hot-rolled SUS 304 stainless steel strip

Abstract : The 780 mm hot rolling mill has advanced equipment and is suitable for producing hot-rolled stainless steel strip . In the process of studying the production process, combined with the characteristics of stainless steel production, the production process of SUS 304 hot-rolled stainless steel strip was studied and formulated, and the rolling results of the stainless steel strip were analyzed. The results showed that the production process of the stainless steel strip Stable and reasonable .
Key words: 1780 mm hot continuous rolling mill; stainless steel strip; production process CLC number: TG 335.5 + 6 Document identification code : A

The 1780 mm hot continuous rolling mill is an important part of the stainless steel project of Baosteel Group Shanghai No. In 2004 , a total of 1.79 million tons of hot-rolled steel strips were produced , including 140,000 tons of stainless steel hot-rolled steel strips . Its steel grades include: SUS 304 , US 304l , US 430 , US 409l ,
SUS 420 , US316 , etc. Since it was put into production, the actual performance of strip steel production has proved that the stainless steel rolling process is reasonable and reliable , which has created conditions for the 1780 mm rolling mill to increase production efficiency and develop new stainless steel products .

1. Determination of Hot Rolling Process of SUS 304 Stainless Steel

1780 mm hot rolling mill includes: 3 walking -type slab heating furnaces , 1 high-pressure water descaling box , 1 roughing mill , 1 set of laminar cooling roller table , 2 underground strip coils Take machine . Its main features are: advanced equipment technology , high level of automation , maximum rolling pressure of 42 000 kN , and high precision of strip steel control . The 1 780 mm hot rolling mill adopts foreign advanced technology and equipment , The performance of the equipment is suitable for the production of hot-rolled stainless steel strip . The layout of the main equipment of the 1780 mm hot rolling mill is shown in Figure 1 .
In order to give full play to the excellent performance of the hot continuous rolling mill, combined with the characteristics of stainless steel, a whole set of strip steel production process has been researched and formulated, so that the capacity of the rolling mill can be fully utilized, and the quality of the strip steel can reach the design level of the rolling mill. 11 Effect of steel composition on deformation ability
SUS304 is an austenitic stainless steel , It is a representative steel grade of w(Cr )18%/ w (Ni )8% ratio stainless steel. w (Cr ) 18% and w (Ni ) 8% are the minimum for austenitic stainless steel to ensure single-phase structure

Billet hot coiling box , 1 flying shear for strip trimming , 7- stand finishing mill ,
Scale ( Figure 2) . A small amount of the second phase in the metallographic structure is beneficial to the steel

High temperature deformation. When w(Ni )<8% in the steel , the austenite structure of the 18-8 type steel is in an unstable state.
It can be seen that when w (Cr ) is lower or higher than 8% , w (Ni ) needs to be increased to ensure the stability of the austenite structure of the steel . For the composition control of S US304 steel , when w (Cr ) is controlled near the standard lower limit ( 18%) , (Ni ) can also be controlled near the standard lower limit (8%) ; when w (Cr ) in steel increases When w(Ni) is high, w(Ni ) should also increase accordingly , so as to maintain the chromium-nickel ratio of the austenitic structure . In actual production , due to the existence of multiple alloying elements in steel , the composition of steel should be controlled according to chromium equivalent / nickel equivalent , so as to minimize the addition of precious metal nickel and reduce smelting costs .
In actual production, due to fluctuations in component control, it is impossible to obtain
Plastic influence . When the second phase structure in the steel is less than 10% , the effect on thermoplasticity is limited; and when it is greater than 10% , the thermoplasticity of the steel begins to deteriorate , and deformation defects will occur .
1. Effect of heating temperature on deformation ability
Heating temperature has a significant effect on the amount of ferrite in 18-8 stainless steel . ICr 18Ni 9Ti and SUS 304 steel belong to 18-8 austenitic stainless steel ( Figure 4). When 1Cr 18Ni 9Ti steel is heated above 1250 C , the amount of ferrite in the steel reaches more than 10% and increases rapidly; when it reaches 1300 At C , the amount of ferrite reaches 29%, and the hot workability of the steel is seriously deteriorated at this time .

To control and reduce the amount of ferrite phase in SUS 304 steel (increase the amount of austenite phase ), two methods can usually be used: one is to adjust the chemical composition of the steel , increase the austenite forming elements in the steel , and stabilize the austenite Phase , to achieve the purpose of reducing the amount of ferrite phase; another method is to reduce the heating temperature of the steel , so that the amount of ferrite phase in the steel does not increase to the extent that it will endanger the deformation ability of the steel . The former can expand the deformation temperature range of steel and increase the maximum deformation temperature of steel , which is beneficial to reduce the deformation resistance of stainless steel during hot working; the latter narrows the high temperature deformation temperature range of steel and reduces the maximum deformation ( heating ) temperature of steel. , Improve the deformation resistance of steel during hot working , and increase the difficulty of deformation processing .
w (Ni ) in steel, hot rolling mills for producing hot-rolled stainless steel strips have been developing toward high power and large rolling capacity since the end of the 20th century . The 1 780 mm hot continuous rolling mill of No. 1 Steel Company meets the requirements of high deformation resistance and narrow deformation temperature range under the condition of minimum steel composition cost , which minimizes the overall production cost of stainless hot-rolled strip .
Equilibrium diagram of metallographic structure of FeCr-Ni alloy with w (Ni ) 8% . When the w (Cr) in the steel is 18% and below 1150 °C , the austenite phase is the most stable; when the temperature reaches above 1150 ° C , the ferrite begins to appear , and with the increase of temperature , its number is also constant Increase according to the capacity of 1780 mm hot rolling mill , in order to ensure the minimum amount of ferrite phase , the heating temperature of SUS 304 slab should be controlled at 1200
~ 1250 °C .
1.3 Setting of the pressing procedure
Figure 6 and Figure 7 show the relationship between deformation speed and deformation resistance of SUS 304 steel obtained by glee ble testing machine . It can be seen from the figure that the lower the temperature of US304 steel , the faster its deformation resistance increases . Therefore, the rolling deformation should be completed at the highest possible temperature to reduce the load of the rolling mill and improve the control accuracy . According to the test data , the deformation resistance of each stand ( pass ) of the rolling mill can be calculated according to the formula , which provides a basis for a reasonable load distribution of the rolling mill . Rolling pressure calculation formula:

