CN103394509A

CN103394509A - Plate rolling method for refining X70 austenite grains

Info

Publication number: CN103394509A
Application number: CN201310288653XA
Authority: CN
Inventors: 温利军; 张大治; 董瑞峰; 戴鑫
Original assignee: Baotou Iron and Steel Group Co Ltd
Current assignee: Baotou Iron and Steel Group Co Ltd; Inner Mongolia Baotou Steel Union Co Ltd
Priority date: 2013-07-10
Filing date: 2013-07-10
Publication date: 2013-11-20

Abstract

The invention relates to a plate rolling method for refining X70 austenite grains and belongs to the field of the steel rolling technology. According to the plate rolling method for refining the X70 austenite grains, the tapping temperature of a plate billet is 1140DEG C-1190 DEG C. After the plate billet is discharged from a furnace, firstly the plate billet is rolled so that the thickness of the plate billet can be 160-200mm, and secondly the plate billet is manually swung on a roller bed until the temperature of the plate billet is 1115DEG C-1123DEG C. Then, the plate billet is rolled again at this moment, and the thickness of the plate billet is made to be 54mm-65mm through rolling, wherein the finishing rolling temperature is higher than 990DEG C in this stage. The cooling method of manual swing in the temperature waiting period is natural cooling. The size of the austenite grain of a steel plate is greatly reduced through rolling after the temperature waiting period. The percent of pass of DWTT values is increased to 98% from 60%. The plate rolling method for refining the X70 austenite grains is simple, easy to grasp and operate, free of addition of any equipment and other investment, and easy to achieve in production.

Description

The plate milling method of refinement X70 austenite crystal

Technical field

The present invention relates to a kind of plate milling method of refinement X70 austenite crystal, belong to the steel rolling process field.

Background technology

The X70 pipe line steel is a kind of high-strength line-pipe steel that requires high tenacity, and X70 is high to the toughness reguirements of steel plate, the DWTT(drop weight tearing of X70) value requires to be not less than 85%.The toughness of X70 steel plate quality is except outside the Pass having with the Design of Chemical Composition of steel plate, tissue after phase transformation, also relevant with austenitic grain size before the steel plate phase transformation, especially the DWTT value depends mainly on the front austenitic grain size of phase transformation, and before phase transformation, austenite crystal is less, and the DWTT value of steel plate is larger.

In order to improve the toughness of X70, improve the DWTT value of X70, refine austenite crystal grain, in the situation that compression ratio is certain, traditional method generally has two kinds.The one, reduce the tapping temperature of slab, lower because heating-up temperature is the tapping temperature of slab, austenite crystal is just more tiny, and the austenite crystal after rolling is also just more tiny like this, and the DWTT value of steel plate is also just larger.if yet reduction slab tapping temperature simply, can serve quality problems by band, while being at first heating, slab shows that the iron scale of production is not easy to remove clean, affect steel plate and show quality, in addition because the X70 Composition Design all contains certain Nb, if heating-up temperature is too low, the carbon of Nb, nitride fully solid solution in austenite, still some rests on austenite grain boundary, hinder the growth of austenite crystal, cause austenite grain size inhomogeneous, mixed crystal phenomenon appears, while is due to the carbon of Nb, nitride does not have abundant solid solution in austenite, cause steel plate in the non-recrystallization controlled rolling stage, the carbon of Nb, nitride is from separating out quantity not sufficient in austenite, affect the controlled rolling effect.

Patent No. CN 102107220 A " a kind of steel for engineering machinery intermediate blank is treated the method that temperature control is rolled " provide a kind of method of refine austenite crystal grain, the method is after slab is come out of the stove, it is rolled down to the secondary open rolling thickness of steel plate fast, then pass through the cooling quickly cooling device that waits of laminar flow, it is cooled to rapidly to the secondary start rolling temperature.Purpose is to avoid the austenite crystal after rolling refined to treat again to grow up in warm process in swing.But this method has certain limitation, mainly because at this moment intermediate blank is thicker, cool time is longer, add the limitation of various fast cooling devices itself and the impact that is subjected to rolled plate plate shape, usually inhomogeneous cooling is even through intermediate blank that fast cooling device is cooling, cause the front austenite grain size inequality of second stage open rolling, after the second stage rolling, the grain size inhomogeneities further strengthens, and finally causes the mechanical performance of steel plate inhomogeneous.Due to inhomogeneous cooling, while causing rolling, the milled sheet shape of steel plate is not easy to control, and some production accidents even occur simultaneously.Finally, owing on roller-way, having increased control-cooling equipment, equipment investment cost and operating cost increase, and ton steel production cost improves, the impact that taken up space by control-cooling equipment, and the rollgang maintenance that control-cooling equipment is corresponding is not easy.

Summary of the invention

The object of the present invention is to provide austenite crystal before a kind of refinement X70 pipe line steel phase transformation that effectively, does not increase any cost convenient and simple for operation, improve the plate milling method of the refinement X70 austenite crystal of X70 mechanical performance.

Technical solution scheme of the present invention is:

1) the slab tapping temperature is 1140-1190 ℃;

2) after slab is come out of the stove, first slab is rolled to 160～200mm thickly, then treat that temperature starts rolling again to 1115～1123 ℃ roller-way left-hand seat movable pendulum is moving, slab thickness is rolled to 54～65mm, require the finishing temperature of this one-phase>990 ℃.

The present invention manually swings and treats that the type of cooling during temperature is natural air cooling.

Steel plate rolling of the present invention slab thickness used is 248-253mm.

