Abstract

Considerable progress in developing flat-rolled steel grades has been made by the Chinese steel industry over the recent two decades. The increasing demand for high-performance products to be used in infrastructural projects as well as in production of consumer and capital goods has been driving this development until today. The installation of state-of-the-art steel making and rolling facilities has provided the possibility of processing the most advanced steel grades. The production of high-performance steel grades relies on specific alloying elements of which molybdenum is one of the most powerful. China is nearly self-sufficient in molybdenum supplies. This paper highlights the potential and advantages of molybdenum alloying over the entire range of flat-rolled steel products. Specific aspects of steel property improvement with respect to particular applications are indicated.

Highlights

  • Flat carbon steel is one of the most versatile materials used in a large number of industrial applications

  • The increasing demand for high-performance products to be used in infrastructural projects as well as in production of consumer and capital goods has been driving this development until today

  • The fine-grained bainitic steel is re-heated to a temperature allowing efficient precipitation [19]. It is important in this process sequence that the initially produced bainitic structure with high dislocation density is not being removed by recovery or recrystallization during the subsequent annealing process

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Summary

Introduction

Flat carbon steel is one of the most versatile materials used in a large number of industrial applications. Accelerated cooling and relatively low cooling-stop or coiling temperature promote dislocation strengthening This mechanism increases strength by about 150 MPa. The microstructure gradually changes from polygonal ferrite to bainite. Despite molybdenum being a carbide former, its alloy range and the low carbon content guarantee full solubility in these steels throughout the process [6]. Along the processing chain of flat rolled products molybdenum alloying: enhances the solubility of the micro-alloys Nb and Ti during slab reheating [10], supports recrystallization delay during austenite conditioning [12], retards precipitation of micro-alloys during austenite conditioning [13], delays phase transformation from fcc to bcc [14], promotes nonpolygonal ferrite formation with high dislocation density [15], controls micro-alloy precipitation in bcc to ultra-fine size and dense particle distribution [16]

Strengthening by microstructural refinement and dislocations
Strengthening by micro-alloy precipitation
Two-step processing with secondary heat treatment
Application examples of high-performance HSLA steels
Alloy concepts and processing routes for martensitic steels
Process variants for producing martensitic steels
Molybdenum alloying effects in martensitic steels
Application examples of martensitic steels
Alloy concepts and processing routes for multiphase steels
Dual-phase steel design and applications
Multi-phase steel containing retained austenite
Findings
Conclusions
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