Aluminium nitride (AlN) nucleates with difficulty in steel, unless precipitation is enhanced by thermal or mechanical treatments. This important characteristic determines the precipitation kinetics of AlN, and accounts for the wide variations in precipitate morphology achieved following different processing histories. The most significant effect of AlN in steel is on grain size control, which directly influences hardenability, hot ductility, texture development, and mechanical properties. In addition, the accompanying removal of nitrogen from solid solution affects the strain aging characteristics, weldability, mechanical properties, and creep performance. Aluminium nitride also exerts important second order effects through its influence on the precipitation of other alloy nitrides. The precipitation of AlN can cause embrittlement and cracking phenomena in castings, continuously cast products, ingots, and rolled or forged products, However, the basic mechanisms are well understood, and the occurre...

Aluminium nitride in steel

An investigation into the production of ultrafine (1 µm) equiaxed ferrite (UFF) grains in low-carbon steel was made using laboratory rolling, compression dilatometry, and hot torsion techniques It was found that the hot rolling of thin strip, with a combination of high shear strain and high undercooling, provided the conditions most suitable for the formation of this type of microstructure Although high strains could be applied in compression and torsion experiments, large volume fractions of UFF were not observed in those samples, possibly due to the lower level of undercooling achieved It is thought that ferrite refinement was due to a strain-induced transformation process, and that ferrite grains nucleated on parallel and linear deformation bands that traversed austenite grains These bands formed during the deformation process, and the undercooling provided by the contact between the strip and the work rolls was sufficient to drive the transformation to homogeneous UFF grains

The production of ultrafine ferrite in low-carbon steel by strain-induced transformation

The microstructure evolution during dynamic recrystallization and the deformation characteristics of a low carbon steel within the temperature range of 600-700℃ and a strain rate range of 10-3 to 10 s-1 have been investigated by means of thermal-compression simulation test, SEM, TEM and EBSD. In order to understand the effect of microstructure on dynamic recrystallization behaviour, two different microstructures were adopted, which consist of ferrite plus pearlite and ferrite plus fine cementite particles respectively. The results show that dynamic recrystallization takes place in these two cases. However, in the microstructure with pearlite higher strain is needed to start recrystallization and reach the steady state, comparing with the microstructure with fine cementite particles. The measurement confirms that ferrite with smaller grain size in steady state can be obtained in microstructure with ferrite and cementite, which indicates a more significant effect of separately distributed fine cementite particles on promoting recrystallization nucleation and hindering the grain growth than that of pearlite.

Dynamic recrystallization of ferrite in a low carbon steel with different minor microstructures

The aim of this paper is to develop a steel having tensile strength of 600 MPa minimum combined with good formability, hole expansion and fatigue strength through a new metallurgical approach for such application. The steel, thus developed, has been successfully applied to automotive wheel disc making. Discs made of 600 MPa strength showed improved durability in dynamic cornering fatigue and dynamic radial fatigue test. This novel steel will be a solution to solve the lack of stretch flangeability and bendability of advanced high strength steel (AHSS) sheets such as dual phase (DP) and transformation induced plasticity (TRIP) steels.

Development of hot rolled steel sheet with 600 MPa UTS for automotive wheel application

Plane strain compression tests were performed on a low-carbon steel from 550 °C to 700 °C (ferritephase range) at strain rates of 10 to 5 × 10−4 s−1, and the deformation microstructure evolution was investigated by means of scanning electron microscopy, transmission electron microscopy (TEM), and electron backscattered diffraction (EBSD). The results indicate that under the present deformation conditions, dynamic recrystallization of ferrite can occur in the low-carbon steel and lead to grain refinement. With increasing Zener-Hollomon parameter Z, the mechanism of this process changes from discontinuous dynamic recrystallization to continuous dynamic recrystallization; the turning point is approximately at Z=1 × 1016 s−1. The increase of parameter Z leads to the decrease of recrystallized grain size of ferrite under steady state of deformation, and can lead to the formation of ultrafine microstructures with average grain size of about 2 µm.