The present invention and former refinement X70 austenite crystal method are relatively

The method of former refine austenite crystal grain is mainly by reducing tapping temperature, or directly rolls secondary open rolling thickness by quickly cooling devices such as laminar flow are cooling, and intermediate blank is cooled fast to the secondary start rolling temperature.Reducing tapping temperature can cause slab iron scale of generation when heating to be not easy to remove, affect the surface quality of steel plate, or because heating-up temperature is low, the carbon of Nb, nitride can not fully dissolve, while mixed crystal phenomenon and non-recrystallization controlled rolling occurring, the carbon of Nb, nitride, from austenite, separating out quantity not sufficient, affect the controlled rolling effect.

By the cooling quickly cooling device that waits of laminar flow, intermediate blank is cooled to rapidly to the method for secondary start rolling temperature, be subjected to the impact of the factor of equipment own and milled sheet shape, usually cause the intermediate blank inhomogeneous cooling even, cause the front austenite grain size inequality of second stage open rolling, after the second stage rolling, the grain size inhomogeneities further strengthens, and finally causes the mechanical performance of steel plate inhomogeneous.Due to inhomogeneous cooling, while causing rolling, the milled sheet shape of steel plate is not easy to control, and some production accidents even occur simultaneously.Increase simultaneously fast cooling device and can increase equipment and artificial the input, increase ton steel production cost.

Adopt the present invention also not affect in the situation of plate quality and performance not increasing any cost, make the significantly refinement of austenite grain size of steel plate, the toughness of steel plate increases substantially.After adopting this method, by the experiment of the DWTT(drop weight tearing of pipe line steel) qualification rate brought up to now 98% by former 60%, to produce 10000 tons of X70 pipe line steels every year, calculate, and compares in the past, can reduce costs 2,000 ten thousand.Before in June, 2011, we adopt the pair rolling method to produce the X70 pipe line steel, and after namely slab was come out of the stove, roughing mill just then was rolled, till rolling second stage open rolling thickness always, middle not stop, do the DWTT check to the steel plate of producing, and the DWTT qualification rate of steel plate only has 61%, when again produce the X70 pipe line steel in September, 2011, employing this method is rolled, and the steel plate of producing is done to the DWTT check, and the DWTT qualification rate of steel plate reaches 98%.The size of DWTT value has been reacted the height of steel plate toughness, shows after deliberation, and the size of DWTT value depends primarily on the size of the front austenite crystal of phase transformation, and austenite crystal is less, and the DWTT value is larger, and austenite crystal is larger, and the DWTT value is less.Therefore the key that improves the DWTT value is refine austenite crystal grain; adopt the pair rolling method; the finishing temperature that steel plate rolls is higher; although the rolling through the several passages in front; austenite crystal obtains refinement significantly; but because finishing temperature is high; the austenite crystal of refinement can be grown up rapidly; because in the situation that treat temperature thickness, treat that Wen Wendu is certain; austenite grain size depends primarily on the height of finishing temperature, and finishing temperature is higher, and the austenite crystal that finally obtains is larger; finishing temperature is lower, and austenite crystal is just less.Adopt the method, because slab is treated temperature a period of time, board briquette reduces, and the finishing temperature that rolls so rear steel plate also can reduce accordingly, through the austenite crystal of former passages refinement, just can how not to grow up, and finally obtains tiny austenite crystal.The present invention, just rolling mill practice is optimized, do not need to add any equipment, so can not increase manufacturing cost, simultaneously to be cooled to the type of cooling that start rolling temperature for the second time adopts be natural air cooling to intermediate blank, therefore intermediate blank is cooling evenly, makes the front austenite grain size of second stage open rolling even.

The accompanying drawing explanation

Fig. 1 is example 1 gained austenite crystal figure of the present invention;

Fig. 2 is example 2 gained austenite crystal figure of the present invention.

The specific embodiment:

Embodiment 1

Produce the thick X70 steel plate of 21mm, the secondary open rolling thickness of steel plate is 61.9mm, and the secondary start rolling temperature is 950 ℃.During production, the tapping temperature of slab is 1154 ℃, and the slab thickness of employing is 252mm, first that slab rolling is thick to 177mm, then in the moving temperature for the treatment of of roller-way left-hand seat movable pendulum, until temperature, start rolling during to 1121 ℃, till being rolled down to 61.9mm, 1079 ℃ of the finishing temperatures of this one-phase.By after this regulation rolling, the austenite crystal of steel plate is tiny, and grain size is 8 grades.Concrete metallographic as shown in Figure 1.

Embodiment 2

Produce the thick X70 steel plate of 21mm, the secondary open rolling thickness of steel plate is 70.1mm, and the secondary start rolling temperature is 950 ℃.During production, the tapping temperature of slab is 1176 ℃, and the slab thickness of employing is 252mm, first that slab rolling is thick to 177mm, then in the moving temperature for the treatment of of roller-way left-hand seat movable pendulum, until temperature, start rolling during to 1120 ℃, till being rolled down to 70.1mm, 1073 ℃ of the finishing temperatures of this one-phase.By after this regulation rolling, the austenite crystal of steel plate is tiny, and grain size is 8 grades.Concrete metallographic as shown in Figure 2.

Claims

1. the milling method of refinement X70 austenite crystal, it is characterized in that, milling method is as follows: the slab tapping temperature is 1140-1190 ℃, after slab is come out of the stove, first roll to 160～200mm slab thick, then treat that temperature starts rolling again to 1115～1123 ℃, rolls slab thickness to 54～65mm finishing temperature>990 ℃ roller-way left-hand seat movable pendulum is moving.

2. according to the milling method of the described refinement X70 of right 1 austenite crystal, it is characterized in that, manually swing and treat that the type of cooling during temperature is natural air cooling.

3. according to the milling method of the described refinement X70 of right 1 austenite crystal, it is characterized in that, steel plate slab used is 248-253mm.