), with good thermoplastic, easy to press. To avoid gross organization and δ- F includes 1. The operating procedures of the simply supported beam impact testing machine are too high, and the initial and final forging temperatures of the forging should not be too high. After stopping forging, the forgings shall be placed in the ash box for slow cooling to prevent cracking. The appropriate forging process specification should be: 850 ℃ preheating + (1140 ± 20) ℃ initial forging + (850 ~ 900) ℃ final forging/ash box cooling

the surface quality of forgings shall be free from overburning cracks and other defects that seriously affect the performance; All small cracks, embedded and flaked oxide scales must be removed; The existence of general defects must ensure that the forgings have a nominal machining allowance of ≥ (2)/(3). The macrostructure shown on the fracture surface of forgings and acid immersion test pieces shall not have white spots, white spots, shrinkage cavities, bubbles, peeling, needle segregation and layered fracture. Once serious quality problems are found, forgings shall be scrapped

2. Heat treatment process

(1) preliminary heat treatment

1cr11ni2w2mov steel blade preliminary heat treatment, i.e. post forging heat treatment, aims to eliminate forging processing defects and stresses, improve its structure, promote the solid solution of fully accumulated carbides, and ensure the required mechanical properties (Brinell hardness requirement d = 3.70 ~ 4.30). The process specification for preliminary heat treatment is: 850 ℃ preheating (depending on the charging amount) + (1000 ± 10) ℃ normalizing/air cooling + (740 ± 10) ℃ tempering/air cooling or 850 ℃ preheating + (740 ± 10) ℃ tempering/air cooling

(2) final heat treatment

1cr11ni2w2mov steel blade final heat treatment correct process specification is: 850 ℃ preheating (depending on the furnace charge) + (1010 ± 10) ℃ quenching/oil cooling + (550 ~ 570) ℃ tempering/air cooling

1) the higher the quenching heating temperature of quenched 1Cr11Ni2W2MoV steel, the more the carbides dissolve. When heated to 1000 ℃, the carbides have all dissolved. If the heating temperature is too high, too much δ- F. The properties of the steel are deteriorated (mainly the strength and toughness, fatigue properties and creep properties are reduced). Therefore, the quenching heating temperature should be such as to ensure that full austenization is achieved, but only a small amount of δ- F is the principle, and (1000 ~ 1020) ℃ is the most appropriate. The steel has good hardenability and hardenability φ 200mm workpieces can be quenched thoroughly. Therefore, for thin-walled parts similar to Aeroengine Blade blanks, in order to avoid deformation and cracking defects caused by too fast cooling speed, oil cooling quenching has a better effect

2) tempering of tempered 1Cr11Ni2W2MoV steel blade is a very important process, which will have a significant impact on the final mechanical properties. There are two temper brittle zones ((350 ~ 530) ℃ and (600 ~ 670) ℃) in the steel, which are the difficulties in the tempering process. The suitable tempering temperature range is very narrow, and a slight deviation will reduce the impact toughness of the steel, so the operation should be very careful. According to the working conditions of 1Cr11Ni2W2MoV steel blade, the best comprehensive mechanical properties can be obtained by selecting the tempering temperature of 550 ~ 570 ℃

IV. test results

after physical and chemical test, the mechanical properties of 1Cr11Ni2W2MoV steel blade after final heat treatment are shown in Table 4. Table 41mechanical properties of cr11ni2w2mov steel blade after final heat treatment (average value)

blade No σ b (MPa) σ 0.2 (MPa) δ 5 (%) ψ (%)ak (KJ/m2)HRC0T. The ion current generated by 634.0 is approximately proportional to the residual gas density, i.e. vacuum degree 0t 037.00T. 335.30T. 434.70T. 835.20t6 and obtain accurate data 035.00T. 036.2

v. result analysis

according to the test results in Table 4, the mechanical properties of aviation 1Cr11Ni2W2MoV steel blades of 7 types and specifications after final heat treatment are basically qualified, among which the comprehensive mechanical properties and strength toughness of OT, OT, ot63 and ot64 are the best; OT and ot23 blades have high impact toughness and plasticity, but the tensile strength is lower than the technical provisions in HB; The comprehensive mechanical properties of OT blade are relatively poor, its toughness index barely meets the requirements, and its tensile strength is 3.6% lower

1. The influence of forging on mechanical properties

the degree of forging deformation (forging ratio) is one of the important factors affecting the comprehensive mechanical properties. The appropriate forging ratio should be greater than 2. Repeated upsetting and drawing is conducive to crushing the coarse and like carbides in the material, and can obtain more uniform mechanical properties and moderate grain size

2. Effect of size effect on mechanical properties

the larger the size of raw material of forgings, the greater the probability of internal original defects. The microstructure of forged steel is not as dense as that of small size, so the size effect is more serious

3. Effect of temper brittleness on mechanical properties

1cr11ni2w2mov steel has temper brittleness, which reduces the impact toughness and may be related to the precipitation of a complex hardening phase [2]. Electronic scanning analysis shows that when the steel is tempered within the tempering brittleness temperature range, the fracture toughness K1C value presents a trough, which corresponds to the tempering secondary hardening peak. The secondary hardening peak is caused by the precipitation of (Cr, W, Mo, V) 2C and (Cr, W, Mo, V) 23c6 complex carbides. The carbides precipitated in the temper brittle zone are all precipitated in the form of thin shells on the M matrix; If tempering is avoided in the temper brittle zone, carbides gather, the thin shell breaks and the impact toughness increases. This is the famous "thin shell embrittlement theory"

4. δ- Effect of F content on mechanical properties

1cr11ni2w2mov steel usually contains a small amount of δ- F. If the content exceeds 5%, the transverse mechanical properties will decrease significantly (Table 5). Therefore, corresponding measures shall be taken for steel smelting, forging and heat treatment to reduce δ- F content. For example, high-quality electroslag steel hot-rolled bars shall be used as raw materials to strengthen the re inspection of chemical composition; The heating temperature of forging and quenching should not be too high in order to achieve full austenitization; The tempering time shall be sufficient to ensure the full diffusion of carbide forming elements, and it shall be appropriate. Too long tempering time will not help to improve performance, which is harmful and unhelpful. It shall be controlled within (2.5 ~ 3.5) H. Table 5 δ- Effect of F content on mechanical properties of steel

δ- F(%) σ b (MPa) σ 0.2 (MPa) δ 5 (%) ψ (%)ak (KJ/m2)<. 551.1680~. 043.7430~. 541.9190~. 829.8170

VI. conclusion

in the process of hot working, the mechanical properties of aviation 1Cr11Ni2W2MoV steel blades are mainly related to the degree of forging deformation, size effect, temper brittleness and δ- F organization and other factors; Conscientiously implementing Hb and other relevant technical regulations and implementing correct hot working process specifications are important guarantees for improving the comprehensive mechanical properties of 1Cr11Ni2W2MoV steel blades, especially for controlling the product quality during mass production

author unit: Air China easy to use air and Gas Turbine Research Institute (621703)

references

[1] Yan Minggao, shichangxu, etc China Aeronautical Materials Manual Beijing: China Standards Press, 1998:658 ~ 670

[2] Huang Chunfeng Optimization of heat treatment process for 1Cr17Ni2 steel blade Metal heat treatment, 1992 (3):37 ~ 38 (end)

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