Dynamic Recrystallization of Ferrite in a Low-Carbon Steel

A method for producing a high tensile strength steel plate which comprises subjecting to a low temperature rolling, a steel composition containing not more than 0.25% of carbon, not more than 0.5% of silicon, 0.5 to 2.0% of manganese, not more than 0.015% of sulfur, 0.005 to 0.1% of aluminum, one or more of niobium, vanadium and titanium in an amount not less than 0.01%, and REM in an amount not less than 1.3 times the amount of sulfur, with optionally one or more of nickel, chromium and copper, with the balance being iron and unavoidable impurities, which steel possesses a low notch toughness transition temperature and high absorbed energy in the notch-impact test, and is suitable in the as rolled condition for use as pipe lines in cold districts.

Method for producing a high toughness and high tensil steel

Recovery and recrystallization behavior of ferrite in low carbon steel during and after intercritical rolling have been investigated using a laboratory mill. The results obtained are as follows:(1) Dynamic recrystallization of ferrite occurs in the intercritical rolling at a high reduction of about 80%.(2) Dynamically recovered ferrite structure formed during intercritical rolling is very stable compared with that formed in the rolling below Ar1.(3) Fine ferrite-pearlite structure is obtained from austenite worked in the intercritical range.Making use of these beneficial effects of intercritical rolling, stronger and tougher steels can be produced by reheating steels at lower temperatures, followed by rolling both in the low temperature range of austenite and intercritical range where the fraction of transformed ferrite is less than that of non-transformed austenite. It is also necessary, for this purpose, that the rolled products be air-cooled or heat treated at a temperature below Ar1. If the total rolling reduction is the same, the properties of the steel obtained by intercritical multipass rolling are nearly equal to those obtained by single pass rolling.

Effects of the Intercritical Rolling on Structure and Properties of Low Carbon Steel

A method for producing a plain low carbon hot rolled steel strip or sheet having a low yield ratio, not higher than 70%, high ductility and high tensile strength comprising: hot rolling a steel slab with its finishing temperature not lower than the Ar 3 transformation temperature, cooling the hot rolled strip from a temperature not lower than Ar 3 transformation temperature and coiling the hot rolled strip at a temperature not higher than 300° C.

Method for producing high tensile strength, high ductility, low yield ratio hot rolled steel sheet

An iron/copper/chromium alloy material for a high-strength lead frame or pin grid array, which comprises 20 to 90% by weight of Cu and 25 to 12% by weight of Cr, with the balance being mainly iron, and which has an average grain size number of at least 10 in each of the iron/chromium phase and the copper phase, is prepared by continuous casting, cold-working, and aging

Iron/copper/chromium alloy material for high-strength lead frame or pin grid array

PURPOSE:To carry out the stable operation always freely from generation of surface cracks, by rolling just cast hot billet, without reheating, at temperatures lower than the embrittlement release temperature corresponding to various surface cooling speeds, previously obtained for every different grade of steel CONSTITUTION:The cooling curves 8, 9, 10, starting at the solidification point 11, and the embrittlement release curve 12 obtained by connecting the border points at which the embrittlement is released, that is, the embrittlement release points 11a- 11c, are previously prepared by directly rolling the hot cast billet of the specified grade of steel, like as the illustrated diagram Next, the hot cast billet, without being reheated, is directly rolled at temperatures lower than above curve 12 That is, if the hot cast billet is cooled to above embrittlement release zone, the restriction on the chemical composition is greatly relaxed For example, in case of the carbon steel (C<=01%) of oxygen content 200ppm or less and Mn/S ratio 7 or more, the surface crack owing to the low melting point non-metallic inclusion, and the austenitic intercrystalline cracks owing to the solid-solution type sulfide to be caused at 1200 degC or lower temperatures, can be prevented

Kunio Watanabe

Papers

Method for producing a high toughness and high tensil steel

Effects of the Intercritical Rolling on Structure and Properties of Low Carbon Steel

Method for producing high tensile strength, high ductility, low yield ratio hot rolled steel sheet

Iron/copper/chromium alloy material for high-strength lead frame or pin grid array

Direct rolling method for hot cast billet