CN103290188A

CN103290188A - Method for controlling martensite/austenite structure in process of straightening WB36 steel pipes

Info

Publication number: CN103290188A
Application number: CN2013102109108A
Authority: CN
Inventors: 刘永长; 张旦天; 马宗青; 余黎明; 高志明
Original assignee: Tianjin University
Current assignee: Tianjin University
Priority date: 2013-05-30
Filing date: 2013-05-30
Publication date: 2013-09-11
Anticipated expiration: 2033-05-30
Also published as: CN103290188B

Abstract

The invention relates to a method for controlling a martensite/austenite structure in the process of straightening WB36 steel pipes. The method comprises the following steps of: preparing WB36 steel into a steel pipe through hot rolling, wherein in order to reach specified heating and cooling rates, the wall thickness of a tubular product is generally required to be not more than 5.42cm to ensure that a batten martensite structure is formed after normalization; performing normalization at 1173K with the heat preserved for 30 minutes; putting the steel pipe into a six-roller straightening machine when the steel pipe is cooled to 860-920K, wherein the straightening speed is 10-15m/min, and the straightening force is 5-40Mpa; and after the steel pipe is straightened, cooling the steel pipe to the room temperature. After the steel pipe is straightened, the smaller the thickness of the strip-shaped martensite/austenite structure in a WB36 steel pipe structure is, the higher the impact property of the steel pipe is; and after the steel pipe is straightened by adopting the method, the room temperature ballistic work of the steel pipe is improved 234% from 41J to 96J, which definitely shows that the temperature and the straightening force significantly influence the comprehensive performance of the steel pipe and also indicates the universality and importance of the method in the production process.

Description

WB36 steel pipe aligning process martensite/austenite organizational controls method

Technical field

The invention belongs to Ni-Cu-Mo type structural low production technical field, WB36 steel pipe aligning process martensite/austenite organizational controls method when particularly a kind of fair speed is cooled off aligning continuously.

Background technology

WB36 steel (be l5NiCuMoNb5, chemical ingredients sees Table 1) is a steel grade in the German Mannasman company company standard, and it is to add the Ni-Cu-Mo alloy development on the basis of carbon manganese steel to get up.WB36 is owing to have excellent high-temperature mechanical property and a high temperature oxidation resistance, therefore is widely used in the collection case, steam-pipe of nuclear power generator group and high-parameters thermal power generation unit etc.The characteristics of this steel are the intensity height, and yield strength is higher by 40% than 20 steel, and use temperature is 400 ℃, also can be used as the heavily stressed pipeline that pipe surface temperature reaches 500 ℃; Or as high-parameters thermal power generation unit, as high temperature, high voltage components such as the boiler-steam dome in the supercritical unit, steam separator, collection case, vapour generator, steam-pipe and nuclear power generating equipments.Use the pipe field at nuclear power, austenitic stainless steel pipe and a spot of main cooling duct and the heat-transfer pipe of evaporator that use in nuclear island one loop that the domestic enterprise of a few family that possesses nuclear level steel pipe's production qualification produces, only as the product of filling a vacancy of imported product, still do not possess the ability of supply in full sets for a long time.Its basic reason is: WB36 structure of steel complex shape, the tissue that may occur has ferrite, bainite, martensite/austenite tissue etc., shortage is controlled thereby cause production process to be difficult to the realization delicate tissues organizing the profound understanding that forms with evolutionary process.And instantly China WB36 compo pipe consumption account for the steel total amount proportion only for developed country half, the WB36 compo pipe uses the expansion in field to provide wide space as industry development.According to the research of the Chinese special steel WB36 of association compo pipe branch, the demand annual growth of following China high pressure WB36 alloy pipe can reach 10-12%.Therefore, the delicate tissues technology of exploitation WB36 hot rolled seamless steel tube has considerable effect to improving weldless steel tube product core competitiveness.

