Visualization of Prior Austenite Grain Boundaries in Low-Carbon Steels

Abstract Knowledge of the size of the prior austenite grain is of key importance. If abnormal grain growth occurs during austenitization, the resultant inhomogeneous microstructure may negatively affect the strength and toughness properties of the final product. The visualization of prior austenite grain boundaries with an etchant based on picric acid has been applied for years. Despite this long-time experience, it is often challenging to achieve sufficiently good visualization of prior austenite grain boundaries in many steel grades, especially low-carbon steels. This work will study the effect of the cooling rate from austenitizing temperature down to room temperature, of the subsequent tempering treatment and the etchant on the visualization of prior austenite grain boundaries in a low-carbon microalloyed steel. All these parameters have an impact on the etching result. A suitable etchant for the visualization of prior austenite grain boundaries in a low-carbon microalloyed steel could be found.

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Novel Etching Technique for Delineation of Prior-Austenite Grain Boundaries in Low, Medium and High Carbon Steels

Materials ◽

10.3390/ma13153296 ◽

2020 ◽

Vol 13 (15) ◽

pp. 3296

Author(s):

Richard Thackray ◽

Eric J. Palmiere ◽

Omar Khalid

Keyword(s):

Grain Boundaries ◽

Prior Austenite ◽

Picric Acid ◽

High Carbon Steel ◽

Sodium Dodecyl ◽

Carbon Steels ◽

Sodium Dodecylbenzene Sulfonate ◽

High Carbon ◽

Austenite Grain ◽

Prior Austenite Grain

The etching of prior austenite grain boundaries in martensite for detailed quantitative metallography of low to high carbon steel has been carried out using aqueous solutions of picric acid containing different wetting agents. The choice of wetting agent was shown to be dependent on the carbon content of the steel, with sodium dodecyl sulfate (SDS) being more suitable for use with low and medium carbon steels, whereas sodium dodecylbenzene sulfonate (SDBS) was shown to be more appropriate for high carbon steels. It is also recommended that, for a particular steel, a variety of temper treatments should be carried out in order to reveal grain boundaries, particularly where more detailed results than simple grain size measurements are required. Finally, the use of dummy specimens prior to etching of the real samples was shown to reduce the need for re-polishing and re-etching of the samples.

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The Oxide Inclusion and Heat-Affected-Zone Toughness of Low Carbon Steels

Materials Science Forum ◽

10.4028/www.scientific.net/msf.654-656.358 ◽

2010 ◽

Vol 654-656 ◽

pp. 358-361 ◽

Cited By ~ 1

Author(s):

Wei Shu ◽

Xue Min Wang ◽

Shu Rui Li ◽

Xin Lai He

Keyword(s):

Heat Affected Zone ◽

Prior Austenite ◽

Oxide Inclusion ◽

Optical Microscope ◽

Carbon Steels ◽

Cooling Time ◽

Low Carbon ◽

Low Carbon Steels ◽

Austenite Grain ◽

Prior Austenite Grain

The relationship between the oxide inclusions and the Heat-affected-zone (HAZ) toughness of microalloying steels has been investigated. The low carbon steels are smelted with special oxide introduction technique and the properties of HAZ has been studied with thermo-simulation. The optical microscope and SEM were used to analyze the size, composition and distribution of the inclusions, the mechanical properties after thermo-simulation was also analyzed. The results show that the inclusions in steel are mainly Ti and Al oxide with MnS, these complex inclusions are well distributed and the size is less than 3 micron. Microstructure of HAZ consists of intragranular acicular ferrite (IAF), intergranular ferrite and small amount of lath bainite while the cooling time during the phase formation is short. After the thermo simulation with the cooling time between 800°C and 500°C (t8/5) increasing the toughness of HAZ decreased and the size of prior austenite grain increased. Inclusions which located near the prior austenite grain boundary couldn’t induce the nucleation of IAF, only the ones inside the prior austenite grain can promote IAF’s growth.

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The Effect of Boron Addition on Precipitation and Hot Ductility of 1.5Mn-0.1Nb-Ti Carbon Steels in As-Cast Condition

Materials Science Forum ◽

10.4028/www.scientific.net/msf.879.990 ◽

2016 ◽

Vol 879 ◽

pp. 990-995 ◽

Cited By ~ 2

Author(s):

Jacek Komenda ◽

David Martin ◽

Johan Lönnqvist

Keyword(s):

Grain Boundaries ◽

Base Composition ◽

Prior Austenite ◽

Carbon Steels ◽

Hot Ductility ◽

Austenite Grain ◽

Reduction In Area ◽

Cast Condition ◽

Prior Austenite Grain ◽

Start Temperature

Twelve experimental steels with a base composition 1.5wt% Mn, 0.01 wt% V and 0.1 wt% Nb and varying C (0.05, 010 and 0.20 wt%), Ti (20 – 260 ppm) and B (0 – 100 ppm) contents have been systematically examined to quantify the effects of composition on precipitation behavio-ur and hot ductility during simulated continuous casting conditions. Nb-rich precipitates were present in the alloys with 0.10 wt-% C and 0.20 wt-% C. Alloys with 0.05, 010 and 0.20wt% C contained 50 – 100 nm size Ti-Nb carbonitrides. Boron was bound in 20 – 100 nm size boronitrides located in prior austenite grain boundaries. A Gleeble 3800 was used to study hot ductility and strain induced precipitation processes in the alloys. Alloys without B and Ti additions exhibited poor hot ductility at 850°C and 950°C, whereas the 0.05 wt-% C and 0.10 wt-% C alloys showed improved hot ductility (reduction in area 40-50%) by the addition of either >50 ppm B or 250 ppm Ti. The 0.2 wt-% C alloys showed no improvement from B or Ti additions. Examination of fracture surfaces of hot ductility specimens showed that boronitrides were located at prior austenite grain boundaries in alloys containing 80 – 100 ppm of B. Compression-relaxation tests showed that alloying with boron caused a noticeable decrease of the start temperature of strain-induced precipitation in the alloys.

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