CN105671453A

CN105671453A - Austenitic heat-resistance steel with high endurance strength

Info

Publication number: CN105671453A
Application number: CN201610163262.9A
Authority: CN
Inventors: 朱丽慧; 李彬彬; 翟国丽; 王起江; 周任远
Original assignee: University of Shanghai for Science and Technology
Current assignee: University of Shanghai for Science and Technology
Priority date: 2016-03-19
Filing date: 2016-03-19
Publication date: 2016-06-15

Abstract

The invention discloses austenitic heat-resistance steel with high endurance strength, and belongs to the technical field of heat-resistance steel. The austenitic heat-resistance steel is prepared from, by weight percent, 0.07%-0.13% of C, not larger than 0.3% of Si, not larger than 1% of Mn, not larger than 0.045% of P, not larger than 0.03% of S, not larger than 0.02% of Al, 17%-19% of Cr, 7.5%-10.5% of Ni, 0.05%-0.50% of V, 2.5%-3.5% of Cu, 0.2%-0.6% of Nb, 0.05%-0.12% of N, 0.10%-0.50% of Mo and the balance Fe. The austenitic heat-resistance steel has the beneficial effects that compared with the prior art, the composition ranges of Mn, Ni and Al are adjusted, a small quantity of V and Mo elements are added, cost increase is not large, but the endurance strength is remarkably improved.

Description

A kind of high-lasting strength austenitic heat-resistance steel

Technical field

The invention belongs to technical field of heat-resistant steel, in particular, provide a kind of austenitic heat-resistance steel, be applicable in power station High Temperature High Pressure or and vapour corrosive environment in steel tube used in boiler.

Background technology

China's rapid economic development, resource and the energy have become the bottleneck of restriction development. It is improve conventional thermal power plant efficiency and reduce the unit capacity the most effective approach of cost that raising steam parameter combines with development large sized unit, therefore develop overcritical and ultra supercritical coal-fired unit to reducing costs, save coal resources, decreasing pollution there is great and long-range meaning. Overcritical and the development of extra-supercritical unit and the development of heat-resisting steel material are closely related. Realize the reliability service of unit under more elevated steam conditions, it is necessary to research and development are adapted to that the intensity of elevated steam conditions is higher, the high temperature steel of more reliable performance.

In existing technology, the boiler material being operated in High Temperature High Pressure or steam corrosion environment, can be divided into three major types: jessop, austenitic heat-resistance steel and nickel-base alloy. Although Ascalloy has the advantage that thermal conductivity is big and the coefficient of expansion is little, but when vapor temperature is more than 650 DEG C, jessop structure stability is deteriorated, and performance sharply declines, and can not adapt to the manufacture of the more parts of elevated steam conditions. Nickel-base alloy cost is higher, can only be used for the advanced extra-supercritical unit that temperature is higher. Therefore, have high temperature microstructure good stability, hot strength, creep rupture strength feature austenite heat-resistant steel paid attention to and be developed. Along with improving constantly of station boiler parameter, it is desired to high-temperature bearing part possesses higher creep rupture strength, anti-steam oxidation and resistance to flue gas corrosion performance. S30432 is the comparatively successfully austenitic heat-resistance steel by Co., Ltd. of Sumitomo Metal Industries of Japan and Mitsubishi Heavy Industries Ltd's joint development, main as superheater and reheating pipeline, owing to power station material is exposed in temperature high-pressure steam environment for a long time, high temperature resistance steam corrosion and creep rupture strength to such material propose requirements at the higher level. For improving the security that power plant runs, generally making superheater and reheater tube wall thickness relatively big, this not only causes heat exchange efficiency to reduce, but also can because of the big initiation other problem of the coefficient of expansion of austenitic steel. , it is to increase S30432 steel high-temperature behavior, therefore it is letter problem to be solved.

