Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
1999-04-30
2002-08-06
Picard, Leo (Department: 2125)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S149000, C700S150000, C700S030000, C700S031000
Reexamination Certificate
active
06430461
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for monitoring and controlling the quality of rolled products from hot-rolling processes in which rolled products such as sheets, strips, profiles, rods, wire, etc. are produced from input stock such as slabs, thin slabs, blooms, billets, etc.
2. Discussion of Background Information
The input stock solidified in the ingot mold has a fairly coarse primary structure, and the individual crystals have grown inward from the walls in the form of columnar crystals or dendrites. In order to achieve sufficient toughness, the structure must be refined. This is most effectively performed by mechanically breaking up the structure during rolling. The hot forming must be carried out essentially above the upper transformation line in the iron-carbon diagram, approximately in the range from 1100 to 850° C., depending on the composition of the steel, the upper temperature range serving mainly for shaping and the lower one for structure refining.
The article “Rechnersimulation der Warmumformung und der Umwandlung am Beispiel der Warmbanderzeugung” [Computer simulation of hot forming and transformation using hot strip production as an example] from Stahl und Eisen [Steel and Iron] 116 (1996) No. 4 of Apr. 15, 1996, presents the intermeshing models of shaping and structure development while taking into account the local forming characteristics. Individual calculations with various partial models, for example for the kinetics of dissolution and precipitation of microalloy elements and for the recrystallization sequence, underline the efficiency of the system with which complex production tasks can be performed. Thus, causes for the occurrence of an inhomogeneous ferrite structure in a tubular steel are derived from the simulation data and measures for improving the homogeneity are proposed.
The calculation of the effect of the cooling conditions on the transformation behavior of construction steel and the effect of the cooling conditions in the finish-rolled material on the changes in the strength properties over the strip length permit a quantitative evaluation of the influencing variables.
In cold working of the material, free dislocations must first be generated, which can then move along the slip planes. The generation occurs either through pulling off of “anchored” dislocations or activation of dislocation sources. Atoms such as C or N attached to dislocations make the pulling off and thus the generation of free dislocations difficult. Macroscopically, the effect is visible by a pronounced yield point. The strain in the material increases until it is sufficient to pull off the dislocation from attached atoms (“upper yield point”), i.e., if there is a sufficient strain, the dislocation is separated from the attached atoms. If the dislocations are then free, less strain is required for further dislocation movement (“lower yield point”). The strain necessary for the movement of free dislocations increases again only when impeded by other dislocations.
If the material is cold worked to a small extent before actual processing, dislocations are already generated. The frequency, distribution, and localization of the dislocations generated is affected by the type of cold working (e.g., stretcher-and-roller leveling, temper passing). The resistance which atoms such as C or N oppose the slip along existing dislocation planes is overcome with sufficient cold working (e.g., stretcher-and-roller leveling, temper passing with normal expansions).
FIG. 2
shows schematically a force-strain diagram (force F, strain &egr;) measured in a tensile strength test of a material with a pronounced yield point (Part X), and
FIG. 3
shows the force-strain diagram (Part Y) of the same specimen when it was subjected before the tensile strength test to cold working, in this case stretching of &egr;
1
%.
FIG. 4
shows part X+Y, which correlates the two aforementioned diagrams of
FIGS. 2 and 3
. In the tensile strength test with prior deformation, the first part of the force-strain curve of the nondeformed material (X) is blended out. With sufficient prior deformation, the pronounced yield point (the peak in (X)) is also blended out. Depending on the extent of the prior deformation, the yield point can rise or fall relative to the nondeformed material, as long as the nondeformed material has a pronounced yield point. If it has no pronounced yield point, the yield point rises in each case.
To determine the mechanical-technical characteristics R
p0.2
and R
m
, the measured forces F
0.2
and F
m
are divided by the cross-sectional area of the specimen (perpendicular to the direction of tension). In the test (Y), this cross-sectional area is already reduced compared to the test (X). Consequently, in our example in the case (Y), the tensile strength is greater than in the case (X), although the same maximum force F
m
was measured.
If sufficient interstitial atoms (C or N) are present in the basic material, they will also diffuse in the cold worked material at room temperature after a more or less longer time period to the dislocations present and pin them. Thus, a pronounced yield point also develops again in the cold worked material under certain circumstances (age hardening). To describe this age hardening, it is above all essential to know the amount of dissolved C and N. In BH-steels (bake hardening steels), this age hardening mechanism is expediently used to obtain a higher yield point after cold working and heat treatment (shortening of the diffusion time).
Only a very small quantity of C can be dissolved in ferrite. With clearly higher C-content, the carbon is precipitated as cementite (Fe
3
C) in various forms (for example, pearlite, grain boundary cementite, intercrystalline), whereby the respective form and quantity of the cementite precipitates also depend very much on the &ggr;-&agr;-phase transformation and the temperature progression. Under ordinary production conditions, in steels with C-content >.20, insufficient carbon to cause age hardening remains dissolved. At a lower C-content, cementite formation occurs more or less completely as a function of the temperature progression, such that sufficient carbon can be dissolved to cause intentional or unintentional age hardening.
In small quantities, carbon can, however, also be bound in precipitates. Above all in steels with very low C-content, alloy elements such as Ti, Nb, V are often used to bind the free carbon by precipitation. In this case, the precise knowledge of the amount and composition of these precipitates is important to calculate the amount of remaining free C.
The nitrogen present in the material can be bound in precipitates with Ti, Nb, Al, among others. Consequently, the precise knowledge of the amount and composition of these precipitates is important to calculate the amount of remaining free N. Above all in steels in which only Al is present as the single significant alloy element for N binding (construction steels and soft steels), under ordinary production conditions in hot-rolled strip production, the cooling curve in the cooling section and in the wound state is significant for AlN formation.
Through knowledge of the amount of dissolved C and N, it is possible to infer a pronounced yield point and thus also the change in the yield point by means of prior cold working. Moreover, it is possible with a cold worked material to calculate the redesigning of a pronounced yield point as a function of the quantity of dissolved C and N and the time elapsed since the cold working as well as the temperature during this time.
SUMMARY OF THE INVENTION
The object of the invention is to provide a process with which the material properties of the end product which are to be expected can be calculated in advance at each step of the hot rolling production process.
The above object is achieved by the invention, wherein production conditions such as temperatures, reductions per pass, etc. are detected on-line throughout the entire rolling proces
Andorfer Josef
Auzinger Dietmar
Pichler Rudolf
Greenblum & Bernstein P.L.C.
Jarrett Ryan
Picard Leo
Voest-Alpine Industriean-lagenbau GmbH
LandOfFree
Process for monitoring and controlling the quality of rolled... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for monitoring and controlling the quality of rolled..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for monitoring and controlling the quality of rolled... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2969213