Q Cal	()=0.8 +CX { jRd Cal ( i )/H Cal ( -1)-0
In the formula	Qp Cal (i )--	- i stand rolling function;
	R d Cal (i )-	-- i stand roll flattening function;
	H Cal (i)--	- i frame outlet thickness;
	C --	- A function related to pass deformation rate .
1.4	Hot-rolled SUS304 strip steel process

The thermal processing characteristics of SUS 304 steel are low thermal conductivity, high temperature deformation resistance and high temperature resistance to oxidation , so full attention should be paid to the thermal processing of strip steel . There is no limit to the heating rate of the slab heating , the high-temperature strength of the steel is high , the risk of cantilever sagging is small , and the temperature drop has no effect on high-temperature deformation.

500	one_one800 _ _ _
400	/ ..Yangyo _
300	・/匸 z —1050 to
200	1 150 to dagger"1 plus n V
100	Township K 1250

0 0.2 0.4 0.5 0.6 0.7
strain

Fig.6 True stress-strain curve of SUS304 ( strain rate at 10s -1 ) Fig.6 True stress -strain curve of SUS304 (strain rate at 10s -1 )

1. Surface roughness of hot-rolled stainless steel strip The surface roughness of hot-rolled stainless steel

very important . The smooth strip surface can guarantee the surface quality of cold-rolled stainless steel sheets . Table 1 shows the measured surface roughness values of hot-rolled stainless steel strip produced by 1780 mm hot rolling . It can be seen that the maximum R a is 3.52 Mm and the average is 2~3 Mm . The hot-rolled steel strip has a smooth surface and good quality , which can meet the requirements of the cold-rolling process .

1. mechanical properties

Table 2 is the mechanical properties of hot-rolled SUS 304 strip steel . Regardless of the strip thickness of 3.0 mm or 5.0 mm , Tensile strength base after hot rolling
Table 1 Measured values ( Ra ) of s urf ace roughness of hot
rolli ng SUS304stri p Mm

	just	opposite	just	opposite
1-1	1.37	2.80	1.39	2.99
1-2	1.36	2.51	1.33	3.34
3-1	3.18	2.14	3.07	2.1
3-2	2.06	2.78	1.65	3.52
7-1	1.52	1.95	1.44	2.06
7-2	1.40	1.85	1.52	1.84

This is equivalent to the lower tensile strength values for hot-rolled ( non-heat-treated ) strip , indicating that the strip rolling process is quite stable .
2.4 Appearance quality and edge of steel coil
The control level of the head and tail of the stainless steel strip in the finishing mill has a great influence on the coil shape , improving the setting accuracy of the finishing rolling of the strip , and stabilizing the rolling conditions at the tail of the strip are conducive to improving the coiling of the steel coil

quality . The optimization of pinch roll and coiler setting parameters has a direct impact on coil coiling quality . Through the above-mentioned control of the two main influencing factors , the coiling of the steel coil can reach an ideal state , and the coiling quality can be obviously improved . The steel coil is tightly coiled , the coil shape is good , and the steel coil tower shape meets the standard requirements .
Since April 2004 , the trial production of SUS 304 stainless steel strip at Yigang has reached 120,000 tons , and stainless steel coils with specifications above 2.0 mm X 1250 mm have been successfully produced and provided to users . Users reported that the surface quality , edge quality , plate shape , thickness uniformity , width deviation, etc. can better meet the requirements of use . The 1780 mm hot rolling mill is continuously increasing the production of stainless steel strip according to market requirements , Create your own stainless steel brand .
in conclusion

 

1. 1780 mm hot continuous rolling mill has played a good role in the equipment's ability, and fully considered the deformation characteristics of SUS 304 stainless steel , so that the hot continuous rolling mill can realize the production of stainless steel strip in a relatively short period of time .
2. stainless steel strip in terms of surface quality , edge quality , shape control and thickness uniformity, etc. , The rationality and stability of the production process are proved . It has laid a good foundation for future mass production .
3. The quality control of the production process of hot-rolled stainless steel strip is very important , which is related to the stability of production and the stability of quality level . With the continuous improvement of the function adjustment of 1780mm hot rolling equipment , the production process system of stainless steel strip closely matches the characteristics of the equipment , By fully utilizing the functions of the rolling mill , the production quality of strip steel is expected to be further improved .

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