Table 1WB36 steel routine chemical components (%)

Component	Content (wt.%)
		C	≤0.017
Si	0.25～0.50
		Mn	0.80～1.20
Cr	≤0.30
		Mo	0.25～0.50
Ni	1.00～1.30
		Cu	0.50～0.80
Nb	0.015～0.045

N	≤0.020
		Al	≤0.050

The WB36 weldless steel tube generally adopts hot rolling production, inevitably exists longitudinal bending and deviation from circular from, these defectives all to need to eliminate by straightening process after the hot rolling.Steel pipe is realized vertically circularity requirement straight and that directly make progress by recoverable deformation and viscous deformation during aligning.Only consider the raising of dimensional precision and production efficiency during tradition WB36 Straightening Seamless Steel Pipe, ignored straightening force and straightener working temperature to WB36 weldless steel tube tissue and Effect on Performance.Studies show that: inappropriate straightening process will cause occurring thick martensite/austenite tissue in the final room temperature texture, thus the impact property of remarkable deterioration steel pipe.Fig. 1 has provided the comparatively thick black strip martensite/austenite tissue that occurs after the WB36 Straightening Seamless Steel Pipe in room temperature texture.If by controlling the thickness that corrective force and straightening temperature reduce the strip martensite/austenite in the steel pipe tissue, this will realize the optimization of steel tube performance in the straightening process process.Consider that the steel pipe straightening temperature generally between 800～950K, appropriately can promote separating out of ferritic phase to minimal-stress deformation in this temperature range, reduce the residual austenite content in the steel simultaneously.Because residual austenite will be changed the strip martensite/austenite in process of cooling subsequently, little deformation technique method of aligning process can be avoided the formation of thick strip martensite/austenite, thereby realize good combination of strength and toughness, this also is the core place of patent of the present invention.

Summary of the invention

A kind of WB36 steel pipe aligning process martensite/austenite organizational controls method of the present invention, its purpose be exactly guarantee that steel pipe is directly spent and the straightening process of dimensional precision in, guarantee to generate the strip martensite/austenite tissue that is evenly distributed by the control straightening force, reduce thick martensite/austenite tissue to the disadvantageous effect of steel performance, and then the over-all properties of raising steel pipe, advance its application in practice.

WB36 steel pipe aligning process martensite/austenite organizational controls method of the present invention, be steel pipe with the hot rolling of WB36 steel, for guaranteeing to meet the requirements of heating and cooling speed, the general requirement tube wall thickness is not more than 5.42 centimetres, guaranteeing that after the normalizing be the lath martensite tissue, after 30 minutes normalizing treatment of 1173K, insulation, when being cooled to 860～920K, steel pipe enters six-roller straightener, aligning speed 10～15m/min, straightening force is 5～40MPa, is cooled to room temperature behind the steel pipe aligning.

The thinning method of strip martensite/austenite tissue in the WB36 steel aligning process that the present invention adopts, be different from traditional steel pipe straightening process method, the size of straightening temperature and straightening force all remarkably influenced strip martensite/austenite thickness of tissue size, Fig. 3 has provided 890K straightening force 5MPa respectively, 10MPa, 15MPa, 20MPa, 25MPa, 30MPa, 35MPa and 40MPa handle strip martensite/austenite thickness of tissue size in the WB36 steel pipe tissue of back, straightening force is the traditional straightening process that does not carry out the control of stress loading direction for the 0MPa indication, therefrom can find, increase along with straightening force, strip martensite/austenite thickness of tissue reduces earlier afterwards to increase, wherein the martensite/austenite tissue thickness minimum during 15MPa is 80nm.Strip martensite/austenite thickness of tissue size in 860K, 870K, 880K, 890K, 900K, 910K and 920K aligning back WB36 steel pipe tissue respectively when Fig. 4 has provided straightening force and is 15MPa, reduction along with straightening temperature, strip martensite/austenite thickness of tissue reduces earlier afterwards to increase, wherein the martensite/austenite tissue thickness minimum during 890K.

There is good corresponding relation in strip martensite/austenite thickness of tissue size with the steel pipe impact property in the WB36 steel pipe tissue of aligning back, Fig. 5 has provided different straightening force respectively with Fig. 6, different straightening temperatures are corrected the impact property size of back steel pipe, all things considered, strip martensite/austenite thickness of tissue is more little, the impact property of steel pipe is more high, after adopting the inventive method aligning, the room temperature ballistic work of steel pipe is brought up to 96J by 41J, increase rate is 234%, this proves absolutely the straightening process parameter, be temperature and straightening force, the over-all properties of remarkably influenced steel pipe also shows this method versatility and importance in process of production simultaneously.

