1. Introduction to Metallurgical Essentials
The fundamental concepts related to steel products metallurgy (composition, crystal structure, microstructure, strength, etc.) will be presented so that the attendee can gain an understanding of the relationship between microstructure and steel properties, as well as how the microstructure is controlled mainly by thermal cycles, which influences the decomposition of austenite. The attendee will also recognize the influence of fundamental steel metallurgy on the choice of industrial processing parameters to obtain specific material properties. An introduction to the metallurgy behind advanced and ultrahigh-strength steel grades will also be provided.
2. Steel Standards
Standards are classification methods to identify steel grades. The use of standards guarantees steel product quality, reliability and interchangeability. They are coherent, simple and convenient, and provide a specific name, symbol(s), number(s), letter(s) or a combination of these. Standards also include data such as composition, dimension and mechanical properties. An overview of the development of standards, the science behind them, and the influence of professional engineering societies, trade associations, government regulation agencies and official standardization institutes will be included.
3. Conventional Hot Strip Mill (HSM) Designs
Hot strip rolling refers to the process of rolling a steel slab while the steel is in a state of recrystallization due to its temperature. While above the recrystallization temperature, the steel is deformed via rolling to adjust the austenitic grain size required for downstream processing. The end product is a semi-finished steel coil. The principles of hot strip processing will be presented, as will HSM designs and the instrumentation and automation systems currently being used. Included in the section will be how cast slab quality impacts the final coil, slab reheating requirements, reheat furnace designs, roughing and finishing mill designs, and the purposes of each mill, descaling, strip and width control, coilbox technologies, roll configurations and roll changes during production, shears, runout tables and downcoilers. An overview of product classifications will also be presented.
4. Alternative Hot Strip Mills (HSMs)
Alternative hot strip mills are fifth-generation HSMs that began in 1989 with the compact strip process (CSP) and have evolved into other designs such as in-line strip processing (ISP), endless strip processing (ESP) and the casting-pressing-rolling (CPR) process. Fifth-generation HSMs are compact, cost-effective facilities whose conversion costs are low due to the utilization of thin-slab casting machines (50–100 mm) directly linked to roller hearth furnaces and minimal or no roughing mill. The CPR process utilizes a 2- to 3-mm cast strip pressed between rolls prior to entering a reheat furnace, then a single-stand rolling mill prior to coiling. This section will present the designs and principles for alternative hot strip mills and the importance of these new technologies in terms of flexibility, productivity and cost-efficiency.
5. Hot Strip Mill Processing of Automotive Grades
Steel is a critical component in the production of automobiles. Sheet steel is required for the body, exhaust, wheels and other components. Each sheet-steel application in an automobile requires specific properties. For example, exterior panels on an automobile have a high degree of formability for material efficiency, as well as strength for passenger safety. The automotive industry has driven the efforts toward making new types of steel that are both stronger and more formable, which has led to the development of high-strength sheet steels and dual-phase steels. The presentation will show how properties required for a specific application are obtained through a combination of composition and thermomechanical processing.
6. Pickling Technology
Pickling of steel is essential in effectively removing surface oxides prior to cold rolling. The different pickling processes will be presented, as will the relationship of temperature and turbulence — the main processing parameters — to the rate of thermal oxide removal. Acid conditioning and regeneration and surface quality abnormalities, such as pitting, copper plating and burned-in scale, will also be discussed.
7. Cold Strip Mill
In the cold strip mill (CSM), a strip is obtained that has the target exit thickness with acceptable shape (flatness), without exceeding the mill limits. The work rolls must be free of marks, and the strip surface appearance must be defect-free. After the CSM, coils are annealed (batch or continuous), coated (electrogalvanized, hot-dip galvanized, etc.), temper rolled and surface treated, if required. Cold rolled strip may also be coil coated with a polymeric paint layer. The essentials of cold strip mill designs and operation, the strip annealing processes, and the function of skinpass or temper rolling will be presented. The influence of processing on the microstructure and the subsequent properties of the cold rolled strip are included, as is the relation between the different process parameters in achieving the final in-service properties of cold rolled strip. Gauge controls and the engineered requirements of rolling lubrication will also be presented.
8. Coating Technology
Much of the success of coated sheet steel is due to a switch from uncoated to coated sheet in the automotive industry and its increased use in the building industry and household appliance manufacturing. By coating steel via galvanizing, Galvalume® or other coating technologies, the steel gains superior corrosion resistance at a low cost without impacting the availability or recyclability of the product, which has in turn led to its widespread use in manufacturing. This session will include cosmetic and perforation corrosion protection of sheet steel, the different types of metallic and organic coatings for hot and cold rolled strip products, and the essentials of the different coating technologies. Also included is the origin of the coating microstructure and the importance of metallic and organic coatings on hot and cold rolled strip products.
9. Strip Properties
In many applications, the required microstructure to obtain mechanical properties within a narrow tolerance is relatively easy to achieve. In addition, narrow tolerance must be achieved for thickness (gauge), strip profile (cross-sectional shape) and flatness. These strip properties are particularly critical in applications for which forming at the production site is limited. The attendee will learn about the essential types of strip defects, along with the relationship between processing and the formation of shape defects on the rolled strip. The importance of different defects in applications and the methods available to minimize them to improve product quality will also be presented.
10. Tube and Plate Production
The large variety of tubular steel products can be classified on the basis of size (diameter), production technology (welded or seamless) and in-service properties. The various types of steel tubes and their production processes will be reviewed, such as slitted strip, spiral pipe, ERW pipe, seamless pipe and tube, etc. Additionally, the use of plate, produced in Steckel plate mills, in the production of large-diameter steel pipes will be discussed. The principles of thermomechanical controlled processing of plate steel will be included. The importance of the strength-toughness combinations for API tube grades will be presented, as will the variety of plate applications and the physical/mechanical properties required for those applications.
11. Long Products: Bar and Wire Mills
Bar and wire mills provide semi-finished steels for many different applications. The end uses of the wire or rod are vast but can be classified into five product groups: tire cord, cold-heading quality steel, spring steel, bearing steel, and free-cutting or free-machining steel. Each product group and the processing necessary to achieve the required properties will be presented. The overall process of rolling as-cast billets into wire or rods will be explained, including the different designs of the mills used to roll wire and rod as specified by the customer. Attention will be given to the importance of the processing on the refinement of the microstructure and to the secondary processes in achieving the final in-service properties for the five product groups.
12. Long Products: Structural Steel and Rails
Production of structural beams and rails differs greatly from the production of wire and rod. The different mill designs for rolling beams and rails will be presented, as will the specialized equipment necessary for achieving the localized properties required in the final product. The principles of shape rolling and the processing by specially designed roll passes will be included. Additionally, the attendee will recognize the importance of strength in the case of structural steels and the importance of hardness in the case of rail steels.
13. Rolls for Rolling Mills
Quality manufactured rolls properly engineered for application in rod and bar mills, beam mills, rail mills and strip mills are critical for consistent and reliable production. Early-stand roughing and breakdown rolls, intermediate rolls and late-stand finishing rolls require different materials and manufacturing processes to provide the properties required in specific applications. Information on the processes used to produce the rolls and the properties inherent to the different types of rolls will be presented, including the metallurgical advantages gained by a particular production process and the different requirements and processes required to produce hot deformation rolls versus cold deformation rolls. Also presented will be specific defects seen in manufactured rolls, such as peeling, banding, firecracks and spalling, and inspection methods to determine such defects.