RU2183516C1 - Method for preparing hot rolled steel strips to etching - Google Patents

Abstract

FIELD: plastic metal working, possibly manufacture of cold rolled steel, namely preparation of rolled pieces to etching. SUBSTANCE: method for preparing hot rolled steel to etching comprises steps of preliminarily reducing of preset length of moving strip in skin pass rolling stand with rolls having predetermined surface roughness and rigidity; varying reduction value ≤ in dependence upon planned tonnage T of strip subjected to skin pass rolling during operational campaign of rolls. At tonnage 0.3T when reduction value 2% ≤ 2.5%; at tonnage more than 0.3T and less or equal to 0.6T when 2.5% ≤ 3%; at tonnage more than 0.6T when 3% R₂ 4%, using rolls with barrel Shore hardness 94-96 and surface roughness parameters of rolls R=(15-35)micrometers and S more than 35 micrometers along basic length l=0.8mm. EFFECT: enhanced quality of cold rolled strip steel due to lowered number of flaws because of etching rolled piece. 1 ex

Description

 The invention relates to the processing of metals by pressure and can be used in the production of cold-rolled strip steel in the preparation of rolled for pickling.

 Hot rolled strips serve as a tack (blank) for the production of cold rolled steel. A necessary operation before the cold rolling of such strips is the removal of scale from their surface, as a rule, by etching in sulfuric or hydrochloric acid solutions on specialized continuous etching units (NTA). To accelerate the etching process, preliminary destruction of scale is widely used, for example, by compressing a small size with rolls of a training stand installed at the entrance to the NTA (see, for example, the manual edited by V.I. Zyuzin and A.V. Tretyakov "Rolling technology production ", book 2. M .: Metallurgy, 1991, p. 636), as a result, the scale layer is crushed and partially crumbles from the moving strip to the entrance to the bathtubs, which increases the etching rate by 1.5-2 times.

Training, i.e. cold rolling with a relative compression of up to 5 ... 8% is carried out in notched rolls with developed microgeometry (see the book “Improving the Cold Rolling Process” by V. K. Belosevich and N. P. Netesov, M.: Metallurgy, 1971 , p. 218). In this case, surface microgeometry is characterized by roughness parameters R _z (average height of profile irregularities at ten points) and S (step of local protrusions). The indicated roughness parameters are determined within the base length l (usually take l = 0.8 mm) in accordance with GOST 2789-73. In addition, roll barrels have a certain hardness (usually in Shore units).

 The known process of removing scale from a continuously moving strip by bending it using a special device with an electric drive (see US Pat. US 3393434, CL 29-81 from 07.23.68). There is also a known method of removing scale from metal sheets by working rollers on which abrasive plates are mounted that perform tangential movement (see US Pat. US 3888048, class B 23 V 7/12 of 06/10/75). A disadvantage of the known methods of descaling is the impossibility of their use for a rapidly moving wide (up to 2 m) strip of relatively large (up to 4 mm) thickness, as well as in the case of a hot rolled strip defect "rolled scale", which can lead to the described devices to breakage.

 The closest analogue to the claimed object is the technology of preparation for pickling hot rolled strip steel, described in the book P.I. Polukhina and others. "Rolling production", M .: "Metallurgy", 1982, p. 485-487.

 This technology involves passing the strip in front of the pickling baths through a roller descaler and a training stand, and is characterized by squeezing the strip in this stand lying within 3 ... 8%, which not only destroys the scale, but also eliminates the breaks in the strip after it is unwound. The disadvantage of this technology is the large upper limit of the relative compression, which leads to accelerated wear of the rolls (smoothing of microroughnesses) and, as a result, to a slowdown of the etching process and the possibility of the occurrence of a defect "undergrav" which is unrecoverable and unacceptable during cold rolling.

 An object of the invention is to improve the quality of cold-rolled strip steel by reducing defects during pickling etching.

To solve this problem, in a method for preparing hot-rolled strip steel for pickling, including preliminary compression of a given value of a moving strip in a training stand with rolls having a given hardness and surface roughness, the compression value ε is changed depending on the planned tonnage T of the strip subjected to tempering during the working campaign rolls, and with tonnage less than or equal to 0.3 T-2% ≤ ε ≤ 2.5%; more than 0.3 T and less than or equal to 0.6 T-2.5% <ε ≤ 3%; more than 0.6 T-3% <ε ≤ 4% and use rolls with a barrel hardness of 94-96 units. along shore; in this case, the parameters of the surface roughness of the rolls R _z = 15-35 μm and S no more than 35 μm on the base length l = 0.8 mm are set.

 The given values of individual parameters were obtained as a result of processing experimental data.