Generally more than 50J, the steel pipe room temperature ballistic work that the straightening process that does not adopt this patent to invent is produced is 41J to the room temperature ballistic work of external WB36 weldless steel tube, is starkly lower than external product.By temperature and the power that control steel pipe aligning is, refinement the martensite/austenite tissue in the WB36 steel pipe tissue, significantly improved the impelling strength of steel pipe, product performance index has been higher than external product.

Description of drawings

Thick strip martensite/austenite tissue in the WB36 weldless steel tube tissue before Fig. 1 aligns;

Fig. 2 aligns thick strip martensite/austenite tissue in the WB36 weldless steel tube tissue of back;

Strip martensite/austenite tissue thickness size in the room temperature texture of Fig. 3 WB36 steel pipe 890K aligning back and the variation relation of straightening force;

Fig. 4 WB36 steel pipe in the room temperature texture of 15MPa aligning back strip martensite/austenite tissue thickness size and the variation relation of straightening temperature;

The variation relation of Fig. 5 WB36 steel pipe 890K aligning back room temperature ballistic work size and straightening force;

Fig. 6 WB36 steel pipe is through the variation relation of 15MPa aligning back room temperature ballistic work size and straightening temperature.

Embodiment

Concrete technical scheme embodiment of the present invention is as follows:

Embodiment 1:

Get the WB36 steel pipe, 2.71 centimetres of tube wall thicknesses after 1173K, 30 minutes normalizing treatment of insulation, enter six-roller straightener when steel pipe is cooled to 860K; Straightening force is 5MPa, is cooled to room temperature behind the steel pipe aligning.

Adopt that strip martensite/austenite tissue thickness is reduced to 131nm by 153nm in the WB36 steel pipe tissue of this technology aligning, the room temperature ballistic work has 32J to bring up to 53J.

Embodiment 2:

Get the WB36 steel pipe, 5.42 centimetres of tube wall thicknesses after 1173K, 30 minutes normalizing treatment of insulation, enter six-roller straightener when steel pipe is cooled to 920K; Set the straightener parameter, aligning speed 15m/min, straightening force is 40MPa, is cooled to room temperature behind the steel pipe aligning.

Adopt that strip martensite/austenite tissue thickness is reduced to 113nm by 153nm in the WB36 steel pipe tissue of this technology aligning, the room temperature ballistic work has 32J to bring up to 52J.

Embodiment 3:

Get the WB36 steel pipe, 1.36 centimetres of tube wall thicknesses after 1173K, 30 minutes normalizing treatment of insulation, enter six-roller straightener when steel pipe is cooled to 900K; Set the straightener parameter, aligning speed 15m/min, straightening force is 30MPa, is cooled to room temperature behind the steel pipe aligning.

Adopt that strip martensite/austenite tissue thickness is reduced to 110nm by 153nm in the WB36 steel pipe tissue of this technology aligning, the room temperature ballistic work has 32J to bring up to 57J.

Embodiment 4:

Get the WB36 steel pipe, 4.07 centimetres of tube wall thicknesses after 1173K, 30 minutes normalizing treatment of insulation, enter six-roller straightener when steel pipe is cooled to 890K; Set the straightener parameter, aligning speed 15m/min, straightening force is 15MPa, is cooled to room temperature behind the steel pipe aligning.

Adopt that strip martensite/austenite tissue thickness is reduced to 80nm by 153nm in the WB36 steel pipe tissue of this technology aligning, the room temperature ballistic work has 32J to bring up to 96J.

A kind of WB36 steel pipe aligning process martensite/austenite organizational controls method that the present invention proposes organizes to improve the over-all properties of steel pipe by obtaining the strip martensite/austenite.Be described by embodiment, person skilled obviously can be changed or suitably change and combination making method as herein described in not breaking away from content of the present invention, spirit and scope, realizes technology of the present invention.Special needs to be pointed out is, the replacement that all are similar and change apparent to those skilled in the artly, they are regarded as being included in spirit of the present invention, scope and the content.

Claims

1.WB36 steel pipe aligning process martensite/austenite organizational controls method, it is characterized in that with the hot rolling of WB36 steel be steel pipe, tube wall thickness is not more than 5.42 centimetres, after 1173K, 30 minutes normalizing treatment of insulation, when being cooled to 860～920K, steel pipe enters six-roller straightener, aligning speed 10～15m/min, straightening force is 5～40Mpa, is cooled to room temperature behind the steel pipe aligning.