S30432 steel is on the basis of TP304H, by reducing Mn upper content limit, adds the copper of about 3%, the nitrogen of 0.45% niobium and trace obtains.This steel is included into ASMECodeCase2328-1, and this standard-required composition (wt%) is: C:0.07-0.13%, Si:0.3%, Mn≤1%, P≤0.045%, S≤0.03%, Al≤0.02%, Cr:17 ~ 19%, Ni:7.5 ~ 10.5%, Cu:2.5 ~ 3.5%, Nb:0.2 ~ 0.6%, N:0.05 ~ 0.12%, Fe: surplus. This steel produces the copper-rich phase of small and dispersed when being on active service and run, Nb (C, N), M23C6 and NbCrN, thus reaches the best of breed of hot strength, high-temp plastic and resistance to high temperature oxidation. But, this kind of steel is after high temperature long service or long-time aging, and precipitated phase is grown up, and creep rupture strength reduces. Wherein, thick Z phase (NbCrN) is formed owing to Cr in lasting and ag(e)ing process diffuses in MX type precipitated phase so that creep rupture strength weakens. Therefore, manage to suppress the growing up of copper-rich phase and Nb (C, N), suppress being formed of thick Z phase (NbCrN) that the creep rupture strength improving S30432 steel is very effective.

Summary of the invention

It is an object of the invention to provide a kind of austenite heat-resistance steel with more high-lasting strength.

Object according to the present invention, the austenite heat-resistance steel with more high-lasting strength proposed by the invention is based on S30432 austenitic heat-resistance steel, by the composition of adjusting and optimizing S30432 steel, increase suitable alloying element so that it is improving creep rupture strength, its chemical composition is as follows:

The chemical component weight percentage composition of the present invention is: C:0.07 ~ 0.13%, Si 0.3%, Mn≤1%, P≤0.045%, S≤0.03%, Al≤0.02%, Cr:17 ~ 19%, Ni:7.5 ~ 10.5%, V:0.05 ~ 0.50%, Cu:2.5 ~ 3.5%, Nb:0.2 ~ 0.6%, N:0.05 ~ 0.12%, Mo:0.10 ~ 0.50%, Fe: surplus.

Adopt on the basis of S30432 high temperature steel according to above-mentioned purpose the present invention, by adding V and Mo element, the composition range of adjustment Mn, Ni, Al, it is achieved that significantly improve the object of creep rupture strength.

Austenitic heat-resistance steel adopts solution strengthening, precipitation strength and grain-boundary strengthening three kinds of schedule of reinforcements usually. The technological principle of foregoing invention technical scheme is that the precipitation strength that impels tiny precipitated phase to precipitate out by V element solution strengthening, V element, Mo element suppress MX phase to grow up, and Mn, Ni, Al element suppresses the acting in conjunction of growing up of copper-rich phase.

Solid solution V in order to reduce energy of dislocation will segregation in subgrain boundary. Due to V velocity of diffusion slowly, the dislocation of accumulation is pinned at subgrain boundary place strongly, dislocation multiplication speed height, to the slippage of dislocation, climb and the migration inhibition of subgrain boundary stronger, then play strengthening effect.

Owing to tiny precipitated phase quantity increases, dislocation and twin boundary are had strong pinning effect by these tiny precipitated phases, climbing of the dislocation that still can effectively lock after long-time creep, thus well improve hot strength.

Under soak state, owing to Mo segregation is to carbonitride/austenite interface, C, N, Nb and V atom is prevented to spread to carbonitride from austenitic matrix, so carbonitride does not occur significantly to grow up in whole process.

In addition, by adjustment Mn, Ni, Al, composition range, suppress the growing up of copper-rich phase. In rich copper clusters except Cu, there is obvious enrichment in inner in cluster and with matrix metal the interface of Mn and Ni. Therefore, when copper-rich phase is grown up, Mn, Ni and Al atom must be repelled so that copper-rich phase is grown up slowly.

Technical scheme according to above-mentioned purpose and technological principle the present invention is: on the basis of S30432 austenite heat-resistance steel chemical composition, add a small amount of V and Mo element, the composition range of adjustment Mn, Ni, Al, under identical thermal treatment process, the creep rupture strength of new high temperature steel can significantly improve.

The present invention compared with prior art, adds a small amount of V, Mo element, and the composition range of adjustment Mn, Ni, Al, cost improves little, but creep rupture strength significantly improves.

Accompanying drawing explanation

Fig. 1 is the transmission electron microscope picture of prior art steel grade sequence number 1#.

Fig. 2 is the transmission electron microscope picture of embodiment of the present invention sequence number 3#.

Fig. 3 is the scanning electron microscope (SEM) photograph of prior art steel grade sequence number 1# after 650 DEG C of lasting rear 178h.

Fig. 4 is the scanning electron microscope (SEM) photograph of prior art steel grade sequence number 1# after 650 DEG C of lasting rear 662h.

