MICROSTRUCTURE CONTROL OF HOT ROLLED TRIP STEEL BASED ON DYNAMIC TRANSFORMATION OF UNDERCOOLED AUSTENITE II. Cooling Rate After Dynamic Transformation of Undercooled Austenite

The microstructure characteristics and tensile properties in a 0.2C-1.5Mn-1.0Al-0.50Si, high strength hot rolled TRIP steel obtained by a new processing based on dynamic transformation of undercooled austenite(DTUA) were investigated. The results show that the main feature of the new technology is that the ferrite was produced by the applied strain during DTUA. Characterization by means of optical and scanning electron microscopy, transmission electron microscopy and X-ray diffraction has shown that the microstructure of the investigated steel contained a ferrite matrix with fine grain size, bainite with small bainitic packets, and high volume fraction of retained austenite with a large number of granular retained austenite. Tensile testing indicates the steels produced by this processing have higher strength (790MPa) and total elongation (35%) as well as low yield ratio..

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Microstructure and Properties Formed at Different Cooling Rates of Low Carbon Alloy Steel for Welding Wire Production

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.304.99 ◽

2020 ◽

Vol 304 ◽

pp. 99-106

Author(s):

Natalya Koptseva ◽

Yulia Efimova ◽

Mikhail Chukin ◽

Alexander Pesin ◽

N. Tokareva ◽

...

Keyword(s):

Cooling Rate ◽

Physical Simulation ◽

Low Carbon ◽

Welding Wire ◽

Continuous Cooling ◽

Hardware Processing ◽

Gleeble 3500 ◽

Hot Rolled ◽

Continuous Cooling Transformation Diagram ◽

Undercooled Austenite

Physical simulation of steel Mn3Ni1CrMo continuous cooling with different speeds from austenitic state was performed using GLEEBLE 3500 complex. The phase transformations are analyzed and the effect of the cooling rate on the structure and hardness is investigated. A continuous cooling transformation diagram of the undercooled austenite decomposition is constructed. It was concluded that it is possible to reduce the hardness of the hot-rolled billet by reducing the cooling rate compared to the existing in the processing at the STELMOR line of PJSC “MMK”, and this will eliminate the heat treatment of welding wire on the hardware processing.

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Continuous Cooling Transformation of Under-Cooled Austenite of SXQ500/550DZ35 Hydropower Steel

Metals ◽

10.3390/met11101562 ◽

2021 ◽

Vol 11 (10) ◽

pp. 1562

Author(s):

Zhenglei Tang ◽

Ran Guo ◽

Yang Zhang ◽

Zhen Liu ◽

Yuezhang Lu ◽

...

Keyword(s):

Cooling Rate ◽

Hardness Measurement ◽

Cooling Rates ◽

Continuous Cooling Transformation ◽

Continuous Cooling ◽

Continuous Cooling Transformation Diagrams ◽

Transformation Diagrams ◽

Hot Rolled ◽

Vickers Hardness Measurement ◽

Undercooled Austenite

The expansion curves of the continuous cooling transformation of undercooled austenite of SXQ500/550DZ35 hydropower steel at different heating temperatures and cooling rates were measured by use of a DIL805A dilatometer. Combined with metallography and Vickers hardness measurement, the continuous cooling transformation diagrams (CCT) of the studied steel under two different states were determined. The results show that in the first group of tests, after the hot-rolled specimens were austenitized at 920 °C, when the cooling rate was below 1 °C·s−1, the microstructure was composed of ferrite (F), pearlite (P) and bainite (B). With the cooling rates between 1 °C·s−1 and 5 °C·s−1, the microstructure was mainly bainite, and martensite (M) formed as the cooling rate reached 5 °C·s−1. When the cooling rate was up to 10 °C·s−1, the microstructure was completely martensite and the hardness value increased significantly. In the second group of tests, after the hot-rolled specimens were quenched at 920 °C and then heated at an intercritical temperature of 830 °C, in comparison with the first group of tests, and except for additional undissolved ferrites in each cooling rate range, the other microstructure types were basically the same. Due to the existence of undissolved ferrite, the microstructures of the specimens heated at intercritical temperatures were much finer, and the toughness values at low temperatures were better.

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Hot-Rolled TRIP Steels Based on Dynamic Transformation of Undercooled Austenite

Materials Science Forum ◽

10.4028/www.scientific.net/msf.654-656.250 ◽

2010 ◽

Vol 654-656 ◽

pp. 250-253 ◽

Cited By ~ 7

Author(s):

Wang Yue Yang ◽

Long Fei Li ◽

Yun Yang Yin ◽

Zu Qing Sun ◽

Xi Tao Wang

Keyword(s):

Volume Fraction ◽

High Volume ◽

Test Machine ◽

Compression Tests ◽

Controlled Cooling ◽

Thermomechanical Process ◽

Trip Steels ◽

Dynamic Transformation ◽

Hot Rolled ◽

Undercooled Austenite

A novel thermomechanical process to manufacture hot-rolled transformation-induced plasticity (TRIP) steels was developed based on dynamic transformation of undercooled austenite (DTUA). Between DTUA and the isothermal bainitic treatment, only one-step controlled-cooling was required. The microstructure evolution of hot-rolled C-Mn-Si and C-Mn-Al-Si TRIP steels based on DTUA was investigated by hot uniaxial compression tests using a Gleeble1500 simulation test machine. The results indicated that during DTUA, the kinetics of ferrite formation was fast, the volume fraction of ferrite formed was determined by applied strain. In comparison with the process based on static transformation of austenite, a more uniform multiphase microstructure with fine ferrite grains was formed, the bainite packets were small and had relatively random orientations, the retained austenite distributed uniformly and had relatively high volume fraction. Hot-rolled TRIP steels based on DTUA demonstrated better mechanical properties, especially for C-Mn-Al-Si TRIP steel.

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Effect of Thermomechanical Parameters on the Microstructure and Retained Austenite Characteristics in a Hot-Rolled TRIP Steel

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.295-297.1294 ◽

2011 ◽

Vol 295-297 ◽

pp. 1294-1299

Author(s):

Yun Yang Yin ◽

Fang Fang ◽

Wei Chen ◽

Yong Tao Fu

Keyword(s):

Strain Rate ◽

Trip Steel ◽

Retained Austenite ◽

Volume Fraction ◽

Isothermal Holding ◽

Bainitic Ferrite ◽

Minor Effect ◽

Coiling Temperature ◽

Hot Rolled ◽

Undercooled Austenite

The influence of thermomechanical parameters on the microstructure and retained austenite characteristics in a hot rolled Al-Si-Mn transformation induced plasticity (TRIP) steel based on dynamic transformation of undercooled austenite was investigated, in an effort to produce a desired microstructure and better control retained content. The results show that strain rate had a minor effect on the microstructure, but the volume fraction of retained austenite decreased with increasing strain rate. Decreasing coiling temperature caused a decrease in volume fraction of retained austenite and decrease in the size of bainitic ferrite platelets. Increasing the isothermal holding time during bainite treatment, the volume fraction of retained austenite first gradually increased then decreased. Moreover, The deformation of undercooled austenite not only can influenc the transformation of bainite, but also can refine the grain size of bainite, increase the chemical and mechanical stabilization of retained austenite.

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