The essence of the technical solution found is to optimize the amount of compression ε (2-4%) of the moving hot-rolled strip by the rolls of the training stand installed at the inlet of the NTA, and the work campaign of the rolls (i.e., after their direct installation in the stand) begins with a minimum amount of compression ( 2%) and change depending on the planned tonnage T of the strip subjected to training during the working campaign of the rolls, and with a tonnage less than or equal to 0.3 T, the compression value is set within 2% ≤ ε ≤ 2.5%; more than 0.3 T and less than or equal to 0.6 T-2.5% <ε ≤ 3%; more than 0.6 T-3% <ε ≤ 4%. In addition, the rolls must have a certain hardness, and their surface must have a given microgeometry (R _z value and the step size of the local protrusions S).

The latter value characterizes the "density" of the distribution of the peaks of microroughness and, as experiments have confirmed (see below), is one of the indicators of the rolls working capacity and the degree of preliminary scale destruction. The recommended range of R _{z is} also optimal in terms of the duration of the working campaign of the rolls and their efficiency. The found value of the hardness of the roll barrels not only increases the duration of their campaign, but also provides the above microgeometry parameters of the barrels. The proposed limits for the amount of compression, depending on the planned tonnage of the strip subjected to training during the working campaign of the rolls, are optimal from the point of view of high-quality descaling. This is explained by the fact that after filling the rolls into the cage, the microrelief of their surface is sufficiently developed, and for a high-quality removal of scale at the beginning of the working campaign of the rolls, a small change in compression is required; as the tonnage of the strip subjected to training increases (at the end of the working campaign of the rolls), the microprotrusions are smoothed out, and a better change in compression is necessary for the best removal of scale.

 The combination of all these factors contributes to the intensive destruction of scale on the surface of a hot-rolled steel strip, guaranteeing the absence of defects such as undergravity and rolled mill scale after etching at maximum speed.

 When implementing the proposed method, heat treatment of roll barrels is preliminarily carried out in order to achieve their necessary hardness, and then microrelief is applied with the required parameters (for example, by shot peening the surface of roll barrels).

 Experimental verification of the proposed method was carried out on a continuous pickling unit for pickling strip steel of various grades. For this purpose, when etching a hot-rolled strip, rolls with different hardness and microgeometry were used to train metal, varying the amount of compression when the strips passed through the NTA training stand. The results of the experiments were assessed by the presence of defects after etching, as well as by the yield of low-quality cold-rolled steel: Ш groups of surface finish of strips (according to GOST 16523) and second grade.

The best results (the absence of the aforementioned defects during etching with the strip speed adopted by the NTA, as well as the sorting of cold-rolled metal in the range up to 0.5%) were obtained using the proposed method. When the hardness of the barrels of rolls of the training stand is less than 94 units. according to Shore, the duration of their working campaign decreased, and with a hardness of more than 96 units. - it was not possible to obtain the required microgeometry of the barrel surface. In turn, at R _z <15 μm and S> 35 μm, scale destruction was less intense, which impaired the quality of etching (and cold-rolled strips), forcing to increase the etching duration, i.e. reduce speed and performance. At R _z > 35 μm, the wear rate of the microgeometry of the barrel surface increased, which reduced the working campaign of the rolls. The microrelief parameters were determined using a model 201 profilograph by taking profilograms at a base length l = 0.8 mm.

 The “control” etching using roll training with optimal (see above) surface microrelief parameters and recommended hardness, but with a compression ratio of more than 4% (that is, according to known technology) reduced the duration of the roll campaign by 1.5 .. .2 times with a corresponding increase in labor costs, and after pickling there was a defect "rolled mill scale", as a result of which the sorting of cold-rolled metal increased to 3 ... 5%. An increase in the reduction during the work roll campaign other than the limits found worsened the descaling by the end of the work roll campaign, which led to an increase in sorting of the cold-rolled strip to 1.2%.

 Thus, the experiments confirmed the acceptability of the technical solution found to fulfill the task and its advantages over the known object.

Concrete example
08ps hot-rolled strip steel with a cross section of 1600 x 2.5 mm is subjected to training before etching using rolls, the barrel hardness of which is 95 units. according to Shore, and the parameters of surface microgeometry (measured at a base length l = 0.8 mm) are R _z = 25 μm and S = 30 μm. The planned duration of the working campaign of the rolls is 800 tons. Immediately after filling the rolls in the stand, the compression ratio is 2%; after training 240 tons of strip compression is increased to 2.5%; having trained 400 tons of metal, set compression of 3%; after training 550 tons, the compression is increased to 4%. The last compression value is stored until the rolls are transshipped.

Claims (1)

 A method of preparing for pickling hot rolled strip steel, comprising pre-compression of a predetermined value of a moving strip in a training stand with rolls having a predetermined hardness and surface roughness, characterized in that the compression value ε is changed depending on the planned tonnage T of the strip subjected to tempering during the working campaign rolls, and with tonnage less than or equal to 0.3 T: 2% ≤ ε ≤ 2.5%, more than 0.3 T and less than or equal to 0.6 T: 2.5% <ε ≤ 3%, more than 0, 6 T: 3% <ε ≤ 4% and use rolls with a barrel hardness of 94-96 units. according to Shore, in this case, the parameters of the surface roughness of the rolls Rz = 15-35 μm and S no more than 35 μm at the base length l = 0.8 mm are set.