Study on Low Temperature Deformation Annealing of P5 and P22 Steel Seamless Tubes by Thermal Expansion Process

grain size, non-metallic inclusions and mechanical properties at room temperature of P5 and P22 heat-expanded seamless steel pipes produced by low temperature deformation annealing were studied . The test results were evaluated with reference to ASIMA 335 and GB 5310 standards, and compared with the original Tubes and steel tubes that have undergone subsequent heat treatment after thermal expansion . The results show that the microstructure, grain size, non-metallic inclusions and mechanical properties at room temperature of P5 and P22 thermally expanded seamless steel pipes produced by low temperature deformation annealing and steel pipes after subsequent heat treatment all conform to ASIM A 335's requirements for P5 , p22 steel and GB 5310 requirements for lCr5Mo, 12C2MG steel . This has laid an important foundation for the further promotion of the thermal expansion process with simple production process, stable quality , economical and practical .
P5 steel P22 steel seamless steel pipe low temperature deformation annealing thermal expansion steel pipe
LOW TEMPERATURE THERMO MECHANICAL ANNEALING
TREATMENT OF P5 AND P22 SEAMLESS STEEL TUBES
[Abstract] MicrDstmctuie grain size nornnetallic inclusbns and mechanical properties at rxm trnperntuee ofP5 and P22 hot expanded semless steel tubes wih kw trnpemtuee Themcme- chanical annealing treamentwere investgated The re suit was evaluated with he reference of ASIM A335 and GB 5310, and ccmpared wih hat of cude sem less steel tubes and he tubes wih subse- quentheat treament The results indicated that them iciostuictLire gain sZe non metallic inc In sons and mechanical properties ofP5 and P22 hot expanded steel tubes and he tubes wt subsequent heat treatment fulymet the requirementsofASTMA335 toP5 andP22 steel orGB5310to1Cr5Moand 12Cr2MoGsteel,Itcouldprovideafoundationtopopularizetheeconomicandpracticalhotexpanding proceswithsimplifiedproductionprocedureandsteadyquality,
[Key Words] P5 Steel P22 Steel SemlessSteelTube LewTmpertureThemcmechan- icalAnnealingTreatment HotExpandedSteelTube

P5 and P22 steels are pearlitic heat-resistant steels suitable for service under high temperature and high pressure conditions under American ASTM standards, which are equivalent to China's 1C 5 Mq 12 Ci2MoG steel . Because this type of steel has good oxidation resistance and heat strength below 550 ° C , it has good heat resistance and corrosion resistance in petroleum media, and is suitable for manufacturing heat exchangers and reheater pipes , Pipes and containers of petroleum distillation equipment, and are widely used in high-temperature equipment such as thermal power plants, nuclear power plants, and petrochemical industries . P2 2 steel also has good hydrogen resistance, and is widely used in the manufacture of hydrogenation reactors and other equipment [ 1_5] . The need for development has promoted the further research of high-temperature and high-strength P 5 P2 2 steel pipes, especially large-diameter pipes . At present, the maximum outer diameter of hot-rolled ( drawn ) seamless steel pipes that can be produced in China is 720 mm [ 6-7 ] . Larger-diameter seamless steel pipes can only be achieved through thermal expansion processes and the like . On the other hand, the production cost is high and the production equipment is expensive

For hot-rolled seamless steel pipes, the push-type thermal expansion process with the characteristics of simple production process, stable quality, economical and practical characteristics can increase the diameter of steel pipes in a short period of time. This process has high production efficiency and low cost. low . At the same time, as the extension of the main line of smelting and rolling, the push-type thermal expansion steel pipe can well fill the gap in the production of non-standard and special -type seamless steel pipes in steel mills, and solve the special needs of users .
The essence of the push-type thermal expansion steel pipe process is a special deformation heat treatment . In this paper, the microstructure and mechanical properties at room temperature of the P 5 and P2 2 seamless steel pipes treated by low temperature deformation annealing , the original pipes and the heat-treated steel pipes after subsequent heat treatment are compared and analyzed, and the AS1M A 335 and GB 5310 standards are referred to was evaluated .

1 Test materials and methods
The chemical composition of the materials used in the test meets the requirements of GB 5310-2008 . The main parameters of the push-type low-temperature deformation annealing process are as follows :
P5 : Tube expansion temperature of 720-770°C , diameter expansion ratio of 125 , tube expansion speed of 240 mm /min > electric heating induction coil specification of 750 mm , coil frequency of 2500 and complete annealing heat treatment system of 910 C ;
P22 : 760-810C expansion temperature, secondary expansion ( primary expansion ratio 133, secondary expansion ratio 116) , expansion speed 50 mm /m n coil size 750 mm , coil frequency 2 500 H^ and 940 C normalizing + 730 C tempering heat treatment system . Sampling and numbering the P 5 P2 2 original pipe, thermally expanded pipe and heat-treated steel pipe respectively by way of on-site sampling .

 Chemical composition of P5 and P22 steel samples ( mass fraction , % )

material	c		mn			Si	Cr	Mo	P	S
	standard value	C0.15	0 .	30-0 .	60	C0.50	4 . 00-6 . 00	0 . 45-0 . 65	C 0.025	C0 . 025
P 5	test value	0 . 12		0 . 36		0 . 27	4 . 79	0 . 49	0 . 012	0 . 006
	standard value	0 . 05-0 . 15	0 .	30-0 .	60	C0.50	1 . 90-2 . 60	0 . 87-1 . 13	C0 . 025	C0 . 020
p 22	test value	0 . 086		0 . 48		0 . twenty two	2 . twenty three	1 . 00	0 . 009	0 . 004

Note: The standard value of ingredients is determined according to ASTM A 335 standard

Table 2 Sample specification and sample number

steel number	Specimen size / mm 2	Sample status	Sample No
	0219X10	Original tube	Y 1
P 5	0273X9.5	thermal expansion tube	K 1
	0273X9 . 5	heat treatment tube	T 1
	0457X50	Original tube	Y 2
p 22	0610X45	thermal expansion tube	K 2
	0705X35	heat treatment tube	T 2

cutting, inlaying, grinding and polishing the sample, and eroding with 4% nitric acid alcohol solution , the microstructure observation and grain size test were carried out according to the standards of GB/T 13298-1991 and GB/ T 6394-2002 , referring to the standard of AS1M A335 Compare the requirements of p5 and p22 .

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