Fig. 5 is the scanning electron microscope (SEM) photograph of embodiment of the present invention sequence number 3# after 650 DEG C of lasting rear 369h.

Fig. 6 is the scanning electron microscope (SEM) photograph of embodiment of the present invention sequence number 3# after 650 DEG C of lasting rear 1004h.

Fig. 7 is the transmission electron microscope picture of embodiment of the present invention sequence number 3# Z phase after 650 DEG C of lasting rear 369h.

Fig. 8 is the transmission electron microscope picture of embodiment of the present invention sequence number 3# Z phase after 650 DEG C of lasting rear 1004h.

Fig. 9 is the details in a play not acted out on stage, but told through dialogues picture figure of embodiment of the present invention sequence number 3# Z phase after 650 DEG C of lasting rear 1004h.

Figure 10 is after to be embodiment of the present invention sequence number 3# lasting at 650 DEG C after 1004h, the diffraction spot point diagram of precipitated phase Z phase.

Embodiment

Testing material is selected on the basis of S30432 austenite stainless steel chemical composition standard, adds the V of 0.18%, the Mo of 0.32%, the composition range of adjustment Mn, Ni, Al, adopts chemical composition in table 1. In above-mentioned list, sequence number 3# is the embodiment of the present invention, and 2# is the steel grade adding Mo element in prior art, and 1# is the steel grade of prior art.

Embodiment 1:

From the made steel pipe of 1# and 2# steel, cut high-temperature and durable sample respectively, test lastingly when 650 DEG C of 280Mpa, 650 DEG C of 220Mpa respectively. Experimental result is as shown in table 2, it can be seen that under identical stress, 2# steel example rupture time is longer, illustrates that adding Mo element can increase creep rupture strength.

Embodiment 2

From the made steel pipe of 1# and 3# steel, cut high-temperature and durable sample respectively, test lastingly when 650 DEG C of 280Mpa, 650 DEG C of 250Mpa respectively. Experimental result is as shown in table 3, it can be seen that under identical stress, embodiment of the present invention rupture time is longer, illustrates that the creep rupture strength of inventive embodiments obtains significant lifting.

Embodiment and prior art lastingly before transmission electron microscope picture contrast see Fig. 1 and Fig. 2, the embodiment of the present invention and prior art all find some tiny precipitated phases, but the embodiment of the present invention has precipitated out the precipitated phase (such as arrow in Fig. 2) taking measurements greatly more tiny along twin boundary and dislocation line.

Fig. 3 ~ Fig. 6 is shown in the rear scanning electron microscope (SEM) photograph contrast lastingly of embodiment and prior art, and embodiment of the present invention precipitated phase is more.

Embodiment lastingly after Z phase transmission electron microscope picture see Fig. 7 ~ Figure 10, embodiment lastingly after Z phase diffraction spot calibration maps see Figure 10. Antenna shape Z phase (such as arrow in figure) Dispersed precipitate on twin boundary and dislocation line, by details in a play not acted out on stage, but told through dialogues as Fig. 9 it can be seen that this kind of antenna shape Z phase pricks dislocation by tiny particle nail to link. Antenna shape Z phase is very tiny, and Z phase during supply state is less, and size is only 6nm, and after lasting 1004h, antenna shape Z phase increases, and Size growth is to 8.6nm. Illustrate and the lasting process of Z phase is grown up very slowly, more stable. Therefore, after adding V element in S30432 steel, once avoid the formation of V (C, N) in solution heat treatment and ensuing cooling. Tiny antenna shape Z phase preferentially precipitates out than V (C, N). These tiny Z have strong pinning effect relative to dislocation and twin boundary, climbing of the dislocation that still can effectively lock after long-time creep, thus well improve creep rupture strength.

Claims

1. a high-lasting strength austenitic heat-resistance steel, it is characterised in that, the weight percentage of this high temperature steel chemical composition is: C:0.07 ~ 0.13%, Si 0.3%, Mn≤1%, P≤0.045%, S≤0.03%, Al≤0.02%, Cr:17 ~ 19%, Ni:7.5 ~ 10.5%, V:0.05 ~ 0.50%, Cu:2.5 ~ 3.5%, Nb:0.2 ~ 0.6%, N:0.05 ~ 0.12%, Mo:0.10 ~ 0.50%, Fe: surplus.