A model for the microstructure behaviour and strength evolution in lath martensite

The microstructure, precipitates and mechanical properties of Nb-V-Ti microalloyed ultra-high strength steel under different tempering temperatures are investigated. With the increasing tempering temperature, the width of martensitic laths gradually increased with reduced dislocations within them, and the volume fraction of retained austenite first increased and then decreased. Furthermore, the Charpy impact toughness, reduction of area and elongation are enhanced at the sacrifice of the strength. Four kinds of precipitates are identified at different tempering temperatures, namely M 3 C, M 2 C, M 23 C 6 and M 7 C 3 . M 3 C precipitated when tempering at 200–400 °C, and it was replaced partially by M 2 C when the temperature is elevated to 500 °C, at which M 23 C 6 also precipitated. For a higher temperature, above 600 °C, M 3 C disappeared, and some M 2 C transformed into M 7 C 3 . The other two types of MC precipitates are found to be the stable phases existing over different tempering temperatures. The correlation between the mechanical properties and microstructure was established, and the precipitation mechanisms of carbides at the different tempering temperatures are explained.

Carbide precipitation in Nb-V-Ti microalloyed ultra-high strength steel during tempering

Microstructure and room temperature strength of 9Cr–3W–3Co martensitic heat resistant steel after normalizing at 900–1200 °C for 1 h and then tempering at 750 °C for 1 h have been experimentally investigated using optical microscope (OM), field emission scanning electron microscope (FESEM), electron back-scattered diffraction (EBSD), field emission transmission electron microscope (FETEM) and tensile tests. The results show that with increasing normalizing temperature, the strength of the 9Cr–3W–3Co steel increases from 900 °C to 1000 °C, then keeps almost the same from 1000 °C to 1100 °C and finally increases again from 1100 °C to 1200 °C. The change in the room temperature strength can mainly be attributed to the change in precipitation strengthening. The size and the amount of particles after tempering are mainly due to the re-dissolution of particles during normalization. The higher the normalizing temperature is, the more the coarse particles formed during manufacturing will be re-dissolved, and then the larger the amount of fine particles precipitated during tempering is.

Effect of normalizing temperature on the strength of 9Cr–3W–3Co martensitic heat resistant steel

Carbide size refinement by controlling the heating rate during induction tempering in a low alloy steel

Effects of vanadium on the microstructure and mechanical properties of a high strength low alloy martensite steel

Effect of microstructure on the strength of 25CrMo48V martensitic steel tempered at different temperature and time

The invention provides a steel grade of a bergol cannula with high intensity and high toughness, wherein the propositions of composition elements are that C 0.22-0.4%, Si 0.17-0.35%, Mn 0.45-0.60%, Cr 0.95-1.10%, Mo 0.70-0.80%, Al 0.015-0.040%, Ni 0.0015%, P<0.010%, S<0.003% and the allowance is iron. The invention also provides a method for rolling the bergol cannula, which comprises the following steps: firstly, smelting batching, secondly, continuously casting and rolling, thirdly, processing a pipe. The method has the advantages of embodying steel grade with higher alloy content is adopted through the method, excellent mechanical property and lower production cost, the making of perforation and rolling techniques are reasonable, mechanical property of cannual is maximally improved, the selection of heat treatment process technique and thermal straightening temperature are reasonable, grain fineness numbers of tissues are refined, residual tension stress of the cannula is greatly lowered, geometric precision control range is strictly planned, and the property of the cannula is improved under the circumstance of reasonable production cost.

Petroleum casing pipe with high-strength and high ductility as well as manufacturing method thereof

In this investigation, a neural network model was established to predict mechanical properties of 25CrMo48V seamless tubes. The sensitivity analysis was also performed to estimate the relative significance of each chemical composition in mechanical behavior of steel tubes. The results of this investigation show that there is a good agreement between experimental and predicted values indicating desirable validity of the model. Among those alloying elements, the elements of carbon, silicon and chromium tended to play a more important role in controlling both the yielding strength and the Charpy-V-Notch transverse impact toughness. In comparison, the impurities such as O, N, S and P have a relatively weak impact. More detailed dependences of mechanical properties on each chemical composition in isolation can be revealed using the established model. The well-trained neural network has a great potential in designing tough and ultrahigh-strength seamless tubes and modeling the on-line production parameters.

Zesheng Yan

Papers

Effect of microstructure on the strength of 25CrMo48V martensitic steel tempered at different temperature and time

Petroleum casing pipe with high-strength and high ductility as well as manufacturing method thereof

Prediction of Mechanical Properties of 25CrMo48V Seamless Tube Using Neural Network Model